System for clock synchronization with polarization-entangled photons

Abstract

To provide systems, devices and methods for synchronizing timing between devices and analyzing quantum signals to determine whether the signals are secure.SOLUTION: In a system 10, a source device includes a quantum light device comprising a light source configured to emit a plurality of pairs of photons, each pair of photons of the plurality of pairs of photons occupying a quantum entangled state. The quantum light device includes optical circuitry configured to receive a first set of photons and a second set of photons, and photon detectors. A set of the photon detectors receives the first set of photons and the second set of photons from the optical circuitry. Additionally, the source device includes processing circuitry configured to determine, based on a set of time signals corresponding to each photon detector of the set of photon detectors, whether a time delay value exists in which a Clauser, Horne, Shimony and Holt (CHSH) parameter is greater than a threshold CHSH parameter value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 215,298, filed June 25, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to quantum communication and time transfer. [Background technology]

[0003] Quantum entanglement is a phenomenon that occurs when a group of photons share a quantum state with other photons in the group, even if the photons in the group are separated by a large distance. The quantum state of a group of photons can affect how a set of photodetectors detects the group of photons. Entangled photon pairs can be used to ensure precise timing synchronization between two or more devices. Systems can use the phenomenon of quantum entanglement to facilitate secure communication between two or more devices. Summary of the Invention

[0004] In general, the present disclosure relates to a system for secure synchronization of polarization-based timing of entangled photons. The entanglement signature can be used to perform synchronization with any offset time difference between devices, mitigating the need for precise control of device separation. The system can transmit quantum signals between a source device and one or more wing devices such that the quantum signals are secure from third-party interference. For example, a quantum optical device can transmit one or more photons to a first wing device and one or more photons to a second wing device. The quantum optical device can emit multiple pairs of photons, each of which occupies a quantum entangled state. Each photon pair can include one photon emitted to the first wing device and one photon emitted to the second wing device. Photons can reflect from each wing device and return to the quantum optical device. The optical device can include a set of photon detectors, each of which generates a set of timestamps corresponding to the returning photons. The processing circuitry can analyze the timestamps to determine which photon pairs are entangled, allowing for time synchronization.

[0005] A light source of a quantum optical device can emit one or more pairs of photons that occupy a quantum entangled state. For example, if a light source splits a single pump photon into a photon pair, the photon pair can occupy a quantum entangled state that affects how the photon pair behaves as it travels through an optical circuit. A quantum entangled state can be preserved when the photon pair is separated by a large distance and when the photon pair is close to each other. This means that if a light source emits a pair of quantum entangled photons such that the first photon of the pair travels to a first wing device and the second photon of the pair travels to a second wing device that is a predetermined distance away from the first wing device, the photon pair can exhibit a quantum entangled state even though the first wing device and the second device are separated by a predetermined distance. If both the first photon and the second photon of the quantum entangled photon pair return to the quantum optical device and travel through the optical circuit to one or more photon detectors, the first photon and the second photon may maintain the same quantum entangled state that they occupied when the photon pair was emitted by the optical device.

[0006] The quantum entanglement state of a photon pair emitted by an optical device can affect how the photon pair travels through an optical circuit to one or more photon detectors. Each of the one or more photon detectors can emit a series of time signals indicating the time at which the detector receives a photon. The system can calculate a parameter value based on the time signals generated by the one or more photon detectors using one or more techniques described herein. If the parameter value is greater than a threshold, this can indicate that a pair of entangled photons emitted by the light source to the wing device has been returned to the quantum optical device and traveled through the optical circuit to one or more photon detectors. By calculating the parameter value for all incoming photon pairs, only photon pairs emitted simultaneously have a parameter value that exceeds the threshold, since photons emitted in separate events are not entangled. The determined simultaneousness of the events can then be used to synchronize the clocks of each device. This can also confirm that communication between the quantum optical device and the wing device is secure.

[0007] When calculating the parameter value, the system can take into account the difference in distance between the quantum optical device and the first wing device and the distance between the quantum optical device and the second wing device. The first and second photons of a quantum entangled photon pair can both travel at the speed of light. When a pair of quantum entangled photons is simultaneously emitted by the optical device, if the distance between the quantum optical device and the first wing device and the distance between the quantum optical device and the second wing device are different, the photons can return to the quantum optical device at different times. The system can calculate the parameter by taking into account the time delay resulting from these distance differences. In some examples, the system can calculate time by analyzing the dependence of the parameter on time, which is considered a free variable.

[0008] In some examples, a system includes a quantum optical device including a light source configured to emit multiple pairs of photons, each of the multiple pairs of photons occupying a quantum entangled state. The quantum optical device also includes an optical circuit configured to receive a first set of photons of the multiple pairs of photons from a first wing device and a second set of photons of the multiple pairs of photons from a second wing device. The quantum optical device also includes a set of photon detectors configured to receive the first set of photons and the second set of photons from the optical circuit, each photon detector of the set of photon detectors configured to generate a set of time signals, each time signal of the set of time signals representing a time at which a respective photon sensor detected a photon. The system further includes a processing circuit configured to determine, based on the set of time signals corresponding to each photon detector of the set of photon detectors, whether a time delay value exists at which a Crowther, Horn, Simonyi, and Holt (CHSH) parameter is greater than a threshold CHSH parameter value.

[0009] In some examples, the method includes emitting, by a light source of the quantum photon device, a plurality of pairs of photons, each photon pair of the plurality of pairs occupying a quantum entangled state, receiving, by an optical circuit of the quantum photon device, a first set of photons of the plurality of pairs of photons from a first wing device, receiving, by the optical circuit, a second set of photons of the plurality of pairs of photons from a second wing device, and receiving, by a set of photon detectors of the quantum photon device, the first set of photons and the second set of photons from the optical circuit. The method further includes generating, by each photon detector of the set of photon detectors, a set of time signals, each time signal of the set of time signals representing a time at which a respective photon sensor detected a photon, and determining, by a processing circuit based on the set of time signals corresponding to each photon detector of the set of photon detectors, whether a time delay value exists at which a Crowther, Horn, Simonyi, and Holt (CHSH) parameter is greater than a threshold CHSH parameter value.

[0010] In some examples, the non-transitory computer-readable medium includes instructions that, when executed, cause one or more processors to control a light source of a quantum optical device to emit a plurality of pairs of photons, where each photon pair of the plurality of pairs of photons occupies a quantum entangled state; cause an optical circuit of the quantum optical device to receive a first set of photons of the plurality of pairs of photons from a first wing device; cause the optical circuit to receive a second set of photons of the plurality of pairs of photons from a second wing device; and cause a set of photon detectors of the quantum optical device to receive the first set of photons and the second set of photons from the optical circuit. The instructions further cause the one or more processors to generate a set of time signals for each photon detector of the set of photon detectors, where each time signal of the set of time signals represents a time at which a respective photon sensor detected a photon; and determine, based on the set of time signals corresponding to each photon detector of the set of photon detectors, whether a time delay value exists at which a Crowther, Horn, Simonyi, and Holt (CHSH) parameter is greater than a threshold CHSH parameter value.

