Communication Devices

Abstract

The quantum communication device element comprises a receiver configured to receive a statistically mixed state quantum input signal consisting of a predetermined set of quantum states, probabilistically determine a plurality of quantum states of the predetermined set of quantum states of the quantum input signal, and output a plurality of input signals corresponding to the plurality of quantum states of the quantum input signal, a combining device coupled to the receiver and configured to convert the plurality of input signals into an output signal by time division multiplexing the plurality of input signals, and a detector coupled to the combining device and configured to receive the output signal.

Description

[Technical field]

[0001] The present invention relates to a communication device element, in particular the device element of the present invention has particular application in quantum communication. [Background technology]

[0002] Quantum communication is a communication method that implements communication protocols that include elements of quantum mechanics. Quantum communication has particular applications, for example, in quantum key distribution (QKD), a secure communication method that implements cryptographic protocols. Quantum communication is, for example, performed via optical signals that contain photons with a particular polarization.

[0003] The optical signals in quantum communication protocols are at the single photon level. Therefore, expensive single photon detectors are required to receive the optical signals. Furthermore, communication protocols tend to require multiple single photon detectors, each of which requires sophisticated thermal cooling units, thus doubling the cost of the already expensive single photon detectors. High-quality multi-channel timing electronics, which are equally expensive, are also required to realize quantum communication protocols.

[0004] In addition to high cost, single photon detectors, thermal cooling units, and multi-channel timing electronics also increase size, weight, and power (SWaP) requirements. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is devised to alleviate or overcome at least some of the problems set forth above. [Means for solving the problem]

[0006] According to a first aspect of the present invention, there is provided a quantum communication device element comprising: a receiver configured to receive a statistically mixed state quantum input signal consisting of a predetermined set of quantum states, probabilistically determine a plurality of quantum states of the predetermined set of quantum states of the quantum input signal, and output a plurality of input signals corresponding to the plurality of quantum states of the quantum input signal; a combining device coupled to the receiver and configured to convert the plurality of input signals into an output signal by time division multiplexing the plurality of input signals; and a detector coupled to the combining device and configured to receive the output signal.

[0007] The predetermined set of quantum states may be generated and transmitted by a quantum communications device configured to transmit quantum information. The detector may be a single pixel detector. Alternatively, the detector may be a multi-pixel detector.

[0008] The present invention may provide a quantum communication device element that combines and time-division multiplexes one or more input signals into one or more output signals. Advantageously, the present invention may provide a device that requires fewer detectors to implement a quantum communication protocol than known quantum communication devices that require, for example, single-photon sensitivity. The present invention may further advantageously provide a device that allows for greater optical throughput than conventional optical beam splitter-type couplers.

[0009] The present invention is a passive optical device that may be fabricated, for example, from single mode or multimode fiber. Advantageously, the device does not require input power to function, thereby reducing the power requirements of the device. Further advantageously, the device may be easily fabricated using known methods.

[0010] Those skilled in the art will appreciate that the present invention is not limited to quantum communication. The receiver may be any receiver suitable for quantum communication, for example the receiver may be a photodetector.

[0011] Advantageously, the present invention provides a device that may reduce the number of detectors required for quantum communication protocols. In turn, the present invention may also advantageously provide a device for achieving quantum communication with reduced size, weight and power requirements.

[0012] The receiver preferably comprises a state discrimination device configured to determine a plurality of quantum states of the quantum input signal. Those skilled in the art will understand that the term "state discrimination device" refers to a device configured to probabilistically determine the quantum state of the quantum input signal. Those skilled in the art will understand that the state discrimination device depends on the quantum communication protocol of the quantum input signal. For example, the Bennett-Brassard 1984 (BB84) protocol may require a state discrimination device having a 50:50 beam splitter, a first polarizing beam splitter, a second polarizing beam splitter, and a half-wave plate.

[0013] The coupling device may be a waveguide device, which includes a plurality of input waveguides in communication with an output waveguide, and a transition region where the waveguide device changes from the plurality of input waveguides to the output waveguide. For example, the waveguide device may include a plurality of optical fibers. The coupling device is preferably a photonic lantern device in an inverted configuration. Those skilled in the art will appreciate that the waveguide device may be any device suitable for propagating and combining signals, such as optical signals, along an axis from a plurality of input waveguides to an output waveguide. The coupling device may differ from known beam splitter devices because it combines light in a lossless manner in both forward and reverse configurations by combining multiple waveguides into a single waveguide that can support at least as many spatial optical modes as all of the combined input waveguides.

