Light quantum logic gates

Abstract

To provide an optical quantum logic gate (OQLG) and a method of operating it.SOLUTION: An OQLG comprises first optical structure including 2n optically-coupled cores with one-to-one correspondence to input binary values specified by the matrix and second optical structure optically connected to the first optical structure and including 2n amplifying channels corresponding to the 2n cores. The first optical structure receives photons in binary fundamental quantum states representing input binary values specified by the matrix and injects the received photons in the 2n cores 211 and 212, uses optical coupling between the cores to mix the injected photons, and outputs the photons to the second optical structure. The output mixed photons correspond to output binary values specified by the matrix. The second optical structure amplifies photons in the amplifying channels in a controllable manner while preserving the binary fundamental quantum states and relative quantities of photons having different binary fundamental quantum states.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims the benefit of U.S. Provisional Application No. 63 / 161,224, filed on 15 March 2021, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to an optical computing device, and more particularly to an optical computing device and optical system suitable for optical quantum computing. [Background technology]

[0003] Optical computing performs computational processes by manipulating visible or infrared light instead of electric current, as is done in electronic computing. Generally, optical computing enables faster computation speeds compared to electronic systems. This is partly because manipulating light pulses can be done faster, potentially allowing for higher information bandwidth transmission. For example, electric signals propagate at only about 10 percent the speed of light because their dielectric constant in the microwave region is much higher than that of optical signals, illustrating how optical computing can improve computing speed by almost tenfold. Also, because photons, unlike electrons, are nonpolar and do not carry charge, optical instruments consume less power and are less susceptible to crosstalk from nearby electric fields.

[0004] Conventional optical processing systems typically utilize hybrid electron-optical processing, commonly referred to as optoelectronic processing. In these systems, optical signals are used for data transmission and some processing operation, and are converted to electronic signals for some other processing operation. Such optoelectronic devices can lose about 30% of the energy when converting electronic energy to photons and vice versa. Furthermore, the conversion from optical signals to electronic signals and vice versa slows down data transmission and processing. Much research effort is directed towards all-optical computing, which reduces power demand and improves processing speed because it eliminates the need for optical-electrical-optical (OEO) conversion.

[0005] The problems with all-optical computing have been recognized in conventional technologies, and various technologies have been developed to provide solutions. Examples are listed below.

[0006] International Patent Publication WO2017 / 033197 teaches an integrated optical module. The optical module has multiple optically coupled channels and enables its use in artificial neural networks (ANNs). According to some embodiments, the integrated optical module comprises a multicore optical fiber, the cores of which are optically coupled.

[0007] International Patent Publication WO2019 / 186548 discloses an artificial neuron unit and neural network for processing input light. The artificial neuron unit comprises a mode mixing unit, such as a multimode optical fiber, configured to receive input light and apply a selected mixing to two or more mode optical components in the input light to provide output light, and a filtering unit configured to provide output light of the artificial neuron unit by applying a pre-selected filter to the output light and selecting one or more modes of the output light.

[0008] International Patent Publication WO2021 / 064727 discloses an artificial neuron network and corresponding neuron units. The neuron network comprises a plurality of layers of two or more artificial neuron units. The layers of artificial neuron units are configured to communicate with each other by an arrangement of two or more optical waveguides (optical fibers). The arrangement of two or more optical waveguides is configured using predetermined couplings between the two or more waveguides to enable communication between the neuron units of the two or more layers.

[0009] The above references provide background information that may be applicable to the subject matter disclosed herein. Accordingly, the entire contents of these publications are incorporated herein by reference where appropriate for providing additional or alternative details, features, and / or technical background. [Overview of the project]

[0010] In the prior studies cited above, the inventors of the present invention disclosed, among other things, an optical unit usable for photonic integrated circuits, including artificial neural networks. According to the inventors' understanding, the optical unit may be configured to operate as an optical quantum logic gate usable for quantum information processing.

[0011] According to some aspects of the subject matter disclosed herein, n qubits act upon 2 n ×2 n Optical quantum logic gates (OQLGs) are provided, characterized by unitary matrices. OQLGs have a one-to-one correspondence between the input binary values ​​specified by the unitary matrix and the two 2-bit matrix. n A first optical structure having optically coupled cores, and two optically connected to the first optical structure n 2 cores corresponding to each core nThe system comprises a first optical structure and a second optical structure having amplified channels. The first optical structure receives a photon in a binary fundamental quantum state representing an input binary value specified by a unitary matrix, and, according to the one-to-one correspondence of the core and the fundamental state of the photon, modifies the received photon. n The system is configured to inject photons into individual cores, use optical coupling between the cores to mix the incident photons, the photons being mixed with weights specified by a unitary matrix, and output the photons to a second optical structure, the output mixed photons corresponding to output binary values ​​specified by the matrix. The second optical structure is configured to amplify photons in an amplification channel, the amplification being performed in a controllable manner with respect to the photons propagating in the amplification channel, while preserving their fundamental quantum states and the relative quantities of photons having different fundamental quantum states.

[0012] As an unrestricted example, a real input binary value specified by a unitary matrix can be represented by the fundamental quantum states of vertical and horizontal polarization. A complex binary value specified by a unitary matrix can be represented by the superposition of photons in each of the fundamental quantum states. Optionally, the first optical structure may be configured to mix received photons and thereby perform superposition before injecting superimposed photons into the core corresponding to the complex binary value.