[0011] The summary is intended to provide an overview of the subject matter described in the present disclosure. It is not intended to provide an exclusive or exhaustive description of the systems, devices, and methods described in detail in the accompanying drawings and the following description. Further details of one or more examples of the present disclosure are set forth in the accompanying drawings and the following description. Other features, objects, and advantages will become apparent from the description, drawings, and claims. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram illustrating a system for secure time synchronization in accordance with one or more techniques of this disclosure. [Figure 2] 2 is a conceptual diagram illustrating components of the first wing device and the second wing device of FIG. 1 in accordance with one or more techniques of the present disclosure. [Figure 3] 2 is a conceptual diagram illustrating one or more components of the quantum optical device of FIG. 1 in accordance with one or more techniques of the present disclosure. [Figure 4]9 is a conceptual diagram illustrating a time diagram 90 including time diagram plots corresponding to each photon detector of the photon detector of FIG. 1 in accordance with one or more techniques of the present disclosure. [Figure 5] 1 is a flow diagram illustrating example operations for determining whether a time transfer is secure, in accordance with one or more techniques of this disclosure.

[0013] Like reference numerals refer to like elements throughout the description and drawings. DETAILED DESCRIPTION OF THE INVENTION

[0014] This disclosure describes apparatus, methods, and techniques for synchronizing timing between devices and analyzing quantum signals to determine whether the signals are secure. The system can use quantum signals for direct clock synchronization between moving objects and for sensitive measurement of distance between objects. In some cases, the system can use quantum entanglement to prevent an adversary from attempting to replace one of the system's nodes and send a false signal. In some examples, the system can measure the time-of-flight delay of photons in a light beam so that the relative distance between one or more nodes can be determined. As a result, the system can be secured against attacks by an adversary because a central node can detect whether an adversary is attempting to attack the system.

[0015] FIG. 1 is a block diagram illustrating a system 10 for secure time synchronization in accordance with one or more techniques of this disclosure. As seen in FIG. 1, system 10 includes a source device 18, a quantum optical device 20, a first wing device 30, a second wing device 40, and processing circuitry 50. Quantum optical device 20 includes a light source 22, optical circuitry 24, and a photon detector 26. First wing device 30 and second wing device 40 may sometimes be referred to collectively herein as "wing devices 30, 40."

[0016] The source device 18 can be configured to perform secure quantum communications. The quantum optical device 20 and the first wing device 30, as well as the source device 18, can be configured to perform secure quantum communications between the quantum optical device 20 and the second wing device 40. For example, the quantum optical device 20 can emit one or more photons to the first wing device 30, emit one or more photons to the second wing device 40, and receive one or more photons from the first wing device 30 and / or the second wing device 40. The source device 18 can be configured to determine whether one or more received photons were emitted by the quantum optical device 20 and “bounced” off the first wing device 30 and / or the second wing device 40. That is, the source device 18 can be configured to determine whether one or more received photons completed a round trip between the quantum optical device 20 and the wing devices 30, 40 without being intercepted by another device. This means that the quantum optical device 20 can determine whether the communication between the quantum optical device 20 and the wing devices 30, 40 is secure or whether the communication between the quantum optical device 20 and the wing devices 30, 40 has been compromised.

[0017] Source device 18 may, in some cases, continue to control quantum optical device 20 to communicate with wing devices 30, 40 based on determining that communication between quantum optical device 20 and wing devices 30, 40 is secure. If source device 18 determines that communication between quantum optical device 20 and wing devices 30, 40 has been compromised, source device 18 may perform one or more actions. For example, source device 18 may cause quantum optical device 20 to cease communication with wing devices 30, 40 based on determining that communication has been compromised. Additionally or alternatively, source device 18 may output one or more messages indicating that communication between quantum optical device 20 and wing devices 30, 40 has been compromised.

[0018] The quantum photonic device 20 may include the light source 22, the optical circuit 24, and the photon detector 26 as part of the same device. In some examples, the quantum photonic device 20 is located on or within another device, but this is not required. In some examples, the quantum photonic device 20 may be a stand-alone device. The quantum photonic device 20 may include the light source 22, the optical circuit 24, and the photon detector 26 within a relatively compact area, such that the distance between the light source 22 and the first wing device 30 is approximately the same as the distance between the optical circuit 24 and the first wing device 30. Furthermore, the distance between the light source 22 and the second wing device 40 may be approximately the same as the difference between the optical circuit 24 and the second wing device 40.

[0019] The light source 22 is configured to emit multiple pairs of photons, each of which occupies a quantum entangled state. The light source 22 may include one or more nonlinear crystals configured to split the photon beam into one or more pairs of photons. In some examples, the one or more pairs of photons have an energy equal to the energy of the photon beam split by the one or more crystals of the light source 22. In some examples, the photon beam may include a series of photons, and the one or more crystals may split each photon of the series into photon pairs, each of which has a lower energy than the photon split by the one or more crystals. In some examples, the one or more crystals may include one or more β-barium borate (BBO) crystals and / or one or more lithium niobate crystals, although this is not required. The one or more crystals of the light source 22 may additionally or alternatively include one or more other types of crystals. In some examples, the one or more crystals may include a nonlinear crystal.

[0020] In some examples, light source 22 generates each photon pair of multiple pairs of photons using the nonlinear optical effect of degenerate spontaneous parametric down-conversion (dSPDC). To generate the photon pairs, light source 22 can emit a pump photon that splits into two "twin" daughter photons that are "born" at approximately the same instant. For example, the amount of time separating the first and second photons of the photon pair can be less than 100 femtoseconds. In some examples, each twin photon pair that light source 22 generates from a pump photon includes a signal photon and an idler photon.

[0021] In some examples, light source 22 emits photon pairs according to a random distribution in time. For example, light source 22 may emit a first photon pair and then emit a second photon pair a random amount of time after light source 22 emits the first photon pair. The random amount of time may be a random time within a range of times.

[0022] In some examples, each photon pair of multiple pairs of photons emitted by the light source 22 occupies a respective Bell state of a set of Bell states. The Bell states may be quantum states that represent examples of quantum entanglement. Quantum entanglement may represent a phenomenon in which two or more photons interact in such a way that the quantum state of each photon cannot be described independently of the quantum states of each of the other photons of the two or more photons. When the light source 22 splits a single pump photon into photon pairs, the photon pairs may exhibit quantum entanglement. In some examples, the photon pairs may exhibit quantum entanglement even when the photon pairs are separated by a large distance. This means that when the light source 22 emits photon pairs split from the same pump photon, the photon pairs exhibit quantum entanglement even when the light source 22 emits the photon pairs into different wing devices 30, 40. When the photon pairs return from the wing devices 30, 40 to the source device 18, the photon pairs may maintain the same state of quantum entanglement that the photons exhibited when the light source 22 emitted them.

[0023] The set of possible Bell states that can be occupied by pairs of photons split from the same pump photon can, in some instances, include four different Bell states.

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[0038] In some examples, as light source 22 emits each photon pair of multiple pairs of photons, light source 22 may emit the first photon of each photon pair to first wing device 30, and light source 22 may emit the second photon of each photon pair to second wing device 40. The first photon and second photon of each photon pair emitted by light source 22 may occupy a quantum entangled state (e.g., a Bell state).

[0039] The quantum entangled photons of each photon pair of photons can be used to determine an offset between a first optical path length and a second optical path length. The first optical path length exists between the quantum optical device 20 and the first wing device 30. The second optical path length exists between the quantum optical device 20 and the second wing device 40. The quantum optical device 20 can determine the optical path length offset by projecting biphotons (e.g., pairs of photons) from the light source 22, reflecting some photons from the first wing device 30 and some photons from the second wing device 40, and recombining one or more of the photons at the light source. In some examples, the first wing device 30 may include a first wing device photon detector, and the second wing device 40 may include a second wing photon detector. The first wing device photon detector and the second wing photon detector may detect a portion of the photons emitted from the light source 22. Therefore, the first wing device 30 and the second wing device 40 may not reflect all photons emitted by the light source 22 .

