Showing 1–50 of 72 results for author: Sun, J

Strain-engineered nanoscale spin polarization reversal in diamond nitrogen-vacancy centers

Authors: Zhixian Liu, Jiahao Sun, Ganyu Xu, Bo Yang, Yuhang Guo, Yu Wang, Cunliang Xin, Hongfang Zuo, Mengqi Wang, Ya Wang

Abstract: The ability to control solid-state quantum emitters is fundamental to advancing quantum technologies. The performance of these systems is fundamentally governed by their spin-dependent photodynamics, yet conventional control methods using cavities offer limited access to key non-radiative processes. Here we demonstrate that anisotropic lattice strain serves as a powerful tool for manipulating spin… ▽ More The ability to control solid-state quantum emitters is fundamental to advancing quantum technologies. The performance of these systems is fundamentally governed by their spin-dependent photodynamics, yet conventional control methods using cavities offer limited access to key non-radiative processes. Here we demonstrate that anisotropic lattice strain serves as a powerful tool for manipulating spin dynamics in solid-state systems. Under high pressure, giant shear strain gradients trigger a complete reversal of the intrinsic spin polarization, redirecting ground-state population from $|0\rangle$ to $|\pm 1\rangle$ manifold. We show that this reprogramming arises from strain-induced mixing of the NV center's excited states and dramatic alteration of intersystem crossing, which we quantify through a combination of opto-magnetic spectroscopy and a theoretical model that disentangles symmetry-preserving and symmetry-breaking strain contributions. Furthermore, the polarization reversal is spatially mapped with a transition region below 120 nm, illustrating sub-diffraction-limit control. Our work establishes strain engineering as a powerful tool for tailoring quantum emitter properties, opening avenues for programmable quantum light sources, high-density spin-based memory, and hybrid quantum photonic devices. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: 9 pages, 5 figures

Experimental Multipartite Entanglement Detection With Minimal-Size Correlations

Authors: Dian Wu, Fei Shi, Jia-Cheng Sun, Bo-Wen Wang, Xue-Mei Gu, Giulio Chiribella, Qi Zhao, Jian Wu

Abstract: Multiparticle entanglement is a valuable resource for quantum technologies, including measurement based quantum computing, quantum secret sharing, and a variety of quantum sensing applications. The direct way to detect this resource is to observe correlations arising from local measurements performed simultaneously on all particles. However, this approach is increasingly vulnerable to measurement… ▽ More Multiparticle entanglement is a valuable resource for quantum technologies, including measurement based quantum computing, quantum secret sharing, and a variety of quantum sensing applications. The direct way to detect this resource is to observe correlations arising from local measurements performed simultaneously on all particles. However, this approach is increasingly vulnerable to measurement imperfections when the number of particles grows, and becomes unfeasible for large-scale entangled states. It is therefore crucial to devise detection methods that minimize the number of simultaneously measured particles. Here we provide the first experimental demonstration of multipartite entanglement detection with minimal-size correlations, showing that our setup is robust to misalignment of the local measurement bases and enables the certification of genuine multipartite entanglement in a regime where the direct approach fails. Overall, our results indicate a promising route to the experimental detection of genuine multipartite entanglement in large-scale entangled states. △ Less

Submitted 26 October, 2025; originally announced October 2025.

Comments: 30 pages, 7 figures, comments are welcome

Direct probing of the simulation complexity of open quantum many-body dynamics

Authors: Lucia Vilchez-Estevez, Alexander Yosifov, Jinzhao Sun

Abstract: Simulating open quantum systems is key to understanding non-equilibrium processes, as persistent influence from the environment induces dissipation and can give rise to steady-state phase transitions. A common strategy is to embed the system-environment into a larger unitary framework, but this obscures the intrinsic complexity of the reduced system dynamics. Here, we investigate the computational… ▽ More Simulating open quantum systems is key to understanding non-equilibrium processes, as persistent influence from the environment induces dissipation and can give rise to steady-state phase transitions. A common strategy is to embed the system-environment into a larger unitary framework, but this obscures the intrinsic complexity of the reduced system dynamics. Here, we investigate the computational complexity of simulating open quantum systems, focusing on two physically relevant parameters, correlation length and mixing time, and explore whether it can be comparable (or even lower) to that of simulating their closed counterparts. In particular, we study the role of dissipation in simulating open-system dynamics using both quantum and classical methods, where the classical complexity is characterised by the bond dimension and operator entanglement entropy. Our results show that dissipation affects correlation length and mixing time in distinct ways at intermediate and long timescales. Moreover, we observe numerically that in classical tensor network simulations, classical complexity does not decrease with stronger dissipation, revealing a separation between quantum and classical resource scaling. △ Less

Submitted 27 August, 2025; originally announced August 2025.

Comments: 16 pages, 9 figures

On the emergence of quantum memory in non-Markovian dynamics

Authors: Alexander Yosifov, Aditya Iyer, Vlatko Vedral, Jinzhao Sun

Abstract: Quantum systems are often hindered by decoherence due to impact from the environment. While memoryless Markovian collision models are commonly used to approximate such evolution, non-Markovian dynamics (with memory) is typical in practice, with memory effects being harnessed as a resource for many tasks like quantum error correction and information processing. Yet, the type of memory, classical or… ▽ More Quantum systems are often hindered by decoherence due to impact from the environment. While memoryless Markovian collision models are commonly used to approximate such evolution, non-Markovian dynamics (with memory) is typical in practice, with memory effects being harnessed as a resource for many tasks like quantum error correction and information processing. Yet, the type of memory, classical or quantum, necessary to realize the dynamics of many collision models is not known. In this work, we extend the quantum homogenizer to the non-Markovian regime by introducing intra-ancilla interactions mediated by Fredkin gates, and study the nature of its memory. Using entanglement measures and relying only on the local dynamics as a witness, we prove the model can be realized with either classical or quantum memory, depending on the initialization of the reservoir and the propagation of non-classical correlations within the reservoir. We further explore how quantum memory emerges across a wide range of practical scenarios. The results shed light on the origin of memory in open quantum systems and can advent the design of near-term quantum technologies for a variety of applications. △ Less

Submitted 29 July, 2025; originally announced July 2025.

Comments: 8 pages, 3 figures

Topological network analysis using a programmable photonic quantum processor

Authors: Shang Yu, Jinzhao Sun, Zhenghao Li, Ewan Mer, Yazeed K Alwehaibi, Oscar Scholin, Gerard J. Machado, Kuan-Cheng Chen, Aonan Zhang, Raj B Patel, Ying Dong, Ian A. Walmsley, Vlatko Vedral, Ginestra Bianconi

Abstract: Understanding topological features in networks is crucial for unravelling complex phenomena across fields such as neuroscience, condensed matter, and high-energy physics. However, identifying higher-order topological structures -- such as $k$-cliques, fundamental building blocks of complex networks -- remains a significant challenge. Here we develop a universal programmable photonic quantum proces… ▽ More Understanding topological features in networks is crucial for unravelling complex phenomena across fields such as neuroscience, condensed matter, and high-energy physics. However, identifying higher-order topological structures -- such as $k$-cliques, fundamental building blocks of complex networks -- remains a significant challenge. Here we develop a universal programmable photonic quantum processor that enables the encoding of arbitrary complex-weight networks, providing a direct pathway to uncovering their topological structures. We demonstrate how this quantum approach can identify weighted $k$-cliques and estimate Betti numbers by leveraging the Gaussian boson sampling algorithm's ability to preferentially select high-weight, dense subgraphs. The unique capabilities of our programmable quantum processor allow us to observe topological phase transitions and identify clique percolation phenomena directly from the entropy of the sampling results. These findings showcase how photonic quantum computing can be applied to analyse the topological characteristics of real-world complex networks, opening new possibilities for quantum-enhanced data analysis. △ Less

Submitted 14 July, 2025; v1 submitted 10 July, 2025; originally announced July 2025.

Universal Quantum Computational Spectroscopy on a Quantum Chip

Authors: Chonghao Zhai, Jinzhao Sun, Jieshan Huang, Jun Mao, Hongchang Bao, Siyuan Zhang, Qihuang Gong, Vlatko Vedral, Xiao Yuan, Jianwei Wang

Abstract: Spectroscopy underpins modern scientific discovery across diverse disciplines. While experimental spectroscopy probes material properties through scattering or radiation measurements, computational spectroscopy combines theoretical models with experimental data to predict spectral properties, essential for advancements in physics, chemistry, and materials science. However, quantum systems present… ▽ More Spectroscopy underpins modern scientific discovery across diverse disciplines. While experimental spectroscopy probes material properties through scattering or radiation measurements, computational spectroscopy combines theoretical models with experimental data to predict spectral properties, essential for advancements in physics, chemistry, and materials science. However, quantum systems present unique challenges for computational spectroscopy due to their inherent complexity, and current quantum algorithms remain largely limited to static and closed quantum systems. Here, we present and demonstrate a universal quantum computational spectroscopy framework that lifts these limitations. Through leveraging coherently controlled quantum dynamics, our method efficiently reconstructs the spectral information for both closed and open systems, furtherly for time-dependent driven systems. We experimentally validate this approach using a programmable silicon-photonic quantum processing chip, capable of high-fidelity time-evolution simulations. The versatility of our framework is demonstrated through spectroscopic computations for diverse quantum systems -- including spin systems, non-Hermitian systems, and quantum Floquet systems -- revealing novel phenomena such as parity-time symmetry breaking and topological holonomy that are inaccessible to conventional spectroscopy or quantum eigenstate algorithms. {Furthermore, systematic benchmarking of UQCS against existing quantum algorithms is numerically performed to demonstrate its unprecedented capabilities and superior performance. This work establishes a noise-robust and transformative paradigm for quantum spectral analysis. △ Less

Submitted 27 June, 2025; originally announced June 2025.

