KR20220115049A - Quantum system and method for measuring state of qubit of quantum processor - Google Patents

Abstract

A method for measuring a state of qubits of a quantum processor and a quantum system provide a control signal for controlling a state of n number of qubits provided in the quantum processor as qubits, perform a bit-flip that inverts the state of at least one among the qubits, enable a read-out of an output qubit value of the bit-flipped qubits, and enable a measurement error for the output qubit value to generate an error model representing a probability of occurrence based on a reading result of the output qubit value.

Description

Quantum system and method for measuring state of qubit of quantum processor

A quantum system and a method of measuring the state of qubits in a quantum processor.

A quantum computer can be defined as a computational machine device that uses quantum mechanical phenomena such as quantum superposition or quantum entanglement as a principle of operation to perform data processing. A unit element (or the information itself) that can store information using quantum mechanical principles is called a quantum bit or qubit, which can be used as a basic unit of information in a quantum computer.

A bit used in a classical information storage device has a state of “0” or “1”, whereas a qubit has a state of “0” and “1” due to superposition. can In addition, interactions between qubits can be made by entanglement. Due to the characteristics of these qubits, 2 ^N pieces of information can be created using N qubits. Accordingly, as the number of qubits is increased, the amount of information and processing speed can be exponentially increased. However, as the number of qubits increases, a method capable of mitigating the measurement error of the states of the accompanying qubits is required.

A quantum system and a method for measuring the state of qubits of a quantum processor are provided, and other technical problems can be inferred from the embodiments described below.

According to one aspect, a method for measuring the state of qubits of a quantum processor includes providing a control signal for controlling the state of n qubits provided in the quantum processor to the qubits. ; performing a bit-flip that inverts the state of at least one of the qubits; reading out the output qubit values of the bit-flipped qubits; and generating an error model representing a probability of occurrence of a measurement error with respect to the output qubit value based on the reading result of the output qubit value.

In addition, performing the bit-flip inverts a state measured for at least one randomly selected qubit among the qubits set by the control signal.

In addition, the error model may be a response matrix including elements representing the probability of a measurement error for each of the 2 ⁿ output qubit values combinable into the n qubits.

In addition, the 2 ⁿ elements include 2 ⁿ x 2 ⁿ elements arranged to have symmetry.

In addition, performing the bit-flip performs the bit-flip to obtain an averaged probability of measurement error by removing the effect of an error bias or quantum entanglement between the qubits.

The method further includes obtaining a true qubit value of the qubits by correcting the output qubit value using the error model.

Also, in the reading step, the output qubit value is read by measuring a state corresponding to |0> or a state corresponding to |1> for each of the qubits.

In addition, the bit-flip is performed using a Pauli X gate.

According to another aspect, a quantum system includes a quantum processor having n qubits; and a quantum controller for controlling the quantum processor, wherein the quantum controller provides a control signal for controlling the state of the qubits to the qubits, and the state of at least one of the qubits. performing a bit-flip inverting , read-out the output qubit values of the bit-flipped qubits, and based on the reading result of the output qubit values, the output queue Creates an error model representing the probability that a measurement error will occur for a bit value.

In addition, the quantum controller inverts the state measured for at least one randomly selected qubit among the qubits set by the control signal.

In addition, the error model may be a response matrix including elements representing the probability of a measurement error for each of the 2 ⁿ output qubit values combinable into the n qubits.

In addition, the 2 ⁿ elements include 2 ⁿ x 2 ⁿ elements arranged to have symmetry.

In addition, the quantum controller performs the bit-flip to obtain an averaged probability of measurement error by removing the effect of an error bias or quantum entanglement between the qubits.

In addition, the quantum controller obtains a true qubit value of the qubits by correcting the output qubit value using the error model.

Also, the quantum controller reads the output qubit value by measuring a state corresponding to |0> or a state corresponding to |1> for each of the qubits.

In addition, the bit-flip is performed using a Pauli X gate.