[0014] Preferably, the number of input waveguides is equal to or greater than the number of detectors required for the quantum communication protocol. Advantageously, the device is capable of fully capturing the information of the quantum input signal. The coupling transition region is preferably configured to adiabatically couple the input signal with the output signal. Preferably, the change from the multiple input waveguides to the output waveguide transition region is gradual enough that the multiple input signals adiabatically couple with the output signal. Advantageously, signal loss along the coupling device may be reduced.

[0015] Preferably, each of the plurality of input waveguides has a different waveguide length. More preferably, the individual waveguide lengths are configured to provide temporal separation between each of the individual input signals. More preferably, the time separation is greater than the timing jitter of the detector and less than the input time interval of the input signals. Advantageously, a time separation greater than the timing jitter may allow correct discrimination between each time state. The longest time separation of the plurality of time separations provided by the input waveguides is preferably less than the input time separation to maintain the output signal as a block, preferably avoiding overlap with subsequent blocks.

[0016] In some embodiments, the input waveguides are single mode waveguides. Preferably, single mode waveguides are applicable to implementations utilizing fiber optics or free space adaptive optics. In another embodiment, the input waveguides are multimode waveguides. Preferably, multimode waveguides are utilized in free space implementations where adaptive optics is not present or is limited.

[0017] In some embodiments, the receiver is configured to receive a polarization encoded optical signal, however, one skilled in the art will appreciate that the receiver may be configured to receive any encoded optical signal suitable for quantum communication, such as phase, time bin, wavelength, spatial mode, or angular orbital momentum state.

[0018] Preferably, the core diameter of the output waveguide is equal to or greater than the core diameter of each of the multiple input waveguides, in this way the multiple input waveguides can be more easily coupled with the output waveguide. Preferably, the input signal is distributed into a first number of spatial modes and the output signal is distributed into a second number of spatial modes, the sum of the first number of spatial modes being less than the second number of spatial modes. In this way, the output waveguide can accommodate the input signal.

[0019] The detector may be a single photon detector. For example, the single photon detector may be a single photon avalanche diode. Those skilled in the art will appreciate that the single photon detector may be any detector suitable for detecting a single photon at a time, such as a pixelated single photon detector. As such, the detector may be suitable for use in quantum communications.

[0020] The input and output optical waveguides may be one or more selected from the range of one or more optical fibers, and one or more waveguides. According to a second aspect of the present invention, there is provided a method of routing a plurality of signals to a detector, the method comprising the steps of: a receiver receiving a quantum input signal; a state discrimination device element of the receiver probabilistically determining a plurality of quantum states of the quantum input signal; the receiver outputting a plurality of input signals corresponding to the plurality of quantum states of the quantum input signal; converting the plurality of input signals into an output signal by time division multiplexing the plurality of input signals using a coupling device coupled to the receiver; and a detector coupled to the coupling device receiving the output signal from the coupling device.

[0021] Preferably, the multiple signals are coupled to the output fibers by applying a delay to each of the multiple input signals at each of a corresponding multiple input fibers, each delay being unique. Preferably, the delay is achieved by a fiber length of each of a plurality of input fibers.

[0022] It will be understood that any feature described herein as suitable for incorporation in one or more aspects or embodiments of the present disclosure is intended to be generalizable across all aspects and embodiments of the present disclosure. Other aspects of the present disclosure can be understood by those skilled in the art in light of the description, claims, and drawings of the present disclosure. The foregoing summary and the following detailed description are exemplary and explanatory only and are not intended to limit the scope of the claims. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram of a quantum communication device element according to a first embodiment of the present invention; [Diagram 2] 2 is a schematic diagram of a coupling device element of the quantum communication device element of FIG. 1 in accordance with the present invention; [Diagram 3] 2 illustrates a method for routing multiple signals to a detector using the quantum communications device elements of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings. 1 is a schematic diagram of a quantum communication device element 100 suitable for implementing a quantum communication protocol. In this example, the quantum communication device element 100 is suitable for use with the known Bennett-Brassard 1984 (BB84) protocol.

[0025] The quantum communication device element 100 includes a receiver 102, a coupling device 104, and a detector 106. The receiver 102 is communicatively coupled to the coupling device 104. In this example, the receiver 102 is optically coupled to the coupling device 104. The detector 106 is also communicatively coupled to the coupling device 104. In this example, the detector 106 is optically coupled to the coupling device 104.

