Quantum device

Abstract

A quantum device (1) has one or more quantum bits (10), the quantum bits having a first conductor (11), a second conductor (12) surrounding the first conductor in a plan view, and a Josephson junction element (13) connected between the first conductor and the second conductor, the first conductor having a first surface (511) facing the second conductor, the second conductor having a second surface (521) facing the first conductor, and the first surface, the second surface, or both surfaces having a shape that includes at least two points (516, 517, 528, 529) at which the curvature radii are mutually different. The quantum device can be used in quantum computing, for example.

Description

quantum devices

[0001] The present disclosure relates to quantum devices.

[0002] A quantum device has been proposed that includes a qubit formed by connecting a Josephson junction element between two conductors.

[0003] US Patent Application No. 2020 / 0265334 US Patent Application No. 2022 / 0376161 JP 2020-61447 A US Patent Application No. 2021 / 0343785

[0004] Recently, there has been an increasing demand for precise control of the state of quantum bits, including Josephson junction devices, by inputting electromagnetic field waveforms.

[0005] An object of the present disclosure is to provide a quantum device that improves the efficiency of confining an electromagnetic field within a quantum bit and can be appropriately controlled by the waveform of the input electromagnetic field.

[0006] According to one aspect of the present disclosure, there is provided a quantum device having one or more quantum bits, the quantum bits including a first conductor, a second conductor surrounding the first conductor in a planar view, and a Josephson junction element connected between the first conductor and the second conductor, the first conductor having a first surface facing the second conductor, the second conductor having a second surface facing the first conductor, and either the first surface or the second surface, or both, having a shape including at least two points with mutually different curvatures in a planar view.

[0007] According to the present disclosure, the efficiency of confining an electromagnetic field within a quantum bit can be improved, and the quantum bit can be appropriately controlled by the waveform of the input electromagnetic field.

[0008] FIG. 1 is a plan view showing a quantum device according to a first embodiment. FIG. 2 is a plan view showing a quantum bit. FIG. 3 is a diagram showing a first structure. FIG. 4 is a diagram showing a second structure. FIG. 5 is a diagram showing a third structure. FIG. 6 is a diagram showing simulation results. FIG. 7 is a schematic diagram showing a quantum device according to a second embodiment. FIG. 8 is a schematic diagram showing a quantum device according to a third embodiment. FIG. 9 is a schematic diagram showing a quantum device according to a fourth embodiment. FIG. 10 is a schematic diagram showing a quantum device according to a fifth embodiment. FIG. 11 is a diagram showing an example of how the quantum device is used.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations may be denoted by the same reference numerals to avoid redundant description. In this disclosure, a planar view refers to viewing an object from a direction perpendicular to the main surface of a substrate, and a planar shape refers to the shape of the object viewed from a direction perpendicular to the main surface of the substrate.

[0010] First Embodiment First, a first embodiment will be described. The first embodiment relates to a quantum device. Fig. 1 is a plan view showing a quantum device according to the first embodiment. Fig. 2 is a plan view showing a quantum bit.

[0011] 1 , the quantum device 1 according to the first embodiment includes a substrate 60, a plurality of quantum bits 10, a readout port 20, a filter 30, a plurality of resonators 40 (readout resonators), a plurality of relay conductors 50, and a ground conductor 90. The quantum bits 10, the readout port 20, the filter 30, the resonators 40, the relay conductor 50, and the ground conductor 90 are provided on a major surface of the substrate 60. The quantum bits 10, the readout port 20, the filter 30, the resonators 40, the relay conductor 50, and the ground conductor 90 each include, for example, a metal film and are formed in a film shape.

[0012] The quantum bits 10 are superconducting quantum bits and have a resonant frequency of, for example, 2 GHz to 10 GHz. A plurality of quantum bits 10 are arranged in a square lattice pattern.

