JP2003067181A - Quantum computer and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To arbitrarily control the mutual action between quantum bits in operation of a quantum computer. SOLUTION: A Josephson joint field effect transistor (JOFET) 102 is used as a switching means for switching (turning on and off a superconducting current) a magnetic flux transfer device 101 constructed by a superconductor between the flowing state of superconducting current and the no-flowing state. The mutual action between magnetic flux quantum bits 104a, 104b is arbitrarily controlled to realize the quantum entangled state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum computer using qubits and a control method therefor.

[0002]

2. Description of the Related Art Since "P.W.Shor" showed in 1995 that a large number of factorizations can be calculated with quantum computation at an overwhelming speed compared to a classical computer, a quantum computer has been developed. The theory and experiments have rapidly progressed. In quantum computers, qubits correspond to classical computer bits. Further, the input, operation, and output in the classical computer correspond to the preparation of the initial state of the system, the time evolution of the system, and the readout of the system in the quantum computer. A general explanation of quantum computers is given in Reference 1, “Akio Hosoya,“ Basics of Quantum Computers ”, Science Co. (1999)”.

A quantum bit, which is a basic element in a quantum computer, is represented by a superposition state of | 0> state and | 1> state in quantum mechanics. This condition is experimentally
Regarding the quantum two-level system, quantum computers using various quantum two-level systems have been proposed. These proposals can be divided into those using solid-state elements and those not using solid-state elements. A solid-state device is advantageous in that it can be easily integrated, but it is difficult to maintain a quantum state because of the influence of the environment around the device. On the other hand, if it is not a solid-state element, it is difficult to integrate it, but it is not easily affected by the surrounding environment.

The magnetic flux qubit is a kind of qubit using a solid-state element, but it uses a superconductor for the element and is considered to be less susceptible to the environment due to the existence of the superconducting gap. A charge qubit using a superconductor has also been proposed, but since magnetic flux noise is smaller than electric charge noise, the magnetic flux qubit is also advantageous in this respect. Therefore, the magnetic flux qubit is
It is considered to be an ideal qubit that is advantageous for integration and is not easily affected by the environment.

The operation in the quantum computer is the time evolution of the quantum system. It has been shown in principle that all operations can be performed if an operation called a phase shifter that is an operation of one quantum bit and an operation called a control NOT that is an operation of two quantum bits can be performed. The operation of two qubits requires that the two qubits be in a quantum entangled state. This requires an interaction between the two qubits.

[0006]

However, in the quantum computers proposed so far, it is usually not possible to arbitrarily turn this interaction on or off. For example, the NM currently realized with the largest number of qubits
In the R quantum computer, a qubit is a nuclear spin, and an interaction between qubits is an interaction between nuclear spins. This interaction is determined by what kind of molecule is selected as an element, and the interaction between nuclear spins always exists.

Therefore, in the NMR quantum computer, there is always interaction between the qubits. Considering that the operation in the quantum computer is the time evolution of the system, the fact that the interaction always exists means that the operation is always performed between bits. This is not preferable for performing an arbitrary operation, and in order to perform an arbitrary operation, another operation that cancels the interaction between qubits that is always performed is required (Reference 1).
(See Chapter 5).

The present invention has been made to solve the above problems, and an object of the present invention is to make it possible to arbitrarily control the interaction between quantum bits in the operation of a quantum computer.

[0009]

A quantum computer according to one aspect of the present invention includes two magnetic flux qubits and two magnetic flux qubits.
A magnetic flux transfer device that interacts between two magnetic flux qubits is provided, and in addition, switching means that turns on and off the superconducting current flowing in the magnetic flux transfer device is provided. According to this quantum computer, the interaction between two magnetic flux qubits that interact with each other due to the flow of a superconducting current is controlled by turning on and off the magnetic flux transfer device by the switching means.

