JP2007250771A - Superconducting quantum multi-bit element and integrated circuit using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconducting quantum multi-bit element in which a quantum tangle state between quantum bits is easily and reliably generated at a high speed, and also to provide an integrated circuit using it. <P>SOLUTION: A plurality of superconducting quantum bit elements 1, 2-N, and a resonator 11 electromagnetically coupled to the inductance of each superconducting quantum bit element, are provided. Each superconducting quantum bit element consists of a superconducting quantum interference device having three Josephson junctions 1d, 1e, 1f, and respective superconducting quantum bit elements 1, 2-N are so arranged that they are not electromagnetically coupled to each other. The quantum tangle state is generated among respective superconducting quantum bit elements 1, 2-N by applying high-frequency pulses to respective superconducting quantum bit elements 1, 2-N. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a superconducting quantum multibit device that can be used in a quantum computer and can generate a entangled state, and an integrated circuit using the same.

  A quantum computer (see Non-Patent Document 1) can perform operations that cannot be performed by a classical computer because states can be superimposed. Theoretically, the quantum computer can perform calculations with a plurality of inputs, and the generation of the superposition state is an indispensable function for the operation of the quantum computer.

  A qubit using superconductivity, in particular, a superconducting quantum interference device, has been proposed as a solid-state quantum arithmetic device for realizing a quantum computer (see Non-Patent Document 2). All operation control of a single qubit using a superconducting quantum interference device has recently been demonstrated (see Non-Patent Document 3). It has been reported that the coherence time of qubits reaches microseconds (see Non-Patent Document 4).

  Recently, an important experiment was carried out in a configuration combining a single qubit and an LC resonator, and the coupling between two qubit systems was shown and the operation of this coupled system in the time domain was reported ( Non-patent document 5).

As a quantum operation element of a quantum computer, it is necessary to realize a so-called entanglement state in which the quantum states of the qubits are entangled with each other as well as the function of superimposing the qubits. The entanglement state is called a quantum entanglement or quantum entanglement state. If the number of qubits is N, and it is used in a entangled state, 2 ^N types of data can be input simultaneously. If the number N of qubits is 40, about 1 trillion input parameters can be calculated simultaneously by a set of arithmetic circuits. As an index indicating the quantum entangled state, concurrence is known (see Non-Patent Document 6).

  Regarding a qubit that generates a entangled state, a superconducting charge quantum multi-bit device in which two superconducting charge qubit devices are coupled by a capacitance device is disclosed in Patent Document 1.

  Non-Patent Documents 7 to 11 propose to generate a entangled state via a virtual level. In the entangled state, the energy of the qubit oscillates between the ground state and the excited state, and this oscillation is called Rabi oscillation. The frequency of this vibration is called the rabbi frequency. In order to generate a entangled state, it has been proposed to use one or more drive frequencies (see Non-Patent Document 8) or to use a variable coupling mechanism (see Non-Patent Documents 9 to 11). Here, the variable coupling mechanism is a mechanism that freely controls the interaction between qubits and qubits in order to generate a entangled state, for example, a high-frequency pulse train composed of a combination of a certain intensity and frequency. Can be used.