[0013] As shown in Fig. 2, the quantum bit 10 has an internal conductor 11, an external conductor 12, and a Josephson junction element 13. In a plan view, the external conductor 12 surrounds the internal conductor 11. The internal conductor 11 and the external conductor 12 are electrically insulated from each other. The Josephson junction element 13 is provided between the internal conductor 11 and the external conductor 12 and is connected between the internal conductor 11 and the external conductor 12. In this embodiment, an electrical control signal is supplied to the internal conductor 11. The internal conductor 11 is an example of a first conductor, and the external conductor 12 is an example of a second conductor.

[0014] The internal conductor 11 has a side surface 511 facing the external conductor 12, and the external conductor 12 has an inner side surface 521 facing the internal conductor and an outer side surface 522 opposite the inner side surface 521. The side surface 511, the inner side surface 521, and the outer side surface 522 are curved surfaces including curves in a plan view. In a plan view, the side surface 511, the inner side surface 521, and the outer side surface 522 each have a shape including at least two points with different curvatures. In other words, none of the planar shapes of the side surface 511, the inner side surface 521, and the outer side surface 522 are circular. The side surface 511 is an example of a first surface, the inner side surface 521 is an example of a second surface, and the outer side surface 522 is an example of a third surface.

[0015] For example, in a plan view, the side surface 511 has convex portions 516 that bulge in a direction away from the center of gravity G of the internal conductor 11 and concave portions 517 that are concave in a direction toward the center of gravity G. The side surface 511 includes a meandering curve in a plan view. In a plan view, the shape of the side surface 511 may have four-fold rotational symmetry. In a polar coordinate system with the center of gravity G as the origin, the convex portions 516 may be arranged at a period of 90 degrees in the circumferential direction, and the concave portions 517 may be arranged between adjacent convex portions 516.

[0016] For example, in a plan view, the inner surface 521 has convex portions 526 that bulge in a direction away from the center of gravity G and concave portions 527 that concave in a direction toward the center of gravity G. The inner surface 521 includes a meandering curve in a plan view. In a plan view, the shape of the inner surface 521 may have four-fold rotational symmetry. In a polar coordinate system with the center of gravity G as the origin, the convex portions 526 may be arranged at a period of 90 degrees in the circumferential direction, and the concave portions 527 may be arranged between adjacent convex portions 526.

[0017] In a polar coordinate system with the center of gravity G as the origin, it is preferable that the positive and negative signs of the rate of change in curvature of the side surface 511 and the rate of change in curvature of the inner surface 521 at the same declination angle (inclination angle, polar angle) match. That is, it is preferable that the inner surface 521 also convex in the circumferential direction where the side surface 511 bulges, and that the inner surface 521 also concave in the circumferential direction where the side surface 511 is concave. It is particularly preferable that the side surface 511 and the inner surface 521 are parallel. That is, it is particularly preferable that the shape of the side surface 511 and the shape of the inner surface 521 are similar in plan view.

[0018] For example, in a plan view, the outer surface 522 has convex portions 528 that bulge in a direction away from the center of gravity G and concave portions 529 that concave in a direction toward the center of gravity G. The outer surface 522 includes a meandering curve in a plan view. In a plan view, the shape of the outer surface 522 may have four-fold rotational symmetry. In a polar coordinate system with the center of gravity G as the origin, the convex portions 528 may be arranged at a period of 90 degrees in the circumferential direction, and the concave portions 529 may be arranged between adjacent convex portions 528.

[0019] In a polar coordinate system with the center of gravity G as the origin, the positive and negative signs of the rate of change in curvature of the inner surface 521 and the rate of change in curvature of the outer surface 522 at the same declination angle (inclination angle, polar angle) may match. That is, in the circumferential direction, the outer surface 522 may also bulge in the portion where the inner surface 521 bulges, and the outer surface 522 may also bulge in the portion where the inner surface 521 is recessed. The inner surface 521 and the outer surface 522 may be parallel. That is, the shapes of the inner surface 521 and the outer surface 522 may be similar in plan view.

[0020] The ground conductor 90 has a ground potential. Around the quantum bit 10, in a plan view, the ground conductor 90 is provided outside the external conductor 12 and surrounds the internal conductor 11 and the external conductor 12. The external conductor 12 and the ground conductor 90 are electrically insulated from each other. The ground conductor 90 has a side surface 92 facing the external conductor 12. The side surface 92 is not parallel to the outer surface 522. The side surface 92 is an example of a fourth surface.