In the above quantum computer, the switching means is composed of a Josephson junction field effect transistor, heating means for heating a part of the magnetic flux transfer device, or a superconductor provided in a part of the magnetic flux transfer device. It may be any of the mechanical switches.

The control method of the quantum computer according to one aspect of the present invention includes two magnetic flux qubits and the two magnetic flux qubits.
The operation of a quantum computer provided with a magnetic flux transfer device that causes an interaction between two magnetic flux qubits is controlled by turning on and off a superconducting current flowing in the magnetic flux transfer device. According to this control method, the interaction between the two magnetic flux qubits that interact with each other due to the flow of the superconducting current is controlled by turning on and off the magnetic flux transfer device.

In the control method of the quantum computer, the on / off of the superconducting current flowing in the magnetic flux transfer device is performed by, for example, heating a Josephson junction field effect transistor or a part of the magnetic flux transfer device, or It may be performed by using one of the mechanical switches provided in part.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing an example of a partial configuration of a quantum computer according to an embodiment of the present invention. The reference numerals in FIG. 1 will be described. First, 101 is a magnetic flux transfer device (flux transformer) composed of a superconductor, and 102 is a Josephson junction field effect transistor (JOFET: switching means).
And the electrode parts 101a and 101b of the magnetic flux transfer device 101.
Connected to.

Further, 103 is a gate wiring connected to the gate electrode of a Josephson junction field effect transistor (JOFET), 104a and 104b are magnetic flux qubits, 10
5 is the SQUID (Super
Conducting Quantum Interference Device (reading means) 106a and 106b are control lines that control the state of each magnetic flux qubit by creating a magnetic field.

Further, 114 and 115 are Josephson junctions composed of tunnel insulating portions. These are formed on a semiconductor substrate (not shown) via an insulating film, and the magnetic flux qubits 104a and 104b and the SQUID 105 are formed.
May be made of a material such as aluminum or niobium that exhibits superconductivity at low temperatures. . Similarly, the magnetic flux transfer device 101 may be made of niobium.
Further, the magnetic flux qubits 104a and 104b are, for example,
Formed in about 5 μm square

With this configuration, the magnetic flux generated by the magnetic flux qubits 104a and 104b is generated by the SQUID 10
5, it is possible to detect whether the state of the magnetic flux qubits 104a and 104b is the | 0> state or the | 1> state.

It should be noted that one using three Josephson junctions
For two magnetic flux qubits, see Reference 2 “JE Mooij, T.
P.Orlando, L.Levitov, Lin Tian, Caspar H.van der Wal,
SethLIoyd, “Josephson Persistent-Current Qubit”, Sc
ience 285 (1999) 1036 ", Reference 3" TP Orlando, JEMoo
ij, Lin Tian, Caspar H. van der Wal, LSLevitov, Seth
Lloyd, JJMazo, “Superconducting persistent-curren
t qubit ", Physical Review B60 (1999) 15398", Reference 4
`` Caspar H. van der Wal, ACJter Haar, FK Wilhelm,
RNSchouten, CJPMHrmans, TPOrlando, Seth Lloy
d, JEMooij, "Quantum Superposition of Macroscopic
Persistent-Current States ", Science 290 (2000) 773"
It is described in.

The states of the magnetic flux qubits 104a and 104b show magnetic field dependence (see FIG. 1 of Document 4). Therefore, the state of one magnetic flux qubit can be controlled to the | 0> state, the | 1> state, or the quantum mechanical superposition state by the magnetic field applied from the outside. The control of the states of the magnetic flux qubits 104a and 104b can be performed by passing a current through the control lines 106a and 106b and generating a magnetic field around them.

Control line 106a and control line 10
The magnetic field generated around 6b is proportional to the currents flowing in the control line 106a and the control line 106b and inversely proportional to the distance from the control line 106a and the control line 106b. Therefore, the states of the magnetic flux qubit 104a and the magnetic flux qubit 104b are changed. Can be controlled individually with good operability.