JP-A-2005-57068 G. Wendin and 1 other, "Superconducting Qubit", Cond-mat., 0508729 (2005) J. E. Mooij and 5 others, "Josephson Persistent-Current Qubit", SCIENCE, vol. 285, pp. 1036 (1999) T. Kutsuzawa and five others, “Coherent Controll of a Flux Qubit by Phase-shifted Resonant Microwave Pulses”, Appl. Phys. Lett., Vol.87, p.073501 (2005) P. Bertet and 6 others, "Relaxation and Dephasing in a Flux-Qubit", Cond-mat., 0508729 (2005) I. Chiorescu and 5 others, "Coherent Quantum Dynamics of a Superconducting Flux Qubit", Nature, Vol.431, pp.159-162 (2004) W. K. Wotters, "Entanglement of Formation of an Arbitrary State of Two Qubits", Phys. Rev. Lett., Vol.80, p.2245 (1998) A. Sorensen and 1 other, "Multiparticle Entanglement of Hot Trapped Ions", Phys. Rev. Lett., Vol.82, p.1971 (1999) C. Rigetti and two others, "Protocol for Universal Gates in Optimally Biased Superconducting Flux Qubit", Phys. Rev. Lett., Vol.94, p. 240502 (2005) L. F. Wei and 2 others, "Quantum Computation with Josephson Qubits Using a Current-biased Information Bus", Phys. Rev. B, Vol.71, p.134506 (2005) D. A. Averin and 1 other, "Variable Electrostatic Transformer: Controllable Coupling of Two Charge Qubits", Phys. Rev. Lett., Vol.91, p.057003 (2003) B. L. T. Plourde and 9 others, "Entangling flux qubits with a bipolar dynamic inductance", Phys. Rev. B, Vol.70, p.140501 (2004)

  However, in the case of the conventional quantum arithmetic elements proposed in Non-Patent Documents 8 to 11, a plurality of high-frequency pulse sources are required to generate a entangled state between two qubits, In order to realize the entangled state, there is a problem that the configuration becomes complicated.

  In view of the above problems, the present invention provides a superconducting quantum multibit device capable of generating a entangled state between qubits in a fast, simple and reliable manner, and an integrated circuit using the same. The purpose is to provide.

In order to achieve the above object, a superconducting quantum multibit device of the present invention comprises a plurality of superconducting qubit devices and a resonator that is electromagnetically coupled to the inductance of each superconducting qubit device. The qubit device is composed of superconducting quantum interference devices having three Josephson junctions, and each superconducting qubit device is arranged so as not to be electromagnetically coupled to each other, and by applying a high frequency pulse to each superconducting qubit device. A entangled state is generated between the superconducting qubit devices.
In the above configuration, preferably, a line is provided that is electromagnetically coupled to the inductance of each superconducting qubit element and that transmits a high-frequency pulse.

  In the above configuration, preferably, the resonance frequency of the resonator is a frequency that does not resonate with the energy of each superconducting qubit device, and the high-frequency pulse includes a frequency corresponding to the sum of the energy of the two superconducting qubit devices.

  Also preferably, the entangled state is controlled in proportion to the degree of electromagnetic coupling between the resonator and each superconducting qubit device or the power amplitude of the high frequency pulse.

  According to the above configuration, a entangled state between superconducting qubit devices composed of superconducting quantum interference devices having three Josephson junctions can be generated quickly, easily and reliably.

The integrated circuit using the superconducting quantum multibit device of the present invention includes a plurality of superconducting qubit devices, a resonator that electromagnetically couples to the inductance of each superconducting qubit device, and the quantum state of each superconducting qubit device. Each of the superconducting qubit devices is composed of a superconducting quantum interference device having three Josephson junctions, and the superconducting qubit devices are arranged so as not to be electromagnetically coupled to each other. In addition, a entangled state is generated between each superconducting qubit device by applying a high frequency pulse to each superconducting qubit device.
In the above configuration, preferably, a line capable of electromagnetically coupling with the inductance of each superconducting qubit element and transmitting a high-frequency pulse is provided.
According to the above configuration, a entangled state between superconducting qubit devices composed of superconducting quantum interference devices having three Josephson junctions can be generated quickly, easily and reliably, and each superconducting quantum An integrated circuit including a readout circuit of a quantum state of a bit element can be provided.

In the above configuration, preferably, the readout circuit is configured by a superconducting quantum interference device including two Josephson junctions electromagnetically coupled to the superconducting qubit device.
According to this configuration, a entangled state can be generated between the superconducting qubit devices, and the quantum state of each superconducting qubit device can be read out by the reading circuit arranged adjacently.

