-
Enhanced spectral range of strain-induced tuning of quantum dots in circular Bragg grating cavities
Authors:
Ivan Gamov,
Matthias Sauter,
Samuel Huber,
Quirin Buchinger,
Peter Gschwandtner,
Ulrike Wallrabe,
Sven Höfling,
Tobias Huber-Loyola
Abstract:
Tunable sources of entangled and single photons are essential for implementing entanglement-based quantum information protocols, as quantum teleportation and entanglement swapping depend on photon indistinguishability. Tunable devices are fabricated from indium arsenide (InAs) quantum dots (QDs) embedded in gallium arsenide (GaAs) nanomembranes placed on monolithic piezoelectric substrates. Circul…
▽ More
Tunable sources of entangled and single photons are essential for implementing entanglement-based quantum information protocols, as quantum teleportation and entanglement swapping depend on photon indistinguishability. Tunable devices are fabricated from indium arsenide (InAs) quantum dots (QDs) embedded in gallium arsenide (GaAs) nanomembranes placed on monolithic piezoelectric substrates. Circular Bragg grating (CBG) resonators enhance emission brightness and exploit the Purcell effect; however, the inclusion of CBGs reduces strain-mediated tunability compared to planar nanomembranes. A simple and effective solution is introduced: filling the CBG trenches with a stiff dielectric (aluminum oxide) via atomic layer deposition (ALD) restores up to 95% of the tunability of planar structures. Finite element analysis (FEA) confirms that the tunability loss originates from bending in the device layers due to strain relief in the CBG geometry. Lowering the stiffness of intermediate layers between the QDs and the piezoelectric actuator, such as in bonding or reflector layers, further increases strain losses in uncoated CBGs. Coated devices maintain 98-99% strain-tuning efficiency across all simulated underlayer stiffnesses. The results demonstrate that advantageous optical cavity properties can be effectively combined with piezoelectric strain tuning, enabling scalable, bright, and tunable quantum light sources.
△ Less
Submitted 12 November, 2025;
originally announced November 2025.
-
Deterministic Quantum Dot Cavity Placement Using Hyperspectral Imaging with High Spatial Accuracy and Precision
Authors:
Quirin Buchinger,
Constantin Krause,
Aileen Zhang,
Giora Peniakov,
Mohamed Helal,
Yorick Reum,
Andreas Theo Pfenning,
Sven Höfling,
Tobias Huber-Loyola
Abstract:
Single emitters in solid state are great sources of single and entangled photons. To boost their extraction efficiency and tailor their emission properties, they are often incorporated in photonic nanostructures. However, achieving accurate and reproducible placement inside the cavity is challenging but necessary to ensure the highest mode overlap and optimal device performance. For many cavity ty…
▽ More
Single emitters in solid state are great sources of single and entangled photons. To boost their extraction efficiency and tailor their emission properties, they are often incorporated in photonic nanostructures. However, achieving accurate and reproducible placement inside the cavity is challenging but necessary to ensure the highest mode overlap and optimal device performance. For many cavity types -- such as photonic crystal cavities or circular Bragg grating cavities -- even small displacements lead to a significantly reduced emitter-cavity coupling. For circular Bragg grating cavities, this yields a significant reduction in Purcell effect, a slight reduction in efficiency and it introduces polarization on the emitted photons. Here we show a method to achieve high accuracy and precision for deterministically placed cavities on the example of circular Bragg gratings on randomly distributed semiconductor quantum dots. We introduce periodic alignment markers for improved marker detection accuracy and investigate overall imaging accuracy achieving $(9.1 \pm 2.5) nm$ through image correction. Since circular Bragg grating cavities exhibit a strong polarization response when the emitter is displaced, they are ideal devices to probe the cavity placement accuracy far below the diffraction limit. From the measured device polarizations, we derive a total spatial process accuracy of $(33.5 \pm 9.9) nm$ based on the raw data, and an accuracy of $(15 \pm 11) nm$ after correcting for the system response, resulting in a device yield of $68 \%$ for well-placed cavities.
△ Less
Submitted 14 May, 2025;
originally announced May 2025.