Randomised composite linear-combination-of-unitaries: its role in quantum simulation and observable estimation

Authors: Jinzhao Sun, Pei Zeng

Abstract: Randomisation is widely used in quantum algorithms to reduce the number of quantum gates and ancillary qubits required. A range of randomised algorithms, including eigenstate property estimation by spectral filters, Hamiltonian simulation, and perturbative quantum simulation, though motivated and designed for different applications, share common features in the use of unitary decomposition and Had… ▽ More Randomisation is widely used in quantum algorithms to reduce the number of quantum gates and ancillary qubits required. A range of randomised algorithms, including eigenstate property estimation by spectral filters, Hamiltonian simulation, and perturbative quantum simulation, though motivated and designed for different applications, share common features in the use of unitary decomposition and Hadamard-test-based implementation. In this work, we start by analysing the role of randomised linear-combination-of-unitaries (LCU) in quantum simulations, and present several quantum circuits that realise the randomised composite LCU. A caveat of randomisation, however, is that the resulting state cannot be deterministically prepared, which often takes an unphysical form $U ρV^\dagger$ with unitaries $U$ and $V$. Therefore, randomised LCU algorithms are typically restricted to only estimating the expectation value of a single Pauli operator. To address this, we introduce a quantum instrument that can realise a non-completely-positive map, whose feature of frequent measurement and reset on the ancilla makes it particularly suitable in the fault-tolerant regime. We then show how to construct an unbiased estimator of the effective (unphysical) state $U ρV^\dagger$ and its generalisation. Moreover, we demonstrate how to effectively realise the state prepared by applying an operator that admits a composite LCU form. Our results reveal a natural connection between randomised LCU algorithms and shadow tomography, thereby allowing simultaneous estimation of many observables efficiently. As a concrete example, we construct the estimators and present the simulation complexity for three use cases of randomised LCU in Hamiltonian simulation and eigenstate preparation tasks. △ Less

Submitted 18 June, 2025; originally announced June 2025.

Comments: 13 pages

Digital quantum simulation of squeezed states via enhanced bosonic encoding in a superconducting quantum processor

Authors: Hengyue Li, Yusheng Yang, Zhe-Hui Wang, Shuxin Xie, Zilong Zha, Hantao Sun, Jie Chen, Jian Sun, Shenggang Ying

Abstract: We present a fully digital approach for simulating single-mode squeezed states on a superconducting quantum processor using an enhanced bosonic encoding strategy. By mapping up to 2^{n} photonic Fock states onto n qubits, our framework leverages Gray-code-based encodings to reduce gate overhead compared to conventional one-hot or binary mappings. We further optimize resource usage by restricting t… ▽ More We present a fully digital approach for simulating single-mode squeezed states on a superconducting quantum processor using an enhanced bosonic encoding strategy. By mapping up to 2^{n} photonic Fock states onto n qubits, our framework leverages Gray-code-based encodings to reduce gate overhead compared to conventional one-hot or binary mappings. We further optimize resource usage by restricting the simulation on Fock states with even number of photons only, effectively doubling the range of photon numbers that can be represented for a given number of qubits. To overcome noise and finite coherence in current hardware, we employ a variational quantum simulation protocol, which adapts shallow, parameterized circuits through iterative optimization. Implemented on the Zuchongzhi-2 superconducting platform, our method demonstrates squeezed-state dynamics across a parameter sweep from vacuum state preparation (r=0) to squeezing levels exceeding the Fock space truncation limit (r>1.63). Experimental results, corroborated by quantum state tomography and Wigner-function analysis, confirm high-fidelity state preparation and demonstrate the potential of Gray-code-inspired techniques for realizing continuous-variable physics on near-term, qubit-based quantum processors. △ Less

Submitted 11 June, 2025; v1 submitted 16 May, 2025; originally announced May 2025.

Non-Markovian dynamics with a driven three-level giant atom in a semi-infinite photonic waveguide

Authors: S. J. Sun, Z. Y. Li, C. Cui, Shuang Xu, H. Z. Shen

Abstract: The non-Markovian effects of open quantum systems subjected to external environments are deemed to be valuable resources in quantum optics and quantum information processing. In this work, we investigate the non-Markovian dynamics of a three-level giant atom coupling with a semi-infinite photonic waveguide through multiple coupling points and driven by a classical driving field. We derive the anal… ▽ More The non-Markovian effects of open quantum systems subjected to external environments are deemed to be valuable resources in quantum optics and quantum information processing. In this work, we investigate the non-Markovian dynamics of a three-level giant atom coupling with a semi-infinite photonic waveguide through multiple coupling points and driven by a classical driving field. We derive the analytical expressions for the probability amplitudes of the driven three-level giant atom and obtain two independent conditions. We find two different types of bound states (including the static bound states and the periodic equal-amplitude oscillating bound states) and discuss the physical origins of the bound states formation. Moreover, we discuss the case of the driven three-level giant atom interacting with the infinite photonic waveguide, where there is only one purely imaginary solution (i.e., only one bound state condition exists) for its complex frequency (coming from the absence of mirror at one end of the waveguide) compared to that of a driven three-level giant atom coupling with a semi-infinite photonic waveguide. With this, we also find two different types of bound states, including the static bound state and the periodic equal-amplitude oscillating bound states. Finally, the above results are generalized to a more general model involving a semi-infinite photonic waveguide coupling with an arbitrary number of noninteracting three-level giant atoms driven by the driving fields. The proposed protocol could provide a pathway to precisely elucidate the non-Markovian dynamics of driven, multi-level giant atoms coupled to semi-infinite or infinite photonic waveguides. △ Less

Submitted 15 May, 2025; originally announced May 2025.

Comments: 23 pages, 15 figures

Dispersive-induced magnon blockade with a superconducting qubit

Authors: Zeng-Xing Liu, Yan-Hua Wu, Jing-Hua Sun

Abstract: We investigate the magnon blockade effect in a quantum magnonic system operating in the strong dispersive regime, where a superconducting qubit interacts dispersively with a magnonic mode in a yttrium-iron-garnet sphere.By solving the quantum master equation, we demonstrate that the magnon blockade, characterized by the second-order correlation function $g^{(2)}(0) \rightarrow 0.04$, emerges under… ▽ More We investigate the magnon blockade effect in a quantum magnonic system operating in the strong dispersive regime, where a superconducting qubit interacts dispersively with a magnonic mode in a yttrium-iron-garnet sphere.By solving the quantum master equation, we demonstrate that the magnon blockade, characterized by the second-order correlation function $g^{(2)}(0) \rightarrow 0.04$, emerges under optimal dispersive coupling and driving detuning.The mechanism is attributed to suppressed two-magnon transitions as a result of qubit-induced anharmonicity. Notably, our study identifies the critical role of dispersive interaction strength and environmental temperature, showing that magnon blockade remains observable under experimentally achievable cryogenic conditions.This work extends the magnon blockade effect into the dispersive regime, offering a robust platform for single-magnon manipulation and advancing applications in quantum sensing and information processing. △ Less

Submitted 21 April, 2025; originally announced April 2025.

Efficient noise tailoring and detection of hypergraph states using Clifford circuits

Authors: Guedong Park, Jinzhao Sun, Hyunseok Jeong

Abstract: Hypergraph states are important magic resources for realizing universal quantum computation and diverse non-local physical phenomena. However, noise detection for such states is challenging due to their large dimension and entanglement. This work proposes an efficient Clifford circuit-based scheme for tailoring and detecting noise in third-ordered hypergraph states generated by CCZ, CZ, and Z gate… ▽ More Hypergraph states are important magic resources for realizing universal quantum computation and diverse non-local physical phenomena. However, noise detection for such states is challenging due to their large dimension and entanglement. This work proposes an efficient Clifford circuit-based scheme for tailoring and detecting noise in third-ordered hypergraph states generated by CCZ, CZ, and Z gates. The core part of our scheme is converting the noisy input state into a diagonal form and obtaining the convolution equation of noise rate via Clifford circuits. The depth of the Clifford circuit can be reduced to a constant, depending on the structure of the hypergraph state. After that, we decode it using the fast Hadamard-Walsh transform or some approximation method. The approximation with respect to the $l_2$-norm can be done efficiently by the number of qubits while keeping sufficient precision. Furthermore, the sparse noise assumption, which frequently holds in current experimental setups, enables $ l_1$ approximation. Compared with state verification methods, our method allows us to attain richer information on noise rates and apply various noise-adapted error correction and mitigation methods. Moreover, it bridges the connection between the convolution equation's nonlinearity and the Clifford hierarchy of the hypergraph state inputs. Our results provide a deeper understanding of the nature of highly entangled systems and drive the interests of the research venues concerning magic state implementation. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Comments: (14+17) pages, 7 figures

Fault-tolerant quantum algorithms for quantum molecular systems: A survey

Authors: Yukun Zhang, Xiaoming Zhang, Jinzhao Sun, Heng Lin, Yifei Huang, Dingshun Lv, Xiao Yuan

Abstract: Solving quantum molecular systems presents a significant challenge for classical computation. The advent of early fault-tolerant quantum computing (EFTQC) devices offers a promising avenue to address these challenges, leveraging advanced quantum algorithms with reduced hardware requirements. This review surveys the latest developments in EFTQC and fully fault-tolerant quantum computing (FFTQC) alg… ▽ More Solving quantum molecular systems presents a significant challenge for classical computation. The advent of early fault-tolerant quantum computing (EFTQC) devices offers a promising avenue to address these challenges, leveraging advanced quantum algorithms with reduced hardware requirements. This review surveys the latest developments in EFTQC and fully fault-tolerant quantum computing (FFTQC) algorithms for quantum molecular systems, covering encoding schemes, advanced Hamiltonian simulation techniques, and ground-state energy estimation methods. We highlight recent progress in overcoming practical barriers, such as reducing circuit depth and minimizing the use of ancillary qubits. Special attention is given to the potential quantum advantages achievable through these algorithms, as well as the limitations imposed by dequantization and classical simulation techniques. The review concludes with a discussion of future directions, emphasizing the need for optimized algorithms and experimental validation to bridge the gap between theoretical developments and practical implementation in EFTQC and FFTQC for quantum molecular systems. △ Less

Submitted 4 February, 2025; originally announced February 2025.

Comments: 28 pages, 1 figure

Report number: e70020

Journal ref: WIREs Computational Molecular Science, 15(3), e70020 (2025)

Two measurement bases are asymptotically informationally complete for any pure state tomography

Authors: Tianfeng Feng, Tianqi Xiao, Yu Wang, Shengshi Pang, Farhan Hanif, Xiaoqi Zhou, Qi Zhao, M. S. Kim, Jinzhao Sun

Abstract: One of the fundamental questions in quantum information theory is to find how many measurement bases are required to obtain the full information of a quantum state. While a minimum of four measurement bases is typically required to determine an arbitrary pure state, we prove that for any states generated by finite-depth Clifford + T circuits, just two measurement bases are sufficient. More general… ▽ More One of the fundamental questions in quantum information theory is to find how many measurement bases are required to obtain the full information of a quantum state. While a minimum of four measurement bases is typically required to determine an arbitrary pure state, we prove that for any states generated by finite-depth Clifford + T circuits, just two measurement bases are sufficient. More generally, we prove that two measurement bases are informationally complete for determining algebraic pure states whose state-vector elements represented in the computational basis are algebraic numbers. Since any pure state can be asymptotically approximated by a sequence of algebraic states with arbitrarily high precision, our scheme is referred to as asymptotically informationally complete for pure state tomography. Furthermore, existing works mostly construct the measurements using entangled bases. So far, the best result requires $O(n)$ local measurement bases for $n$-qubit pure-state tomography. Here, we show that two measurement bases that involve polynomial elementary gates are sufficient for uniquely determining sparse algebraic states. Moreover, we prove that two local measurement bases, involving single-qubit local operations only, are informationally complete for certain algebraic states, such as GHZ-like and W-like states. Besides, our two-measurement-bases scheme remains valid for mixed states with certain types of noises. We numerically test the uniqueness of the reconstructed states under two (local) measurement bases with and without measurement and depolarising types of noise. Our scheme provides a theoretical guarantee for pure state tomography in the fault-tolerant quantum computing regime. △ Less

Submitted 28 January, 2025; originally announced January 2025.

