Quantum error detection method, quantum bit device, and quantum computer

Abstract

In the present invention, data quantum bits are positioned at vertices of a square grid, a syndrome quantum bit is positioned at the center of a plane of the square grid, the syndrome quantum bit is moved to the position of a quantum dot adjacent to a transfer-source data quantum bit, and the information of the data quantum bit is transferred to the syndrome quantum bit.

Description

Quantum error detection method, quantum bit device, and quantum computer

[0001] The present invention relates to a quantum error detection method, a quantum bit device, and a quantum computer.

[0002] The ultimate goal of quantum computer development is a fault-tolerant quantum computer (FTQC), and various research and developments are active aiming at it. There are many candidates for what kind of physical system to use for qubits, which are the basic elements of quantum computers, and each is being intensively studied. From the perspective of integration, a method using silicon electron spin is advantageous.

[0003] Silicon has very high integration and is advantageous for large-scale production. However, due to its extremely high integration, there is also a problem that sufficient space for control lines etc. cannot be secured.

[0004] One solution is shuttling that focuses on the fact that electrons can move. An example of this is a method in which a qubit operation unit and its control lines and circuits are arranged on a substrate, and the qubit is brought to the operation unit when an operation is required (see Non-Patent Document 1).

[0005] However, in this method, the shuttling distance is large, and decoherence becomes a major problem. Another example of shuttling is Patent Document 1.

[0006] Patent Document 1 discloses a method in which when encoding qubits, the roles are shared between data qubits and syndrome qubits, and each is arranged linearly and processed pipelinedly.

[0007] However, here too, the shuttling distance required for data qubits and syndrome qubits is large, and decoherence becomes a major problem. Also, even if a plurality of the above one-dimensional arranged qubit groups are arranged two-dimensionally, the arrangement of the qubits is not the arrangement at the time of encoding, and there are also problems from the perspective of code operation.

[0008] Search result US2022 / 0172097A1

[0009] J. M. Boteret al. , Phys. Rev. Appl. 18,024053 (2022).

[0010] As described above, in Patent Document 1 and Non-Patent Document 1, the shuttle distance is large, and decoherence becomes a major problem. Furthermore, even if multiple one-dimensional qubit groups are arranged in two dimensions, the qubit arrangement does not match the arrangement during encoding, which presents challenges from the standpoint of code operation.

[0011] The objective of this invention is to realize error-tolerant quantum computing in a quantum computer that performs quantum error detection or quantum error correction by minimizing decoherence by minimizing the shuttle distance.

[0012] A quantum computer according to one aspect of the present invention is a quantum computer having a quantum dot array and a control device for controlling the quantum dot array, wherein the qubit device has a plurality of data qubits and a plurality of syndrome qubits arranged thereon, a logic qubit is formed by a portion of the plurality of data qubits, the relative positions of the plurality of data qubits are fixed within the logic qubit, and the control device moves the syndrome qubits to adjacent positions to the data qubits that the syndrome qubits are responsible for, interacts the syndrome qubits and the data qubits to transfer the information of the data qubits to the syndrome qubits, and controls the device to measure the transferred syndrome qubits.

[0013] According to one aspect of the present invention, in a quantum computer that performs quantum error detection or quantum error correction, error-tolerant quantum computing can be realized by minimizing decoherence by minimizing the shuttle distance.

[0014] This figure shows an example of surface code implementation for a distance of 3. This figure shows the procedure for syndrome measurement (stabilizer measurement), where (a) shows the case of bit inversion detection (Z stabilizer) and (b) shows the case of phase inversion detection (X stabilizer). This figure shows the data qubits and syndrome qubits constituting the code arranged on a quantum dot array. This figure explains the CNOT operation and the movement of the syndrome qubit in syndrome measurement. This figure divides the operation of Figure 4A(a) into three steps. This figure divides the movement from Figure 4A(b) to Figure 4A(c) into four steps. This figure shows the position of the reference electron used for measuring the syndrome qubit. This figure shows the arrangement with the code state stretched horizontally. This figure shows the configuration for measuring the syndrome qubit in a two-dimensional arrangement. This figure shows the location where the reference electron is retracted when moving the syndrome qubit. This figure shows multiple logic qubits arranged in a row. This figure shows a state in which two logic qubits are coupled and a qubit array that secures a path for moving the logic qubits. This is a diagram showing the entire quantum computer.

