Optical communication system for quantum computer, quantum computer, and method for manufacturing quantum computer

Abstract

This optical communication system 6A comprises: a plurality of modulators 63 that generate a respective plurality of optical control signals on the basis of a plurality of first microwave control signals; a multicore optical fiber 65 that transmits the plurality of optical control signals individually; and a light receiving substrate 67 that receives each of the plurality of optical control signals transmitted by the multicore optical fiber 65, converts the plurality of optical control signals into a plurality of second microwave control signals, and transmits the plurality of second microwave control signals to a quantum circuit 2.

Description

Optical communication system for quantum computers, quantum computers, and methods for manufacturing quantum computers

[0001] The present invention relates to an optical communication system for a quantum computer, a quantum computer, and a method for manufacturing a quantum computer. For designated states where incorporation by reference of literature is permitted, the content of Japanese Patent Application No. 2024-099965, filed in Japan on June 20, 2024, is incorporated by reference into this specification and made a part of the description of this specification.

[0002] In quantum computing, a signal distribution system including a photonic link is known (see, for example, Patent Document 1 and Non-Patent Document 1). The operating environment of this signal distribution system includes a cryogenic environment, a continuous wave (CW) laser, a microwave generator, an electro-optic modulator, an optical fiber arranged in the cryogenic environment, and a photodetector (see, for example, Figure 5 of Patent Document 1 and Figure 1 of Non-Patent Document 1).

[0003] U.S. Pat. No. 1,1742,955

[0004] Lecocq et al. “Control and readout of a superconducting qubit using a photonic link”, 2021, Nature

[0005] In the above-mentioned Patent Document 1 and Non-Patent Document 1, light emitted from a plurality of CW laser light sources with different wavelengths is coupled to a single-core optical fiber for transmission. Therefore, it is necessary to use WDM (Wavelength Division Multiplexing) as the communication method for the optical signal input to the single-core optical fiber, and it is therefore necessary to place a wavelength multiplexer and a wavelength demultiplexer at the upstream and downstream stages of the single-core optical fiber, respectively. However, there is a problem in that the wavelength multiplexer and wavelength demultiplexer have large volumes, which results in an increase in the size of the signal distribution system.

[0006] The problem to be solved by the present invention is to provide an optical communication system for a quantum computer, a quantum computer, and a method for manufacturing the same that can reduce space.

[0007] [1] Aspect 1 of the present invention is an optical communication system for a quantum computer, comprising: an optical signal generator that generates a plurality of optical control signals based on a plurality of first microwave control signals; a multi-core optical fiber including a plurality of first cores that transmit the plurality of optical control signals, respectively, and a cladding that surrounds the plurality of first cores; and a plurality of photodetectors that receive the plurality of optical control signals from the plurality of first cores, convert the plurality of optical control signals into a plurality of second microwave control signals, respectively, and transmit the second microwave control signals to a quantum circuit.

[0008] [2] A second aspect of the present invention may be an optical communication system for a quantum computer according to the first aspect, wherein at least a part of the multi-core optical fiber is disposed inside a refrigerator of the quantum computer.

[0009] [3] Aspect 3 of the present invention may be an optical communication system for a quantum computer according to aspect 2, wherein the cladding is exposed over the entire or part of the area of ​​the multi-core optical fiber arranged within the refrigerator.

[0010] [4] A fourth aspect of the present invention may be an optical communication system for a quantum computer according to any one of the first to third aspects, wherein the multi-core optical fiber further includes a coating layer that coats the cladding, and the material constituting the coating layer is carbon or a metal.

[0011] [5] Aspect 5 of the present invention may be an optical communication system for a quantum computer according to any one of aspects 1 to 4, wherein the optical signal generator includes a carrier generator that generates a plurality of carrier waves, and a plurality of modulators that generate the plurality of optical control signals by superimposing the plurality of first microwave control signals on the plurality of carrier waves, respectively.

[0012] [6] A sixth aspect of the present invention may be an optical communication system for a quantum computer according to the fifth aspect, wherein the wavelengths of the plurality of carrier waves generated by the carrier wave generator are the same.

[0013] [7] A seventh aspect of the present invention may be an optical communication system for a quantum computer according to the fifth or sixth aspect, wherein the optical communication system for a quantum computer further includes a pair of connectors optically connected to the plurality of first cores of the multi-core optical fiber and capable of transmitting the plurality of optical control signals, the connectors including a plurality of transmission lines for transmitting the plurality of optical control signals, the connectors including expanding portions where the distance between the plurality of transmission lines increases with increasing distance from an end face of the multi-core optical fiber, one of the connectors being disposed between one end of the multi-core optical fiber and the modulator, and the other of the connectors being disposed between the other end of the multi-core optical fiber and the photodetector.

[0014] [8] Aspect 8 of the present invention may be an optical communication system for a quantum computer according to Aspect 7, wherein the connector comprises a plurality of single-core optical fibers provided at positions corresponding to the first cores of the multi-core optical fibers and having second cores optically connected to the first cores, and a capillary into which one ends of the plurality of single-core optical fibers are inserted and integrated, wherein the single-core optical fibers include a small diameter portion abutting against the first cores of the multi-core optical fibers, a large diameter portion having a diameter larger than a diameter of the small diameter portion, and an intervening portion interposed between the small diameter portion and the large diameter portion and expanding in diameter from the small diameter portion toward the large diameter portion, the intervening portion includes the expanding portion, and a spacing between the second cores in the small diameter portion is smaller than a spacing between the second cores in the large diameter portion.

[0015] [9] Aspect 9 of the present invention may be an optical communication system for a quantum computer in any one of aspects 5 to 8, wherein the carrier wave generator is provided with a plurality of light-emitting elements that respectively generate the plurality of carrier waves.