[0026] The receiver 102 includes a light receiving means 103 and a state determination device 105. In this example, the light receiving means 103 is an optical fiber. 2 shows a coupling device 104. The coupling device 104 is a waveguide device that includes multiple input waveguides, a transition region 116, and an output waveguide 118.

[0027] In this example, the multiple input waveguides consist of a first optical fiber 108, a second optical fiber 110, a third optical fiber 112, and a fourth optical fiber 114. One skilled in the art will appreciate that the multiple input waveguides must include at least as many input waveguides as there are detectors required for the subject quantum communication protocol using known techniques. In this example, the BB84 protocol requires four detectors using known techniques.

[0028] The optical fibers 108, 110, 112, 114 each include a single mode core having a respective core diameter, in this example each single mode core having a core diameter of 5 μm. In this example, the output waveguide 118 is an output optical fiber 118. The output optical fiber 118 includes a multimode core having a core diameter. The core diameter of the multimode core is larger than the core diameter of each of the single mode cores. In this example, the core diameter of the multimode core is 10 μm.

[0029] Those skilled in the art will appreciate that the optical fibers 108, 110, 112, 114 may also be comprised of multimode cores, so long as the multimode cores support fewer modes than the multimode core of the output optical fiber 118. In this example, the sum of the core diameters of each multimode optical fiber core is less than the core diameter of the multimode core.

[0030] The transition region 118 is the region where the optical fibers 108, 110, 112, 114 transition to the output optical fiber 118. In particular, the coupling device 104 smoothly changes from the optical fibers 108, 110, 112, 114 to the output optical fiber 118. In this manner, light propagating along the coupling device 104 follows the transition and the input signal is adiabatically coupled to the output signal.

[0031] To achieve the transition, the optical fibers 108 , 110 , 112 , 114 are fused together to form an integrated body, and the cross-sectional scale of the integrated body is reduced to form the output optical fiber 118 .

[0032] In this example, the detector 106 is a single-photon detector 106. In particular, the detector 106 is a single-photon avalanche diode 106. The optical receiving means 103 of the receiver 102 is configured to receive an input signal, such as a quantum input signal, from an external source (not shown). The quantum input signal comprises quantum information. The quantum information may be represented as a series of qubits in non-orthogonal quantum states that must be determined probabilistically. The series of qubits may be received at the frequency of the source. For example, the quantum information may be encoded as a series of qubits encoded as polarization-encoded photons. In particular, the quantum information may be encoded in a rectilinear basis (i.e. horizontal and vertical polarization) and a diagonal basis (i.e. 45° and 135° polarization).

[0033] The state discrimination device 105 according to this example includes a 50:50 beam splitter 105A, a first polarizing beam splitter 105B, a second polarizing beam splitter 105C, and a half-wave plate 105D. The state discrimination device 105 is connected to a first optical fiber 108, a second optical fiber 110, a third optical fiber 112, and a fourth optical fiber 114 so as to be capable of optical communication.

[0034] The state discrimination device 105 is configured such that an incident photon passes through the 50:50 beam splitter 105A. If the photon is reflected by the 50:50 beam splitter 105A, the first polarizing beam splitter 105B directs the photon to the first optical fiber 108 or the second optical fiber 110 depending on the polarization of the photon. If the photon is transmitted through the 50:50 beam splitter 105A, the photon passes through the half-wave plate 105D and the second polarizing beam splitter 105C directs the photon to the third optical fiber 112 or the fourth optical fiber 114.

[0035] For example, if an incident photon is a vertically polarized photon reflected by the 50:50 beam splitter 105A, the photon is received by the first optical fiber 108. If an incident photon is a vertically polarized photon transmitted through the 50:50 beam splitter 105A, the photon is received by the third optical fiber 112 or the fourth optical fiber 114 with equal probability.

[0036] Each of the optical fibers 108, 110, 112, 114 is configured to direct individual photons to reach the transition region 116 or the output waveguide 118 at an individual time. In particular, the first optical fiber 108 directs photons at a first time t 1 The second optical fiber 110 is configured to transmit the photons to the transition region 116 at a second time t 2 The third optical fiber 112 is configured to transmit the photons to the transition region 116 at a third time t 3 The fourth optical fiber 114 is configured to transmit the photons to the transition region 116 at a fourth time t 4 1 and 2. The optical fibers 108, 110, 112, and 114 are configured to transmit at different times to the transition region 116. In this example, the distinct times are achieved by the difference in the optical fiber lengths of the optical fibers 108, 110, 112, and 114.