[0015] As mentioned above, in quantum computers utilizing highly integrated silicon electron spins, the challenge lies in minimizing decoherence by keeping the shuttle distance to a minimum, while simultaneously enabling the implementation of codes, thereby realizing fault-tolerant quantum computing.

[0016] To solve the above problems, in an embodiment of the present invention, in the case of a surface code, which is a typical code, data qubits are placed at the vertices of a two-dimensional lattice and syndrome qubits are placed at the centers of the faces of the two-dimensional lattice. To achieve this, quantum dots are formed on a semiconductor substrate and electrons that carry out the qubits are placed therein. In addition to the vertices and faces mentioned above, quantum dots are also placed in the intermediate parts of the edges connecting the vertices. As a result, about half of the quantum dots are empty (occupancy rate is about 1 / 2).

[0017] The qubit filling rate for the quantum dots constituting the quantum dot array is 1 / 2 or less.

[0018] In quantum error detection, information from data qubits is transferred to syndrome qubits, and these syndrome qubits are measured. This transfer is performed for, for example, four data qubits in a single syndrome measurement.

[0019] This is why the syndrome qubit is positioned at the center of the face. In embodiments of the present invention, instead of fixing the position of the syndrome qubit, it is moved to the nearest position (quantum dot between edges) of the source data qubit and then transferred. Since the movement is limited to within each face, the shuttle distance can be kept to a minimum.

[0020] Note that the gate lines of semiconductor LSI devices are arranged in both vertical and horizontal directions (see Japanese Patent Application Publication No. 2021-027142). The quantum dots shown in Figures 1 to 10 are arranged in both vertical and horizontal directions. This is based on the fact that the gate lines are spread out in both vertical and horizontal directions.

[0021] Here, it is conceivable to transfer information from data qubits to syndrome qubits by adding diagonal gate lines. However, due to wiring constraints, adding diagonal gate lines is difficult. Adding diagonal gate lines to vertical and horizontal gate lines is undesirable from both a manufacturing and control perspective. Therefore, performing interactions in a diagonal direction is difficult and undesirable from a manufacturing standpoint.

[0022] Therefore, in the embodiment of the present invention, the syndrome qubits are moved in the row direction to make the interaction vertical.

[0023] Furthermore, while densely arranged quantum dot arrays lack sufficient wiring space, sparsely arranging the quantum bits reduces the number of required wires, making the necessary wiring possible. For this reason, in the embodiments of the present invention, the qubit packing ratio in the quantum dot array is set to 1 / 2 or less.

[0024] In the measurement, a reference electron is placed in an empty quantum dot adjacent to the syndrome qubit, the information from the syndrome qubit is transferred to the reference electron, and then measured. While the information in the syndrome qubit is held using spin state, in the reference electron it is converted into charge information. If a current line is required for the measurement of the reference electron, an empty quantum dot is added to secure it. Other modifications are made as needed.

[0025] According to embodiments of the present invention, the shuttle distance is minimized, resulting in minimal decoherence. Furthermore, the arrangement of qubits is consistent with the arrangement of the code implementation. Additionally, the region necessary for measurement and other operations is secured within the qubit array.

[0026] The transfer of information from data qubits to syndrome qubits is performed by moving the syndrome qubits along the edges of a two-dimensional lattice. Therefore, the direction of interaction is along the edge direction. This means that quantum error detection is possible by device control that controls each qubit with a common gate line by arranging gate lines in the vertical and horizontal directions, thus facilitating the implementation and control of devices for quantum error detection.

[0027] The series of operations for syndrome measurement are performed in sync with all syndrome qubits. That is, all syndrome qubits perform the same operations simultaneously. This means that device control can be performed on a row-by-row or column-by-column basis, which is consistent with the above-mentioned simplification aspect.

[0028] Thanks to the effects described above, it is possible to realize a fault-tolerant quantum computer using a silicon qubit array.

