A method for preparing non-local quantum entangled states of fault-tolerant logical quantum bits

Abstract

The present invention discloses a method for preparing a fault-tolerant logical quantum bit non-local quantum entangled state, comprising: first, in two remote nodes, using a single photon to act on four physical bits in one node in sequence, each time a physical bit is acted on, the photon is encoded by a linear optical element, its polarization state is changed and time delay information is added, forming a logical bit composed of four physical bits and a hybrid entanglement between the photon and the logical bit; then the photon is transmitted over a long distance, and acts on the physical bit in another node in sequence, forming a logical bit again. Finally, the entanglement of the photon and the logical bit is converted into the entanglement between two logical bits. By measuring the state of the photon and flipping the physical bit, the present invention can use a high-dimensionally encoded single photon to prepare a logical bit non-local entangled state with high fault tolerance, which can greatly reduce transmission losses and save quantum resources.

Description

Technical Field

[0001] The present invention belongs to the field of quantum error correction technology, and in particular to the field of entangled state preparation technology, in particular to a method for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit. Background Art

[0002] In actual quantum channels and quantum storage devices, quantum information errors are easily caused by various noises and quantum coherence. To achieve effective storage and transmission of quantum information, quantum error correction is necessary. Due to the randomness of errors in single physical quantum bits, logical quantum bits are used to solve the problem of computational errors caused by imperfect hardware.

[0003] The physical systems that can currently realize quantum bits mainly include ion traps, superconducting quantum bits, quantum dots and diamond NV centers. Among them, the NV center in diamond has attracted widespread attention due to its advantages such as high stability and long coherence time. The NV center is a crystallographic defect in diamond, which provides a mixed spin physics system composed of electron spin and nuclear spin. The electron spin and nuclear spin of the NV center can be manipulated, initialized and read at room temperature using microwaves or lasers. The electron spin of the NV center can be entangled with photons, and quantum teleportation between long-distance NV centers has been achieved experimentally. Therefore, the NV center is considered to be a promising candidate for the preparation of quantum entanglement in the solid-state physics system.

[0004] To achieve quantum error correction, the preparation of logical quantum bit entangled states has become a top priority. Experts at home and abroad have conducted extensive research on this. In 2018, the Basic Department of the Rocket Force Engineering University proposed a theoretical scheme to realize the entanglement between two separated quantum nodes in a hybrid system coupled with a diamond NV color center spin system and a superconducting quantum circuit, which can realize quantum entanglement between two separated quantum nodes with high fidelity. However, the superconducting quantum circuit has a high degree of freedom of electrons, resulting in a high error rate. In order to ensure the decoherence time, superconducting quantum bits must operate in a vacuum environment close to absolute zero. This not only requires the superconducting system to have a powerful low-temperature refrigeration system, but also limits the expansion of quantum bits to a certain extent. In 2021, Zhihao Xie proposed a method for preparing multiple pairs of non-local quantum entangled states based on single photon transmission by regulating the encoding method of high-dimensional time mode freedom and polarization mode freedom. However, this entangled state does not have error correction. In 2022, researchers at the quantum computing company Quantinuum demonstrated for the first time an entanglement gate between two logical qubits by entangling logical qubits in a fault-tolerant circuit using real-time quantum error correction, and completed it in a fully fault-tolerant manner using real-time error correction, indicating that the performance of logical qubits is superior to that of physical qubits. However, the preparation environment for the entangled state of its logical qubits is not superior to the diamond NV color center system, which has advantages such as high stability and long coherence time.

[0005] In summary, the physical bit entangled states prepared at this stage generally do not have error correction capabilities, and the logical bit entangled states prepared have strict requirements on the system working environment and are not as stable as the diamond NV color center system. Summary of the invention

[0006] The purpose of the present invention is to provide a solution that uses a high-dimensionally encoded single photon to form a logical bit at two distant nodes while allowing two logical bits to form an entangled state, so as to solve the problem that a single physical bit is difficult to perform reliable quantum computing because it is easily affected by environmental noise.

