Quantum device and quantum information processing device

Abstract

Provided are a quantum device and a quantum information processing device capable of improving Fidelity and suppressing a leakage magnetic field while suppressing an increase in Joule heat. The quantum device comprises: a quantum dot formation layer including a semiconductor layer having quantum dots arranged in rows; gate electrode layers including gate electrodes for applying a magnetic field to the quantum dots; and a magnetic shield layer that is provided between the gate electrode layers and the quantum dot formation layer, includes a plurality of magnetic shield parts composed of a superconducting material, and has gaps formed between the magnetic shield parts.

Description

Quantum devices and quantum information processing devices

[0001] The present invention relates to a quantum device and a quantum information processing device.

[0002] Silicon quantum computers are computers that process information using quantum bits (qubits). Due to their long coherence time and compatibility with existing semiconductor manufacturing techniques, silicon quantum computers are being researched and developed as promising candidates for quantum computing.

[0003] Patent Literature 1 discloses a flexible substrate applicable to a quantum information processing system. The flexible substrate has a plurality of conductive traces arranged in an array on a first side and an electron shielding layer formed on a second side opposite the first side. The flexible substrate includes a folded region between the first conductive traces and the second conductive traces such that the electromagnetic shielding layer provides electromagnetic shielding between the first conductive traces and the second conductive traces.

[0004] Patent Document 2 discloses a quantum computing device that includes a chipset made of a superconductor, at least one superconducting data line attached to the chipset die by a set of wirebonds, and a magnetic shielding wall that separates each set of wirebonds.

[0005] Japanese Patent Application Laid-Open No. 2022-136080 Special Publication No. 2021-521626

[0006] The quantum dot array chip operates at cryogenic temperatures (e.g., 100 mK) and selectively controls the arrayed quantum bits. In addition to an externally applied magnetic field (e.g., 0.7 T), a local current is applied to the orthogonal gate electrodes to generate a local magnetic field, which shifts the precession frequency of the selected quantum bit and manipulates the quantum bit. The local magnetic field actually spreads to unselected quantum bits (leakage magnetic field), which causes a degradation of fidelity.

[0007] Therefore, in order to cancel the leakage magnetic field, currents are applied in opposite directions to two parallel gate electrodes (hereinafter, this method may be referred to as the "two-wire method"). However, the two-wire method increases the number of wires through which current flows, which results in increased Joule heat.

[0008] The technology of Patent Document 1 is electromagnetic shielding using a flexible substrate. Patent Document 1 does not describe a configuration in which an electromagnetic shielding layer with a gap is disposed, as in the present invention. Patent Document 2 describes the installation of a magnetic shielding wall that runs vertically and has no gap between wire bonds to separate horizontal spaces, but like Patent Document 1, it does not describe the configuration of the present invention.

[0009] The present invention has been made to solve the above-mentioned problems. That is, one of the objects of the present invention is to provide a quantum device and a quantum information processing device that can suppress an increase in Joule heat, suppress a leakage magnetic field, and improve fidelity.

[0010] In order to solve the above problems, the quantum device of the present invention comprises a quantum dot-forming layer including a semiconductor layer having quantum dots arranged in rows; a gate electrode layer including a gate electrode that applies a magnetic field to the quantum dots; and a magnetic shielding layer provided between the gate electrode layer and the quantum dot-forming layer, the magnetic shielding layer including a plurality of magnetic shielding portions made of a superconducting material, with gaps formed between the magnetic shielding portions.

[0011] The quantum device of the present invention comprises a quantum dot formation layer including a semiconductor layer having quantum dots arranged in a row, a gate electrode layer including a gate electrode, and a bimetallic wiring layer including a plurality of bimetallic wirings each including a magnetic shielding layer made of a superconducting material and a normal conductor layer made of a normal conductor, with gaps formed between the bimetallic wirings.

[0012] The quantum information processing device of the present invention is a quantum information processing device comprising: a control device that controls quantum bits; and a quantum device including quantum dots, wherein the quantum device comprises: a quantum dot formation layer including a semiconductor layer having the quantum dots arranged in a row; a gate electrode layer including a gate electrode that applies a magnetic field to the quantum dots; and a magnetic shielding layer provided between the gate electrode layer and the quantum dot formation layer, the magnetic shielding layer including a plurality of magnetic shielding portions made of a superconducting material, with gaps formed between the magnetic shielding portions.

[0013] According to the present invention, it is possible to suppress an increase in Joule heat, suppress leakage magnetic fields, and improve fidelity. Note that the effects described here are not necessarily limited to those described herein, and may be any of the effects described in this disclosure.

[0014] FIG. 1 is a diagram showing an example of the configuration of a quantum device according to a first embodiment of the present invention. FIG. 2A is a plan view of a magnetic shielding layer viewed from above in the z direction. FIG. 2B is a plan view showing a state in which a plurality of first gate electrodes and second gate electrodes are overlapped on the magnetic shielding layer of FIG. 2A. FIG. 3 is an x-z ​​cross-sectional view of a quantum device for explaining the operation of the quantum device. FIG. 4 is a y-z cross-sectional view of a quantum device for explaining the operation of the quantum device. FIG. 5 is a diagram for explaining an example of the configuration of a quantum device according to a second embodiment. FIG. 6 is a diagram for explaining an example of the configuration of a quantum device according to the second embodiment. FIG. 7 is a plan view showing an example of the configuration of a first bimetal wiring layer and a second bimetal wiring layer when the quantum device is viewed from below. FIG. 8 is a diagram for explaining an apparatus to which a quantum device control method according to a third embodiment is applied. FIG. 9 is a flowchart for explaining the processing flow executed by a control chip. FIG. 10A is a diagram showing an example of the functional blocks of a quantum information processing device according to a fourth embodiment. FIG. 10B is a block diagram showing an example of the hardware configuration of a control device. FIG. 11 is a diagram showing an example of the configuration of a quantum information processing device.

