Method and apparatus for detecting a quantum state

Abstract

The present disclosure relates to a method and apparatus for detecting a quantum graph state. Wherein the method comprises: measuring a first expectation value of a product of components of all first type of sites in a quantum information system along a first direction in a state space; measuring a v-1th expectation value of a product of components of each quantum bit and quantum bits coupled with the quantum bit along a vth direction in a state space; and determining whether the quantum information system is in a graph state according to the first expectation value and all v-1th expectation values.

Description

Technical Field

[0001] This disclosure belongs to the field of quantum information technology, and specifically relates to a method and apparatus for detecting quantum patterns. Background Technology

[0002] In the quantum realm, a graph state is a multi-component entangled state that can be mapped to a mathematical graph. The vertices of the graph represent qubits, and the lines represent the interactions or couplings between two qubits. Graph states on a lattice are called cluster states. Cluster states are a commonly used type of entangled state in quantum mechanics. Compared to other entangled states, they possess maximum connectivity and sustained entanglement, making them a promising candidate for applications in quantum computing, quantum communication, and quantum information processing.

[0003] For example, in the field of quantum computing, cluster states are a universal quantum resource and a fundamental building block of measurement-based quantum computing, used to implement quantum gate operations and quantum algorithms. Compared to other types of quantum states, one of the characteristics of cluster states is their relatively simple construction method, while also possessing a certain degree of robustness, making them practical for quantum computing. Furthermore, in the field of quantum communication, quantum cluster states can be used for tasks such as quantum key distribution and quantum long-distance transmission.

[0004] Quantum cluster states can be realized through different physical systems, such as ion traps, superconducting qubits, and photonic systems. Summary of the Invention

[0005] According to a first aspect of this disclosure, a method for detecting a quantum graph state is provided, comprising: measuring a first expected value of the product of the components of all qubits of a first type of lattice in a state space along a first direction in a quantum information system, wherein the quantum information system includes first type of lattice and second type of lattice, each first type of lattice being coupled to one or more second type of lattice, and each second type of lattice being coupled to an even number of first type of lattice; measuring a (v-1)th expected value of the product of the components of each qubit and the qubit coupled to that qubit in the state space along a v-th direction in the quantum information system, wherein v takes the value of an integer from 3 to k+4, k is less than or equal to the number of coupled qubits, the second direction is perpendicular to the first direction and is the direction of the line connecting the ground state and excited state of the qubit in the state space, the v-th direction is the direction of the linear combination of the unit vector of the first direction and the unit vector of the second direction, and the v-th direction varies with the value of v; and determining whether the quantum information system is in a quantum graph state based on the first expected value and all (v-1)th expected values.

[0006] In some embodiments, measuring the first expected value of the product of components along a first direction includes: rotating the qubit in the state space so that the component originally in the first direction is rotated to the second direction, and measuring the first expected value along the second direction; measuring the (v-1)th expected value of the product of components along the v-th direction includes: rotating the qubit in the state space so that the component originally in the v-th direction is rotated to the second direction, and measuring the (v-1)th expected value along the second direction.

[0007] In some embodiments, the rotation includes at least one of the following: adjusting at least one of the Rabi frequency and the detuning frequency such that the Rabi frequency and the detuning frequency are equal and greater than the coupling coefficient, so that the qubit rotates in the state space about the direction of the sum of the unit vectors of the first direction and the unit vectors of the second direction; adjusting the Rabi frequency and the detuning frequency such that the Rabi frequency is greater than the coupling coefficient and the detuning frequency is less than the coupling coefficient, so that the qubit rotates in the state space about the first direction; adjusting the Rabi frequency and the detuning frequency such that the detuning frequency is greater than the coupling coefficient and the Rabi frequency is less than the coupling coefficient, so that the qubit rotates in the state space about the second direction.

[0008] In some embodiments, the quantum information system is a cluster state of a qubit chain with N qubits, where N is an odd number, and the qubits of the first type of lattice point are the odd-numbered points of the qubit chain, wherein each qubit is coupled to the qubits of the adjacent numbered lattice points.

[0009] In some embodiments, determining whether a quantum information system is in a quantum graph state based on a first expected value and all (v-1)th expected values ​​includes: determining whether the quantum information system is in a quantum cluster state based on the difference between the first expected value and 1, and the difference between the expected value of the stabilizer at each lattice point and 1; wherein, X u Z is the component of the qubit at the u-th lattice point along the first direction in the state space. u It is the component of the qubit at the u-th lattice point along the second direction in the state space, where u takes the value of an integer from 1 to N, and the first expected value M0 satisfies: M0 = <∏X i >, where i takes the value of an odd number from 1 to N; the second expected value of the product of the qubit at the i-th lattice point and the component of the qubit coupled to the qubit at the i-th lattice point along a third direction in the state space. satisfy: Wherein, the third direction is the same as the first direction, and the value of i is an integer between 2 and N-1; the third expected value is the product of the qubit at the i-th lattice point and the component of the qubit coupled to the qubit at the i-th lattice point along the fourth direction in the state space. Satisfy the following condition: when i = 1, When i takes the value of an integer between 2 and N-1, When i = N, Wherein, the fourth direction is the direction of the sum of the unit vectors of the second and first directions; the fourth expected value is the product of the qubit at the i-th lattice point and the component of the qubit coupled to the qubit at the i-th lattice point along the fifth direction in the state space. Satisfy the following condition: when i = 1, When i takes the value of an integer between 2 and N-1, When i = N, Wherein, the fifth direction is the direction of the difference between the unit vector of the second direction and the unit vector of the first direction; the expected value M of the stabilizer at the i-th lattice point. i Satisfy the following condition: when i = 1, When i takes the value of an integer between 2 and N-1, When i = N,

[0010] In some embodiments, a quantum information system is a divisible multidimensional graph with N qubits.