[0037] In this example, time t 1 , t 2 , t 3 , t 4 are separated by an arrival time interval value Δt. Thus, the first time t1 is 1 and at the second time t 2 is 1 +Δt, and the third time t 3 is 1 +2Δt, and the fourth time t 4 is 1 +2Δt.

[0038] The optical fibers 108, 110, 112, 114 are configured such that the arrival time interval value Δt is greater than the timing jitter of the single photon detector 106 and less than the input time interval of the quantum input signal corresponding to the frequency of the source. For example, if the input time interval is 50 ns, the arrival time interval value Δt may be 12.5 ns. Alternatively, the arrival time interval value Δt may be 500 ps. Alternatively, the arrival time interval value Δt may be asymmetric. In particular, the arrival time interval value Δt may be 1 ns for the second optical fiber 110, 5 ns for the third optical fiber 112, and 32 ns for the fourth optical fiber 114.

[0039] Thus, an incident photon of the quantum input signal is routed to transition region 116 or output waveguide 118 at different times depending on the quantum state of the incident photon. The output waveguide 118 is configured to transmit an output signal consisting of the incident photons arranged according to quantum states to the single-photon detector 106 .

[0040] The quantum information of the quantum input signal can be deduced from the output signal according to the arrival time of the incident photons. In use, and with reference to the signal routing method 300 of FIG. 3, a quantum input signal containing quantum information is sent from an external source to the quantum communications device element 100. The quantum information is comprised of a plurality of signals. In this example, the plurality of signals is encoded as a series of quantum bits encoded as polarization-encoded photons according to a selected basis. For example, the plurality of signals may be comprised of a first quantum bit, a second quantum bit, and a third quantum bit. The first quantum bit may have a vertical polarization, the second quantum bit may have a horizontal polarization, and the third photon may have a 45° polarization.

[0041] In a first step 302 , the receiver 102 receives a plurality of quantum input signals via the optical receiving means 103 . In a second step 304 , the combining device 104 combines the multiple signals into an output optical fiber 118 .

[0042] In particular, if the first quantum bit is reflected by the 50:50 beam splitter 105A, the first quantum bit is directed by the first polarizing beam splitter 105B to the first optical fiber 108. If the second quantum bit is transmitted through the 50:50 beam splitter 105A, the second quantum bit passes through the half-wave plate 105D and is directed by the second polarizing beam splitter 105C with equal probability to either the third optical fiber 112 or the fourth optical fiber 114. If the third quantum bit is transmitted through the 50:50 beam splitter 105A, the third quantum bit passes through the half-wave plate 105D and is directed to the third optical fiber 112.

[0043] The first quantum bit is transmitted by the first optical fiber 108 at time t 1 The second quantum bit is transmitted to the output optical fiber 118 at time t 1 +2Δt or t 1 +3Δt to the output optical fiber 118. The third quantum bit is transmitted by the third optical fiber 112 at time t 1 It is transmitted to the output optical fiber 118 at +2Δt.

[0044] In a third step 306, the detector 106 receives the output signal from the output optical fiber 118. In particular, the detector 106 detects the first quantum bit, the second quantum bit, and the third quantum bit at times t 1 , t 1 +2Δt, and t 1 Received at +3Δt.

[0045] The description provided herein may be directed to particular embodiments, and it should be understood that the description provided herein is provided for the purpose of enabling one of ordinary skill in the art to make and use any subject matter defined herein by the subject matter of the claims.

[0046] The subject matter of the claims is not limited to the embodiments and illustrations provided herein, but is intended to include modifications of those embodiments, including portions of the embodiments and combinations of elements of different embodiments, in accordance with the scope of the claims. As with any engineering or design project, it will be recognized that the development of such an embodiment will require numerous embodiment-specific decisions to be made in order to achieve the developer's particular goals, such as compliance with system-related and business-related constraints, which may vary from embodiment to embodiment. Moreover, it will be appreciated that such a development effort may be complex and time-consuming, but will nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill in the art having the benefit of the present invention.

[0047] Reference will be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings and figures. In the detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention provided herein. However, the invention provided herein may be practiced without these specific details. In some other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure the details of the embodiments.

