Single quantum bit relative phase determination method, device, equipment and storage medium

Abstract

The present application discloses a method, device, equipment and storage medium for determining the relative phase of a single quantum bit. The method comprises: performing a first scan on the phase gate on the Bloch sphere by rotating a first set angle around the z axis; performing a second scan at each scanning point by rotating a second set angle around the y axis; when the phase gate rotates the quantum bit state vector to the (+x, z) half plane, a heat map is drawn with the first scanning range and the second scanning range as axes, and the highest probability point of the |1> state is measured from the heat map; the relative phase angle of the single quantum bit is calculated by subtracting the phase angle of the phase gate corresponding to the highest probability point from 2π. The present application converts the problem of finding the relative phase of a single quantum bit pure state into what angle of phase gate can be used to rotate the bit state vector to the (+x, z) half plane, and the entire determination process is simple and intuitive.

Description

Technical Field

[0001] The present invention relates to the field of quantum computing technology, and in particular to a method, device, equipment and storage medium for determining the relative phase of a single quantum bit. Background Art

[0002] In 1965, Gordon Moore proposed the famous Moore's Law. He pointed out that the number of transistors per square millimeter of integrated circuit chips will double every 18 months. However, as the size of transistors becomes smaller and smaller, they will face the quantum limit problem, which will lead to the failure of Moore's Law and the improvement of classical computer computing power will become increasingly difficult. Quantum computing is a potential technology to solve this problem.

[0003] Unlike classical computing, which uses the level of electricity to represent a bit of binary 0 or 1, quantum computing often uses various two-level systems to represent the |0> or |1> of a quantum bit (here, the Dirac symbol is used). In addition, due to the superposition principle of quantum mechanics, a single quantum bit can be in a superposition state of the form a|0>+b|1>, where a and b are called probability amplitudes, both in complex form. Since there is no physical observation effect on the global phase of a quantum bit, the general form of the pure state of a quantum bit can be written as Where c and d are both real numbers, and the relative phase of a single quantum bit is reflected in the e exponential term.

[0004] The general pure state of a single qubit is written as Due to c 2 +d 2 =1, so if Figure 1 As shown, the pure state of a single quantum bit can be represented by a unit vector pointing from the origin in the three-dimensional coordinate system to the unit sphere (Bloch sphere), and without loss of generality, the pure state of a single quantum bit can be written as When measuring the quantum bit, we will have (cosθ) 2 The probability of measuring the |0> state, (sinθ) 2 The probability of measuring the |1> state is that the measurement result is only related to θ. Since the measurement of the quantum bit is a projection process to the calculation basis vector, the quantum bit will collapse to the state of one of the calculation basis vectors with probability after the measurement, so the relative phase of the quantum bit cannot be directly measured from the measurement result. However, this phase information is the basis for distinguishing quantum states from classical states, and is also a condition for realizing quantum error correction and quantum Fourier transform algorithms. It is particularly important to find a method that can simply determine the phase angle of the measured state. The traditional method for determining the phase angle is quantum state tomography, but accurately determining the phase angle through quantum state tomography depends on high-precision quantum bit measurement, control and reading, and quantum state tomography requires solving overdetermined equations. Due to the introduction of control and measurement errors, it is generally impossible to obtain an analytical solution to the overdetermined equation.

[0005] Therefore, how to simply determine the relative phase size of a single quantum bit is a technical problem that needs to be urgently solved by technicians in this field. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a method, device, equipment and storage medium for determining the relative phase of a single quantum bit, which can easily and intuitively determine the relative phase of a single quantum bit. The specific scheme is as follows:

[0007] A method for determining the relative phase of a single quantum bit, comprising:

[0008] Performing a first scan on the phase gate on the Bloch sphere by rotating the phase gate around the z-axis by a first set angle;

[0009] At each scanning point, performing a second scan by rotating about the y-axis by a second set angle;

[0010] When the phase gate rotates the quantum bit state vector to the (+x, z) half plane, a heat map is drawn with the first scanning range and the second scanning range as axes, and the highest probability point of the |1> state is measured from the heat map;

[0011] The relative phase angle of a single quantum bit is calculated by subtracting the phase angle of the phase gate corresponding to the highest probability point from 2π.