[0011] In some embodiments, determining whether a quantum information system is in a quantum graph state based on a first expected value and all (v-1)th expected values ​​includes: determining whether the quantum information system is in a quantum graph state based on the difference between the first expected value and 1, and the difference between the expected value of the stabilizer at each lattice point and 1; wherein, X u Z is the component of the qubit at the u-th lattice point along the first direction in the state space. u It is the component of the qubit at the u-th lattice point along the second direction in the state space, where u takes the value of an integer from 1 to N, and the first expected value M0 satisfies: M0 = <∏ i X i > where the value of i is the number of the qubit at the first type of lattice point; the (v-1)th expected value of the product of the qubit at the i-th lattice point and the component of the qubit coupled to the qubit at the i-th lattice point along the v-th direction in the state space. satisfy: Where i takes the value of an integer from 1 to N, j is the number of the qubit coupled to the qubit at the i-th lattice point, θ is the angle between the v-th direction and the second direction; and M is the expected value of the stabilizer at the i-th lattice point. i satisfy: where \(i\) takes integer values from 1 to \(N\), \(\theta\) is the angle between the \(v\)-th direction and the second direction, and \(a\) θ is the linear combination coefficient corresponding to the \(v\)-th direction.

[0012] In some embodiments, when the difference between the first expected value and the expected value of the stabilizer of each lattice point from 1 is less than \(1 / N\) 2 it is determined that the quantum information system is in a quantum graph state.

[0013] In some embodiments, measuring the expected value along the second direction includes: operation a. using a laser to remove qubits in the excited state; operation b. performing fluorescence imaging on the remaining qubits in the ground state to obtain the values of the qubits at the positions to be measured; repeating operations a and b, and taking the average of the obtained qubit values as the expected value.

[0014] In some embodiments, the qubit is a Rydberg atom system, and the Hamiltonian of the Rydberg atom system is where \(\Omega(t)\) is the Rabi frequency, \(\Delta(t)\) is the detuning frequency, \(C_6\) is the coupling coefficient of the van der Waals force between Rydberg atoms, \(|g\rangle\) and \(\langle g|\) are the ground state, \(|r\rangle\) and \(\langle r|\) are the Rydberg states, \(i\) and \(j\) each represent the lattice point numbers, and \(j > i\), and \(n\) is the Rydberg particle number operator.

[0015] In some embodiments, the method further includes: when adjusting the Rabi frequency \(\Omega\) and the detuning frequency \(\Delta\) to satisfy \(\Omega=\Delta = h\gg C_6\), evolving the Rydberg atom system measuring in the second direction to obtain the expected value of the component along the first direction in the state space; when adjusting the Rabi frequency \(\Omega\) and the detuning frequency \(\Delta\) to satisfy \(\Omega = 0\), \(\Delta = h\gg C_6\), evolving the Rydberg atom system for \(\Delta t_3 = 1 / (4h)\), and then when adjusting the Rabi frequency \(\Omega\) and the detuning frequency \(\Delta\) to satisfy \(\Delta = 0\), \(\Omega = h\gg C_6\), evolving the Rydberg atom system for \(\Delta t_4 = 1 / (8h)\), and measuring in the second direction to obtain the expected value of the component along the third direction in the state space, where the third direction is the direction where the sum of the unit vectors of the first direction and the second direction lies; when adjusting the Rabi frequency \(\Omega\) and the detuning frequency \(\Delta\) to satisfy \(\Omega = 0\), \(-\Delta = h\gg C_6\), evolving the Rydberg atom system for \(\Delta t_3 = 1 / (4h)\), and then when adjusting the Rabi frequency \(\Omega\) and the detuning frequency \(\Delta\) to satisfy \(\Delta = 0\), \(\Omega = h\gg C_6\), evolving the Rydberg atom system for \(\Delta t_4 = 1 / (8h)\), and measuring in the second direction to obtain the expected value of the component along the fourth direction in the state space, where the fourth direction is the direction where the difference between the unit vector of the second direction and the unit vector of the first direction lies.

[0016] In some embodiments, the qubit is one of an ion trap, a superconducting qubit, and a photon system.

[0017] According to a second aspect of this disclosure, an apparatus for detecting quantum graph states is provided, comprising: a measurement module configured to: measure a first expected value of the product of the components of all qubits of a first type of lattice point in a quantum information system along a first direction in the state space; wherein the quantum information system includes first type of lattice points and second type of lattice points, each first type of lattice point being coupled to one or more second type of lattice points, and each second type of lattice point being coupled to an even number of first type of lattice points; and measure the product of the components of each qubit and the qubit coupled to that qubit along a first direction in the state space in the quantum information system. The expected value of the product of the components of the direction, where v is an integer from 3 to k+4, k is less than or equal to the number of coupled qubits, the second direction is perpendicular to the first direction and is the direction of the line connecting the ground state and excited state of the qubit in the state space, the v-th direction is the direction of the linear combination of the unit vector of the first direction and the unit vector of the second direction, and the v-th direction is different with different values ​​of v; and a processing module configured to determine whether the quantum information system is in a quantum graph state based on the first expected value and all v-1 expected values.

[0018] In some embodiments, the measurement module includes: a laser configured to generate laser light capable of rotating qubits in state space and removing qubits in excited states; and an imaging unit configured to perform fluorescence imaging on the remaining qubits in the ground state to obtain the desired value of the qubit at the position to be measured.

[0019] Other features and advantages of this disclosure will become clearer from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, illustrate embodiments of this disclosure and, together with the specification, serve to explain the principles of this disclosure.

[0021] This disclosure will become clearer with reference to the accompanying drawings and the following detailed description, wherein:

[0022] Figure 1 A flowchart illustrating a method for detecting quantum patterns according to an exemplary embodiment of the present disclosure is shown;

[0023] Figure 2 A flowchart illustrating step S100 according to a specific embodiment of the present disclosure is shown;

[0024] Figure 3 A flowchart illustrating step S200 according to a specific embodiment of the present disclosure is shown;

[0025] Figure 4 A schematic flowchart illustrating the process of measuring a desired value along a second direction according to a specific embodiment of the present disclosure is shown.

[0026] Figure 5 A schematic diagram of the structure of a quantum cluster state according to an exemplary embodiment of the present disclosure is shown;

[0027] Figure 6 A schematic diagram of the structure of a quantum diagram state according to an exemplary embodiment of the present disclosure is shown;

[0028] Figure 7 An example block diagram of an apparatus for detecting quantum patterns according to an exemplary embodiment of the present disclosure is shown;

[0029] Figure 8 A schematic diagram illustrating the preparation and detection of quantum cluster states according to a specific embodiment of the present disclosure is shown.

[0030] Note that in the embodiments described below, the same reference numerals are sometimes used across different figures to denote the same parts or parts having the same function, and repeated descriptions are omitted. In this specification, similar reference numerals and letters are used to denote similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0031] For ease of understanding, the positions, dimensions, and extents of the structures shown in the accompanying drawings and other materials may not represent actual positions, dimensions, and extents. Therefore, the disclosed embodiments are not limited to the positions, dimensions, and extents disclosed in the accompanying drawings and other materials. Furthermore, the drawings are not necessarily drawn to scale, and some features may be enlarged to show details of specific components. Detailed Implementation

[0032] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present disclosure.

