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

Peihao Huang,Neil M Zimmerman,Garnett W Bryant

doi:10.1038/s41534-018-0112-0

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.

Highlights

An electron spin confined in a semiconductor quantum dot (QD) is a promising candidate quantum bit for quantum information processing because of its potential scalability and miniaturization.[1,2]
For two electrons in a double quantum dot (DQD), where the spins can be used to define a single singlet-triplet (S-T0) qubit or two single-spin qubits coupled by exchange interaction, the 1/f charge noise can significantly affect the spin coherence and the number of gate operations
We show that tunneling fluctuation can play an important role for two electrons in a DQD used for a two-qubit CPHASE gate

Summary

Introduction

An electron spin confined in a semiconductor quantum dot (QD) is a promising candidate quantum bit (qubit) for quantum information processing because of its potential scalability and miniaturization.[1,2] Tremendous progress has been made during the last decade.[3,4,5,6,7,8,9,10,11] The spin qubit in a silicon QD has attracted wide interest because of its long coherence time and compatibility with Si electronics nanofabrication.[12,13] With advances in fabricating QDs using accumulation mode,[14] several groups have demonstrated two-qubit gates in silicon based on the exchange interaction.[15,16,17] The recent achievement of strong coupling between spin qubits and microwave photons will enable long-distance gate operations for spin qubits.[18,19,20]Two-qubit gate operation is an essential but challenging task for the building of a quantum computer. For two electrons in a double quantum dot (DQD), where the spins can be used to define a single singlet-triplet (S-T0) qubit or two single-spin qubits coupled by exchange interaction, the 1/f charge noise can significantly affect the spin coherence and the number of gate operations. The tunneling fluctuation and the detuning fluctuation from the 1/f charge noise will cause the spin decoherence during the CPHASE gate operation.

Results

Conclusion