  According to the superconducting quantum multibit device of the present invention, each superconducting qubit device has a simple configuration consisting of three Josephson junctions, and a entangled state is formed by a resonator that is electromagnetically coupled to each superconducting qubit device. Can be generated at high speed and with high reliability.

  In addition, according to the integrated circuit using the superconducting quantum multibit device of the present invention, the quantum state of each superconducting qubit device can be read out by a readout circuit arranged close to each superconducting qubit device. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same or corresponding members are denoted by the same reference numerals.
First, a superconducting quantum multibit device according to the present invention will be described.
FIG. 1 is a schematic plan view showing a configuration of a superconducting quantum multibit device according to the present invention. As shown in the figure, a superconducting quantum multibit device 10 of the present invention includes superconducting qubit devices 1 and 2 to N made of superconducting quantum interference devices, and inductances 1a and 2a located above each superconducting qubit device. And the resonator 11 that is electromagnetically coupled (also referred to as inductive coupling) via Na. And the 2nd track | line 14 mentioned later which is electromagnetically coupled via the mutual inductance 1b and 2b-Nb under each superconducting qubit element 1,2-N is arrange | positioned. A high frequency pulse source 12 is applied to the second line 14.
Here, the high-frequency pulse source 12 is a power source that applies a microwave frequency from a high frequency to the second line 14, that is, a power supply. The high-frequency pulse source 12 may be any power source capable of generating a high-frequency pulse or pulse train. In the following description, the high-frequency pulse power source 12 will be described as a high-frequency pulse generator.

  Each of the superconducting qubit devices 1, 2 to N is a superconducting quantum interference device having three Josephson junctions. The superconducting qubit device 1 is formed of a thin wire 1c made of a ring or a rectangular shape made of a superconducting material, and three Josephson junctions 1d, 1e, and 1f. Each Josephson junction 1d, 1e, and 1f has a structure in which a thin insulating film that becomes a tunnel junction is sandwiched between thin wires 1c made of a superconducting material. The superconducting qubit elements 1, 2 to N used in the present invention operate at a temperature showing superconductivity.

  The superconducting qubit elements 1, 2 to N are arranged so as not to be electromagnetically coupled to each other. In this case, the distance between adjacent superconducting qubit elements 1, 2 to N is separated, or the total length of the thin wires made of superconductors constituting each superconducting qubit element 1, 2 to N is appropriately designed. Thus, unnecessary electromagnetic coupling between the superconducting qubit elements 1 and 2 to N can be reduced. Specifically, when the superconducting qubit device 1 is a rectangle having a side of about 10 μm, a current of 1 μA is passed, and the interval between adjacent superconducting qubit devices 2 is 10 μm. At this time, the magnitude of the electromagnetic coupling between the adjacent superconducting qubit elements 1 and 2 is about 1/100 or less when they are arranged close to each other. Therefore, the adjacent superconducting qubit elements 1 and 2 can be handled as having substantially no electromagnetic coupling.

  The resonator 11 can be composed of a resonator portion 11a and a first line portion 11b provided on or adjacent to the insulating film covering the superconducting qubits 1 and 2 to N. In the illustrated case, the resonator 11 is an LC resonator. One ends of the capacitor (C) and the inductance (L) are connected to each other, and the other ends that are not connected are connected to the line portion 11b. In this case, the equivalent inductance 11c in the first line portion 11b and the inductances 1a and 2a to Na at the top of each superconducting qubit element are electromagnetically coupled.

  Here, the resonator 11 can be configured by an LC resonator, a distributed constant resonator, a resonator including a lumped constant component and a distributed constant component, and the like.

  The high-frequency pulse generator 12 for qubit operation is composed of a resonator composed of an LC resonator or a distributed constant resonator, an active element, and the like. It can comprise from the 2nd track | line 14 provided adjacently. A high frequency pulse is sent from one end of the second line 14 from the high frequency pulse generator 12, and a high frequency pulse is applied to each superconducting qubit element 1, 2 to N. In this case, a high-frequency pulse having a predetermined intensity is electromagnetically coupled for a predetermined time via the equivalent inductance 14a in the second line 14 and the mutual inductances 1b and 2b to Nb in each superconducting qubit element. It becomes possible to manipulate the quantum states of the conduction qubits 1, 2 to N.