In FIG. 1, the magnetic flux qubits 104a, 10a
Although 4b is shown by using three Josephson junctions, the operation of the magnetic flux transfer device 101 using the JOFET in the present invention is the same in the case of other magnetic flux qubits. As an example for other flux qubits, 1
There are magnetic flux qubits using two Josephson junctions.
This is document 5 “Jonath AN R. Fried-man, Vijay Patel, WC.
hen, SK, Tolpygo, JELukens, “Quantum superposition
Macro-scopic states ", Nature 406 (2000) 43".

Two magnetic flux qubits 104a, 104b
Has a magnetic interaction through the current flowing through the magnetic flux transfer unit 101, and has two magnetic flux qubits 104a and 104a.
An entangled state of b can be realized. FIG. 2 schematically illustrates this magnetic interaction. In FIG. 2, a magnetic flux transfer device 101 made of a superconductor is connected to two magnetic flux qubits 104.
The state sandwiched by a and 104b is equivalently shown.

The self-inductances of the magnetic flux qubit 104a, the magnetic flux qubit 104b, and the magnetic flux transfer device 101 are L ₁ , L ₂ , and L _T , respectively. Also, the magnetic flux qubit 104
The mutual inductance between a and the magnetic flux transfer device 101 is M ₁ , and the mutual inductance between the magnetic flux qubit 104 b and the magnetic flux transfer device 101 is M ₂ .

The magnetic interaction between the magnetic flux qubit 104a and the magnetic flux qubit 104b will be considered below. Now, assuming that the magnetic flux in the magnetic flux qubit 104a has changed by ΔΦ ₁ , this change in magnetic flux is caused by the magnetic flux qubit 1
The self-inductance L ₁ of 04a causes a change in current ΔI ₁ = ΔΦ ₁ / L ₁ in the flux qubit 104a.

The change ΔI ₁ in the current in the magnetic flux qubit 104a causes a change in magnetic flux ΔΦ _T = M ₁ ΔI ₁ in the magnetic flux transfer device 101 due to the mutual inductance M ₁ between the magnetic flux qubit 104a and the magnetic flux transfer device 101. . The change in magnetic flux ΔΦ _T in the magnetic flux transfer device 101 causes a change in current ΔI _T = ΔΦ _T / L _T in the magnetic flux transfer device 101 due to the self-inductance L _T of the magnetic flux transfer device 101.

The change ΔI _T in the current in the magnetic flux transfer device 101 is determined by the magnetic flux transfer device 101 and the magnetic flux qubit 104b.
The mutual inductance M ₂ of the magnetic flux qubit 10
Causes a change ΔΦ ₂ = M ₂ ΔI _T of flux 4b. Therefore, the change ΔΦ _T of the magnetic flux in the magnetic flux qubit 104a is
A change in the magnetic flux in the magnetic flux qubit 104b due to the current flowing through the magnetic flux transfer unit 101, ΔΦ ₂ = M ₁ M ₂ Δ
It will cause the Φ ₁ / L ₁ L _T.

Considering that the state of the magnetic flux qubit shows magnetic field dependence, this means that the magnetic flux qubit 104a.
The state of means changing the state of the magnetic flux qubit 104b and having an interaction. That is, the state of the magnetic flux qubit 104a is also affected by the | 0> state or the | 1> state. The reverse is also true, and the two flux qubits 104
a and 104b will have an interaction.

Here, it is not necessary to consider the direct mutual inductance of the magnetic flux qubit 104a and the magnetic flux qubit 104b. This is because the magnitude of this direct mutual inductance becomes a small value if the magnetic flux qubit 104a and the magnetic flux qubit 104b are sufficiently far apart. At this time, the direct interaction is caused by the magnetic flux transfer device 10
It is small compared to the magnitude of interaction through 1 and can be ignored.