[0007] The technical solution to achieve the purpose of the present invention is: a method for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit, the method comprising the following steps:

[0008] Step 1: A photon with an initial polarization state of |D0> interacts with the first NV color center s1 of a node, and then enters the T1 system for photon state encoding;

[0009] Step 2: The photon interacts with the second NV color center s2 of the node, and then enters the T2 system for photon state encoding. After the encoding is completed, the photon only exists in the |D> polarization state;

[0010] Step 3, the photon interacts with the third NV center s3 of the node, then enters the T′1 system for photon state encoding, realizes the exchange of different degrees of freedom between |A> polarization states, and then interacts with the fourth NV center s4 of the node to form the first logical bit;

[0011] Step 4: The photons are transmitted over long distances to another node, and then enter the T″1 system for photon state encoding, so that each |A> polarization state is transformed into a |D> polarization state with different degrees of freedom;

[0012] Step 5, the photon interacts with the eighth NV color center s8, the sixth NV color center s6, the seventh NV color center s7, and the fifth NV color center s5 of the other node in turn, and is encoded by the T′2 system, T3 system, and T′3 system in turn. While forming a logical bit at the node, the entanglement of the logical bits between the two nodes is realized. At the same time, the corresponding entangled state is judged by measuring the polarization state of the current photon; the T3 system is used to realize the transition from the |A> polarization state to the |D> polarization state, and the T′2 system and T′3 system are used to realize the exchange of different degrees of freedom between the |A> polarization states.

[0013] Furthermore, in step 1, the photon interacts with the first NV color center s1, specifically including: when the electron spin state in s1 is |g>, the polarization state of the photon remains unchanged; when the electron spin state in s1 is |e>, the polarization state of the photon flips and becomes the polarization state |A0>.

[0014] Furthermore, the T1 system and the T2 system each include a polarization beam splitter PBS, a half-wave plate H and an optical switch;

[0015] In the T1 system, under the action of the polarization beam splitter PBS, the |A0> polarization state of the photon is emitted to the half-wave plate H, and then a time degree of freedom delay is added, so that the |D0> polarization state is changed to the |D1> polarization state. Then, under the action of the optical switch OS1, the |D0> and |D1> polarization states are merged into one spatial mode;

[0016] In the T2 system, the |A0> and |A1> polarization states of photons are changed to |D2> and |D3> polarization states respectively, and then merged into one spatial mode through the optical switch OS2.

[0017] Furthermore, the T′1 system in step 3 is: using a polarization beam splitter and an optical switch to exchange the polarization states of |A> with different temporal degrees of freedom of photons, to achieve the interchange of polarization states between |A0> and |A3>, |A1> and |A2>, at which time, the three NV color centers and photons merge; wherein, the |A2> and |A3> polarization states are the result of the interaction between the photon and the second NV color center s2 and the third NV color center s3 of the node, respectively.

[0018] Furthermore, the T″1 system in step 4 is: using a polarization beam splitter, a half-wave plate and an optical switch to add different time degrees of freedom to the polarization state of the photon |A> and convert it into the polarization state |D>, so as to realize the conversion of the photon |A> t >Polarization state encoded as |D 7-t >Polarization state, at this time, the four NV color centers merge with the photons; where t = 0, 1, 2, 3.

[0019] Furthermore, in step 5, the corresponding entangled state is determined by measuring the polarization state of the current photon, which specifically includes:

[0020] Step 5-1, based on the measured polarization state of the current photon, collapse the superposition state after passing through the eight NV color centers and the coding system into a logical bit entangled state corresponding to the measured photon polarization state, thereby determining the logical bit entangled state composed of the eight NV color centers;

[0021] Step 5-2: Based on the logical bit entangled state, perform phase flipping on a single bit to obtain a logical bit entangled state with fault tolerance.

[0022] Compared with the prior art, the present invention has the following significant advantages:

[0023] (1) Only a single photon is used to prepare the logical bit entangled state between distant nodes, so that the high loss of photons in the transmission channel reduces the limitation of the preparation efficiency of this scheme, and a logical bit entangled state with high fault tolerance can be prepared.

[0024] (2) The entangled state of logical bits is prepared based on the diamond NV color center system, which has a long coherence time and can reach the millisecond level at room temperature. For quantum bits encoded in the ground state of the NV color center, they can not only be initialized, measured and read using lasers, but also be quantum manipulated using microwaves, which has high application value.

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a method for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit in one embodiment.

[0027] Figure 2 It is a specific principle flow chart of a method for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit in an embodiment.