An important feature of the superconducting quantum multibit device 10 of the present invention is that each superconducting qubit device 1, 2 to N is electromagnetically coupled to a common resonator 11 with an electromagnetic coupling degree λ _i. The superconducting qubit devices 1, 2 to N are electromagnetically coupled to each other only very weakly. In the present invention, the superconducting qubit elements 1, 2 to N are electromagnetically coupled very weakly, and the superconducting qubit elements 1, 2 to N are substantially not electromagnetically coupled.

In the superconducting quantum multibit device 10 of the present invention, the following is performed in order to generate a entangled state in the superconducting qubit devices 1, 2 to N. The case of superconducting qubit devices 1 and 2 will be described below.
The resonance frequency (f _res ) of the resonator 11 is set so that it does not resonate with the energies E ₁ and E ₂ of the superconducting qubit elements 1 and ₂ . In the superconducting quantum multibit devices 1 and 2 to 2 including two or more superconducting qubit devices, other amounts of the superconducting qubit devices 3 to N are prevented from being in a resonance state.

  Since the energy states of the superconducting qubit elements 1, 2 to N can be adjusted by applying a static magnetic field from the outside, a resonance state different from the resonance frequency of the resonator 11 can be obtained. The application of the static magnetic field may be performed by applying a stable pulse magnetic field that can be regarded as a constant magnetic field to each superconducting qubit element 1, 2 to N until the entire calculation is completed. Such a pulsed magnetic field can be generated by passing a rectangular wave current through a wiring arranged close to the superconducting quantum multibit device 10.

  Also, it is difficult to manufacture completely the same superconducting qubit devices 1, 2 to N, and the fact that some fluctuations occur in the energy between the superconducting qubit devices 1, 2 to N The energy of each superconducting qubit device 1, 2 to N can be designed to be different from the resonance frequency of the resonator 11.

  The quantum states of the superconducting qubit devices 1, 2 to N of the present invention are controlled by, for example, Rabi oscillation by a resonance microwave by applying a pulse from the high-frequency pulse generator 12 through the second line 12b. The

FIG. 2 is an energy level diagram schematically illustrating the entangled state of the superconducting quantum multibit device 10 of the present invention. As shown in the figure, in the superconducting quantum multibit device 10 of the present invention, the frequency of the high-frequency pulse generator 12 is the energy (E _The frequency f _ext is equivalent to the sum of _qb1 and E _qb2 ). The high frequency pulse generator 12 either generates f _ext, or a high-frequency pulse suffices generation comprising at least f _ext.
This energy relationship is given by the following equation (1).
Here, h is a Planck's constant (6.626068 × 10 ⁻³⁴ J · s).

The minimum energy gap of the superconducting qubit elements 1, 2 to N is energy corresponding to 1 to 6 GHz as a frequency. When used as a superconducting qubit, the energy separation of the quantum two levels is energy corresponding to approximately 1 to 15 GHz as a frequency. The frequency f _ext of the high-frequency pulse generator 12 depends on the structure and dimensions of the superconducting quantum multi-bit devices 1 and 2 to N, but is about 1 to 10 GH, typically several GHz.

In the entangled state, the energy levels in the two superconducting qubit devices 1 and 2 are the ground state (| g, g, 0>) and the excited state (| e, e, 0>) in the coherent state. Transition between. The maximum entangled energy level Ψ in the intermediate state is given by the following equation (2).