[0015] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts may be denoted by the same reference numerals.

[0016] <<First Embodiment>> A quantum device according to a first embodiment of the present invention will be described. Fig. 1 is a diagram showing an example of the configuration of a quantum device. The quantum device shown in Fig. 1 includes a quantum bit array, which is a two-dimensional array of quantum bits. The quantum bits are spin quantum bits in which the spin of electrons in a semiconductor is a degree of freedom.

[0017] The quantum device forms a quantum bit array with a quantum dot formation layer 110, a first gate electrode layer 120, a magnetic shielding layer 130, and a second gate electrode layer 140. Although not shown, the device is also provided with a microwave antenna and an external magnetic field source required for controlling the quantum bits.

[0018] The quantum dot formation layer 110 is a layer containing a semiconductor, and includes a silicon substrate 111 and an SOI (Silicon On Insulator) layer 112. An array of quantum dots (quantum dots arranged in two-dimensional rows) for storing bits having a two-dimensional matrix structure is formed in the SOI layer 112 of the quantum dot formation layer 110. The quantum dots are formed at positions corresponding to where the gate electrode SG1 and the gate electrode FG2 overlap in the z direction (directly below the intersection). In the quantum dot formation layer 110, a two-dimensional matrix (two-dimensional row) of quantum bits (quantum bit array) confined in the two-dimensional matrix of quantum dots is formed.

[0019] The first gate electrode layer 120 includes a plurality of gate electrodes FG1 and a plurality of gate electrodes SG1 arranged such that their longitudinal directions are aligned with the x-direction. In the first gate electrode layer 120, the plurality of gate electrodes FG1 and the plurality of gate electrodes SG1 are arranged alternately in the y-direction. In FIG. 1 , the direction normal to the quantum dot formation layer 110 is defined as the z-direction, a first direction in a plane normal to the z-direction is defined as the y-direction, and a second direction perpendicular to the first direction in the plane is defined as the x-direction. The quantum dot formation layer 110 has a rectangular shape in plan view, with two opposing first sides and two opposing second sides. In FIG. 1 , the first side is aligned with the y-direction, and the second side is aligned with the x-direction.

[0020] Adjacent gate electrodes FG1 and SG1 are insulated from each other by an insulating layer (not shown) formed between them. The gate electrodes FG1 and SG1 are connected to a control device (not shown), and different voltages can be applied to the gate electrodes FG1 and SG1, respectively, or currents can be selectively passed through the gate electrodes FG1 and SG1.

[0021] The second gate electrode layer 140 includes a plurality of gate electrodes FG2 and a plurality of gate electrodes SG2 arranged such that their longitudinal direction is aligned with the y-direction. In the second gate electrode layer 140, the plurality of gate electrodes FG2 and the plurality of gate electrodes SG2 are arranged alternately in the x-direction. Adjacent gate electrodes FG2 and SG2 are insulated from each other by an insulating layer (not shown) formed between them. The plurality of gate electrodes FG2 and the plurality of gate electrodes SG2 are connected to a control device (not shown), which allows different voltages to be applied to the plurality of gate electrodes FG2 and the plurality of gate electrodes SG2, respectively, or allows current to be selectively passed through the plurality of gate electrodes FG2 and the plurality of gate electrodes SG2. Note that some of the gate electrodes in the second gate electrode layer 140 may have a shape having a protrusion that protrudes downward.

[0022] A plurality of N-channel field effect transistors (FETs) are formed at predetermined locations in the quantum dot formation layer 110, the first gate electrode layer 120, and the second gate electrode layer 140. The N-channel field effect transistors (FETs) are formed at locations where a plurality of predetermined column-shaped regions R1 extending in the y direction of the quantum dot formation layer 110 overlap with each of the plurality of gate electrodes FG1 and SG1 of the first gate electrode layer 120 and each of the plurality of gate electrodes FG2 and SG2 of the second gate electrode layer 140. These N-channel field effect transistors (FETs) can be used to form quantum dots for confining electrons, which are quantum bits, and can also be used to form potential barriers between the quantum dots.

[0023] In this example, the locations where each of the plurality of columnar regions R1 of the quantum dot formation layer 110, each of the plurality of gate electrodes SG1 of the first gate electrode layer 120, and each of the plurality of gate electrodes FG2 of the second gate electrode layer 140 overlap are used as quantum dots. The locations where each of the plurality of columnar regions R1 of the quantum dot formation layer 110, each of the plurality of gate electrodes FG1 of the first gate electrode layer 120, and each of the plurality of gate electrodes SG2 of the second gate electrode layer 140 overlap are used as potential barriers.

[0024] The control device (not shown) can apply a voltage to the gate electrodes FG1, SG1, FG2, and SG2 to change the potential, or pass a direct current or an alternating current to generate a pulse. This allows the control device (not shown) to confine electrons, which are quantum bits, in quantum dots or move electrons between quantum dots. The control device (not shown) can also perform quantum gate operations that change the spin state of electrons (quantum bits), such as controlling the phase of the electron spin or operating a controlled NOT gate.