[0033] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this disclosure or its application or use. Those skilled in the art will understand that they merely illustrate exemplary ways that can be used to implement this disclosure, and are not exhaustive.

[0034] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0035] Before performing quantum computing, quantum communication, or quantum information processing, it is usually necessary to first determine whether the quantum states prepared in the quantum information system meet the expected standards. Specifically, for quantum information systems that use graph states (including cluster states) as computing resources, it is usually necessary to detect the proportion of graph states in the prepared quantum states. When the proportion of graph states is higher than the expected standard, the prepared quantum states are considered to meet the requirements for use.

[0036] A quantum graphical state (including quantum cluster states) is a specific class of stable substates. A quantum state is a complete quantum graphical state when the expectation value of all stable substates is 1. Therefore, the presence or absence of a quantum information system in the desired state can be confirmed by measuring the expectation values ​​of its stable substates.

[0037] However, to detect or verify whether the prepared quantum state is a graph state or a cluster state, different operations are generally required on different qubits to obtain the expected value of the stable quantum of the quantum information system. On existing atomic quantum computing platforms, this requires moving the atoms to be operated on to different operating regions, which consumes a lot of resources, making detection or verification relatively difficult.

[0038] To address the aforementioned issues, this disclosure proposes a method for detecting quantum patterns.

[0039] In one exemplary embodiment of this disclosure, such as Figure 1 As shown, a method for detecting a quantum graph state may include: step S100, measuring the first expected value of the product of the components of all qubits of the first type of lattice points in the state space along a first direction in the quantum information system; step S200, measuring the (v-1)th expected value of the product of the components of each qubit and the qubit coupled to that qubit in the state space along the v-th direction in the quantum information system; and step S300, determining whether the quantum information system is in a quantum graph state based on the first expected value and all (v-1)th expected values.

[0040] To clearly and intuitively describe the contents of this disclosure, the quantum state of a qubit is described in state space. Specifically, in state space, the line connecting the excited state and the ground state of the qubit can be taken as a second direction, which is perpendicular to the first direction. The origin is taken as the midpoint of the line connecting the excited state and the ground state, and the diameter is the length of the line connecting the excited state and the ground state. The position of the qubit within or on the surface of the Bloch sphere is the current state of the qubit.

[0041] In this disclosure, the X direction is used to represent the first direction, the Z direction is used to represent the second direction, and linear combinations of X and Z, such as Z+X, ZX, etc., are used to represent other directions pointed to by the unit vectors of X and Z under that linear combination. Unless otherwise specified, all first directions, second directions, up to the v-th direction, etc., appearing in this disclosure refer to directions in the state space.

[0042] In this context, the quantum information system is divisible, and at least one subclass of lattice nodes has an even degree, where the degree of a lattice node refers to the number of lattice nodes coupled to that lattice node. Specifically, the quantum information system can include first-class lattice nodes and second-class lattice nodes, with each first-class lattice node coupled to one or more second-class lattice nodes, and each second-class lattice node coupled to an even number of first-class lattice nodes. In graph states or cluster states, coupling refers to an interaction between qubits on two coupled lattice nodes, such that the two qubits are sufficiently strongly entangled to enable the quantum information system to be used for quantum computing, quantum communication, or quantum information processing. In this paper, coupling can also be replaced by adjacency, entanglement, interaction, connection, etc. Furthermore, coupling between lattice nodes and coupling between qubits on lattice nodes have the same meaning in this paper.

[0043] Some examples of quantum information systems, such as Figure 5 and Figure 6 As shown. Among them, Figure 5 The example shown is a qubit chain consisting of 9 qubits 1-9, where even-numbered qubits are coupled to an even number of other qubits and thus can be considered as a second-class lattice point, and odd-numbered qubits are coupled to one or more other qubits and thus can be considered as a first-class lattice point. Figure 5 The nine qubits shown are merely an example; other examples may contain different numbers of qubits. Additionally, Figure 6 The diagram shows an example of a multidimensional qubit pattern, consisting of 10 qubits 1-10. Qubits numbered 2, 4, 7, and 9 are coupled with an even number of other qubits and can therefore be considered as second-class lattice points. Qubits numbered 1, 3, 5, 6, 8, and 10 are coupled with one or more other qubits and can therefore be considered as first-class lattice points. Figure 6 The 10 qubits shown are merely an example; other examples may contain different numbers of qubits. In some other embodiments, where the degree of all lattice points in the system is even (i.e., all lattice points are coupled to an even number of another type of lattice point), either type of lattice point can be designated as the first type and the other as the second type.

[0044] In this system, the expected value of the stabilizer can include: the expected value M0 of the stabilizers at all first-class lattice points and the expected value M of the stabilizer at each lattice point. i The expected value of the stabilizer at all first-type lattice points is the first expected value M0 of the product of the components of the qubits at all first-type lattice points along the first direction in the state space, satisfying M0 = <∏ i X i > where i is the qubit number of the first type of lattice point. The expected value of each lattice point is the expected value M of the product of the component of the qubit at each lattice point in the state space along the first direction and the components of the qubits at all lattice points coupled to that lattice point in the state space along the second direction. i Satisfying M i = <X i ∏ j Z j > where i and j are the qubit numbers at each lattice point. For example, in N lattice points, the value of i is an integer from 1 to N, and the value of j is the qubit number coupled to the qubit at the i-th lattice point. X i Z is the component of the qubit at the i-th lattice point along the first direction in the state space. j It is the component of the qubit at the j-th lattice point along the second direction in the state space.

[0045] In step S100, the first expected value of the product of the components of all qubits of the first type of lattice points in the state space along the first direction in the quantum information system is measured. In some embodiments, M0 can be obtained directly by measurement.

[0046] In some embodiments, such as Figure 2 As shown, step S100 may include: step S110, rotating the qubit in the state space so that the component originally in the first direction is rotated to the second direction; and step S120, measuring along the second direction to obtain the first desired value. Wherein, as... Figure 4 As shown, step S120 may include: step S122, operation a. using a laser to remove the qubits in the excited state; step S124, operation b. performing fluorescence imaging on the remaining qubits in the ground state to obtain the value of the qubit at the position to be measured; step S126, repeating operation a and operation b, and taking the average of the obtained qubit values ​​as the expected value.

