Abstract
In many physical approaches to quantum computation, error-correction schemes assume the ability to form two-dimensional qubit arrays with nearest-neighbor couplings and parallel operations at multiple qubit sites. While semiconductor spin qubits exhibit long coherence times relative to their operation speed and single-qubit fidelities above error correction thresholds, multiqubit operations in two-dimensional arrays have been limited by fabrication, operation, and readout challenges. We present a two-by-two array of four singlet-triplet qubits in gallium arsenide and show simultaneous coherent operations and four-qubit measurements via exchange oscillations and frequency-multiplexed single-shot measurements. A larger multielectron quantum dot is fabricated in the center of the array as a tunable interqubit link, which we utilize to demonstrate coherent spin exchange with selected qubits. Our techniques are extensible to other materials, indicating a path towards quantum processors with gate-controlled spin qubits.
Highlights
Semiconducting spin qubits are one of the leading candidates for enabling quantum computation and have demonstrated relatively long coherence times [1,2], figures of merit at the fault tolerance threshold [3], and high-fidelity single- and two-qubit gates [4,5,6,7]
By applying voltage pulses to the central multielectron dot, intended as a coupler, we demonstrate coherent qubit-coupler spin exchange processes. (Qubit-qubit spin exchange, mediated by the coupler, is not demonstrated in this work.) The size
Fast voltage pulses can be applied to gates labeled VRi,Li [false colored in gold in Fig. 1(a)], allowing fast manipulation of all DQDs
Summary
Semiconducting spin qubits are one of the leading candidates for enabling quantum computation and have demonstrated relatively long coherence times [1,2], figures of merit at the fault tolerance threshold [3], and high-fidelity single- and two-qubit gates [4,5,6,7]. In this work we simultaneously operate and read out four singlet-triplet (S-T0) qubits, arranged around a central quantum dot in a two-by-two array with four integrated charge sensors. Synchronized voltage pulses applied to eight gate electrodes initialize all qubits and induce coherent Overhauser or exchange rotations. By applying voltage pulses to the central multielectron dot, intended as a coupler, we demonstrate coherent qubit-coupler spin exchange processes. By applying voltage pulses to the central multielectron dot, intended as a coupler, we demonstrate coherent qubit-coupler spin exchange processes. (Qubit-qubit spin exchange, mediated by the coupler, is not demonstrated in this work.) The size
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