[0048] In this specification, terms such as first, second, etc. may be used to describe various elements, but it should be understood that these elements should not be limited by these terms. These terms are used only to distinguish one element from another element. For example, a first element may be called a second element, and similarly, a second element may be called a first element. Although a first element and a second element are each elements, they should not be considered to be the same element.

[0049] The terms used in the description of the invention provided herein are intended to describe particular embodiments and are not intended to limit the invention provided herein. When used in the description of the invention provided herein and in the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms, unless the context clearly dictates otherwise. The term "and / or" as used herein refers to and encompasses any possible combination of one or more of the associated listed items. The terms "includes", "including", "comprises" and / or "comprising", as used herein, specify the presence of stated features, components, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, components, steps, operations, elements, components and / or groups thereof.

[0050] As used herein, the term "if" may be interpreted to mean "when" or "upon" or "upon determining" or "in response to detecting," depending on the context. Similarly, the phrases "if determined" or "if [a particular condition or event] is detected" may be interpreted to mean "upon determining" or "upon determining" or "upon detecting [a particular condition or event]" or "in response to detecting [a particular condition or event]," depending on the context.

[0051] While the foregoing is directed to embodiments of the various techniques described herein, other and further embodiments may be devised in accordance with the inventions herein, as may be determined by the following claims. Although the subject matter has been described in terms of specific structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms for implementing the claims.

Claims

1. Quantum communication device elements, It is a receiver, A quantum input signal consisting of a predetermined set of quantum states in a statistical mixed state is received. Multiple quantum states of a predetermined set of quantum states of the quantum input signal are determined probabilistically. The receiver outputs a plurality of input signals corresponding to the plurality of quantum states of the quantum input signal, A coupling device coupled to the receiver, configured to convert the plurality of input signals into output signals by time-division multiplexing the plurality of input signals, A detector coupled to the coupling device, wherein the detector is configured to receive the output signal, The coupling device is a waveguide device, the waveguide device includes a plurality of input waveguides that can communicate with an output waveguide, and a transition region in which the waveguide device changes from the plurality of input waveguides to the output waveguide, the transition region being configured to couple the plurality of input signals with the output signal, the quantum communication device element.

2. The device element according to claim 1, wherein the receiver comprises a state determination device configured to determine the plurality of quantum states of the quantum input signal.

3. The device element according to claim 1, wherein the number of input waveguides is greater than or equal to the number of detectors required for the quantum communication protocol.

4. The device element according to claim 1, wherein the transition region is configured to adiabatically couple the plurality of input signals with the output signal.

5. The device element according to claim 1, wherein each of the plurality of input waveguides has a different waveguide length.

6. The device element according to claim 5, wherein the individual waveguide lengths are configured such that a time interval is created between each of the individual plurality of input signals.

7. The device element according to claim 6, wherein the time interval is greater than the timing jitter of the detector and smaller than the input time interval of the plurality of input signals.

8. The device element according to any one of claims 1 to 7, wherein the plurality of input waveguides are a plurality of single-mode waveguides.

9. The device element according to any one of claims 1 to 7, wherein the plurality of input waveguides are a plurality of multimode waveguides.

10. The device element according to any one of claims 1 to 7, wherein the core diameter of the output waveguide is greater than or equal to the core diameter of each of the plurality of input waveguides.

11. The receiver is configured to receive an optical signal, according to any one of claims 1 to 7.

12. The device element according to claim 11, wherein the input signal is distributed to a first spatial mode number, the output signal is distributed to a second spatial mode number, and the sum of the first spatial mode numbers is less than the second spatial mode number.

13. The device element according to claim 11, wherein the detector is a single-photon detector.

14. The plurality of input waveguides and the output waveguides are, One or more fibers, One or more waveguides and A device element according to any one of claims 1 to 7, which is one or more selected from the range.

15. A method for routing multiple signals to a detector, The receiver receives the quantum input signal, The state determination device element of the receiver probabilistically determines a plurality of quantum states of the quantum input signal, The receiver outputs a plurality of input signals corresponding to the plurality of quantum states of the quantum input signal, The steps include converting the multiple input signals into output signals by time-division multiplexing the multiple input signals using a coupling device coupled to the receiver, A method comprising the step of a detector coupled to the coupling device receiving the output signal from the coupling device.

16. The method according to claim 15, wherein the plurality of input signals are coupled to an output fiber by applying a delay to each of the plurality of input signals in each of the corresponding plurality of input fibers, and each delay is unique.

17. The method according to claim 16, wherein the delay is achieved by the fiber length of each of the plurality of input fibers.

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