[0047] In step S200, the expected value of the product of each qubit and the component coupled to that qubit along the v-th direction in the state space is measured in the quantum information system. Here, v is an integer from 3 to k+4, and the v-th direction varies with the value of v. Specifically, to avoid the difficulty of operating on a single qubit, the expected value M of the stabilizer at the i-th lattice point is obtained more easily. i It is possible to measure the (v-1)th desired value along the v-th direction in state space by operating multiple qubits together as a whole. satisfy Then we can rely on linear combinations Eliminate those that do not have <X i ∏ j Z j +Z i ∑ j X j ∏ g Z g Terms of the form > and the coefficients of the remaining terms are set to 1, i.e., linear combinations yield the following: According to the Cauchy-Schwarz inequality or the anti-commutation relation, we can obtain... <Z i ∑ j X j ∏ g Z g >=0, that is Thus, the stabilizer M of the lattice point is obtained. i Where i is the lattice node number corresponding to the stabilizer, j is the qubit number coupled to the qubit at the lattice node containing the stabilizer, and ∑ is calculated for all j. j Accumulation or finding π j Multiply by g, where g is the number of the qubit coupled to the lattice point where the stabilizer resides, and g is the number of the qubit that is not the same as j. Calculate π over all g. g Multiplication, where i is coupled to only one j and g does not exist, ∏ g Z g =1. X i X is the component of the qubit at the i-th lattice point along the first direction in the state space. j Z is the component of the qubit at the j-th lattice point along the first direction in the state space. i Z is the component of the qubit at the i-th lattice point along the second direction in the state space. j Z is the component of the qubit at the j-th lattice point along the second direction in the state space. g Let be the component of the qubit at the g-th lattice point along the second direction in the state space. Here, θ is the angle between the v-th direction and the second direction, and a... θLet M be the linear combination coefficients corresponding to the v-th direction, and let M be the summation of M with respect to θ. i It is the sum of multiple products obtained by multiplying a component along the first direction with multiple components along the second direction, i.e., satisfying Where k is less than or equal to the number of qubits coupled to the qubit, the v-th direction is the direction of the linear combination of the unit vector of the first direction and the unit vector of the second direction, one of the v-th directions can be the same as the first direction, and one of the v-th directions can be the same as the second direction.

[0048] In some embodiments, such as Figure 3 As shown, step S200 may include: step S210, rotating the qubit in the state space so that the component originally in the v-th direction rotates to the second direction; and step S220, measuring the (v-1)-th desired value along the second direction. The specific operation process of step S220 may be similar to or the same as the specific operation process of step S120. Figure 4 As shown, step S220 may include: step S122, operation a. using a laser to remove the qubits in the excited state; step S124, operation b. performing fluorescence imaging on the remaining qubits in the ground state to obtain the value of the qubit at the position to be measured; step S126, repeating operation a and operation b, and taking the average of the obtained qubit values ​​as the expected value.

[0049] As mentioned above, Figure 2 The specific process of step S100 is shown, which may include: step S110, rotating the qubit in the state space so that the component originally in the first direction is rotated to the second direction; step S120, measuring along the second direction to obtain the first expected value. Figure 3 The specific process of step S200 is shown, which may include: S210, rotating the qubit in the state space so that the component originally in the v-th direction is rotated to the second direction; step S220, measuring the expected value of the v-1-th direction along the second direction.

[0050] The rotation in steps S110 and S210 can include at least one of the following: adjusting at least one of the Rabi frequency and detuning frequency, such that the Rabi frequency and detuning frequency are equal and much larger than the coupling coefficient, so that the qubit rotates in state space about the direction containing the sum of the unit vectors in the first direction and the unit vectors in the second direction; adjusting the Rabi frequency and detuning frequency of the system, such that the Rabi frequency is much larger than the coupling coefficient and the detuning frequency is much smaller than the coupling coefficient, so that the qubit rotates in state space about the first direction; or adjusting the Rabi frequency and detuning frequency of the system, such that the detuning frequency is much larger than the coupling coefficient and the Rabi frequency is much smaller than the coupling coefficient, so that the qubit rotates in state space about the second direction. The Rabi frequency is the frequency at which the qubit changes between its ground state and excited state under the influence of an external light field; on a Bloch sphere, this is rotation about the X-axis. The Rabi frequency can be adjusted by changing the laser intensity, such as the power of the laser. The detuning frequency is the frequency of phase change of the qubit under the influence of an external light field; on a Bloch sphere, this is rotation about the Z-axis. The detuning frequency can be adjusted by changing the difference between the laser frequency and the intrinsic frequency of the atoms, such as using an acousto-optic modulator. The coupling coefficient represents the strength of the interaction between multiple qubits. A Rabi frequency and / or detuning frequency much larger than the coupling coefficient means that the corresponding frequency is large enough that the influence of the coupling coefficient can be eliminated during operation, allowing the qubit to rotate in state space. A Rabi frequency or detuning frequency much smaller than the coupling coefficient means that the frequency is small enough that the unwanted rotation of the qubit in state space due to this small frequency can be eliminated during operation.

[0051] As mentioned above, refer to Figure 4 Steps S120 and S220 may include: Step S122, operation a. using a laser to remove the qubits in the excited state; Step S124, operation b. performing fluorescence imaging on the remaining qubits in the ground state to obtain the value of the qubit at the position to be measured; Step S126, repeating operation a and operation b, and taking the average of the obtained qubit values ​​as the expected value.

[0052] In step S122, specifically, a laser with photon energy between the excited state and the ground state can be input, so that the excited state qubit is ionized while the ground state qubit remains unchanged. Under the action of the ambient electric field, the ionized excited state qubit leaves the system, leaving only the ground state qubit.

[0053] In step S124, specifically, after the excited-state qubits leave the system, only the ground-state qubits remain. Fluorescence imaging can be performed on the system. Based on the location and number of residual qubits obtained from the fluorescence imaging, the result of the measurement can be determined. For example, if a qubit is present at the imaging location, it indicates that the qubit is in the ground state; if no qubit is present at the imaging location, it indicates that the qubit is in the excited state. After the residual qubits are determined by fluorescence imaging, the measurement value of the qubit in the ground state is 1, and the measurement value of the qubit in the excited state is -1.