[0016]

[10] Aspect 10 of the present invention may be an optical communication system for a quantum computer according to any one of aspects 1 to 4, wherein the optical signal generator comprises a laser driver and a plurality of light-emitting elements, the laser driver generates and transmits a plurality of modulated signals suitable for each of the plurality of light-emitting elements based on the plurality of first microwave control signals, and the plurality of light-emitting elements generate the plurality of optical control signals based on the plurality of modulated signals transmitted from the laser driver.

[0017]

[11] Aspect 11 of the present invention may be an optical communication system for a quantum computer according to Aspect 10, wherein the plurality of light-emitting elements are two-dimensionally arranged, the plurality of light-receiving elements are two-dimensionally arranged corresponding to the arrangement of the plurality of light-emitting elements, and the plurality of first cores of the multi-core optical fiber are two-dimensionally arranged corresponding to the arrangement of the plurality of light-emitting elements, and the system may include a plurality of incident ends into which the plurality of optical control signals are respectively incident, and a plurality of exit ends which are two-dimensionally arranged corresponding to the arrangement of the plurality of light-receiving elements and from which the plurality of optical control signals are respectively exited.

[0018]

[12] Aspect 12 of the present invention is a quantum computer comprising the quantum computer optical communication system of any one of aspects 1 to 11, a quantum circuit, and a refrigerator that houses the quantum circuit and cools the quantum circuit.

[0019]

[13] A thirteenth aspect of the present invention may be the quantum computer of the twelfth aspect, further comprising a plurality of microwave generators that generate the plurality of first microwave control signals and transmit the plurality of first microwave control signals to the optical signal generator, respectively.

[0020]

[14] A fourteenth aspect of the present invention may be the quantum computer of Aspect 12 or 13, wherein the refrigerator includes a plurality of freezing chambers and a plurality of metal plates arranged so as to separate the plurality of freezing chambers, the metal plates include through holes through which the multi-core optical fiber is inserted, the multi-core optical fiber further includes a coating layer that coats the cladding, and the coating layer is joined to the metal plates at the through holes.

[0021]

[15] A fifteenth aspect of the present invention is a method for manufacturing a quantum computer, comprising a first step of incorporating the quantum computer optical communication system according to any one of aspects 1 to 11 into a refrigerator.

[0022]

[16] A sixteenth aspect of the present invention may be the quantum computer manufacturing method of Aspect 15, wherein the refrigerator includes a plurality of freezing chambers and a plurality of metal plates arranged so as to separate the plurality of freezing chambers, the metal plates include through holes for inserting the multi-core optical fibers, and the multi-core optical fibers further include a coating layer for coating the cladding, and the first step includes inserting the multi-core optical fibers into the through holes and joining the metal plates and the coating layer at the through holes.

[0023]

[17] A seventeenth aspect of the present invention may be a method for manufacturing a quantum computer according to the fifteenth aspect, wherein the multi-core optical fiber further includes a coating layer that coats the cladding, and the method for manufacturing a quantum computer further includes a second step of removing the coating layer.

[0024] In the present invention, a plurality of optical control signals are transmitted by a multicore fiber having a plurality of first cores, and therefore, the present invention does not require a multiplexer or demultiplexer, thereby enabling space saving.

[0025] FIG. 1 is a schematic diagram showing an example of a quantum computer according to a first embodiment of the present invention. FIG. 2(a) is a cross-sectional view taken along line II-II in FIG. 1, and FIG. 2(b) is a cross-sectional view showing a first modified example of the multi-core optical fiber according to the first embodiment of the present invention. FIG. 3(a) is a perspective view showing a light-emitting substrate and a first single-core optical fiber according to the first embodiment of the present invention. FIG. 3(b) is a side view showing the light-emitting substrate and the first single-core optical fiber according to the first embodiment of the present invention. FIG. 3(c) is a perspective view showing a third single-core optical fiber and a light-receiving substrate according to the first embodiment of the present invention. FIG. 3(d) is a side view showing the third single-core optical fiber and a light-receiving substrate according to the first embodiment of the present invention. FIG. 4(a) is a cross-sectional view taken along line IVa-IVa in FIG. 1, and FIG. 4(b) is a cross-sectional view taken along line IVb-IVb in FIG. 1. FIG. 5(a) is a cross-sectional view showing a second modified example of the multi-core optical fiber according to the first embodiment of the present invention. FIG. 5(b) is a cross-sectional view taken along line Vb-Vb in FIG. 5(a). FIG. 6 is a schematic diagram showing an example of a quantum computer according to the second embodiment of the present invention.

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0027] First Embodiment

[0028] Fig. 1 is a schematic diagram showing an example of a quantum computer 1A according to this embodiment. Fig. 2(a) is a cross-sectional view taken along line II-II in Fig. 1.

[0029] As shown in Fig. 1, the quantum computer 1A in this embodiment includes a quantum circuit 2, a dilution refrigerator 3, and a control system 4. The quantum circuit 2 has a plurality of integrated quantum bits and input / output terminals for controlling and reading out the quantum bits. The quantum bits are, for example, superconducting, semiconductor spin, or annealing quantum bits, and operate in an extremely low temperature environment. The quantum circuit 2 in this embodiment performs calculations, initialization, etc. under the control of the control system 4.

[0030] The quantum circuit 2 is housed in a dilution refrigerator 3. The dilution refrigerator 3 is a refrigerator capable of cooling the interior to extremely low temperatures, and cools the quantum circuit 2. The dilution refrigerator 3 in this embodiment is, but is not limited to, a refrigerator that uses a mixed solution of helium-3 and helium-4. The dilution refrigerator 3 corresponds to an example of a "refrigerator" in an aspect of the present invention.

[0031] This dilution refrigerator 3 includes a plurality of freezing chambers 31 to 33 and a plurality of metal plates 34. Note that, although the number of freezing chambers in this embodiment is three, the number is not limited to this.