[0021] The readout port 20 is located at the center of a square 15 formed by four quantum bits 10 in a planar view. The filter 30 is capacitively coupled to one readout port 20 and is coupled to four resonators 40. For example, the filter 30 is capacitively coupled to four resonators 40. Each of the four resonators 40 is capacitively coupled to a quantum bit 10. The resonant frequencies of the four resonators 40 may be different. For example, the resonant frequency of one resonator 40 may be 10.1 GHz, the resonant frequency of another resonator 40 may be 10.2 GHz, the resonant frequency of yet another resonator 40 may be 10.3 GHz, and the resonant frequency of the remaining resonators 40 may be 10.4 GHz. The relay conductors 50 are provided on each side of the square 15 in a planar view and are capacitively coupled to two quantum bits 10. The relay conductors 50 face the external conductor 12 and are capacitively coupled to the external conductor 12. The relay conductor 50 faces, for example, the recess 529 of the external conductor 12. The two quantum bits 10 are capacitively coupled to each other via the relay conductor 50. The ground conductor 90 is also provided around the readout port 20, the filter 30, the resonator 40, and the relay conductor 50.

[0022] In the quantum device 1, in a plan view, the side surface 511 and the inner surface 521 each have a shape that includes at least two points with different curvatures. Therefore, compared to when the planar shapes of the side surface 511 and the inner surface 521 are circular, the opposing areas of the side surface 511 and the inner surface 521 are larger, and the electric field lines converge without spreading between the internal conductor 11 and the external conductor 12. Therefore, a high Q value can be obtained, and the efficiency of confining the electromagnetic field within the quantum bit 10 can be improved.

[0023] Here, the results of a simulation of the Q value will be described with reference to reference examples. Fig. 3 is a diagram showing a first structure that imitates the first embodiment. Fig. 4 is a diagram showing a second structure according to the first reference example. Fig. 5 is a diagram showing a third structure according to the second reference example.

[0024] As shown in Fig. 3, the first structure A has an internal conductor 111, an external conductor 112, and a Josephson junction element 113 that are modeled after the internal conductor 11, the external conductor 12, and the Josephson junction element 13 in the quantum device 1. The first structure A has a resonator 140 that is capacitively coupled to the external conductor 112. Although only a portion of the resonator 140 is shown in Fig. 3, it may have a structure similar to that of the resonator 40 in Fig. 1. Note that the shape of the resonator 140 at the capacitive connection portion between the resonator 140 and the quantum bit 10 may be convex or concave toward the quantum bit 10.

[0025] As shown in Fig. 4, the second structure B has an internal conductor 211, an external conductor 212, and a Josephson junction element 213. The side surface of the internal conductor 211 facing the external conductor 212, the inner surface of the external conductor 212 facing the internal conductor 211, and the inner surface of the external conductor 212 opposite to the inner surface have a circular planar shape. The Josephson junction element 213 is connected between the internal conductor 211 and the external conductor 212. The second structure B has a resonator 240 capacitively coupled to the external conductor 212. Although only a portion of the resonator 240 is shown in Fig. 4 as well, it may have a structure similar to that of the resonator 40 in Fig. 1.

[0026] As shown in FIG. 5 , the third structure C has a first conductor 311, a second conductor 312, and a Josephson junction element 313. The first conductor 311 and the second conductor 312 are formed in a linear shape parallel to each other. The side surface of the first conductor 311 facing the second conductor 312 and the side surface of the second conductor 312 facing the first conductor 311 have a linear planar shape. The Josephson junction element 313 is connected between the first conductor 311 and the second conductor 312. The third structure C has a resonator 340 capacitively coupled to the second conductor 312. Although only a portion of the resonator 340 is shown in FIG. 5 , it may have a structure similar to that of the resonator 40 in FIG. 1 .

[0027] The quantum bits of the first structure A, the second structure B, and the third structure C have approximately the same size in plan view, and all have a resonant frequency of 8 GHz.