[0013] In further embodiments, and optionally in combination with other embodiments of the subject matter disclosed herein, the weights can be predetermined as a function of the coupled length of the first optical structure, the coupled length can be predetermined by selection of optical and geometric parameters of the core and the cladding therebetween.

[0014] In further embodiments, and optionally in combination with other embodiments of the subject matter disclosed herein, the first optical structure and the second optical structure may be integrated and implemented on the same core of a multicore optical fiber. Optionally, two within a multicore optical fiber nEach core of the multicore can be configured to include a first segment which is part of a first optical structure, and a second segment which is part of a second optical structure following the first segment. Optionally, the multicore optical fiber can be configured to have a tapered configuration, where the first segment of each core is positioned in the tapered portion to enable optical coupling between the first segments, and the second segment is positioned in the wider portion to allow sufficient distance to prevent optical interaction between the second segments.

[0015] In a further embodiment, and optionally in combination with other embodiments of the subject matter disclosed herein, each amplification channel is associated with a control port configured to enable the required amplification in the amplification channel in response to a control signal specifying a desired amplification coefficient. Each amplification channel may be impregnated with a gain medium configured to provide gain in a first wavelength range corresponding to the output mixed photons, and the gain is achievable in response to a pumping optical signal received via the control port and having a pumping wavelength range different from the first wavelength range.

[0016] In further embodiments, and optionally in combination with other embodiments of the subject matter disclosed herein, the amplification coefficient can be controlled by defining at least the parameters of the pumping optical signal, the gain medium, and / or the effective length of the amplification channel.

[0017] In further embodiments, and optionally in combination with other embodiments of the subject matter disclosed herein, the above OQLG may be configured to be organized into a total optical configuration of multiple OQLGs.

[0018] According to a further aspect, and optionally in combination with other aspects of the subject matter disclosed herein, using entanglement phenomena can further improve the connectivity and / or cascaded connection of OQLGs in all-optical knitting. For example, an OQLG can be operably connected to at least one second OQLG, and a logical connection between the output of the OQLG and the input of the at least one second OQLG can be provided using an optical structure, the optical structure generating a plurality of photons having entangled binary basic quantum states and configured to allow the generated entangled photons to be incident on the input of the OQLG and the input of the at least one second OQLG in a specific ratio.

[0019] According to other aspects of the subject matter disclosed herein, a method of operating an optical quantum logic gate (OQLG) characterized by a unitary matrix acting on n qubits is provided. The method includes receiving, by the OQLG, a plurality of photons in binary basic quantum states representing input binary values specified by the unitary matrix, the OQLG comprising an optical structure having two optical coupling cores having a one-to-one correspondence with the input binary values specified by the unitary matrix and the received photons being incident on the cores according to the one-to-one correspondence, using optical coupling between the cores to mix the incident photons, the photons being mixed with a pre-specified weight made possible by the design of the optical structure, outputting the photons to two optical amplification channels corresponding to the two cores, the output mixed photons corresponding to the output binary values specified by the matrix, amplifying the photons in the amplification channels, the amplification being performed in a controllable manner while preserving the basic quantum state of the photons propagating in the amplification channels and the relative amounts of photons having different basic quantum states, and performing quantum readout of the photons output from the amplification channels.

[0020] ​​​​​​​​​​According to a further aspect, and optionally, in combination with other aspects of the subject matter disclosed herein, the weights can be predefined as a function of the coupling length of the optical structure, and the coupling length can be predefined by the selection of the optical and geometrical parameters of the core and the cladding therebetween.

[0021] According to a further aspect, and optionally, in combination with other aspects of the subject matter disclosed herein, the method can further include receiving, by a control port of the OQLG, a control signal specifying a desired amplification factor in an amplification channel and performing amplification in response thereto.

[0022] Each amplification channel can be impregnated with a gain medium configured to provide gain in a first wavelength range corresponding to the output mixed photons, while the control signal can be a pumping optical signal received via the control port and having a pumping wavelength range different from the first wavelength range.

[0023] The amplification factor can be controlled by defining at least parameters of the pumping optical signal, the gain medium and / or the effective length of the amplification channel.

[0024] According to a further aspect, and optionally, in combination with other aspects of the subject matter disclosed herein, the OQLG and its configuration can act on photons having substantially the same wavelength or photons having different, relatively close wavelengths multiplexed prior to input to the OQLG.

[0025] To understand the present invention and to see how it can be actually implemented, embodiments are described as non-limiting examples with reference to the following accompanying drawings.

Brief Description of the Drawings

[0026] [Figure 1] It is a diagram showing a non-limiting example of a quantum logical gate (QLG: quantum logical gate) known in the art. [Figure 2] Figure 2a is a generalized functional block diagram of an optical quantum logic gate (OQLG) according to several embodiments of the subject matter disclosed herein. Figure 2b is a generalized functional block diagram of an optical quantum logic gate (OQLG) combined with a wavelength multiplexer according to several embodiments of the subject matter disclosed herein. [Figure 3] Figures 3a-3b show non-limiting examples of optical structures that can be used for linear coupling units in OQLG, which are comprised of several embodiments of the subject matter disclosed herein. [Figure 4a] This figure shows a non-limiting example of the dependence of the coupling coefficient on the relative difference between gap size, core radius, and refractive index, which is known in the art. [Figure 4b] This figure shows a non-limiting example of the dependence of the coupling coefficient on the relative difference between gap size, core radius, and refractive index, which is known in the art. [Figure 4c] This figure shows a non-limiting example of the dependence of the coupling coefficient on the relative difference between gap size, core radius, and refractive index, which is known in the art. [Figure 5] This is a generalized flowchart illustrating the operation of OQLG according to several embodiments of the subject matter disclosed herein. [Figure 6] This is a generalized diagram of a fragment of an optical array in which OQLG is connected by some embodiments of the subject matter disclosed herein. [Modes for carrying out the invention]