[0025] Furthermore, a control device (not shown) can input and output electrons (quantum bits) from terminals at both ends of region R1 of quantum dot formation layer 110. The control device (not shown) can perform initialization including an operation to confine quantum bits in quantum dots, operate a rotation gate which is a one-qubit gate, operate a controlled NOT gate which is a two-qubit gate, and output electrons (quantum bits) from the terminals of quantum dot formation layer 110 to a measurement device (not shown) to allow the measurement device (not shown) to measure the state of the electrons (quantum bits). As a result, when a quantum device is applied to a quantum information processing device, arbitrary quantum operations become possible.

[0026] The gate electrode SG1 arranged along the x-direction and the gate electrode FG2 arranged along the y-direction are used by a control device (not shown) to pass a current through them to generate a local magnetic field that is selectively applied to the quantum bit.

[0027] The magnetic shielding layer 130 is disposed between the first gate electrode layer 120 and the second gate electrode layer 140 in the z direction. Fig. 2A is a plan view of the magnetic shielding layer 130 as viewed from above in the z direction. Fig. 2B is a plan view showing a state in which a plurality of first gate electrode layers 120 (gate electrodes FG1, SG1) and second gate electrode layers 140 (gate electrodes FG2, SG2) are superimposed on the magnetic shielding layer 130 of Fig. 2A. Note that in Fig. 2B, quantum bits (quantum dots) are illustrated by dashed lines to show the positional relationship between the magnetic shielding layer 130, the gate electrodes, and the quantum bits.

[0028] 2A and 2B , the magnetic shielding layer 130 includes a plurality of magnetic shielding portions 131 arranged such that their longitudinal direction is aligned with the y direction. The magnetic shielding layer 130 is arranged such that the entire lower surface of the gate electrode FG2 overlaps with the magnetic shielding portions 131 in the z direction. The magnetic shielding portions 131 are arranged such that they overlap with a row of quantum bits (quantum dots) in the z direction. The plurality of magnetic shielding portions 131 are arranged such that adjacent magnetic shielding portions 131 are spaced apart from each other in the x direction. Therefore, a gap is formed between adjacent magnetic shielding portions 131 in the magnetic shielding layer 130. The gap is formed, for example, along the row of quantum dots aligned in the y direction and perpendicular to the row of quantum dots aligned in the y direction.

[0029] The magnetic shielding portion 131 is made of a superconducting material (a superconductor (e.g., TiN (titanium nitride) or the like), with a thickness of, for example, several nm). Utilizing the property of the superconductor that constitutes the magnetic shielding portion 131 to shield magnetic fields (Meissner effect), a magnetic shielding layer 130 (superconducting wiring) having a gap is disposed between the quantum bit and the second gate electrode layer 140 to shield leakage magnetic fields, thereby enabling quantum bit selection using a single-wire method. Note that the single-wire method differs from a method in which current is applied to two parallel gate electrodes, as in the two-wire method, in that current is applied to one gate electrode (one gate electrode in the first gate electrode layer 120 and one gate electrode in the second gate electrode layer 140) required to selectively control the quantum bit.

[0030] In quantum devices, in order to selectively control a quantum bit, a local magnetic field is generated by applying a local current to orthogonal gate electrodes (SG1, FG2) in addition to an externally applied magnetic field of, for example, 0.7 T (external magnetic field B), which shifts the resonant frequency of the precession of the selected quantum bit. The quantum bit is then manipulated by irradiating a high-frequency signal (high-frequency electromagnetic wave) of the same frequency as the shifted resonant frequency from a microwave antenna (not shown). At this time, the local magnetic field spreads to unselected quantum bits (leakage magnetic field), which causes a deterioration of fidelity.

[0031] In conventional quantum devices, the leakage magnetic field is cancelled by applying currents in opposite directions to two parallel gate electrodes (two-wire method). Note that the two-wire gate electrodes are, for example, SG1 immediately above the selected quantum bit and the SG1 adjacent to the SG1 (the SG1 adjacent via FG1) in the first gate electrode layer 120, and FG2 immediately above the selected quantum bit and the FG2 adjacent to the FG2 (the FG2 adjacent via SG2) in the second gate electrode layer 140.

[0032] However, in the two-wire system, Joule heat increases due to an increase in the number of wirings (number of gate electrodes) through which current flows.

[0033] Therefore, the quantum device according to the first embodiment has a magnetic shielding layer 130 disposed between the first gate electrode layer 120 and the second gate electrode layer 140 in the z direction. In the magnetic shielding layer 130, a gap is formed between adjacent magnetic shielding portions 131. With this configuration, the quantum device can suppress the leakage magnetic field (the influence of the leakage magnetic field) on unselected quantum bits and can improve fidelity.

[0034] 3 and 4 are xz and yz cross-sectional views of the quantum device, respectively, for explaining the operation of the quantum device.

[0035] 3 and 4, in order to selectively control a quantum bit, an external magnetic field B (Bx (x component of B), By (y component of B)) is applied, and currents are passed through gate electrodes SG1 and FG2 whose crossing points correspond to the selected quantum bit q1 (current Ia is passed through gate electrode SG1, and current Ib is passed through gate electrode FG2). As a result, a local magnetic field is generated from the crossing point of gate electrodes SG1 and FG2.

[0036] In this case, in the second gate electrode layer 140, as shown by the arrows, a local magnetic field passes through the gap between the magnetic shields 131 and is applied to the selected quantum bit q1. On the other hand, the magnetic shields 131 block the leakage magnetic field to the unselected particle bit q2, as shown by the arrows. In this way, even in a single-line quantum device, by shielding the leakage magnetic field with the magnetic shields 131, it is possible to suppress the leakage magnetic field while suppressing an increase in Joule heat and improving fidelity. Note that, as shown in FIG. 4 , in the first gate electrode layer 120, the distance between the gate electrode SG1 and the SOI layer 112 is short, and therefore the leakage magnetic field is small, and therefore magnetic shielding between the gate electrode SG1 and the SOI layer 112 is not necessary.