In FIG. 1, the magnetic flux transfer device 101 is arranged so as to surround the two magnetic flux qubits 104a and 104b. However, as can be seen from the schematic diagram of FIG.
If the magnetic flux qubit 104a and the magnetic flux qubit 104b magnetically interact with each other through the mutual inductance between the magnetic flux tranfer 101 and the respective magnetic flux qubits, the magnetic flux tranfer may have any arrangement and shape. If so, the same effect of interaction is obtained.

Flux qubits 104a and 104 using the flux transfer device 101 in the quantum computer shown in FIG.
In the system of b, the energy of the interaction flows through the self-inductance L _T of the magnetic flux transfer device 101, the magnitudes of the mutual inductances M ₁ and M ₂ with the magnetic flux qubits 104a and 104b, and the magnetic flux qubits 104a and 104b. It is determined by the currents I ₁ and I ₂ .

Change in magnetic flux in the magnetic flux qubit 104a Δ
Φ is the change in magnetic flux in the magnetic flux qubit 104b ΔΦ
₂ = M ₁ M ₂ ΔΦ ₁ / L ₁ L _T Therefore, work flux qubit 104b receives _{(energy), I 2 ΔΦ 2 = M 1} M 2 I 2 ΔΦ 1 / L 1 L T = M 1 M 2 I 2 ΔI 1 / L
_T , ΔΦ ₁ = L ₁ ΔI ₁ . Also, the work that the magnetic flux qubit 104b received
(Energy) is considered to be the energy of interaction, and if the energy of interaction is J, then J = M ₁ M ₂ I ₂ I ₁ / L
_Represented by _T.

Quantum computer operation requires an entangled state. In the magnetic flux qubits 104a and 104b of this embodiment, a quantum entangled state can be realized by the magnetic interaction described above. Magnetic flux qubit 104 connected by interaction
a and 104b become quantum entangled states as they evolve over time. If Pauli's spin matrix in the z-axis direction is σ _z and the Hamiltonian of the interaction is H _int ,
Using the energy J of interaction,

[0032]

[Equation 1]

It becomes Where σ _1z is magnetic flux qubit 1
Z component of magnetic flux of 04a, σ _2z is magnetic flux qubit 104b
Is the z component of the magnetic flux of, and H _int is the direct product of σ _1z and σ _2z ,
It is the product of the interaction energy J. Two magnetic flux qubits connected by this interaction develop with time.

The state of the magnetic flux qubit 104a is set to | a>, and the state of the magnetic flux qubit 104b is set to | b>. First, it is assumed that the magnetic flux transfer device 101 is in a state where no superconducting current flows and there is no interaction between the magnetic flux qubit 104a and the magnetic flux qubit 104b. The initial states of the magnetic flux qubit 104a and the magnetic flux qubit 104b are
It is assumed that the | 0> state and the | 1> state are the same,
For each state, | I> = (| 0> + | 1>) / √2, | II> = (| 0
> + | 1>) / √2. These are Pauli's spin matrix σ _{x in} the X-axis direction.
Is the eigenvector of.

The states of the two qubits at this time are: | I> | II> = (| 0> | 0> + | 0> | 1> + | 1
> | 1>) / 2. At time t = 0, the magnetic flux transfer device 101 changes to a state in which a superconducting current can flow, and the two magnetic flux qubits 104
The state of a, 104b changes to the state with interaction,
The system based on these will evolve over time.

Next, the state of the two magnetic flux qubits 104a and 104b at time t is defined as | Ψ (t)>. The state | Ψ (t)> evolves over time due to the influence of the interaction, and this time dependence is | Ψ (t)> = exp (−2πiH _int t / h) | Ψ
(0)>, | Ψ (0)> = | I> | II>.

Substituting the Hamiltonian of the interaction into the above time-dependent equation, | Ψ (t)> = {exp (−2πiJt / h) | 0> |
0> + exp (2πiJt / h) | 0> | 1> + exp
(2πiJt / h) | 1> | 0> + exp (-2πiJJ
t / h) | 1> | 1>} / 2. Now, consider time t = h / (8J). The state of the system at this time is | Ψ (t)> = {(1-i) | 0> | 0> + (1 + i)
| 0> | 1> 10 (1 + i) | 1> | 0> + (1-i) |
1> | 1>} / 2√2.