-
Quantum teleportation with dissimilar quantum dots over a hybrid quantum network
Authors:
Alessandro Laneve,
Giuseppe Ronco,
Mattia Beccaceci,
Paolo Barigelli,
Francesco Salusti,
Nicolas Claro-Rodriguez,
Giorgio De Pascalis,
Alessia Suprano,
Leone Chiaudano,
Eva Schöll,
Lukas Hanschke,
Tobias M. Krieger,
Quirin Buchinger,
Saimon F. Covre da Silva,
Julia Neuwirth,
Sandra Stroj,
Sven Höfling,
Tobias Huber-Loyola,
Mario A. Usuga Castaneda,
Gonzalo Carvacho,
Nicolò Spagnolo,
Michele B. Rota,
Francesco Basso Basset,
Armando Rastelli,
Fabio Sciarrino
, et al. (2 additional authors not shown)
Abstract:
Photonic quantum information processing in metropolitan quantum networks lays the foundation for cloud quantum computing [1, 2], secure communication [3, 4], and the realization of a global quantum internet [5, 6]. This paradigm shift requires on-demand and high-rate generation of flying qubits and their quantum state teleportation over long distances [7]. Despite the last decade has witnessed an…
▽ More
Photonic quantum information processing in metropolitan quantum networks lays the foundation for cloud quantum computing [1, 2], secure communication [3, 4], and the realization of a global quantum internet [5, 6]. This paradigm shift requires on-demand and high-rate generation of flying qubits and their quantum state teleportation over long distances [7]. Despite the last decade has witnessed an impressive progress in the performances of deterministic photon sources [8-11], the exploitation of distinct quantum emitters to implement all-photonic quantum teleportation among distant parties has remained elusive. Here, we overcome this challenge by using dissimilar quantum dots whose electronic and optical properties are engineered by light-matter interaction [12], multi-axial strain [13] and magnetic fields [14] so as to make them suitable for the teleportation of polarization qubits. This is demonstrated in a hybrid quantum network harnessing both fiber connections and 270 m free-space optical link connecting two buildings of the University campus in the center of Rome. The protocol exploits GPS-assisted synchronization, ultra-fast single photon detectors as well as stabilization systems that compensate for atmospheric turbulence. The achieved teleportation state fidelity reaches up to 82+-1%, above the classical limit by more than 10 standard deviations. Our field demonstration of all-photonic quantum teleportation opens a new route to implement solid-state based quantum relays and builds the foundation for practical quantum networks.
△ Less
Submitted 19 November, 2024;
originally announced November 2024.
-
Wavevector-resolved polarization entanglement from radiative cascades
Authors:
Alessandro Laneve,
Michele B. Rota,
Francesco Basso Basset,
Mattia Beccaceci,
Valerio Villari,
Thomas Oberleitner,
Yorick Reum,
Tobias M. Krieger,
Quirin Buchinger,
Saimon F. Covre da Silva,
Andreas Pfenning,
Sandra Stroj,
Sven Höfling,
Armando Rastelli,
Tobias Huber-Loyola,
Rinaldo Trotta
Abstract:
The generation of entangled photons from radiative cascades has enabled milestone experiments in quantum information science with several applications in photonic quantum technologies. Significant efforts are being devoted to pushing the performances of near-deterministic entangled-photon sources based on single quantum emitters often embedded in photonic cavities, so to boost the flux of photon p…
▽ More
The generation of entangled photons from radiative cascades has enabled milestone experiments in quantum information science with several applications in photonic quantum technologies. Significant efforts are being devoted to pushing the performances of near-deterministic entangled-photon sources based on single quantum emitters often embedded in photonic cavities, so to boost the flux of photon pairs. The general postulate is that the emitter generates photons in a nearly maximally entangled state of polarization, ready for application purposes. Here, we demonstrate that this assumption is unjustified. We show that in radiative cascades there exists an interplay between photon polarization and emission wavevector, strongly affecting quantum correlations when emitters are embedded in micro-cavities. We discuss how the polarization entanglement of photon pairs from a biexciton-exciton cascade in quantum dots strongly depends on their propagation wavevector, and it can even vanish for large emission angles. Our experimental results, backed by theoretical modelling, yield a brand-new understanding of cascaded emission for various quantum emitters. In addition, our model provides quantitative guidelines for designing optical microcavities that retain both a high degree of entanglement and collection efficiency, moving the community one step further towards an ideal source of entangled photons for quantum technologies.