[0029] The following examples illustrate embodiments of the present invention using surface reference numerals as an example. The same principle applies when applying the present invention to other reference numerals.

[0030] To illustrate embodiments of the present invention, we will first describe the implementation and operation of surface codes.

[0031] Figure 1 shows an example of surface coding implementation. Quantum bits are classified into data qubits and syndrome qubits based on their function. The former are placed at the vertices of a two-dimensional lattice, and the latter at the centers of each face of the lattice. The former are shown as white circles, and the latter as black circles. Data qubits (white circles) are qubits that hold information, while syndrome qubits (black circles) are qubits used for measurement to detect errors. In Figure 1, three data qubits are arranged vertically and horizontally, representing a surface coding with a distance of 3. The greater the distance, the higher the error correction capability.

[0032] Syndrome qubits are located at the center of each face, and the four data qubits located at the vertices of that face are responsible for that syndrome qubit. At the edges, one syndrome qubit is responsible for two data qubits. Each data qubit is protected by multiple syndrome qubits. For example, the central data qubit 151 is protected by four syndrome qubits.

[0033] Errors detected after quantum error detection fall into one of three categories: bit inversion, phase inversion, or both. Therefore, it is sufficient to detect both bit inversion and phase inversion. In Figure 1, the syndrome qubits on the mesh-like surface are for bit inversion detection, and the syndrome qubits on the white surface are for phase inversion detection.

[0034] Figure 2 shows the procedure for quantum error detection.

[0035] (a) shows the procedure for detecting a bit inversion error. The information of data qubit a is transferred to a syndrome qubit initialized to |0> by a CNOT gate. Similarly, the information of data qubits b, c, and d is transferred to syndrome qubits. Then, a measurement based on |0> and |1> (Z basis measurement) is performed. This is one cycle of the syndrome measurement and is also called a stabilizer measurement. The syndrome measurement is performed repeatedly and continuously, and the difference in the measurement results indicates that an error occurred.

[0036] (b) shows the procedure for detecting a phase inversion error. It is similar to (a), but the control and target of the CNOT are reversed, the initialization of the syndrome qubit is |+>=(|0>+|1>) / √2, and the measurement basis is |+>,|->=(|0>-|1>) / √2. For this reason, after initializing to |0>, the y-axis rotation gate R ｙ (π / 2), R before measurement ｙ Perform (-π / 2).

[0037] While Figure 2 focuses on two syndrome qubits, the same process is performed for all syndrome qubits, and all syndrome measurements are performed synchronously. That is, in the circuit diagrams of Figures 2(a) and (b), the same processes are arranged vertically. The positions of initialization, CNOT, and measurement coincide in (a) and (b). In the left-hand diagram of Figure 2, when syndrome qubit (a) is performing a CNOT operation with data qubit a, syndrome qubit (b) is performing a CNOT operation with data qubit c.

[0038] Similarly, when syndrome qubit (a) is performing a CNOT operation with data qubit b, syndrome qubit (b) performs a CNOT operation with data qubit d. The same applies to subsequent operations. By synchronizing in this way, it is no longer possible for two or more syndrome qubits to interact with a single data qubit simultaneously.

[0039] In Figure 1, there are nine white circles and eight black circles. The state of eight data qubits is determined by the eight syndrome measurements. The remaining degree of freedom is that of one qubit. This one degree of freedom is that of the encoded qubit (logical qubit). The group of qubits in Figure 1 constitutes one logical qubit.

[0040] Quantum computers implement a large number of these logical qubits, and the overall operation is performed by performing operations on these logical qubits.

[0041] The above describes the operations required for surface code syndrome measurement. Below, we will describe how to implement this using a silicon qubit array with electron spin.

[0042] A quantum dot array is formed, and electrons responsible for qubits are arranged (Fig. 3). The dotted circles represent quantum dots, and data qubits and syndrome qubits are arranged in the quantum dots. From the perspective of the surface code arrangement, in addition to the vertices and the centers of the faces of the two-dimensional lattice, quantum dots are also arranged in the middle of the edges.