Comments: 28 pages, 8 figures, 1 table

An experimental proposal certification for any three-qubit generalized Greenberger-Horne-Zeilinger states based on the fine-grained steering inequality

Authors: Zhi-Hao Bian, Jia-Qi Sun, Yi Shen

Abstract: Multi-party quantum steering is an important concept in quantum information theory and quantum mechanics, typically related to quantum entanglement and quantum nonlocality. It enables precise manipulation of large quantum systems, which is essential for large-scale quantum computing, simulations, and quantum communication. Recently, a quantum steering certification for any three-qubit generalized… ▽ More Multi-party quantum steering is an important concept in quantum information theory and quantum mechanics, typically related to quantum entanglement and quantum nonlocality. It enables precise manipulation of large quantum systems, which is essential for large-scale quantum computing, simulations, and quantum communication. Recently, a quantum steering certification for any three-qubit generalized Greenberger-Horne-Zeilinger (GGHZ) states based on the fine-grained steering inequality was proved [Quantum Studies: Mathematics and Foundations, 2022, 9(2): 175-198]. Here we provide an experimental proposal to prepare the GGHZ states in photon system. The measurement observalbes in each party can be realized by different polarization optical elements. By choosing the angles of the waveplates, our experiment proposal can observe the maximum quantum violation for any three-qubit GGHZ states. Our proposal can be easily extended to high-dimensional qubits and multi-photon GHZ states, which provides a method to study the complex multi-party quantum protocols. △ Less

Submitted 25 December, 2024; originally announced December 2024.

Rydberg Atomic Quantum Receivers for Classical Wireless Communications and Sensing: Their Models and Performance

Authors: Tierui Gong, Jiaming Sun, Chau Yuen, Guangwei Hu, Yufei Zhao, Yong Liang Guan, Chong Meng Samson See, Mérouane Debbah, Lajos Hanzo

Abstract: The significant progress of quantum sensing technologies offer numerous radical solutions for measuring a multitude of physical quantities at an unprecedented precision. Among them, Rydberg atomic quantum receivers (RAQRs) emerge as an eminent solution for detecting the electric field of radio frequency (RF) signals, exhibiting great potential in assisting classical wireless communications and sen… ▽ More The significant progress of quantum sensing technologies offer numerous radical solutions for measuring a multitude of physical quantities at an unprecedented precision. Among them, Rydberg atomic quantum receivers (RAQRs) emerge as an eminent solution for detecting the electric field of radio frequency (RF) signals, exhibiting great potential in assisting classical wireless communications and sensing. So far, most experimental studies have aimed for the proof of physical concepts to reveal its promise, while the practical signal model of RAQR-aided wireless communications and sensing remained under-explored. Furthermore, the performance of RAQR-based wireless receivers and their advantages over classical RF receivers have not been fully characterized. To fill these gaps, we introduce the RAQR to the wireless community by presenting an end-to-end reception scheme. We then develop a corresponding equivalent baseband signal model relying on a realistic reception flow. Our scheme and model provide explicit design guidance to RAQR-aided wireless systems. We next study the performance of RAQR-aided wireless systems based on our model, and compare them to classical RF receivers. The results show that the RAQR is capable of achieving a substantial received signal-to-noise ratio (SNR) gain of over $27$ decibel (dB) and $40$ dB in the photon shot limit regime and the standard quantum limit regime, respectively. △ Less

Submitted 13 May, 2025; v1 submitted 7 December, 2024; originally announced December 2024.

Comments: 16 pages, 8 figures

Manipulating spectral transitions and photonic transmission in a non-Hermitian optical system through nanoparticle perturbations

Authors: Bo-Wang Zhang, Cheng Shang, J. Y. Sun, Zhuo-Cheng Gu, X. X. Yi

Abstract: In recent years, extensive research has been dedicated to the study of parity-time ($\mathcal{PT}$) symmetry, which involves the engineered balance of gain and loss in non-Hermitian optics. Complementary to $\mathcal{PT}$ symmetry, the concept of anti-$\mathcal{PT}$ symmetry has emerged as a natural framework for describing the dynamics of open systems with dissipations. In this work, we study spe… ▽ More In recent years, extensive research has been dedicated to the study of parity-time ($\mathcal{PT}$) symmetry, which involves the engineered balance of gain and loss in non-Hermitian optics. Complementary to $\mathcal{PT}$ symmetry, the concept of anti-$\mathcal{PT}$ symmetry has emerged as a natural framework for describing the dynamics of open systems with dissipations. In this work, we study spectral transitions and photon transmission in a linear spinning resonator perturbed by nanoparticles. First, we show that by precisely controlling the nanoparticle perturbations, the eigenvalues (or spectra) of a non-Hermitian system satisfying anti-$\mathcal{PT}$ symmetry can transit to that of a quasi-closed Hermitian system. Second, we outline the essential conditions for constructing a quasi-closed system and analyze its dynamic behavior with respect to photon transmission. By adjusting the rotational angular velocity of the spinning resonator and the strength of the nanoparticle perturbations, the quasi-closed system enables a variety of photon distribution behaviors, which may have significant applications in quantum devices. Our findings offer valuable insights for the design of dissipative quantum devices under realistic conditions and for understanding their responses to external perturbations. △ Less

Submitted 9 January, 2025; v1 submitted 22 November, 2024; originally announced November 2024.

Comments: 9 pages, 3 figures

Journal ref: Phys. Rev. A 111, 063702 (2025)

Microwave-activated two-qubit gates for fixed-coupling and fixed-frequency transmon qubits

Authors: Ling Jiang, Peng Xu, Shengjun Wu, Jian-An Sun, Fu-Quan Dou

Abstract: All-microwave control of fixed-frequency superconducting quantum systems offers the potential to reduce control circuit complexity and increase system coherence. Nevertheless, due to the limited control flexibility in qubit parameters, one has to address several issues, such as quantum crosstalk and frequency crowding, for scaling up qubit architecture with non-tunable elements. This study propose… ▽ More All-microwave control of fixed-frequency superconducting quantum systems offers the potential to reduce control circuit complexity and increase system coherence. Nevertheless, due to the limited control flexibility in qubit parameters, one has to address several issues, such as quantum crosstalk and frequency crowding, for scaling up qubit architecture with non-tunable elements. This study proposes a microwave-activated two-qubit gate scheme for two fixed-frequency transmon qubits coupled via a fixed-frequency transmon coupler. The protocol relies on applying a microwave pulse exclusively to the coupler, enabling the implementation of a controlled-Z (CZ) gate. We show that the gate fidelity exceeding 0.999 can be achieved within 150 ns, excluding decoherence effects. Moreover, we also show that leakage from the computational subspace to non-computational states can also be effectively suppressed. △ Less

Submitted 10 October, 2024; originally announced October 2024.

Purification and correction of quantum channels by commutation-derived quantum filters

Authors: Sowmitra Das, Jinzhao Sun, Michael Hanks, Bálint Koczor, M. S. Kim

Abstract: Reducing errors is essential for reliable quantum computation. Quantum error mitigation (QEM) and quantum error correction (QEC) are two leading approaches for this task, each with challenges: QEM suffers from high sampling costs and cannot recover states, while QEC incurs large qubit and gate overheads. We combine ideas from both and introduce an information-theoretic device called a quantum filt… ▽ More Reducing errors is essential for reliable quantum computation. Quantum error mitigation (QEM) and quantum error correction (QEC) are two leading approaches for this task, each with challenges: QEM suffers from high sampling costs and cannot recover states, while QEC incurs large qubit and gate overheads. We combine ideas from both and introduce an information-theoretic device called a quantum filter that can purify or correct quantum channels. We present an explicit construction capable of correcting arbitrary noise in an n-qubit Clifford circuit using 2n ancillary qubits through a commutation-derived error-detection circuit. This scheme can also partially purify noise in non-Clifford gates such as T and CCZ. Unlike QEC, it achieves deterministic error reduction without encoding the input state. Under the assumption of clean ancillas, it overcomes the exponential sampling overhead in QEM using a single query to the channel. We also propose an ancilla-efficient Pauli filter that removes nearly all low-weight erroneous Pauli components in noisy Clifford circuits using only two ancillas. For local depolarizing noise, it achieves a quadratic reduction in average infidelity. Beyond existing QEM methods, our approach enables systematic error correction as the infidelity can be exponentially reduced with each added ancilla. Through numerical simulations under ancilla noise, we identify regimes where quantum filters outperform other techniques, demonstrating their effectiveness as a scalable error-reduction tool for quantum information processing. △ Less

Submitted 7 October, 2025; v1 submitted 29 July, 2024; originally announced July 2024.