1 is a diagram for explaining a quantum system according to an embodiment.
2 is a diagram for explaining a hardware configuration of a quantum controller according to an embodiment.
3 is a diagram for explaining a cycle of measurement error correction in a quantum system according to an embodiment.
4 is a diagram for explaining a measurement error of qubits according to an embodiment.
5 is a diagram for explaining a measurement error in a known quantum system.
6 is a flowchart of a method for measuring the state of qubits of a quantum processor according to an embodiment.
7 is a diagram for explaining a general error model.
8A and 8B are diagrams for explaining bit-flip on a measured qubit state according to an embodiment.
9 is a diagram for explaining a response matrix of an error model according to an embodiment.
FIG. 10 is a diagram for explaining a simulation result comparing response matrix fidelity of a scheme using bit-flip and a conventional scheme.
11 is a graph for explaining a simulation result comparing the fidelity of a response matrix between a technique using a bit-flip and a conventional technique.
12 is a graph for explaining how the benefit of response matrix fidelity increases with the number of measured qubits.

Hereinafter, various embodiments will be described with reference to the accompanying drawings. Terms used for the description of the embodiments are not intended to limit the scope of the rights to the specific embodiments, and various changes, equivalents, and/or substitutes other than the specific embodiments may be included in the scope of rights. In connection with the description of the drawings, like reference numerals may be used for like components. The singular expression may include the plural expression unless the context clearly dictates otherwise. Expressions such as “A or B” or “A and/or B” may include all possible combinations of the items listed together. Expressions such as "first," "second," etc. can modify the corresponding elements regardless of order or importance, and are used only to distinguish one element from another element, and do not limit the elements. .

In the description of the embodiments, when a certain part is connected to another part, it includes not only a case in which it is directly connected, but also a case in which another component is interposed therebetween. Also, when a part 'includes' a component, this means that other components may be further included, rather than excluding other components, unless otherwise stated. However, the term 'comprising' should not be construed as necessarily including all of the various elements or various steps described in the specification.

1 is a diagram for explaining a quantum system according to an embodiment.

Referring to FIG. 1 , a quantum system 1 may include a quantum processor 10 and a quantum controller 20 . The quantum processor 10 may include a multi-qubit 100 including a first qubit 110-1, a second qubit 1102, ..., an n-th qubit 110-n. have. (n is a natural number)

The quantum system 1 is a computing system using multi-qubits 100 as a unit element (or information itself) capable of storing information using quantum mechanical principles.

Specifically, the quantum system 1 may be implemented using various techniques capable of manipulating and measuring the quantum state of the multi-qubit 100 . For example, the quantum system 1 is a quantum dot device (spin based and spatial based), a trapped-ion device, a superconducting quantum computer, an optical grating. lattices), nuclear magnetic resonance computers, solid-state NMR Kane quantum devices, electrons-on-helium quantum computers, cavity quantum electrodynamics (CQED) devices, It may be implemented using a molecular magnet computer, a fullerene-based ESR (ESR) quantum computer, or the like, but is not necessarily limited thereto.

That is, the driving principle of the quantum system 1 in this embodiment can be implemented using the examples described above, and the specific physical implementation used for the multi-qubit 100 is the driving employed in the quantum system 1 . It may be employed or modified in any suitable manner according to the principle.

The quantum system 1 can perform calculations using quantum mechanical phenomena such as superposition and entanglement. Unlike classical digital computers, which store data in one of two distinct states (0 or 1), quantum computation is qubits (quantum bits) that allow superposition of states (110-1, 110-2, . .., 110-n) can be used.

The qubits 110-1, 110-2, ..., 110-n may be implemented using physically distinct quantum states of elementary particles such as electrons and photons. For example, two states of qubits 110-1, 110-2, ..., 110-n using the polarization of a photon can be distinguished as vertical polarization and horizontal polarization, and similarly, using the spin of an electron Two states of the qubits 110-1, 110-2, ..., 110-n can be distinguished as up-spin and down-spin.