Further, the energy levels of the two superconducting qubit devices are represented by | qubit ₁ , qubit ₂ , i>. In this case, the ground state is represented as g, the excited state is represented as e, and the Fock state of the resonator 11 is represented as i.
Here, the Fock state display is a method of designating how many resonance quanta are excited in the resonator 11. | 0> is a vacuum state where there is no resonance quantum, that is, a ground state. | 1> indicates a state in which one resonance quantum exists, and | n> indicates a state in which n resonance quanta exist.

FIG. 3 is a diagram showing numerical calculation results of the energy dependence and concurrence time dependence of the entangled state in the superconducting quantum multibit device of the present invention. In FIG. 3, the horizontal axis indicates the application duration (ns) of the resonant high-frequency pulse, the left vertical axis indicates the energy of the entangled state (arbitrary scale), and the right vertical axis indicates the concurrence (C).
The energy of the i-level superconducting qubit device on the left vertical axis is expressed by the following equation (3).
Here, i is 1 or 2.
The concurrence (C) shown on the right vertical axis is represented by the following formula (4).
Where Ψ is the state function of the two qubit (1,2) coupled system, Ψ ^* is the complex conjugate of Ψ, and the terms related to σ _y are the y-direction spins for qubits 1 and 2, respectively. It is an operator.

  In FIG. 3, it can be seen that the energy of the superconducting qubit device makes a coherent transition from the ground state to the excited state. The maximum entangled energy level Ψ is indicated by black circles (see ● in FIG. 3) in FIG.

  It can be seen that concurrence (C), which is an index of entanglement shown on the right vertical axis, approaches 1 in the application duration at which the energy level Ψ is entangled to the maximum.

  In the numerical calculation result of this time transition, very strong excitation is performed so that the maximum entangled energy level Ψ is generated in 22 ns. In the case of such strong excitation, the concurrence (C) at the time when 22 ns elapses reaches 0.95. In this case, the reason why the concurrence (C) does not reach 1 is that when strong excitation is performed, the ground state (| g, g, 0>) transitions to the excited state (| e, e, 0>). This is because | g, g, 1>, which is a state in which one quantum is excited, is excited to the resonator 11 having a close energy value. By lowering the excitation, it is possible to prevent this decrease in concurrence (C). In this case, the stronger the excitation of the resonant high frequency or resonant microwave pulse, the greater the Rabi frequency, and the shorter the time required to generate the maximum entangled state.

  The generation time of 22 ns is very short as compared to 100 to 1000 ns, which is a coherent time of a single qubit. The exact coherent time of a qubit exhibiting superconductivity is not yet known.

  The Rabi frequency for the transition from the desired ground state to the excited state (| g, g, 0> → | e, e, 0>) depends on the interaction between the superconducting qubit elements 1, 2 and the resonator 11. Determined by. If there is no interaction, no transition occurs.

In the above-described quantum entangled state of the present invention, an equation for giving a Rabi frequency was found in the electromagnetic coupling between the resonator 11 and each of the superconducting qubit elements 1 to 2 -N.
By obtaining a second-order perturbation expansion equation that gives the lowest contribution, the lowest contribution (Ω _Rabi ) of the _Rabi frequency is given by the following equation (5).
Here, λ ₁ is the degree of electromagnetic coupling between the superconducting qubit device 1 and the resonator 11, and λ ₂ is the degree of electromagnetic coupling between the superconducting qubit device 2 and the resonator 11, A is the power amplitude of the high-frequency pulse generator 12.

Λ ₁ , which is the degree of electromagnetic coupling between the superconducting qubit device 1 and the resonator 11, is an inductance 1 a at the top of the superconducting qubit device 1 and an inductance 11 c of a line portion connected to the resonator 11. Is the degree of electromagnetic coupling.
In order to change the electromagnetic coupling degree λ ₁ , the adjacent distance between the superconducting qubit element 1 and the inductance 11c of the line portion is separated, or the total length of the thin wires made of the superconductor constituting the superconducting qubit element is set. What is necessary is just to design suitably. Similarly, in the case of the superconducting qubit elements 2 and 3 to N, λ ₂ that is the degree of electromagnetic coupling with the resonator 11 can be changed.

