JP2003209301A - Method for recording information, calculating method, method for communicating information, method for storing energy, method for measuring magnetic flux and method for constituting quantum bit utilizing superconductor comprising a plurality of bands - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recording information in soliton unit, a method for calculating it, a method for communicating information, a method for storing energy, a method for measuring magnetic flux, and a method for constituting a quantum bit by utilizing behavior of a phase soliton appearing between superconducting order parameters present in a plurality of bands. <P>SOLUTION: Since a phase difference of a soliton is maintained, an information is recorded in terms of the phase difference. In a reverse direction for carting round the same energy, a phase slip of a -Θ soliton is also present, so the soliton itself has signs of + and -, thereby performing calculation by utilizing it. Owing to the soliton, energy with no magnetic flux is stored. By discriminating an external magnetic flux in soliton unit, the magnetic flux is measured more precisely. Further, by using the soliton and an anti-soliton, a quantum bit required for quantum computing is constituted. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconductor having a plurality of bands, an information recording method, a computing method, an information transmitting method and an energy storage method using the phase between superconducting order parameters existing in the plurality of bands. The present invention relates to a method, a magnetic flux measurement method, and a qubit configuration method.

[0002]

2. Description of the Related Art In conventional superconductivity, all superconducting electronics utilizing the phase difference of superconductivity utilize only the phase difference at spatially different places. Regarding the energy storage, a current was passed through the superconductor to induce the magnetic field, and the energy was stored.

[0003]

A typical superconducting device utilizing such a technique is a Josephson device. That is, it is a superconductor device using a method in which two different superconductors are spatially adjacent to each other and a phase difference between them is used (hereinafter, a superconductor device using this method is referred to as “spatial space”). Josephson device according to the arrangement "). The Josephson device based on the spatial arrangement requires control of the interface properties. Especially, in the Josephson device in high temperature superconductors, the difficulty of interface control of the Josephson junction is the biggest obstacle to its practical application. .

In the field of energy storage by superconductors,
A method of applying a permanent current to a superconducting magnet and accumulating electromagnetic energy there, levitating the superconductor in a magnetic field,
There is a method of accumulating energy by kinetic energy due to the rotation. In this method, since magnetic flux is always generated, the operating temperature becomes considerably lower than the superconducting transition temperature in the case where the energy loss due to the magnetic flux creep cannot be ignored like the high temperature superconductor. As a method of constructing a qubit, a method using nuclear magnetism, a method of operating a magnetic flux quantum using a solid-state device, and the like have been proposed, but the former cannot integrate several hundreds of bits, and the latter requires Precise nanotechnology is required for integration, and the technology is incomplete.

The present invention relates to an information recording method, an arithmetic method, an information transmitting method, a magnetic flux measuring method, which utilizes the principle of a new Josephson device which does not require interface control in a superconductor.
It is an object of the present invention to provide a qubit configuration method, an energy storage method that does not generate a magnetic field due to a persistent current, and a qubit configuration method that can be integrated by the current technology.

[0006]

An information recording method according to the present invention records information in a superconductor having a plurality of bands by utilizing a phase difference between superconducting order parameters existing in the plurality of bands. . In a calculation method according to the present invention, in a superconductor having a plurality of bands, a phase difference soliton between superconducting order parameters existing in the plurality of bands is used for calculation. In the information transmission method according to the present invention, in a superconductor having a plurality of bands, information is transmitted in units of phase difference solitons between superconducting order parameters existing in the plurality of bands. The energy storage method according to the present invention is based on a phase difference soliton between superconducting order parameters existing in a plurality of bands in a superconductor having a plurality of bands. A magnetic flux measuring method according to the present invention measures a magnetic flux in a superconductor having a plurality of bands by a unit phase difference soliton between superconducting order parameters existing in the plurality of bands. The method for constructing a qubit according to the present invention constructs a qubit in a superconductor having a plurality of bands by utilizing the phase difference between superconducting order parameters existing in the plurality of bands. As described above, in the present invention, the interface of the Josephson junction is not required, and in the superconductor having a plurality of bands, the properties of the phase difference soliton appearing between the superconducting order parameters existing in the plurality of bands. Is utilized, it is easy to put it into practical use, and energy loss can be suppressed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention utilizes a phase difference between superconducting electrons existing in each band in a superconductor having a plurality of bands. Cu _x Ba ₂ Ca ₃ CuO _y is a superconductor having a plurality of bands. FIG. 1 is a one-dimensional conceptual view showing the relationship between the electron energy and the wave number of a superconductor having two bands. Hereinafter, in the one-dimensional model, a case where two order parameters Ψ ₁ and Ψ ₂ exist on different bands and they interact weakly will be described. It can be easily analogized when the interaction is strong or when there are three or more bands, and it is clear that the same effect can be obtained.