△ Less
Submitted 12 September, 2024;
originally announced September 2024.
-
Purcell-Enhanced Single-Photon Emission in the Telecom C-Band
Authors:
Jochen Kaupp,
Yorick Reum,
Felix Kohr,
Johannes Michl,
Quirin Buchinger,
Adriana Wolf,
Giora Peniakov,
Tobias Huber-Loyola,
Andreas Pfenning,
Sven Höfling
Abstract:
Purcell-enhanced quantum dot single-photon emission in the telecom C-band from InAs quantum dots inside circular Bragg grating cavities is shown. The InAs quantum dots are grown by means of molecular beam epitaxy on an InP substrate and are embedded into a quaternary $\mathrm{In}_{0.53}\mathrm{Al}_{0.23}\mathrm{Ga}_{0.24}\mathrm{As}$ membrane structure. In a post-growth flip-chip process with subs…
▽ More
Purcell-enhanced quantum dot single-photon emission in the telecom C-band from InAs quantum dots inside circular Bragg grating cavities is shown. The InAs quantum dots are grown by means of molecular beam epitaxy on an InP substrate and are embedded into a quaternary $\mathrm{In}_{0.53}\mathrm{Al}_{0.23}\mathrm{Ga}_{0.24}\mathrm{As}$ membrane structure. In a post-growth flip-chip process with subsequent substrate removal and electron beam-lithography, circular Bragg grating ("bullseye") resonators are defined. Micro-photoluminescence studies of the devices at cryogenic temperatures of T = 5 K reveal individual quantum dot emission lines into a pronounced cavity mode. Time-correlated single-photon counting measurements under above-band gap excitation yield Purcell-enhanced excitonic decay times of $τ= (180 \pm 3)$ ps corresponding to a Purcell factor of $F_P = (6.7 \pm 0.6)$. Pronounced photon antibunching with a background limited $g^{(2)}(0) = (0.057 \pm 0.004)$ is observed, which demonstrates that the light originated mostly from one single quantum dot.
△ Less
Submitted 3 November, 2023;
originally announced November 2023.
-
Polarized and Un-Polarized Emission from a Single Emitter in a Bullseye Resonator
Authors:
Giora Peniakov,
Quirin Buchinger,
Mohamed Helal,
Simon Betzold,
Yorick Reum,
Michele B. Rota,
Giuseppe Ronco,
Mattia Beccaceci,
Tobias M. Krieger,
Saimon F. Covre Da Silva,
Armando Rastelli,
Rinaldo Trotta,
Andreas Pfenning,
Sven Hoefling,
Tobias Huber-Loyola
Abstract:
We present polarized |S|=0.99$\pm$0.01, and unpolarized |S|=0.03$\pm$0.01 emission from a single emitter embedded in a single, cylindrically symmetric device design. We show that the polarization stems from a position offset of the single emitter with respect to the cavity center, which breaks the cylindrical symmetry, and a position-dependent coupling to the frequency degenerate eigenmodes of the…
▽ More
We present polarized |S|=0.99$\pm$0.01, and unpolarized |S|=0.03$\pm$0.01 emission from a single emitter embedded in a single, cylindrically symmetric device design. We show that the polarization stems from a position offset of the single emitter with respect to the cavity center, which breaks the cylindrical symmetry, and a position-dependent coupling to the frequency degenerate eigenmodes of the resonator structure. The experimental results are interpreted by using numerical simulations and by experimental mapping of the polarization-resolved far-field emission patterns. Our findings can be generalized to any nanophotonic structure where two orthogonal eigenmodes are not fully spatially overlapping.
△ Less
Submitted 5 October, 2023; v1 submitted 11 August, 2023;
originally announced August 2023.