As it is, the state of this system cannot be intuitively understood. Therefore, rewrite this system with the eigenvectors of the Pauli spin matrix σ _{x in} the x-axis direction used in the initial state. The eigenvector of Pauli's spin matrix σ _{x in} the x-axis direction is: | x +> = (| 0> + | 1>) / √2, | x −> = (|
0> − | 1>) / √2. When | Ψ (t)> is rewritten using this, | Ψ (t)> = (| x +> | x +> − i | x−> | x−
>} / √2.

At time t = h / (8J), the entire system of two qubits cannot be represented only from the state of each qubit. This is a quantum mechanical state that cannot be displayed in a classical state, because the states of the system cannot be displayed separately for each qubit state. This state is the state in which the entanglement of quanta described above (entan
gled state). Two magnetic flux qubits 104a,
By providing an interaction between the magnetic flux transfer units 101 during 104b, the quantum entangled state necessary for the above-described operation of the quantum computer can be realized.

In the case of the magnetic flux transfer device 101 of this embodiment,
When the magnitude of this interaction is estimated from the actual shape and arrangement of the sample, J = 0.34 [GHz] = 1.41 [μe
V]. At this time, the time required for the two magnetic flux qubit systems to be in a state of quantum entanglement is 0.37 [n
S]. This is a maximum of 2.7 billion times per second (2.7
It corresponds to the fact that the calculation of GHz) is possible.

As described above, the magnetic flux qubit 104a and the magnetic flux qubit 104b interact with each other through the current flowing through the magnetic flux transfer unit 101. Here, the magnetic flux transfer device 10
If the on / off of the current flowing through 1 can be controlled, the occurrence of the interaction between the two magnetic flux qubits 104a and 104b can be controlled. If these controls become possible, the magnetic flux qubits can be made to interact at any time.

It is also possible to cut the interaction at any time and individually control the states of the magnetic flux qubits 104a and 104b by the control lines 106a and 106b. Unlike the other qubit systems, the point that the interaction between the magnetic flux qubits can be arbitrarily controlled in this manner uses the controllable magnetic flux transfer device 101, and the magnetic flux qubits 104a and 10a.
This is a great advantage in the 4b system.

In this embodiment, the magnetic flux transfer device 101 made of a superconductor is provided with a switching means for switching a state in which a superconducting current can flow and a state in which no superconducting current can flow (turning the superconducting current on and off). I chose As the switching means, for example, either the above-mentioned Josephson junction field effect transistor (JOFET) 102 or a thermal heater (heating means) described later or a mechanical switch composed of superconductivity may be used. First, a method of controlling the magnetic flux transfer device 101 by the JOFET 102 will be described.

<First Embodiment> In the first embodiment, a state in which a superconducting current can flow and a state in which a superconducting current does not flow (on / off) in a magnetic flux transfer device 101 made of a superconductor is described as JOF.
What is produced by the ET 102 will be described. JO
By changing the voltage applied to the gate electrode of the FET 102, on / off control of the superconducting current can be performed. JOFET1
Regarding the specific structure and gate voltage operation of No. 02, refer to Reference 6 “Tatsushi Akazaki, Hideaki Takayanagi, Junsaku Ni.
tta, Takatomo Enoki, “A Josehson field effect trans
istor using an InAs-inserted-channel In _0.52 Al _0.48 A
s / In _0.53 Ga _0.47 As inverted modulation-doped structr
e ", Appl. Phys. Lett, 68 (1996) 418".

