Prediction type high-fidelity entanglement quantum logic gate method

Abstract

The invention discloses a prediction type high-fidelity entangled quantum logic gate method, which is suitable for quantum computing physical systems such as neutral atom quantum bits and superconducting quantum bits. According to the method, on the basis of a multi-body physical system formed by coupling mediating atoms with quantum bit atoms, a special modulation waveform driving system with space-time symmetry is designed according to the requirement for realizing a two-bit entangled quantum logic gate; the induction quantum interference effect enables the specific quantum internal state of the mediating atom to correspond to the quantum state of which the error first-order effect of the whole quantum logic gate of the system is subjected to mutual interference cancellation after the driving is finished; thus, by measuring the quantum internal state of the mediating atom, a specific measurement result can forecast that the high-fidelity quantum logic gate has been established between two quantum bit atoms. According to the method, errors can be suppressed and relieved on a quantum computing hardware level, so that a forecast type high-fidelity two-bit quantum logic gate is implemented, a high-quality hardware basis can be provided for an advanced quantum error correction algorithm, and the method has important significance in realizing high-fidelity quantum computing.

Description

Technical Field

[0001] The present invention relates to the field of quantum computing, specifically a predictive high-fidelity quantum logic gate method with error suppression and mitigation functions, applicable to quantum computing physical systems such as neutral atom qubits and superconducting qubits. Background Art

[0002] The research on quantum computing has entered the era of noisy intermediate-scale quantum (NISQ) devices, and quantum error correction (QEC) technology has emerged. To efficiently and practically run quantum computing tasks and construct logical qubits, high-quality physical qubits are required to implement quantum logic gates with very high fidelity, especially two-qubit entangled quantum logic gates. This problem is closely related to the specific characteristics of physical qubits, but currently, there is still a relatively large gap between the quality of two-qubit quantum logic gates on various physical platforms and the expected level. This is mainly due to factors such as the interaction between qubits, decoherence, and noise.

[0003] Among many competing technical routes, neutral atom qubits and superconducting qubits have become attractive choices for exploring the potential of two-qubit quantum logic gates. For the research on neutral atom quantum computing, since the experimental realization of the Rydberg blockade two-qubit quantum logic gate, the dipole-dipole interaction based on atomic Rydberg states has played a crucial role, so the coherent driving of the ground state-Rydberg state transition is essential. Along with the progress of laser technology, the improvement of neutral atom two-qubit quantum gates comes from using the continuously modulated synthetic pulse method to replace the early proposed discrete resonance pulse sequence method; currently, through techniques such as efficiently filling cold atoms in optical potential wells, the number of neutral atom qubits can reach up to 1000. In addition, the buffer atom framework, including the buffer-atom-mediated gate scheme and the SWAP gate scheme, provides a solution for high-speed and high-connectivity for large-scale qubit arrays.

[0004] Although the neutral atom qubit system or the superconducting qubit system shows the potential to build a practical quantum processor, even with well-tuned post-selection techniques, the fidelity of neutral atom or superconducting two-qubit entangled quantum logic gates at the physical hardware implementation level has not exceeded the optimistic estimated level of 0.999 so far.

[0005] This current situation highlights the deficiencies of the existing technologies in realizing high-fidelity two-bit entangled quantum logic gates, and also points out the direction for future research efforts. To promote the further development of quantum computing, it is necessary to continuously explore new technical paths and optimization methods to improve the fidelity of quantum logic gates, so as to construct a more efficient and stable quantum processor. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the existing technologies, provide a physical basis for constructing a large-scale quantum bit system and running a quantum error correction algorithm, and propose a predictive high-fidelity entangled quantum logic gate method, which is applicable to quantum computing physical systems such as neutral atom qubits and superconducting qubits. The core lies in a multi-body quantum physical system composed of mediator atoms coupling qubit atoms. Aiming at the requirement of realizing two-bit entangled quantum logic gates, a special modulation waveform with parity-time symmetry is designed to drive the system, inducing a specific quantum interference effect, so that after the driving ends, there is a quantum state in which the first-order effects of quantum logic gate errors have mutually interfered and canceled out, and it corresponds to a specific quantum internal state of the mediator atom; thus, by measuring the quantum internal state of the mediator atom, the measurement result of the aforementioned specific quantum internal state can deterministically predict that a high-fidelity quantum logic gate has been established between two qubit atoms. The present invention is beneficial to suppressing and alleviating errors at the quantum computing hardware level, thereby implementing a predictive high-fidelity two-bit quantum logic gate.