[0043] The probability that a quantum dot is occupied by a data qubit and a syndrome qubit is about 1 / 2 or less. That is, the filling rate of qubits in the quantum dot array is 1 / 2 or less than 1 / 2. By doing so, a qubit device capable of implementing a procedure (the present invention) for quantum error detection involving the movement of syndrome qubits is realized.

[0044] The procedure of syndrome measurement is shown in FIGS. 4A, 4B, and 4C.

[0045] FIG. 4A is a diagram for explaining the CNOT operation and the movement of syndrome qubits in syndrome measurement.

[0046] All syndrome qubits are moved (shuttled) one quantum dot to the left (Fig. 4A(a)). Here, focus on the dotted syndrome qubit 101. At this position, it interacts (CNOT operation) with the data qubit a.

[0047] The position of the syndrome qubit 101 remains the same, and then it is subjected to a CNOT operation with the data qubit b (Fig. 4A(b)).

[0048] Next, all syndrome qubits are moved two quantum dots (equivalent to one side) to the right (Fig. 4A(c)).

[0049] At that position, the dotted syndrome qubit 101 is subjected to a CNOT operation with the data qubit c, and then a CNOT operation with the data qubit d (Fig. 4A(d)). The four CNOTs required for one cycle of syndrome measurement are thus completed.

[0050] Although this description focuses on the dot-pattern syndrome qubit 101, the series of CNOT operations are performed synchronously for all syndrome qubits. That is, at the timing shown in Figure 4A(a), all syndrome qubits perform CNOT operations with the data qubit above them.

[0051] The shaded (e.g., 111) or open (e.g., 112) diagrams shown between the syndrome qubit and the data qubit indicate interaction (CNOT). The shaded diagram represents a CNOT operation for bit inversion error detection (Z-stabilizer measurement), and the open diagram represents a CNOT operation for phase inversion error detection (X-stabilizer measurement).

[0052] Therefore, in both CNOT operations, the control and target are reversed. If there is no data qubit above a syndrome qubit, no operation is performed. Similarly, at the timing shown in Figure 4A(b), all syndrome qubits (all black circles in Figures 1-10) perform a CNOT operation with the data qubit below them (if there is no data qubit below a syndrome qubit, no operation is performed). At the timing shown in Figure 4A(c), all syndrome qubits perform a CNOT operation with the data qubit above them. At the timing shown in Figure 4A(d), all syndrome qubits perform a CNOT operation with the data qubit below them.

[0053] As can be seen in Figures 4A(a) to (d), the CNOT calculations at each timing have the control and target alternating, but they are aligned vertically and horizontally. This indicates that device control is in vertical and horizontal units, which facilitates device implementation. Furthermore, the fact that both the control and target pairs of the CNOT are arranged in a column is also advantageous from a device control perspective.

[0054] Figure 4B is a diagram showing the operation in Figure 4A(a) divided into three steps.

[0055] First, the syndrome qubit 101 at the center of the face (Figure 4B(a1)) is moved to the left edge (Figure 4B(a2)). Next, it interacts with the data qubit a (111) (Figure 4B(a3)).

[0056] Figure 4C shows the transition from Figure 4A(b) to Figure 4A(c) divided into four steps.

[0057] First, the syndrome qubit 101 located on the edge (Figure 4C(b1)) is moved to the center of the face (Figure 4C(b2)). Then, it is moved to the right edge (Figure 4C(c1)) and made to interact with the data qubit c (Figure 4B(c2)).

[0058] As seen above, the implementation of Example 1 not only ensures that the qubits are aligned with the sign configuration, but also facilitates device control. Furthermore, the movement (shutting) of the syndrome qubits is limited to within a single plane (edge ​​to edge), minimizing the decoherence associated with shuttle operations.

[0059] Example 1 described a procedure for performing the CNOT operation required for syndrome measurement while shutting down the syndrome qubit. This example shows one form of measurement.

[0060] After the CNOT operation in Figure 4A(d), the syndrome qubit is returned to the center of the face as shown in Figure 5. The position of the nearest neighbor above the syndrome qubit (e.g., 101) is an empty quantum dot on the edge. A reference electron is placed there (e.g., 121).