These two states of qubits 110-1, 110-2, ..., 110-n can be expressed as binary information such as |0> or |1> using Dirac notation. have. However, the qubits 110-1, 110-2, ..., 110-n of the quantum system 1 may be in the superposition of two states at the same time, which may be a unique and basic characteristic of quantum computing. That is, the two states |0> and |1> may exist at the same time, and in this case, the multi-qubit 100 may perform an operation in the two states at once. Accordingly, 2 ⁿ binary representations of n qubits 110-1, 110-2, ..., 110-n are possible, and 2 ⁿ operations are simultaneously performed through superposition of 2 ⁿ states. You may.

The multi-qubit 100 provided in the quantum processor 10 may be controlled in response to a signal transmitted from the quantum controller 20 . The quantum controller 20 is a magnetic field source or electric field source that is inductively or capacitively coupled to each of the qubits 110-1, 110-2, ..., 110-n. ) can be used to control the qubit state.

For example, quantum controller 20 may execute instructions included in compiled quantum program code that specify a quantum runtime. The quantum program code may be implemented as software running on the processor of the quantum controller 20 . An example of quantum program code may be specifying operations according to Open Quantum Assembly Language (QASM). However, the code used by the quantum controller 20 is not limited to a specific language.

2 is a diagram for explaining a hardware configuration of a quantum controller according to an embodiment.

Referring to FIG. 2 , the quantum controller 20 may include a quantum control circuit 210 , a measurement circuit 220 , an error analyzer 230 , and an interface 240 . In the quantum controller 20 illustrated in FIG. 2 , hardware components related to the embodiment are mainly illustrated for convenience of description. Accordingly, although not shown in FIG. 2 , the quantum controller 20 includes other hardware components (eg, memory) or other general-purpose components for driving the quantum controller 20 . more may be included.

The quantum control circuit 210 may include both a general-purpose or special-purpose processor for executing quantum program code or a dedicated circuit for controlling the multi-qubit 100 . The quantum control circuit 210 may be coupled or integrated with one or more physical layer (PHY) devices for performing operation control on the qubits 100 designated by the quantum runtime. For example, the physical layer device may include an electromagnetic transmitter for generating microwave pulses. Alternatively, the physical layer device may generate another electromagnetic signal for manipulating the qubit 100 according to the quantum program code.

The quantum control circuit 210 provides a control signal for controlling the qubit state of the multi-qubit 100 to the multi-qubit 100, and in response, each qubit of the multi-qubit 100 is set to a predetermined state. can be controlled to have

Each qubit state of the multi-qubit 100 may be measured or read-out by the measurement circuit 220 . As described above, during measurement, each qubit may be measured in a state corresponding to |0> or a state corresponding to |1>.

The error analyzer 230 generates an error model for error correction in consideration of a measurement error occurring during qubit measurement. Noise, such as measurement error, is one of the important factors that can reduce the accuracy of quantum computation. Due to the nature of quantum computing, a measurement error may occur due to short qubit decoherence times. The error analyzer 230 corrects this measurement error for the difference between the true qubit state and the measured qubit state. An error model suitable for the quantum system 1 may be generated by probabilistically analyzing the errors.

3 is a diagram for explaining a cycle of measurement error correction in a quantum system according to an embodiment.

In operation 310 , the multi-qubit 100 included in the quantum processor 10 may initialize the qubit state under the control of the quantum controller 20 . For example, each qubit may be initialized to a particular spin direction or initialized to an entangled state.

In step 320 , the quantum controller 20 provides the multi-qubit 100 with a qubit control signal for controlling the multi-qubit 100 to a predetermined state.

In step 330 , the quantum controller 20 (eg, the measurement circuit 220 ) measures the state of each qubit of the multi-qubit 100 . In other words, the quantum controller 20 may read the output qubit value of the multi-qubit 100 .

In operation 340 , the quantum controller 20 (eg, the error analyzer 230 ) generates an error model representing the probability that a measurement error for the output qubit value will occur based on the reading result of the output qubit value. .

The cycle of steps 310 to 340 may be repeatedly performed until an error model suitable for the multi-qubit 100 is generated.

4 is a diagram for explaining a measurement error of qubits according to an embodiment.