Comments: 35 pages, 19 figures, 1 table

High-precision and low-depth eigenstate property estimation: theory and resource estimation

Authors: Jinzhao Sun, Pei Zeng, Tom Gur, M. S. Kim

Abstract: Estimating the eigenstate properties of quantum many-body systems is a long-standing, challenging problem for both classical and quantum computing. For the task of eigenstate preparation, quantum signal processing (QSP) has established near-optimal query complexity $O( Δ^{-1} \log(ε^{-1}) )$ by querying the block encoding of the Hamiltonian $H$ where $Δ$ is the energy gap and $ε$ is the target pre… ▽ More Estimating the eigenstate properties of quantum many-body systems is a long-standing, challenging problem for both classical and quantum computing. For the task of eigenstate preparation, quantum signal processing (QSP) has established near-optimal query complexity $O( Δ^{-1} \log(ε^{-1}) )$ by querying the block encoding of the Hamiltonian $H$ where $Δ$ is the energy gap and $ε$ is the target precision. However, QSP is challenging for both near-term noisy quantum computers and early fault-tolerant quantum computers (FTQC), which are limited by the number of logical qubits and circuit depth. To date, early FTQC algorithms have focused on querying the perfect time evolution $e^{-iHt}$. It remains uncertain whether early FTQC algorithms can maintain good asymptotic scaling at the gate level. Moreover, when considering qubit connectivity, the circuit depth of existing FTQC algorithms may scale suboptimally with system size. Here, we present a full-stack design of a random sampling algorithm for estimating the eigenenergy and the observable expectations on the eigenstates, which can achieve high precision and good system size scaling. The gate complexity has a logarithmic dependence on precision $ {O}(\log^{1+o(1)} (1/ε))$ for generic Hamiltonians, which cannot achieved by methods using Trottersiation to realise $e^{-iHt}$ like in QETU. For $n$-qubit lattice Hamiltonians, our method achieves near-optimal system size dependence with the gate complexity $O(n^{1+o(1)})$. When restricting the qubit connectivity to a linear nearest-neighbour architecture, The method shows advantages in circuit depth, with $O(n^{o(1)})$ for lattice models and $O(n^{2+o(1)})$ for electronic structure problems. We compare the resource requirements (CNOT gates, T gates and qubit numbers) by phase estimation, QSP, and QETU, in lattice and molecular problems. △ Less

Submitted 6 June, 2024; originally announced June 2024.

Comments: 48 pages, 7 figures, and 4 tables

Separability and lower bounds of quantum entanglement based on realignment

Authors: Jiaxin Sun, Hongmei Yao, Shao-Ming Fei, Zhaobing Fan

Abstract: The detection and estimation of quantum entanglement are the essential issues in the theory of quantum entanglement. We construct matrices based on the realignment of density matrices and the vectorization of the reduced density matrices, from which a family of separability criteria are presented for both bipartite and multipartite systems. Moreover, new lower bounds of concurrence and convex-roof… ▽ More The detection and estimation of quantum entanglement are the essential issues in the theory of quantum entanglement. We construct matrices based on the realignment of density matrices and the vectorization of the reduced density matrices, from which a family of separability criteria are presented for both bipartite and multipartite systems. Moreover, new lower bounds of concurrence and convex-roof extended negativity are derived. Criteria are also given to detect the genuine tripartite entanglement. Lower bounds of the concurrence of genuine tripartite entanglement are presented. By detailed examples we show that our results are better than the corresponding ones in identifying and estimating quantum entanglement as well as genuine multipartite entanglement. △ Less

Submitted 20 May, 2024; originally announced May 2024.

Comments: 11pages, 5 figures and 2 tables

Efficient photon-pair generation in layer-poled lithium niobate nanophotonic waveguides

Authors: Xiaodong Shi, Sakthi Sanjeev Mohanraj, Veerendra Dhyani, Angela Anna Baiju, Sihao Wang, Jiapeng Sun, Lin Zhou, Anna Paterova, Victor Leong, Di Zhu

Abstract: Integrated photon-pair sources are crucial for scalable photonic quantum systems. Thin-film lithium niobate is a promising platform for on-chip photon-pair generation through spontaneous parametric down-conversion (SPDC). However, the device implementation faces practical challenges. Periodically poled lithium niobate (PPLN), despite enabling flexible quasi-phase matching, suffers from poor fabric… ▽ More Integrated photon-pair sources are crucial for scalable photonic quantum systems. Thin-film lithium niobate is a promising platform for on-chip photon-pair generation through spontaneous parametric down-conversion (SPDC). However, the device implementation faces practical challenges. Periodically poled lithium niobate (PPLN), despite enabling flexible quasi-phase matching, suffers from poor fabrication reliability and device repeatability, while conventional modal phase matching (MPM) methods yield limited efficiencies due to inadequate mode overlaps. Here, we introduce a layer-poled lithium niobate (LPLN) nanophotonic waveguide for efficient photon-pair generation. It leverages layer-wise polarity inversion through electrical poling to break spatial symmetry and significantly enhance nonlinear interactions for MPM, achieving a notable normalized second-harmonic generation (SHG) conversion efficiency of 4615% W^{-1}cm^{-2}. Through a cascaded SHG and SPDC process, we demonstrate photon-pair generation with a normalized brightness of 3.1*10^6 Hz nm^{-1} mW^{-2} in a 3.3 mm long LPLN waveguide, surpassing existing on-chip sources under similar operating configurations. Crucially, our LPLN waveguides offer enhanced fabrication reliability and reduced sensitivity to geometric variations and temperature fluctuations compared to PPLN devices. We expect LPLN to become a promising solution for on-chip nonlinear wavelength conversion and non-classical light generation, with immediate applications in quantum communication, networking, and on-chip photonic quantum information processing. △ Less

Submitted 17 May, 2024; originally announced May 2024.

Journal ref: Light: Science & Applications 13, 282 (2024)

Photon blockade in non-Hermitian optomechanical systems with nonreciprocal couplings

Authors: J. Y. Sun, H. Z. Shen

Abstract: We study the photon blockade at exceptional points for a non-Hermitian optomechanical system coupled to the driven whispering-gallery-mode microresonator with two nanoparticles under the weak optomechanical coupling approximation, where exceptional points emerge periodically by controlling the relative angle of the nanoparticles. We find that conventional photon blockade occurs at exceptional poin… ▽ More We study the photon blockade at exceptional points for a non-Hermitian optomechanical system coupled to the driven whispering-gallery-mode microresonator with two nanoparticles under the weak optomechanical coupling approximation, where exceptional points emerge periodically by controlling the relative angle of the nanoparticles. We find that conventional photon blockade occurs at exceptional points for the eigenenergy resonance of the single-excitation subspace driven by a laser field, and discuss the physical origin of conventional photon blockade. Under the weak driving condition, we analyze the influences of the different parameters on conventional photon blockade. We investigate conventional photon blockade at non-exceptional points, which exists at two optimal detunings due to the eigenstates in the single-excitation subspace splitting from one (coalescence) at exceptional points to two at non-exceptional points. \textbf{Unconventional photon blockade can occur at non-exceptional points, while it does not exist at exceptional points since the destructive quantum interference cannot occur due to the two different quantum pathways to the two-photon state being not formed.} The realization of photon blockade in our proposal provides a viable and flexible way for the preparation of single-photon sources in the non-Hermitian optomechanical system. △ Less

Submitted 17 April, 2024; originally announced April 2024.

Comments: 17 pages, 13 figures

Journal ref: Phys. Rev. A 107, 043715 (2023)

Utilizing Quantum Processor for the Analysis of Strongly Correlated Materials

Authors: Hengyue Li, Yusheng Yang, Pin Lv, Jinglong Qu, Zhe-Hui Wang, Jian Sun, Shenggang Ying

Abstract: This study introduces a systematic approach for analyzing strongly correlated systems by adapting the conventional quantum cluster method to a quantum circuit model. We have developed a more concise formula for calculating the cluster's Green's function, requiring only real-number computations on the quantum circuit instead of complex ones. This approach is inherently more suited to quantum circui… ▽ More This study introduces a systematic approach for analyzing strongly correlated systems by adapting the conventional quantum cluster method to a quantum circuit model. We have developed a more concise formula for calculating the cluster's Green's function, requiring only real-number computations on the quantum circuit instead of complex ones. This approach is inherently more suited to quantum circuits, which primarily yield statistical probabilities. As an illustrative example, we explored the Hubbard model on a 2D lattice. The ground state is determined utilizing Xiaohong, a superconducting quantum processor equipped with 66 qubits, supplied by QuantumCTek Co., Ltd. Subsequently, we employed the circuit model to compute the real-time retarded Green's function for the cluster, which is then used to determine the lattice Green's function. We conducted an examination of the band structure in the insulator phase of the lattice system. This preliminary investigation lays the groundwork for exploring a wealth of innovative physics within the field of condensed matter physics. △ Less

Submitted 1 August, 2024; v1 submitted 3 April, 2024; originally announced April 2024.

Journal ref: Phys. Scr. 99 105117 (2024)

Reweight-annealing method for evaluating the partition function via quantum Monte Carlo calculations

Authors: Yi-Ming Ding, Jun-Song Sun, Nvsen Ma, Gaopei Pan, Chen Cheng, Zheng Yan

Abstract: Efficient and accurate algorithm for partition function, free energy and thermal entropy calculations is of great significance in statistical physics and quantum many-body physics. Here we present an unbiased but low-technical-barrier algorithm within the quantum Monte Carlo framework, which has exceptionally high accuracy and no systemic error. Compared with the conventional specific heat integra… ▽ More Efficient and accurate algorithm for partition function, free energy and thermal entropy calculations is of great significance in statistical physics and quantum many-body physics. Here we present an unbiased but low-technical-barrier algorithm within the quantum Monte Carlo framework, which has exceptionally high accuracy and no systemic error. Compared with the conventional specific heat integral method and Wang-Landau sampling algorithm, our method can obtain a much more accurate result of the sub-leading coefficient of the entropy. This method can be widely used in both classical and quantum Monte Carlo simulations and is easy to be parallelized on computer. △ Less

Submitted 30 October, 2024; v1 submitted 13 March, 2024; originally announced March 2024.

Comments: 10 pages, 7 figures

Journal ref: Phys. Rev. B 110.165152 (2024)

Stabilizer ground states for simulating quantum many-body physics: theory, algorithms, and applications

Authors: Jiace Sun, Lixue Cheng, Shi-Xin Zhang

Abstract: Stabilizer states, which are also known as the Clifford states, have been commonly utilized in quantum information, quantum error correction, and quantum circuit simulation due to their simple mathematical structure. In this work, we apply stabilizer states to tackle quantum many-body ground state problems and introduce the concept of stabilizer ground states. We establish an equivalence formalism… ▽ More Stabilizer states, which are also known as the Clifford states, have been commonly utilized in quantum information, quantum error correction, and quantum circuit simulation due to their simple mathematical structure. In this work, we apply stabilizer states to tackle quantum many-body ground state problems and introduce the concept of stabilizer ground states. We establish an equivalence formalism for identifying stabilizer ground states of general Pauli Hamiltonians. Moreover, we develop an exact and linear-scaled algorithm to obtain stabilizer ground states of 1D local Hamiltonians and thus free from discrete optimization. This proposed equivalence formalism and linear-scaled algorithm are not only applicable to finite-size systems, but also adaptable to infinite periodic systems. The scalability and efficiency of the algorithms are numerically benchmarked on different Hamiltonians. Finally, we demonstrate that stabilizer ground states are promising tools for not only qualitative understanding of quantum systems, but also cornerstones of more advanced classical or quantum algorithms. △ Less

Submitted 18 June, 2025; v1 submitted 13 March, 2024; originally announced March 2024.

