Analytical structure and analytical system of quantum entangled light source

Abstract

A quantum entangled light source analysis structure and analysis system, including a polarization beam splitter, two 1×2 optical switches, a first 2×2 coupler, a second 2×2 coupler, two 2×1 optical distributors, a first optical path and a second optical path, and a third 2×2 coupler, the input end of the polarization beam splitter is configured to receive a quantum entangled light source, the first optical path includes a third 1×2 optical switch to form two branches with different delays; at least one of the first optical path and the second optical path includes a second phase shifter. The analysis structure has a simple structure and stable performance.

Description

Technical Field

[0001] The disclosed embodiments relate to a quantum entangled light source analysis structure and analysis system. Background Art

[0002] Quantum entanglement is a core tool in quantum information science. It is applicable to quantum key distribution, quantum computing and super-dense coding. As a carrier of quantum state, photons are relatively easy to achieve simultaneous entanglement of multiple degrees of freedom. By applying multi-degree-of-freedom entanglement (also known as super-entanglement), the dimension of Hilbert space can be greatly increased, thereby effectively increasing the quantum information carried by the transmitted photons. At present, the generation of super-sources can be achieved by using nonlinear optical crystals, such as periodically polarized lithium niobate waveguides with Sagnac ring optical path structures. However, for the analysis of super-entangled sources, due to the large number of entangled degrees of freedom, the use of discrete optical devices will result in complex optical paths and poor stability, making the performance evaluation of super-entangled sources more difficult, and also not conducive to improving the performance of high-dimensional quantum key distribution (QKD) protocols. Summary of the invention

[0003] At least one embodiment of the present disclosure provides a quantum entangled light source analysis structure, including a polarization beam splitter, two 1×2 optical switches, a first 2×2 coupler, a second 2×2 coupler, two 2×1 optical distributors, a first optical path and a second optical path, wherein the input end of the polarization beam splitter is configured to receive a quantum entangled light source, and the two output ends are respectively coupled to the input ends of the two 1×2 optical switches, the two 1×2 optical switches each have an output end connected to the input end of the first 2×2 coupler, and the other output end is respectively connected to one input end of each of the two 2×1 optical distributors; the two 2 The other input end of the 2×1 optical distributor is respectively connected to the output end of the first 2×2 coupler; the output end of at least one of the two 2×1 optical distributors is coupled to the second 2×2 coupler through a first phase shifter, and the two output ends of the second 2×2 coupler are respectively coupled to the first optical path and the second optical path; the first optical path and the second optical path are respectively coupled to the two input ends of the third 2×2 coupler for output; the first optical path includes a third 1×2 optical switch to form two branches with different delays; at least one of the first optical path and the second optical path includes a second phase shifter.

[0004] In some examples, two output ends of the third 1×2 optical switch are respectively connected to the two branches, one of which is provided with a delay waveguide.

[0005] In some examples, the second optical path includes an adjustable attenuator.

[0006] In some examples, the first optical path includes the second phase shifter, and the two branches are connected to the second phase shifter via a third 2×1 optical distributor.

[0007] In some examples, the first optical path and the second optical path are connected to two output optical ports through a third 2×2 coupler.

[0008] In some examples, the 2×1 optical distributor is a 2×1 coupler or a 2×1 optical switch.

[0009] In some examples, the polarization beam splitter is a polarization beam rotator.

[0010] In some examples, when the optical path between the polarization beam splitter and the two 2×1 optical distributors is connected, the second 2×2 coupler is connected to the branch with the shorter delay among the two branches.

[0011] In some examples, when the optical path between the polarization beam splitter and the first 2×2 optical coupler is connected, the optical path between the second 2×2 coupler and the branch with the longer delay of the two branches is connected.

[0012] At least one embodiment of the present disclosure further provides a quantum entangled light source analysis system, comprising two quantum entangled light source analysis structures provided by any one of the above embodiments, wherein the polarization beam splitters of the two quantum entangled light source analysis structures are respectively configured to receive two photons in an entangled photon pair. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments or related technical descriptions will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present disclosure and are not limitations of the present disclosure.