[0032] Freezing chambers 31 to 33 are closed spaces partitioned by a metal plate 34 and a cylindrical radiation plate (not shown), and the interiors can be cooled to several mK to several K. Although not particularly shown, freezing chambers 31 to 33 have a nested structure, with freezing chamber 31 being located on the outermost side, freezing chamber 32 being located between freezing chambers 31 and 33, and freezing chamber 33 being located on the innermost side. The diameters of freezing chambers 31 to 33 become smaller as they are positioned on the -Z direction side, with freezing chamber 31 having the largest diameter and freezing chamber 33 having the smallest diameter. Freezing chamber 33 is located inside freezing chamber 32, and freezing chamber 31 is located inside freezing chamber 32.

[0033] The internal temperatures of freezer compartments 31 to 33 decrease stepwise toward the center. That is, the internal temperature of freezer compartment 33 is the lowest among freezer compartments 31 to 33, the internal temperature of freezer compartment 32 is higher than the internal temperature of freezer compartment 33 but lower than the internal temperature of freezer compartment 31, and the internal temperature of freezer compartment 33 is the highest. The quantum circuit 2 is placed inside freezer compartment 33, which has the lowest temperature.

[0034] The plurality of metal plates 34 are arranged so as to separate the plurality of freezing chambers 31 to 33. As shown in Fig. 2, the metal plates 34 include through holes 341 for inserting the multi-core optical fibers 65 described below.

[0035] 1, the control system 4 is a system for controlling the quantum bits included in the quantum circuit 2. In this embodiment, the control system 4 controls the quantum bits using a control signal (a second microwave control signal, which will be described later) generated based on microwaves. Although not specifically shown, the quantum computer 1A also includes an output system that outputs an output signal from the quantum circuit 2 in response to the second microwave control signal.

[0036] The control system 4 in this embodiment includes a microwave generating unit 5 and an optical communication system 6A. The microwave generating unit 5 generates a first microwave control signal and transmits the first microwave control signal to the optical communication system 6A. The microwave generating unit 5 in this embodiment includes a plurality of microwave generators 51. Each microwave generator 51 is electrically connected to a modulator 63, which will be described later, and outputs a first microwave control signal to the modulator 63.

[0037] The optical communication system 6A is a system for outputting a second microwave control signal to the quantum circuit 2 by means of a carrier wave. This optical communication system 6A is provided from the outside to the inside of the dilution refrigerator 3. The optical communication system 6A corresponds to an example of an "optical communication system for a quantum computer" in an aspect of the present invention.

[0038] The optical communication system 6A in this embodiment includes a light-emitting substrate 61, a plurality of first single-core optical fibers 62, a plurality of modulators 63, a first connector 64, a multi-core optical fiber 65, a second connector 66, and a light-receiving substrate 67. The light-emitting substrate 61, the plurality of first single-core optical fibers 62, and the plurality of modulators 63 correspond to an example of an "optical signal generator" in an aspect of the present invention.

[0039] Figure 3(a) is an oblique view showing the light emitting substrate 61 and the first single-core optical fiber 62 in this embodiment, and Figure 3(b) is a side view showing the light emitting substrate 61 and the first single-core optical fiber 62 in an embodiment of the present invention.

[0040] As shown in Figures 1, 3(a), and 3(b), the light-emitting substrate 61 is disposed outside the dilution refrigerator 3. This light-emitting substrate 61 includes a first substrate 611 and a plurality of light-emitting elements 612. The first substrate 611 is a circuit board. In this embodiment, four light-emitting elements 612 are mounted on a main surface of the first substrate 611. Such a light-emitting substrate 61 corresponds to an example of a "carrier wave generator" in accordance with an aspect of the present invention.

[0041] The plurality of light-emitting elements 612 are two-dimensionally arranged on the main surface of the first substrate 611. Specifically, the plurality of light-emitting elements 612 in this embodiment are arranged in a lattice pattern of two rows and two columns. The number of light-emitting elements 612 is not particularly limited as long as it is two or more. Furthermore, the arrangement of the plurality of light-emitting elements 612 is not limited to a lattice pattern as long as it is a two-dimensional arrangement. For example, the plurality of light-emitting elements 612 may be arranged irregularly.

[0042] The light-emitting elements 612 in this embodiment generate light of a single wavelength. By using light-emitting elements 612 that generate light of a single wavelength in this manner, costs can be reduced compared to using a light source that generates light of multiple wavelengths. Furthermore, in this embodiment, the wavelengths of light generated by the light-emitting elements 612 are the same. However, the wavelengths of light generated by the light-emitting elements 612 may be different from each other. Examples of such light-emitting elements 612 include light-emitting diodes (LEDs) and laser diodes (LDs) such as vertical cavity surface-emitting lasers (VCSELs).

[0043] The light-emitting elements 612 in this embodiment are elements capable of surface emission, and can emit light in a direction perpendicular to the main surface of the first substrate 611 in this embodiment. Light generated by each light-emitting element 612 is used as a carrier wave that carries a signal. Note that the light-emitting elements 612 may also be elements capable of edge emission. In this case, the light-emitting elements 612 emit light in a direction perpendicular to the edge surface (side surface) of the first substrate 611.

[0044] 1 , the plurality of first single-core optical fibers 62 are respectively arranged between the light-emitting element 612 and the modulator 63 outside the dilution refrigerator 3. The first single-core optical fibers 62 transmit the light emitted from the light-emitting substrate 61 to the modulator 63.

[0045] 3( a) and 3(b), the number of the plurality of first single-core optical fibers 62 is the same as the number of the light-emitting elements 612, and the first single-core optical fibers 62 are arranged such that the incident ends 621 of the first single-core optical fibers 62 face the light-emitting elements 612. As a result, the light emitted from the light-emitting elements 612 enters the inside of the first single-core optical fiber 62 from the incident ends 621.