[0012] Preferably, in the above-mentioned method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention, performing a first scan on the phase gate on the Bloch sphere by rotating the first set angle around the z-axis specifically includes:

[0013] The first state vector corresponding to the single quantum bit is rotated counterclockwise around the z-axis by a first set angle to a second state vector, and a first scan is performed on the phase gate on the Bloch sphere;

[0014] While changing the first set angle, the first scanning operation is repeated.

[0015] Preferably, in the above-mentioned method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention, at each scanning point, performing a second scan by rotating a second set angle around the y-axis specifically includes:

[0016] After scanning each phase gate, the target state vector is rotated around the y-axis by a second set angle to a third state vector for a second scan;

[0017] While changing the second set angle, the second scanning operation is repeated.

[0018] Preferably, in the above-mentioned method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention, the second scan rotates the quantum bit state vector to the |1> state when and only when the phase gate just rotates the quantum bit state vector to the (+x, z) half-plane.

[0019] Preferably, in the above-mentioned method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention, the adjustment range of the first setting angle is [0, 2π]; the adjustment range of the second setting angle is [0, π].

[0020] The embodiment of the present invention further provides a single quantum bit relative phase determination device, comprising:

[0021] A first scanning module, used for performing a first scan on the phase gate on the Bloch sphere by rotating a first set angle around the z-axis;

[0022] A second scanning module, used for performing a second scan at each scanning point by rotating around the y-axis at a second set angle;

[0023] A heat map making module is used to draw a heat map with the first scanning range and the second scanning range as axes when the phase gate rotates the quantum bit state vector to the (+x, z) half plane, and measure the highest probability point of the |1> state from the heat map;

[0024] The phase angle calculation module is used to calculate the relative phase angle of a single quantum bit by subtracting the phase angle of the phase gate corresponding to the highest probability point from 2π.

[0025] Preferably, in the above-mentioned single quantum bit relative phase determination device provided in an embodiment of the present invention, the first scanning module is specifically used to rotate the first state vector corresponding to the single quantum bit counterclockwise around the z-axis by a first set angle to a second state vector, and perform a first scan on the phase gate on the Bloch sphere; while changing the first set angle, repeat the first scanning operation.

[0026] Preferably, in the above-mentioned single quantum bit relative phase judgment device provided in an embodiment of the present invention, the second scanning module is specifically used to rotate the target state vector around the y-axis by a second set angle to the third state vector for a second scan after scanning each phase gate; while changing the second set angle, repeat the second scanning operation.

[0027] An embodiment of the present invention also provides a single quantum bit relative phase determination device, comprising a processor and a memory, wherein the processor implements the above-mentioned single quantum bit relative phase determination method provided in the embodiment of the present invention when executing the computer program stored in the memory.

[0028] An embodiment of the present invention further provides a computer-readable storage medium for storing a computer program, wherein when the computer program is executed by a processor, the method for determining the relative phase of a single quantum bit as provided in an embodiment of the present invention is implemented.

[0029] It can be seen from the above technical scheme that a method, device, equipment and storage medium for determining the relative phase of a single quantum bit provided by the present invention include: performing a first scan on the phase gate on the Bloch sphere by rotating a first set angle around the z-axis; performing a second scan at each scanning point by rotating a second set angle around the y-axis; when the phase gate rotates the quantum bit state vector to the (+x, z) half-plane, a heat map is drawn with the first scanning range and the second scanning range as axes, and the highest probability point of the |1> state is measured from the heat map; the relative phase angle of the single quantum bit is calculated by subtracting the phase angle of the phase gate corresponding to the highest probability point from 2π.

[0030] The present invention converts the problem of finding the relative phase of a single quantum bit pure state into what angle of phase gate can be used to rotate the bit state vector to the (+x, z) half-plane. Specifically, a heat map is drawn by scanning the phase gate of [0,2π] and the Ry gate of [0,π] to find the point with the highest probability of measuring the |0> state. The phase angle to be found is obtained by subtracting the corresponding phase gate angle from 2π. The whole process is simple and intuitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings required for use in the embodiments or related technical descriptions are briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0032] Figure 1 Schematic diagram of the state of an existing single quantum bit vector;

[0033] Figure 2 A flow chart of a method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention;

[0034] Figure 3 A schematic diagram of possible states of a single quantum bit state vector after applying Rz(α) provided in an embodiment of the present invention;

[0035] Figure 4 A schematic diagram of possible states of a single quantum bit state vector after applying Ry(α) provided in an embodiment of the present invention;

[0036] Figure 5 A schematic diagram of a heat map provided by an embodiment of the present invention;