[0037] In the quantum device according to the first embodiment, when an external magnetic field B is applied in the z direction, the superconductor constituting the magnetic shielding portion 131 may easily exceed the critical magnetic field and transition to a normal conductor, so it is preferable to apply the external magnetic field B in a predetermined direction (e.g., 45 degrees) within the xy plane. The external magnetic field is irradiated onto the gate electrode in a predetermined direction (e.g., 45 degrees) within the xy plane. If the local magnetic fields of the gate electrodes SG1 and FG2 are of similar strength, the local magnetic field is applied to the selected quantum bit at the same predetermined angle (45 degrees) within the xy plane as the external magnetic field.

[0038] <Effects> As described above, the quantum device according to the first embodiment of the present invention can suppress the leakage magnetic field while suppressing the increase in Joule heat, and can also improve fidelity, by shielding the leakage magnetic field with the magnetic shielding layer 130 having a gap.

[0039] <<Second Embodiment>> A quantum device according to a second embodiment of the present invention will be described. Fig. 5 is a diagram for explaining an example of the configuration of a quantum device according to the second embodiment. Fig. 6 is a diagram for explaining an example of the configuration of a quantum device according to the second embodiment. Fig. 7 is a plan view showing an example of the configuration of a first bimetal wiring layer 150 and a second bimetal wiring layer 160 when the quantum device is viewed from below.

[0040] 5 and 6, the quantum device according to the second embodiment includes a first bimetal wiring layer 150, a second bimetal wiring layer 160, a quantum dot formation layer 110 having a configuration similar to that of the first embodiment, a first gate electrode layer 120, and a second gate electrode layer 140. The second gate electrode layer 140 differs from the second gate electrode layer 140 of the first embodiment only in that the positions of the gate electrode FG2 and the gate electrode SG2 are interchanged.

[0041] The first bimetal wiring layer 150 includes multiple bimetal wirings 500 arranged with their longitudinal direction aligned along the y direction (see FIG. 7 ). The bimetal wirings 500 include normal-conducting wirings 501 (normal-conducting wiring layers) and a magnetic shielding layer 502. The magnetic shielding layer 502 is made of a superconducting material (a superconductor (e.g., TiN, etc.)). Note that the superconducting material may be NbTi, etc., other than TiN, as long as it is superconducting at 100 mK. In the superconducting state, the magnetic shielding layer 502 shields an external magnetic field B applied in the z direction from below the first bimetal wiring layer 150 due to the Meissner effect. On the other hand, when the magnetic shielding layer 502 changes from the superconducting state to the normal conducting state due to the flow of a current greater than or equal to the critical current, the Meissner effect is lost, and the external magnetic field B applied in the z direction is transmitted through the magnetic shielding layer 502.

[0042] When the magnetic shielding layer 502 (e.g., a superconducting thin film such as TiN) transitions from a superconducting state to a normal conducting state, the resistance value of the bimetallic wiring 500 increases sharply and Joule heat is generated. Therefore, the bimetallic wiring 500 has a magnetic shielding layer 502 (e.g., a superconducting thin film) formed on a low-resistance normal conducting wiring 501 (a normal conductor (e.g., silicide), which may be a material that is normally conductive at 100 mK (e.g., copper (Cu))). This allows the quantum device of the second embodiment to mitigate the increase in resistance when the magnetic shielding layer 502 transitions from a superconducting state to a normal conducting state. The wiring 500 is connected to a control device (not shown), and the current flowing through the wiring 500 can be controlled by the control device (not shown).

[0043] The second bimetal wiring layer 160 includes a plurality of bimetal wirings 600 arranged with their longitudinal direction aligned along the x-direction (see FIG. 7 ). The bimetal wirings 600 include normal conducting wirings 601 (normal conducting wiring layers) and a magnetic shielding layer 602. The magnetic shielding layer 602 is made of a superconducting material. In the superconducting state, the magnetic shielding layer 602 shields from an external magnetic field B due to the Meissner effect. On the other hand, when a current greater than or equal to the critical current flows through the magnetic shielding layer 602, the magnetic shielding layer 602 changes from the superconducting state to the normal conducting state, losing the Meissner effect and allowing the external magnetic field B to pass through.

[0044] When the magnetic shielding layer 602 (e.g., a superconducting thin film such as TiN) transitions from a superconducting state to a normal conducting state, the resistance value of the bimetallic wiring 600 increases sharply and Joule heat is generated. Therefore, the bimetallic wiring has the magnetic shielding layer 602 (e.g., a superconducting thin film) formed on a normal conducting layer (normal conductor) with a low resistance. This allows the quantum device according to the second embodiment to mitigate the increase in resistance when the magnetic shielding layer 602 transitions from a superconducting state to a normal conducting state. The wiring 600 is connected to a control device (not shown), and the current flowing through the wiring 600 can be controlled by the control device (not shown).

[0045] In the quantum device according to the second embodiment, with an external magnetic field B applied from the outside in the z direction, a local current equal to or greater than the critical current is applied to the superconducting wiring (magnetic shielding layer 502 (602)) of the first bimetal wiring layer 150 and the second bimetal wiring layer 160, causing a transition from the superconducting state to the normal conducting state, thereby allowing the magnetic field at a specific location to pass through and controlling the selected quantum bit.