[0046] The incident end 621 of the first single-core optical fiber 62 does not have to face the light-emitting element 612. When the incident end 621 does not face the light-emitting element 612, light emitted from the light-emitting element 612 may be guided to the incident end 621 by an optical element such as a mirror. Also, the light-emitting substrate 61 may be provided with a single light-emitting element, and multiple first single-core optical fibers 62 may be arranged to face this single light-emitting element. In other words, since the light generated by the light-emitting element has a single wavelength, multiple first single-core optical fibers 62 may share one light source.

[0047] 1, the multiple modulators 63 are arranged outside the dilution refrigerator 3. The number of the modulators 63 is the same as the number of the first single-core optical fibers 62. To each of the modulators 63, an exit end 622 of the first single-core optical fiber 62 is connected.

[0048] The modulator 63 modulates the carrier wave input from the exit end 622 of the first single-core optical fiber 62 to generate an optical control signal. The modulator 63 in this embodiment is an electro-optic modulator (EOM). The modulator 63 generates an optical control signal by superimposing the first microwave control signal input from the microwave generator 51 on the light (carrier wave) input from the first single-core optical fiber 62. That is, the modulation method in this embodiment is an external modulation method. The modulator 63 then outputs the generated optical control signal to the second single-core optical fiber 643 of the first connecting body 64.

[0049] The first connector 64 in this embodiment is disposed outside the dilution refrigerator 3. The first connector 64 is disposed between the multiple modulators 63 and the first end 655 of the multi-core optical fiber 65, and optically connects the multiple modulators 63 and the multi-core optical fiber 65.

[0050] 2A, the multi-core optical fiber 65 has a plurality of first cores 652 provided in one cladding 653, and the distance between the first cores 652 is shorter than the distance between the modulators 63. The first connector 64 is an Fi / Fo (Fan-in / Fan-out) device that adjusts the distance between the transmission paths of the optical signals output from the plurality of modulators 63 to be approximately the same as the distance between the first cores 652.

[0051] Fig. 4(a) is a cross-sectional view taken along line IVa-IVa in Fig. 1. As shown in Fig. 4(a), the first connector 64 in this embodiment is, but is not limited to, a Fi / Fo device. The first connector 64 is fused to a first end 655 of a multi-core optical fiber 65. The first connector 64 includes a first capillary 641 and a plurality of second single-core optical fibers 643.

[0052] Glass can be exemplified as a material for forming the first capillary 641. The first capillary 641 holds a plurality of second single-core optical fibers 643.

[0053] The second single-core optical fiber 643 is a single-core optical fiber. The plurality of second single-core optical fibers 643 have interposed portions 646 that are etched to narrow their diameters toward their tips, and the tips are fixed in the first capillary 641 with an adhesive. The number of second single-core optical fibers 643 is the same as the number of modulators 63. One end of the second single-core optical fiber 643 is optically connected to the modulator 63, and the other end of the second single-core optical fiber 643 is optically connected to a first core 652 of the multi-core optical fiber 65.

[0054] The second single-core optical fiber 643 includes a large-diameter portion 644, an interposed portion 646, and a small-diameter portion 647. The large-diameter portion 644 is the portion having the largest diameter in the second single-core optical fiber 643, and the diameter of the large-diameter portion 644 is larger than the diameters of the interposed portion 646 and the small-diameter portion 647. The large-diameter portion 644 is the portion located on the modulator 63 side, and is optically connected to the modulator 63 at an incident end 645, as shown in FIG.

[0055] 4A, an interposed portion 646 is connected to the large diameter portion 644. The interposed portion 646 is interposed between the large diameter portion 644 and the small diameter portion 647, and the diameter of the interposed portion 646 increases as it approaches the large diameter portion 644 from the small diameter portion 647.

[0056] A small diameter portion 647 is connected to this interposed portion 646. The small diameter portion 647 is provided at a position corresponding to the first core 652. The small diameter portion 647 in this embodiment abuts against the first core 652 of the multi-core optical fiber 65 at an exit end 648, and the second core 649 of the second single-core optical fiber 643 abuts against the first core 652 of the multi-core optical fiber 65 at this small diameter portion 647. This optical control signal generated by the modulator 63 is incident on the second single-core optical fiber 643 from the entrance end 645, and is emitted from the first core 652 to the second core 649 at the exit end 648.

[0057] In such a first connector 64, the distance L between the second cores 649 in the small diameter portion 647 is ２ is the distance L between the second cores 649 in the large diameter portion 644 １ is smaller than (L ２ <L １ ). Therefore, the first connector 64 in this embodiment can narrow the distance between the transmission paths of the optical control signal (the distance between the first cores 652 of the second single-core optical fibers 643 that are the transmission paths) as it approaches the second core 652. This intervening portion 646 corresponds to an example of the "expanding portion" in the aspects of the present invention.

[0058] 1 , the multi-core optical fiber 65 is arranged from the outside to the inside of the dilution refrigerator 3. That is, in this embodiment, the multi-core optical fiber 65 is used as a means for transmitting an optical control signal from the outside to the inside of the dilution refrigerator 3.

[0059] The above-mentioned Patent Document 1 and Non-Patent Document 1 also describe the use of coaxial cables as a means for transmitting electrical control signals inside the dilution refrigerator, but for integration of 1000 quantum bits or more, the wiring volume and heat inflow of the coaxial cables are too large. Note that heat inflow refers to the inflow of heat between adjacent freezing chambers of a multi-stage dilution refrigerator.

