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Entropy

Virtual Photon-Mediated Quantum State Transfer and Remote Entanglement between Spin Qubits in Quantum Dots Using Superadiabatic Pulses

Yue Wang, Ting Wang, Xingyu Zhu

Published Apr 29, 2024• 1 citation
Publisher

Abstract

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.

DOI
10.3390/e26050379

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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.
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.
Reliable information transmission between spatially separated nodes is fundamental to a network architecture for scalable quantum technology. Spin qubit in semiconductor quantum dots is a promising candidate for quantum information processing. However, there remains a challenge to design a practical path from the existing experiments to scalable quantum processor. Here we propose a module consisting of spin singlet-triplet qubits and single microwave photons. We show a high degree of control over interactions between the spin qubit and the quantum light field can be achieved. Furthermore, we propose preparation of a shaped single photons with an efficiency of 98%, and deterministic quantum state transfer and entanglement generation between remote nodes with a high fidelity of 90%. This spin-photon module has met the threshold of particular designed error-correction protocols, thus provides a feasible approach towards scalable quantum network architecture.
Spin qubits in semiconductor quantum dots are a promising candidate for scalable quantum computation. A key step in quantum error correction with spin qubits is the capability to perform high-fidelity parity measurement much faster than the coherence time and to generate entanglement deterministically. Here we propose a parity measurement scheme for two spin qubits by modulated pulses, using a superconducting resonator as a detector. We show that the distinction between spin-parity states can be achieved with a high fidelity within a short measurement time. The combination of parity measurement and feedback control allows the deterministic preparation of various spin entangled states. In addition, the method can be directly applied to parity measurements and surface codes of multiple spin qubits. These results pave the way for fault-tolerant quantum computation with spin qubits.
Hybrid quantum systems consisting of quantum dot spins and superconducting circuits have emerged as a promising platform for quantum information processing. However, the development of scalable architectures requires the ability to entangle different quantum systems over long distances, which remains an outstanding challenge for hybrid systems with complex interactions and multiple energy levels. Here, we devise methods to implement entangling gates by using engineered virtual photons as a transducer to couple spin-superconducting systems. We propose to tailor such transducers by tuning the driving pulse using shortcuts to adiabaticity. We demonstrate the realization of high-fidelity entangling gates of 99% in short timescales of a few tens of nanoseconds, and we show the robustness of this approach to control parameters. Furthermore, our method enables state transfer and remote entanglement between different modules of the hybrid system with fidelity exceeding the fault-tolerance threshold, thus demonstrating the scalability of this approach. These results pave the way for fast, high-fidelity quantum information processing on leading hybrid platforms.
Abstract We propose a scheme for the rapid and high-fidelity transmission of quantum states and the generation of entanglement among at least five qubits in a circuit quantum electrodynamics system, based on optimized microwave-driven pulses. By designing appropriate microwave pulses applied to the qubits, quantum state transfer among five or more qubits can be realized, enabling bidirectional transfer and control over the residence time of quantum states on any arbitrary qubit by adjusting the parameters of the driving pulses. Furthermore, by optimizing the microwave pulse parameters, the scheme facilitates the creation of entangled states involving five or more qubits in a time-efficient manner. Additionally, we evaluate the fidelity of the transferred quantum state and the generated entanglement, taking into account the effects of decoherence. The results demonstrate that the proposed scheme enables high-fidelity quantum state transfer and entanglement generation with minimal photon leakage from the cavity and energy relaxation of the qubits.
Self-assembled quantum dots can act as an interface between single spins and photons. They combine the flexibility and scalability of semiconductor systems with near-perfect two level systems, emitting highly coherent single photons. In potential quantum information processing architectures based upon optical networks, quantum dots permit light-matter coupling between matter qubits and photonic links. Single trapped charge carriers in quantum dots can be addressed optically, generating spin-photon entanglement between the matter qubits and \lq flying' photon qubits, a key first step in creation of a network. Such an optically linked network of spins in quantum dots has yet to be realized. The semiconductor environment presents a key challenge; it broadens the spectrum of the emitted light, which reduces the fidelity of schemes based upon photon exchange or interference. In addition, these quantum dots are subject to hyperfine coupling to a bath of >>> 105^{5}5 nuclear spins. While this presents an opportunity to study the physics of a central spin in a spin bath, it degrades the spin coherence of a trapped electron or hole. The suggested gate operations to generate entanglement, and the spin measurements to verify a created state, rely upon photon detection. Thus a second limitation occurs due to low efficiency of detectors and photon collection probability. Recent developments in detector technology have enabled us to bring generation and verification of entangled states with quantum dots into the realm of possibility. This dissertation begins with a detailed study of the interaction of a single electron spin with the solid state environment of the quantum dot, analysing the intensity noise of scattered light under resonant excitation to uncover the timescales and relative amplitudes of identified noise sources. A technique for rapid characterization of samples is presented, focusing in particular upon comparison of spectral broadening of the optical transitions relevant to a spin-photon interface. Having identified the extent of environmental factors acting upon the quantum dots, we turn to a demonstration of photon-mediated entanglement between two distant electron spins using a probabilistic scheme. We are able to generate entangled states at 7 kHz, the fastest yet reported for photon-mediated protocols. The average state fidelity of the created Bell states is 63.5 ±\pm± 3.0 \%., violating the classical limit by over 4 standard deviations of the mean. In addition, we demonstrate full optical phase tuning of the Bell state ∣Ψ=12(∣↑∣↓+eiϕ∣↓∣↑)|{\Psi} = \frac{1}{\sqrt{2}}\left(|{\uparrow}|{\downarrow} + e^{i\phi}|{\downarrow}|{\uparrow} \right)∣Ψ=2​1​(∣↑∣↓+eiϕ∣↓∣↑). This is a proof of principle experiment, and sets a fidelity benchmark upon which gains can be made by mitigation of environmental dynamics.