[0027] The field of quantum processing is a rapidly growing new area for new technologies. Conventional computers operate by manipulating bits that exist in either a 0 state or a 1 state. In contrast, quantum computers encode information as qubits, which can exist in a 0 state, a 1 state, or a superposition of 0 and 1 states. Thus, instead of making a deterministic choice between 0 and 1, qubits can be in either a 0 or a 1 state with different probabilities.

[0028] Superposition, quantum measurement, and entanglement are three phenomena central to quantum computing. Superposition is the ability of a quantum system to exist in many different states simultaneously. Quantum measurement is the act of observing a quantum particle in a superposition state, resulting in one of the possible states.

[0029] The superposition of qubits gives quantum computers an inherent parallelism, allowing them to perform many calculations at once, whereas conventional computers perform one calculation at a time. When a quantum computing memory consists of N bits of information, it can perform 2 N It has n possible states. Therefore, the vector representing all memory states is 2 N It has n components (one for each state). This vector is considered a probability vector and represents the fact that memory can be found in a particular state. In the classical view, if one component has a value of 1 (i.e., a 100% probability of being in this state), all other components are 0, whereas in quantum mechanics, the probability vector is generalized to a density operator. In that case, quantum memory can be found in any quantum superposition of its classical states.

[0030] Entanglement is the possibility that quantum particles correlate their measurement results with one another. When particles entangle, they form a single system such that the quantum state of any one particle cannot be described independently of the quantum states of the other particles. This means that any action or process applied to one particle will correlate with the other entangled particles. Since the effects of quantum measurements also apply to entangled particles, if one particle is measured and collapses, the other particles also collapse. The correlation between entangled particles means that measuring the state of one particle can provide information about the states of the other particles. Thus, the effect of entanglement makes it possible to indirectly measure qubits in order to preserve the integrity of the qubits (i.e., without changing their values). Examples of entangled states include position, angular momentum, spin, polarization, energy, and time.

[0031] Just as classical logic gates are the building blocks for conventional digital circuits, quantum logic gates are the building blocks for quantum circuits.

[0032] A logic gate, whether classical or quantum, is any physical structure that takes a set of binary inputs and produces a single binary output, the output of which is governed by a Boolean function.

[0033] Classical logic gates implement classical logic operations. For example, as follows: - An inverter, or NOT gate, is a fundamental logic gate that implements logic negation. An inverter circuit outputs a voltage that represents the opposite logic level to its input. Its primary function is to invert a given input signal. If the given input is low, the output is high, and vice versa. - The AND gate is a basic logic gate that implements logical conjunction. A HIGH output (1) is produced only when all inputs to the AND gate are HIGH (1). A LOW output is produced when none of the inputs to the ANG gate are HIGH, or when not all inputs are HIGH. - The OR gate is a basic logic gate that implements logical disjunction. If one or both inputs to the gate are HIGH (1), a HIGH output (1) is produced. If neither input is HIGH, a LOW output (0) is produced.

[0034] Conventional technologies have shown that quantum computers can use non-classical logic operations in addition to classical logic operations.

[0035] Figure 1 shows examples of various quantum logic gates (represented by 11-21) known in this field.

[0036] As an example of classical logic functions, we can consider the Pauli X logic gate, which implements the conventional NOT operation, simply flipping the value of a single qubit from 0 to 1, or from 1 to 0. In addition to the usual NOT, quantum computers can also implement a new type of logic operation, known as the square root of NOT. When this operation is applied twice (squared), it produces a regular NOT, but when applied only once, it gives a logic operation without classical interpretation.

[0037] The logic of quantum logic gates is represented by unitary matrices. The number of qubits at the input and output of a gate must be equal, and a gate acting on n qubits has 2 n ×2 n It is represented by a unitary matrix. The quantum state on which the gate acts is 2 n These are complex-dimensional vectors. The basis vectors represent the possible outcomes when measured, and the quantum state is a linear combination of these outcomes. The output quantum state can be represented as the output vector obtained by multiplying each matrix.

[0038] Just as typical classical logic gates act on 1 or 2 bits, the most common quantum gates act on a space of 1 or 2 qubits.

[0039] With the above in mind, we focus on Figure 2, which shows a generalized functional block diagram of an all-optical structure configured to operate as an optical quantum logic gate, according to some embodiments of the subject matter disclosed herein.

[0040] Quantum logic gates (QLGs) can act on a space of one or more qubits, depending on the type of QLG. For example, QLGs 11-16 shown in Figure 1 act on a space of one qubit, QLGs 17-20 are two-qubit gates, and Toffoli gate 21 is a three-qubit gate.

[0041] For illustrative purposes only, the following description is provided for a 1-qubit QLG. As will be readily apparent to those skilled in the art, the teachings of the subject disclosed herein are equally applicable to QLGs operating with other qubit counts, as well as to suitable combinations of the same and / or different types of QLGs.