[0028] Figure 3 Schematic diagram of an embodiment in which the same temporal degree of freedom is added to the |A> polarization state of a photon and converted to the |D> polarization state.

[0029] Figure 4 Schematic diagram of an optical path for exchanging the polarization states of |A> with different temporal degrees of freedom of photons in one embodiment.

[0030] Figure 5 A light path diagram showing an embodiment in which different temporal degrees of freedom are added to the |A> polarization state of a photon and converted to the |D> polarization state. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] It should be noted that if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0033] The present invention provides a method for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit, the method comprising the following steps:

[0034] Step 1, a photon with an initial polarization state of |D0> interacts with the first NV color center s1 of a node, and then enters the T1 system for photon state encoding; wherein the photon interacts with the first NV color center s1, specifically including: when the electron spin state in s1 is |g>, the polarization state of the photon remains unchanged; when the electron spin state in s1 is |e>, the polarization state of the photon flips and becomes the polarization state |A0>;

[0035] Step 2: The photon interacts with the second NV color center s2 of the node, and then enters the T2 system for photon state encoding. After the encoding is completed, the photon only exists in the |D> polarization state;

[0036] The T1 system and the T2 system both include a polarization beam splitter PBS, a half-wave plate H and an optical switch;

[0037] In the T1 system, under the action of the polarization beam splitter PBS, the polarization state of the photon |A0> is emitted to the half-wave plate H, and then a time degree of freedom delay is added, so that the polarization state |D0> changes to the polarization state |D1>, and then the optical switch OS l Under the effect of |D0> and |D l >Polarization states merge into one spatial pattern;

[0038] In the T2 system, the photon's |A0> and |A l >polarization states are changed into |D2> and |D3> polarization states respectively, and then merged into one spatial mode through the optical switch OS2.

[0039] Step 3, the photon interacts with the third NV center s3 of the node, then enters the T′1 system for photon state encoding, realizes the exchange of different degrees of freedom between |A> polarization states, and then interacts with the fourth NV center s4 of the node to form the first logical bit;

[0040] The T′1 system is as follows: using a polarization beam splitter and an optical switch to exchange the polarization states of |A> with different time degrees of freedom of photons, to achieve the exchange of polarization states between |A0> and |A3>, |A1> and |A2>, at which time, the three NV color centers and photons merge; wherein, the polarization states of |A2> and |A3> are the results of the interaction between the photon and the second NV color center s2 and the third NV color center s3 of the node, respectively;

[0041] Step 4: The photons are transmitted over long distances to another node, and then enter the T″1 system for photon state encoding, so that each |A> polarization state is transformed into a |D> polarization state with different degrees of freedom;

[0042] The T″1 system uses a polarization beam splitter, a half-wave plate and an optical switch to add different time degrees of freedom to the |A> polarization state of the photon and convert it into the |D> polarization state, thereby realizing the conversion of the photon's |A t >Polarization state encoded as |D 7-t >Polarization state, at this time, four NV color centers merge with photons; where t = 0, 1, 2, 3;

[0043] In step 5, the photon interacts with the eighth NV color center s8, the sixth NV color center s6, the seventh NV color center s7, and the fifth NV color center s5 of the other node in turn, and is encoded in turn through the T′2 system, the T3 system, and the T′3 system. While forming a logical bit at the node, the entanglement of the logical bit between the two nodes is realized. At the same time, the corresponding entangled state is judged by measuring the polarization state of the current photon; the T3 system is used to realize the transition from the |A> reflection polarization state to the |D> transmission polarization state, and the T′2 system and T′3 system are used to realize the exchange of different degrees of freedom between the |A> reflection polarization states.

[0044] The method of determining the corresponding entangled state by measuring the polarization state of the current photon specifically includes:

[0045] Step 5-1, based on the measured polarization state of the current photon, collapse the superposition state after passing through the eight NV color centers and the coding system into a logical bit entangled state corresponding to the measured photon polarization state, thereby determining the logical bit entangled state composed of the eight NV color centers;

[0046] Step 5-2: Based on the logical bit entangled state, perform phase flipping on a single bit to obtain a logical bit entangled state with fault tolerance.