[0061] Set the reference electron spin to |↑>. The |0> and |1> of the syndrome qubit correspond to |↑> and |↓>. Consider lowering the potential barrier between the syndrome qubit and the reference electron to move the syndrome qubit to the reference electron's dot. If the syndrome qubit is |↓> (i.e., |1>), it can move, but if the syndrome qubit is |↑> (i.e., |0>), it cannot move due to the Pauli spin blockade.

[0062] In other words, if the syndrome qubit is |1>, the reference electron position will have 2 electrons, and if the syndrome qubit is |0>, the reference electron position will remain at 1 electron. Here, by performing a measurement that can identify the number of electrons, it is possible to determine whether the syndrome qubit was |0> or |1>.

[0063] One measurement method is dispersion measurement (reflection type measurement). A microwave waveguide is formed perpendicular to the plane of the paper at the position (for example, 121) of a quantum dot (let's call it the reference dot) where the reference electron is placed, and the detection microwave is reflected by the reference dot.

[0064] The amplitude and phase of the reflection differ depending on whether the reference dot has one or two electrons, and by detecting this difference, it is possible to determine whether the syndrome qubit was |0> or |1>. By changing the frequency of the detection microwave for each reference dot being measured, microwave waveguides can be bundled by wavelength division multiplexing.

[0065] After electron count detection (measurement), if there are two electrons in the reference dot, one is returned to the position of the syndrome qubit. At that time, the potentials of the reference dot and the quantum dot containing the syndrome qubit are appropriately controlled so that the electrons in the reference dot are |↑> and the electrons in the syndrome qubit are |↓>.

[0066] If the reference dot has one electron, then the electron in the reference dot is |↑> and the syndrome qubit is also |↑>. Depending on the measurement result, the syndrome qubit becomes |↑> (i.e., |0>) or |↓> (i.e., |1>). This state becomes the starting point for one cycle of the next syndrome measurement. In this case, the initialization becomes |0> or |1> depending on the measurement result.

[0067] The above measurement is a Z-basis measurement that determines whether a syndrome qubit is |0> or |1>, and corresponds to the case of bit inversion error detection.

[0068] For phase inversion error detection, it is necessary to perform an X basis measurement to detect |+> and |->. To do this, before moving the syndrome qubit to the reference electron dot, a y-axis rotation gate R must be placed on the syndrome qubit. ｙ Multiply by (-π / 2) to convert |+> to |0> and |-> to |1> (see Figure 2(b)). Since the basis has been converted to |0> and |1>, the subsequent processing is the same as in the case of Z basis measurement.

[0069] During initialization after measurement, it is also necessary to convert the Z basis to the X basis. After initializing the syndrome qubit to |0> or |1> in the same way as with the Z basis, the y-axis rotation gate R ｙ (π / 2) converts |0> to |+> and |1> to |->.

[0070] The series of operations is performed synchronously for all syndrome qubits (all black circles in Figure 5) and all reference electrons (all dotted circles in Figure 5). In this embodiment, it is assumed that the output is generated using microwaves in a direction perpendicular to the plane of the paper. That is, it is a three-dimensional device implementation.

[0071] In summary, it has been confirmed that all the necessary initialization, CNOT calculation, and measurement for syndrome measurement are possible. Both bit inversion error detection and phase inversion error detection are also possible. All necessary functions, including measurement, are implemented within the array.

[0072] One factor that enabled the realization of such high-performance devices is that the probability of a data qubit or syndrome qubit occupying a quantum dot is approximately 1 / 2 or less. In other words, the qubit filling rate of the quantum dot array is 1 / 2 or less.

[0073] In Example 2, the output was obtained using a three-dimensional device arrangement. In this example, the output is obtained using a two-dimensional device arrangement.

[0074] Similar to Example 2, a reference electron and a quantum dot to position it are required. A path for the output signal is also necessary.

[0075] Therefore, the square lattice in Figure 3 is made horizontally elongated as shown in Figure 6 to secure empty quantum dots. This allows for the securing of reference electrons and output paths as shown in Figure 7.