[0037] Figure 6 A schematic diagram of the structure of a device for determining the relative phase of a single quantum bit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The present invention provides a method for determining the relative phase of a single quantum bit, such as Figure 2 As shown, the following steps are included:

[0040] S201, performing a first scan on the phase gate on the Bloch sphere by rotating the phase gate around the z-axis by a first set angle;

[0041] It should be noted that any single-qubit pure state can be represented by a state vector with the center of the sphere pointing to the Bloch sphere in a three-dimensional coordinate system. The problem of finding the relative phase of a single-qubit pure state is transformed into what angle of phase gate can be used to rotate the bit state vector to the (+x, z) half plane (i.e., the +x direction in the (x, z) plane); here, the phase gate can be scanned with a certain step size; the adjustment range of the first set angle can be set to [0,2π];

[0042] S202, performing a second scan at each scanning point by rotating around the y-axis by a second set angle;

[0043] In practical applications, at each scanning point, the scanning is performed by rotating at certain specific angles around the Y axis. These angles can be scanning values ​​with certain step lengths within [0, π], that is, the adjustment range of the second set angle can be set to [0, π].

[0044] S203, when the phase gate rotates the quantum bit state vector to the (+x, z) half plane, a heat map is drawn with the first scanning range and the second scanning range as axes, and the highest probability point of the |1> state is measured from the heat map;

[0045] S204, using 2π minus the phase angle of the phase gate corresponding to the highest probability point to calculate the relative phase angle of the single quantum bit;

[0046] It can be understood that since the phase gate rotates counterclockwise, and the phase angle of the bit is defined as the angle between the projection of the bit state vector in the XY plane and the positive direction of the X-axis, the phase angle of the bit is 2π minus the phase value corresponding to the above phase gate.

[0047] In the above-mentioned method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention, the problem of finding the relative phase of a single quantum bit pure state is converted into what angle of phase gate can be used to rotate the bit state vector to the (+x, z) half-plane. Specifically, a heat map is drawn by scanning the phase gate of [0,2π] and the Ry gate of [0,π] to find the point with the highest probability of measuring the |0> state. The phase angle to be found is obtained by subtracting the corresponding phase gate angle from 2π. The whole process is simple and intuitive.

[0048] Further, in a specific implementation, in the above-mentioned method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention, step S201 performs a first scan on the phase gate on the Bloch sphere by rotating the first set angle around the z-axis, which may specifically include: first, rotating the first state vector corresponding to the single quantum bit counterclockwise around the z-axis by the first set angle to the second state vector, and performing a first scan on the phase gate on the Bloch sphere; then, while changing the first set angle, repeating the first scanning operation.

[0049] Specifically, a phase gate is applied to the quantum bit, and the phase gate can be written as Rz(α). Figure 3 As shown in the figure, first, the phase gate on the Bloch sphere is to rotate the state vector corresponding to the single quantum bit P around the z axis in the counterclockwise direction by an angle α to the state vector P'; then, while changing the angle α, the Rz(α) phase gate is repeatedly applied to the initial quantum bit to be measured, where the adjustment range of α is [0,2π], and the adjustment step of α should be as small as possible to ensure that the accuracy of the final result is high enough. The possible states of the quantum bit state vector in the Bloch sphere after the Rz(α) operation are as follows: Figure 3 As shown in P'.

[0050] Furthermore, in a specific implementation, in the above-mentioned method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention, step S202 performs a second scan at each scanning point by rotating around the y-axis by a second set angle, specifically including: after scanning each phase gate, rotating the target state vector around the y-axis by a second set angle to a third state vector for a second scan; while changing the second set angle, repeating the second scanning operation.

[0051] Specifically, Figure 4As shown in, first, after applying each Rz(α), the Ry(β) operation is applied to the bit state vector P' at this time. The Ry(β) operation is reflected in the Bloch sphere as a rotation of the target state vector around the y axis, with a rotation angle of β, and the rotated state vector is P"; then, while changing the β angle, the Ry(β) operation is repeatedly applied to P' after the Rz(α) operation in S2, where the adjustment range of β is [0,π], and the adjustment step of β should be as small as possible to ensure that the accuracy of the final result is high enough. The possible states of the quantum bit state vector in the Bloch sphere after the Ry(β) operation are as follows: Figure 4 As shown in "P" in the figure.