[0054] In step S126, specifically, since quantum mechanical measurements are probabilistic, a single measurement of a quantum state can only yield either the ground state or an excited state. Specifically, the value of the endpoint position in the Z-direction of the Bloch sphere can only be obtained with a probability proportional to the proportion of states, and the actual expected value in the Z-direction cannot be directly obtained. Therefore, it is necessary to average the values ​​of the obtained qubits after multiple measurements to obtain the actual expected value in the Z-direction. Furthermore, in the case of obtaining the expected value of the product of multiple quantum state components, the components of multiple quantum states are first measured and multiplied, and then the average of the products obtained from multiple measurements is taken as the expected value of the product of components.

[0055] Back Figure 1 In step S300, based on the first expected value and all (v-1)th expected values, it is determined whether the quantum information system is in a quantum cluster state. Specifically, according to the method of the aforementioned embodiment, based on the first expected value and a linear combination of all (v-1)th expected values, a stable element M0 and multiple stable elements M are obtained. i The expected value. In some embodiments, when the difference between the expected value of all stabilizers and 1 is less than 1 / N. 2 That is, the difference between the first expected value and the expected value of the stabilizer at each grid point and 1 is less than 1 / N. 2 In the case of N, it is determined that the quantum information system is in a quantum graph state, where N is the number of qubits in the quantum information system.

[0056] Next, in conjunction with similar disclosures Figure 5 The specific implementation examples illustrate the values ​​of each v-th direction and the linear combination methods in the cluster state of the qubit chain.

[0057] As mentioned above, a quantum information system can be a cluster state of a qubit chain with N qubits, where N is an odd number. One of the endpoints is numbered starting from 1. Each qubit is coupled to the qubits with the adjacent number. The qubits of the first type of lattice point are the odd-numbered points of the qubit chain, and the qubits of the second type of lattice point are the even-numbered points of the qubit chain.

[0058] The first expected value M0 satisfies: M0=<∏X i>, where i takes the value of an odd number from 1 to N, X i It is the component of the qubit at the i-th lattice point along the first direction in the state space.

[0059] The second expected value of the product of the qubit at the i-th lattice point and the component of the qubit coupled to the qubit at the i-th lattice point along the third direction in the state space. satisfy: Where i takes the value of an integer from 2 to N-1, the third direction is the same as the first direction, X i X is the component of the qubit at the i-th lattice point along the first direction in the state space. i-1 X is the component of the qubit at the (i-1)th lattice point along the first direction in the state space. i+1 It is the component of the qubit at the (i+1)th lattice point along the first direction in the state space.

[0060] The third expected value of the product of the qubit at the i-th lattice point and the component of the qubit coupled to that qubit at the i-th lattice point along the fourth direction in the state space. Satisfy the following condition: when the value of i is an integer between 2 and N-1, When i = 1, And when i=N, The fourth direction is the direction of the sum of the unit vectors in the second and first directions, X. i X is the component of the qubit at the i-th lattice point along the first direction in the state space. i-1 X is the component of the qubit at the (i-1)th lattice point along the first direction in the state space. i+1 Z is the component of the qubit at the (i+1)th lattice point along the first direction in the state space. i Z is the component of the qubit at the i-th lattice point along the second direction in the state space. i-1 Z is the component of the qubit at the (i-1)th lattice point along the second direction in the state space. i+1 X1 is the component of the qubit at the (i+1)th lattice point along the second direction in the state space; X2 is the component of the qubit at the 1st lattice point along the first direction in the state space; X3 is the component of the qubit at the 2nd lattice point along the first direction in the state space; X4 is the component of the qubit at the 2nd lattice point along the first direction in the state space; X5 is the component of the qubit at the 1st lattice point along the first direction in the state space; X6 is the component of the qubit at the 2nd lattice point along the first direction in the state space; X7 is the component of the qubit at the 1st lattice point along the first direction in the state space; X8 is the component of the qubit at the 2nd lattice point along the first direction in the state space; X9 is the component of the qubit at the 1st lattice point N X is the component of the qubit at the Nth lattice point along the first direction in the state space. N-1 Z1 is the component of the qubit at the (N-1)th lattice point along the first direction in the state space; Z2 is the component of the qubit at the 1st lattice point along the second direction in the state space; Z3 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z4 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z5 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z6 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z7 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z8 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z9 is the component of the qubit at the 2nd lattice point NZ is the component of the qubit at the Nth lattice point along the second direction in the state space. N-1 It is the component of the qubit at the (N-1)th lattice point along the second direction in the state space.

[0061] The fourth expected value of the product of the qubit at the i-th lattice point and the component of the qubit coupled to that qubit at the i-th lattice point along the fifth direction in the state space. Satisfy the following condition: when i takes the value of an integer between 2 and N-1, When i = 1, And when i=N, The fifth direction is the direction of the difference between the unit vector in the second direction and the unit vector in the first direction, X. i X is the component of the qubit at the i-th lattice point along the first direction in the state space. i-1 X is the component of the qubit at the (i-1)th lattice point along the first direction in the state space. i+1 Z is the component of the qubit at the (i+1)th lattice point along the first direction in the state space. i Z is the component of the qubit at the i-th lattice point along the second direction in the state space. i-1 Z is the component of the qubit at the (i-1)th lattice point along the second direction in the state space. i+1 X1 is the component of the qubit at the (i+1)th lattice point along the second direction in the state space; X2 is the component of the qubit at the 1st lattice point along the first direction in the state space; X3 is the component of the qubit at the 2nd lattice point along the first direction in the state space; X4 is the component of the qubit at the 2nd lattice point along the first direction in the state space; X5 is the component of the qubit at the 1st lattice point along the first direction in the state space; X6 is the component of the qubit at the 2nd lattice point along the first direction in the state space; X7 is the component of the qubit at the 1st lattice point along the first direction in the state space; X8 is the component of the qubit at the 2nd lattice point along the first direction in the state space; X9 is the component of the qubit at the 1st lattice point N X is the component of the qubit at the Nth lattice point along the first direction in the state space. N-1 Z1 is the component of the qubit at the (N-1)th lattice point along the first direction in the state space; Z2 is the component of the qubit at the 1st lattice point along the second direction in the state space; Z3 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z4 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z5 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z6 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z7 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z8 is the component of the qubit at the 2nd lattice point along the second direction in the state space; Z9 is the component of the qubit at the 2nd lattice point N Z is the component of the qubit at the Nth lattice point along the second direction in the state space. N-1 It is the component of the qubit at the (N-1)th lattice point along the second direction in the state space.