The above equation (5) shows that the rabbi frequency is proportional to λ ₁ and λ ₂ and proportional to the power amplitude of the high-frequency pulse generator 12. In this case, the rabbi frequency is, for example, about several MHz to GHz, and typically about 10 MHz.

  From the above calculation results, according to the superconducting quantum multibit device 10 of the present invention, since the Rabi frequency is proportional to the power amplitude of the high-frequency pulse generator 12, compared with the cases reported in Non-Patent Documents 7 to 11, It has an excellent feature that a quantum entangled state is generated very quickly. In the conventional case, a plurality of high-frequency pulse generators are used to form a entangled state via a virtual level, but the rabbi frequency is proportional to the square of the excitation microwave amplitude. Therefore, as in the superconducting quantum multibit device of the present invention, the Rabi frequency is slower than the case where the Rabi frequency is proportional to the excitation microwave amplitude.

  Furthermore, the superconducting quantum multibit device 10 of the present invention has an excellent feature that the device configuration and the structure of the pulse series are simple. In the case of the prior arts of Non-Patent Documents 7 to 11, a plurality of driving frequencies and / or adjustable couplers required to operate two qubits are used. In contrast, the superconducting quantum multibit device 10 of the present invention does not require a plurality of drive frequencies and / or variable coupling mechanisms.

As described above, the superconducting quantum multibit device 10 of the present invention described above can realize a entangled state between the superconducting qubit devices 1, 2 to N.
Next, a method for initializing each superconducting qubit device and realizing an arbitrary superposition state will be described.
(1) Initialization of superconducting qubit devices 1, 2 to N:
Initialization of the superconducting qubit elements 1 and 2 to N can be realized by leaving them to stand for a predetermined time in a state of being cooled to a cryogenic temperature at which the superconducting state is achieved, for example, 20 mK.
(2) Arbitrary superposition state in each of the superconducting qubit devices 1, 2 to N:
Using a resonant high frequency pulse tuned to the energy level difference of the superconducting qubit devices 1 and 2 to N, a Rabi oscillation is generated, and the duration (pulse width) of the resonant high frequency pulse is changed. Any superposition (rotation) control of the state of the superconducting qubit can be performed. Alternatively, by using a plurality of phase-modulated high-frequency pulses, arbitrary superposition control of the state of a superconducting qubit represented by a Hadamard gate can be performed.

  FIG. 4 is a schematic plan view showing the configuration of the integrated circuit 30 using the superconducting quantum multibit device 10 according to the present invention. As shown in the figure, an integrated circuit 30 using the superconducting quantum multibit device 10 of the present invention is placed above the superconducting qubit devices 1, 2 to N of the superconducting quantum multibit device 10 shown in FIG. An element coupled to certain inductances 1 a and 2 a to Na is added as a readout circuit 20. The read circuit 20 may be anything as long as it can read the quantum states of the superconducting qubit elements 1, 2 to N.

  In the illustrated case, the readout circuit 20 is composed of superconducting quantum interference elements 21, 22 to 2N. The superconducting quantum interference device 21 is a SQUID having two so-called Josephson junctions, which are formed of a thin wire 21c made of a superconducting material, such as a ring shape or a rectangular shape, and two Josephson junctions 21a and 21b. is there. The other superconducting quantum interference elements 22 to 2N have the same structure. The superconducting quantum interference devices 21, 22 to 2N are provided with electrodes, for example, 21d, 21e, and 21f. Each superconducting quantum interference device 21, 22-2N is electromagnetically coupled to the inductances 1a, 2a-Na above the respective superconducting qubit devices 1, 2-N via inductances 21g, 22g-2Ng, respectively. is doing.