Comments: 34 pages, 10 figures

Journal ref: Quantum 9, 1782 (2025)

Experimental demonstration of scalable cross-entropy benchmarking to detect measurement-induced phase transitions on a superconducting quantum processor

Authors: Hirsh Kamakari, Jiace Sun, Yaodong Li, Jonathan J. Thio, Tanvi P. Gujarati, Matthew P. A. Fisher, Mario Motta, Austin J. Minnich

Abstract: Quantum systems subject to random unitary evolution and measurements at random points in spacetime exhibit entanglement phase transitions which depend on the frequency of these measurements. Past work has experimentally observed entanglement phase transitions on near-term quantum computers, but the characterization approach using entanglement entropy is not scalable due to exponential overhead of… ▽ More Quantum systems subject to random unitary evolution and measurements at random points in spacetime exhibit entanglement phase transitions which depend on the frequency of these measurements. Past work has experimentally observed entanglement phase transitions on near-term quantum computers, but the characterization approach using entanglement entropy is not scalable due to exponential overhead of quantum state tomography and postselection. Recently, an alternative protocol to detect entanglement phase transitions using linear cross entropy was proposed, attempting to eliminate both bottlenecks. Here, we report demonstrations of this protocol in systems with one-dimensional and all-to-all connectivities on IBM's quantum hardware on up to 22 qubits, a regime which is presently inaccessible if postselection is required. We demonstrate data collapses onto scaling functions with critical exponents in semiquantitative agreement with theory. Our demonstration of the cross entropy benchmark (XEB) protocol paves the way for studies of measurement-induced entanglement phase transitions and associated critical phenomena on larger near-term quantum systems. △ Less

Submitted 9 May, 2025; v1 submitted 1 March, 2024; originally announced March 2024.

Comments: 23 pages, 15 figures. v2: published version

Journal ref: Phys. Rev. Lett. 134, 120401 (2025)

Observation of topology transition in Floquet non-Hermitian skin effects in silicon photonics

Authors: Zhiyuan Lin, Wange Song, Li-Wei Wang, Haoran Xin, Jiacheng Sun, Shengjie Wu, Chunyu Huang, Shining Zhu, Jian-Hua Jiang, Tao Li

Abstract: Non-Hermitian physics has greatly enriched our understanding of nonequilibrium phenomena and uncovered novel effects such as the non-Hermitian skin effect (NHSE) that has profoundly revolutionized the field. NHSE is typically predicted in systems with nonreciprocal couplings which, however, are difficult to realize in experiments. Without nonreciprocal couplings, the NHSE can also emerge in system… ▽ More Non-Hermitian physics has greatly enriched our understanding of nonequilibrium phenomena and uncovered novel effects such as the non-Hermitian skin effect (NHSE) that has profoundly revolutionized the field. NHSE is typically predicted in systems with nonreciprocal couplings which, however, are difficult to realize in experiments. Without nonreciprocal couplings, the NHSE can also emerge in systems with coexisting gauge fields and loss or gain (e.g., in Floquet non-Hermitian systems). However, such Floquet NHSE remains largely unexplored in experiments. Here, we realize the Floquet NHSEs in periodically modulated optical waveguides integrated on a silicon photonics platform. By engineering the artificial gauge fields induced by the periodical modulation, we observe various Floquet NHSEs and unveil their rich topological transitions. Remarkably, we discover the transitions between the normal unipolar NHSEs and an unconventional bipolar NHSE which is accompanied by the directional reversal of the NHSEs. The underlying physics is revealed by the band winding in complex quasienergy space which undergoes a topology change from isolated loops with the same winding to linked loops with opposite windings. Our work unfolds a new route toward Floquet NHSEs originating from the interplay between gauge fields and dissipation effects and offers fundamentally new ways for steering light and other waves. △ Less

Submitted 14 February, 2024; originally announced February 2024.

Comments: 12 pages, 3 figures

Quantum steering for two-mode states with Continuous-variable in laser channel

Authors: Kaimin Zheng, Jifeng Sun, Liyun Hu, Lijian Zhang

Abstract: The Einstein-Podolsky-Rosen steering is an important resource for one-sided device independent quantum information processing. This steering property will be destroyed during the interaction between quantum system and environment for some practical applications. In this paper, we use the representation of characteristic function for probability to examine the quantum steering of two-mode states wi… ▽ More The Einstein-Podolsky-Rosen steering is an important resource for one-sided device independent quantum information processing. This steering property will be destroyed during the interaction between quantum system and environment for some practical applications. In this paper, we use the representation of characteristic function for probability to examine the quantum steering of two-mode states with continuous-variable in laser channel, where both the gain factor and the loss effect are considered. Firstly, we analyse the steering time of two-mode squeezed vacuum state under one-mode and two-mode laser channel respectively. We find the gain process will introduce additional noise to the two-mode squeezed vacuum state such that the steerable time is reduced. Secondly, by quantising quantum Einstein-Podolsky-Rosen steering, it shows that two-side loss presents a smaller steerability than one-side loss although they share the same two-way steerable time. In addition, we find the more gained party can steer the others state, while the other party cannot steer the gained party in a certain threshold value. In this sense, it seems that the gain effect in one party is equivalent to the loss effect in the others party. Our results pave way for the distillation of Einstein-Podolsky-Rosen steering and the quantum information processing in practical quantum channels. △ Less

Submitted 28 November, 2023; originally announced November 2023.

Hyperfine Structure of Quantum Entanglement

Authors: Liang-Hong Mo, Yao Zhou, Jia-Rui Sun, Peng Ye

Abstract: Quantum entanglement, crucial for understanding quantum many-body systems and quantum gravity, is commonly assessed through various measures such as von Neumann entropy, mutual information, and entanglement contour, each with its inherent advantages and limitations. In this work, we introduce the hyperfine structure of entanglement, which decomposes entanglement contours known as the fine structur… ▽ More Quantum entanglement, crucial for understanding quantum many-body systems and quantum gravity, is commonly assessed through various measures such as von Neumann entropy, mutual information, and entanglement contour, each with its inherent advantages and limitations. In this work, we introduce the hyperfine structure of entanglement, which decomposes entanglement contours known as the fine structure into particle-number cumulants. This measure exhibits a set of universal properties with its significance in quantum information science. We apply it across diverse contexts: in Fermi gases, establishing connections to mutual information and interacting conformal field theory; in AdS$_3$/CFT$_2$ correspondence, unveiling finer subregion-subregion duality; and in Chern insulators, distinguishing between different quantum phases, especially topological gapped state and trivial gapped state. Our findings suggest experimental accessibility, offering fresh insights into quantum entanglement across physical systems. △ Less

Submitted 4 July, 2025; v1 submitted 3 November, 2023; originally announced November 2023.

Comments: 37 pages, 8 figures; extended version

Towards chemical accuracy with shallow quantum circuits: A Clifford-based Hamiltonian engineering approach

Authors: Jiace Sun, Lixue Cheng, Weitang Li

Abstract: Achieving chemical accuracy with shallow quantum circuits is a significant challenge in quantum computational chemistry, particularly for near-term quantum devices. In this work, we present a Clifford-based Hamiltonian engineering algorithm, namely CHEM, that addresses the trade-off between circuit depth and accuracy. Based on variational quantum eigensolver and hardware-efficient ansatz, our meth… ▽ More Achieving chemical accuracy with shallow quantum circuits is a significant challenge in quantum computational chemistry, particularly for near-term quantum devices. In this work, we present a Clifford-based Hamiltonian engineering algorithm, namely CHEM, that addresses the trade-off between circuit depth and accuracy. Based on variational quantum eigensolver and hardware-efficient ansatz, our method designs Clifford-based Hamiltonian transformation that (1) ensures a set of initial circuit parameters corresponding to the Hartree--Fock energy can be generated, (2) effectively maximizes the initial energy gradient with respect to circuit parameters, (3) imposes negligible overhead for classical processing and does not require additional quantum resources, and (4) is compatible with any circuit topology. We demonstrate the efficacy of our approach using a quantum hardware emulator, achieving chemical accuracy for systems as large as 12 qubits with fewer than 30 two-qubit gates. Our Clifford-based Hamiltonian engineering approach offers a promising avenue for practical quantum computational chemistry on near-term quantum devices. △ Less

Submitted 10 December, 2023; v1 submitted 21 June, 2023; originally announced June 2023.

Comments: 14 pages, 6 figures. SI is included

Probing spectral features of quantum many-body systems with quantum simulators

Authors: Jinzhao Sun, Lucia Vilchez-Estevez, Vlatko Vedral, Andrew T. Boothroyd, M. S. Kim

Abstract: The efficient probing of spectral features is important for characterising and understanding the structure and dynamics of quantum materials. In this work, we establish a framework for probing the excitation spectrum of quantum many-body systems with quantum simulators. Our approach effectively realises a spectral detector by processing the dynamics of observables with time intervals drawn from a… ▽ More The efficient probing of spectral features is important for characterising and understanding the structure and dynamics of quantum materials. In this work, we establish a framework for probing the excitation spectrum of quantum many-body systems with quantum simulators. Our approach effectively realises a spectral detector by processing the dynamics of observables with time intervals drawn from a defined probability distribution, which only requires native time evolution governed by the Hamiltonian without ancilla. The critical element of our method is the engineered emergence of frequency resonance such that the excitation spectrum can be probed. We show that the time complexity for transition energy estimation has a logarithmic dependence on simulation accuracy and how such observation can be guaranteed in certain many-body systems. We discuss the noise robustness of our spectroscopic method and show that the total running time maintains polynomial dependence on accuracy in the presence of device noise. We further numerically test the error dependence and the scalability of our method for lattice models. We present simulation results for the spectral features of typical quantum systems, either gapped or gapless, including quantum spins, fermions and bosons. We demonstrate how excitation spectra of spin-lattice models can be probed experimentally with IBM quantum devices. △ Less

Submitted 10 February, 2025; v1 submitted 12 May, 2023; originally announced May 2023.