[0028] Then, the relationship between several maximum coherence times and Q values ​​was calculated for each of the first structure A, the second structure B, and the third structure C. The results are shown in FIG. 6 . FIG. 6 illustrates the simulation results. As shown in FIG. 6 , the second structure B achieves a higher Q value than the third structure C. This is because the electric field lines in the third structure C extend beyond the opposing portions of the first conductor 311 and the second conductor 312. Furthermore, the first structure A achieves a higher Q value than the second structure B. This is because the opposing area between the internal conductor 111 and the external conductor 112 in the first structure A is larger than the opposing area between the internal conductor 211 and the external conductor 212 in the second structure B, allowing the electric field lines to converge without spreading. In other words, the distance over which the internal conductor 111 and the external conductor 112 face each other in a plan view is longer than the distance over which the internal conductor 211 and the external conductor 212 face each other, allowing the electric field lines to converge without spreading.

[0029] Furthermore, in the quantum device 1, the side surface 92 of the ground conductor 90 is not parallel to the outer surface 522 of the external conductor 12, and the recesses 517, 527, and 529 are particularly far from the ground conductor 90. This allows the capacitance between the external conductor 12 and the ground conductor 90 to be kept low. Therefore, even if the capacitance between the external conductor 12 and the relay conductor 50 is small, a distinguishable capacitive coupling can be obtained between two quantum bits 10 via the relay conductor 50. Therefore, even if a quantum bit 10 is capacitively coupled to another quantum bit 10, crosstalk can be suppressed. The capacitance of the external conductor 12 with respect to the ground potential is, for example, 10 fF or more and 180 fF or less.

[0030] Furthermore, when the resonant frequencies differ among the four resonators 40, the states of the four quantum bits 10 can be read out simultaneously by inputting a 10 GHz signal to the readout port 20. In other words, the states of the four quantum bits 10 can be read out simultaneously by frequency-separating the readout signal.

[0031] Second Embodiment Next, a second embodiment will be described. The second embodiment relates to a quantum device. FIG. 7 is a schematic diagram showing a quantum device according to the second embodiment. In the following description, an XYZ Cartesian coordinate system is used, and when viewed from an arbitrary point, the +Z side may be referred to as the upper side, upper side, or top, and the −Z side may be referred to as the lower side, lower side, or bottom. However, this coordinate system is defined for the purpose of explanation and does not limit the attitude of the quantum device.

[0032] 7 , quantum device 1100 according to the second embodiment includes quantum bit 1110, quantum bit 1140, ground conductor 1120, relay conductor 1150, readout conductor 1191, readout conductor 1192, and substrate 1130. Quantum bit 1110 includes internal conductor 1111, external conductor 1112, and Josephson junction element 1113. Quantum bit 1140 includes internal conductor 1141, external conductor 1142, and Josephson junction element 1143. Internal conductor 1111, internal conductor 1141, external conductor 1112, external conductor 1142, Josephson junction element 1113, Josephson junction element 1143, relay conductor 1150, readout conductor 1191, readout conductor 1192, and ground conductor 1120 are provided on the main surface of substrate 1130. In a plan view perpendicular to the main surface of the substrate 1130, the external conductor 1112 surrounds the internal conductor 1111, and the external conductor 1142 surrounds the internal conductor 1141. The internal conductors 1111 and 1112 are electrically insulated from each other, and the internal conductors 1141 and 1142 are electrically insulated from each other. In a plan view, the internal conductors 1111 and 1141 have shapes that are concave along the X-axis, concave along the Y-axis, and bulge in four directions inclined at 45 degrees from the X-axis and Y-axis. In a plan view, the external conductors 1112 and 1142 have shapes that follow the outer edges of the internal conductors 1111 and 1141, i.e., shapes that are concave along the X-axis, concave along the Y-axis, and bulge in four directions inclined at 45 degrees from the X-axis and Y-axis. The inner conductors 1111 and 1141 are examples of first conductors, and the outer conductors 1112 and 1142 are examples of second conductors. The ground conductor 1120 has a ground potential.