[0046] 5, 6, and 7, with an external magnetic field B applied from the outside in the z direction, a current of a predetermined magnitude equal to or greater than the critical current (hereinafter, sometimes referred to as a "superconducting state control current") is applied to bimetallic wiring 500 and wiring 600, including a position overlapping with selected quantum bit q1 in the z direction. As a result, magnetic shielding layer 502 of bimetallic wiring 500 transitions from a superconducting state to a normal conducting state, and magnetic shielding layer 602 of bimetallic wiring 600 transitions from a superconducting state to a normal conducting state.

[0047] Therefore, at positions overlapping with the selected quantum bit q1 in the z direction, the Meissner effect (magnetic shielding property) of both the magnetic shielding layer 502 of the bimetallic wiring 500 and the magnetic shielding layer 602 of the bimetallic wiring 600 is lost, and the external magnetic field B passes through the magnetic shielding layer 502 and the magnetic shielding layer 602 at those positions. On the other hand, at positions other than those overlapping with the magnetic shielding layer 502 and the magnetic shielding layer 602 in the z direction where the Meissner effect is lost, the external magnetic field B is shielded by the Meissner effect of the magnetic shielding layer 502 and / or the magnetic shielding layer 602. As a result, the quantum device according to the second embodiment can locally apply a relatively strong magnetic field (magnetic field Bz in the z direction) to the selected quantum bit q1, as shown in graph Gr1 in FIG. 5 and graph Gr2 in FIG. 6 . In this way, the quantum device according to the second embodiment can operate the selected quantum bit q1 by controlling the current flowing through the wiring 500 of the first bimetal wiring layer 150 and the wiring 600 of the second bimetal wiring layer 160, thereby locally applying a relatively strong magnetic field to the selected quantum bit q1.

[0048] Furthermore, in the quantum device according to the second embodiment, the bimetallic wiring 500 and wiring 600 are provided with normal conducting wiring 501 and normal conducting wiring 601, thereby mitigating the increase in resistance when the magnetic shielding layer 602 transitions from the superconducting state to the normal conducting state, thereby suppressing the generation of Joule heat.

[0049] The first bimetal wiring layer 150 and the second bimetal wiring layer 160 are provided, for example, on the opposite side of the surface of the silicon substrate 111 (quantum dot formation layer 110) on which the gate electrode is arranged. In order to control the precession of the quantum bit, a high-frequency signal (high-frequency electromagnetic wave) is irradiated onto the quantum bit from the side on which the gate electrode is arranged by a microwave antenna. In order to avoid interfering with this irradiation, it is preferable that the second bimetal wiring layer 160 (and the first bimetal wiring layer 150) be provided on the opposite side of the surface of the silicon substrate 111 (quantum dot formation layer 110) on which the gate electrode is arranged.

[0050] The gap that can be formed using current processes is approximately 50 nm, and in the first embodiment, if the quantum bit spacing is short, there is a possibility that the magnetic field will leak from the gap due to diffraction and reach the unselected quantum bits. Therefore, to achieve a sufficient shielding effect, the quantum bit spacing must be widened, which reduces the integration of the quantum bit array. In contrast, in the second embodiment, unlike the first embodiment, local currents are not applied to orthogonal gate electrodes (SG1, FG2) to generate local magnetic fields to selectively control the quantum bits, so problems caused by magnetic field leakage as in the first embodiment do not occur, improving the accuracy of quantum bit selection and allowing the quantum bit spacing to be shorter than in the first embodiment.

[0051] <Effects> As described above, the quantum device according to the second embodiment of the present invention can improve fidelity while suppressing an increase in Joule heat by selectively changing the state of the magnetic shielding layer 602 .

[0052] Third Embodiment A quantum device control method according to a third embodiment of the present invention will be described. The quantum device control method according to the third embodiment is a control method applied to the quantum device according to the second embodiment. FIG. 8 is a diagram illustrating an apparatus to which the quantum device control method according to the third embodiment is applied. The apparatus includes a refrigerator 800, a control chip 801, wiring 802, and a quantum chip 803. The refrigerator 800 includes a control chip 801 (control device) in a first refrigerator section (e.g., a 4K environment), and a quantum chip 803 electrically connected to the control chip 801 (control chip 801 including a control circuit) via wiring 802 in a second refrigerator section (e.g., an extremely low temperature environment of 0.1K). The quantum chip 803 includes a quantum device according to the second embodiment.

[0053] The control chip 801 includes a voltage measurement unit 804 (voltmeter) for measuring the voltage V between both ends of the magnetic shielding layer 602 of the wiring 600 of the second bimetal wiring layer 160, a current measurement unit 805 (ammeter) for measuring the current flowing through the wiring 802, and a current source 806 (variable current source) for supplying current to the wiring 802 and the wiring 600. The wiring 802 electrically connects the control chip 801 and a specific wiring 600 (sometimes referred to as a "test wiring") of the second bimetal wiring layer 160 of the quantum device included in the quantum chip 803.

[0054] For a quantum device, the current value that causes the superconductor (e.g., TiN) constituting the magnetic shielding layer 602 to transition to normal conduction should be close to the critical current in order to minimize Joule heat. However, the critical current of a superconductor (e.g., TiN) varies greatly depending on factors such as temperature, process, magnetic field, and dimensions, making it difficult to predict at the design stage. Therefore, by providing test wiring for the superconductor (e.g., TiN) within the quantum chip 803 and a voltage measurement unit 804, a current measurement unit 805, and a current source 806 with a variable current magnitude within the control chip 801, it is possible to measure the critical current value when the quantum device is mounted within the refrigerator 800.