Comments: 29 pages, 12 figures

Journal ref: Nat Commun 16, 1403 (2025)

A Herculean task: Classical simulation of quantum computers

Authors: Xiaosi Xu, Simon Benjamin, Jinzhao Sun, Xiao Yuan, Pan Zhang

Abstract: In the effort to develop useful quantum computers simulating quantum machines with conventional computing resources is a key capability. Such simulations will always face limits preventing the emulation of quantum computers of substantial scale but by pushing the envelope as far as possible through optimal choices of algorithms and hardware the value of the simulator tool is maximized. This work r… ▽ More In the effort to develop useful quantum computers simulating quantum machines with conventional computing resources is a key capability. Such simulations will always face limits preventing the emulation of quantum computers of substantial scale but by pushing the envelope as far as possible through optimal choices of algorithms and hardware the value of the simulator tool is maximized. This work reviews the state-of-the-art numerical simulation methods i.e. the classical algorithms that emulate quantum computer evolution under specific operations. We focus on the mainstream state-vector and tensor-network paradigms while briefly mentioning alternative methods. Moreover we review the diverse applications of simulation across different facets of quantum computer development such as understanding the fundamental difference between quantum and classical computations exploring algorithm design spaces for quantum advantage predicting quantum processor performance at the design stage and characterizing fabricated devices efficiently for fast iterations. This review complements recent surveys on today's tools and implementations here we seek to acquaint the reader with an essential understanding of the theoretical basis of classical simulations detailed discussions on the advantages and limitations of different methods and the demands and challenges arising from practical use cases. △ Less

Submitted 17 February, 2023; originally announced February 2023.

Comments: 14 pages

Defining a universal sign to strictly probe a phase transition

Authors: Nvsen Ma, Jun-Song Sun, Gaopei Pan, Chen Cheng, Zheng Yan

Abstract: The mystery of the infamous sign problem in quantum Monte Carlo simulations mightily restricts applications of the method in fermionic and frustrated systems. A recent work [Science 375, 418 (2022)] made a remarkable breakthrough in the sign problem by pointing out that the sign can be used to probe phase transition. In this work, we proposed a general argument based on the definition of the sign… ▽ More The mystery of the infamous sign problem in quantum Monte Carlo simulations mightily restricts applications of the method in fermionic and frustrated systems. A recent work [Science 375, 418 (2022)] made a remarkable breakthrough in the sign problem by pointing out that the sign can be used to probe phase transition. In this work, we proposed a general argument based on the definition of the sign that is related to the difference in free energy between the original and reference systems to clarify that the sign problem and phase transition cannot always be strictly related. The sign can exactly probe phase transition only if the free energy in the reference system is flat under variable parameters, which is almost impossible to design. Generally speaking, the conclusion that the sign can probe phase transition is survivorship bias without universality. To solve this problem, we define a modified sign that excludes the influence of the reference system, which can probe the phase transition strictly. The work gives an unbiased solution for detecting phase transition by the new modified sign. △ Less

Submitted 26 September, 2024; v1 submitted 29 January, 2023; originally announced January 2023.

Journal ref: Phys. Rev. B 110, 125141 (2024)

Experimental quantum computational chemistry with optimised unitary coupled cluster ansatz

Authors: Shaojun Guo, Jinzhao Sun, Haoran Qian, Ming Gong, Yukun Zhang, Fusheng Chen, Yangsen Ye, Yulin Wu, Sirui Cao, Kun Liu, Chen Zha, Chong Ying, Qingling Zhu, He-Liang Huang, Youwei Zhao, Shaowei Li, Shiyu Wang, Jiale Yu, Daojin Fan, Dachao Wu, Hong Su, Hui Deng, Hao Rong, Yuan Li, Kaili Zhang , et al. (13 additional authors not shown)

Abstract: Quantum computational chemistry has emerged as an important application of quantum computing. Hybrid quantum-classical computing methods, such as variational quantum eigensolvers (VQE), have been designed as promising solutions to quantum chemistry problems, yet challenges due to theoretical complexity and experimental imperfections hinder progress in achieving reliable and accurate results. Exper… ▽ More Quantum computational chemistry has emerged as an important application of quantum computing. Hybrid quantum-classical computing methods, such as variational quantum eigensolvers (VQE), have been designed as promising solutions to quantum chemistry problems, yet challenges due to theoretical complexity and experimental imperfections hinder progress in achieving reliable and accurate results. Experimental works for solving electronic structures are consequently still restricted to nonscalable (hardware efficient) or classically simulable (Hartree-Fock) ansatz, or limited to a few qubits with large errors. The experimental realisation of scalable and high-precision quantum chemistry simulation remains elusive. Here, we address the critical challenges {associated with} solving molecular electronic structures using noisy quantum processors. Our protocol presents significant improvements in the circuit depth and running time, key metrics for chemistry simulation. Through systematic hardware enhancements and the integration of error mitigation techniques, we push forward the limit of experimental quantum computational chemistry and successfully scale up the implementation of VQE with an optimised unitary coupled-cluster ansatz to 12 qubits. We produce high-precision results of the ground-state energy for molecules with error suppression by around two orders of magnitude. We achieve chemical accuracy for H$_2$ at all bond distances and LiH at small bond distances in the experiment, even beyond the two recent concurrent works. Our work demonstrates a feasible path towards a scalable solution to electronic structure calculation, validating the key technological features and identifying future challenges for this goal. △ Less

Submitted 17 June, 2024; v1 submitted 15 December, 2022; originally announced December 2022.

Comments: 11 pages, 4 figures in the main text, and 29 pages supplementary materials with 17 figures

Simple and high-precision Hamiltonian simulation by compensating Trotter error with linear combination of unitary operations

Authors: Pei Zeng, Jinzhao Sun, Liang Jiang, Qi Zhao

Abstract: Trotter and linear-combination-of-unitary (LCU) are two popular Hamiltonian simulation methods. We propose Hamiltonian simulation algorithms using LCU to compensate Trotter error, which enjoy both of their advantages. By adding few gates after the Kth-order Trotter, we realize a better time scaling than 2Kth-order Trotter. Our first algorithm exponentially improves the accuracy scaling of the Kth-… ▽ More Trotter and linear-combination-of-unitary (LCU) are two popular Hamiltonian simulation methods. We propose Hamiltonian simulation algorithms using LCU to compensate Trotter error, which enjoy both of their advantages. By adding few gates after the Kth-order Trotter, we realize a better time scaling than 2Kth-order Trotter. Our first algorithm exponentially improves the accuracy scaling of the Kth-order Trotter formula. In the second algorithm, we consider the detailed structure of Hamiltonians and construct LCU for Trotter errors with commutator scaling. Consequently, for lattice Hamiltonians, the algorithm enjoys almost linear system-size dependence and quadratically improves the accuracy of the Kth-order Trotter. △ Less

Submitted 27 March, 2025; v1 submitted 8 December, 2022; originally announced December 2022.

Comments: 44 pages, 17 figures. Comments are welcome

Journal ref: PRX Quantum 6, 010359 (2025)

Numerical issues of the two-dimensional Dirac equation

Authors: Jiale Sun, Xiaoshui Lin

Abstract: The two-dimensional Dirac equation has been widely used in graphene physics, the surface of topological insulators, and especially quantum scarring. Although a numerical approach to tackling an arbitrary confining problem was proposed several years ago, several fundamental issues must be thoroughly understood and solved. In this work, we conceal and address these challenges and finally develop a c… ▽ More The two-dimensional Dirac equation has been widely used in graphene physics, the surface of topological insulators, and especially quantum scarring. Although a numerical approach to tackling an arbitrary confining problem was proposed several years ago, several fundamental issues must be thoroughly understood and solved. In this work, we conceal and address these challenges and finally develop a complete method, validated by comparison with analytical results. △ Less

Submitted 5 September, 2023; v1 submitted 20 November, 2022; originally announced November 2022.

Comments: A new and more complete paper (including the idea of this paper but much more detailed and advanced) will be published in several months (The same first author). This paper includes some uncertain descriptions and not-fully-verified claims, and therefore need to be withdrawn to avoid misleading. Please check the new paper when available on arxiv

Orbital Expansion Variational Quantum Eigensolver: Enabling Efficient Simulation of Molecules with Shallow Quantum Circuit

Authors: Yusen Wu, Zigeng Huang, Jinzhao Sun, Xiao Yuan, Jingbo B. Wang, Dingshun Lv

Abstract: In the noisy-intermediate-scale-quantum era, Variational Quantum Eigensolver (VQE) is a promising method to study ground state properties in quantum chemistry, materials science, and condensed physics. However, general quantum eigensolvers are lack of systematical improvability, and achieve rigorous convergence is generally hard in practice, especially in solving strong-correlated systems. Here, w… ▽ More In the noisy-intermediate-scale-quantum era, Variational Quantum Eigensolver (VQE) is a promising method to study ground state properties in quantum chemistry, materials science, and condensed physics. However, general quantum eigensolvers are lack of systematical improvability, and achieve rigorous convergence is generally hard in practice, especially in solving strong-correlated systems. Here, we propose an Orbital Expansion VQE~(OE-VQE) framework to construct an efficient convergence path. The path starts from a highly correlated compact active space and rapidly expands and converges to the ground state, enabling simulating ground states with much shallower quantum circuits. We benchmark the OE-VQE on a series of typical molecules including H$_{6}$-chain, H$_{10}$-ring and N$_2$, and the simulation results show that proposed convergence paths dramatically enhance the performance of general quantum eigensolvers. △ Less

Submitted 13 October, 2022; originally announced October 2022.

Comments: Wu et al 2023 Quantum Sci. Technol

Ab initio Quantum Simulation of Strongly Correlated Materials with Quantum Embedding

Authors: Changsu Cao, Jinzhao Sun, Xiao Yuan, Han-Shi Hu, Hung Q. Pham, Dingshun Lv

Abstract: Quantum computing has shown great potential in various quantum chemical applications such as drug discovery, material design, and catalyst optimization. Although significant progress has been made in quantum simulation of simple molecules, ab initio simulation of solid-state materials on quantum computers is still in its early stage, mostly owing to the fact that the system size quickly becomes pr… ▽ More Quantum computing has shown great potential in various quantum chemical applications such as drug discovery, material design, and catalyst optimization. Although significant progress has been made in quantum simulation of simple molecules, ab initio simulation of solid-state materials on quantum computers is still in its early stage, mostly owing to the fact that the system size quickly becomes prohibitively large when approaching the thermodynamic limit. In this work, we introduce an orbital-based multi-fragment approach on top of the periodic density matrix embedding theory, resulting in a significantly smaller problem size for the current near-term quantum computer. We demonstrate the accuracy and efficiency of our method compared with the conventional methodologies and experiments on solid-state systems with complex electronic structures. These include spin polarized states of a hydrogen chain (1D-H), the equation of states of a boron nitride layer (h-BN) as well as the magnetic ordering in nickel oxide (NiO), a prototypical strongly correlated solid. Our results suggest that quantum embedding combined with a chemically intuitive fragmentation can greatly advance quantum simulation of realistic materials, thereby paving the way for solving important yet classically hard industrial problems on near-term quantum devices. △ Less

Submitted 16 February, 2023; v1 submitted 7 September, 2022; originally announced September 2022.