[0033] A relay conductor 1150 is provided between quantum bit 1110 and quantum bit 1140. Relay conductor 1150 has a convex portion 1151 that protrudes toward external conductor 1112 and a convex portion 1152 that protrudes toward external conductor 1142. External conductor 1112 of quantum bit 1110 has a concave portion 1112A that is recessed away from convex portion 1151, and external conductor 1142 of quantum bit 1140 has a concave portion 1142A that is recessed away from convex portion 1152. Relay conductor 1150 is capacitively coupled to external conductors 1112 and 1142. External conductors 1112 and 1142 are capacitively coupled to each other via relay conductor 1150.

[0034] In this embodiment, electrical control signals are supplied to internal conductors 1111 and 1141. Readout conductor 1191 is capacitively coupled to external conductor 1112, and readout conductor 1192 is capacitively coupled to external conductor 1142. The state of quantum bit 1110 is read out to the outside via readout conductor 1191, and the state of quantum bit 1140 is read out to the outside via readout conductor 1192.

[0035] Ground conductor 1120 surrounds qubit 1110, qubit 1140, relay conductor 1150, readout conductor 1191, and readout conductor 1192. Quantum device 1100 may have other qubits capacitively coupled to qubit 1110, may have other qubits capacitively coupled to qubit 1140, and may have relay conductors that capacitively couple these qubits. In this case, these qubits and relay conductors are also surrounded by ground conductor 1120.

[0036] For example, the capacitance of qubit 1110 to ground and the capacitance of qubit 1140 to ground may be 10 fF or more and 180 fF or less. The capacitance of the capacitor including outer conductor 1112 and ground conductor 1120 and the capacitance of the capacitor including outer conductor 1142 and ground conductor 1120 may be 10 fF or more and 180 fF or less.

[0037] According to the second embodiment, an excellent electromagnetic field confinement effect can be obtained for quantum bits 1110 and 1140. Furthermore, a large internal current can be obtained for quantum bits 1110 and 1140. Furthermore, even when quantum bit 1110 or 1140 is capacitively coupled to another quantum bit, crosstalk can be suppressed. In FIG. 7 , readout conductor 1191 is placed on the lower left side of quantum bit 1110, but this is not limited to this. A quantum device such as that shown in FIG. 1 may be configured using two more quantum bits in addition to quantum bit 1110 and quantum bit 1140. In this case, if quantum bit 1110 and quantum bit 1140 correspond to the upper two quantum bits 10 in FIG. 1 , readout conductor 1191 is placed on the lower right side of quantum bit 1110 in FIG. 7 .

[0038] Third Embodiment Next, a third embodiment will be described. The third embodiment differs from the second embodiment mainly in the configuration of the capacitive coupling between quantum bits. Fig. 8 is a schematic diagram showing a quantum device according to the third embodiment.

[0039] 8 , in the quantum device 1200 according to the third embodiment, in a plan view, the internal conductors 1111 and 1141 protrude along the X-axis, protrude along the Y-axis, and have shapes concave in four directions inclined at 45 degrees from the X-axis and the Y-axis. In a plan view, the external conductors 1112 and 1142 have shapes that follow the outer edges of the internal conductors 1111 and 1141. That is, in a plan view, the external conductor 1112 has two protruding portions 1112B protruding along the X-axis and two protruding portions 1112C protruding along the Y-axis, and the external conductor 1142 has two protruding portions 1142B protruding along the X-axis and two protruding portions 1142C protruding along the Y-axis.

[0040] The relay conductor 1150 has a convex portion 1153 located on the +Y side of the +X side convex portion 1112B and capacitively coupled to the +X side convex portion 1112B, and a convex portion 1154 located on the -Y side of the -X side convex portion 1142B and capacitively coupled to the -X side convex portion 1142B.

[0041] Other configurations of the third embodiment are the same as those of the second embodiment, and the third embodiment can also achieve the same effects as those of the second embodiment.