[0047] In summary, in two remote nodes, the present invention first uses a single photon to sequentially interact with four physical bits in one node. Each time a physical bit is interacted with, the photon is encoded by a linear optical element, its polarization state is changed, and time delay information is added to form a logical bit composed of four physical bits and a hybrid entanglement between the photon and the logical bit. Then, the photon is transmitted over a long distance and sequentially interacts with the physical bit in another node to form a logical bit again. Finally, the entanglement of the photon and the logical bit is converted into the entanglement between two logical bits.

[0048] In one embodiment, a system for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit is provided, the system comprising:

[0049] The first module is used to realize: a photon with an initial polarization state of |D0> interacts with the first NV color center s1 of a node, and then enters the T1 system for photon state encoding;

[0050] The second module is used to realize: the photon interacts with the second NV color center s2 of the node, and then enters the T2 system for photon state encoding. After the encoding is completed, the photon only exists in the |D> polarization state;

[0051] The third module is used to realize: the photon interacts with the third NV color center s3 of the node, then enters the T′1 system for photon state encoding, realizes the exchange of different degrees of freedom between |A> polarization states, and then interacts with the fourth NV color center s4 of the node to form the first logical bit;

[0052] The fourth module is used to achieve: photons reach another node through long-distance transmission, and then enter the T″1 system for photon state encoding, so that each |A> polarization state is transformed into a |D> polarization state with different degrees of freedom;

[0053] The fifth module is used to achieve: the photon interacts with the eighth NV color center s8, the sixth NV color center s6, the seventh NV color center s7, and the fifth NV color center s5 of the other node in turn, and is encoded in turn through the T′2 system, the T3 system, and the T′3 system. While forming a logical bit at the node, the entanglement of the logical bits between the two nodes is achieved. At the same time, the corresponding entangled state is judged by measuring the polarization state of the current photon; the T3 system is used to realize the transition from the |A> polarization state to the |D> polarization state, and the T′2 system and T′3 system are used to realize the exchange of different degrees of freedom between the |A> polarization states.

[0054] For the specific limitations of the fault-tolerant logic quantum bit non-local quantum entangled state preparation system, please refer to the limitations of the fault-tolerant logic quantum bit non-local quantum entangled state preparation method above, which will not be repeated here. Each module in the above-mentioned fault-tolerant logic quantum bit non-local quantum entangled state preparation system can be implemented in whole or in part through software, hardware and a combination thereof. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules.

[0055] In one embodiment, as a specific example, the present invention is further described in detail.

[0056] See also Figure 1 and Figure 2 , the figure includes: two distant nodes L1 and L2, each node contains four diamond NV color center systems, this system can be regarded as an electron with two energy levels |g> and |e>, and each diamond color center QM i The electron spin states in (i=1, ..., 8) are initialized to superposition state of .

[0057] See also Figure 3 , T nRepresents a system that encodes the state of photons. PBS (polarizing beam-splitter) is a polarization beam splitter that transmits photons with a polarization state of |D> and reflects photons with a polarization state of |A>; HWP (half waveplate) is a half-wave plate; OS (optical switch) is an optical switch; D(t) represents a time delay t imposed on the photon. When a photon passes through this optical path system, its polarization state can be flipped and the same time delay can be added.

[0058] See also Figure 4 , which can realize the exchange between |A> polarization states with different temporal degrees of freedom by adding different temporal degrees of freedom to the |D> and |A> polarization states.

[0059] See also Figure 5 ,and Figure 4 Similar, but the difference is that the final output photons only have the |D> polarization state.

[0060] The method for preparing the non-local quantum entangled state of fault-tolerant logical quantum bits is specifically implemented as follows:

[0061] The photon with the initial state D0 interacts with the first NV color center s1. When the electron spin state in s1 is |g>, the polarization state of the photon remains unchanged; when the electron spin state in s1 is |e>, the polarization state of the photon flips and a superposition state is obtained:

[0062]

[0063] The subscripts |D0> and |A0> represent the length of the time delay, that is, the time degrees of freedom, and the subscripts involved below have the same meaning.