[0052] In specific implementation, in the above-mentioned method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention, the second scan can rotate the quantum bit state vector to the |1> state when and only when the phase gate just rotates the quantum bit state vector to the (+x, z) half plane. It can be seen from the basic assumptions of quantum mechanics that the probability of measuring the quantum bit to obtain the |1> state is the highest at this time.

[0053] Therefore, when executing step S203 and step S204, a heat map is drawn after scanning Rz and Ry, where the heat is the probability of measuring the |1> state, and Rz(α) corresponding to the maximum probability of measuring the |1> state in the heat map is found. Subtracting α from 2π is the phase angle to be found. .

[0054] In initial state For example, Figure 5 FIG. 4 shows a heat map obtained by using the above phase angle determination method. Figure 5 It can be seen from the figure that the α angle of the Rz(α) operation corresponding to the maximum probability point of the |1> state is 9π / 5, so the phase angle to be found is It is 2π-9π / 5=π / 5.

[0055] Based on the same inventive concept, an embodiment of the present invention also provides a device for determining the relative phase of a single quantum bit. Since the principle of solving the problem by the device is similar to that of the aforementioned method for determining the relative phase of a single quantum bit, the implementation of the device can refer to the implementation of the method for determining the relative phase of a single quantum bit, and the repeated parts will not be repeated.

[0056] In a specific implementation, the single quantum bit relative phase determination device provided by the embodiment of the present invention is as follows: Figure 6 As shown, specifically including:

[0057] A first scanning module 11 is used to perform a first scan on the phase gate on the Bloch sphere by rotating a first set angle around the z-axis;

[0058] The second scanning module 12 is used to perform a second scan at each scanning point by rotating around the y-axis by a second set angle;

[0059] A heat map making module 13 is used to draw a heat map with the first scanning range and the second scanning range as axes when the phase gate rotates the quantum bit state vector to the (+x, z) half plane, and measure the highest probability point of the |1> state from the heat map;

[0060] The phase angle calculation module 14 is used to calculate the relative phase angle of a single quantum bit by subtracting the phase angle of the phase gate corresponding to the highest probability point from 2π.

[0061] In the above-mentioned single quantum bit relative phase determination device provided in an embodiment of the present invention, through the interaction of the above-mentioned four modules, a heat map can be drawn by scanning the phase gate of [0,2π] and the Ry gate of [0,π] to find the point with the largest probability of measuring the |0> state, and the phase angle to be found is obtained by subtracting the corresponding phase gate angle from 2π. The processing process of the device is simple and intuitive.

[0062] In the specific implementation, in the above-mentioned method for determining the relative phase of a single quantum bit provided in an embodiment of the present invention, the first scanning module 11 can be specifically used to rotate the first state vector corresponding to the single quantum bit around the z-axis in a counterclockwise direction by a first set angle to a second state vector, and perform a first scan on the phase gate on the Bloch sphere; while changing the first set angle, repeat the first scanning operation. The adjustment range of the first set angle can be set to [0,2π].

[0063] In the specific implementation, in the above-mentioned single quantum bit relative phase determination method provided in the embodiment of the present invention, the second scanning module 12 can be specifically used to rotate the target state vector around the y-axis by a second set angle to a third state vector for a second scan after scanning each phase gate; while changing the second set angle, repeat the second scanning operation. The adjustment range of the second set angle can be set to [0,π].

[0064] For more specific working processes of the above modules, please refer to the corresponding contents disclosed in the above embodiments, which will not be repeated here.

[0065] Correspondingly, an embodiment of the present invention also discloses a single quantum bit relative phase determination device, comprising a processor and a memory; wherein, when the processor executes a computer program stored in the memory, the single quantum bit relative phase determination method disclosed in the aforementioned embodiment is implemented.

[0066] For more specific processes of the above method, please refer to the corresponding contents disclosed in the aforementioned embodiments, which will not be repeated here.

[0067] Furthermore, the present invention also discloses a computer-readable storage medium for storing a computer program; when the computer program is executed by a processor, the aforementioned method for determining the relative phase of a single quantum bit disclosed above is implemented.

[0068] For more specific processes of the above method, please refer to the corresponding contents disclosed in the aforementioned embodiments, which will not be repeated here.

[0069] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the devices, equipment, and storage media disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method part.