[0042] Fourth Embodiment Next, a fourth embodiment will be described. The fourth embodiment differs from the third embodiment mainly in the configuration of the capacitive coupling between quantum bits. Fig. 9 is a schematic diagram showing a quantum device according to the fourth embodiment.

[0043] 9 , the quantum device 1300 according to the fourth embodiment does not have a relay conductor 1150. The external conductor 1112 has an extension 1312 extending toward the external conductor 1142, and the external conductor 1142 has an extension 1342 extending toward the external conductor 1112. The extension 1312 has a convex portion 1312A protruding toward the external conductor 1142, and the extension 1342 has a concave portion 1342A recessed away from the external conductor 1112. The extensions 1312 and 1342 face each other and are capacitively coupled to each other.

[0044] Other configurations of the fourth embodiment are the same as those of the third embodiment, and the fourth embodiment can also achieve the same effects as those of the third embodiment.

[0045] Fifth Embodiment Next, a fifth embodiment will be described. The fifth embodiment differs from the third embodiment mainly in the configuration of the capacitive coupling between quantum bits. Fig. 10 is a schematic diagram showing a quantum device according to the fifth embodiment.

[0046] As shown in FIG. 10 , in the quantum device 1400 according to the fifth embodiment, in plan view, the relay conductor 1150 has a recess 1155 located on the +X side of the +X side convex portion 1112B and capacitively coupled to the +X side convex portion 1112B, and a recess 1156 located on the −X side of the −X side convex portion 1142B and capacitively coupled to the −X side convex portion 1142B.

[0047] Furthermore, in quantum device 1200, readout conductor 1191 extends from quantum bit 1110 to the +X side and the −Y side, whereas in quantum device 1400, readout conductor 1191 extends from quantum bit 1110 to the −X side and the −Y side.

[0048] Other configurations of the fifth embodiment are the same as those of the third embodiment. The fifth embodiment can also achieve the same effects as those of the third embodiment.

[0049] In the present disclosure, the first surface of the first conductor and the second surface of the second conductor do not need to be parallel, and the shape of the first surface of the first conductor and the shape of the second surface of the second conductor do not need to be similar in plan view. Furthermore, the shapes of the first surface and the second surface do not need to be four-fold rotationally symmetric in plan view; they may be two-fold, three-fold, or five-fold or more rotationally symmetric. The shapes of the first surface and the second surface do not need to be rotationally symmetric in plan view. Furthermore, in a polar coordinate system with the center of gravity G as the origin, the sign of the rate of change in curvature of the first surface and the sign of the rate of change in curvature of the second surface at the same deflection angle do not need to match. Furthermore, as long as at least one of the first surface and the second surface has a shape that includes at least two points with different curvatures in plan view, the planar shape of the other surface may be circular.

[0050] Here, we will explain an example of how the quantum device 1 is used. Fig. 11 is a diagram showing an example of how the quantum device is used.

[0051] In this usage form, two quantum devices 1 each having four quantum bits 10 are used. In each quantum device 1, the four quantum bits 10 are coupled to a readout port 20. Although not shown, each quantum device 1 includes a filter 30, a resonator 40, a relay conductor 50, a ground conductor 90, and the like. The two quantum devices 1 are capacitively coupled to each other via a cover chip 600. The cover chip 600 includes a substrate 601 and a resonator 602. The resonator 602 has a path length of half the wavelength λ of the signal input to the quantum device 1 during readout. One quantum device 1 is capacitively coupled to one end of the resonator 602, and the other quantum device 1 is capacitively coupled to the other end of the resonator 602. For a total of eight quantum bits 10, the resonators 40 for the respective readout ports 20 are different in resonance frequency. In this case, the resonator 602 of each quantum bit 10 is coupled to the readout port 20 via a filter (e.g., a Purcell filter). For example, when attention is focused on the two quantum bits 10 at the top left of FIG. 11, this corresponds to the case in FIG. 7 where the readout conductor 1191 is placed on the −X side (the −Y side of the relay conductor 1150).