[0060] On the other hand, the multi-core optical fiber 65 can reduce the wiring volume compared to a coaxial cable. Furthermore, since the heat inflow into the dilution refrigerator 3 through the multi-core optical fiber 65 is much smaller than that through a coaxial cable, this embodiment can significantly reduce the heat inflow into the dilution refrigerator 3 and ensure stable operation of the quantum circuit 2. For example, the thermal conductivity of the glass that makes up the optical fiber is about 1 / 400 of that of the copper that makes up the coaxial cable, so the heat inflow can be significantly reduced. Furthermore, by significantly reducing the heat inflow, the load on the dilution refrigerator 3 can also be reduced.

[0061] 2( a), the multi-core optical fiber 65 includes a bare fiber 651 and a coating layer 654. The bare fiber 651 includes four first cores 652 and a cladding 653. The bare fiber 651 has a circular cross-sectional shape as a whole. Although not particularly limited, the number of first cores 652 included in the multi-core optical fiber 65 is preferably 4 or 7. With a multi-core optical fiber 65 having such a number of cores, it is structurally easy to manufacture a Fi / Fo device corresponding to the number of cores, thereby enabling the cost of the optical communication system 6A to be reduced.

[0062] Each of the first cores 652 has a circular cross-sectional shape and extends along the axial direction of the multi-core optical fiber 65. In this embodiment, the plurality of first cores 652 have the same diameter, but this is not particularly limited, and the plurality of first cores 652 may have different diameters. The cladding 653 is a common cladding that contains all of the first cores 652 and surrounds and covers all of the first cores 652.

[0063] The first core 652 and the cladding 653 are made of a material whose main component is silica glass, and their refractive indices are adjusted by adding impurities as necessary. The refractive index of the first core 652 is higher than the refractive index of the cladding 653. In this embodiment, the refractive indexes of the multiple first cores 652 are the same, but this is not particularly limited, and the refractive indexes of the multiple first cores 652 may be different from each other.

[0064] The coating layer 654 covers the entire outer periphery of the bare fiber 651. The material constituting the coating layer 654 in this embodiment is not particularly limited, but examples include carbon and metal. These materials shrink less in low-temperature environments than resin materials, and therefore can reduce the lateral pressure applied to the bare fiber 651. This can suppress an increase in transmission loss in the bare fiber 651. While the coating layer 654 in this embodiment has a single-layer structure, the present invention is not limited thereto, and the coating layer 654 may have a multi-layer structure.

[0065] Alternatively, the coating layer 654 may be omitted as in a first modified example described below. Fig. 2(b) is a cross-sectional view showing a first modified example of the multi-core optical fiber 65 in this embodiment. In this first modified example, the multi-core optical fiber 65 does not have the coating layer 654. Therefore, the bare fibers 651 are exposed to the outside.

[0066] In this way, since the multi-core optical fiber 65 does not have the coating layer 654, lateral pressure due to contraction of the coating layer 654 in a low-temperature environment is not generated, and therefore an increase in transmission loss in the bare fiber 651 can be further suppressed.

[0067] As in a second modified example described below, the coating layer 654 and the metal plate 34 may be joined together. Fig. 5(a) is a cross-sectional view showing a second modified example of the multi-core optical fiber 65 according to the embodiment of the present invention, and Fig. 5(b) is a cross-sectional view taken along the line Vb-Vb in Fig. 5(a).

[0068] The coating layer 654 in this embodiment is bonded and fixed to the metal plate 34. For example, the coating layer 654 may be directly bonded to the metal plate 34 by welding, indirectly bonded to the metal plate 34 via brazing, or indirectly bonded to the metal plate 34 via a resin adhesive or the like.

[0069] In this way, since the coating layer 654 is bonded to the metal plate 34, no gap is formed between the multi-core optical fiber 65 and the metal plate 34, and therefore, heat flow between the freezing chambers 31 to 33 through the through hole 341 can be reduced.

[0070] Moreover, the multi-core optical fiber 65 in the second modification includes a plurality of coating layers 654. The coating layers 654 are formed only in the vicinity of the through-hole 341 of the metal plate 34. Therefore, the plurality of coating layers 654 are arranged intermittently along the extending direction of the multi-core optical fiber 65. As a result, the outer circumferential surface of the bare fiber 651 is exposed between the plurality of coating layers 654. With such a multi-core optical fiber 65, the formation area of ​​the coating layers 654 can be reduced, and therefore the lateral pressure applied to the bare fiber 651 can be reduced, and an increase in transmission loss in the bare fiber 651 can be suppressed.

[0071] 1 and 4(b), a second connector 66 is connected to a second end 656 of the multi-core optical fiber 65. The second connector 66 is disposed inside the freezing chamber 33 of the dilution refrigerator 3. The second connector 66 is disposed between the second end 656 of the multi-core optical fiber 65 and the light-receiving substrate 67, and optically connects the second end 656 of the multi-core optical fiber 65 and the light-receiving substrate 67.

[0072] The second connector 66 is a Fi / Fo device that adjusts the distance between the transmission paths of the optical control signals output from the plurality of first cores 652 to be approximately the same as the distance between the plurality of light-receiving elements 672 of the light-receiving substrate 67, which will be described later. Therefore, the second connector 66 can increase the distance between the optical signals as they move away from the first core 652.

[0073] Fig. 4(b) is a cross-sectional view taken along line IVb-IVb in Fig. 1. As shown in Fig. 4(b), the second connector 66 is, although not limited to, a Fi / Fo device, similar to the first connector 64. This second connector 66 is fused to the second end 656 of the multi-core optical fiber 65.

[0074] The second connector 66 has the same structure as the first connector 64, and is disposed in the opposite direction to the first connector 64. The second connector 66 includes a second capillary 661 and a plurality of third single-core optical fibers 663.

[0075] Glass can be exemplified as a material for forming the second capillary 661. The second capillary 661 holds a plurality of third single-core optical fibers 663.