[0040] In some examples, the wing devices 30, 40 may represent photonic devices each including one or more mirrors. The one or more mirrors of each of the wing devices 30, 40 may reflect one or more photons received by the respective wing device back to the source device 18. In some examples, each of the wing devices 30, 40 may include one or more photon detectors configured to generate an electrical signal each time a photon strikes the detector. In some examples, the one or more mirrors of each of the wing devices 30, 40 may reflect one or more photons received from the source device 18 back to the source device 18. In some examples, the one or more photon detectors of each of the wing devices 30, 40 may receive one or more photons received from the source device 18 without the one or more mirrors of each of the wing devices 30, 40 reflecting the photons back to the source device 18. This means that not all photons emitted by the source device 18 to either of the wing devices 30, 40 are returned to the source device 18. However, there may be one or more cases where source device 18 emits a first photon of an entangled photon pair to the first wing device 30, source device 18 emits a second photon of the entangled photon pair to the second wing device 40, and both the first and second photons are reflected back to source device 18. In these cases, source device 18 may be configured to identify whether the first and second photons were emitted by source device 18 as part of the same photon pair, and source device 18 may be configured to determine whether communication between source device 18 and wing devices 30, 40 is impaired.

[0041] In some examples, the quantum optical device 20 and / or processing circuitry 50 may perform Bell state measurements based on one or more photon measurements to determine which pairs of photons returning to the quantum optical device 20 were emitted by the light source 22 in the same photon pair. In some cases, only photon pairs generated at the same instant in time exhibit a correlation that violates Bell inequality.

[0042] For example, the optical circuit 24 may include a set of beam splitters and a set of wave plates. Each photon reaching the optical circuit 24 may pass through one or more beam splitters in the set of beam splitters and one or more wave plates in the set of wave plates before reaching a photon detector in the photon detector 26. Each photon detector in the photon detector 26 may generate an electrical signal each time a photon strikes it. This means that the photon detector 26 may generate, for each photon detector in the photon detector 26, a time plot indicating each time the respective photon detector registers a photon. The processing circuit 50 may analyze the time plot corresponding to each photon detector in the set of photon detectors to determine whether the time plot indicates any pairs of quantum entangled photons emitted by the light source 22.

[0043] In some examples, the optical circuit 24 can receive a first set of photons from the first wing apparatus 30. In some examples, the optical circuit 24 can receive a second set of photons from the second wing apparatus 40. In some examples, the first set of photons can include one or more photons emitted from the light source 22 to the first wing apparatus 30. In some examples, the second set of photons can include one or more photons emitted from the light source 22 to the second wing apparatus 40. The light source 22 can emit one or more pairs of photons, emitting a first photon of each photon pair to the first wing apparatus 30 and emitting a second photon of each photon pair to the second wing apparatus 40. In some examples, the distance between the source apparatus 18 and the first wing apparatus 30 is different from the distance between the source apparatus 18 and the second wing apparatus 40. This means that when source device 18 emits photon pairs to wing devices 30, 40 and the photon pairs return to source device 18, the photons of the photon pairs that source device 18 emits to a wing device closer to source device 18 can return to source device 18 before the photons of the photon pairs that source device 18 emits to a wing device farther from source device 18.

[0044] Because source device 18 can simultaneously emit photon pairs to wing devices 30, 40, but the photon pairs do not necessarily return to source device 18 simultaneously, source device 18 can use one or more techniques described herein to identify photon pairs returning to source device 18 that were emitted by source device 18 simultaneously when light source 22 split a pump photon. For example, optical circuit 24 can direct photons received by quantum optical device 20 to photon detector 26. Photon detector 26 can, in some examples, include four photon detectors. Optical circuit 24 can include a set of beam splitters and a set of wave plates. In some examples, the set of beam splitters and the set of wave plates can direct each photon reaching optical circuit 24 to one of photon detectors in photon detector 26.

[0045] In some examples, photon detector 26 is configured to detect the time at which each photon of the multiple photons reaching optical circuit 24 reaches a respective photon detector of photon detector 26. For example, a first photon detector of photon detector 26 can output a first set of time signals, where each time signal in the first set of time signals corresponds to a time at which the first photon detector receives a photon. A second photon detector of photon detector 26 can output a second set of time signals, where each time signal in the second set of time signals corresponds to a time at which the second photon detector receives a photon. A third photon detector of photon detector 26 can output a third set of time signals, where each time signal in the third set of time signals corresponds to a time at which the third photon detector receives a photon. A fourth photon detector of photon detector 26 can output a fourth set of time signals, where each time signal in the fourth set of time signals corresponds to a time at which the fourth photon detector receives a photon. This means that, in one example, photon detector 26 can generate four sets of time signals, each corresponding to one of the sets of four photon detectors. The present disclosure is not limited to photon detector 26 having four photon detectors, in some examples, photon detector 26 can have more than four photon detectors or less than four photon detectors.

[0046] Processing circuitry 50, in some examples, may include one or more processors configured to perform functions and / or process instructions for execution within system 10. Processing circuitry 50 may include, for example, a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or equivalent discrete or integrated logic circuitry, or a combination of any of the foregoing devices or circuits. Thus, processing circuitry 50 may include any suitable structure of hardware, software, firmware, or any combination thereof, to perform the functions attributed to processing circuitry 50 herein.

[0047] The memory 52 can be configured to store information within the system 10 during operation. The memory can include a computer-readable storage medium or a computer-readable storage device. In some examples, the memory includes one or both of short-term memory and long-term memory. The memory can include, for example, random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), magnetic disk, optical disk, flash memory, or forms of electrically programmable memory (EPROM) or electrically erasable programmable memory (EEPROM). In some examples, the memory is used to store program instructions for execution by the processing circuitry 50.

[0048] In some examples, the processing circuit 50 can receive one or more sets of time signals from the photon detector 26. In some examples, the processing circuit 50 can identify one or more pairs of photons based on the one or more sets of time signals received from the photon detector 26, where each photon pair of the one or more pairs of photons is emitted by the light source 22 simultaneously when the light source 22 splits a pump photon into a respective pair of photons. In some examples, the processing circuit 50 identifies one or more pairs of photons by analyzing the one or more sets of time signals. For example, the processing circuit 50 can determine, based on the one or more sets of time signals, whether there is a time delay value between two time signals in the one or more sets of time signals, where the Crowther, Horn, Simonyi, and Holt (CHSH) parameter is greater than a threshold CHSH parameter value. If there is a time delay value between two time signals in the one or more sets of time signals, where the CHSH parameter is greater than a threshold CHSH parameter value, then the two photons corresponding to the two time signals can represent a photon pair emitted by the light source 22 when the light source 22 splits a pump photon. Processing circuitry 50 can identify one or more pairs of time signals having time delay values ​​corresponding to CHSH parameters that are greater than a threshold CHSH parameter value.

[0049] In some examples, the time delay values ​​corresponding to photon pairs simultaneously emitted by the light source 22 and transmitted to the wing devices 30, 40 can depend on a first distance between the quantum photon device 20 and the first wing device 30 and a second distance between the quantum photon device 20 and the second wing device 40. The first and second distances can determine the time it takes for the first photon of the photon pair to travel from the light source 22 to the first wing device 30 and back to the quantum photon device 20, and can determine the time it takes for the second photon of the photon pair to travel from the light source 22 to the second wing device 40 and back to the quantum photon device 20. For example, if the second distance is longer than the first distance, the time it takes for the second photon to travel from the light source 22 to the second wing device 40 and back to the quantum photon device 20 can be longer than the time it takes for the first photon to travel from the light source 22 to the first wing device 30 and back to the quantum photon device 20. This means that a pair of photons emitted by the light source 22 at the same time may return to the quantum photonic device at different times, with a time delay between the photons depending on the respective distances between the quantum photonic device 20 and each of the wing devices 30, 40.

