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Modern Physics Letters A

Long-range entanglement between spin qubits in quantum dots by virtual photon process

Ye-Bin Hu, Rong Chen, Guoqing Yan, Xingyu Zhu

Published Mar 21, 2023• 1 citation
Publisher

Abstract

Electron spin qubits in silicon quantum dots are an attractive candidate for large-scalable quantum computation. An essential step for quantum information processing based on spin qubits is to realize the spatially separated two-qubit gate and entanglement with high fidelity. Here, we consider two spin qubits coupled to a common superconducting resonator in circuit quantum electrodynamics. We investigate the long-range two-qubit iSWAP gate mediated by virtual microwave photons using a Gaussian smoothing pulse. We show that the entangling gate fidelity can reach [Formula: see text] under realistic experimental conditions and analyze the factors limiting gate fidelity. Moreover, we numerically demonstrate the generation of remote Bell entangled states of spin qubits with high fidelity. In addition, this spin–resonator architecture can be used to implement quantum algorithms using our scheme. These results pave the way for quantum information processing with spin qubits.

DOI
10.1142/s0217732323500530

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Electron spin qubits in silicon quantum dots are an attractive candidate for large-scalable quantum computation. An essential step for quantum information processing based on spin qubits is to realize the spatially separated two-qubit gate and entanglement with high fidelity. Here, we consider two spin qubits coupled to a common superconducting resonator in circuit quantum electrodynamics. We investigate the long-range two-qubit iSWAP gate mediated by virtual microwave photons using a Gaussian smoothing pulse. We show that the entangling gate fidelity can reach [Formula: see text] under realistic experimental conditions and analyze the factors limiting gate fidelity. Moreover, we numerically demonstrate the generation of remote Bell entangled states of spin qubits with high fidelity. In addition, this spin–resonator architecture can be used to implement quantum algorithms using our scheme. These results pave the way for quantum information processing with spin qubits.
Spin qubits in semiconductor quantum dots are an attractive candidate for scalable quantum information processing. Reliable quantum state transfer and entanglement between spatially separated spin qubits is a highly desirable but challenging goal. Here, we propose a fast and high-fidelity quantum state transfer scheme for two spin qubits mediated by virtual microwave photons. Our general strategy involves using a superadiabatic pulse to eliminate non-adiabatic transitions, without the need for increased control complexity. We show that arbitrary quantum state transfer can be achieved with a fidelity of 95.1% within a 60 ns short time under realistic parameter conditions. We also demonstrate the robustness of this scheme to experimental imperfections and environmental noises. Furthermore, this scheme can be directly applied to the generation of a remote Bell entangled state with a fidelity as high as 97.6%. These results pave the way for fault-tolerant quantum computation on spin quantum network architecture platforms.
We report the coherent coupling of two electron spins at a distance via virtual microwave photons. Each spin is trapped in a silicon double quantum dot at either end of a superconducting resonator, achieving spin-photon couplings up to around gs/2π=40MHzg_s/2\pi = 40 \text{MHz}gs​/2π=40MHz. As the two spins are brought into resonance with each other, but detuned from the photons, an avoided crossing larger than the spin linewidths is observed with an exchange splitting around 2J/2π=20MHz2J/2\pi = 20 \text{MHz}2J/2π=20MHz. In addition, photon number states are resolved from the shift 2χs/2π=−13MHz2\chi_s/2\pi = -13 \text{MHz}2χs​/2π=−13MHz they induce on the spin frequency. These results could enable long-range two-qubit gates between spin qubits and scalable networks of spin qubits on a chip.
We report the coherent coupling of two electron spins at a distance via virtual microwave photons.Each spin is trapped in a silicon double quantum dot at either end of a superconducting resonator, achieving spinphoton couplings up to around g s =2π ¼ 40 MHz.As the two spins are brought into resonance with each other, but detuned from the photons, an avoided crossing larger than the spin linewidths is observed with an exchange splitting around 2J=2π ¼ 20 MHz.In addition, photon-number states are resolved from the shift 2χ s =2π ¼ -13 MHz that they induce on the spin frequency.These observations demonstrate that we reach the strong dispersive regime of circuit quantum electrodynamics with spins.Achieving spin-spin coupling without real photons is essential to long-range two-qubit gates between spin qubits and scalable networks of spin qubits on a chip.
Abstract Nonlocal qubit interactions are a hallmark of advanced quantum information technologies1–5. The ability to transfer quantum states and generate entanglement over distances much larger than qubit length scales greatly increases connectivity and is an important step towards maximal parallelism and the implementation of two-qubit gates on arbitrary pairs of qubits6. Qubit-coupling schemes based on cavity quantum electrodynamics2, 7, 8 also offer the possibility of using high-quality-factor resonators as quantum memories3, 9. Extending qubit interactions beyond the nearest neighbour is particularly beneficial for spin-based quantum computing architectures, which are limited by short-range exchange interactions10. Despite the rapidly maturing device technology for silicon spin qubits11–16, experimental progress towards achieving long-range spin–spin coupling has so far been restricted to interactions between individual spins and microwave photons17–20. Here we demonstrate resonant microwave-mediated coupling between two electron spins that are physically separated by more than four millimetres. An enhanced vacuum Rabi splitting is observed when both spins are tuned into resonance with the cavity, indicating a coherent interaction between the two spins and a cavity photon. Our results imply that microwave-frequency photons may be used to generate long-range two-qubit gates between spatially separated spins.
The recent realization of a coherent interface between a single electron in a silicon quantum dot and a single photon trapped in a superconducting cavity opens the way for implementing photon-mediated two-qubit entangling gates. In order to couple a spin to the cavity electric field, some type of spin-charge hybridization is needed, which impacts spin control and coherence. In this work we propose a cavity-mediated two-qubit gate and calculate cavity-mediated entangling gate fidelities in the dispersive regime, accounting for errors due to the spin-charge hybridization, as well as photon- and phonon-induced decays. By optimizing the degree of spin-charge hybridization, we show that two-qubit gates mediated by cavity photons are capable of reaching fidelities exceeding 9090%90 in present-day device architectures. High iswap gate fidelities are achievable even in the presence of charge noise at the level of $2\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\text{eV}$.
We investigate a hybrid quantum system consisting of spatially separated resonant exchange qubits, defined in three-electron semiconductor triple quantum dots, that are coupled via a superconducting transmission line resonator. Drawing on methods from circuit quantum electrodynamics and Hartmann-Hahn double resonance techniques, we analyze three specific approaches for implementing resonator-mediated two-qubit entangling gates in both dispersive and resonant regimes of interaction. We calculate entangling gate fidelities as well as the rate of relaxation via phonons for resonant exchange qubits in silicon triple dots and show that such an implementation is particularly well suited to achieving the strong coupling regime. Our approach combines the favorable coherence properties of encoded spin qubits in silicon with the rapid and robust long-range entanglement provided by circuit QED systems.