The interaction between order parameters is mathematically the same as the Josephson type interaction. Express the order parameter as an electron-pair wave function (Ginzburg model:
Ginzburg Model) and the superconducting order parameter existing in band ν are given by the following equation (1). Where N _ν and θ _ν
Represents the phase of superconducting electron density and order parameter in band ν.

[0009]

[Equation 1]

Based on the one-dimensional Ginzburg model, it is known that the energy density of super-electrical electrons in two Gibbs bands can be expressed by the following expression (2). The formula (2) can be approximately represented by the following formulas (3) to (5). Here, α _ν , β _ν , and γ are parameters (γ is a parameter representing an interaction between superconducting electrons between bands), and m _ν represents a mass of superconducting electrons in the band ν.

[0011]

[Equation 2]

[0012]

[Equation 3]

[0013]

[Equation 4]

[0014]

[Equation 5]

When no superconducting current flows in the superconductor
(Je = ΣehN_ν/ M_ν・ ∇_xθ _ν= 0) is the following formula
There are relationships (6) to (9).

[0016]

[Equation 6]

[0017]

[Equation 7]

[0018]

[Equation 8]

[0019]

[Equation 9]

The free energy represented by the equation (2) is
The minimum energy exists as a stable state. Setting the variation δg = 0 in the equation (2), the following equation (10) is obtained.

[0021]

[Equation 10]

This equation (10) is the sign Gordon (si
ne-Gordon) equation, the phase difference (θ ₁ −θ ₂ ) = 0,
It is known that a soliton solution can be obtained as a minimum value solution and a ground state solution of π. The solution of the ground state of the phase difference when the magnitude of the interaction (represented by the parameter γ) does not spatially fluctuate is 0 when γ <0 and π when γ> 0. Which is the case depends on the sign of the property γ of the substance. The energy corresponding to the soliton solution that exists as another minimal solution is slightly higher than the energy for the ground state.

The phase difference rotates from 0 to 2π when γ <0, and from −π to π when γ> 0. Soliton 1
The individual energy Esoliton is obtained by the following equation (11), and the total phase difference slip Θ soliton of the soliton is obtained by the following equation (12).

[0024]

[Equation 11]

[0025]

[Equation 12]

2 and 3 schematically show the soliton which is the phase difference (θ ₁ -θ ₂ ) in the one-dimensional case. The horizontal axis of FIG. 2 is the length of the superconductor with the standardization constant L (defined by equation (10)) as a unit, and the vertical axis is the phase difference (θ ₁ −θ ₂ ). The phase difference near x ₀ represents a soliton. Before and after the soliton, the entire superconductor also has a phase slip (Θ soliton in Fig. 3).
). Soliton proceeds superconductors, the end of the superconductor x _-∽, reflected by x _∽. FIG. 3 shows an example in which the order parameter is represented by a vector on the complex plane.

Since the phase difference which is the soliton is retained, information can be stored in the form of the phase difference. Also, the direction of carrying the same energy is opposite, −Θsoli
Since there is also a ton phase slip, the soliton itself can have + and-signs. Soliton enables the storage of energy without magnetic flux. Also, energy can be stored in solitons.

[0028] When connecting the x _-∽ in FIG 2 and x _∽ and the superconductor ring, soliton phase slip Θsoliton
Is compensated for the boundary condition by the superconducting current. Therefore, the superconducting current Je is expressed by the following equations (13) to (15). The superconducting circulating current Je is Jesoli.
Since ton = 0, only the current JeA component flowing by the vector flows.