Referring to FIG. 4 , even if a control signal for controlling the multi-qubit 10 having n qubits to a predetermined state (eg, |0 1 … 1 0 > state) is applied, in a specific qubit Due to the measurement error of , an output qubit state (eg, |0 1 … 0 0 > state) different from the input qubit state may be measured. Such a measurement error may be caused by entanglement between each qubit or an error of a measurement device (ie, a readout error).

Meanwhile, although the measurement error in one qubit has been exemplarily described in FIG. 4 , the measurement error may occur simultaneously in several qubits. As the number of qubits included in the quantum processor 10 increases, the probability of occurrence of a measurement error also increases, and accordingly, the reliability of qubit operation may be lowered. Therefore, a method for reducing the error by correcting the measurement error of the qubit state is required.

5 is a diagram for explaining a measurement error in a known quantum system. 5 is a graph showing the average qubit measurement error rate of the quantum system of ' ibmq_paris '. Referring to this, it can be seen that the probability that a measurement error occurs mostly increases as the number of qubits increases. .

6 is a flowchart of a method for measuring the state of qubits of a quantum processor according to an embodiment. Since the method of FIG. 6 relates to the steps processed in time series by the quantum system 1 of FIG. 1 , the contents described for the quantum system 1 are also applied to the method of FIG. 6 , even if omitted below. can

In step 601, the quantum controller 20 generates a control signal for controlling the state of the n qubits 110-1, 110-2, ..., 110-n provided in the quantum processor 10, It is provided as qubits 110-1, 110-2, ..., 110-n.

In step 602, the quantum controller 20 performs a bit-flip that inverts the state of at least one of the qubits 110-1, 110-2, ..., 110-n. carry out Here, the quantum controller 20 may invert the state measured for at least one randomly selected qubit among the qubits 110-1, 110-2, ..., 110-n set by the control signal. can The reason for performing the bit-flip scheme in this way is to reduce the effect of an error bias or quantum entanglement between the qubits 110-1, 110-2, ..., 110-n. This may be in order to obtain an averaged probability of the measurement error by removing it.

In step 603, the quantum controller 20 reads out the output qubit values of the bit-flipped qubits. That is, the quantum controller 20 outputs a state corresponding to |0> or a state corresponding to |1> for each of the qubits 110-1, 110-2, ..., 110-n. The qubit value can be read.

In step 604 , the quantum controller 20 generates an error model representing the probability of occurrence of a measurement error for the output qubit value based on the reading result of the output qubit value. The error model is a response matrix including elements representing the probability of a measurement error for each of 2 ⁿ output qubit values combinable into n qubits, which will be described in more detail below.

7 is a diagram for explaining a general error model.

Referring to FIG. 7 , assuming a quantum system having two qubits, a general error model can be expressed as a response matrix M as shown in Equation 1 below.

Each element M _i,j of the response matrix may be expressed as a probability p _(i|j) . p _(i|j) means the probability (possibility) that the input state |j> of the qubit is read-out as |i>. For example, p _(10|01) means the probability that the input state of a certain qubit was |01>, but was read as |10> as a measurement result.

As a result of generating a general error model in any system, a response matrix M having elements of probabilities as in table 701 can be obtained. According to the table 701, the probability p _(10|01) that the input state was |01> but was read as |10> is 0.0002.

However, the error model of the response matrix M according to the conventional method has a problem in that a probability must be obtained for the number of combinations possible with all qubits. That is, when two qubits are provided, an error model can be generated only by calculating the probability for the number of 16 (ie, 4(=2 ² ) x 4(=2 ² )) cases. Therefore, since it may take a lot of time to calculate the probability in all combinations of qubit states, the problem that the error model may be inaccurate and the number of qubits may be inaccurate due to the nature of qubits whose states may change over time As the number increases, there is a problem that more time is required to generate the error model. For example, as the number of qubits increases, the number of probabilities p _(i|j) to be calculated also increases exponentially, so the error model according to the general method may be less efficient.

In contrast, according to the present embodiment, as a method for generating an error model only by measuring a single input state, the efficiency of generating the error model can be increased.

8A and 8B are diagrams for explaining bit-flip on a measured qubit state according to an embodiment.