[0052] When a signal 611 is input to the readout port 20 of one of the first quantum devices 1, the states of the four quantum bits 10 included in the first quantum device 1 are read out and input to the readout port 20 of the other, second quantum device 1, via the resonator 602. As a result, the states of the four quantum bits 10 included in the second quantum device 1 are also read out, and a signal 612 in which the states of eight quantum bits 10 are superimposed is output. By frequency-separating the signal 612, the states of eight quantum bits 10 can be read out simultaneously. In this example, eight-multiplexing can be achieved.

[0053] In another example of usage, the cover chip 600 may not be provided with the resonator 602 that functions as a filter, and may be used as a quantum device 1 that uses multiplexing when reading out four quantum bits 10. In this case, the resonator 40 for each quantum bit 10 is arranged so as to be coupled to a filter 30 (Purcell filter) that capacitively couples the readout port 20, as shown in FIG. 1 . In this case, a four-multiplexed readout can be realized.

[0054] The state of the quantum bit 10 can be manipulated, for example, by inputting a signal from a pogo pin to an electrode capacitively coupled to the internal conductor 11 via the substrate. Furthermore, the signal may be input to the electrode capacitively coupled to the internal conductor 11 via the substrate from a bump provided on an interposer, wiring board, or the like. The number of quantum bits 10 included in one quantum device 1 is not limited. For example, one quantum device 1 may include 64 or 256 quantum bits 10, or may include 1,000 or more quantum bits 10.

[0055] Quantum devices according to the present disclosure can be used, for example, in quantum computing.

[0056] Although the preferred embodiments have been described in detail above, the present disclosure is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0057] 7 to 10, the Josephson junction is placed on the X-axis, but the position is not limited to this. It may be placed at an angle of 45 degrees from the center of gravity G, connecting the internal conductor 11 and the external conductor 12. In this way, the position of the Josephson junction is not limited to the above-mentioned embodiments.

[0058] 1, 1100, 1200, 1300, 1400: quantum device 10, 1110, 1140: quantum bit 11, 1111, 1141: internal conductor 12, 1112, 1142: external conductor 13, 1113, 1143: Josephson junction element 15: square 20: readout port 30: filter 40: resonator 50, 1150: relay conductor 60, 1130: substrate 90, 1120: ground conductor 92: side surface 511: side surface 516, 526, 528: convex portion 517, 527, 529: concave portion 521: inner surface 522: outer surface

Claims

1. A quantum device having one or more quantum bits, the quantum bits comprising: a first conductor; a second conductor surrounding the first conductor in a planar view; and a Josephson junction element connected between the first conductor and the second conductor, wherein the first conductor has a first surface facing the second conductor, and the second conductor has a second surface facing the first conductor, and wherein, in a planar view, the first surface or the second surface, or both, have a shape including at least two points having mutually different curvatures.

2. The quantum device as described in claim 1, wherein, in a planar view, the first surface or the second surface, or both, have a shape including a convex portion that bulges away from the center of gravity of the first conductor, and a concave portion that is concave toward the center of gravity.

3. The quantum device according to claim 1 or 2, wherein, in a plan view, the first surface and the second surface have shapes including at least two points having mutually different curvatures.

4. The quantum device of claim 2, wherein, in a planar view, in a polar coordinate system with the center of gravity as the origin, the sign of the rate of change of curvature of the first surface and the sign of the rate of change of curvature of the second surface at the same deflection angle are the same.

5. The quantum device of claim 4, wherein the first surface and the second surface are parallel.

6. The quantum device according to claim 4 or 5, wherein the shape of the first surface and the shape of the second surface are four-fold rotationally symmetric in a planar view.

7. The quantum device according to claim 1 or 2, wherein the two quantum bits are capacitively coupled to each other.

8. A quantum device as claimed in claim 1 or 2, comprising: a plurality of resonators capacitively coupled to each of a plurality of said quantum bits; a filter coupled to the plurality of said resonators; and a port capacitively coupled to the filter.

9. A quantum device as described in claim 1 or 2, further comprising a ground conductor having a ground potential arranged around the second conductor, the second conductor having a third surface facing the ground conductor, the ground conductor having a fourth surface facing the second conductor, and the third surface and the fourth surface are not parallel to each other.

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