[0055] 9 is a diagram illustrating the processing flow executed by the control chip 801. The control chip 801 starts processing at step 900 and proceeds to step 910 to determine whether or not there has been an environmental change. The environmental change is detected, for example, by detecting whether or not there has been a chip replacement or a change in the settings of the external magnetic field. If a chip replacement or a change in the settings of the external magnetic field is detected, it is determined that there has been an environmental change.

[0056] If there is no change in the environment, the control chip 801 determines "NO" in step 910 and executes the process of step 910 again.

[0057] If an environmental change has occurred, the control chip 801 determines "YES" in step 910, executes the processes of steps 930 and 940 described below, and then proceeds to step 950.

[0058] Step 930: The control chip 801 applies a current to the test wiring at the initial value set in step 920.

[0059] Step 940: The control chip 801 measures the current and voltage using the current measuring unit 805 and voltage measuring unit 804, and calculates and stores the resistance value from the measured current and voltage values.

[0060] Step 950: The control chip 801 determines whether the current has reached the critical current. Specifically, the control chip 801 determines whether the resistance value calculated in step 940 has increased significantly since the previous calculation (e.g., whether the increase from the previous resistance value is equal to or greater than a predetermined threshold). If the resistance value calculated in step 940 has not increased significantly since the previous calculation, the control chip 801 determines that the current has not reached the critical current. If the resistance value calculated in step 940 has increased significantly since the previous calculation, the control chip 801 determines that the current has reached the critical current.

[0061] If the current has not reached the critical current, the control chip 801 determines "NO" in step 950 and proceeds to step 960, where it sets the current value of the current to be applied in step 930 to be increased by a predetermined amount from the previously applied current value, and then returns to step 930.

[0062] When the control chip 801 returns to step 930, it applies a current to the test wiring at the current value set in step 960. Thereafter, the control chip 801 executes steps 940 and 950 already described.

[0063] If the current reaches the critical current in step 950, the control chip 801 determines "YES" in step 950 and proceeds to step 970, where it sets the current value (magnitude of the current) applied in step 930 to the critical current value. In other words, the control chip 801 uses the current with the set critical current value as the superconducting state control current for controlling the state of the magnetic shielding layer 502 (602). Note that the control chip 801 may set a current that is a predetermined current value greater than the critical current value.

[0064] Thereafter, the control chip 801 proceeds to step 995 and temporarily ends this processing flow.

[0065] <Effects> As described above, according to the quantum device control method of the third embodiment of the present invention, the critical current value of the magnetic shielding layer 502 (602) in a state in which the quantum device is implemented in the refrigerator 800 is measured with high accuracy, and a current with as small a value as possible is used as the superconducting state control current, thereby making it possible to suppress Joule heat.

[0066] <<Fourth Embodiment>> A quantum information processing device 1000 according to a fourth embodiment of the present invention will be described. As shown in Fig. 10A, the quantum information processing device 1000 includes a quantum processing device 1010 that manipulates electrons, which are quantum bits, a control device 1020 that controls the quantum processing device 1010, and a measurement device 1030 that measures the state of the electrons. The quantum device described above is applied to the quantum processing device 1010.

[0067] The control device 1020 has a quantum bit processing unit 1020a that controls the quantum processing device 1010. The measurement device 1030 is connected to the quantum processing device 1010 and the control device 1020. The measurement device 1030 measures the state of the electrons (quantum bits), such as the number of electrons (quantum bits), related to the electrons output from the quantum processing device 1010, and outputs the measurement result to the control device 1020. The state of the electrons (quantum bits) measured by the measurement device 1030 is the result of the quantum operation.

[0068] 10B is a diagram showing an example of the hardware configuration of the control device 1020. As shown in FIG. 10B, the control device 1020 has, as its hardware configuration, a processor 1021, a main memory device 1022, a secondary memory device 1023, an input / output device 1024, a quantum processing device I / F 1025 that connects to the quantum processing device 1010, and a bus 1026 that connects these. The control device 1020 may be a dedicated circuit that performs specific processing, such as an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a CPLD (Complex Programmable Logic Device).

[0069] The processor 1021 reads data and programs stored in the secondary storage device 1023 into the main storage device 1022 and executes processing defined by the programs. The main storage device 1022 has volatile storage elements such as RAM and is a device that stores programs, data, etc. The secondary storage device 1023 has nonvolatile storage elements and is a device such as an HDD (Hard Disk Drive) or SSD (Solid State Drive) that stores programs, data, etc. A quantum bit processing program 1023a is stored in the secondary storage device 1023. The processor 1021 realizes the quantum bit processing unit 1020a by reading the quantum bit processing program 1023a stored in the secondary storage device 1023 into the main storage device 1022 and executing it.

[0070] The input / output device 1024 includes devices for accepting user operations such as a keyboard and a mouse, and devices for outputting information such as a display, and is capable of accepting operations from the user and presenting information to the user.

[0071] A user inputs the content of an operation using quantum bits to the control device 1020 using the input / output device 1024. The processor 1021 of the control device 1020 executes the processing of the quantum bit processing program 1023a using the content of the operation using quantum bits input by the user. In the processing of the quantum bit processing program 1023a, an operation using quantum bits is performed using the quantum processing device 1010.

[0072] FIG. 11 is a diagram showing an example configuration of a quantum information processing device 1000. The quantum information processing device 1000 includes a quantum chip 1101, an analog chip 1102 that receives control signals for controlling the quantum chip 1101, a digital processing device 1103 that receives control signals for controlling the analog chip 1102, and a dilution refrigerator 1104. The quantum chip 1101 includes a quantum device and peripheral circuits according to the first embodiment. The quantum chip 1101 may also include a quantum device according to the second embodiment. When the quantum device according to the second embodiment is applied to the quantum chip 1101, a quantum device control method according to the third embodiment may also be applied to the quantum chip 1101. The quantum chip 1101 and the analog chip 102 correspond to the quantum processing device 1010 in FIG. 10A, the digital processing device 1103 corresponds to the control device 1020 in FIG. 10A, and the peripheral circuits included in the quantum chip 1101 correspond to the measurement device 1030 in FIG. 10A.