[0029]

[Equation 13]

[0030]

[Equation 14]

[0031]

[Equation 15]

Since the boundary condition of the order parameter in the superconducting ring is that the phase difference of one round is 2nπ (n is an integer), the following formula (16) holds for the superconducting ring, and the points x − _{∽ at} both ends to be joined And the phase difference between x _∽ is given by equation (17), the magnetic flux Φ induced in the superconducting ring is
It is represented by 8). Here, Φ ₀ is a magnetic flux quantum.

[0033]

[Equation 16]

[0034]

[Equation 17]

[0035]

[Equation 18]

According to the present invention, in a superconductor having a plurality of bands, a recording method for recording information in soliton units by utilizing the property of a phase difference soliton appearing between superconducting order parameters existing in a plurality of bands, Calculation method to calculate,
An information transmission method, an energy storage method, a magnetic flux measurement method, and a qubit configuration method are provided.

Instead of the Josephson device by spatial arrangement, Josephson coupling between a plurality of superconducting order parameters existing in the same space in superposition
To use. By this method, the strength of the Josephson bond is determined by the bulk property rather than the interface property, and thus the dependence on the device process is almost eliminated. Also,
Josephson junc between three or more superconducting order parameters (Josephson junc)
tion) is also possible.

By using solitons, energy can be stored without generating a magnetic field. Such an arrangement can be realized by a phase difference soliton between a plurality of order parameters.

Next, a recording method, a calculation method for calculating, a method for transmitting information, a method for storing energy, a method for measuring magnetic flux, and a method for constructing a quantum bit according to the present invention will be individually described with reference to the drawings.

Information Recording Method FIG. 4 conceptually shows an example of a method of recording solitons on a superconductor ring (hereinafter, ring) of the present invention. The superconductor is Cu _x Ba ₂ Ca ₃ CuO _y as a superconductor with multiple bands.
And so on. The superconducting switch (hereinafter, switch) R ₀ of the ring R is turned on to form the ring R (see FIG. 4).
(A)) When a magnetic field B is applied to the ring and a magnetic flux passes through the ring, solitons S are generated in the ring R (FIG. 4).
(B)). The soliton S exists even when the applied magnetic field is removed and the switch R ₀ is turned off (FIG. 4 (c)). Switch R ₀
When is turned on, magnetic flux Φ is generated due to boundary conditions. When a magnetic field B'in the opposite direction is applied in the ring, the magnetic fluxes cancel each other out and the permanent circulating current does not flow (Fig. 4 (d)).

FIG. 4C corresponds to the memory state, and FIG. 4D corresponds to the memory erasing operation. Also, the memory can be erased by raising the temperature of the superconductor. When a magnetic field is applied in the opposite direction, a soliton S'in the opposite direction is generated. Digital information can be stored by making solitons S and S'correspond to "1" and "0", respectively.

Calculation Method FIG. 5 conceptually shows an example of the calculation method of the present invention. The two rings R _A and R _B are connected to two changeover switches A ₀ and B _0.
It is a superconducting circuit in which connection is changed to one ring by.
The switch A ₀ is connected to the terminal a and the switch B ₀ is connected to the terminal b to form two rings R _A and R _B (FIG. 5A).
The ring R _A, flux respectively in R _{B Φ A,} passing the [Phi _B, ring R _A, soliton to R _B S _A, is S _B occurs (Figure 5 (b)). The magnetic fluxes Φ _A and Φ _B are magnetic fluxes that generate one soliton, respectively. Magnetic fluxes Φ _A and Φ _B are repeatedly applied to the ring to generate solitons corresponding to the calculations. The soliton exists even when the switches A ₀ and B ₀ are turned off (FIG. 5 (c)). When the switch A ₀ is connected to the terminal b and the switch B ₀ is connected to the terminal a to form one ring, the superconducting currents I _A and I _B flow due to the boundary condition, and the magnetic flux Φ is generated by the combined current. By measuring this magnetic flux, it is possible to calculate the sum of solitons (the difference if the applied magnetic flux is reversed as shown in FIG. 5B).