[0062] The expected value of the stabilizer at the i-th lattice point satisfies the following condition when i = 1: When i takes the value of an integer from 2 to N-1, And when i=N,

[0063] In the above embodiments, θ in the third direction is taken as 90°, which is the same as the first direction. θ in the fourth direction is taken as 45°, which is the direction where the sum of the unit vectors of the second direction and the first direction lies. θ in the fifth direction is taken as -45°, which is the direction where the difference between the unit vector of the second direction and the unit vector of the first direction lies.

[0064] In some other embodiments, as Figure 6 shown, the quantum information system can be a bipartite multi-dimensional graph state. In the case where there are w coupled qubits at a certain qubit, it is in the form of Each term in contains a total of w + 1 Z or X direction component operators. It can be divided into w + 2 classes according to the number of Z direction component operators and X direction component operators in each term. Then, w + 2 different θs can be obtained through linear combination to get the required M that contains only 1 X direction operator i = <X i ∏ j Z j +Z i ∑ j X j ∏ g Z g >. By choosing some θs, the number of θs that need to be measured can be further reduced. For example, by simultaneously choosing θ and -θ and then taking the difference, the terms with an even number of X direction component operators can be eliminated together. For example, as shown in the previous Figure 5 embodiment of the cluster state of the one-dimensional qubit chain, when w is 1, that is, at the endpoints, such a choice only requires 2 θs. And when w is 2, one group is in the form of θ and -θ, then a total of only 3 θs are required. Similarly, for any w, θ can be selected in this form so that only w + 1 θs are required to implement this method.

[0065] Next, in combination with the specific embodiments of the present disclosure, steps S110 and step S210 in the method for detecting a quantum graph state according to the present disclosure are implemented in a specific quantum system of the cluster state of a one-dimensional qubit chain, as Figure 8 shown.

[0066] According to a specific embodiment of the present disclosure, the qubit is a Rydberg atom system, and the Hamiltonian of the Rydberg atom system is where Ω(t) is the Rabi frequency, Δ(t) is the detuning frequency, C6 is the coupling coefficient of the van der Waals force between Rydberg atoms, |g> and <g| are the ground states, |r> and <r| are the Rydberg states, n is the Rydberg particle number operator, i and j each represent the lattice point numbers, ∑ i is the sum over all i, and ∑ i＜j is the sum over all i and j that satisfy j > i. For example, for the case of a total of 3 lattice points, ∑i＜j We need to sum the values ​​for the following cases of i and j: i = 1, j = 2; i = 1, j = 3; i = 2, j = 3.

[0067] Cluster states can be prepared by adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Ω=Δ=h>>C6, and then allowing the Rydberg atom system to evolve. Subsequently, by adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Ω = Δ = 0, the Rydberg atom system is allowed to evolve Δt2 = 1 / (2C6). Figure 8 The intermediate state preparation section is shown. Here, h is any frequency value that satisfies the formula conditions, and h >> C6 means that h is large enough that the coupling effect can be ignored during rotation; therefore, h can be chosen to be as large as possible. In other embodiments according to this disclosure, cluster states or pattern states can also be prepared using other methods.

[0068] After obtaining the cluster state, steps S110 and S210 of this method can be implemented in the following way.

[0069] By adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Ω=Δ=h>>C6, that is, to make the Rydberg atomic system... The angular frequency of the Rydberg atom rotates counterclockwise around the Z+X axis in state space, causing the Rydberg atom system to evolve. That is, by rotating 180° counterclockwise around the Z+X axis in the state space, the desired value in the X direction can be measured in the Z direction, such as... Figure 8 The measurement section in the X direction is shown. Here, h is any frequency value that satisfies the formula conditions. h >> C6 means that h is large enough that the coupling effect can be ignored during rotation; therefore, h can be chosen to be as large as possible.

[0070] By adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Ω=0 and Δ=h>>C6, that is, by rotating the Rydberg atom system counterclockwise around the Z-axis in state space at an angular frequency of 2πh, the Rydberg atom system evolves Δt3=1 / (4h), that is, by rotating 90° counterclockwise around the Z-axis in state space; then, by adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Δ=0 and Ω=h>>C6, that is, by rotating the Rydberg atom system counterclockwise around the X-axis in state space at an angular frequency of 2πh, the Rydberg atom system evolves Δt4=1 / (8h), that is, by rotating 45° counterclockwise around the X-axis in state space, the desired value in the Z+X direction can be measured in the Z direction, such as... Figure 8 The measurement section in the Z+X direction is shown. Here, h is any frequency value that satisfies the formula conditions. h >> C6 means that h is large enough that the coupling effect can be ignored during rotation; therefore, h can be chosen to be as large as possible.

[0071] By adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Ω=0, -Δ=h>>C6, that is, by rotating the Rydberg atom system clockwise around the Z-axis in state space at an angular frequency of 2πh, the Rydberg atom system evolves Δt3=1 / (4h), that is, by rotating 90° clockwise around the Z-axis in state space. Then, by adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Δ=0, Ω=h>>C6, that is, by rotating the Rydberg atom system counterclockwise around the X-axis in state space at an angular frequency of 2πh, the Rydberg atom system evolves Δt4=1 / (8h), that is, by rotating the system counterclockwise around the X-axis in state space by 45°, the desired value in the ZX direction can be measured in the Z direction, such as... Figure 8 The measurement section in the ZX direction is shown. Here, h is any frequency value that satisfies the formula conditions. h >> C6 means that h is large enough that the coupling effect can be ignored during rotation; therefore, h can be chosen to be as large as possible.

[0072] Furthermore, by combining different Rabi frequencies and detuning frequencies with different durations, it is possible to measure more desired values ​​in other directions in the Z direction.

[0073] In other specific embodiments according to this disclosure, the quantum bit may also be an ion trap, a superconducting quantum bit, or a photonic system, etc.

[0074] In embodiments according to this disclosure, the quantum information system may be a quantum computing system, a quantum communication system, or a quantum information processing system, etc.