[0042] The optical quantum logic gate (OQLG) 200 comprises a ray coupling unit 201 optically connected to an optical amplification unit 202. According to some embodiments of the subject matter disclosed herein, the OQLG 200 may be implemented as a photonic device based on a multicore optical fiber in which at least a portion of the core is optically coupled.

[0043] The OQLG200 is optically connected to a source unit 203 configured to allow multiple photons in binary fundamental quantum states (e.g., horizontally polarized and vertically polarized photon states) to be incident on the OQLG200. The fundamental quantum states correspond to binary values ​​represented by photons, for example, the vertically polarized and horizontally polarized states may correspond to values ​​0 and 1, respectively. In this case, any other binary values ​​available in the OQLG200 (e.g., the values ​​in QLG12-16 or 18 shown in Figure 1) may correspond to superpositions of these two states.

[0044] The source unit 203 may comprise an optical structure based on a nonlinear crystal capable of splitting an input optical signal into photon pairs (i.e., two simultaneously generated photons having optical properties distinguishable as binary values). In some embodiments, the source unit 203 may be further configured to generate entangled photons. The optical structure, depending on the substrate material, is second-order (χ (2) ) or 3rd order (χ (3) It can operate using a spontaneous nonlinear parametric process resulting from the nonlinearity of ) and in this process, one (χ) from a powerful pump laser (2) (in the case of) or 2 (χ (3) In this case, one of the photons annihilates, resulting in two daughter photons. (2) The process is called spontaneous parametric down-conversion (SPDC), while χ (3) The process is called spontaneous four-wave mixing (SFWM). As a non-limiting example, source unit 203 may be implemented in accordance with U.S. Patent No. 10133147, U.S. Patent No. 9274274, U.S. Patent No. 9030731 or any other suitable technical teaching.

[0045] The linear coupling unit 201 is configured to receive multiple photons in a binary fundamental quantum state and to inject the received photons as inputs to different optically coupled cores of a multicore fiber. Each core is configured to correspond one-to-one with an input binary value specified by a unitary matrix, and each is dedicated to an input photon corresponding to a predefined binary input value. The number of cores is equal to the number of inputs (and outputs, respectively) in the corresponding OQLG, and the input and output binary values ​​are defined by their respective unitary matrices.

[0046] Figure 2 shows a non-restrictive example of the Pauli-X OQLG. The linear coupling unit 201 shown there comprises a core 211 dedicated to input photons with vertical polarization (corresponding to a value of 1) and a core 212 dedicated to input photons with horizontal polarization (corresponding to a value of 0).

[0047] As another (not shown) non-limiting example, a linear coupling unit of a CNOT OQLG or swap OQLG may be configured to have four optical cores dedicated to input photons corresponding to the values ​​{1,0,0,0}, respectively, and a linear coupling unit of a Toffoli OQLG may be configured to have eight optical cores dedicated to input photons corresponding to the values ​​{1,0,0,0,0,0,0,0}.

[0048] The input values ​​for some of the QLGs (e.g., Pauli Y QLG, Hadamard QLG) can take complex numbers and may correspond to the superposition of photons with vertical and horizontal polarization, respectively. The required superposition can be provided by the source unit 203 before the photons are injected into the core of the linear coupling unit 201, and each core may be dedicated to a complex binary input value. Alternatively, the linear coupling unit 201 may include a preprocessing unit (not shown) that provides the required superposition after the photons in their fundamental state have been injected into the core, before the superposition of photons is used as binary input to each dedicated core.

[0049] As further detailed with reference to Figures 3 and 4, the linear coupling unit 201 further mixes the binary inputs with a constant weight made possible by the prior design of the distance between the cores, their sizes, and the refractive indices of the various media of the fiber. The mixing is designed according to the unitary matrix representing each OQLG, and the fundamental quantum state of the photons output from the linear coupling unit 201 corresponds to the binary output value specified by that matrix.

[0050] Figures 3a and 3b show non-limiting examples of optical structures usable for OQLG, which are comprised of several embodiments of the subject matter disclosed herein.

[0051] Figure 3a shows in detail a two-core optical structure that can be used for a linear coupling unit in a one-qubit OQLG. Note that the teachings of the subject disclosed herein are similarly applicable to OQLGs operating with other qubit counts and the respective number of cores in multi-core optical structures.

[0052] For illustrative purposes only, the following description provides for a linear coupling unit 201 integrated with an amplification unit 202 mounted on a separate fiber within an all-optical structure. As will be readily apparent to those skilled in the art, the teachings of the subject disclosed herein are equally applicable to a linear coupling unit 201 and amplification unit 202 mounted on the same fiber and optionally on the same core.

[0053] An illustrated example of a two-core optical fiber 300 comprises a fiber body 301 extending between a first fiber end 302 and a second fiber end 303. The fiber body 301 houses a first cylindrical core 211 and a second cylindrical core 212, along with a fiber cladding 330 between them. In non-limiting examples, the cores 211 and 212 may consist of glass, silicon, silica, or other materials known in the art of optical fiber manufacturing. The material of the cladding 230 must have a refractive index lower than that of the cores 211 and 212. The cores are configured to allow directional light propagation along the multicore optical fiber.