Referring to FIGS. 8A and 8B , the quantum controller 20 may perform a bit-flip on the qubit state measured from at least one qubit among all n qubits. Here, the qubits to be bit-flip may be randomly selected.

The example of FIG. 8A is a case in which 'qubit 1' and 'qubit n' among n qubits are selected to perform bit-flip, and the example of FIG. 8B is 'qubit 2' among n qubits. and 'qubit n-1' are selected to perform bit-flip.

As such, when bit-flips are arbitrarily performed on the measured qubit states, correlations due to entanglement between qubits or error bias of qubit states are removed, so that errors can be averaged.

For example, in the response matrix M in FIG. 7, p _(10|01) = 0.0002 and p _(10|11) = 0.0286 were obtained with different probability values. This may be due to differences due to correlation between qubits such as qubit entanglement or error bias in the |01> state and the |11> state. Therefore, by performing bit-flip by random qubit selection and averaging the error between qubits, the generation of the error model can be simplified and more efficient.

Meanwhile, the bit-flip in the present embodiment may be performed as a Pauli X operation using a Pauli X gate, but is not limited thereto.

The quantum controller 20 repeatedly calculates the probability of being read into an output qubit state different from the input qubit state by repeatedly performing bit-flip of randomly selected qubits when measuring n qubits. , an error model can be created.

9 is a diagram for explaining a response matrix of an error model according to an embodiment.

의 에러 모델을 생성할 수 있다.Referring to FIG. 9 , assuming a quantum system equipped with two qubits, the quantum controller 20 (that is, the error analyzer 230 ) uses the result of reading the output qubit values of the bit-flipped qubits. Based on the response matrix as in Equation 2

You can create an error model of

(i)는 미리 설정된 단일 입력 상태가 비트-플립에 의해 |i>로 독출되었을 확률을 의미한다. 예를 들어, 2개의 큐비트들이 미리 설정된 입력 상태로부터 비트-플립에 의해 |00>으로 독출된 경우,

(00)은 |00>으로 잘못 측정되었을 확률을 나타낸다. 유사하게,

(01),

(10) 및

(11) 각각은 비트-플립에 의해 |01>, |10>, |11> 으로 각각 잘못 측정되었을 확률을 나타낸다.According to Equation 2,

(i) denotes a probability that a preset single input state is read as |i> by bit-flip. For example, when two qubits are read as |00> by bit-flip from a preset input state,

(00) indicates the probability of being measured incorrectly as |00>. Similarly,

(01),

(10) and

(11) Each represents the probability of being incorrectly measured as |01>, |10>, and |11> by bit-flip, respectively.

는 비트-플립에 의한 인위적인 측정 에러를 유발함으로써, 얽힘이나 에러 바이어스와 같은 영향을 제거하여 에러를 평균화할 수 있다. 또한, 입력 큐비트 상태의 모든 조합에 대응하는 출력 큐비트 상태의 모든 조합의 경우의 수를 계산하지 않고, 단순히 출력 큐비트 상태(즉, 출력 큐비트 값)의 측정만으로도 에러 모델의 응답 매트릭스를 획득할 수 있다. 즉, 도 9에 도시된 바와 같이, 본 실시예에 따른 에러 모델은 응답 매트릭스

는 2ⁿ개 엘리먼트들(즉,

(00),

(01),

(10) 및

(11))이 대칭성을 갖도록 배치된 2ⁿ x 2ⁿ 엘리먼트들을 포함할 수 있으므로, 보다 빠른 시간 내에 효율적으로 에러 모델을 생성하여 에러 보정을 수행할 수 있다.Response matrix of the error model according to the present embodiment

By causing an artificial measurement error due to bit-flip, it is possible to average the error by eliminating influences such as entanglement or error bias. In addition, without counting the number of cases of all combinations of output qubit states corresponding to all combinations of input qubit states, simply measuring the output qubit state (i.e., the output qubit value) is enough to calculate the response matrix of the error model. can be obtained That is, as shown in Fig. 9, the error model according to the present embodiment is a response matrix

is 2 ⁿ elements (i.e.,

(00),

(01),

(10) and

Since (11)) may include 2 ⁿ x 2 ⁿ elements arranged to have symmetry, error correction can be performed by efficiently generating an error model within a shorter time.