[0014] Figure 1 A schematic diagram of a structure of a quantum entangled light source analysis structure provided for at least one embodiment of the present disclosure;

[0015] Figure 2 and Figure 3 They are schematic diagrams of the structures of a quantum entangled light source analysis system provided in at least one embodiment of the present disclosure in two degree-of-freedom analysis modes. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. With reference to the non-limiting exemplary embodiments shown in the accompanying drawings and described in detail in the following description, the exemplary embodiments of the present disclosure and their various features and advantageous details are more fully described. It should be noted that the features shown in the figures are not necessarily drawn to scale. The present disclosure omits the description of known materials, components and process technologies so as not to obscure the exemplary embodiments of the present disclosure. The examples given are only intended to facilitate the understanding of the implementation of the exemplary embodiments of the present disclosure, and to further enable those skilled in the art to implement the exemplary embodiments. Therefore, these examples should not be construed as limiting the scope of the embodiments of the present disclosure.

[0017] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. "First", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. In the absence of conflict, the embodiments of the present disclosure and the features in the embodiments can be combined with each other to obtain new embodiments.

[0018] At least one embodiment of the present disclosure provides a quantum entangled light source analysis structure, including a polarization beam splitter, two 1×2 optical switches, a second 2×2 coupler, a first 2×2 coupler, two 2×1 optical distributors, a first optical path, and a second optical path. The input end of the polarization beam splitter is configured to receive a quantum entangled light source, and the two output ends are respectively coupled to the input ends of the two 1×2 optical switches, each of the two 1×2 optical switches has an output end connected to the input end of the first 2×2 coupler, and the other output end is respectively connected to an input end of each of the two 2×1 optical distributors; the other input ends of the two 2×1 optical distributors are respectively connected to the output ends of the first 2×2 couplers; the output end of at least one of the two 2×1 optical distributors is coupled to the second 2×2 coupler through a first phase shifter, and the two output ends of the second 2×2 coupler are respectively coupled to the first optical path and the second optical path; the first optical path and the second optical path are respectively coupled to the two input ends of the third 2×2 coupler for output; the first optical path includes a third 1×2 optical switch to form two branches with different delays; at least one of the first optical path and the second optical path includes a second phase shifter.

[0019] In the quantum entangled light source analysis structure provided in at least one embodiment of the present disclosure, through the above-mentioned settings, the device can be multiplexed to analyze the multi-degree-of-freedom entangled light source, avoiding the cumbersome problem of optical path reorganization when characterizing entangled light sources with different degrees of freedom. For example, by selecting the states of two 1×2 optical switches and selecting two branches with different delays, the polarization degree of freedom or energy-time degree of freedom of the quantum entangled light source can be analyzed. For example, by setting and adjusting the second phase shifter, the measurement basis vector can be selected, and on this basis, the phase of the first phase shifter is scanned, and the polarization degree of freedom of the quantum entangled light source can be analyzed. For example, by scanning the second phase shifter, the energy-time degree of freedom of the quantum entangled light source can be analyzed. The intensity modulator composed of the second 2×2 coupler, the third 2×2 coupler and the second phase shifter between the two outputs an optical signal, and the purpose of analyzing the entangled light source can be achieved by observing the optical signals of the two output ports. In addition, when analyzing the energy-time degree of freedom, the first phase shifter can be adjusted, thereby adjusting the intensity modulator composed of the first 2×2 coupler, the second 2×2 coupler and the first phase shifter therebetween to adjust the optical power at the two output ends of the second 2×2 coupler, which helps to balance the optical power on the first optical path and the second optical path, thereby improving the accuracy of the analysis.

[0020] For example, the polarization beam splitter is a polarization beam rotator, which can unify the TE waves and TM waves in the light source into TE waves or TM waves with higher conduction efficiency for conduction according to the waveguide performance, thereby reducing conduction loss and improving conduction efficiency.

[0021] For example, the 2×2 coupler may be a 2×2 multimode interference coupler.

[0022] For example, the 2×1 optical distributor may be a 2×1 coupler, such as a 2×1 multimode interference coupler. In other examples, the 2×1 optical distributor may also be a 2×1 optical switch.

[0023] For example, the couplers involved in the present disclosure are all 50:50 couplers.