[0054] The first fiber end 302 is configured to receive photons transmitted to it from the source unit 203 (through an input port, not shown) and the second fiber end 303 is configured to emit photons from there (through an output port, not shown) to the amplification unit 202. The input ports are configured to allow the transmission of photons to dedicated cores, and the output ports are configured to allow photons to be output from the cores. Optionally, each core may be organized to have separate input and / or output ports.

[0055] As is known, each core in a multicore optical fiber can be used as an independent channel for data transfer. Such transmission channels are configured to allow the propagation of light along the channel without substantially altering the light intensity.

[0056] According to some embodiments of the subject matter disclosed herein, the cores within the linear coupling unit 201 are designed in such a manner that they enable a desired degree of optical coupling between the cores (e.g., the distance between the cores, their sizes, refractive indices, etc.).

[0057] Optical coupling between cores in a multicore optical fiber is generally achieved through evanescent wave coupling. The term "evanescent wave coupling" refers to the phenomenon in which light propagates from a first medium to a second medium as a wave that separates the first medium from the second and passes through a third medium having a refractive index lower than that of the first and second media, attenuating exponentially. Evanescent wave leakage between two optical propagation media, such as the two cores in an optical fiber, refers to the transmission of light from one medium to the other via evanescent wave coupling.

[0058] Evanescent wave coupling between cores is highly dependent on the core diameter, the distance between cores, and the mode of optical propagation within the cores. Optical coupling is considered significant when the signal transmitted from the first core to the second core via optical coupling has an intensity significantly higher than the noise level within the second core. As a non-limiting example, in fibers manufactured from materials commonly used in the art, substantial evanescent wave coupling between cores having a diameter of, for example, about 8 μm can be achieved when the distance between the core centers is less than about 20 μm, preferably less than about 10 μm.

[0059] Figure 3b schematically shows a cross-sectional view of a two-core optical fiber 300. As a non-limiting example, cores 211 and 212 may be identical and have the same radius a and refractive index n1. The refractive index of the cladding is n0, and the size of the gap between the cores is d. g That is the case.

[0060] The coupling length L is defined as the shortest fiber length required for the incident optical power to be completely transferred from one core to another.

[0061] The coupling length can be calculated, for example, using the coupling mode or supermode theory disclosed in the paper (2021) "Calculation of the Coupling Coefficient of Twin-Core Fiber Based on the Supermode Theory with Finite Element Method" by Zhao, TH, Ren, WH, Yin, TY, and Wang, F., Optics and Photonics Journal, Vol. 11, pp. 402-411.

[0062] As disclosed in the paper, the bond length L can be calculated as L = π / k, where k is the bond coefficient.

[0063] Figures 4a to 4c show examples of the dependence of the coupling coefficient on gap size, core radius, and relative refractive index difference, as disclosed by Zhao et al. Figure 4a shows the coupling coefficient as a function of gap size for an operating wavelength of 1.55 μm, a core radius of 3.5 μm, a cladding refractive index of 1.444, and a relative refractive index difference of 0.25%. Figure 4b shows the coupling coefficient as a function of core radius for a gap size of 2 μm, an operating wavelength of 1.55 μm, a cladding refractive index of 1.444, and a relative refractive index difference of 0.25%. Figure 4c shows the coupling coefficient as a function of relative refractive index difference for an operating wavelength of 1.55 μm, a core radius of 3.5 μm, a cladding refractive index of 1.444, and a gap size of 2 μm.

[0064] Thus, the graphs in Figures 4a to 4c show that the coupling length L can be pre-designed with respect to a given working length by selecting the gap size, core radius, and relative difference of refractive index. The desired degree of optical coupling between cores can be defined as a function of the coupling length.

[0065] Returning to Figure 2, as mentioned earlier, selecting the geometric and optical parameters of each optical structure (e.g., core radius, gap size, core and cladding refractive index) allows for mixing the weights and binary inputs (photons) specified by the unitary matrix representing each OQLG.

[0066] In the Pauli-X OQLG, shown in Figure 2 as a non-restrictive example, the geometric and optical parameters must be selected such that the length of the linear mixing unit 201 corresponds to the coupling length L. In such a case, the optical coupling allows all photons input to core 211 to be output from core 212 (while each photon retains its fundamental quantum state), and vice versa. This allows the illustrated linear mixing unit 201 to flip the value of a single qubit from 0 to 1, or from 1 to 0, as required.

[0067] Similarly, in the case of the Hadamard OQLG, the geometric and optical parameters of the two-core linear mixing unit 201 must be selected such that the optical coupling gives the following equation:

[0068] TIFF0007832658000001.tif16170

[0069] As another example, in the case of swap OQLG, the geometric and optical parameters of the 4-core linear mixing unit 201 must be selected so that the optical coupling gives two swapped qubits of the following equation: SWAP|00〉=|00〉 SWAP|01〉=|10〉 SWAP|10〉=|01〉 SWAP|11〉=|11〉

[0070] After being output from the linear mixing unit 201, the photons are propagated to the amplification unit 202.

[0071] The amplification unit 202 is configured to enable controllable nonlinear operation, thereby controlling amplification of the intensity of the optical signal.

[0072] The amplification unit 202 may be configured as a separate amplification optical structure optically connected to the linear mixing unit 201. The separate amplification optical structure may be configured to have controllable amplification channels corresponding to channels (cores) in the linear mixing unit 201. The amplification channels in the separate amplification optical structure may operate in a manner similar to the amplification channels in the integrated amplification unit described below.

