Time-optimal universal quantum gates on superconducting circuits

TL;DR

This paper presents a time-optimal control scheme for implementing high-fidelity universal quantum gates on superconducting qubits, significantly reducing gate times and decoherence effects for scalable quantum computing.

Contribution

It introduces a novel time-optimal control method based on the quantum brachistochrone equation for fast quantum gate implementation on superconducting circuits.

Findings

Two-qubit gate fidelity approaches 99.9%

Gate acceleration achieved by detuning adjustment

Decoherence-free subspace encoding reduces dephasing errors

Abstract

Decoherence is inevitable when manipulating quantum systems. It decreases the quality of quantum manipulations and thus is one of the main obstacles for large-scale quantum computation, where high-fidelity quantum gates are needed. Generally, the longer a gate operation is, the more decoherence-induced gate infidelity will be. Therefore, how to shorten the gate time becomes an urgent problem to be solved. To this end, time-optimal control based on solving the quantum brachistochrone equation is a straightforward solution. Here, based on time-optimal control, we propose a scheme to realize universal quantum gates on superconducting qubits in a two-dimensional square lattice configuration, and the two-qubit gate fidelity approaches 99.9\%. Meanwhile, we can further accelerate the Z-axis gate considerably by adjusting the detuning of the external driving. Finally, in order to reduce the influence of the dephasing error, decoherence-free subspace encoding is also incorporated in our physical implementation. Therefore, we present a fast quantum scheme which is promising for large-scale quantum computation.