A read operation of the read circuit 20 will be described.
A bias current is applied to the current terminals 21d, 21e, and 21f of the superconducting quantum interference device. It is possible to read out the quantum state of the superconducting qubit device 1 of the superconducting quantum multibit device 10 by measuring a current value (switching current) that generates a finite voltage when the bias current is increased. it can. In the case of the other superconducting quantum interference devices 22 to 2N, the quantum states of the superconducting qubit devices 2 to N can be read in the same manner.

The superconducting quantum multibit device 10 and the integrated circuit 30 according to the present invention having the above-described configuration can be manufactured as follows.
First, a superconductor having a predetermined thickness to be the superconducting quantum multibit device 10 and the readout circuit 20 is deposited on an insulating substrate by sputtering. A thin line that becomes the superconducting quantum multibit device 10 and the readout circuit 20 is formed by selective etching using a mask. In this case, the superconductor in the region where the insulator of the superconducting quantum multibit device 10 and the readout circuit 20 is formed is also etched.
As the superconductor, a material made of high temperature superconductor such as aluminum, niobium, niobium nitride, lead, magnesium diboride (MgB ₂ ) or copper oxide superconductor can be used. As the copper oxide superconductor, a compound composed of Bi, Sr, Ca, Cu and O (BSCCO), a compound composed of Y, Ba, Cu and O (YBCO), a compound composed of La, Sr, Cu and O ( LSCO).

Next, an insulating film material such as an alumina oxide film that becomes an insulator having a predetermined thickness used for the Josephson junction is deposited by a sputtering method or a CVD method. When aluminum is deposited, it may be oxidized to form an alumina oxide film. Then, excess insulator is removed by selective etching. In this step, a superconducting quantum interference device used for the superconducting quantum multibit device 10 and the readout circuit 20 is formed.
Aluminum oxide can be used as the insulating film of the Josephson junction. In c-axis oriented BSCCO, which is a copper oxide superconductor, an intrinsic Josephson junction made of a BaO layer may be used.

Next, an insulating film having a predetermined thickness is deposited on the entire surface of the substrate by sputtering or the like.
Finally, the line 13 of the resonator 11 and the line 14 of the high-frequency pulse generator 12 for electromagnetic coupling with predetermined locations of the superconducting qubit elements 1, 2 to N on the insulating film are deposited or selected by a metal film. It is formed by an etching method or the like.
For the deposition of each material, an ordinary thin film forming method such as an evaporation method, a laser ablation method, or an MBE method can be used in addition to the sputtering method and the CVD method. Moreover, light exposure, EB exposure, etc. can be used for the mask process for forming a Josephson junction of a predetermined shape, a line, and a current terminal.

  The superconducting quantum multibit device 10 and the resulting resonator 11, high-frequency pulse generator 12, or second line 14 in the integrated circuit 30 can be externally attached to the integrated circuit 30. In addition, when a semiconductor substrate such as Si having an insulating film is used as the insulating substrate, the resonator 11 composed of a passive component such as an LC resonator composed of a capacitor and an inductance and a distributed constant resonator is disposed on the same substrate. It may be integrated. Similarly, the high-frequency pulse generator 12 including passive components such as various types of transistors, LC resonators including capacitors and inductances, and distributed constant resonators may be integrated on the same substrate.

  The entangled state in the superconducting quantum multibit device 10 of the present invention applies not only to two superconducting qubit devices, but also to many superconductors connected to the common resonator 11 and the line 14 for the high-frequency pulse generator 12. It can be applied between any pair with a conducting qubit device.

Hereinafter, the present invention will be described in more detail based on examples.
As an example, an integrated circuit 30 using a superconducting quantum multibit device was manufactured. A superconducting quantum multibit device 10 using a niobium (Nb) superconducting material and an aluminum oxide as an insulating film and a readout circuit 20 using a SQUID were integrated on a substrate. The size of the superconducting quantum multibit device and the SQUID was a square pattern of 5 μm × 5 μm to 40 μm × 40 μm, and the thin line width was 0.3 μm.