[0073] Alternatively, the amplification unit 202 may be integrated with the linear mixing unit 201 and configured on the same core. As shown in Figure 2, each core (211, 212) in the multicore optical fiber may be configured to include at least one mixing segment (represented by 213-1 and 213-2, respectively) which is part of the linear mixing unit 201, and at least one amplification segment (represented by 214-1 and 214-2, respectively) which is part of the amplification unit 202 following each mixing segment. The mixing segments 213-1 and 213-2 are optically coupled to enable weighted mixing of photons according to the unitary matrices representing their respective OQLGs. The amplification segments 214-1 and 214-2 constitute an amplification channel, and the optical coupling between the amplification segments is minimized to minimize crosstalk between cores.

[0074] Optionally, an OQLG having integrated amplification units can be implemented using a multicore fiber having a tapered configuration. Such a configuration allows for the implementation of a linear mixing unit 201 in the tapered region that enables optical coupling between each segment of the core, and provides sufficient distance to prevent optical interaction between the amplification segments of the core by implementing amplification units 202 in the wider portion.

[0075] The amplification segments 214-1 and 214-2 may be impregnated with a gain medium (e.g., doped with erbium ions) configured to provide gain in the wavelength range of photons received from and passing through the linear mixing unit (hereinafter also referred to as the "information wavelength" and "information photon," respectively). Gaining may be achieved in response to a pumping optical signal in a pumping wavelength range different from the information wavelength range.

[0076] Each amplification channel is associated with a control port (not shown) that controls the amplification in its respective channel. The control port is configured to enable the required amplification in the channel in response to a control signal specifying the desired amplification coefficient. Optionally, the control port may be located at the first fiber end 302. Optionally, the amplification channels of the amplification unit 202 may share a common control port configured to allow separate control of the amplification in each channel.

[0077] The control port allows a pumping optical signal to propagate through the amplification channel, propagating in parallel with the propagation of information photons. The pumping optical signal does not directly contribute to the output of the amplification unit (it can be filtered out, for example, before or during each measurement). The gain medium of the amplification channel (e.g., an erbium dopant ion) absorbs the pumping optical signal, generating excitation of each electron, while the information photons facilitate subsequent relaxation. During the relaxation process, the dopant ion emits additional photons whose wavelength and polarization are the same as those of the information photons used for relaxation. The amplification coefficient can be controlled by specifying at least the parameters of the pumping optical signal, the gain medium, and / or the effective length of the amplification channel.

[0078] Thus, the amplification process in the amplification unit 202 can be configured to controllly increase the number of information photons output from it, while preserving the polarization and relative quantity of the information photons, and therefore the binary value (real or complex) received from the linear mixing unit 201.

[0079] For example, in the Pauli-X OQLG shown in Figure 2 as a non-restrictive example, information photons (corresponding to the binary value "1") receive gain in the amplification channel based on segment 214-2, while amplification is not required in the amplification channel based on segment 214-1 (corresponding to the binary value "0").

[0080] The output of the amplification unit 202 can be read out by quantum readout, i.e., by any suitable interferometer capable of extracting the fundamental state of the output photons. The readout results are further decoded into their respective output binary values ​​(real and / or complex numbers defined by their respective unitary matrices).

[0081] It should be noted that the subject teachings disclosed herein are not limited to the optical systems described with reference to Figure 2. Equivalent and / or modified functions can be combined or separated in other ways and implemented using single-mode or multi-mode fibers, photonic crystal fibers, etc. Similarly, the disclosed optical systems can be implemented as 3D photonic devices (e.g., 3D photonic crystals, 3D patterned silica, or 3D printed transparent blocks of polymers) that implement the disclosed teachings.

[0082] It should be noted that OQLGs and their configurations can act on photons having substantially the same wavelength, or on photons having different but relatively close wavelengths. Figure 2b shows a generalized functional block diagram of an optical quantum logic gate (OQLG) combined with a wavelength multiplexer.

[0083] N source units (denoted as 203-1 to 203-n) each receive N input optical signals, each signal having its own unique wavelength. The wavelengths of the N input signals are relatively close enough to allow for substantially identical optical coupling behavior under common geometric and optical parameters of the linear coupling unit 201, while remaining distinguishable during multiplexing. As a non-limiting example, the relative difference between wavelengths may be 0.1% < (Δλ / λ) < 1%.

[0084] Each source unit is in a binary fundamental quantum state and generates multiple photons, each with its own wavelength. The generated photons are multiplexed by a WDM terminal 220-1, which is configured to allow the multiplexed photons to be injected into a designated optical coupling core that corresponds one-to-one with the input binary value, as detailed with reference to Figure 2a.

[0085] The OQLG200 processes the incident photons in the manner detailed with reference to Figure 2a. The output of the OQLG200 is further demultiplexed by the WDM terminal 220-2 and transferred to the respective optical / electrical transponders (represented as 221-1 to 221-N), each transponder converting the demultiplexed signal having a wavelength corresponding to the input signal.

[0086] Referring to Figure 5, a generalized flowchart is shown illustrating the operation of OQLG according to several embodiments of the subject matter disclosed herein.

[0087] n qubits act on 2 n ×2 n Before operating a given OQLG characterized by a unitary matrix, two geometric and optical parameters are predefined to correspond one-to-one with the input binary values ​​specified by the matrix and designed in relation to the matrix. n An optical structure is constructed with an optical coupling core (501).