Comments: 23 pages, 7 figures, and 3 tables

Charging advantages of Lipkin-Meshkov-Glick quantum battery

Authors: Fu-Quan Dou, Yuan-Jin Wang, Jian-An Sun

Abstract: We investigate the performance of the Lipkin-Meshkov-Glick quantum battery based on shortcuts to adiabaticity (STA). We mainly consider the situation where the coupling strength of any two sites in the quantum battery is a sinusoidal function with respect to time. The charging efficiency of the quantum battery can be greatly enhanced via STA. We also analyze the influences of parameters, including… ▽ More We investigate the performance of the Lipkin-Meshkov-Glick quantum battery based on shortcuts to adiabaticity (STA). We mainly consider the situation where the coupling strength of any two sites in the quantum battery is a sinusoidal function with respect to time. The charging efficiency of the quantum battery can be greatly enhanced via STA. We also analyze the influences of parameters, including particle number, anisotropic parameter, the amplitude and frequency of the driving fields. It is found that an efficient charging process and thus high charging advantages can be achieved by adjusting these parameters properly. Moreover, we calculate the energy fluctuation, von Neumann entropy and energy cost during charging. The STA can make the stored energy and the von Neumann entropy change periodically during the charging process and reduce the energy fluctuation, and the minimal energy fluctuation always occurs in the proximity of minima of the von Neumann entropy. △ Less

Submitted 9 August, 2022; originally announced August 2022.

Comments: 8 pages,5 figures

Quantum computing quantum Monte Carlo algorithm

Authors: Yukun Zhang, Yifei Huang, Jinzhao Sun, Dingshun Lv, Xiao Yuan

Abstract: Quantum computing and quantum Monte Carlo (QMC) are respectively the state-of-the-art quantum and classical computing methods for understanding many-body quantum systems. Here, we propose a hybrid quantum-classical algorithm that integrates these two methods, inheriting their distinct features in efficient representation and manipulation of quantum states and overcoming their limitations. We first… ▽ More Quantum computing and quantum Monte Carlo (QMC) are respectively the state-of-the-art quantum and classical computing methods for understanding many-body quantum systems. Here, we propose a hybrid quantum-classical algorithm that integrates these two methods, inheriting their distinct features in efficient representation and manipulation of quantum states and overcoming their limitations. We first introduce non-stoquasticity indicators (NSIs) and their upper bounds, which measure the sign problem, the most notable limitation of QMC. We show that our algorithm could greatly mitigate the sign problem, which decreases NSIs with the assistance of quantum computing. Meanwhile, the use of quantum Monte Carlo also increases the expressivity of shallow quantum circuits, allowing more accurate computation that is conventionally achievable only with much deeper circuits. We numerically test and verify the method for the N$_2$ molecule (12 qubits) and the Hubbard model (16 qubits). Our work paves the way to solving practical problems with intermediate-scale and early-fault tolerant quantum computers, with potential applications in chemistry, condensed matter physics, materials, high energy physics, etc. △ Less

Submitted 9 November, 2025; v1 submitted 21 June, 2022; originally announced June 2022.

Cavity-Heisenberg spin chain quantum battery

Authors: Fu-Quan Dou, Hang Zhou, Jian-An Sun

Abstract: We propose a cavity-Heisenberg spin chain (CHS) quantum battery (QB) with the long-range interactions and investigate its charging process. The performance of the CHS QB is substantially improved compared to the Heisenberg spin chain (HS) QB. When the number of spins $N \gg 1$, the quantum advantage $α$ of the QB's maximum charging power can be obtained, which approximately satisfies a superlinear… ▽ More We propose a cavity-Heisenberg spin chain (CHS) quantum battery (QB) with the long-range interactions and investigate its charging process. The performance of the CHS QB is substantially improved compared to the Heisenberg spin chain (HS) QB. When the number of spins $N \gg 1$, the quantum advantage $α$ of the QB's maximum charging power can be obtained, which approximately satisfies a superlinear scaling relation $P_{max} \propto N^α$. For the CHS QB, $α$ can reach and even exceed $1.5$, while the HS QB can only reach about $α=0.75$. We find that the maximum stored energy of the CHS QB has a critical phenomenon. By analyzing the Wigner function, von Neumann entropy, and logarithmic negativity, we demonstrate that entanglement can be a necessary ingredient for QB to store more energy, but not sufficient. △ Less

Submitted 21 June, 2022; originally announced June 2022.

Journal ref: Phys. Rev. A 106 032212 (2022)

TensorCircuit: a Quantum Software Framework for the NISQ Era

Authors: Shi-Xin Zhang, Jonathan Allcock, Zhou-Quan Wan, Shuo Liu, Jiace Sun, Hao Yu, Xing-Han Yang, Jiezhong Qiu, Zhaofeng Ye, Yu-Qin Chen, Chee-Kong Lee, Yi-Cong Zheng, Shao-Kai Jian, Hong Yao, Chang-Yu Hsieh, Shengyu Zhang

Abstract: TensorCircuit is an open source quantum circuit simulator based on tensor network contraction, designed for speed, flexibility and code efficiency. Written purely in Python, and built on top of industry-standard machine learning frameworks, TensorCircuit supports automatic differentiation, just-in-time compilation, vectorized parallelism and hardware acceleration. These features allow TensorCircui… ▽ More TensorCircuit is an open source quantum circuit simulator based on tensor network contraction, designed for speed, flexibility and code efficiency. Written purely in Python, and built on top of industry-standard machine learning frameworks, TensorCircuit supports automatic differentiation, just-in-time compilation, vectorized parallelism and hardware acceleration. These features allow TensorCircuit to simulate larger and more complex quantum circuits than existing simulators, and are especially suited to variational algorithms based on parameterized quantum circuits. TensorCircuit enables orders of magnitude speedup for various quantum simulation tasks compared to other common quantum software, and can simulate up to 600 qubits with moderate circuit depth and low-dimensional connectivity. With its time and space efficiency, flexible and extensible architecture and compact, user-friendly API, TensorCircuit has been built to facilitate the design, simulation and analysis of quantum algorithms in the Noisy Intermediate-Scale Quantum (NISQ) era. △ Less

Submitted 27 January, 2023; v1 submitted 20 May, 2022; originally announced May 2022.

Comments: Whitepaper for TensorCircuit, 43 pages, 11 figures, 9 tables

Journal ref: Quantum 7, 912 (2023)

Efficient quantum imaginary time evolution by drifting real time evolution: an approach with low gate and measurement complexity

Authors: Yifei Huang, Yuguo Shao, Weiluo Ren, Jinzhao Sun, Dingshun Lv

Abstract: Quantum imaginary time evolution (QITE) is one of the promising candidates for finding eigenvalues and eigenstates of a Hamiltonian. However, the original QITE proposal [Nat. Phys. 16, 205-210 (2020)], which approximates the imaginary time evolution by real time evolution, suffers from large circuit depth and measurements due to the size of the Pauli operator pool and Trotterization. To alleviate… ▽ More Quantum imaginary time evolution (QITE) is one of the promising candidates for finding eigenvalues and eigenstates of a Hamiltonian. However, the original QITE proposal [Nat. Phys. 16, 205-210 (2020)], which approximates the imaginary time evolution by real time evolution, suffers from large circuit depth and measurements due to the size of the Pauli operator pool and Trotterization. To alleviate the requirement for deep circuits, we propose a time-dependent drifting scheme inspired by the qDRIFT algorithm [Phys. Rev. Lett 123, 070503 (2019)], which randomly draws a Pauli term out of the approximated unitary operation generators of QITE according to the strength and rescales that term by the total strength of the Pauli terms. We show that this drifting scheme removes the depth dependency on size of the operator pool and converges inverse linearly to the number of steps. We further propose a deterministic algorithm that selects the dominant Pauli term to reduce the fluctuation for the ground state preparation. Meanwhile, we introduce an efficient measurement reduction scheme across Trotter steps, which removes its cost dependence on the number of iterations, and a measurement distribution protocol for different observables within each time step. We also analyze the main source of error for our scheme both theoretically and numerically. We numerically test the validity of depth reduction, convergence performance, and faithfulness of measurement reduction approximation of our algorithms on LiH, BeH$_2$ and N$_2$ molecules. In particular, the results on LiH molecule give circuit depths comparable to that of the advanced adaptive variational quantum eigensolver~(VQE) methods while requiring much fewer measurements. △ Less

Submitted 5 September, 2022; v1 submitted 21 March, 2022; originally announced March 2022.

Journal ref: J. Chem. Theory Comput. 2023, 19, 13, 3868-3876

Controllable multiple beam splitting in Hermitian and non-Hermitian symmetric coupled waveguide systems

Authors: Fu-Quan Dou, Ya-Ting Wei, Min-Peng Han, Jian-An Sun

Abstract: We investigate high-fidelity multiple beam splitting in Hermitian and non-Hermitian symmetric coupled waveguides with one input and 2N output waveguide channels. In Hermitian systems, we realize adiabatically light splitting in resonant case based on the stimulated Raman adiabatic passage (STIRAP) and arbitrary proportion from the middle waveguide to outer waveguides in propagation coefficients mi… ▽ More We investigate high-fidelity multiple beam splitting in Hermitian and non-Hermitian symmetric coupled waveguides with one input and 2N output waveguide channels. In Hermitian systems, we realize adiabatically light splitting in resonant case based on the stimulated Raman adiabatic passage (STIRAP) and arbitrary proportion from the middle waveguide to outer waveguides in propagation coefficients mismatch case using shortcuts to adiabaticity (STA) technique. In non-Hermitian systems with even waveguides being dissipative, the compact and robust beam splitting can be achieved by eliminating the non-adiabatic coupling via the non-Hermitian STA method. We further verify the feasibility of our theoretical predictions by means of the beam propagation method (BPM). The suggested multiple beam splitters open new opportunities for the realization of on-chip high-bandwidth photonics with high fidelity in short distances. △ Less

Submitted 16 April, 2022; v1 submitted 16 February, 2022; originally announced February 2022.

