WO2013009161A1

WO2013009161A1 - Quantum states for 6dp quantum key distribution protocol

Info

Publication number: WO2013009161A1
Application number: PCT/MY2012/000130
Authority: WO
Inventors: Abdul Khir Mohd Fared; Suryadi; Nawi MOHD NURIMAN; Saiyed Rasol SAIYED ABDUL FATAH; Mohd Zain Mohd Nor Zaliman
Original assignee: Mimos Berhad
Priority date: 2011-07-13
Filing date: 2012-06-20
Publication date: 2013-01-17

Abstract

Quantum states for 6DP quantum key distribution protocol of the present invention utilize the use of biphoton with single wavelength as the new source of 6DP to generate and control photons. The approach of the present invention minimizes the probability of attack from third parties to gain information. The present invention comprises of three (3) main parts, the first part for Spontaneous Parametric Down Conversion (SPDC) photon pair generation (302), the second part refers to the delay process to control the polarization of each photon independently by delaying one photon from its pair (304, 306, 308) and the final part (310) relates to pair polarizations that is controlled independently by using the active polarization controller base on the time delay factor.

Description

QUANTUM STATES FOR 6DP QUANTUM KEY DISTRIBUTION PROTOCOL

FIELD OF INVENTION The present invention relates to an apparatus, system and method for generating biphoton of quantum state for 6DP quantum key distribution protocol.

BACKGROUND ART Quantum key distribution relates to the application of quantum mechanics in cryptography which guarantees secure communication wherein photons are usually used for quantum states. In practice many implementations use laser pulses which are attenuated to very low level to send quantum states. These laser pulses contain very small number of photons, for example 0.2 photons per pulse, which are distributed according to Possionian distribution.

At present, preparation of biphoton quantum states results in usage of multiple wavelengths. The existing methodology for preparation of biphoton quantum states using multiple wavelengths is prone to spectral attack. Spectral attack is attack that can differentiate and filter out multi-wavelength used in preparing biphoton of quantum states, thus the probability of gaining the information is very high.

The methodology for preparing and transforming quantum states for quantum key distribution unitarily (disclosed in Malaysia Patent Application No. PI 20082369) relates to preparation of biphoton quantum states using multiple wavelengths. The existing protocol has a weakness at the source part which is prone to attack during the preparation stage wherein attacker is have high probability in gaining information after the states being sent out to receiver. Therefore, it is advantageous to use biphoton with single wavelength as the new source of 6DP Quantum Key Distribution Protocol which minimizes the probability of attack to gain information.

The present invention provides quantum states for 6DP quantum key distribution protocol to generate and control photons using single wavelength as new source of 6DP. The propose solution minimizes probability of attack by third parties in gaining information.

The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practice.

SUMMARY OF INVENTION

The present invention provides an apparatus for generating biphoton of quantum state for 6DP quantum key distribution protocol. The apparatus comprising at least one laser source for pumping laser into non-linear crystal to generate at least one pair of correlated photons with same wavelength, a first beam splitter to reflect correlated photons, a second beam splitter to split each of said photons, a third beam splitter to combine each of said photons into single mode communication and at least one active polarization controller to polarize each of said photons.

Preferably, the said non-linear crystal is cut according to collinear and frequency non- degenerate Type 2 Spontaneous Parametric Down Conversion (SPDC) to form correlated photons at same frequencies and same directions. Further, the said first beam splitter is a Dichroic Beam Splitter (DBS) and the second and third beam splitter is a Polarization Beam Splitter (PBS).

Another aspect of the present invention provides a system for generating biphoton of quantum state for 6DP quantum key distribution protocol. The system comprising at least one laser source for pumping laser into non-linear crystal to generate at least one pair of correlated photons with same wavelength, a first beam splitter to reflect correlated photons, a second beam splitter to split each of said photons, a third beam splitter to combine each of said photons into single mode communication and at least one active polarization controller to polarize each of said photons. A further aspect of the present invention provides a method for generating biphoton of quantum state for 6DP quantum key distribution protocol. The method comprising steps of pumping laser to non-linear crystal to generate at least one pair of correlated photons with same wavelength, reflecting both correlated photons with dichroic beam splitter (DBS), splitting each of said photons with polarization beam splitter (PBS), combining each of said photons into single mode communication and polarizing each of said photons via SU (2) transformations.

Preferably, pumping laser to non-linear crystal to generate at least one pair of correlated photons is Spontaneous Parametric Down Conversion (SPDC) and correlated photons of Spontaneous Parametric Down Conversion (SPDC) having orthogonal polarization states with same wavelength.

Further, the method for splitting each of said photons with polarization beam splitter (PBS) further comprises steps of reflecting each of said photons to longer path to delay one photon from its pair and transmitting one photon to normal path.