[0076] A reference dot (e.g., 121) is placed to the right of the syndrome qubit (e.g., 101), and the number of electrons in the reference dot is set to 1 or 2 by a Pauli spin blockade, as in Example 2. The qubits in the column to the right of the reference dot are all empty (e.g., 131) and are used as current lines.

[0077] The electrostatic potential changes according to the number of electrons in the reference dot, and this difference is measured as a current value to determine the number of electrons in the reference dot. Each current line is used to detect the number of electrons in all adjacent reference dots (for example, 121, 122, 123). In this case, it is not possible to measure the reference dots arranged vertically simultaneously, so they must be measured one by one in sequence (serially).

[0078] When the syndrome qubit 101 performs a CNOT operation with data qubit c or d, it will be in the position shown in Figure 8.

[0079] To move 101 in Figure 7 to the position in Figure 8, the reference electron 121 in Figure 7 is an obstacle. Therefore, as shown in Figure 8(a), the reference electron 121 is moved down or up by one quantum dot to be moved out of the way. Alternatively, as shown in Figure 8(b), the reference electron 121 is moved to the right in accordance with the movement of the syndrome qubit 101.

[0080] As described above, the present invention is also applicable to two-dimensional arrangements. As in Example 2, all necessary functions, including measurement, are implemented within the array. Although the amount of movement of the syndrome qubits (shutting length) increases due to the horizontal arrangement of the data qubits, it is kept to about twice the original amount, thus maintaining the shutting suppression feature of the present invention.

[0081] One factor that enabled the realization of high-performance devices even with a two-dimensional arrangement is that the number of empty quantum dots was increased, further reducing the probability that a data qubit or syndrome qubit occupies a quantum dot from "about 1 / 2 or less."

[0082] In other words, the qubit-filling ratio of the quantum dot array is 1 / 2 or less.

[0083] Examples 1 through 3 described syndrome measurement for one logical qubit. To handle multiple logical qubits, they are arranged in a quantum dot array as shown in Figure 9.

[0084] Operations between two logical qubits (e.g., CNOT) are realized by combining and separating the two logical qubits. The state in which two logical qubits are combined is shown in the upper left of Figure 10. In order to perform operations between logical qubits that are not adjacent, it is necessary to move the logical qubits.

[0085] For example, in Figure 10, the second row and third column of the logical qubits in Figure 9 are left empty as quantum dots. This area is used to move the entire logical quantity vibit by performing a shuttle or SWAP operation.

[0086] Furthermore, the empty qubits between the logical qubits in Figures 9 and 10 are not necessarily empty; they may contain data qubits, syndrome qubits, or electrons waiting to act as reference electrons. They are simply not operating at the timings shown in Figures 9 and 10.

[0087] Up to Example 4, we described how to arrange and operate qubits, focusing on syndrome measurement for error detection, and the operation methods of logical qubits. In this example, we will describe how these operations are utilized when viewed from the perspective of the entire system.

[0088] Figure 11 shows an example of the computer configuration of this embodiment. Figure 11 is similar to the configuration of a normal computer, but is characterized by the inclusion of a quantum computing device 1000. The quantum computing device 1000 is a quantum computing device consisting of a qubit array as described in Examples 1 to 4. Other general calculations are performed by the general computing device 2002.

[0089] The above configuration may be implemented as an integrated computer, or any part of it, such as the main memory 2001, general processing unit 2002, control unit 2003, auxiliary storage device 2004, input device 2005, output device 2006, etc., may be implemented using other computers connected via a network.

[0090] General calculations are performed using the same procedures as a regular computer. Data is exchanged between the main memory 2001 (storage unit) and the general arithmetic unit 2002 (processing unit), and calculations are carried out by repeating this process. The control unit 2003 directs the entire process. Programs executed by the general arithmetic unit 2002 are stored in the main memory 2001. If the storage capacity of the main memory 2001 is insufficient, the auxiliary storage device 2004, also a storage unit, is used. An input device 2005 is used for inputting data and programs, and an output device 2006 is used for outputting results. The input device 2005 includes manual input devices such as a keyboard, as well as an interface for network connection. This interface also doubles as an output device.