Comments: Accepted

Journal ref: Journal of Optics 24 (2022) 065801

Robust and Efficient Hamiltonian Learning

Authors: Wenjun Yu, Jinzhao Sun, Zeyao Han, Xiao Yuan

Abstract: With the fast development of quantum technology, the sizes of both digital and analog quantum systems increase drastically. In order to have better control and understanding of the quantum hardware, an important task is to characterize the interaction, i.e., to learn the Hamiltonian, which determines both static and dynamic properties of the system. Conventional Hamiltonian learning methods either… ▽ More With the fast development of quantum technology, the sizes of both digital and analog quantum systems increase drastically. In order to have better control and understanding of the quantum hardware, an important task is to characterize the interaction, i.e., to learn the Hamiltonian, which determines both static and dynamic properties of the system. Conventional Hamiltonian learning methods either require costly process tomography or adopt impractical assumptions, such as prior information on the Hamiltonian structure and the ground or thermal states of the system. In this work, we present a robust and efficient Hamiltonian learning method that circumvents these limitations based only on mild assumptions. The proposed method can efficiently learn any Hamiltonian that is sparse on the Pauli basis using only short-time dynamics and local operations without any information on the Hamiltonian or preparing any eigenstates or thermal states. The method has a scalable complexity and a vanishing failure probability regarding the qubit number. Meanwhile, it performs robustly given the presence of state preparation and measurement errors and resiliently against a certain amount of circuit and shot noise. We numerically test the scaling and the estimation accuracy of the method for transverse field Ising Hamiltonian with random interaction strengths and molecular Hamiltonians, both with varying sizes and manually added noise. All these results verify the robustness and efficacy of the method, paving the way for a systematic understanding of the dynamics of large quantum systems. △ Less

Submitted 23 June, 2023; v1 submitted 1 January, 2022; originally announced January 2022.

Comments: 41 pages, 6 figures, Open source implementation available at https://github.com/zyHan2077/HamiltonianLearning

Journal ref: Quantum 7, 1045 (2023)

Extended Dicke quantum battery with interatomic interactions and driving field

Authors: Fu-Quan Dou, You-Qi Lu, Yuan-Jin Wang, Jian-An Sun

Abstract: We investigate the charging process of quantum battery (QB) systems in an extended Dicke model with both atomic interactions and an external driving field. We focus on the effects of the atomic interaction and the external driving field on the charging performance of QB and find that the maximum stored energy of QB has a critical phenomenon. We analyze the critical behavior and obtain the analytic… ▽ More We investigate the charging process of quantum battery (QB) systems in an extended Dicke model with both atomic interactions and an external driving field. We focus on the effects of the atomic interaction and the external driving field on the charging performance of QB and find that the maximum stored energy of QB has a critical phenomenon. We analyze the critical behavior and obtain the analytical expression of the critical atomic interaction. The dependence of the maximum stored energy, the energy quantum fluctuations and the maximum charging power on the number $N$ of the two-level systems are also discussed. In particular, for the maximum charging power, we obtain the quantum advantage of the QB, which approximately satisfies a superlinear scaling relation $P_{max}\propto N^α$, where scaling exponent $α$ varies with the number $N$ of the two-level systems. In the ultra-strong coupling regime, the atomic interaction can lead to a faster battery charging, and the quantum advantage $α= 1.88$ can be achieved. While in the deep-strong coupling regime, the quantum advantage of the QB's maximum charging power is the same as that of the Dicke QB, i.e., $α=1.5$. △ Less

Submitted 25 December, 2021; originally announced December 2021.

Journal ref: Phys. Rev. B 105, 115405 (2022)

Universal quantum algorithmic cooling on a quantum computer

Authors: Pei Zeng, Jinzhao Sun, Xiao Yuan

Abstract: Quantum cooling, a deterministic process that drives any state to the lowest eigenstate, has been widely used from studying ground state properties of chemistry and condensed matter quantum physics, to general optimization problems. However, the cooling procedure is generally non-unitary, hence its realization on a quantum computer either requires deep circuits or assumes specific input states wit… ▽ More Quantum cooling, a deterministic process that drives any state to the lowest eigenstate, has been widely used from studying ground state properties of chemistry and condensed matter quantum physics, to general optimization problems. However, the cooling procedure is generally non-unitary, hence its realization on a quantum computer either requires deep circuits or assumes specific input states with variational circuits. Here, we propose universal quantum cooling algorithms that overcome these limitations. By utilizing a dual phase representation of decaying functions, we show how to universally and deterministically realize a general cooling procedure with shallow quantum circuits. We demonstrate its applications in cooling an arbitrary input state with known ground state energy, corresponding to satisfactory, linear algebra tasks, and quantum state compiling tasks, and preparing unknown eigenvalues and eigenstates, corresponding to quantum many-body problems. Compared to quantum phase estimation, our method uses only one ancillary qubit and much shallower circuits, showing exponential improvement of the circuit complexity with respect to the final state infidelity. We numerically benchmark the algorithms for the $8$-qubit Heisenberg model and verify its feasibility for accurately finding eigenenergies and obtaining eigenstate measurements. Our work paves the way for efficient and universal quantum algorithmic cooling with near-term as well as universal fault-tolerant quantum devices. △ Less

Submitted 2 June, 2022; v1 submitted 30 September, 2021; originally announced September 2021.

Comments: 35 pages, 7 figures. Comments are welcome

Toward Practical Quantum Embedding Simulation of Realistic Chemical Systems on Near-term Quantum Computers

Authors: Weitang Li, Zigeng Huang, Changsu Cao, Yifei Huang, Zhigang Shuai, Xiaoming Sun, Jinzhao Sun, Xiao Yuan, Dingshun Lv

Abstract: Quantum computing has recently exhibited great potentials in predicting chemical properties for various applications in drug discovery, material design, and catalyst optimization. Progress has been made in simulating small molecules, such as LiH and hydrogen chains of up to 12 qubits, by using quantum algorithms such as variational quantum eigensolver (VQE). Yet, originating from limitations of th… ▽ More Quantum computing has recently exhibited great potentials in predicting chemical properties for various applications in drug discovery, material design, and catalyst optimization. Progress has been made in simulating small molecules, such as LiH and hydrogen chains of up to 12 qubits, by using quantum algorithms such as variational quantum eigensolver (VQE). Yet, originating from limitations of the size and the fidelity of near-term quantum hardware, how to accurately simulate large realistic molecules remains a challenge. Here, integrating an adaptive energy sorting strategy and a classical computational method, the density matrix embedding theory, which effectively finds a shallower quantum circuit and reduces the problem size, respectively, we show a means to circumvent the limitations and demonstrate the potential toward solving real chemical problems. We numerically test the method for the hydrogenation reaction of C6H8 and the equilibrium geometry of the C18 molecule, with basis sets up to cc-pVDZ (at most 144 qubits). The simulation results show accuracies comparable to those of advanced quantum chemistry methods such as coupled-cluster or even full configuration interaction, while the number of qubits required is reduced by an order of magnitude (from 144 qubits to 16 qubits for the C18 molecule) compared to conventional VQE. Our work implies the possibility of solving industrial chemical problems on near-term quantum devices. △ Less

Submitted 16 September, 2021; originally announced September 2021.

Comments: 14 pages, 5 figures, 1 table

Towards a variational Jordan-Lee-Preskill quantum algorithm

Authors: Junyu Liu, Zimu Li, Han Zheng, Xiao Yuan, Jinzhao Sun

Abstract: Rapid developments of quantum information technology show promising opportunities for simulating quantum field theory in near-term quantum devices. In this work, we formulate the theory of (time-dependent) variational quantum simulation of the 1+1 dimensional $λφ^4$ quantum field theory including encoding, state preparation, and time evolution, with several numerical simulation results. These algo… ▽ More Rapid developments of quantum information technology show promising opportunities for simulating quantum field theory in near-term quantum devices. In this work, we formulate the theory of (time-dependent) variational quantum simulation of the 1+1 dimensional $λφ^4$ quantum field theory including encoding, state preparation, and time evolution, with several numerical simulation results. These algorithms could be understood as near-term variational quantum circuit (quantum neural network) analogs of the Jordan-Lee-Preskill algorithm, the basic algorithm for simulating quantum field theory using universal quantum devices. Besides, we highlight the advantages of encoding with harmonic oscillator basis based on the LSZ reduction formula and several computational efficiency such as when implementing a bosonic version of the unitary coupled cluster ansatz to prepare initial states. We also discuss how to circumvent the "spectral crowding" problem in the quantum field theory simulation and appraise our algorithm by both state and subspace fidelities. △ Less

Submitted 28 December, 2022; v1 submitted 12 September, 2021; originally announced September 2021.

Comments: v2: modified style, add references, clear typos. v3; v4: significant change, authors added

Journal ref: Mach. Learn.: Sci. Technol. 3 045030, 2022

Experimental quantum state measurement with classical shadows

Authors: Ting Zhang, Jinzhao Sun, Xiao-Xu Fang, Xiao-Ming Zhang, Xiao Yuan, He Lu

Abstract: A crucial subroutine for various quantum computing and communication algorithms is to efficiently extract different classical properties of quantum states. In a notable recent theoretical work by Huang, Kueng, and Preskill [Nat. Phys. 16, 1050 (2020)], a thrifty scheme showed how to project the quantum state into classical shadows and simultaneously predict $M$ different functions of a state with… ▽ More A crucial subroutine for various quantum computing and communication algorithms is to efficiently extract different classical properties of quantum states. In a notable recent theoretical work by Huang, Kueng, and Preskill [Nat. Phys. 16, 1050 (2020)], a thrifty scheme showed how to project the quantum state into classical shadows and simultaneously predict $M$ different functions of a state with only $\mathcal{O}(\log_2 M)$ measurements, independent of the system size and saturating the information-theoretical limit. Here, we experimentally explore the feasibility of the scheme in the realistic scenario with a finite number of measurements and noisy operations. We prepare a four-qubit GHZ state and show how to estimate expectation values of multiple observables and Hamiltonians. We compare the measurement strategies with uniform, biased, and derandomized classical shadows to conventional ones that sequentially measure each state function exploiting either importance sampling or observable grouping. We next demonstrate the estimation of nonlinear functions using classical shadows and analyze the entanglement of the prepared quantum state. Our experiment verifies the efficacy of exploiting (derandomized) classical shadows and sheds light on efficient quantum computing with noisy intermediate-scale quantum hardware. △ Less

Submitted 18 November, 2021; v1 submitted 18 June, 2021; originally announced June 2021.

Comments: 20 pages, 13 figures, 2 tables

Journal ref: Phys. Rev. Lett. 127, 200501 (2021)