FIG. 3 is a perspective view schematically showing a configuration example of the JOFET 102 (FIG. 1). Numerals shown in FIG. 3 will be described. First, 307 is a source electrode made of a superconductor made of niobium, and 308 is a drain electrode made of a superconductor made of niobium. The source electrode 307 corresponds to the electrode portion 101a shown in FIG. 1, and the drain electrode 308 corresponds to the electrode portion 101b shown in FIG.

Reference numeral 309 denotes a channel layer composed of InAs, and a two-dimensional electron gas is formed in the channel layer 309. Reference numeral 310 denotes a gate electrode, which is connected to the gate wiring 103 in FIG. Reference numeral 311 denotes a carrier supply layer made of InAlAs having n-type impurities introduced,
312 is a non-doped InA1As layer, 313 is a non-doped InGaAs layer, 314 is a non-doped InAlAs layer.
The layers 315 are semiconductor substrates made of InP.

The carrier supply layer 3 is formed on the channel layer 309.
Electrons are supplied from 11 through the non-doped InA1As layer 312 and the non-doped InGaAs layer 313, and the supplied electrons form a two-dimensional electron gas. When a gate voltage is applied to the gate electrode 310, the channel layer 309
The carrier concentration of the two-dimensional electron gas formed in the film changes. This change in carrier concentration changes the superconducting current flowing in the two-dimensional electron gas layer. Figure 4 shows JOFE
The gate voltage characteristic of T102 is shown. The horizontal axis of the graph is voltage and the vertical axis is current. When the gate voltage V _g is 0 V, a superconducting current of about 5.5 μA flows at a voltage of 0 mV.

When a negative gate voltage is applied to this, the superconducting current that can flow decreases, and V _g =
When applied to -1.1V, no current flows between the source and drain of JOFET 102. Thus, by simply operating the gate voltage of JOFET 102,
The superconducting current flowing in the magnetic flux transfer device 101 can be manipulated, and the interaction between the magnetic flux qubits 104a and 104b can be easily controlled. Further, InA is formed in the channel layer 309 of the JOFET 102 where the two-dimensional electron gas is formed.
Since s is used, JOFET by operating the gate voltage
The response speed of 102 is fast, and the switching of interaction can be performed at high speed.

<Second Embodiment> Next, the magnetic flux transfer device 10 will be described.
A case where the on / off control of No. 1 is controlled by heating the magnetic flux transfer unit 101 will be described. FIG. 5 is a plan view showing a partial configuration of a quantum computer according to another mode of the present invention. Here, the on / off control of the magnetic flux transfer device 101 is performed by the thermal heater (heating means) 502. The other parts are similar to those of the quantum computer of FIG.

When the heat heater 502 is not energized and is in a non-heated state, all of the magnetic flux transfer devices 101 are in a superconducting state, in which a superconducting current can flow. In contrast,
The magnetic flux transfer device 1 is turned on by energizing the thermal heater 502.
If a part of 01 is heated above the superconducting transition temperature to break the superconducting state, the superconducting current does not flow. In this way, the non-heating / heating switching operation of the thermal heater 502 enables ON / OFF control of the magnetic flux transfer device 101, which makes it possible to easily control the interaction between the magnetic flux qubits 104a and 104b.

<Third Embodiment> Next, the magnetic flux transfer device 10 will be described.
A case where the on / off control of No. 1 is created by a mechanical switch performed by a mechanical operation will be described. FIG. 6 is a plan view showing a partial configuration of a quantum computer according to another mode of the present invention. Here, on / off control of the magnetic flux transfer device 101 is performed by a mechanical switch 60 made of a superconductor.
2. The other parts are similar to those of the quantum computer of FIG. The mechanical switch 602 may be operated by, for example, a piezo element or the like.

When the mechanical switch 602 is ON and the circuit of the magnetic flux transfer device 101 is closed, the mechanical switch 602 is
Since is a superconductor, a state in which a superconducting current can flow can be created. By turning off the mechanical switch 602 and disconnecting the circuit of the magnetic flux transfer unit 101, a state in which no superconducting current flows can be created. In this way, the operation of the mechanical switch 602 can easily control the interaction between the magnetic flux qubits 104a and 104b.