[0073] Dilution refrigerator 1104 is separated by a housing 1105 and a room temperature plate 1106 to separate the air atmosphere outside the dilution refrigerator 1104 from the vacuum atmosphere inside the dilution refrigerator 1104. The degree of vacuum inside the housing 1105 of the dilution refrigerator 1104 is controlled by using a pump device installed outside the dilution refrigerator 1104 to exhaust air through a vacuum tube 1107. Temperature control inside the dilution refrigerator 1104 is achieved by circulating diluted liquid helium through a pulse tube 1108 shown in Figure 11. Figure 11 shows an example in which two pulse tubes 1108 are connected. The diluted liquid helium is a mixture of two isotopes of helium, ３ He and ４ He is liquefied, ３ He phase ４ It was poured into the He phase and diluted.

[0074] In the example of dilution refrigerator 1104 in FIG. 11, multiple metal (mainly oxygen-free copper) plates (plate 1109 (set to -223°C), plate 1110 (set to -269°C), plate 1111, plate 1112, and plate 1113 (set to approximately -273°C)) are installed and stored inside housing 1105 of dilution refrigerator 1104.

[0075] Plates 1111 and 1112 are controlled at a temperature between 4 K (-269°C) and 11 mK (approximately -273°C). The temperature is controlled and maintained in a thermal equilibrium state using temperature control heaters (not shown) mounted on each plate (plate 1109, plate 1110, plate 1111, plate 1112, and plate 1113) and a temperature controller (not shown) installed outside dilution refrigerator 1104 that controls the amount of power input to the temperature control heaters. In the example of FIG. 11 , diluted liquid helium is circulated from pulse tube 1108 to heat sink 1114. This causes plates 1110 and 1113, connected to heat sink 1114, to be cryogenically cooled via heat sink 1114 through which diluted liquid helium circulates. Therefore, plates 1110 and 1113 can be maintained in a cryogenic atmosphere of 10 mK to 100 mK.

[0076] The quantum chip 1101 is mounted on a cooling plate 1115 for the quantum chip 1101, which is arranged below the plate 1113. The cooling plate 1115 is thermally connected to the plate 1113 via four cooling rods 1116 (two of which are not shown). In other words, the heat sink 1114 is a refrigerating tube that cools the cooling plate 1115, which is a metal body, using diluted liquid helium. The cooling plate 1115, which is a metal body, is thermally connected to the plate 1113 via the cooling rods 1116.

[0077] In this embodiment, the quantum chip 1101 is not mounted directly on the plate 1113, but is installed below the plate 1113. The reason for this is to perform quantum operations while applying a static magnetic field (external magnetic field) to the quantum chip 1101. Due to space constraints for arranging the magnet 1117 for generating the static magnetic field in the lowest layer of the dilution refrigerator 1104, the quantum chip 1101 is arranged as shown in FIG. 11 in the configuration example of the dilution refrigerator 1104 of this embodiment. Note that electrical signals required for quantum operations of the quantum chip 1101 are output from a digital processing device 1103 and an analog chip 1102 installed outside the dilution refrigerator 1104, and the control signals among the electrical signals are electrically connected to the quantum chip 1101 via coaxial wiring 1118a and 1118b, and the power supply voltage and power supply current among the electrical signals are electrically connected to the quantum chip 1101 via DC twisted wiring 1118c and 1118d. By using the above-described mounting configuration, the quantum information processing device 1000 can be realized.

[0078] <<Modifications>> The present invention is not limited to the above-described embodiments, and various modifications can be adopted within the scope of the present invention. Furthermore, the above-described embodiments and the following modifications can be combined with each other without departing from the scope of the present invention.

[0079] The features of the second embodiment may be applied to the first embodiment.

[0080] In the first embodiment, the structure (shape and size) of the voids formed in the magnetic shielding layer 130 is not limited to the above. The magnetic shielding layer 130 may have a void, and adjacent magnetic shielding portions 131 may be partially connected to each other.

[0081] In the second embodiment, the first bimetal wiring layer 150 and the second bimetal wiring layer 160 may be disposed above the second gate electrode layer 140, or the first bimetal wiring layer 150 and the second bimetal wiring layer 160 may be disposed between the quantum dot formation layer 110 and the first gate electrode layer 120. In this case, the same effects as those of the second embodiment are achieved.

[0082] In the second embodiment, the bimetallic wiring 500 (600) may be formed of a magnetic shielding layer (single magnetic shielding layer). In this case, the same effect as in the second embodiment is achieved (however, the effect of suppressing Joule heat generation is reduced compared to the second embodiment).

[0083] The present invention can also have the following configuration.

[0084] [1] A quantum device comprising: a quantum dot formation layer including a semiconductor layer having quantum dots arranged in a row; a gate electrode layer including a gate electrode; and a magnetic shielding layer including a plurality of magnetic shielding portions made of a superconducting material, with gaps formed between the magnetic shielding portions.