는 수학식 3 및 수학식 4를 참고하여 획득될 수 있다.Meanwhile, in FIG. 9, an error model was generated assuming two qubits, but the response matrix of the generalized error model for n qubits

can be obtained with reference to Equations 3 and 4.

Referring to Equations 3 and 4, s means a decimal value of the measured qubit state (that is, the output qubit state), and X ^(s) is Pauli x by Pauli X gate operation (ie bit-flip).

와 같은 에러 모델을 이용하여 출력 큐비트 값(또는 출력 큐비트 상태)을 보정함으로써, 큐비트들의 실제(true) 큐비트 값(또는 실제 큐비트 상태)을 획득할 수 있다. 예를 들어, 측정된 큐비트 값 p_obs는 아래와 같은 수학식 5를 이용하여 보정됨으로써 실제 큐비트 값 p_true가 획득될 수 있다.When the quantum controller 20 performs qubit operation, the response matrix

By correcting the output qubit value (or output qubit state) using an error model such as For example, the measured qubit value p _obs may be corrected using Equation 5 below to obtain an actual qubit value p _true .

를 빠른 시간 내에 생성하여 에러 보정을 수행함으로써, 큐비트 개수가 증가하더라도 큐비트 연산의 처리 속도 및 성능을 효율적으로 증대시킬 수 있다.As such, the quantum system 1 according to the present embodiment provides a response matrix of an error model through measurement of bit-flipped qubit values.

By quickly generating and performing error correction, it is possible to efficiently increase the processing speed and performance of qubit operation even if the number of qubits increases.

FIG. 10 is a diagram for explaining a simulation result comparing response matrix fidelity of a scheme using bit-flip and a conventional scheme.

The simulation data of FIG. 10 is a quantum measurement error reduction using a conventional technique (full mitigation, tensor product noise model (TPN)) and a technique using a bit-flip according to the present embodiment (Bit-flip, TPN+Bit-flip) The horizontal axis of the data is the number of measurements, and the vertical axis is the fidelity of the measured response matrix. The closer the fidelity of the matrix is to 1, the more it means that the measurement error is removed. The data in Figure 10 has 5 qubits. This is the result measured in a quantum system.For each calibration shot, in the case of full-mitigation, it is necessary to measure 32 (= 2 ⁵ ) states, and for Bit-flip, |00000> one qubit state is required. measurement is required, and TPN requires measurement of two states, |00000> and |11111> Bit-flip and TPN+Bit-flip require only one measurement, so it will be explained in the data of FIG. As described above, it can be seen that the method of this embodiment using the bit-flip converges to 1 in the fidelity of the matrix faster than the conventional methods.

11 is a graph for explaining a simulation result comparing the fidelity of a response matrix between a technique using a bit-flip and a conventional technique.

The simulation data of FIG. 11 is data obtained by the simulation of FIG. 10 after increasing a specific error in the existing response matrix (ε > 0) in order to understand the effect on the error correlated by entanglement between qubits. In the case of the simulation of FIG. 11, a more complex model is required to calculate the existing response matrix due to the increased error. It can be seen that in the technique (Bit-flip) of this embodiment using bit-flip, the fidelity of a matrix approaches 1 even when a correlated error is increased, whereas the conventional technique (TPN) does not.

12 is a graph for explaining how the benefit of response matrix fidelity increases with the number of measured qubits. 12 is a simulated result under the condition that the response matrix measured in ibmq_manhattan is used and the correlation error is increased to 10 (ε=10). The total number of measurements was fixed at 2 ⁿ * 100 (n is the number of qubits). The conventional technique (Full Mitigation) is a method of acquiring all elements of each column of the response matrix, and it can be seen that the fidelity is lowered because the number of measurements allocated to each column decreases exponentially with respect to the number of qubits.

Referring to the simulation results described in FIGS. 10 to 12 , compared to the conventional techniques (full mitigation, TPN), in the technique using the bit-flip according to the present embodiment, the fidelity of the response matrix is reduced to 1 in a short time under any conditions. Since convergence, it can be understood by those skilled in the art that it can be applied to more efficient correction of measurement errors.