[0024] Figure 1 A quantum entangled light source analysis structure is provided for at least one embodiment of the present disclosure. Figure 1As shown, the quantum entangled light source analysis structure includes a polarization beam splitter, two 1×2 optical switches (1×2 optical switch-1 and 1×2 optical switch-2) respectively coupled to the two output ends A and B of the polarization beam splitter, a 2×2 multimode interference coupler-1 (an example of the first 2×2 coupler disclosed in the present invention) coupled to each output end of the two 1×2 optical switches, two 2×1 multimode interference couplers (i.e., 2×1 multimode interference coupler-1 and 2×1 multimode interference coupler-2), a 2×2 multimode interference coupler-2 (an example of the second 2×2 coupler disclosed in the present invention), and a first optical path and a second optical path respectively coupled to the two output ends of the 2×2 multimode interference coupler-2, and the first optical path and the second optical path are respectively coupled to the two input ends of a 2×2 multimode interference coupler-3 (an example of the third 2×2 coupler disclosed in the present invention) for output.

[0025] For example, the input end of the polarization beam splitter is configured to be connected to an input light port to receive a quantum entangled light source. For example, the quantum entangled light source is a photon in a quantum entangled photon pair.

[0026] One output terminal of the 1×2 optical switch-1 (such as Figure 1 Port E) and one output end of the 2×2 multimode interference coupler-1 are respectively coupled to the two input ends of the 2×1 multimode interference coupler-1, and the other output end of the 1×2 optical switch-1 (such as Figure 1 Port G) is coupled to an input end of the 2×2 multimode interference coupler-1; an output end of the 1×2 optical switch-2 (such as Figure 1 Port F) and the other output end of the 2×2 multimode interference coupler-1 are respectively coupled to the two input ends of the 2×1 multimode interference coupler-2, and the other output end of the 1×2 optical switch-2 (such as Figure 1 Port H) is coupled to the other input end of the 2×2 multimode interference coupler-1.

[0027] At least one of the two 2×1 multimode interference couplers is coupled to the 2×2 multimode interference coupler-2 through a phase shifter. Figure 1 As shown, the two 2×1 multimode interference couplers are coupled to the two input ends of the 2×2 multimode interference coupler-2 through a phase shifter (phase shifter-1 and phase shifter-2), respectively, which helps to balance the optical losses on the two optical paths.

[0028] The first optical path includes a 1×2 optical switch-3 (an example of the third 1×2 optical switch disclosed in the present invention), an input end I of the 1×2 optical switch-3 is coupled to an output end of the 2×2 multimode interference coupler-2, and two output ends J and K are respectively connected to two branches, one of which is provided with a delay waveguide, so that the delay on the branch is longer than that on the other branch.

[0029] The two branches are coupled to one optical path through a 2×1 multimode interference coupler-3 (an example of the third optical distributor of the present disclosure).

[0030] At least one of the first optical path and the second optical path includes a phase shifter to select a measurement basis vector when performing polarization degree of freedom resolution.

[0031] For example, the first optical path includes a phase shifter, and the two branches are connected to the second phase shifter through a third 2×1 optical distributor. In other examples, the phase shifter may also be located between the 2×2 multimode interference coupler-2 and the 1×2 optical switch-3.

[0032] like Figure 1 As shown, the first optical path and the second optical path are phase shifter-3 and phase shifter-4 respectively, that is, phase shifters are provided on both optical paths, which helps to balance the optical losses on the two optical paths. The two branches in the first optical path are coupled to the phase shifter-3 through the 2×1 multimode interference coupler-3.

[0033] The second optical path also includes an adjustable attenuator. When the input end I and the output end J of the 1×2 optical switch-3 are connected, that is, when the branch with a longer delay is selected, the adjustable attenuator can balance the loss of the delay waveguide.

[0034] For example, the first optical path and the second optical path are connected to two output optical ports through a third 2×2 coupler. By observing the optical signals of the two output optical ports, the purpose of analyzing the entangled light source can be achieved. For example, the two output optical ports 2 and 3 are respectively connected to a single photon detector. For example, the single photon detector is a single photon avalanche photodiode (SPAD).