[0050] The processing circuitry 50 can determine the correlation parameters of all incoming photon pairs within the expected range of time delays. In some cases, only photon pairs emitted simultaneously by the light source 22 exhibit entanglement. This means that the time delay that must be applied is determined by which time delay results in the greatest correlation between the incoming photon pairs. Once the time delays from the entangled photon pairs are established, pairs of events recorded on the wing device photon detectors 66 and 69 can be identified and used as part of a protocol for synchronizing the independent clocks at the two wing locations.

[0051] In some examples, the processing circuit 50 is configured to determine a first correlation parameter corresponding to the correlation between a first photon detector of the photon detector 26 and a third photon detector of the photon detector 26. In some examples, the processing circuit 50 is configured to determine a second correlation parameter corresponding to the correlation between the first photon detector of the photon detector 26 and a fourth photon detector. In some examples, the processing circuit 50 may determine a third correlation parameter corresponding to the correlation between a second photon detector of the photon detector 26 and a third photon detector of the photon detector 26. In some examples, the processing circuit 50 may determine a fourth correlation parameter corresponding to the correlation between the second photon detector and a fourth photon detector. In some examples, the processing circuit 50 may calculate the sum of the first correlation parameter, the second correlation parameter, the third correlation parameter, and the fourth correlation parameter to determine CHSH parameters for a pair of time signals separated by an expected time delay corresponding to the distance between the quantum optical device 20 and the first wing device 30 and the distance between the quantum optical device 20 and the second wing device 40.

[0052] In some examples, processing circuitry 50 may determine that a pair of time signals corresponds to a quantum entangled photon pair emitted by light source 22 if the CHSH parameter of the pair of time signals is greater than a threshold CHSH parameter value. In some examples, the threshold CHSH parameter is a constant value (e.g., 2). In some cases, when the pair of time signals corresponds to non-entangled photons (e.g., the photon pair was not emitted simultaneously by splitting a pump photon), it may be impossible for the pair of time signals to have a CHSH parameter value greater than the threshold CHSH parameter value.

[0053] 2 is a conceptual diagram illustrating components of the first wing apparatus 30 and the second wing apparatus 40 of FIG. 1 in accordance with one or more techniques of the present disclosure. As seen in FIG. 2, the first wing apparatus 30 can include a first mirror 62, a second mirror 64, a first wing apparatus photon detector 66, and a first atomic clock 70. The second wing apparatus 40 can include a third mirror 67, a fourth mirror 68, a second wing apparatus photon detector 69, and a second atomic clock 71.

[0054] The first wing device 30 can receive one or more photons from the quantum optics device 20. In some examples, each photon of the one or more photons received from the quantum optics device 20 can represent one photon of a photon pair emitted by the light source 22. In some examples, each photon of the one or more photons received by the first wing device 30 from the quantum optics device 20 is quantum entangled with another photon of each photon pair, and both photons of each photon pair are emitted by the quantum optics device 20 substantially simultaneously. In some examples, another photon corresponding to each photon of the one or more photons received by the wing device 30 from the quantum optics device 20 is received by the second wing device 40. Each photon received by the first wing device 30 from the quantum optics device 20 can travel through the first wing device 30 until the photon reaches the first mirror 62.

[0055] The first mirror 62 may represent a partially reflective mirror. The partially reflective mirror, in some examples, may reflect one or more photons from a first surface of the mirror and allow one or more photons to pass through the mirror, such that the photons cross the first surface of the mirror, pass through the mirror, and exit the mirror through a second surface of the mirror. For example, at least one photon of the one or more photons received from the quantum photon device 20 may pass through the first mirror 62 to the first wing device photon detector 66, and at least one photon of the one or more photons received from the quantum photon device 20 may reflect from the first mirror 62 toward the second mirror 64. The first mirror 62 may have a reflection coefficient that determines the proportion of the one or more photons received by the first wing device 30 that are reflected from the first mirror 62 and the proportion of the one or more photons received by the first wing device 30 that pass through the first mirror 62. In some examples, the reflection coefficient of the first mirror 62 may be relatively high such that more than half of the one or more photons received by the first wing device 30 are reflected to the second mirror 64.

[0056] The second mirror 64 may be fully reflective such that all photons striking the second mirror 64 from the first mirror 62 are reflected from the second mirror 64. In some examples, each photon reflecting from the second mirror 64 may exit the first wing device 30 toward the quantum photonic device 20. In some examples, the first wing device 30 reflects more than half of one or more photons received from the quantum photonic device 20 back to the quantum photonic device 20. The time delay for photons returning from the first wing device 30 to the quantum photonic device 20 may depend on the distance between the quantum photonic device 20 and the first wing device 30.

[0057] The photon detector 66, in some examples, may include a single photon detector (SPD) configured to emit a time signal each time a photon reaches the photon detector 66. In some examples, the time signal emitted by the photon detector 66 may be an electrical signal. A processing circuit (not shown in FIG. 2 ) of the first wing device 30 may be configured to receive each time signal emitted by the photon detector 66 and generate a timestamp record that records each time a photon reaches the photon detector 66. In some examples, the first mirror 62 may reflect more than half of the photons that reach the first wing device 30, meaning that less than half of the photons that reach the wing device 30 from the quantum optical device 20 pass through the first mirror 62 to reach the photon detector 66.

[0058] The second wing device 40 can receive one or more photons from the quantum optics device 20. In some examples, each photon of the one or more photons received by the second wing device 40 from the quantum optics device 20 can represent one photon of a photon pair emitted by the light source 22. In some examples, each photon of the one or more photons received by the second wing device 40 from the quantum optics device 20 is quantum entangled with another photon of each photon pair, and both photons of each photon pair are emitted by the quantum optics device 20 substantially simultaneously. In some examples, another photon corresponding to each photon of the one or more photons received by the second wing device 40 from the quantum optics device 20 is received by the second wing device 40. Each photon received by the second wing device 40 from the quantum optics device 20 can travel through the second wing device 40 until the photon reaches the third mirror 67.

[0059] The third mirror 67 may represent a partially reflective mirror. The partially reflective mirror, in some examples, can reflect one or more photons from a first surface of the mirror and allow one or more photons to pass through the mirror, such that the photon crosses the first surface of the mirror, passes through the mirror, and exits the mirror through a second surface of the mirror. For example, at least one photon of the one or more photons received from the quantum photon device 20 can pass through the third mirror 67 to the first wing device photon detector 66, and at least one photon of the one or more photons received from the quantum photon device 20 can reflect from the third mirror 67 toward the fourth mirror 68. The third mirror 67 may have a reflection coefficient that determines the proportion of the one or more photons received by the second wing device 40 that are reflected from the third mirror 67 and the proportion of the one or more photons received by the second wing device 40 that pass through the third mirror 67. In some examples, the reflection coefficient of the third mirror 67 may be relatively high such that more than half of the one or more photons received by the second wing device 40 are reflected to the fourth mirror 68.

[0060] The fourth mirror 68 may be fully reflective such that all photons striking the fourth mirror 68 from the third mirror 67 may be reflected from the fourth mirror 68. In some examples, each photon reflecting from the fourth mirror 68 may exit the second wing device 40 toward the quantum optics device 20. In some examples, the second wing device 40 reflects more than half of one or more photons received from the quantum optics device 20 back to the quantum optics device 20. The time delay for photons returning from the second wing device 40 to the quantum optics device 20 may depend on the distance between the quantum optics device 20 and the second wing device 40.