[0088] During operation, multiple photons in the binary fundamental quantum state corresponding to the binary value are incident on a given OQLG (502), 2 n Each of the pre-designed optically coupled cores is predefined according to a matrix to receive photons representing a specific binary input value. The input photons are further mixed with a fixed weight by the pre-designed optical coupling (503), the weight being made possible by the core design.

[0089] The mixed photons are output to the amplification channel corresponding to the core (504), and the output mixed photons correspond to the binary output value specified by the matrix.

[0090] Further controlled amplification (505) of photons is performed in the amplification channel. The amplification is carried out in a manner that preserves the fundamental quantum state of photons propagating within the channel and the relative quantity of photons having different fundamental quantum states. After amplification, quantum readout (506) of photons output from the amplification channel is performed.

[0091] According to some embodiments of the subject matter disclosed herein, OQLG can be organized into composite all-optical configurations such as field-programmable gate arrays (FPGAs) and artificial neural networks (ANNs). As a non-limiting example, the principles for combining optical gates into all-optical configurations and training and operating each configuration are disclosed in international patent applications WO2017 / 033197, WO2019 / 186548, and WO2021 / 064727.

[0092] According to some embodiments of the subject matter disclosed herein, the use of the entanglement phenomenon can further improve the connectivity and / or cascading of OQLGs in an all-optical configuration. Referring to Figure 6, a generalized diagram of a fragment of an all-optical configuration is shown, comprising several OQLGs of the same or different types and configured to operate as detailed with reference to Figures 2-5. The illustrated fragment comprises an OQLG 601 having input 611 and output 612, and an OQLG 602 having input 621 and output 622, where output 612 is logically connected to input 621 (logical connections are shown by dotted lines). In some embodiments, the logical connection from output 612 to input 621 may be provided without requiring a physical connection between them.

[0093] OQLG601 and OQLG602 can be connected to a shared source unit 603, which is configured to generate a plurality of photons having entangled binary fundamental quantum states and to allow the generated entangled photons to be incident at a specific ratio on input 611 of OQLG601 and input 621 of OQLG602.

[0094] Photons incident on OQLG601 are further mixed and amplified as detailed with reference to Figures 2-5. Injecting photons, each having an entangled binary fundamental quantum state, into input 621 can be delayed compared to injecting photons into input 611. Optionally, the delay can be provided using an optical delay structure 604, placed between source unit 603 and input 621 and configured to enable the required delay (e.g., by selecting the length and optical properties of the internal optical fiber). Note that, optionally, the optical delay structure 604 can be integrated with OQLG602.

[0095] As a non-restrictive example, the delay may correspond to the duration T during which a photon propagates from input 611 to output 612 within OQLG601. The distribution of entangled photons between inputs 611 and 621 can be 1:G, where G is the respective amplification by OQLG601. Thus, source unit 603 may allow N photons 605 in a particular binary fundamental quantum state to be injected into OQLG601, and N×G photons 606 in an entangled binary fundamental quantum state to be injected into OQLG602. In this way, the number and fundamental quantum states of photons 606 are the same as the number and fundamental quantum states of photons 607 output from output 612, while photons 606 are injected into input 621 at the same time that photons 607 could be injected into input 621 assuming their respective physical connections exist.

[0096] This allows the incidence of entangled photons into the inputs of logically connected gates, as detailed above, to replace the respective physical connections. It should be noted that the teaching of the subject disclosed herein is not limited to the details described with reference to Figure 6. The ratio for distributing entangled photons between the inputs of different gates can be predetermined (e.g., in FPGA configurations) or trained to achieve the desired result (e.g., in ANN configurations).

[0097] It goes without saying that the present invention is not limited in its application to the details described herein or illustrated in the drawings. Other embodiments of the present invention are possible and can be carried out and implemented in various ways. It should therefore be understood that the words and terms used herein are for illustrative purposes only and should not be considered limiting. Accordingly, as will be understood by those skilled in the art, the concepts on which this disclosure is based can be readily used as a basis for designing other structures, methods, and systems to accomplish some of the purposes of the subject matter disclosed herein.

[0098] As will be readily apparent to those skilled in the art, various modifications and variations can be applied to the embodiments of the present invention without departing from the scope of protection of the present invention as defined in the appended claims.

Claims

1. Acts on n qubits and 2 ｎ x2 ｎ A quantum logic gate (OQLG) characterized by a unitary matrix, wherein the OQLG is Two input binary values ​​that correspond one-to-one with the unitary matrix specified above. ｎ A first optical structure having optically coupled cores, and the two optically connected to the first optical structure ｎ Two cores corresponding to each individual core ｎ A second optical structure having individual amplification channels and The first optical structure comprises, The system receives a photon in a binary fundamental quantum state that represents the input binary value specified by the unitary matrix, and according to the one-to-one correspondence of the core and the fundamental quantum state of the photon, the received photon is processed by the 2 ｎ The injection into individual cores, Mixing between the cores while propagating incident photons along the cores using significant evanescent optical coupling between the cores, wherein the photons are mixed with weights specified by the unitary matrix, which are made possible by prior design of the distance between the cores, the size of the cores, and the refractive index of the medium between the cores. Outputting photons to the second optical structure, wherein the output mixed photons correspond to the output binary values ​​specified by the matrix. It is configured to do the following: OQLG, wherein the second optical structure is configured to amplify mixed and output photons within the amplification channel, the amplification being controlled with respect to the mixed and output photons propagating within the amplification channel, while preserving the fundamental quantum state and the relative quantity of mixed and output photons having different fundamental quantum states, the amplification in each amplification channel being provided using a pumping optical signal propagating simultaneously with the propagation of mixed and output photons, and the amplification coefficient of each channel being controllable by defining at least the pumping optical signal, the gain medium, and / or the effective length of the amplification channel.