[0035] The quantum entangled light source analysis structure can realize the analysis of multi-degree-of-freedom entangled light sources. When the optical path between the polarization beam splitter and the 2×1 multimode interference coupler-1 and the 2×1 multimode interference coupler-2 is connected, the 2×2 multimode interference coupler-2 is connected to the branch with the shorter delay in the two branches, and the polarization degree of freedom of the quantum entangled light source can be analyzed. When the optical path between the polarization beam splitter and the 2×2 multimode interference coupler-1 is connected, the 2×2 multimode interference coupler-2 is connected to the branch with the longer delay in the two branches, and the energy-time degree of freedom of the quantum entangled light source can be analyzed.

[0036] For example, in the above optical path structure, the connections or couplings between the components are all waveguide connections or couplings, and except for the delay waveguide, the rest are non-delay waveguides.

[0037] All components in the above optical path structure can be integrated on a chip, and the structure is simple, the performance is stable, and it is conducive to cost saving. For example, based on silicon photonics integration technology, using the existing silicon photonics design toolkit (PDK, process design kit), on-chip super entanglement source resolution can be achieved.

[0038] At least one embodiment of the present disclosure also provides a quantum entangled light source analysis system, which includes two quantum entangled light source analysis structures, and the polarization beam splitters of the two quantum entangled light source analysis structures are respectively configured to receive two photons in an entangled photon pair. The visibility of two-photon interference is observed by observing the output light port for signal detection, so as to determine the fidelity of the entangled source under each degree of freedom, thereby evaluating the quality of the entangled photon pair source. For example, when the two-photon interference visibility exceeds 81%, the entangled source can be used in a quantum key distribution (QKD) protocol, so that two-way communication can be achieved. For example, the structures of the two quantum entangled light source analysis structures are the same.

[0039] The following Figure 1 The quantum entangled light source analysis structure shown realizes two-way communication in polarization degree of freedom analysis and energy-time degree of freedom analysis modes as an example to illustrate the quantum entangled light source analysis system provided by at least one embodiment of the present disclosure, but this is not intended to limit the present disclosure.

[0040] like Figure 2 As shown, the quantum entanglement light source analysis system includes two Figure 1 The quantum entangled light source analysis structure shown. The two quantum entangled light source analysis structures are respectively located at the two ends of the communication, such as Alice and Bob. The two quantum entangled light source analysis structures are both in the polarization freedom analysis mode, the input end C and the output end E of the 1×2 optical switch-1 are connected, the input end D and the output end F of the 1×2 optical switch-2 are connected, and the input end I and the output end K of the 1×2 optical switch-3 are connected, so that the optical path between the polarization beam splitter rotator and the 2×1 multimode interference coupler-1 and the 2×1 multimode interference coupler-2 is connected, and the optical path between the 2×2 multimode interference coupler-2 and the delay waveguide is connected.

[0041] For example, the signal light is input from the optical port 1 and the optical port 1' respectively, and after passing through the polarization rate rotator, the TE mode light in the signal light is output from the output terminal A, and the TM mode light in the signal light is converted into the TE mode and output from the output terminal B. The phase shifter-3 or phase shifter-4 of the analytical structure at both ends of Alice and Bob is adjusted, the measurement basis vector of the polarization state (such as the HV basis vector or the AD basis vector) is selected, and the phase of the phase shifter-1 or phase shifter-2 at either end is scanned, and the single photon coincidence count between the output optical port 2 and the output optical port 2', or the output optical port 2 and the output optical port 3', or the output optical port 3 and the output optical port 2', or the output optical port 3 and the output optical port 3' is observed, and the fidelity of the polarization entanglement source is determined by measuring the visibility of the two-photon interference, thereby realizing the polarization degree of freedom analysis.

[0042] like Figure 3 As shown, the two quantum entangled light source analysis structures are both in the energy-time degree of freedom analysis mode, the input end C and the output end G of the 1×2 optical switch-1 are connected, the input end D and the output end H of the 1×2 optical switch-2 are connected, and the input end I and the output end J of the 1×2 optical switch-3 are connected, so that the optical path between the polarization beam splitter rotator and the 2×2 multimode interference coupler-1 is connected, and the 2×2 multimode interference coupler-2 is connected to the branch with the shorter delay in the two branches.