[0061] The photon detector 69, in some examples, may include an SPD configured to emit a time signal each time a photon reaches the photon detector 69. In some examples, the time signal emitted by the photon detector 69 may be an electrical signal. A processing circuit (not shown in FIG. 2 ) of the second wing device 40 may be configured to receive each time signal emitted by the photon detector 69 and generate a timestamp record that records each time a photon reaches the photon detector 69. In some examples, the third mirror 67 may reflect more than half of the photons that reach the second wing device 40, meaning that less than half of the photons that reach the second wing device 40 from the quantum optical device 20 pass through the third mirror 67 to reach the photon detector 69.

[0062] In some examples, the first wing apparatus 30 may include a first atomic clock 70 and the second wing apparatus 40 may include a second atomic clock 71. In some cases, it may be beneficial to synchronize the first atomic clock 70 and the second atomic clock 71 so that both the first atomic clock 70 and the second atomic clock 71 show substantially the same time.

[0063] In some examples, the first wing device 30 and the second wing device 40 may synchronize the first atomic clock 70 and the second atomic clock 71 by comparing a first timestamp record generated by the photon detector 66 with a second timestamp record generated by the photon detector 69. The photon detector 66 may generate a first timestamp record to record each time a photon hits the photon detector 66. The photon detector 69 may generate a second timestamp record to record each time a photon hits the photon detector 69. In some examples, the first wing device 30 and / or the second wing device 40 may receive from the quantum device 20 the time delay between the first photon of the entangled pair returning from the first wing device 30 to the quantum optical device 20 and the second photon of the entangled pair returning from the second wing device 40 to the quantum optical device 20. The first wing device 30 and / or the second wing device 40 may use the time delay received from the quantum optical device 20 to synchronize the atomic clocks 70, 71 to account for the difference between the time it takes for a photon to travel between the quantum optical device 20 and the first wing device 30 and the time it takes for a photon to travel between the quantum optical device 20 and the second wing device 40.

[0064] In some examples, the quantum optics device 20 may emit one or more pairs of photons, with one photon of each pair being emitted to the first wing device 30 and one photon of each pair being emitted to the second wing device 40. Because some photons emitted to the first wing device 30 are not reflected back to the quantum optics device 20 through the first mirror 62, and some photons emitted to the second wing device 40 are not reflected back to the quantum optics device 20 through the third mirror 67, not all pairs of photons emitted by the quantum optics device 20 are returned to the quantum optics device 20. However, it is possible for the quantum optics device 20 to emit a pair of photons, including a first photon emitted to the first wing device 30 and a second photon emitted to the second wing device 40, with both the first photon and the second photon returning to the quantum optics device 20, one or more times. While FIGS. 1 and 2 show two wing devices, the technology of the present disclosure is not limited to systems having two wing devices. The techniques described herein may be used to synchronize the clocks of three or more wing units.

[0065] 3 is a conceptual diagram illustrating one or more components of quantum optical device 20 of FIG. 1 in accordance with one or more techniques of the present disclosure. As seen in FIG. 3, quantum optical device 20 includes optical circuit 24 and photon detectors 26A-26D (collectively "photon detectors 26"). Quantum optical device 20 may further include light source 22, although light source 22 is not shown in FIG. 3. Optical circuit 24 includes a first beam splitter 72, a first wave plate 74, a second beam splitter 76, a second wave plate 78, and a third beam splitter 80.

[0066] In some examples, the first beam splitter 72 is a non-polarizing beam splitter. For example, the first beam splitter 72 can pass or deflect photons regardless of the polarization of the photons. The first beam splitter 72 can receive one or more photons returning from the first wing apparatus 30 and one or more photons returning from the second wing apparatus 40. In some examples, the first beam splitter 72 can direct approximately half of the photons reaching the first beam splitter 72 to the first wave plate 74, and the first beam splitter 72 can direct approximately half of the photons reaching the first beam splitter 72 to the second wave plate 78.

[0067] In some examples, photons reaching the optical circuit 24 from the first wing apparatus 30 can arrive via the first channel 73, and photons reaching the optical circuit 24 from the second wing apparatus 40 can arrive via the second channel 73′. Photons arriving via the first channel 73 may contact a first surface of the first beam splitter 72, and photons arriving via the second channel 73′ may contact a second surface of the first beam splitter 72. In some cases, one or more photons reaching the beam splitter 72 via the first channel 73 can pass through the beam splitter 72 to reach the first wave plate 74, and one or more photons reaching the beam splitter 72 via the first channel 73 can reflect from the first surface of the beam splitter 72 towards the second wave plate 78. In some cases, one or more photons that reach the beam splitter 72 via the second channel 73′ may pass through the beam splitter 72 and reach the second wave plate 78, and one or more photons that reach the beam splitter 72 via the second channel 73′ may be reflected from the second surface of the beam splitter 72 towards the first wave plate 74.

[0068] In some examples, the first wave plate 74 may represent a polarizing wave plate configured to polarize passing photons according to a first predetermined angle. For example, each photon reaching the first wave plate 74 may include a polarization angle, and the first wave plate 74 may change the polarization angle of each arriving photon by a predetermined angle. In some examples, the second wave plate 78 may represent a polarizing wave plate configured to polarize passing photons according to a second predetermined angle. For example, each photon reaching the second wave plate 78 may include a polarization angle, and the second wave plate 78 may change the polarization angle of each arriving photon by a second predetermined angle. In some examples, the first predetermined angle may be the same as the second predetermined angle, but this is not required. In some examples, the first predetermined angle is different from the second predetermined angle. In some examples, the first wave plate 74 and / or the second wave plate 78 may represent λ / 2 wave plates.

[0069] In some examples, the second beam splitter 76 may represent a polarizing beam splitter. For example, the second beam splitter 76 may have a first angle prism secured to a second angle prism at a boundary 77. One or more photons reaching the second beam splitter 76 from the first wave plate 74 may travel through the first and second angle prisms, across the boundary 77 toward the photon detector 26D. One or more photons reaching the second beam splitter 76 from the first wave plate 74 may travel through the first angle prism and reflect from the boundary 77 toward the photon detector 26C.

[0070] In some examples, the third beam splitter 80 may represent a polarizing beam splitter. For example, the third beam splitter 80 may include a first angle prism secured to a second angle prism at a boundary 81. One or more photons reaching the third beam splitter 80 from the second wave plate 78 may cross the boundary 81 and travel through the first and second angle prisms toward the photon detector 26A. One or more photons reaching the third beam splitter 80 from the second wave plate 78 may pass through the first angle prism and reflect from the boundary 81 toward the photon detector 26B.

[0071] Polarizing beam splitters, such as second beam splitter 76 and third beam splitter 80, may be configured to "pass" photons with one or more polarization angles and "reflect" photons with one or more polarization angles. For example, photons polarized parallel or perpendicular to the polarizing beam splitter surface can either pass through or be reflected from the surface. Photons with polarization along the medial axis can have some probability of being reflected and some probability of being transmitted.