The operation in the quantum computer is the time evolution of the system composed of qubits as described above. In a normal quantum computer, the interaction between qubits cannot be cut, and this interaction also constantly evolves with each qubit. Therefore, operations between qubits are always performed regardless of whether they like it or not. For this reason, in a system of qubits that cannot break an ordinary interaction, another operation for canceling the interaction is required.

On the other hand, in the quantum computer according to the above-described embodiment, the magnetic flux transfer device 101 capable of on / off control is used, and the interaction between the magnetic flux qubit 104a and the magnetic flux qubit 104b is cut off at an arbitrary time. I did it. Therefore, another operation for canceling the interaction is not necessary, and only the simple operation of each switching means for turning the magnetic flux transfer device 101 on and off is required. Therefore, according to the present embodiment, it becomes possible to perform simpler and more flexible arithmetic operations in the quantum computer.

[0055]

As described above, according to the present invention, the interaction between two magnetic flux qubits that interact with each other due to the flow of a superconducting current is controlled by turning on and off the magnetic flux transfer device by the switching means. did. As a result, according to the present invention, an excellent effect that the interaction between the quantum bits in the operation of the quantum computer can be arbitrarily controlled can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of a partial configuration of a quantum computer according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an equivalent circuit of a magnetic flux qubit and a magnetic flux transfer device.

FIG. 3 is a perspective view schematically showing a configuration example of JOFET 102 (FIG. 1).

FIG. 4 is a characteristic diagram showing a gate voltage characteristic of JOFET 102.

FIG. 5 is a plan view showing a partial configuration of a quantum computer according to another mode of the present invention.

FIG. 6 is a plan view showing a partial configuration of a quantum computer according to another mode of the present invention.

[Explanation of symbols]

101 ... Flux transformer (flux transformer),
102 ... Josephson junction field effect transistor (JO
FET: switching means), 103 ... Gate wiring, 104
a, 104b ... magnetic flux qubit, 105 ... SQUID (S
uperconductingQuantum Interference Device), 10
6a, 106b ... Control line.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hayato Nakano             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Tatsushi Akasaki             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor ▲ High ▼ Hideaki Yanagi             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F-term (reference) 4M113 AB01 AB11 AC08 AC45 AD04                       AD21 CA11 CA13                 5B016 AA04 GA04

Claims (8)

[Claims] 1. A quantum computer provided with two magnetic flux qubits and a magnetic flux transfer device for causing an interaction between these two magnetic flux qubits, and switching means for turning on and off a superconducting current flowing through the magnetic flux transfer device. A quantum computer characterized by having. 2. The quantum computer according to claim 1, wherein the switching means is a Josephson junction field effect transistor. 3. The quantum computer according to claim 1, wherein the switching unit is a heating unit that heats a part of the magnetic flux transfer device. 4. The quantum computer according to claim 1, wherein the switching means is a mechanical switch made of a superconductor provided in a part of the magnetic flux transfer device. 5. A quantum computer provided with two magnetic flux qubits and a magnetic flux transfer device for causing an interaction between the two magnetic flux qubits, by turning on and off a superconducting current flowing in the magnetic flux transfer device. A method of controlling a quantum computer, which comprises controlling an operation of the quantum computer. 6. The method for controlling a quantum computer according to claim 5, wherein the superconducting current flowing through the magnetic flux transfer device is turned on and off by a Josephson junction field effect transistor. 7. The quantum computer control method according to claim 5, wherein the superconducting current flowing through the magnetic flux transfer device is turned on and off by heating a part of the magnetic flux transfer device. Control method. 8. The quantum computer control method according to claim 5, wherein the superconducting current flowing in the magnetic flux transfer device is turned on and off by a mechanical switch provided in a part of the magnetic flux transfer device. Computer control method.