  5A is a view showing a scanning electron microscope image of the integrated circuit 30 using the superconducting quantum multibit device of the embodiment, and FIG. 5B is an explanatory view of FIG. In the illustrated case, an enlarged image of one superconducting qubit device and its readout SQUID is shown. As is apparent from FIG. 5, a SQUID 21 for reading having a size of 13 μm × 13 μm is arranged around the superconducting quantum element 1 having a size of 10 μm × 10 μm.

  The present invention is not limited to these examples, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these are also included in the scope of the present invention. .

It is a typical top view which shows the structure of the superconducting quantum multibit device by this invention. It is an energy level figure which illustrates typically the quantum entanglement state of the superconducting quantum multibit device of the present invention. It is a figure which shows the numerical calculation result of the time dependence of the energy of a entanglement state and concurrence in the superconducting quantum multibit device of this invention. It is a typical top view which shows the structure of the integrated circuit using the superconducting quantum multibit element by this invention. (A) is a figure which shows the scanning electron microscope image of the integrated circuit by the superconducting quantum multibit element of an Example, (B) is explanatory drawing of (A).

Explanation of symbols

1, 2 to N: Superconducting qubit element 1a, 2a to Na: Inductance 1b above the superconducting qubit element, 2b to Nb: Inductance 1c below the superconducting qubit element: Superconducting wire 1d, 1e, 1f, 21a, 21b: Josephson junction 10: Superconducting quantum multibit device 11: Resonator 11a: Resonator unit 11b: Line unit 11c: Equivalent inductance 12 in the line unit 12: High-frequency pulse generator 14: Second line 14a: Equivalent inductance 20 in second line 20: Read-out circuits 21, 22 to 2N: Superconducting quantum interference device (SQUID)
21c: Fine wires 21d, 21e, 21f made of superconducting material: Current terminals 21g, 22g-2Ng: Inductance 30: Integrated circuit

Claims (7)

A plurality of superconducting qubit devices;
A resonator that electromagnetically couples to the inductance of each of the superconducting qubit devices;
With
Each of the superconducting qubit devices comprises a superconducting quantum interference device having three Josephson junctions,
The superconducting qubit devices are arranged so as not to be electromagnetically coupled to each other,
A superconducting quantum multi-bit device, wherein a quantum entangled state is generated between each superconducting qubit device by applying a high-frequency pulse to each superconducting qubit device.   The superconducting quantum multibit device according to claim 1, further comprising a line that electromagnetically couples with the inductance of each of the superconducting qubit devices and through which the high-frequency pulse is transmitted.   The resonance frequency of the resonator is a frequency that does not resonate with the energy of each superconducting qubit device, and the high-frequency pulse includes a frequency corresponding to the sum of the energy of two superconducting qubit devices. The superconducting quantum multibit device according to claim 1 or 2.   The entangled state is controlled in proportion to the degree of electromagnetic coupling between the resonator and each superconducting qubit device or the power amplitude of the high-frequency pulse. Superconducting quantum multibit device. A plurality of superconducting qubit devices;
A resonator that electromagnetically couples to the inductance of each of the superconducting qubit devices;
A readout circuit for reading out the quantum state of each superconducting qubit device;
With
Each of the superconducting qubit devices comprises a superconducting quantum interference device having three Josephson junctions,
The superconducting qubit devices are arranged so as not to be electromagnetically coupled to each other,
An integrated circuit using a superconducting quantum multibit device, wherein a quantum entangled state is generated between the superconducting qubit devices by applying a high frequency pulse to each of the superconducting qubit devices.   6. The superconducting quantum multibit device according to claim 5, further comprising a line that electromagnetically couples with the inductance of each of the superconducting qubit devices and through which the high-frequency pulse is transmitted. 6. The superconducting quantum multibit device according to claim 5, wherein the readout circuit is constituted by a superconducting quantum interference device having two Josephson junctions electromagnetically coupled to the superconducting qubit device. Integrated circuit using.