When a plurality of solitons and antisolitons are present, the effect obtained by subtracting the total effect of the phase slips generated by both of them from an integer multiple of h / 2e becomes the magnetic flux captured by the ring. An operation called addition of can be performed on this ring.

Information Transmission Method FIG. 6 shows an example of the information transmission method according to the present invention. Figure 6
( _A ) shows a superconductor circuit formed by connecting rings R _{A to} R _E. A _{0 to} E ₀ represent switches. The switch A ₀ is turned on, the magnetic field B is applied to the ring R _A ,
Generates magnetic flux. Then, solitons S are generated in the ring R _A (FIG. 6 (b)). After generating the soliton, the switch B ₀ is turned on to turn off the magnetic field. If the band parameter is adjusted so that the energy is lower than the antisoliton S'cannot be generated, the magnetic flux is wound around the superconductor L _A , and the soliton S is generated outside the rings R _A and R _B ( FIG. 6C).

Next, the switch C ₀ is turned on (see FIG. 6).
(D)). When switch A ₀ is turned off (Fig. 6)
(E)) Since energy gains when moving to the outer ring of the next rings R _B and R _C , the soliton moves to the rings R _B and R _C. Information (S, S ') corresponding to the applied magnetic flux is transmitted. Information (S ′, S) will be transmitted by applying a magnetic field opposite to that in the figure. Digital information can be transmitted by associating these pairs of information with "1" and "0".

Energy Storage Method FIG. 7 shows an example of the energy storage method according to the present invention. When the switch Z ₀ is connected to the terminal a and the switch R ₀ is turned on to form the ring R and the magnetic field B is applied to the ring, solitons S are generated in the ring R (FIG. 7).
(B)). When the applied magnetic field is removed after turning off the switch R ₀ , the soliton S advances to the superconducting line Z, where the soliton S is accumulated (FIG. 7C). Switch Z ₀
Is connected to the terminal b, the soliton surely exists in the superconducting line (FIG. 7 (d)). When the switch R ₀ is turned on, a permanent current flows due to boundary conditions, and the superconducting transformer T
The energy stored in the superconducting line is output via (FIG. 7 (e)). The amount of energy stored is determined by the number of times the applied magnetic field is applied.

Magnetic Flux Measuring Method FIG. 8 shows an example of a measuring apparatus for carrying out an example of the magnetic flux measuring method of the present invention. In the absence of solitons, the magnetic flux trapped in the superconducting ring is an integral multiple of Φ = h / 2e from the boundary conditions. However, as shown in FIG. 8, when one soliton enters, the boundary condition changes, and the superconducting current must flow so as to cancel the phase difference due to the captured soliton. The magnetic flux generated inside the superconducting ring by this superconducting current is Φ ₀ =
It is a value obtained by subtracting the phase slip (1 / (2π) × h / 2e) generated by the soliton from the integer multiple of h / 2e. Thus, a magnetic flux smaller than the magnetic flux quantum unit defined by Φ ₀ = h / 2e can be measured.

The magnetic flux trapped in the ring R in FIG. 8 causes solitons in the ring. The generated soliton is n
_In the case of one, the equations (18) to (19) are obtained, and the output voltage V _T of the tank circuit is an output proportional to Φ in the following equation (19). The principle of this detection circuit is the same as that of RfSQUID.

[0049]

[Formula 19]

Φsoliton is calculated by discriminating the difference between the periods of the signals generated by Φsoliton and Φ ₀ by the CPU in FIG. Compared to the magnetic flux Φ ₀ in units of Φ soliton, it is determined by constants such as m ₁ , m ₂ , N ₁ and N _{2 of the} superconductor material (equation (1
2)), for example, soliton-based magnetic flux measurement has a high resolution of about 1/2. The detected Φ soliton displays and records the measured value of the external magnetic flux by the display / recording device.