[0070] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0071] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0072] In summary, the present invention provides a method, device, equipment and storage medium for determining the relative phase of a single quantum bit, including: performing a first scan on the phase gate on the Bloch sphere by rotating a first set angle around the z axis; performing a second scan at each scanning point by rotating a second set angle around the y axis; when the phase gate rotates the quantum bit state vector to the (+x, z) half plane, a heat map is drawn with the first scanning range and the second scanning range as axes, and the highest probability point of the |1> state is measured from the heat map; the phase angle of the phase gate corresponding to the highest probability point is subtracted from 2π to calculate the relative phase angle of the single quantum bit. The present invention converts the problem of finding the relative phase of a single quantum bit pure state into what angle of the phase gate can be used to rotate the bit state vector to the (+x, z) half plane, specifically by scanning the phase gate of [0,2π] and the Ry gate of [0,π] to draw a heat map, find the point where the probability of the |0> state is the highest, and the phase angle to be found is subtracted from the corresponding phase gate angle from 2π, and the whole process is simple and intuitive.

[0073] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0074] The above is a detailed introduction to the single quantum bit relative phase determination method, device, equipment and storage medium provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for determining the relative phase of a single quantum bit, characterized in that: include: Performing a first scan on the phase gate on the Bloch sphere by rotating the phase gate around the z-axis by a first set angle; At each scanning point, performing a second scan by rotating about the y-axis by a second set angle; When the phase gate rotates the quantum bit state vector to the (+x, z) half plane, a heat map is drawn with the first scanning range and the second scanning range as axes, and the highest probability point of the |1> state is measured from the heat map; The relative phase angle of a single quantum bit is calculated by subtracting the phase angle of the phase gate corresponding to the highest probability point from 2π.

2. The method for determining the relative phase of a single quantum bit according to claim 1, characterized in that: The phase gate on the Bloch sphere is first scanned by rotating the phase gate on the Bloch sphere by a first set angle around the z-axis, specifically including: The first state vector corresponding to the single quantum bit is rotated counterclockwise around the z-axis by a first set angle to a second state vector, and a first scan is performed on the phase gate on the Bloch sphere; While changing the first set angle, the first scanning operation is repeated.

3. The method for determining the relative phase of a single quantum bit according to claim 2, characterized in that: At each scanning point, a second scan is performed by rotating about the y-axis by a second set angle, specifically including: After scanning each phase gate, the target state vector is rotated around the y-axis by a second set angle to a third state vector for a second scan; While changing the second set angle, the second scanning operation is repeated.

4. The method for determining the relative phase of a single quantum bit according to claim 2, characterized in that: If and only if the phase gate rotates the qubit state vector exactly into the (+x, z) half-plane, the second scan rotates the qubit state vector to the |1> state.

5. The method for determining the relative phase of a single quantum bit according to claim 4, characterized in that: The adjustment range of the first setting angle is [0, 2π]; the adjustment range of the second setting angle is [0, π].

6. A device for determining the relative phase of a single quantum bit, characterized in that: include: A first scanning module, used for performing a first scan on the phase gate on the Bloch sphere by rotating a first set angle around the z-axis; A second scanning module, used for performing a second scan at each scanning point by rotating around the y-axis at a second set angle; A heat map making module is used to draw a heat map with the first scanning range and the second scanning range as axes when the phase gate rotates the quantum bit state vector to the (+x, z) half plane, and measure the highest probability point of the |1> state from the heat map; The phase angle calculation module is used to calculate the relative phase angle of a single quantum bit by subtracting the phase angle of the phase gate corresponding to the highest probability point from 2π.

7. The single quantum bit relative phase determination device according to claim 6, characterized in that: The first scanning module is specifically used to rotate the first state vector corresponding to the single quantum bit around the z-axis in a counterclockwise direction by a first set angle to a second state vector, and perform a first scan on the phase gate on the Bloch sphere; while changing the first set angle, repeat the first scanning operation.

8. The single quantum bit relative phase determination device according to claim 7, characterized in that: The second scanning module is specifically used to rotate the target state vector around the y-axis by a second set angle to a third state vector for a second scan after scanning each phase gate; while changing the second set angle, repeat the second scanning operation.

9. A single quantum bit relative phase determination device, characterized in that: It comprises a processor and a memory, wherein the processor implements the method for determining the relative phase of a single quantum bit as described in any one of claims 1 to 5 when executing the computer program stored in the memory.

10. A computer-readable storage medium, characterized in that: Used to store a computer program, wherein when the computer program is executed by a processor, the method for determining the relative phase of a single quantum bit as described in any one of claims 1 to 5 is implemented.

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