[0075] According to another aspect of this disclosure, an apparatus for detecting quantum patterns is also provided. For example... Figure 7As shown, the device 400 for detecting quantum states may include a measurement module 402 and a processing module 404. The measurement module 402 may be configured to: measure the first expected value of the product of the components of all qubits of the first type of lattice points in the state space along a first direction in the quantum information system, wherein the quantum information system includes first and second type lattice points, each first type lattice point is coupled to one or more second type lattice points, and each second type lattice point is coupled to an even number of first type lattice points; and measure the (v-1)th expected value of the product of the components of each qubit and the qubits coupled to it along the v-th direction in the state space, where v is an integer from 3 to k+4, k is less than or equal to the number of coupled qubits, the second direction is perpendicular to the first direction, and the second direction is the direction of the line connecting the ground state and excited state of the qubit in the state space, and the v-th direction is the direction of the linear combination of the unit vectors of the first and second directions. Processing module 404 can be configured to determine whether the quantum information system is in a quantum graph state based on a first expected value and all (v-1)th expected values. Specifically, measurement module 402 may include a laser and an imaging unit. The laser is configured to generate laser light capable of rotating qubits in state space and removing qubits in excited states. The imaging unit is configured to perform fluorescence imaging on the remaining qubits in the ground state to obtain the expected value of the qubit at the position to be measured. The device 400 for detecting quantum graph states can be configured to perform the method described in any of the above-described method embodiments of this disclosure.

[0076] In the technical solution disclosed herein, a first expected value of the product of the components of all qubits of the first type of lattice along a first direction in the state space can be measured in a quantum information system; a (v-1)th expected value of the product of the components of each qubit and the qubit coupled to that qubit along a v-th direction in the state space can be measured in the quantum information system; and based on the first expected value and all v-th expected values, it can be determined whether the quantum information system is in a quantum graph state. In this way, by transforming the expected value of the stabilizer from the expected value of the product of the component of one qubit along the first direction and the components of multiple qubits along the second direction into the expected value of the product of multiple qubits along multiple single directions, the problem of individually adjusting a single qubit is avoided, the resource requirements for measurement are reduced, and the difficulty of detecting or authenticating quantum graph states (including quantum cluster states, etc.) is reduced.

[0077] The foregoing has described one or more exemplary embodiments of this disclosure. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0078] The terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, product, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, product, or apparatus. Without further limitation, the presence of other identical or equivalent elements in the process, method, product, or apparatus that includes said elements is not excluded. For example, the use of terms such as "first" or "second" to denote names does not indicate any particular order.

[0079] For ease of description, the above devices are described in terms of function, divided into various modules. Of course, when implementing one or more embodiments of this disclosure, the functions of each module can be implemented in one or more software and / or hardware, or a module that performs the same function can be implemented by a combination of multiple sub-modules or sub-units. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division; in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual coupling, direct coupling, or communication coupling can be through some interfaces; indirect coupling or communication coupling between devices or units can be electrical, mechanical, or other forms.

[0080] The same or similar parts between the various embodiments of this disclosure can be referred to mutually, and each embodiment focuses on describing the differences from other embodiments. In particular, for the apparatus embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and relevant parts can be referred to the description of the method embodiments. In the description of this disclosure, the reference to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," "exemplary," etc., means that the specific feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of this disclosure. In this disclosure, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this disclosure and the features of different embodiments or examples.

[0081] Additionally, when used in this disclosure, the terms “here,” “above,” “below,” “below,” “in the following,” “overall,” and similar terms should refer to the entirety of this disclosure and not any particular part thereof. Furthermore, unless expressly stated otherwise or otherwise understood in the context in which they are used, conditional language used herein, such as “may,” “possibly,” “for example,” “like,” etc., is generally intended to express that certain embodiments include, while other embodiments do not, certain features, elements, and / or states. Therefore, such conditional language is not generally intended to imply that one or more embodiments require features, elements, and / or states in any way, or whether such features, elements, and / or states are included or performed in any particular embodiment.

[0082] The above description is merely an embodiment of one or more embodiments of this disclosure and is not intended to limit the scope of the one or more embodiments of this disclosure. Various modifications and variations can be made to the one or more embodiments of this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of the claims.

Claims

1. A method for detecting quantum patterns, comprising: The first expected value of the product of the components of the qubits of all first-type lattice points in the state space along a first direction in a quantum information system is measured. The quantum information system includes first-type lattice points and second-type lattice points, each first-type lattice point is coupled to one or more second-type lattice points, and each second-type lattice point is coupled to an even number of first-type lattice points. In the quantum information system, the expected value of the (v-1)th component of the product of each qubit and the components of the qubit coupled to it along the v-th direction in the state space is measured, where v is an integer from 3 to k+4, k is less than or equal to the number of coupled qubits, the second direction is perpendicular to the first direction, and the second direction is the direction of the line connecting the ground state and excited state of the qubit in the state space, the v-th direction is the direction of the linear combination of the unit vectors of the first direction and the second direction, and the v-th direction varies with the value of v; and Based on the first expected value and all v-1 expected values, determine whether the quantum information system is in a quantum graph state.

2. The method according to claim 1, wherein, Measuring the first expected value of the product of the components along the first direction includes: rotating the qubit in the state space so that the component originally in the first direction is rotated to the second direction, and measuring the first expected value along the second direction. Measuring the (v-1)th expected value of the product of the components along the v-th direction includes: rotating the qubit in the state space so that the component originally in the v-th direction is rotated to the second direction, and measuring the (v-1)th expected value along the second direction.

3. The method according to claim 2, wherein, Rotation includes at least one of the following: Adjust at least one of the Rabi frequency and the detuning frequency such that the Rabi frequency and the detuning frequency are equal and greater than the coupling coefficient, so that the qubit rotates in the state space about the direction of the sum of the unit vector of the first direction and the unit vector of the second direction; Adjust the Rabi frequency and the detuning frequency so that the Rabi frequency is greater than the coupling coefficient and the detuning frequency is less than the coupling coefficient, so that the quantum bit rotates around the first direction in the state space; The Rabi frequency and detuning frequency are adjusted such that the detuning frequency is greater than the coupling coefficient and the Rabi frequency is less than the coupling coefficient, so that the qubit rotates around the second direction in the state space.

4. The method according to claim 1, wherein, The quantum information system is a cluster state of a qubit chain with N qubits, where N is an odd number. The qubits of the first type of lattice point are the odd-numbered points of the qubit chain, and each qubit is coupled to the qubits of the adjacent numbered lattice points.