[0076] The third single-core optical fiber 663 is a single-core optical fiber, similar to the second single-core optical fiber 643. The number of the third single-core optical fibers 663 is the same as the number of the first cores 652.

[0077] Figure 3(c) is an oblique view showing the third single-core optical fiber 663 and the light-receiving substrate 67 in this embodiment, and Figure 3(d) is a side view showing the third single-core optical fiber 663 and the light-receiving substrate 67 in this embodiment.

[0078] As shown in Figure 4(b), one end of the third single-core optical fiber 663 is optically connected to the first core 652, and as shown in Figures 3(c) and 3(d), the other end of the third single-core optical fiber 663 is optically connected to the light-receiving substrate 67.

[0079] As shown in FIG. 4( b), the third single-core optical fiber 663 includes a large-diameter portion 664, an interposed portion 666, and a small-diameter portion 667. The large-diameter portion 664 is the portion having the largest diameter in the third single-core optical fiber 663. As shown in FIG. 1, the large-diameter portion 664 includes an exit end 665, whereas the large-diameter portion 644 of the second single-core optical fiber 643 includes an entrance end 645. As shown in FIGS. 1 and 4( b), the large-diameter portion 664 is a portion located on the light-receiving substrate 67 side. As shown in FIGS. 3( c) and 3( d), the large-diameter portion 664 is arranged so that the exit end 665 faces the light-receiving substrate 67.

[0080] 4B, an interposed portion 666 is connected to the large diameter portion 664. The interposed portion 666 is interposed between the large diameter portion 664 and the small diameter portion 667, and the diameter of the interposed portion 666 increases as it approaches the large diameter portion 664 from the small diameter portion 667.

[0081] A small diameter portion 667 is connected to the interposed portion 666. The small diameter portion 667 is provided at a position corresponding to the first core 652. The small diameter portion 667 in this embodiment abuts against the first core 652 of the multi-core optical fiber 65 at an incident end 668, and a third core 669 of the third single-core optical fiber 663 abuts against the first core 652 of the multi-core optical fiber 65 at this small diameter portion 667. As a result, the first and third cores 652, 669 are optically connected. Therefore, the optical control signal transmitted by the multi-core optical fiber 65 is incident on the third single-core optical fiber 663 from the incident end 668 and is emitted from the emission end 665 to the light-receiving substrate 67.

[0082] In the second connector 66, the distance L between the third cores 669 in the small diameter portion 667 is ３ is the distance L between the third cores 669 in the large diameter portion 664 ４ is smaller than (L ３ <L ４ Therefore, in the second connector 66 of this embodiment, the distance between the transmission paths of the optical control signal can be increased as the distance from the first core 652 increases.

[0083] 1, 3(c), and 3(d), the light-receiving substrate 67 is disposed inside the freezing chamber 33 so as to face the exit end 665 of the third single-core optical fiber 663. As shown in FIGS. 3(c) and 3(d), the light-receiving substrate 67 includes a second substrate 671 and a plurality of light-receiving elements 672.

[0084] The second substrate 671 is a circuit board. In this embodiment, four light receiving elements 672, the same number as the light emitting elements 612, are mounted on the main surface of the second substrate 671. The multiple light receiving elements 672 are two-dimensionally arranged on the main surface of the second substrate 671. Specifically, in this embodiment, the multiple light receiving elements 672 are arranged in a lattice pattern of two rows and two columns. The number of light receiving elements 672 is not particularly limited as long as it is two or more. The multiple light receiving elements 672 may also be arranged irregularly.

[0085] The light receiving element 672 converts an optical signal into an electrical signal and outputs the electrical signal to the quantum circuit 2. Such a light receiving element 672 is not particularly limited, but examples thereof include a PIN photodiode and an avalanche photodiode.

[0086] This light-receiving element 672 is electrically connected to the quantum bit of the quantum circuit 2 via an electric circuit or the like. The light-receiving element 672 converts the control signal made up of light into a control signal made up of electricity (a second microwave control signal) and outputs it to the quantum circuit 2. In this way, the quantum bit of the quantum circuit 2 is controlled.

[0087] In the present embodiment as described above, multiple optical control signals are individually transmitted through the multiple first cores 652 of the multi-core optical fiber 65, eliminating the need to convert the optical control signals into a WDM system. This eliminates the need for a demultiplexer and a multiplexer, reducing the volume occupied by the optical communication system 6A and enabling space saving. Eliminating the need for a demultiplexer and a multiplexer also reduces costs, and eliminates insertion loss in the demultiplexer and the multiplexer.

[0088] Furthermore, in this embodiment, the plurality of light-emitting elements 612 and the plurality of light-receiving elements 672 are all integrated, which allows further space-saving of the optical communication system 6A.

[0089] Next, a manufacturing method of the quantum computer 1A in this embodiment will be described. The manufacturing method of the quantum computer 1A in this embodiment includes a first step of incorporating an optical communication system 6A as shown in Fig. 1 into a dilution refrigerator 3. Specifically, this first step includes at least inserting a multi-core optical fiber 65 into the through-hole 341 of the metal plate 34 of the dilution refrigerator 3.

[0090] 2(b), when manufacturing a quantum computer 1A using a multi-core optical fiber 65 without a coating layer 654, the manufacturing method of the quantum computer 1A further includes a second step of removing the coating layer 654. In this case, for example, a water-soluble material can be used as the material constituting the coating layer 654, and after completing the first step of incorporating the optical communication system 6A into the dilution refrigerator 3, the coating layer 654 may be dissolved and wiped off with a solvent containing water in the second step. Note that the wiping may also be performed before (immediately before) the incorporation.