[0072] Entangled photon pairs emitted by the light source 22 (e.g.,

[0073]

number

[0074] In some examples, the S parameter represents one or more measures of correlation between pairs of photon detectors 26. In some examples, the S parameter is defined as S = E(a,c) - E(a,d) + E(b,c) + E(b,d). E(x,y) is the correlation between each pair of photon detectors 26. For example, E(a,c) is the correlation between photon detector 26A and photon detector 26C, E(a,d) is the correlation between photon detector 26A and photon detector 26D, E(b,c) is the correlation between photon detector 26B and photon detector 26C, and E(b,d) is the correlation between photon detector 26B and photon detector 26D. The correlation between two photon detectors can represent the probability that a photon is found simultaneously at two particular detectors. For example, a photon detector can assign a value of 1 whenever a photon is detected at the detector and a value of 0 when the detector does not register a photon. The correlation between two photon detectors can be determined using the formula E(x,y)=P(0,0)-E(1,0)+E(0,1)+E(1,1). Processing circuitry 50 can calculate the probabilities P(0,0), E(1,0), E(0,1), and E(1,1) as probabilities over many photon collection events.

[0075] In some examples, the S-parameter values ​​may take into account a time delay corresponding to the difference between the distance from the quantum optical device 20 to the first wing device 30 and the distance from the quantum optical device 20 to the second wing device 40. The light source 22 emits one photon of each pair of entangled photons to the first wing device 30 and the other photon of each pair of entangled photons to the second wing device 40. Because there may be a difference between the distance from the quantum optical device 20 to the first wing device 30 and the distance from the quantum optical device 20 to the second wing device 40, two entangled photons emitted by the light source 22 at the same time may not return to the quantum optical device 20 at the same time. The processing circuitry 50 may, in some cases, first calculate the S-parameter values ​​by considering an expected time delay. For example, E(x,y) may measure the probability that two photons will arrive at two respective photon detectors separated by an expected time delay.

[0076] In some examples, processing circuitry 50 may calculate E(x,y) for all pairs of photon detectors in photon detector 26. Processing circuitry 50 may calculate S-parameter values ​​based on the E(x,y) values ​​corresponding to each pair of photon detectors in photon detector 26. In some cases, it may be impossible for a pair of classical photons reaching photon detector 26 to result in processing circuitry 50 calculating an S-parameter greater than a threshold S-parameter value.

[0077] In some examples, there is a maximum possible value for the S-parameter. For example, the maximum possible value of the S-parameter value may be 2√2. In some examples, the maximum possible S-parameter value may only be achieved when the quantum optical device 20 receives entangled photons. Quantum-entangled photons reaching the quantum optical device 20 may, in some examples, cause the processing circuitry 50 to calculate an S-parameter value greater than the threshold S-parameter value but less than the maximum possible value of the S-parameter. For example, entangled photons may cause the processing circuitry 50 to calculate an S-parameter greater than 2. In some examples, losses from dark counts or extra time signals may reduce the an-S-parameter value resulting from one or more entangled states. However, non-entangled photon pairs may, in some cases, not cause the processing circuitry 50 to calculate an S-parameter value greater than the threshold S-parameter value.

[0078] 4 is a conceptual diagram illustrating a time diagram 90 including a time diagram plot corresponding to each photon detector in photon detector 26 of FIG. 1, in accordance with one or more techniques of this disclosure. Time diagram plot 90 includes a set of time signals 92A-92D (collectively, "set of time signals 92").

[0079] In some examples, photon detector 26A can generate set of time signals 92A, photon detector 26B can generate set of time signals 92B, photon detector 26C can generate set of time signals 92C, and photon detector 26D can generate set of time signals 92D. For example, photon detector 26A may generate a time signal from set of time signals 92A each time photon detector 26A detects a photon, photon detector 26B may generate a time signal from set of time signals 92B each time photon detector 26B detects a photon, photon detector 26C may generate a time signal from set of time signals 92C each time photon detector 26C detects a photon, and photon detector 26D may generate a time signal from set of time signals 92D each time photon detector 26D detects a photon.

[0080] In one example, photon detector 26B may generate time signal 94 when photon detector 26B detects a photon at time T1. To account for the varying time delays resulting from wing devices 30, 40 being at different distances from quantum optical device 20, processing circuitry 50 may calculate the time delay (t d ) 96 can be added to time T1. In some examples, the time delay can represent the difference between the expected amount of time it takes for a photon to travel round trip between the quantum optical device 20 and the first wing device 30 and the amount of time it takes for the photon to travel round trip between the quantum optical device 20 and the second wing device 40. The time delay 96 can extend from time T1 to time T2. In some examples, as shown in FIG. 4, a time delay T1 is added between photon detectors 26A, 26B and photon detectors 26C, 26D. In other words, if a first photon of an entangled photon pair arrives at photon detector 26A or photon detector 26B, the second photon of the entangled photon pair can be expected to arrive at photon detector 26C or photon detector 26D at time T2, where T1 and T2 are separated by the expected time delay 96. Alternatively, the first photon of the quantum entangled pair can be expected to arrive at photon detector 26C or photon detector 26D at time T1, and the second photon of the entangled pair can be expected to arrive at detector 26A or photon detector 26B at time T2, with T1 and T2 separated by the expected time delay 96.

[0081] The photon detectors 26 can emit signals in a sequence corresponding to the time a photon arrives at each photon detector. The processing circuitry 50 can calculate S-parameters based on averaging the correlations for one or more time delay values. For example, the system can measure S-parameters for one or more different angles corresponding to the photon detectors 26. In some examples, the angle of the photon detectors 26 can be changed by rotating the first wave plate 74 and the second wave plate 78. Rotating the first wave plate 74 can affect whether the polarizing beam splitter 76 directs one or more photons to photon detector 26C or photon detector 26D. Rotating the second wave plate 78 can affect whether the polarizing beam splitter 80 directs one or more photons to photon detector 26A or photon detector 26B.

[0082] In some examples, the processing circuitry 50 can determine an S-parameter for one or more time delay values. The time delay value that results in the largest S-parameter can represent the true time delay corresponding to the distance between the quantum optical device 20 and the first wing device 30 and the distance between the quantum optical device 20 and the second wing device 40. In some examples, the largest S-parameter is 2√2. Because only photons emitted at the exact same instant, e.g., entangled pairs, exhibit quantum correlation, the distance between the wings (e.g., the first wing device 30 and the second wing device 40) and the source (e.g., the quantum optical device 20) is the time delay value that has the largest S-parameter. d can be determined.

[0083] In some embodiments, the retro-reflective optics on each wing device are only partially reflective so that some of the down-converted photons pass through and are detected, and the timestamp is used locally for atomic clock synchronization.

[0084] In some instances, system 10 has an advantage over other methods of establishing the time-of-flight delay between the source and the two wings because measuring the quantum correlation allows a user to identify whether there has been any interception or manipulation of the photons used in the protocol. If an adversary attempts to intercept the photons with the intent of eavesdropping on the protocol or to send back new pulses with the intent of spoofing the protocol, the photons may not exhibit the correct quantum correlation.

[0085]

[0013] Figure 5 is a flow diagram illustrating example operations for determining whether quantum time transfer is secure, in accordance with one or more techniques of this disclosure. Figure 5 is described with respect to system 10 of Figure 1. However, the techniques of Figure 5 may be performed by different components of system 10 or by additional or alternative devices.

[0086] The light source 22 of the quantum optical device 20 can emit multiple pairs of photons, with each photon pair of the multiple pairs of photons occupying a quantum entangled state (102). In some examples, to emit the multiple pairs of photons, the light source 22 can emit one photon of each photon pair of the multiple pairs of photons to the first wing device 30, and the light source 22 can emit one photon of each photon pair of the multiple pairs of photons to the second wing device 40. In some examples, the quantum entangled state includes a Bell state of a set of Bell states. The light source 22 can emit each photon pair of the multiple photons by splitting a pump photon having a higher energy than each of the pairs of entangled photons.