Quantum Bit Construction Method FIG. 9 shows an example of the quantum bit construction method of the present invention. FIG. 9 shows an example of forming 3 qubits, a double wire indicates a multi-band superconductor electric wire, and a single wire indicates an ordinary superconductor or a multi-band superconductor electric wire. The numbers 1, 2, 3, 1 ', 2', 3'indicate how the wires are connected. First, the switches C _{1 to} C ₃ and the switches D _{1 to} D ₃
Is turned on to align the phases of the reference superconductor Θ = 0 and the three multiband superconductors indicated by double lines, and eliminate solitons. If necessary, solitons are eliminated by an external field by the method shown in FIG.

Next, all the switches A, B, switch C ₁ -C _3, turns OFF the switch D ₁ to D _3. Then, photons having the same energy as the soliton generation energy are irradiated from the light source to the superconductor to generate solitons and antisolitons with a probability of 50% and 50%. The generated solitons and antisolitons are trapped by three multiband superconductors, respectively, and a superposed state of solitons and antisolitons is generated in the superconductor. The superposed state of the soliton and the anti-soliton corresponds to 1 QuBit (1 qubit).

The operation between qubits can be realized by performing an ON / OFF state of the switches A and B in an arbitrary combination and performing an arbitrary number of times at an arbitrary time interval for an arbitrary time. After calculation, switches C _{1 to} C ₃ and switches D _{1 to} D
Turn on ₃ and measure the magnitude of the superconducting current flowing between the reference superconductor and between the multi-band superconductors.
Observe the state of t.

[0054]

As described above, it is possible to record, transfer and calculate information by utilizing the phase difference between a plurality of order parameters, and to control superconducting electronics by eliminating the interface of the Josephson device due to the spatial arrangement. It is useful as a principle. As an energy application, it is also useful as an energy storage technology that does not generate a magnetic flux that can operate even if the irreversible magnetic field is low. In addition, the integration technology is the same as or easier than the existing superconducting device manufacturing technology,
A qubit that can be easily integrated can be provided by utilizing the phase difference between multiple order parameters.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an order parameter of a superconductor having a plurality of bands according to the present invention.

FIG. 2 is a diagram illustrating solitons generated in a superconductor having a plurality of bands.

FIG. 3 is a diagram showing phase difference rotation between order parameters generated in a superconductor having a plurality of bands.

FIG. 4 is a diagram illustrating a recording method of the present invention.

FIG. 5 is a diagram illustrating a calculation method of the present invention.

FIG. 6 is a diagram illustrating an information transmission method of the present invention.

FIG. 7 is a diagram illustrating an energy storage method of the present invention.

FIG. 8 is a diagram illustrating a magnetic flux measuring method of the present invention.

FIG. 9 is a diagram illustrating a qubit configuration method of the present invention.

[Explanation of symbols]

S ₁ , S ₂ , S _A , S _B soliton S ′ anti-soliton Ψ ₁ , Ψ ₂ order parameter θ ₁ , θ ₂ order parameter phase Θ soliton phase difference slip Z superconducting line R, R _A ~ R _E superconducting ring A _{0 to} E ₀ , R ₀ , Z ₀ superconducting switch Φ ₀ magnetic flux quantum

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Claims (6)

[Claims] 1. A superconductor having a plurality of bands, wherein information is recorded by utilizing a phase difference between superconducting order parameters existing in the plurality of bands. Information using a superconductor having a plurality of bands. Recording method. 2. In a superconductor having a plurality of bands, a computing method using a superconductor having a plurality of bands, which is performed using a phase difference soliton between superconducting order parameters existing in the plurality of bands. . 3. In a superconductor having a plurality of bands, information transmission using a superconductor having a plurality of bands, which transmits information in units of phase difference solitons between superconducting order parameters existing in the plurality of bands. Method. 4. A method for storing energy in a superconductor having a plurality of bands, the method utilizing a superconductor having a plurality of bands by a phase difference soliton between superconducting order parameters existing in the plurality of bands. 5. In a superconductor having a plurality of bands, the magnetic flux is measured by a unit phase difference soliton between superconducting order parameters existing in the plurality of bands, and a magnetic flux measurement using a superconductor having a plurality of bands. Method. 6. A superconductor having a plurality of bands, wherein a qubit is constituted by using a phase difference between superconducting order parameters existing in the plurality of bands in a superconductor having a plurality of bands. How to construct a qubit.