[0091] Quantum computation is performed using a similar procedure. Data is exchanged between the main memory 2001, which is the memory unit, and the quantum computing device 1000, which is the calculation unit, and the calculation proceeds by repeating this process. The control unit 2003 directs the entire process. The program executed by the quantum computing device 1000 is stored in the main memory 2001, which is the memory unit.

[0092] The program is converted into a language used by the quantum computing device 1000 using the general processing unit 2002 and stored in the main memory 2001. If the storage capacity is insufficient, the auxiliary memory device 2004, which is also a memory unit, is used. This language-based program is sent from the main memory 2001 to the quantum computing device 1000, and the control unit 2003 sends control signals to the quantum computing device 1000 according to the language-based program to execute the calculations. The execution results of the quantum computing device 1000 are sent to the main memory 2001 and, if necessary, are post-processed by the general processing unit 2002.

[0093] By minimizing the decoherence by keeping the shuttle distance to a minimum, as described in the above embodiment, fault-tolerant quantum computing can be realized.

[0094] 101 Syndrome qubit 111 Interaction 112 Interaction 121 Reference electron 122 Reference electron 123 Reference electron 131 Output current line path 151 Data qubit 1000 Quantum computing unit 2001 Main memory 2002 General computing unit 2003 Control unit 2004 Auxiliary memory 2005 Input device 2006 Output device

Claims

1. A quantum error detection method using a plurality of data qubits and a plurality of syndrome qubits, comprising: a first step of forming a lattice with edges having at least three quantum dots, placing the data qubits in the quantum dots at the vertices of the lattice, and placing the syndrome qubits in the quantum dots inside the lattice; a second step of moving the syndrome qubits in a first row direction and placing them in the quantum dots on the first edge of the lattice, and transferring the information of the first data qubit and the second data qubit placed in the quantum dots at the vertices of the lattice on the first edge to the syndrome qubit, respectively; a third step of moving the syndrome qubits in a second row direction opposite to the first row direction and placing them in the quantum dots on the second edge facing the first edge, and transferring the information of the third data qubit and the fourth data qubit placed in the quantum dots at the vertices of the lattice on the second edge to the syndrome qubit, respectively; A quantum error detection method characterized by comprising: a fourth step of measuring the syndrome qubit on which the information of the data qubit has been transferred in the second and third steps.

2. The quantum error detection method according to claim 1, characterized in that the plurality of data qubits and the plurality of syndrome qubits are arranged in a two-dimensional array in which quantum dots are arranged in the column direction and row direction.

3. The quantum error detection method according to claim 1, characterized in that, in the third step, the syndrome qubit is moved in the second row direction to be placed in a quantum dot inside the lattice, and then the syndrome qubit placed in the quantum dot inside the lattice is moved in the second row direction to be placed in a quantum dot on the second edge.

4. The quantum error detection method according to claim 1, characterized in that, in the second step, the syndrome qubit is positioned at the location of a first quantum dot on the first edge adjacent to both the first data qubit and the second data qubit, and the information of the first data qubit and the information of the second data qubit are transferred to the syndrome qubit, respectively, and in the third step, the syndrome qubit is positioned at the location of a second quantum dot on the second edge adjacent to both the third data qubit and the fourth data qubit, and the information of the third data qubit and the information of the fourth data qubit are transferred to the syndrome qubit, respectively.

5. The quantum error detection method according to claim 1, characterized in that, in the fourth step, a reference electron is placed on a quantum dot on the third edge in the row direction connecting the first data qubit and the third data qubit; the syndrome qubit is moved in the second row direction and placed on a quantum dot inside the lattice; the information of the syndrome qubit is transferred to the reference electron; and the syndrome qubit is measured indirectly by measuring the reference electron.

6. The quantum error detection method according to claim 1, characterized in that, in the fourth step, a reference electron is placed in a quantum dot between the quantum dot inside the lattice and the quantum dot on the second edge, a current path for detecting the charge state of the quantum dot where the reference electron is located is formed between the quantum dot where the reference electron is located and the quantum dot on the second edge using a plurality of quantum dots arranged in a first column direction perpendicular to the first row direction, and the syndrome qubit is measured via the current path.

