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Advanced Quantum Technologies

Error‐Detected Robust‐fidelity SWAP and (SWAP)1/m Gates for Quantum‐Dot Spins

Xin‐Shan Du, Qiulin Tan, Fang‐Fang Du

Published Jan 14, 2025• 0 citations
Publisher

Abstract

Abstract Quantum logic gate forms the cornerstone of quantum computing. Here, two error‐detected, circuit‐compact, and fidelity‐robust SWAP and (SWAP) () gates are set for quantum‐dot (QD) spins with the aid of the scattering property of photon off QD fixed in double‐sided microcavity. For an ideal single‐photon scattering, the efficiencies and fidelities of both the SWAP and (SWAP) gates can, in principle, be close to unity. Otherwise, being directed against a nonideal scattering, the error‐detected units of two gates make their fidelities near perfect at the expense of slight reductions of their efficiencies. Moreover, the two quantum gates work in an error‐detected way and may be experimentally feasible with current technique on regulating the QD‐cavity system. Further, additional spin qubits are not required, thereby reducing both quantum resource usages and error rates.

DOI
10.1002/qute.202400619

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Abstract Quantum logic gate forms the cornerstone of quantum computing. Here, two error‐detected, circuit‐compact, and fidelity‐robust SWAP and (SWAP) () gates are set for quantum‐dot (QD) spins with the aid of the scattering property of photon off QD fixed in double‐sided microcavity. For an ideal single‐photon scattering, the efficiencies and fidelities of both the SWAP and (SWAP) gates can, in principle, be close to unity. Otherwise, being directed against a nonideal scattering, the error‐detected units of two gates make their fidelities near perfect at the expense of slight reductions of their efficiencies. Moreover, the two quantum gates work in an error‐detected way and may be experimentally feasible with current technique on regulating the QD‐cavity system. Further, additional spin qubits are not required, thereby reducing both quantum resource usages and error rates.
Abstract Semiconductor quantum‐dot (QD) spins hold great promise in quantum information science and technology. The implementation of high‐fidelity quantum gates on QD‐spin qubits is of great importance. Here, two schemes are presented to implement two universal quantum controlled gates, that is, the two‐qubit controlled‐not gate and the three‐qubit Toffoli gate, on stationary electron‐spin qubits in QDs inside single‐sided optical microcavities, based on the cavity‐assisted photon scattering under the balance condition. Compared with the previous schemes based on the ideal giant circular birefringence, the present schemes use the balance condition of the single‐sided QD‐cavity system, which can be achieved in both the weak‐ and strong‐coupling regimes of cavity quantum electrodynamics. Under the balance condition, the noise caused by the unbalanced reflectance between the coupled and uncoupled QD‐cavity systems can be efficiently depressed, so that the fidelity of each quantum gate operation can be increased to unity in principle. The schemes exhibit the possibility of realizing high‐fidelity and scalable quantum computing with single QD spins and single photons using the feasible and robust light–matter quantum interface. These high‐fidelity quantum controlled gates can lead to more efficient construction of quantum circuits for quantum computing, and provide a convenient avenue for quantum networking.
High-fidelity quantum logic gates are essential in quantum computation, and both photons and electron spins in quantum dots (QDs) have their own unique advantages in implementing quantum computation. It is of critical significance to achieve high-fidelity quantum gates for photon-QD hybrid systems. Here, we propose two schemes for implementing high-fidelity universal quantum gates including Toffoli gate and Fredkin gate for photon-QD hybrid systems, utilizing the practical scattering of a single photon off a QD-cavity system. The computation errors from the imperfections involved in the practical scattering are detected and prevented from arising in the final results of the two gates. Accordingly, the unity fidelity of each quantum gate is obtained in the nearly realistic condition, and the requirement for experimental realization is relaxed. Furthermore, the quantum circuits for the two gates are compact and no auxiliary qubits are required, which would also be the advantages regarding their experimental feasibility. These features indicate that our schemes may be useful in the practical quantum computation tasks.
Abstract Efficient ways are presented to accomplish photonic controlled‐phase‐flip gate and entangler with the assistance of imperfect double‐sided quantum‐dot‐microcavity systems, but without ancillary qubits. Compact quantum circuits for implementing entanglement swapping between photon pairs and electron pairs are then designed. Unity fidelities of the schemes can be achieved, and physical imperfections in the construction processes are detected by single‐photon detectors. Also, the efficiencies of the schemes can be further improved by repeating the operation processes when the undesired performances are detected. The evaluations show that the schemes are possible with current experiment parameters.
We present an efficient proposal for error-rejecting quantum computing with quantum dots (QDs) embedded in single-sided optical microcavities based on the interface between the circularly polarized photon and QDs. An almost unity fidelity of the quantum entangling gate (EG) can be implemented with a detectable error that leads to a recycling EG procedure, which improves further the efficiency of our proposal along with the robustness to the errors involved in imperfect input-output processes. Meanwhile, we discuss the performance of our proposal for the EG on two solid-state spins with currently achieved experiment parameters, showing that it is feasible with current experimental technology. It provides a promising building block for solid-state quantum computing and quantum networks.
Abstract The interconversion between different types of entangled states is an essential process. It is particularly important for tasks requiring specific forms of entanglement, as it greatly enhances the versatility, robustness, and efficiency of quantum systems. In the paper, deterministic schemes are proposed for interconversion between three‐logic‐qubit W state and three‐logic‐qubit Knill‐Laflamme‐Milburn state within a decoherence‐free subspace (DFS). The process of mutual transformation leverages the state‐selective nature of a quantum dot (QD) confined in a double‐sided microcavity, along with high‐fidelity, error‐predictable quantum control gates. Furthermore, the incorporation of single‐photon detectors helps to identify and mitigate potential failures arising from imperfect interactions between photons and the QD‐cavity system, thereby significantly enhancing experimental viability. In‐depth analyses of both protocols confirm that they can, in principle, achieve near‐unit fidelities and outstanding efficiencies. Additionally, the protocols offer advanced solutions to decoherence challenges through the use of DFS, paving the way for the development of practical quantum technologies.
Quantum logic gates are the key elements in quantum computing. Here we investigate the possibility of achieving a scalable and compact quantum computing based on stationary electron-spin qubits, by using the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics. We design the compact quantum circuits for implementing universal and deterministic quantum gates for electron-spin systems, including the two-qubit CNOT gate and the three-qubit Toffoli gate. They are compact and economic, and they do not require additional electron-spin qubits. Moreover, our devices have good scalability and are attractive as they both are based on solid-state quantum systems and the qubits are stationary. They are feasible with the current experimental technology, and both high fidelity and high efficiency can be achieved when the ratio of the side leakage to the cavity decay is low.