The present invention consists of features and a combination of parts hereinafter fully described and illustrated in the accompanying drawings, it being understood that various changes in the details may be made without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

To further clarify various aspects of some embodiments of the present invention, a more particular description of the invention will be rendered by references to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the accompanying drawings where: FIG. 1 illustrates a block diagram of an arrangement for generating biphoton of quantum state for 6DP quantum key distribution protocol.

FIG. 2 illustrates an apparatus and system for generating biphoton of quantum state for 6DP quantum key distribution protocol.

FIG. 3 illustrates three main parts of the present invention.

FIG. 4 is a flowchart illustrating a method for generating biphoton of quantum state for 6DP quantum key distribution protocol.

FIG. 5 is a flowchart illustrating a method for splitting each of said photons with polarization beam splitter (PBS).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an apparatus, system and method for generating biphoton of quantum state for 6DP quantum key distribution protocol. Hereinafter, this specification will describe the present invention according to the preferred embodiments. It is to be understood that limiting the description to the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned without departing from the scope of the appended claims. Reference is first being made to FIG. 1. FIG. 1 illustrates a block diagram of an arrangement for generating biphoton of quantum state for 6DP quantum key distribution protocol. As illustrated in FIG. 1 , a Bob preparation is produce based on the arrangement of the present invention and an Alice transformation is formed according to the quantum states for 6DP quantum key distribution protocol of the present invention which generates and control photons using single wavelength as new source of 6DP.

Reference is now being made to FIG. 2, FIG. 3, FIG, 4 and FIG. 5 respectively. FIG. 2 illustrates an apparatus and system for generating biphoton of quantum state for 6DP quantum key distribution protocol while FIG. 3 illustrates

FIG. 4 is a flowchart illustrating a method for generating biphoton of quantum state for 6DP quantum key distribution protocol and FIG. 5 is a flowchart illustrating a method for splitting each of said photons with polarization beam splitter (PBS).

As illustrated in FIG. 2, an apparatus (200) for generating biphoton of quantum state for 6DP quantum key distribution protocol comprising at least one laser source (202) for pumping laser into non-linear crystal (206) to generate at least one pair of correlated photons with same wavelength, a first beam splitter (210) to reflect correlated photons, a second beam splitter (218) to split each of said photons, a third beam splitter (228) to combine each of said photons into single mode communication and at least one active polarization controller (232) to polarize each of said photons.

The present invention also provides for a system (200) for generating biphoton of quantum state for 6DP quantum key distribution protocol. The system comprising at least one laser source (202) for pumping laser into non-linear crystal (206) to generate at least one pair of correlated photons with same wavelength, a first beam splitter (210) to reflect correlated photons, a second beam splitter (218) to split each of said photons, a third beam splitter (228) to combine each of said photons into single mode communication and at least one active polarization controller (232) to polarize each of said photons.

The said non-linear crystal (206) is cut according to collinear and frequency non- degenerate Type 2 Spontaneous Parametric Down Conversion (SPDC) to form correlated photons at same frequencies and same directions. The said first beam splitter (210) is a Dichroic Beam Splitter (DBS) while the second and third beam splitter (218, 228) is a Polarization Beam Splitter (PBS).

As illustrated in FIG. 3, the approach of the present invention comprises of three (3) main parts as detailed below:

First Part (Spontaneous Parametric Down Conversion (SPDC) photon pair generation) (302)

Other type of SPDC process is used in producing biphoton. Pulsed laser source is injected into the type II nonlinear crystal to generate a pair of entangled photons with orthogonal polarization in the same optical propagation direction. The remaining pumped source is removed from the pair of photons using Dichroic Beam Splitter (DBS). Hence, the required wavelength of the pair will be filtered.

Second Part (304, 306, 308)

Subsequent part refers to the delay process to control the polarization of each photon independently by delaying one photon from its pair. The pair is split by using the Polarization Beam Splitter (PBS). The other half of the pair will be reflected and go through a delay path. The pair (one photon with a time delay) is recombined by using another PBS. The recombined pair will go into the same path again one after another.

Final Part (310)

Pair polarizations are controlled independently by using the active polarization controller base on the time delay introduced. Biphoton source which comprises of at least one pair of correlated photons with same wavelength of quantum state for 6DP quantum key distribution protocol is first generated by pumping laser to non-linear crystal (402). Pumping laser to non-linear crystal to generate at least one pair of correlated photons is Spontaneous Parametric Down Conversion (SPDC). The said correlated photons of Spontaneous Parametric Down Conversion (SPDC) having orthogonal polarization .states with same wavelength. Further, the pulse laser source (202) will be down converted into two light sources with the signal and idler (208) having a polarization of V and H respectively or in the same optical propagation direction. Thereafter, the two light sources (208) are being reflected wherein both correlated photons are reflected via dichroic beam splitter (DBS) (404) to filter remaining unconverted pump laser (212). The reflected light sources travel along the same path.