2. The OQLG according to claim 1, wherein the real input binary value specified by the unitary matrix is ​​represented by the fundamental quantum states of vertical and horizontal polarization.

3. The OQLG according to claim 1, wherein the complex binary value specified by the unitary matrix is ​​represented by the superposition of each photon in the fundamental quantum state.

4. The OQLG according to claim 3, wherein the first optical structure is configured to mix the received photons and perform the superposition before the superposition of the superpositioned photons is injected into the core corresponding to the complex binary value.

5. The OQLG according to claim 1, wherein the weight is predetermined as a function of the coupling length of the first optical structure, and the coupling length is predetermined by a selection of optical and geometric parameters of the core and the cladding therebetween.

6. The OQLG according to claim 1, wherein the first optical structure and the second optical structure are integrated and mounted on the same core of a multicore optical fiber.

7. Two within the multicore optical fiber ｎ The OQLG according to claim 6, wherein each core of the individual cores is configured to include a first segment which is part of the first optical structure and a second segment which is part of the second optical structure following the first segment.

8. The OQLG according to claim 7, wherein the multicore optical fiber is configured to have a tapered structure, the first segment of each core is arranged in the tapered portion to enable optical coupling between the first segments, and the second segment is arranged in the wide portion to allow a sufficient distance to prevent optical interaction between the second segments.

9. The OQLG according to claim 1, wherein each amplification channel is associated with a control port configured to enable the required amplification in the amplification channel in response to a control signal specifying a desired amplification coefficient.

10. The OQLG according to claim 9, wherein each amplification channel is impregnated with a gain medium configured to provide gain in a first wavelength range corresponding to the output mixed photons, and the gain is achievable in response to a pumping optical signal received via the control port and having a pumping wavelength range different from the first wavelength range.

11. The OQLG according to claim 10, wherein the amplification coefficient is controlled by defining at least the parameters of the pumping optical signal, the gain medium, and / or the effective length of the amplification channel.

12. The OQLG according to claim 1, configured to be able to be configured into a full optical configuration of multiple OQLGs.

13. The OQLG according to claim 1, wherein the output of the OQLG is configured to be operably connected to the input of at least one second OQLG using an optical structure, the optical structure being configured to generate a plurality of photons having entangled binary fundamental quantum states, and to allow the generated entangled photons to be incident on the input of the OQLG and the input of the at least one second OQLG in a specific ratio.

14. Acting on n qubits and 2 ｎ ×2 ｎ A method for operating an optical quantum logic gate (OQLG) characterized by a unitary matrix, the method comprising The OQLG receives a plurality of photons in a binary fundamental quantum state that represent an input binary value specified by the unitary matrix, wherein the OQLG has a one-to-one correspondence with the input binary value specified by the unitary matrix. ｎ The optical structure comprises an optical coupling core having a number of optical coupling cores, wherein the received photons are incident on the core according to the one-to-one correspondence, and the reception is performed. Mixing photons between the cores while propagating them along the cores using significant evanescent optical coupling between the cores, wherein the photons are mixed by predetermined weights made possible by prior design of the distance between the cores, the size of the cores, and the refractive index of the medium between the cores. The above 2 ｎ Two cores corresponding to each individual core ｎ Outputting photons to individual optical amplification channels, wherein the output mixed photons correspond to the output binary values ​​specified by the matrix, The amplification of mixed and output photons within the amplification channel is performed in a controllable manner while preserving the fundamental quantum state of the mixed and output photons propagating within the amplification channel and the relative quantity of photons having different fundamental quantum states, wherein the amplification in each amplification channel is provided using a pumping optical signal that propagates simultaneously with the propagation of the mixed and output photons, and the amplification coefficient of each channel is controllable by defining at least the parameters of the pumping optical signal, the gain medium, and / or the effective length of the amplification channel. The quantum readout of photons output from the aforementioned amplification channel is performed. Methods that include...

15. The method according to claim 14, wherein the weight is predetermined as a function of the coupling length of the optical structure, and the coupling length is predetermined by a selection of optical and geometric parameters of the core and the cladding therebetween.

16. The method according to claim 14, wherein the real input binary value specified by the unitary matrix is ​​represented by the fundamental quantum states of vertical and horizontal polarization.

17. The method according to claim 14, wherein the complex binary value specified by the unitary matrix is ​​represented by the superposition of each photon in the fundamental quantum state.

18. The method according to claim 17, further comprising mixing the received photons in order to perform the superposition before injecting the superposition photons into the core corresponding to the complex binary value.

19. The method according to claim 14, further comprising receiving a control signal specifying a desired amplification coefficient in the amplification channel via the control port of the OQLG and performing amplification in response thereto.

20. The method according to claim 19, wherein each amplification channel is impregnated with a gain medium configured to provide gain in a first wavelength range corresponding to the output mixed photons, and the control signal is a pumping optical signal received via the control port and having a pumping wavelength range different from the first wavelength range.

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