[0064] Then the photon P enters the T1 system. Under the action of the polarization beam splitter PBS, the photon's |A0> polarization state is emitted to the half-wave plate H, and then a time degree of freedom delay is added, so that the polarization state becomes |D1>. Then, under the action of the optical switch OS1, the |D0> and |D1> polarization states are merged into one spatial mode, and the total superposition evolves as follows:

[0065]

[0066] Then, the photon P interacts with the second NV color center s2. After passing through the T2 system, the polarization states of P |A0> and |A1> become |D2> and |D3> respectively. After being merged into one spatial mode by the optical switch OS2, its superposition state becomes:

[0067]

[0068] Where t is a decimal number that can be converted to a binary number QM i The polarization state is |g i >(|e i >), the corresponding is 0(1). Satisfies the following equation:

[0069]

[0070] Among them, I i =|g> i |g>+|e> i |e> does not affect the electron spin state, Represents flipping the spin state of an electron.

[0071] Subsequently, the photon P interacts with the third NV color center s3 and realizes the state exchange between |A0> and |A3>, |A1> and |A2> in T′1. Subsequently, the three QM s The fusion state of photon P becomes:

[0072]

[0073] After the photon interacts with the fourth NV color center s4, the photon is transmitted over a long distance to another node, and in the T″1 system, the photon’s |A t >Polarization state encoded as |D 7-t >Polarization state (t=0, 1, 2, 3). At this time, the four QM s The fusion state with photon P becomes:

[0074]

[0075] The photon then interacts with the eighth NV color center s8 and is then input into T′2, realizing the exchange between polarization states of |A> with different degrees of freedom, and the entangled state becomes:

[0076]

[0077] in, represents the i-th logical bit (i=1, 2), t=0, 1, ..., 7, |t L >There are four electron spin GHZ states, which can be described as:

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086] After the photon interacts with the sixth NV color center s6, it is encoded through the T3 system and |A t >Convert to |D t+8 >, (t=0, 1, 2…, 7), the entangled state of the photon and the color center becomes:

[0087]

[0088] The photon then interacts with the seventh NV center s7, is encoded by the T′3 system, realizes the exchange between polarization states of |A> with different degrees of freedom, and finally interacts with the fifth NV center s5:

[0089]

[0090] Photons pass through Figure 1 After the system is built, the photon state is measured by the photon detector. Once the state of the photon is measured, its state will quickly collapse from the original multiple superposition states to a certain eigenstate (|D t >、|A t >, t = 0, 1, ..., 15). At the same time, since the 8 NV color centers have formed an entangled state with the photon, the state of the 8 NV color centers will also instantly collapse into the logical bit entangled state corresponding to the measured photon state. For example, if the measured photon state is |D4>, then the state of the 8 NV color centers will become Then, according to the state of the photon, the phase of a single bit is flipped to obtain one of the following two GHZ states of the logical bit:

[0091]

[0092]

[0093] For example, for the state of the collapsed NV center, if the state of QM1 is flipped, then and will be converted to and The overall state will also be converted to |Φ + >. Similarly, if the state of QM3 is reversed, then and will be converted to and The final state will become |Ψ + >.

[0094] For other measured photon states, |Φ can still be obtained through similar operations. + > and |Ψ + > Status.

[0095] In summary, the present invention achieves the entanglement preparation of two logical bits by sequentially interacting a high-dimensionally coded single photon with eight NV color centers and encoding them with the help of a series of optical elements.

[0096] The present invention utilizes a high-dimensionally encoded single photon to prepare a highly fault-tolerant non-local entangled state of logical bits, which can significantly reduce transmission losses and save quantum resources.