[0085] [2] The quantum device according to [1], wherein the gate electrode layer includes a first gate electrode layer and a second gate electrode layer each including the gate electrode; the magnetic shielding layer includes a first magnetic shielding layer in which the magnetic shielding portion is arranged along a first direction, and a second magnetic shielding layer in which the magnetic shielding portion is arranged along a second direction perpendicular to the first direction; and when a direction along a normal direction of the quantum dot formation layer is defined as a z direction, the second magnetic shielding layer is arranged on the first magnetic shielding layer in the z direction, the quantum dot formation layer is arranged on the second magnetic shielding layer, the first gate electrode layer is arranged on the quantum dot formation layer, and the second gate electrode layer is arranged on the first gate electrode layer.

[0086] 110... quantum dot forming layer, 111... silicon substrate, 112... SOI layer, 120... first gate electrode layer, 130... magnetic shielding layer, 131... magnetic shielding portion, 140... second gate electrode layer, 150... first bimetal wiring layer, 160... second bimetal wiring layer

Claims

1. A quantum device comprising: a quantum dot-forming layer including a semiconductor layer having quantum dots arranged in a row; a gate electrode layer including a gate electrode that applies a magnetic field to the quantum dots; and a magnetic shielding layer provided between the gate electrode layer and the quantum dot-forming layer, the magnetic shielding layer including a plurality of magnetic shielding portions made of a superconducting material, with gaps formed between the magnetic shielding portions.

2. A quantum device according to claim 1, wherein the gate electrode layer includes a first gate electrode layer and a second gate electrode layer each including the gate electrode, and when the direction normal to the quantum dot formation layer is defined as the z direction, the first gate electrode layer is disposed on the quantum dot formation layer in the z direction, the magnetic shielding layer is disposed on the first gate electrode layer, and the second gate electrode layer is disposed on the magnetic shielding layer.

3. A quantum device according to claim 2, wherein the magnetic shielding portion is provided at a position overlapping the quantum dot in the z direction.

4. A quantum device according to claim 3, wherein the gate electrode of the second gate electrode layer is provided at a position overlapping the magnetic shielding portion in the z direction.

5. A quantum device according to claim 1, wherein the quantum dots are arranged such that the gaps in the magnetic shielding layer are formed along the rows of the quantum dots.

6. A quantum device according to claim 1, wherein the quantum dots are arranged in a two-dimensional array, and the gaps are formed in the magnetic shielding layer so as to align with the array of quantum dots aligned in a first direction and to be perpendicular to the array of quantum dots aligned in the first direction.

7. A quantum device according to claim 2, wherein an external magnetic field is applied to the quantum dot-forming layer in a predetermined direction in a plane perpendicular to the z direction.

8. A quantum device comprising: a quantum dot formation layer including a semiconductor layer having quantum dots arranged in a row; a gate electrode layer including a gate electrode; and a bimetallic wiring layer including a plurality of bimetallic wirings including a magnetic shielding layer made of a superconducting material and a normal conductor layer made of a normal conductor, with gaps formed between the bimetallic wirings.

9. A quantum device according to claim 8, wherein the gate electrode layer includes a first gate electrode layer and a second gate electrode layer each including the gate electrode, and the bimetal wiring layer includes a first bimetal wiring layer in which wiring of the bimetal structure is arranged along a first direction, and a second bimetal wiring layer in which wiring of the bimetal structure is arranged along a second direction perpendicular to the first direction, and wherein, when the direction along the normal direction of the quantum dot formation layer is defined as the z direction, the second bimetal wiring layer is arranged on the first bimetal wiring layer in the z direction, the quantum dot formation layer is arranged on the second bimetal wiring layer, the first gate electrode layer is arranged on the quantum dot formation layer, and the second gate electrode layer is arranged on the first gate electrode layer.

10. A quantum device according to claim 8, wherein the wiring of the bimetal structure is arranged at a position that overlaps with the quantum dots in the z direction, where the direction along the normal to the quantum dot-forming layer is the z direction.

11. A quantum device as defined in claim 9, wherein the quantum dot is formed at a position where the first bimetallic wiring layer and the second bimetallic wiring layer overlap in the z direction, and by selectively passing a current equal to or greater than the critical current of the superconducting material through the bimetallic wiring of the first bimetallic wiring layer and the bimetallic wiring of the second bimetallic wiring layer, the magnetic shielding layer corresponding to the quantum bit is transitioned from a superconducting state to a normal conducting state, thereby controlling the shielding and transmission of an external magnetic field applied to the quantum bit from outside.

12. A quantum device according to claim 11, comprising a control circuit including an ammeter, a voltmeter, and a variable current source for measuring the critical current value at which the magnetic shielding layer transitions from the superconducting state to the normal conducting state when the quantum device is mounted in a refrigerator, and the magnetic shielding layer is connected to the control circuit.

13. A quantum device according to claim 12, wherein the control circuit measures the current flowing through the magnetic shielding layer with the ammeter, measures the voltage of the magnetic shielding layer with the voltmeter, calculates a change in resistance value when the magnitude of the current is changed by the variable current source based on the measured current and voltage, determines the critical current value when the magnetic shielding layer transitions to the normal conducting state based on the change in resistance value, and sets the magnitude of the current to be passed through the magnetic shielding layer to control the shielding and transmission of the external magnetic field applied to the quantum bit from the outside based on the determined critical current value.

14. A quantum information processing device comprising: a control device that controls quantum bits; and a quantum device including quantum dots, wherein the quantum device comprises: a quantum dot-forming layer including a semiconductor layer having the quantum dots arranged in a row; a gate electrode layer including a gate electrode that applies a magnetic field to the quantum dots; and a magnetic shielding layer provided between the gate electrode layer and the quantum dot-forming layer, including a plurality of magnetic shielding portions made of a superconducting material, with gaps formed between the magnetic shielding portions.

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