The above-described embodiments are merely examples, and do not limit the technical scope in any way. For brevity of the specification, descriptions of well-known electronic components, control systems, software, and other functional aspects have been omitted. In addition, the connections or connecting members of the lines between the components shown in the drawings exemplarily represent functional connections and/or physical or circuit connections, and in an actual device, various functional connections, physical connections that are replaceable or additional It may be implemented as a connection, or circuit connections.

Meanwhile, the above-described embodiments can be written as a program that can be executed on a computer, and can be implemented in a general-purpose digital computer that operates the program using a computer-readable recording medium. In addition, the structure of data used in the above-described embodiments may be recorded in a computer-readable recording medium through various means. The computer-readable recording medium includes a storage medium such as a magnetic storage medium (eg, a ROM, a floppy disk, a hard disk, etc.) and an optically readable medium (eg, a CD-ROM, a DVD, etc.).

Those of ordinary skill in the art related to the present embodiment will understand that the embodiment may be implemented in a modified form without departing from the essential characteristics of the above description. Therefore, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense. The scope of the rights is indicated in the claims rather than the above description, and all differences within the scope equivalent thereto should be construed as included in the present embodiment.

Claims (16)

In a method for measuring the state of qubits of a quantum processor,
providing a control signal for controlling the state of n qubits provided in the quantum processor to the qubits;
performing a bit-flip that inverts the state of at least one of the qubits;
reading out the output qubit values of the bit-flipped qubits; and
and generating an error model representing a probability of occurrence of a measurement error for the output qubit value based on a reading result of the output qubit value. The method of claim 1,
The step of performing the bit-flip is
Inverting the measured state for at least one randomly selected qubit among the qubits set by the control signal. The method of claim 1,
The error model is
a response matrix comprising elements representing the probability of a measurement error for each of the 2 ⁿ output qubit values combinable into the n qubits. 3. The method of claim 2,
The response matrix is
and 2 ⁿ x 2 ⁿ elements arranged such that the 2 ⁿ elements are symmetric. The method of claim 1,
The step of performing the bit-flip is
performing the bit-flip to obtain an averaged probability of measurement error by removing the effect of an error bias or quantum entanglement between the qubits. The method of claim 1,
and correcting the output qubit value using the error model to obtain a true qubit value of the qubits. The method of claim 1,
The reading step is
Reading the output qubit value by measuring a state corresponding to |0> or a state corresponding to |1> for each of the qubits. The method of claim 1,
The bit-flip is
A method performed using a Pauli X gate. In a quantum system,
a quantum processor with n qubits; and
A quantum controller for controlling the quantum processor,
The quantum controller is
providing a control signal for controlling the state of the qubits to the qubits;
performing a bit-flip that inverts the state of at least one of the qubits;
reading out the output qubit values of the bit-flipped qubits,
generating an error model indicating a probability of occurrence of a measurement error with respect to the output qubit value based on the reading result of the output qubit value,
quantum system. 10. The method of claim 9,
The quantum controller is
Inverting the measured state for at least one randomly selected qubit among the qubits set by the control signal. 10. The method of claim 9,
The error model is
A quantum system, which is a response matrix including 2 ⁿ elements representing the probability of a measurement error for each of the 2 ⁿ output qubit values combinable into the n qubits. 12. The method of claim 11,
The response matrix is
and 2 ⁿ x 2 ⁿ elements arranged such that the 2 ⁿ elements are symmetric. 10. The method of claim 9,
The quantum controller is
performing the bit-flip to obtain an averaged probability of measurement error by removing the effect of an error bias or quantum entanglement between the qubits. 10. The method of claim 9,
The quantum controller is
and correcting the output qubit value using the error model to obtain a true qubit value of the qubits. 10. The method of claim 9,
The quantum controller is
A quantum system for reading the output qubit value by measuring a state corresponding to |0> or a state corresponding to |1> for each of the qubits. 10. The method of claim 9,
The bit-flip is
A quantum system, performed using a Pauli X gate.

Images