[0007] The technical solution route of the present invention is as follows:

[0008] Compared with the existing technologies, the beneficial effects of the present invention are as follows:

[0009] 1) By means of the coupling of mediator atoms and a special modulation waveform, a quantum interference effect is generated during the implementation of the quantum logic gate, so that after the driving ends, there is a quantum state in which the first-order effects of quantum logic gate errors have mutually interfered and canceled out, and it corresponds to a specific quantum internal state of the mediator atom; thus, by measuring a specific result of the quantum internal state of the mediator atom, it can be deterministically predicted that a high-fidelity entangled quantum logic gate has been established between two qubit atoms; compared with the previous quantum logic gate schemes, it additionally has the characteristics of error cancellation and prediction, which is more conducive to improving the convenience and fidelity of entangled quantum logic gate operations.

[0010] 2) Under the post-selection condition where spontaneous emission does not occur, for neutral atom qubits and superconducting qubits, in the operating condition of a predictive quantum logic gate, the present invention can improve the fidelity of a two-qubit entangled quantum logic gate to a level of approximately 0.9999 to 0.999999. The performance has been greatly improved compared to previous quantum logic gate schemes, which is equivalent to achieving error suppression or error mitigation at the quantum computing hardware level, providing a better physical basis for constructing a large-scale qubit system and running quantum error correction algorithms. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of the implementation process of a predictive high-fidelity entangled quantum logic gate method of the present invention;

[0012] Figure 2 Taking the neutral atom qubit system as an example, it involves two Rydberg energy levels of the mediating atom, and is an atomic energy level diagram of a multi-body qubit physical system that cooperates with a simultaneous execution method to control a waveform group;

[0013] Figure 3 Taking the neutral atom qubit system as an example, it only involves one Rydberg energy level of the mediating atom, but is an atomic energy level diagram of the mediating atom that can utilize the polarization degree of freedom and cooperate with a simultaneous execution method to control a waveform group;

[0014] Figure 4 Taking the neutral atom qubit system as an example, it is an atomic energy level diagram of a multi-body qubit physical system that cooperates with a step-by-step execution method to control a waveform group. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following takes the controlled-Z phase gate (CZ gate) of neutral atom qubits as an example and further illustrates the present invention in conjunction with the drawings, but the protection scope of the present invention should not be limited thereby.

[0016] The predictive high-fidelity entangled quantum logic gate method includes the following steps:

[0017] Step 1. Construct a multi-body qubit physical system containing mediating atoms suitable for a predictive high-fidelity entangled quantum logic gate. This system should have the following characteristics:

[0018] 1. There is a coupling between the mediating atom and the qubit atom in this system, and this coupling can be quantum coherently turned on and off according to the requirements of quantum logic gate operations. This coupling should enable the mediating atom to participate in the quantum evolution process during the execution of the quantum logic gate and sense the state of the qubit atom;

[0019] 2. Driven by a modulation waveform combination that meets the requirements, both the mediated atomic quantum states |0> and |1> participate in the execution process of the quantum logic gate and produce different responses when errors occur;

[0020] 3. In this system, the value of the direct interaction strength between qubit atoms can take any value, including the case where there is no direct interaction between qubits at all.

[0021] Step 2. To implement a predictive high-fidelity entangled quantum logic gate, design parity-time symmetric modulation waveform combinations A and B according to the multi-body qubit physical system in Step 1. Such modulation waveform combinations should have the following characteristics:

[0022] 1. Both modulation waveform combinations A and B act on the entire qubit physical system formed by the coupling of mediated atoms and qubit atoms. However, modulation waveform combination A only interacts with the mediated atomic quantum state |0>, modulation waveform combination B only interacts with the mediated atomic quantum state |1>, and either modulation waveform combination A or B can drive the mediated quantum logic gate alone;

[0023] 2. Modulation waveform combinations A and B will induce quantum interference effects, such that after the drive ends, the overall physical system has a quantum state in which the first-order effects of errors in the quantum logic gate operation process have mutually interfered and canceled out, and this corresponds to the mediated atomic quantum state |0>;

[0024] 3. Through specific modes such as detuned modulation drive and resonant modulation drive, calculate the specific expansion coefficients of the required modulation waveforms according to the selected complete function basis by physical methods, and the adaptability to the actual physical situation can be achieved by changing the expansion coefficients according to experimental feedback.