7. The quantum error detection method according to claim 1, characterized in that the plurality of syndrome qubits operate in synchronization with one another.

8. The quantum error detection method according to claim 1, characterized in that, in the first step, the data qubits are placed in the quantum dots at the vertices of the plurality of lattices, the syndrome qubits are placed in the quantum dots inside the plurality of lattices, and the second step, the third step, and the fourth step are performed simultaneously with respect to the plurality of syndrome qubits placed in the quantum dots inside the plurality of lattices.

9. A qubit device comprising a plurality of data qubits and a plurality of syndrome qubits arranged in a quantum dot array, wherein a logic qubit is formed from a portion of the plurality of data qubits, the relative positions of the plurality of data qubits are fixed within the logic qubit, the syndrome qubit is moved to an adjacent position to the data qubit that the syndrome qubit is responsible for, the syndrome qubit and the data qubit interact to transfer information from the data qubit to the syndrome qubit, and the transferred syndrome qubit is measured.

10. The qubit device according to claim 9, characterized in that the qubit filling rate of the quantum dot array is 1 / 2 or less.

11. The qubit device according to claim 9, characterized in that the transfer of information from the data qubit to the syndrome qubit is performed for at least two of the data qubits.

12. The qubit device according to claim 9, characterized in that the number of data qubits to be transferred to the syndrome qubit is in the range of 2 to 4, and the data qubits are arranged adjacent to the syndrome qubit to which they are transferred.

13. The quantum dot array is provided with a plurality of reference electrons, and in the measurement of the syndrome qubit, the syndrome qubit is made to interact with the reference electrons to transfer information of the syndrome qubit to the reference electrons, and information of the syndrome qubit is obtained through the measurement of the reference electrons, as described in claim 9.

14. The qubit device according to claim 13, characterized in that the syndrome qubit holds information as a spin state, and when the information of the syndrome qubit is transferred to the reference electron, it is converted into charge information.

15. The qubit device according to claim 9, characterized in that the data qubit is arranged in a quantum dot at the vertex of a lattice having an edge having at least three quantum dots, the syndrome qubit is arranged in a quantum dot inside the lattice, the syndrome qubit is moved in the row direction so that the data qubit and the syndrome qubit are in nearest neighbor, and the syndrome qubit is positioned on the edge of the lattice in the column direction, and the information of the data qubit is transferred to the syndrome qubit.

16. The qubit device according to claim 15, characterized in that the syndrome qubit is measured indirectly by arranging a reference electron at a predetermined position in the lattice and measuring the reference electron.

17. The qubit device according to 16, characterized in that the reference electrons are arranged on the edges of the lattice in the row direction of the lattice so as not to hinder the movement of the syndrome qubit in the row direction.

18. The qubit device according to 16, characterized in that the reference electron is placed in a quantum dot between a quantum dot inside the lattice and a quantum dot on the edge of the lattice in the column direction, and a current path for detecting the charge state of the quantum dot where the reference electron is located is formed between the quantum dot where the reference electron is located and the quantum dot on the edge of the lattice in the column direction using a plurality of quantum dots arranged in the column direction, and the syndrome qubit is measured via the current path.

19. The qubit device according to claim 9, characterized in that the plurality of syndrome qubits operate in synchronization with one another.

20. A quantum computer comprising a quantum dot array and a control device for controlling the quantum dot array, wherein the quantum dot array has a plurality of data qubits and a plurality of syndrome qubits arranged thereon, a portion of the plurality of data qubits constitutes a logic qubit, the relative positions of the plurality of data qubits are fixed within the logic qubit, the control device moves the syndrome qubits to adjacent positions to the data qubits that the syndrome qubits are responsible for, the syndrome qubits and the data qubits interact to transfer information from the data qubits to the syndrome qubits, and controls the device to measure the transferred syndrome qubits.

21. The quantum computer according to claim 20, characterized in that the qubit filling rate of the quantum dot array is 1 / 2 or less.

22. The quantum computer according to claim 20, characterized in that the plurality of syndrome qubits operate in synchronization with one another.

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