-
A source of entangled photons based on a cavity-enhanced and strain-tuned GaAs quantum dot
Authors:
Michele B. Rota,
Tobias M. Krieger,
Quirin Buchinger,
Mattia Beccaceci,
Julia Neuwirth,
Hêlio Huet,
Nikola Horová,
Gabriele Lovicu,
Giuseppe Ronco,
Saimon F. Covre da Silva,
Giorgio Pettinari,
Magdalena Moczała-Dusanowska,
Christoph Kohlberger,
Santanu Manna,
Sandra Stroj,
Julia Freund,
Xueyong Yuan,
Christian Schneider,
Miroslav Ježek,
Sven Höfling,
Francesco Basso Basset,
Tobias Huber-Loyola,
Armando Rastelli,
Rinaldo Trotta
Abstract:
A quantum-light source that delivers photons with a high brightness and a high degree of entanglement is fundamental for the development of efficient entanglement-based quantum-key distribution systems. Among all possible candidates, epitaxial quantum dots are currently emerging as one of the brightest sources of highly entangled photons. However, the optimization of both brightness and entangleme…
▽ More
A quantum-light source that delivers photons with a high brightness and a high degree of entanglement is fundamental for the development of efficient entanglement-based quantum-key distribution systems. Among all possible candidates, epitaxial quantum dots are currently emerging as one of the brightest sources of highly entangled photons. However, the optimization of both brightness and entanglement currently requires different technologies that are difficult to combine in a scalable manner. In this work, we overcome this challenge by developing a novel device consisting of a quantum dot embedded in a circular Bragg resonator, in turn, integrated onto a micromachined piezoelectric actuator. The resonator engineers the light-matter interaction to empower extraction efficiencies up to 0.69(4). Simultaneously, the actuator manipulates strain fields that tune the quantum dot for the generation of entangled photons with corrected fidelities to a maximally entangled state up to 0.96(1). This hybrid technology has the potential to overcome the limitations of the key rates that plague QD-based entangled sources for entanglement-based quantum key distribution and entanglement-based quantum networks.
△ Less
Submitted 30 April, 2024; v1 submitted 23 December, 2022;
originally announced December 2022.
-
Signatures of the Optical Stark Effect on Entangled Photon Pairs from Resonantly-Pumped Quantum Dots
Authors:
Francesco Basso Basset,
Michele B. Rota,
Mattia Beccaceci,
Tobias M. Krieger,
Quirin Buchinger,
Julia Neuwirth,
Hêlio Huet,
Sandra Stroj,
Saimon F. Covre da Silva,
Giuseppe Ronco,
Christian Schimpf,
Sven Höfling,
Tobias Huber-Loyola,
Armando Rastelli,
Rinaldo Trotta
Abstract:
Two-photon resonant excitation of the biexciton-exciton cascade in a quantum dot generates highly polarization-entangled photon pairs in a near-deterministic way. However, the ultimate level of achievable entanglement is still debated. Here, we observe the impact of the laser-induced AC-Stark effect on the quantum dot emission spectra and on entanglement. For increasing pulse-duration/lifetime rat…
▽ More
Two-photon resonant excitation of the biexciton-exciton cascade in a quantum dot generates highly polarization-entangled photon pairs in a near-deterministic way. However, the ultimate level of achievable entanglement is still debated. Here, we observe the impact of the laser-induced AC-Stark effect on the quantum dot emission spectra and on entanglement. For increasing pulse-duration/lifetime ratios and pump powers, decreasing values of concurrence are recorded. Nonetheless, additional contributions are still required to fully account for the observed below-unity concurrence.
△ Less
Submitted 2 August, 2023; v1 submitted 14 December, 2022;
originally announced December 2022.