[0025] Step 3. To implement a predictive high-fidelity entangled quantum logic gate, select a reasonable execution method according to the multi-body qubit physical system in Step 1 and modulation waveform combinations A and B in Step 2. This execution method should have the following characteristics:

[0026] 1. Modulation waveform combinations A and B can be executed simultaneously or step by step. It is necessary to set the coupling paths between the mediated atomic quantum states |0>, |1> and the qubit atoms in the physical system respectively;

[0027] 2. There are differences in the suppression effects of errors during the operation of the quantum logic gate between the two execution methods of simultaneous execution and distributed execution. A more appropriate method should be selected according to the physical characteristics of the overall system and the nature of possible errors.

[0028] Step 4. To implement a predictive high-fidelity entangled quantum logic gate, according to the multi-body qubit physical system in Step 1, the modulation waveform combinations A and B in Step 2, and the execution method in Step 3, perform corresponding control processes to complete the required quantum logic gate. The control process should include the following specific operations:

[0029] Step 41. The mediating atom has two quantum internal states |0> and |1>. First, initialize the mediating atom in the |0> state, and then apply a local resonant pulse 1-1 to prepare the mediating atom into the state

[0030] Step 42. To meet the requirement of implementing a two-qubit entangled quantum logic gate, design a modulation waveform combination 1-2 with parity-time symmetry to drive this system. Among them, the modulation waveform combination A drives the multi-body quantum state composed of the mediating atom in the |0> state and the qubit atom, and the modulation waveform combination B drives the multi-body quantum state composed of the mediating atom in the |1> state and the qubit atom;

[0031] Step 43. Apply a second local resonant pulse 1-3 to the mediating atom;

[0032] Step 44. Using the quantum internal states |0> and |1> as the measurement basis, perform a quantum projection measurement on the mediating atom. For example, for the quantum internal state |0> scattered by applying laser driving and collecting atomic fluorescence, the possible results include that the mediating atom is in the quantum internal state |0> and thus photon 1-4 is collected, and the mediating atom is in the quantum internal state |1> and thus no photon 1-5 is collected. The measurement result is used as the prediction of this quantum logic gate operation;

[0033] Step 45. If it is measured by a measuring instrument 1-6 such as a single-photon counter or an electron-multiplying charge-coupled device (EMCCD) according to the operation in Step 41 that the mediating atom is in the |0> state, it represents the successful implementation of a predictive high-fidelity entangled quantum logic gate, that is, an entangled quantum logic gate has been established between the two qubit atoms.

[0034] Figure 2Taking the neutral atom qubit system as an example, it involves the energy level schematic diagram of a multi-body qubit physical system that mediates two Rydberg energy levels of atoms and cooperates with a simultaneous execution method to control the waveform group. This system realizes quantum logic gate operations through neutral atom qubits and mediating atoms. The main components of the system include a control qubit atom, a mediating atom, and a target qubit atom, each of which has a specific energy level structure and is regulated by an external drive. The left, middle, and right parts respectively represent the main energy level structures and external drives of the control qubit atom, the mediating atom, and the target qubit atom. Among them, the control qubit atom has a quantum internal state |0>2-1, a quantum internal state |1>2-2, and a Rydberg state |r>2-3; the mediating atom has a quantum internal state |0>2-4, a quantum internal state |1>2-5, a Rydberg state |r′>2-6, and a Rydberg state |r">2-7; the target qubit atom has a quantum internal state |0>2-8, a quantum internal state |1>2-9, and a Rydberg state |r>2-10. The electric dipole interaction between the Rydberg state of the mediating atom and the qubit atom exists between 2-7 and 2-3, between 2-7 and 2-10, as well as between 2-6 and 2-3, and between 2-6 and 2-10. The regulation 2-11 between the quantum internal states of the mediating atom provides Figure 1 The single-bit quantum logic gate pulse for mediating atom localization described in Step 1 and Step 3. Figure 1 The transitions driven by the modulated waveform combination described in Step 2 include: the transition 2-12 of the quantum internal state |1> of the control qubit atom to the Rydberg state |r>, the transition 2-13 of the quantum internal state |1> of the mediating atom to the Rydberg state |r′>, the transition 2-14 of the quantum internal state |0> of the mediating atom to the Rydberg state |r">, and the transition 2-15 of the quantum internal state |1> of the target qubit atom to the Rydberg state |r>.