[0087] The optical circuit 24 of the quantum optical device 20 may receive (104) a first set of photons from the first wing device 30. Additionally or alternatively, the optical circuit 24 may receive (106) a second set of photons from the second wing device 40. In some examples, the first set of photons and the second set of photons may represent pairs of photons emitted to the first wing device 30 and the second wing device 40. That is, the first set of photons may include one or more photons emitted by the optical device 22 to the first wing device 30 and returned to the quantum optical device 20, and the second set of photons may include one or more photons emitted by the optical device 22 to the second wing device 40 and returned to the quantum optical device 20. In some examples, one or more of the pairs of photons may include a first photon emitted to the first wing device 30 and returning to the quantum photonic device 20, and a second photon emitted to the second wing device 40 and returning to the quantum photonic device 20. The first distance between the quantum photonic device 20 and the first wing device 30 may be different from the second distance between the quantum photonic device 20 and the second wing device 40. This means that when a photon pair is emitted to the first wing device 30 and the second wing device 40, the photons may return to the quantum photonic device 20 at different times.

[0088] Photon detector 26 of quantum optical device 20 can receive the first set of photons and the second set of photons from optical circuit 24 (108). Each photon detector of photon detector 26 can generate a set of time signals (110). In some examples, a first photon detector of photon detector 26 can output a first set of time signals, where each time signal in the first set of time signals corresponds to a time at which the first photon detector receives a photon of the first set of photons or the second set of photons. In some examples, a second photon detector of photon detector 26 can output a second set of time signals, where each time signal in the second set of time signals corresponds to a time at which the second photon detector receives a photon of the first set of photons or the second set of photons. In some examples, a third photon detector of photon detector 26 can output a third set of time signals, where each time signal in the third set of time signals corresponds to a time at which the third photon detector receives a photon of the first set of photons or the second set of photons. In some examples, a fourth photon detector of photon detector 26 may output a fourth set of time signals, where each time signal in the fourth set of time signals corresponds to a time at which the fourth photon detector receives a photon of the first set of photons or the second set of photons.

[0089] Processing circuit 50 can determine whether a time delay value exists where the CHSH parameter is greater than a threshold CHSH parameter value based on the set of time signals corresponding to each photon detector of photon detector 26 (112). In some examples, processing circuit 50 is configured to determine a first correlation parameter corresponding to the correlation between a first photon detector of photon detector 26 and a third photon detector of photon detector 26. In some examples, processing circuit 50 is configured to determine a second correlation parameter corresponding to the correlation between the first photon detector of photon detector 26 and a fourth photon detector of photon detector 26. In some examples, processing circuit 50 is configured to determine a third correlation parameter corresponding to the correlation between the second photon detector of photon detector 26 and the third photon detector of photon detector 26. In some examples, processing circuit 50 is configured to determine a fourth correlation parameter corresponding to the correlation between the second photon detector of photon detector 26 and the fourth photon detector of photon detector 26. In some examples, processing circuitry 50 may calculate the sum of the first correlation parameter, the second correlation parameter, the third correlation parameter, and the fourth correlation parameter to determine the CHSH parameter.

[0090] The following examples are examples of the systems, devices, and methods described herein.

[0091] Example 1: A system comprising a quantum optical device comprising: a light source configured to emit a plurality of pairs of photons, each photon pair of the plurality of pairs occupying a quantum entangled state; and an optical circuit configured to receive a first set of photons of the plurality of pairs of photons from a first wing device and a second set of photons of the plurality of pairs of photons from a second wing device. The quantum optical device further comprises a set of photon detectors configured to receive the first set of photons and the second set of photons from the optical circuit, each photon detector of the set of photon detectors configured to generate a set of time signals, each time signal of the set of time signals representing a time at which a respective photon sensor detected a photon. The system further comprises a processing circuit configured to determine, based on the set of time signals corresponding to each photon detector of the set of photon detectors, whether a time delay value exists at which a Crowther, Horn, Simonyi, and Holt (CHSH) parameter is greater than a threshold CHSH parameter value.

[0092] Example 2: The system of example 1, wherein a first distance between the quantum optical device and the first wing device is different from a second distance between the quantum optical device and the second wing device, and the time delay value corresponds to the difference between the first distance and the second distance.

[0093] Example 3: The system of any of Examples 1-2, wherein to emit multiple pairs of photons, the light source is configured to emit one photon of each photon pair of the multiple pairs of photons to the first wing device and one photon of each photon pair of the multiple pairs of photons to the second wing device.

[0094] Example 4: The set of photon detectors includes: a first photon detector of the set of photon detectors outputs a first set of time signals, where each time signal of the first set of time signals corresponds to a time at which the first photon detector receives a photon of the first set of photons or the second set of photons; and a second photon detector of the set of photon detectors outputs a second set of time signals, where each time signal of the second set of time signals corresponds to a time at which the second photon detector receives a photon of the first set of photons or the second set of photons; The system of any of Examples 1 to 3, configured to output, by a third photon detector of the set, a third set of time signals, where each time signal of the third set of time signals corresponds to a time at which the third photon detector receives a photon of the first set of photons or the second set of photons; and configured to output, by a fourth photon detector of the set of photon detectors, a fourth set of time signals, where each time signal of the fourth set of time signals corresponds to a time at which the fourth photon detector receives a photon of the first set of photons or the second set of photons.

[0095] Example 5: The system of example 4, wherein the time delay value corresponds to a time delay between a first photon of a photon pair occupying the quantum entangled state arriving at the first photon detector or the second photon detector and a second photon of the photon pair arriving at the third photon detector or the fourth photon detector.

[0096] Example 6: The system of any of Examples 4-5, wherein the processing circuit is further configured to determine a first correlation parameter corresponding to a correlation between the first photon detector and the third photon detector, determine a second correlation parameter corresponding to a correlation between the first photon detector and the fourth photon detector, determine a third correlation parameter corresponding to a correlation between the second photon detector and the third photon detector, determine a fourth correlation parameter corresponding to a correlation between the second photon detector and the fourth photon detector, and calculate a sum of the first correlation parameter, the second correlation parameter, the third correlation parameter, and the fourth correlation parameter to determine the CHSH parameter.

[0097] Example 7: The system of any of Examples 1-6, wherein the light source is configured to emit each photon pair of the plurality of pairs of photons at a random time.

[0098] Example 8: The system of any of Examples 1-7, wherein the quantum entangled state comprises a Bell state of a set of Bell states.

[0099] Example 9: The system of any of Examples 1-8, wherein the processing circuitry is further configured to verify that communication between the quantum optical device and the first wing device and communication between the quantum optical device and the second wing device is secure based on an existing time delay value where the CHSH parameter is greater than a threshold CHSH parameter value.

[0100] Example 10: A system described in any of Examples 1 to 9, wherein the light source is configured to emit pairs of photons such that, for each photon pair of the pairs of photons, the time separating the first photon of each photon pair from the second photon of each photon pair is less than 100 femtoseconds.

[0101] Example 11: The system of any of Examples 1-10, wherein to determine whether there is a time delay value for which the CHSH parameter is greater than a threshold CHSH parameter value, the processing circuitry is configured to: determine a plurality of CHSH parameters, each CHSH parameter of the plurality of CHSH parameters corresponding to a respective time delay value of the plurality of time delay values; and determine whether a CHSH parameter of the plurality of CHSH parameters is greater than a threshold CHSH parameter value.

[0102] Example 12: The system of any of Examples 1 to 11, wherein the quantum optical device is configured to output a time delay value to the first wing device and the second wing device to synchronize a first atomic clock of the first wing device with a second atomic clock located in the second wing device.

