Spin decoherence in a two-qubit CPHASE gate: the critical role of tunneling noise

TL;DR

This paper reveals that tunneling noise from 1/f charge noise, rather than detuning noise, can dominate spin decoherence in two-qubit quantum gates, impacting qubit design and operation.

Contribution

It demonstrates that tunneling noise can be the primary source of decoherence in two-qubit spin gates, challenging previous assumptions and highlighting the need to consider tunneling noise in qubit optimization.

Findings

Tunneling noise can dominate decoherence over detuning noise.

Decoherence dependence on detuning differs between tunneling and detuning noise.

Experimental data indicates tunneling noise was the main decoherence source in recent two-qubit gates.

Abstract

Rapid progress in semiconductor spin qubits has enabled experimental demonstrations of a two-qubit logic gate. Understanding spin decoherence in a two-qubit logic gate is necessary for optimal qubit operation. We study spin decoherence due to $1/f$ charge noise for two electrons in a double quantum dot used for a two-qubit controlled-phase gate. In contrast to the usual belief, spin decoherence can be dominated by the tunneling noise from $1/f$ charge noise instead of the detuning noise. Tunneling noise can dominate because the effect of tunneling noise on the spin qubit is first order in the charge admixture; while the effect of the detuning noise is only second order. The different orders of contributions result in different detuning dependence of the decoherence, which provides a way to identify the noise source. We find that decoherence in a recent two-qubit experiment was dominated by the tunneling noise from $1/f$ charge noise. The results illustrate the importance of considering tunneling noise to design optimal operation of spin qubits.