[0035] Figure 3Taking the neutral atom qubit system as an example, it only involves one Rydberg level of the mediating atom, but can use the polarization degree of freedom to cooperate with the simultaneous execution method to control the schematic diagram of the mediating atom energy levels of the waveform group. Its characteristic lies in using different sub-energy states within the same Rydberg level to realize two paths of interaction between the mediating atom and the Rydberg state of the qubit atom. For typical alkali metal atoms, the internal state of the qubit is realized among two hyperfine split energy levels of the atomic ground state. For example, the energy level 3-1 corresponding to the lower energy, 3-2 corresponding to the higher energy, and the Rydberg level 3-3, each containing multiple magnetic sub-energy states. Among them, the magnetically insensitive sub-energy state 3-4 in the energy level 3-1 is selected as the quantum internal state |0>, and the magnetically insensitive sub-energy state 3-5 in the energy level 3-2 is selected as the quantum internal state |1>. In this case, driving the transition from the ground state to the Rydberg state requires using the polarization degree of freedom. Among them, the right-handed polarized laser drives the transition 3-6 of the quantum internal state |0> to the Rydberg state, and the left-handed polarized laser drives the transition 3-7 of the quantum internal state |1> to the Rydberg state.

[0036] Figure 4 Taking the neutral atom qubit system as an example, it is a schematic diagram of the atomic energy levels of a multi-body qubit physical system that controls the waveform group in a step-by-step execution manner. In this case, Figure 1 the controlled waveform group 1-2 is executed step by step, and the left and right parts of this figure represent the first and second steps of the step-by-step execution. Among them, the controlled qubit atom has the quantum internal state |0> 4-1, the quantum internal state |1> 4-2, and the Rydberg state |r> 4-3; the mediating atom has the quantum internal state |0> 4-4, the quantum internal state |1> 4-5, and the Rydberg state |r′> 4-6; the target qubit atom has the quantum internal state |0> 4-7, the quantum internal state |1> 4-8, and the Rydberg state |r> 4-9. The situations of the controlled waveform group on the left part driving atomic transitions include: the transition 4-10 of the quantum internal state |1> of the controlled qubit atom to the Rydberg state |r>, the transition 4-11 of the quantum internal state |1> of the mediating atom to the Rydberg state |r′>, and the transition 4-12 of the quantum internal state |1> of the target qubit atom to the Rydberg state |r>; the situations of the controlled waveform group on the right part driving atomic transitions include: the transition 4-13 of the quantum internal state |1> of the controlled qubit atom to the Rydberg state |r>, the transition 4-14 of the quantum internal state |0> of the mediating atom to the Rydberg state |r′>, and the transition 4-15 of the quantum internal state |1> of the target qubit atom to the Rydberg state |r>; in order to meet the requirements of the parity-time symmetry modulation waveform combination, the detuning of 4-10 needs to be opposite to the detuning of 4-13, the detuning of 4-11 needs to be opposite to the detuning of 4-14, and the detuning of 4-12 needs to be opposite to the detuning of 4-15.