[0103] Example 13: A method comprising: emitting, by a light source of a quantum photon device, a plurality of pairs of photons, each photon pair of the plurality of pairs of photons occupying a quantum entangled state; receiving, by an optical circuit of the quantum photon device, a first set of photons of the plurality of pairs of photons from a first wing device; receiving, by the optical circuit, a second set of photons of the plurality of pairs of photons from a second wing device; and receiving, by a set of photon detectors of the quantum photon device, the first set of photons and the second set of photons from the optical circuit. The method further includes generating, by each photon detector of the set of photon detectors, a set of time signals, each time signal of the set of time signals representing a time at which a respective photon sensor detected a photon; and determining, by a processing circuit based on the set of time signals corresponding to each photon detector of the set of photon detectors, whether a time delay value exists at which a Crowther, Horn, Simonyi, and Holt (CHSH) parameter is greater than a threshold CHSH parameter value.

[0104] Example 14: The method of example 13, wherein a first distance between the quantum optical device and the first wing device is different from a second distance between the quantum optical device and the second wing device, and the time delay value corresponds to the difference between the first distance and the second distance.

[0105] Example 15: The method of any of Examples 13-14, wherein emitting the plurality of pairs of photons includes: emitting, by the light source, one photon of each photon pair of the plurality of pairs of photons to the first wing device; and emitting, by the light source, one photon of each photon pair of the plurality of pairs of photons to the second wing device.

[0106] Example 16: outputting, by a first photon detector of the set of photon detectors, a first set of time signals, where each time signal of the first set of time signals corresponds to a time at which the first photon detector receives a photon of the first set of photons or the second set of photons; and outputting, by a second photon detector of the set of photon detectors, a second set of time signals, where each time signal of the second set of time signals corresponds to a time at which the second photon detector receives a photon of the first set of photons or the second set of photons; and a set of photon detectors. outputting, by a third photon detector in the set of photon detectors, a third set of time signals, where each time signal in the third set of time signals corresponds to a time at which the third photon detector receives a photon of the first set of photons or the second set of photons; and outputting, by a fourth photon detector in the set of photon detectors, a fourth set of time signals, where each time signal in the fourth set of time signals corresponds to a time at which the fourth photon detector receives a photon of the first set of photons or the second set of photons.

[0107] Example 17: The method of example 16, further comprising: determining, by the processing circuit, a first correlation parameter corresponding to the correlation between the first photon detector and the third photon detector; determining, by the processing circuit, a second correlation parameter corresponding to the correlation between the first photon detector and the fourth photon detector; determining, by the processing circuit, a third correlation parameter corresponding to the correlation between the second photon detector and the third photon detector; determining, by the processing circuit, a fourth correlation parameter corresponding to the correlation between the second photon detector and the fourth photon detector; and calculating, by the processing circuit, a sum of the first correlation parameter, the second correlation parameter, the third correlation parameter, and the fourth correlation parameter to determine the CHSH parameter.

[0108] Example 18: The method of any of Examples 13-17, wherein emitting each photon pair of photon pairs comprises emitting each photon pair of photon pairs at a random time.

[0109] Example 19: The method of any of Examples 13-18, further comprising verifying, by the processing circuitry, that the communication between the quantum optical device and the first wing device and the communication between the quantum optical device and the second wing device is secure based on the present time delay value where the CHSH parameter is greater than a threshold CHSH parameter value.

[0110] Example 20: A non-transitory computer-readable medium comprising instructions that, when executed, cause one or more processors to control a light source of a quantum optical device to emit a plurality of pairs of photons, wherein each photon pair of the plurality of pairs of photons occupies a quantum entangled state; cause an optical circuit of the quantum optical device to receive a first set of photons of the plurality of pairs of photons from a first wing device; cause the optical circuit to receive a second set of photons of the plurality of pairs of photons from a second wing device; cause a set of photon detectors of the quantum optical device to receive the first set of photons and the second set of photons from the optical circuit; cause each photon detector of the set of photon detectors to generate a set of time signals, each time signal of the set of time signals representing a time at which a respective photon sensor detected a photon; and determine, based on the set of time signals corresponding to each photon detector of the set of photon detectors, whether a time delay value exists at which a Crowther, Horn, Simonyi, and Holt (CHSH) parameter is greater than a threshold CHSH parameter value.

[0111] In one or more examples, the techniques described herein may utilize hardware, software, firmware, or any combination thereof to achieve the described functions. These software-implemented functions may be stored on a computer-readable medium or transmitted as one or more instructions or code and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which correspond to tangible media such as data storage media, or communication media, including any medium that facilitates transfer of a computer program from one place to another, for example, according to a communications protocol. In this manner, computer-readable media may generally correspond to (1) tangible computer-readable storage media that is non-transitory, or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code, and / or data structures for implementing the techniques described in this disclosure.

[0112] The instructions may be executed by one or more processors in the system or communicatively coupled to the system. The one or more processors may include, for example, one or more DSPs, general-purpose microprocessors, application-specific integrated circuits (ASICs), FPGAs, or other equivalent integrated or discrete logic circuitry. Accordingly, the term "processor," as used herein, may refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Furthermore, in some aspects, the functionality described herein may be provided in dedicated hardware and / or software modules configured to perform the techniques described herein. Alternatively, the techniques may be implemented entirely in one or more circuits or logic elements.

[0113] The techniques of the present disclosure can be implemented in a wide variety of devices or apparatuses, including an integrated circuit (IC) or set of ICs (e.g., a chipset). While various components, modules, or units are described in this disclosure to highlight functional aspects of apparatus configured to perform the disclosed techniques, they do not necessarily require realization by different hardware units. Rather, the various units may be combined or provided by a collection of interoperable hardware units, including one or more processors, as described above, along with appropriate software and / or firmware.

Claims

1. 1. A system comprising: A quantum optical device, comprising: a light source configured to emit pairs of photons, each photon pair of the photons occupying a quantum entangled state; An optical circuit comprising: receiving a first set of photons of the pairs of photons from a first wing device; an optical circuit configured to receive a second set of photons of the pairs of photons from a second wing device; a set of photon detectors configured to receive the first set of photons and the second set of photons from the optical circuit; a quantum optical device configured such that each photon detector of the set of photon detectors generates a set of time signals, each time signal of the set of time signals representing a time at which a respective photon sensor detected a photon; A processing circuit, and processing circuitry configured to determine whether a time delay value exists for which a Crowther, Horn, Simonyi, and Holt (CHSH) parameter is greater than a threshold CHSH parameter value based on the set of time signals corresponding to each photon detector of the set of photon detectors.

2. To emit the pairs of photons, the light source emitting one photon of each photon pair of the plurality of pairs of photons to the first wing device; The system of claim 1 , configured to emit one photon of each photon pair of the plurality of pairs of photons to the second wing device.

3. 1. A method comprising: emitting, by a light source of a quantum optical device, pairs of photons, each photon pair of the photon pairs occupying a quantum entangled state; receiving, by an optical circuit of the quantum optical device, a first set of photons of the pairs of photons from a first wing device; receiving, by the optical circuit, a second set of photons of the pairs of photons from a second wing device; receiving the first set of photons and the second set of photons from the optical circuit by a set of photon detectors of the quantum optical device; generating, by each photon detector of the set of photon detectors, a set of time signals, each time signal of the set of time signals representing a time at which a respective photon sensor detected a photon; determining, by a processing circuit based on the set of time signals corresponding to each photon detector in the set of photon detectors, whether there is a time delay value for which a Crowther, Horn, Simonyi, and Holt (CHSH) parameter is greater than a threshold CHSH parameter value.

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