[0091] With this manufacturing method, in the first step, the bare fibers 651 can be assembled while being protected by the coating layer 654, and it is possible to prevent scratches and the like from occurring on the bare fibers 651. Therefore, it is possible to prevent an increase in transmission loss in the multi-core optical fiber 65.

[0092] 5(a) and 5(b), in the case of manufacturing a quantum computer 1A having a structure in which the coating layer 654 of the multi-core optical fiber 65 is bonded to the metal plate 34, the first step further includes bonding the metal plate 34 and the coating layer 654 in the through hole 341. Note that examples of a method for bonding the metal plate 34 and the coating layer 654 include the above-mentioned method of directly bonding them by welding, the indirect brazing method, or the indirect bonding method using an adhesive.

[0093] Second Embodiment

[0094] 6 is a schematic diagram showing an example of a quantum computer 1B according to the second embodiment. The quantum computer 1B according to the second embodiment differs from the first embodiment in that it includes a direct modulation optical communication system 6B. Only the differences between the quantum computer 1B according to the second embodiment and the first embodiment will be described below, and parts having the same configuration as the first embodiment will be assigned the same reference numerals and their description will be omitted.

[0095] The optical communication system 6B in the second embodiment includes, instead of the external modulation type modulator 63, a laser driver 68 electrically connected to the microwave generating unit 5, and a light emitting substrate 61 electrically connected to the laser driver 68. The laser driver 68 and the light emitting substrate 61 correspond to an example of the "optical signal generator" in the aspects of the present invention.

[0096] The laser driver 68 receives a plurality of first microwave control signals from the plurality of microwave generators 51 of the microwave generating unit 5. The laser driver 68 generates and transmits modulation signals suitable for the plurality of light-emitting elements 612 of the light-emitting substrate 61 based on the plurality of first microwave control signals received.

[0097] The light emitting substrate 61 in the second embodiment is electrically connected to a laser driver 68. Each light emitting element 612 of the light emitting substrate 61 generates an optical control signal based on each modulation signal transmitted from the laser driver 68.

[0098] The light emitting element 612 in the second embodiment faces the first core 652 of the multi-core optical fiber 65. Therefore, the optical control signal emitted from the light emitting substrate 61 directly enters the first core 652. Note that the light emitting element 612 does not have to face the first core 652. In that case, the optical control signal emitted from the light emitting element 612 may be guided to the first core 652 by an optical element such as a mirror.

[0099] In the second embodiment, similarly to the first embodiment, multiple optical control signals are individually transmitted through the multiple first cores 652 of the multi-core optical fiber 65, and therefore conversion of the optical control signals into a WDM system is not required. Therefore, a demultiplexer and a multiplexer are not required, and the volume occupied by the optical communication system 6B can be reduced, thereby achieving space saving. Furthermore, since a demultiplexer and a multiplexer are not required, costs can be reduced and insertion loss in the demultiplexer and the multiplexer does not occur.

[0100] Furthermore, in the second embodiment, the structure of the optical communication system 6B inside the dilution refrigerator 3 is the same as that in the first embodiment. Therefore, the quantum computer 1B in the second embodiment can be manufactured by the same manufacturing method as the quantum computer 1A in the first embodiment.

[0101] It should be noted that the above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, the elements disclosed in the above embodiments are intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0102] For example, in the first and second embodiments, for convenience, an example is shown in which four control signals are input to the quantum circuit 2, but the number of control signals, the number of light-emitting elements 612, the number of first to third single-core optical fibers 62, 643, 663, the number of modulators 63, the number of first cores 652, and the number of light-receiving elements 672 are not limited to this. The number of wirings for transmitting control signals can be changed depending on the number of quantum bits and is not particularly limited, but may be about two to four per quantum bit.

[0103] In the first and second embodiments, for convenience, the optical communication systems 6A and 6B are illustrated as including one multi-core optical fiber 65. However, the present invention is not limited to this. The optical communication systems 6A and 6B may include a plurality of multi-core optical fibers 65, and the plurality of multi-core optical fibers 65 may be inserted into the through-holes 341 of the respective metal plates 34.

[0104] In the first and second embodiments, the multi-core optical fiber 65 and the light-receiving substrate 67 are optically connected using the second connector 66, but the present invention is not limited to this. When the two-dimensional arrangement of the plurality of first cores 652 in the multi-core optical fiber 65 and the two-dimensional arrangement of the plurality of light-receiving elements 672 in the light-receiving substrate 67 can be made to correspond to each other so that the first cores 652 and the light-receiving elements 672 face each other, the second connector 66 may be omitted.

[0105] In the second embodiment, the light emitting element 612 and the first core 652 are optically connected by being opposed to each other, but this is not limiting. For example, the light emitting element 612 and the first core 652 may be optically connected to each other using the first connector 64.

[0106] Although the first and second embodiments illustrate the case where a plurality of light-emitting elements 612 are provided as light sources, the present invention is not limited to this. For example, a single light source and a splitter may be provided, and the light emitted from the single light source may be split by the splitter into a plurality of carrier waves having the same wavelength to generate an optical control signal.

[0107] DESCRIPTION OF SYMBOLS 1A, 1B...Quantum computer 2...Quantum circuit 3...Dilution refrigerator 31-33...Freezing chamber 34...Metal plate 341...Through hole 4...Control system 5...Microwave generating unit 51...Microwave generator 6A, 6B...Optical communication system 61...Light emitting substrate 611...First substrate 612...Light emitting element 62...First single-core optical fiber 621...Input end 622...Output end 63...Modulator 64...First connector 641...First capillary 643...Second single-core optical fiber 644...Large diameter portion 645...Input end 646...Intervening portion 647...Small diameter portion 648...Output end 649...Second core 65...Multi-core optical fiber 651...Bare fiber 652...First core 653...Cladding 654...Coating layer 655...First end 656...Second end 66...Second connector 661...Second capillary 662...Through hole 663...Third single-core optical fiber 664...Large diameter portion 665...Output end 666...Intervening portion 667...Small diameter portion 668...Input end 669...Third core 67...Light-receiving substrate 671...Second substrate 672...Light-receiving element 68...Laser driver

Claims

1. An optical communication system for a quantum computer, comprising: an optical signal generator that generates a plurality of optical control signals based on a plurality of first microwave control signals; a multi-core optical fiber including a plurality of first cores that transmit the plurality of optical control signals, and a cladding that encloses the plurality of first cores; and a plurality of photodetectors that receive the plurality of optical control signals from the plurality of first cores, convert the plurality of optical control signals into a plurality of second microwave control signals, and transmit them to a quantum circuit.