Thereafter, each of said photons is being split via polarization beam splitter (PBS) (406). Splitting each of said photons with polarization beam splitter (PBS) further comprises steps of reflecting each of said photons to longer path to delay one photon from its pair (502) and transmitting one photon to normal path (504). The said delay is determined by known means wherein the said means is by time factor. Polarization beam splitters (PBS) (218) separates the signal (216) and idler (214) light sources by reflecting one with vertical polarization light wherein the reflected vertical polarization light will go a longer path (224) through mirrors (222, 226) comparing to transmitted horizontal polarization light which travels along a straight path (220) which produces a delay of time, t. Both the signals (216, 214) will then recombine at another polarization beam splitter (228) wherein each of said photons is combined into single mode communication (408). The prepared biphoton polarizations (230) are now ready to be controlled. The biphoton polarization (230) will then be controlled by an active polarization controller (232) with respect to time. Each of said photons will be polarized via SU (2) transformations (410) wherein the active polarization controller (232) will be activated to control polarization to the specific light polarization when the first signal or idler (214) arrives. Thereafter, it will be turned off and on again when another signal arrives. The prepared states (234) are now ready to be transmitted to Alice. The present invention provides quantum states for 6DP quantum key distribution protocol to generate and control photons using single wavelength as new source of 6DP which minimizes probability of attack by third parties in gaining information. The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore indicated by the appended claims rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the claims, are to be embraced within their scope.

Claims

1. An apparatus (200) for generating biphoton of quantum state for 6DP quantum key distribution protocol comprising:

at least one laser source (202) for pumping laser into non-linear crystal (206) to generate at least one pair of correlated photons with same wavelength;

a first beam splitter (210) to reflect correlated photons;

a second beam splitter (218) to split each of said photons; a third beam splitter (228) to combine each of said photons into single mode communication; and

at least one active polarization controller (232) to polarize each of said photons.

2. An apparatus (200) according to Claim 1 , wherein said non-linear crystal (206) is cut according to collinear and frequency non-degenerate Type 2 Spontaneous Parametric Down Conversion (SPDC) to form correlated photons at same frequencies and same directions.

3. An apparatus (200) according to Claim 1 , wherein the said first beam splitter (210) is a Dichroic Beam Splitter (DBS).

4. An apparatus (200) according to Claim 1 , wherein the second and third beam splitter (214, 228) is a Polarization Beam Splitter (PBS).

5. A system (200) for generating biphoton of quantum state for 6DP quantum key distribution protocol comprising:

a first beam splitter (210) to reflect correlated photons;

a second beam splitter (218) to split each of said photons;

a third beam splitter (228) to combine each of said photons into single mode communication; and at least one active polarization controller (232) to polarize each of said photons.

A system (200) according to Claim 5, wherein said non-linear crystal (206) is cut according to collinear and frequency non-degenerate Type 2 Spontaneous Parametric Down Conversion (SPDC) to form correlated photons at same frequencies and same directions.

A system (200) according to Claim 5, wherein the said first beam splitter (210) is a Dichroic Beam Splitter (DBS).

8. A system (200) according to Claim 5, wherein the second and third beam splitter (218, 228) is a Polarization Beam Splitter (PBS).

9. A method (400) for generating biphoton of quantum state for 6DP quantum key distribution protocol comprising steps of:

pumping laser to non-linear crystal to generate at least one pair of correlated photons with same wavelength (402);

reflecting both correlated photons with dichroic beam splitter (DBS) (404); splitting each of said photons with polarization beam splitter (PBS) (406); combining each of said photons into single mode communication (408); and

polarizing each of said photons via SU (2) transformations (410).

10. A method (400) according to Claim 9, wherein pumping laser to non-linear crystal to generate at least one pair of correlated photons is Spontaneous Parametric Down Conversion (SPDC).

11. A method (400) according to Claim 9 and 10, wherein correlated photons of Spontaneous Parametric Down Conversion (SPDC) having orthogonal polarization states with same wavelength.

12. A method (400) according to Claim 10, wherein said correlated photons having orthogonal polarization states with same wavelength satisfies energy conservation and propagates in one direction to satisfy momentum conservation.

13. A method according to Claim 9, wherein splitting each of said photons with polarization beam splitter (PBS) further comprises steps of:

reflecting each of said photons to longer path to delay one photon from its pair (502); and

transmitting one photon to normal path (504).

14. A method (500) according to Claim 13, wherein said delay is determined by known means.

15. A method (500) according to Claim 14, wherein the said means is by time factor.