Claims

1. A predictive high-fidelity entangled quantum logic gate method, characterized in that: The following steps are involved: S1. Construct a multi-body quantum bit physical system, which includes multiple quantum bit atoms and at least one mediating atom. There is a controllable quantum coherent coupling between the mediating atom and the quantum bit atom, and the coupling can turn on and off the quantum coherence according to the needs of the quantum logic gate operation, so that the mediating atom can participate in the quantum evolution during the execution of the quantum logic gate and sense the state of the quantum bit atom; driven by a modulation waveform combination that meets the requirements, the quantum internal state of the mediating atom participates in the execution of the quantum logic gate and produces different responses when an error occurs; the direct interaction strength between the quantum bit atoms can be any value, including the situation where there is no direct interaction between the quantum bits, and the mediating atom has two quantum internal states |0> and |1>; S2. Design a modulation waveform combination A and a modulation waveform combination B with parity-time symmetry to realize a predicted high-fidelity entangled quantum logic gate, wherein the modulation waveform combination A and the modulation waveform combination B both act on the multi-body quantum bit physical system, the modulation waveform combination A only interacts with a specific quantum internal state of the mediating atom, and the modulation waveform combination B also only interacts with another specific quantum internal state of the mediating atom, and the modulation waveform combination A or B can drive the mediated quantum logic gate when used alone; the modulation waveform combination A and B induce quantum interference, so that after the drive is completed, the first-order effects of the quantum logic gate operation process errors existing in the physical system as a whole have interfered with each other, corresponding to the specific quantum internal state of the mediating atom; through the detuned modulation drive and resonant modulation drive modes, the specific expansion coefficients of the required modulation waveforms are obtained by computational physics methods according to the selected complete function basis, and the expansion coefficients are adjusted according to experimental feedback to achieve self-adaptation; S3. Select a reasonable execution method to realize the predicted high-fidelity entangled quantum logic gate. The execution method includes executing the modulation waveform combination A and B simultaneously or executing them in steps. It is necessary to set up the coupling paths between the atomic quantum internal state and the quantum bit atom in the physical system respectively, and select a more appropriate execution method according to the physical characteristics of the overall system and the nature of the possible errors. S4. Carry out corresponding control process to complete the required quantum logic gate.

2. The predicted high-fidelity entangled quantum logic gate method according to claim 1, characterized in that: The control process comprises the following steps: S4.

1. Initialize the mediating atom: initialize the mediating atom in the |0> state, one of the two quantum internal states |0> and |1>; S4.

1. Preparation of mediated atomic specific states: Imposing the first local resonance pulse, prepare the initialized mediating atoms to state; S4.

3. In order to realize the two-bit entangled quantum logic gate, a modulation waveform combination A and a modulation waveform combination B with parity-time symmetry are designed, wherein the modulation waveform combination A drives the multi-body quantum state composed of the |0> state-mediated atoms and the qubit atoms, and the modulation waveform combination B drives the multi-body quantum state composed of the |1> state-mediated atoms and the qubit atoms; S4.4 Under the drive of the modulation waveform combination, the quantum internal state of the mediating atom participates in the execution process of the quantum logic gate, and when an error occurs in the operation of the quantum logic gate, the quantum internal state of the mediating atom will produce a different response, thereby providing a basis for error detection; the direct interaction intensity value between the quantum bit atoms can take any value, including the situation where there is no direct interaction between the quantum bits, thereby providing a flexible quantum logic gate operation environment; S4.5 The modulation waveform combination A and the modulation waveform combination B both act on the entire quantum bit physical system composed of the coupling of the mediating atom and the quantum bit atom. The modulation waveform combination A only interacts with the quantum internal state |0> of the mediating atom, and the modulation waveform combination B only interacts with the quantum internal state |1> of the mediating atom, and the modulation waveform combination A or B itself can drive the mediated quantum logic gate alone; at the same time, the modulation waveform combination A and B will induce quantum interference, so that after the drive is completed, there will be a quantum state in which the first-order effects of the error in the quantum logic gate operation process have interfered with each other and destructed each other, and it corresponds to the quantum internal state |0> of the mediating atom; through specific modes such as detuned modulation drive and resonant modulation drive, the specific expansion coefficient of the required modulation waveform is obtained by computational physics method according to the selected complete function basis, and adaptation to the actual physical conditions can be achieved by changing the expansion coefficient according to experimental feedback. S4.6 Quantum projection measurement: Imposing a second local resonance on the mediating atom Pulse, using the quantum internal states |0> and |1> as the measurement basis, to perform quantum projection measurement on the mediating atom, and the measurement result is used as the prediction of this quantum logic gate operation; S4.7 If the mediating atom is measured to be in the |0> state, it means that a predicted high-fidelity entangled quantum logic gate has been performed, that is, an entangled quantum logic gate between the two quantum bit atoms has been established.

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