2. An optical communication system for a quantum computer according to claim 1, wherein at least a portion of the multi-core optical fiber is disposed inside a refrigerator of the quantum computer.

3. An optical communication system for a quantum computer according to claim 2, wherein the cladding is exposed over the entire or part of the area of ​​the multi-core optical fiber that is placed inside the refrigerator.

4. An optical communication system for a quantum computer according to any one of claims 1 to 3, wherein the multi-core optical fiber further includes a coating layer that coats the cladding, and the material constituting the coating layer is carbon or metal.

5. An optical communication system for a quantum computer according to any one of claims 1 to 4, wherein the optical signal generator includes: a carrier generator that generates a plurality of carrier waves; and a plurality of modulators that generate the plurality of optical control signals by superimposing the plurality of first microwave control signals respectively on the plurality of carrier waves.

6. An optical communication system for a quantum computer according to claim 5, wherein the wavelengths of the plurality of carrier waves generated by the carrier wave generator are the same.

7. An optical communication system for a quantum computer according to claim 5 or 6, further comprising a pair of connectors optically connected to the plurality of first cores of the multi-core optical fiber and capable of transmitting the plurality of optical control signals, the connectors comprising a plurality of transmission paths for transmitting the plurality of optical control signals, the connectors comprising expanding portions where the distance between the plurality of transmission paths increases with increasing distance from the end face of the multi-core optical fiber, one of the connectors being disposed between one end of the multi-core optical fiber and the modulator, and the other of the connectors being disposed between the other end of the multi-core optical fiber and the light-receiving element.

8. An optical communication system for a quantum computer according to claim 7, wherein the connector comprises: a plurality of single-core optical fibers provided at positions corresponding to the first cores of the multi-core optical fiber and having second cores optically connected to the first cores; and a capillary into which one ends of the plurality of single-core optical fibers are inserted and integrated, wherein the single-core optical fibers include: a small diameter portion abutting against the first core of the multi-core optical fiber; a large diameter portion having a diameter larger than that of the small diameter portion; and an intervening portion interposed between the small diameter portion and the large diameter portion and expanding in diameter as it approaches from the small diameter portion to the large diameter portion, wherein the intervening portion includes the expanding portion, and the spacing between the second cores in the small diameter portion is smaller than the spacing between the second cores in the large diameter portion.

9. An optical communication system for a quantum computer according to any one of claims 5 to 8, wherein the carrier wave generator comprises a plurality of light-emitting elements that respectively generate the plurality of carrier waves.

10. An optical communication system for a quantum computer according to any one of claims 1 to 4, wherein the optical signal generator comprises a laser driver and a plurality of light-emitting elements, the laser driver generates and transmits a plurality of modulated signals suited to each of the plurality of light-emitting elements based on the plurality of first microwave control signals, and the plurality of light-emitting elements generate the plurality of optical control signals based on the plurality of modulated signals transmitted from the laser driver.

11. An optical communication system for a quantum computer according to claim 10, wherein the plurality of light-emitting elements are arranged two-dimensionally, the plurality of light-receiving elements are arranged two-dimensionally to correspond to the arrangement of the plurality of light-emitting elements, and the plurality of first cores of the multi-core optical fiber include: a plurality of incident ends, which are arranged two-dimensionally to correspond to the arrangement of the plurality of light-emitting elements and into which the plurality of optical control signals are respectively incident; and a plurality of exit ends, which are arranged two-dimensionally to correspond to the arrangement of the plurality of light-receiving elements and from which the plurality of optical control signals are respectively emitted.

12. A quantum computer comprising: an optical communication system for a quantum computer according to any one of claims 1 to 11; a quantum circuit; and a refrigerator that houses the quantum circuit and cools the quantum circuit.

13. A quantum computer as recited in claim 12, further comprising a plurality of microwave generators that generate the plurality of first microwave control signals and transmit the plurality of first microwave control signals to the optical signal generator, respectively.

14. A quantum computer according to claim 12 or 13, wherein the refrigerator includes a plurality of freezing chambers and a plurality of metal plates arranged so as to separate the plurality of freezing chambers, the metal plates include through holes for inserting the multi-core optical fiber, the multi-core optical fiber further includes a coating layer that coats the cladding, and the coating layer is joined to the metal plates at the through holes.

15. A method for manufacturing a quantum computer, comprising a first step of incorporating the optical communication system for a quantum computer according to any one of claims 1 to 11 into a refrigerator.

16. A method for manufacturing a quantum computer according to claim 15, wherein the refrigerator includes a plurality of freezing chambers and a plurality of metal plates arranged so as to separate the plurality of freezing chambers, the metal plates include a through hole for inserting the multi-core optical fiber, and the multi-core optical fiber further includes a coating layer for coating the cladding, and the first step includes inserting the multi-core optical fiber into the through hole, and joining the metal plate and the coating layer at the through hole.

17. A method for manufacturing a quantum computer according to claim 15, wherein the multi-core optical fiber further includes a coating layer that coats the cladding, and the method for manufacturing a quantum computer further comprises a second step of removing the coating layer.

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