-
Experimental Multi-state Quantum Discrimination in the Frequency Domain with Quantum Dot Light
Authors:
Alessandro Laneve,
Michele B. Rota,
Francesco Basso Basset,
Nicola P. Fiorente,
Tobias M. Krieger,
Saimon F. Covre da Silva,
Quirin Buchinger,
Sandra Stroj,
Sven Hoefling,
Tobias Huber-Loyola,
Armando Rastelli,
Rinaldo Trotta,
Paolo Mataloni
Abstract:
The quest for the realization of effective quantum state discrimination strategies is of great interest for quantum information technology, as well as for fundamental studies. Therefore, it is crucial to develop new and more efficient methods to implement discrimination protocols for quantum states. Among the others, single photon implementations are more advisable, because of their inherent secur…
▽ More
The quest for the realization of effective quantum state discrimination strategies is of great interest for quantum information technology, as well as for fundamental studies. Therefore, it is crucial to develop new and more efficient methods to implement discrimination protocols for quantum states. Among the others, single photon implementations are more advisable, because of their inherent security advantage in quantum communication scenarios. In this work, we present the experimental realization of a protocol employing a time-multiplexing strategy to optimally discriminate among eight non-orthogonal states, encoded in the four-dimensional Hilbert space spanning both the polarization degree of freedom and photon energy. The experiment, built on a custom-designed bulk optics analyser setup and single photons generated by a nearly deterministic solid-state source, represents a benchmarking example of minimum error discrimination with actual quantum states, requiring only linear optics and two photodetectors to be realized. Our work paves the way for more complex applications and delivers a novel approach towards high-dimensional quantum encoding and decoding operations.
△ Less
Submitted 17 September, 2022;
originally announced September 2022.
-
Optical properties of circular Bragg gratings with labyrinth geometry to enable electrical contacts
Authors:
Quirin Buchinger,
Simon Betzold,
Sven Höfling,
Tobias Huber-Loyola
Abstract:
We present an optical study of various device designs for electrically contactable circular Bragg grating cavities in labyrinth geometries. To create an electrical connection between the central disk and the surrounding membrane, which are separated through air gaps, we introduce connections between the adjacent rings. We propose to rotate these connections, creating a labyrinth like structure, to…
▽ More
We present an optical study of various device designs for electrically contactable circular Bragg grating cavities in labyrinth geometries. To create an electrical connection between the central disk and the surrounding membrane, which are separated through air gaps, we introduce connections between the adjacent rings. We propose to rotate these connections, creating a labyrinth like structure, to disable waveguiding and keep the mode confinement. To investigate how different arrangement and size of the connections affect the optical properties and to find the optimal design, six different layouts with either 3-fold or 4-fold symmetry and one with 2-fold symmetry are investigated experimentally and by numerical simulations. Reflectivity measurements and simulations show that rotating the connections improves the mode confinement, far-field pattern and Purcell factor compared to layouts with connections arranged in straight lines. We compare results between different layouts for different connection widths and perform polarization resolved measurements to investigate whether the connections create asymmetries in the photonic confinement that would impede the performance of the device.
△ Less
Submitted 12 May, 2023; v1 submitted 15 September, 2022;
originally announced September 2022.
-
Purcell-enhanced single photon source based on a deterministically placed WSe$_{2}$ monolayer quantum dot in a circular Bragg grating cavity
Authors:
O. Iff,
Q. Buchinger,
M. Moczała-Dusanowska,
M. Kamp,
S. Betzold,
S. Tongay,
C. Antón-Solanas,
S. Höfling,
C. Schneider
Abstract:
We demonstrate a deterministic Purcell-enhanced single-photon source realized by integrating an atomically thin WSe$_{2}$ layer with a circular Bragg grating cavity. The cavity significantly enhances the photoluminescence from the atomically thin layer, and supports single-photon generation with $g^{(2)}(0)<0.25$. We observe a consistent increase of the spontaneous emission rate for WSe$_{2}$ emit…
▽ More
We demonstrate a deterministic Purcell-enhanced single-photon source realized by integrating an atomically thin WSe$_{2}$ layer with a circular Bragg grating cavity. The cavity significantly enhances the photoluminescence from the atomically thin layer, and supports single-photon generation with $g^{(2)}(0)<0.25$. We observe a consistent increase of the spontaneous emission rate for WSe$_{2}$ emitters located in the center of the Bragg grating cavity. These WSe$_{2}$ emitters are self-aligned and deterministically coupled to such a broadband cavity, configuring a new generation of deterministic single-photon sources, characterized by their simple and low-cost production and intrinsic scalability.
△ Less
Submitted 4 February, 2021;
originally announced February 2021.