[0043] The signal light is input from the optical port 1 and the optical port 1' respectively. After passing through the polarization speed rotator, the TE mode light in the signal light is output from the A port, and the TM mode light is converted into the TE mode and output from the B port. The phase shifter-1 or phase shifter-2 of the analytical structure at both ends of Alice and Bob is adjusted to balance the optical power of the two input ports of the 2×2 multimode interference coupler-3, thereby reducing the influence of the optical power imbalance on the first optical path and the second optical path caused by the delay waveguide. The phase shifter-3 or phase shifter-4 at either end is phase scanned to observe the single photon coincidence count between the output optical port 2 and the output optical port 2', or the output optical port 2 and the output optical port 3', or the output optical port 3 and the output optical port 2', or the output optical port 3 and the output optical port 3'. By measuring the visibility of the two-photon interference, the fidelity of the energy-time entanglement source is determined, and the energy-time degree of freedom analysis is realized.

[0044] In other embodiments, the quantum entangled light source analysis system may also include three or more quantum entangled light source analysis structures, so as to realize the communication of quantum networks based on multi-photon entangled source distribution.

[0045] The above description is merely an exemplary embodiment of the present disclosure and is not intended to limit the protection scope of the present disclosure. The protection scope of the present disclosure is determined by the appended claims.

Claims

1. A quantum entangled light source analysis structure, comprising a polarization beam splitter, two 1×2 optical switches, a first 2×2 coupler, a second 2×2 coupler, two 2×1 optical distributors, a first optical path and a second optical path, and a third 2×2 coupler, in, The input end of the polarization beam splitter is configured to receive a quantum entangled light source, and the two output ends are respectively coupled to the input ends of the two 1×2 optical switches; the two 1×2 optical switches each have an output end respectively connected to the input end of the first 2×2 coupler, and the other output end is respectively connected to an input end of each of the two 2×1 optical distributors; The other input ends of the two 2×1 optical distributors are respectively connected to the output ends of the first 2×2 coupler; the output end of at least one of the two 2×1 optical distributors is coupled to the second 2×2 coupler through a first phase shifter, and the two output ends of the second 2×2 coupler are respectively coupled to the first optical path and the second optical path; The first optical path and the second optical path are respectively coupled to two input ends of the third 2×2 coupler for output; The first optical path includes a third 1×2 optical switch to form two branches with different delays; at least one of the first optical path and the second optical path includes a second phase shifter.

2. The quantum entangled light source analysis structure according to claim 1, wherein: The two output ends of the third 1×2 optical switch are respectively connected to the two branches, one of which is provided with a delay waveguide.

3. The quantum entangled light source analysis structure according to claim 2, wherein: The second optical path includes an adjustable attenuator.

4. The quantum entangled light source analysis structure according to claim 1, wherein: The first optical path includes the second phase shifter, and the two branches are connected to the second phase shifter via a third 2×1 optical distributor.

5. The quantum entangled light source analysis structure according to claim 1, wherein: The first optical path and the second optical path are connected to two output optical ports through the third 2×2 coupler.

6. The quantum entangled light source analysis structure according to claim 1, wherein: The 2×1 optical distributor is a 2×1 coupler or a 2×1 optical switch.

7. The quantum entangled light source analysis structure according to claim 1, wherein: The polarization beam splitter is a polarization beam splitter rotator.

8. The quantum entangled light source analysis structure according to any one of claims 1 to 7, wherein: When the optical path between the polarization beam splitter and the two 2×1 optical distributors is connected, the second 2×2 coupler is connected to the branch with the shorter delay among the two branches.

9. The quantum entangled light source analysis structure according to any one of claims 1 to 7, wherein: When the optical path between the polarization beam splitter and the first 2×2 optical coupler is connected, the optical path between the second 2×2 coupler and the branch with the longer delay among the two branches is connected.

10. A quantum entangled light source analysis system, comprising two quantum entangled light source analysis structures as described in any one of claims 1 to 9, wherein: The two polarization beam splitters of the quantum entangled light source analysis structure are respectively configured to receive two photons in the entangled photon pair.

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