[0097] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit, characterized in that: The method comprises the following steps: Step 1: A photon with an initial polarization state of |D0> interacts with the first NV color center s1 of a node, and then enters the T1 system for photon state encoding. After the encoding is completed, the photon only exists in the |D> polarization state; Step 2, the photon interacts with the second NV color center s2 of the node, and then enters the T2 system for photon state encoding. After the encoding is completed, the photon only exists in the |D) polarization state; Step 3, the photon interacts with the third NV center s3 of the node, then enters the T′1 system for photon state encoding, realizes the exchange of different degrees of freedom between |A> polarization states, and then interacts with the fourth NV center s4 of the node to form the first logical bit; Step 4: The photon reaches another node through long-distance transmission and then enters T″ i The system encodes the photon state so that each |A> polarization state is transformed into a |D> polarization state with different degrees of freedom; Step 5, the photon interacts with the eighth NV color center s8, the sixth NV color center s6, the seventh NV color center s7, and the fifth NV color center s5 of the other node in turn, and is encoded in turn through the T′2 system, the T3 system, and the T′3 system, and while forming a logical bit at the node, the entanglement of the logical bits between the two nodes is realized. At the same time, the corresponding entangled state is determined by measuring the polarization state of the current photon; the T3 system is used to realize the transition from the |A> polarization state to the |D> polarization state, and the T′2 system and the T′3 system are used to realize the exchange of different degrees of freedom between the |A> polarization states; The T′1 system is as follows: using a polarization beam splitter and an optical switch to exchange the polarization states of |A> with different time degrees of freedom of photons, to achieve the exchange of polarization states between |A0> and |A3>, |A1> and |A2>, at which time, the three NV color centers and photons merge; wherein, the polarization states of |A2> and |A3> are the results of the interaction between the photon and the second NV color center s2 and the third NV color center s3 of the node, respectively; The T″1 system uses a polarization beam splitter, a half-wave plate and an optical switch to add different time degrees of freedom to the |A> polarization state of the photon and convert it into the |D> polarization state, thereby realizing the conversion of the photon's |A t >Polarization state encoded as |D 7-t >Polarization state, at this time, the four NV color centers merge with the photons; where t = 0, 1, 2, 3.

2. The method for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit according to claim 1, characterized in that: In step 1, the photon interacts with the first NV color center s1, specifically including: when the electron spin state in s1 is |g>, the polarization state of the photon remains unchanged; when the electron spin state in s1 is |e>, the polarization state of the photon flips and becomes the polarization state |A0>.

3. The method for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit according to claim 2, characterized in that: The T1 system and the T2 system both include a polarization beam splitter PBS, a half-wave plate H and an optical switch; In the T1 system, under the action of the polarization beam splitter PBS, the |A0> polarization state of the photon is emitted to the half-wave plate H, and then a time degree of freedom delay is added, so that the |D0> polarization state is changed to the |D1> polarization state. Then, under the action of the optical switch OS1, the |D0> and |D1> polarization states are merged into one spatial mode; In the T2 system, the |A0> and |A1) polarization states of the photons are changed into |D2> and |D3) polarization states respectively, and then merged into one spatial mode through the optical switch OS2.

4. The method for preparing a non-local quantum entangled state of a fault-tolerant logical quantum bit according to claim 1, characterized in that: In step 5, the corresponding entangled state is determined by measuring the polarization state of the current photon, which specifically includes: Step 5-1, based on the measured polarization state of the current photon, collapse the superposition state after passing through the eight NV color centers and the coding system into a logical bit entangled state corresponding to the measured photon polarization state, thereby determining the logical bit entangled state composed of the eight NV color centers; Step 5-2: Based on the logical bit entangled state, perform phase flipping on a single bit to obtain a logical bit entangled state with fault tolerance.

5. A fault-tolerant logic quantum bit non-local quantum entangled state preparation system based on the method according to any one of claims 1 to 4, characterized in that: The system comprises: The first module is used to realize: a photon with an initial polarization state of |D0> interacts with the first NV color center s1 of a node, and then enters the T1 system for photon state encoding; The second module is used to realize: the photon interacts with the second NV color center s2 of the node, and then enters the T2 system for photon state encoding. After the encoding is completed, the photon only exists in the |D> polarization state; The third module is used to realize: the photon interacts with the third NV color center s3 of the node, then enters the T′1 system for photon state encoding, realizes the exchange of different degrees of freedom between |A> polarization states, and then interacts with the fourth NV color center s4 of the node to form the first logical bit; The fourth module is used to achieve: photons reach another node through long-distance transmission, and then enter the T″1 system for photon state encoding, so that each |A> polarization state is transformed into a |D> polarization state with different degrees of freedom; The fifth module is used to achieve: the photon interacts with the eighth NV color center s8, the sixth NV color center s6, the seventh NV color center s7, and the fifth NV color center s5 of the other node in turn, and is encoded in turn through the T′2 system, the T3 system, and the T′3 system. While forming a logical bit at the node, the entanglement of the logical bits between the two nodes is achieved. At the same time, the corresponding entangled state is judged by measuring the polarization state of the current photon; the T3 system is used to realize the transition from the |A> polarization state to the |D> polarization state, and the T′2 system and T′3 system are used to realize the exchange of different degrees of freedom between the |A> polarization states.

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