5. The method according to claim 4, wherein, Determining whether the quantum information system is in a quantum graph state based on the first expected value and all (v-1)th expected values ​​includes: Based on the difference between the first expected value and 1, and the difference between the expected value of the stabilizer at each lattice point and 1, it is determined whether the quantum information system is in a quantum cluster state; Among them, X u Z is the component of the qubit at the u-th lattice point along the first direction in the state space. u It is the component of the qubit at the u-th lattice point along the second direction in the state space, where u takes the value of an integer from 1 to N. The first expected value M0 satisfies: M0 = <∏X i >, where the value of i is an odd number from 1 to N; The second expected value of the product of the qubit at the i-th lattice point and the component of the qubit coupled to the qubit at the i-th lattice point along the third direction in the state space. satisfy: Wherein, the third direction is the same as the first direction, and the value of i is an integer between 2 and N-1; The third expected value of the product of the qubit at the i-th lattice point and the component of the qubit coupled to that qubit at the i-th lattice point along the fourth direction in the state space. satisfy: When i = 1, When i takes the value of an integer between 2 and N-1, When i = N, Wherein, the fourth direction is the direction containing the sum of the unit vectors of the second direction and the unit vectors of the first direction; The fourth expected value of the product of the qubit at the i-th lattice point and the component of the qubit coupled to that qubit at the i-th lattice point along the fifth direction in the state space. satisfy: When i = 1, When i takes the value of an integer between 2 and N-1, When i = N, Wherein, the fifth direction is the direction where the difference between the unit vector of the second direction and the unit vector of the first direction lies; The expected value M of the stabilizer at the i-th lattice point i satisfy: When i = 1, When i takes the value of an integer between 2 and N-1, When i = N, 6. The method according to claim 1, wherein, The quantum information system is a bipartite multi-dimensional graph state with N qubits.

7. The method according to claim 6, wherein, Determining whether the quantum information system is in a quantum graph state according to the first expectation value and all the (v - 1)th expectation values includes: Determining whether the quantum information system is in a quantum graph state based on the difference between the first expectation value and 1, and the difference between the expectation value of the stabilizer of each lattice point and 1; Among them, X u Z is the component of the qubit at the u-th lattice point along the first direction in the state space. u It is the component of the qubit at the u-th lattice point along the second direction in the state space, where u takes the value of an integer from 1 to N. The first expected value M0 satisfies: M0 = <∏ i X i >, where the value of i is the number of the qubit of the first type of lattice point; The (v-1)th expected value of the product of the qubit at the i-th lattice point and the component of the qubit coupled to the qubit at the i-th lattice point along the v-th direction in the state space. satisfy: Where i takes the value of an integer from 1 to N, j takes the value of the number of the qubit coupled to the qubit at the i-th lattice point, and θ is the angle between the v-th direction and the second direction; The expected value M of the stabilizer at the i-th lattice point i satisfy: Where i takes the value of an integer from 1 to N, θ is the angle between the v-th direction and the second direction, and a θ denoted as the linear combination coefficient corresponding to the v-th direction.

8. The method according to claim 5 or 7, wherein, The difference between the first expected value and the expected value of the stabilizer at each lattice point and 1 is less than 1 / N. 2 Under these circumstances, it is determined that the quantum information system is in a quantum graph state.

9. The method according to claim 2, wherein measuring to obtain an expectation value along the second direction includes: Operation a. Using a laser to remove qubits in the excited state; Operation b. Performing fluorescence imaging on the remaining qubits in the ground state to obtain the values of the qubits at the positions to be measured; Repeating Operation a and Operation b, and taking the average of the obtained qubit values as the expectation value.

10. The method according to claim 1, wherein, The qubit is a Rydberg atomic system, and the Hamiltonian of the Rydberg atomic system is... Where, Ω(t) is the Rabi frequency, Δ(t) is the detuning frequency, C6 is the coupling coefficient of the van der Waals force between Rydberg atoms, |g> and <g| are the ground states, |r> and <r| are the Rydberg states, i and j each represent the number of lattice points, and j > i, and n is the Rydberg particle number operator.

11. The method according to claim 10, further comprising: By adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Ω=Δ=h>>C6, the Rydberg atom system is allowed to evolve. The measurement is performed in the second direction to obtain the expected value of the component in the state space along the first direction; When adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Ω = 0, Δ = h >> C6, letting the Rydberg atom system evolve for Δt3 = 1 / (4h), and then when adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Δ = 0, Ω = h >> C6, letting the Rydberg atom system evolve for Δt4 = 1 / (8h), and measuring in the second direction to obtain the expectation value of the component along the third direction in the state space, wherein the third direction is the direction where the sum of the unit vector of the first direction and the unit vector of the second direction lies; When adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Ω = 0, -Δ = h >> C6, letting the Rydberg atom system evolve for Δt3 = 1 / (4h), and then when adjusting the Rabi frequency Ω and the detuning frequency Δ to satisfy Δ = 0, Ω = h >> C6, letting the Rydberg atom system evolve for Δt4 = 1 / (8h), and measuring in the second direction to obtain the expectation value of the component along the fourth direction in the state space, wherein the fourth direction is the direction where the difference between the unit vector of the second direction and the unit vector of the first direction lies.

12. The method according to claim 1, wherein, The qubit is one of an ion trap, a superconducting qubit, and a photon system.

13. A device for detecting a quantum graph state, comprising: A measurement module, the measurement module being configured to: Measure the first expectation value of the product of the components along the first direction in the state space of the qubits of all first-type lattice points in the quantum information system, wherein the quantum information system includes first-type lattice points and second-type lattice points, each first-type lattice point is coupled to one or more second-type lattice points, and each second-type lattice point is coupled to an even number of first-type lattice points; and In the quantum information system, the expected value of the (v-1)th component of the product of each qubit and the components of the qubit coupled to it along the v-th direction in the state space is measured, where v is an integer from 3 to k+4, k is less than or equal to the number of coupled qubits, the second direction is perpendicular to the first direction, and the second direction is the direction of the line connecting the ground state and excited state of the qubit in the state space, the v-th direction is the direction of the linear combination of the unit vectors of the first direction and the second direction, and the v-th direction varies with the value of v; and A processing module configured to determine whether the quantum information system is in a quantum graph state based on the first expected value and all v-1 expected values.

14. The apparatus according to claim 13, wherein, The measurement module includes: A laser configured to generate laser light, the laser light being capable of rotating qubits in state space and removing qubits in excited states; An imaging unit is configured to perform fluorescence imaging on the remaining qubits in the ground state to obtain the desired value of the qubit at the position to be measured.

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