Spin decoherence in a two-qubit CPHASE gate: the critical role of tunneling noise. (December 2018)

• Record Type: Journal Article
• Authors: Huang, Peihao; Zimmerman, Neil; Bryant, Garnett
• Is Part Of: Npj quantum information. Volume 4(2018)
• Page Start: 1
• Page End: 5
• Publication Date: 2018-12
• Subjects: Quantum computers -- Periodicals; Quantum communication -- Periodicals; Information theory -- Periodicals; Quantum theory -- Periodicals; Quantum theory; Information theory; Quantum communication; Quantum computers; Periodicals; 006.3843
• DOI: 10.1038/s41534-018-0112-0
• Languages: English
• ISSNs: 2056-6387

Abstract

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. Semiconductor qubits: The nuisance of noisy tunnelling Often-neglected fluctuations in the rate of quantum tunneling can be the dominant source of decoherence in semiconductor spin qubits. Semiconductor-based qubits are promising because of their existing industrial-scale capability for making high-precision devices. A common approach is to design quantum dots that trap electrons using electric fields and use the quantum tunnelling between nearby dots to create the qubit behaviour. Unfortunately, random fluctuations of nearby charges introduce decoherence that limits semiconductor qubits' performance. Peihao Huang and colleagues from the National Institute of Standards and Technology, USA have shown that changes in quantum tunnelling due to charge fluctuations can be more important than the more commonly considered fluctuations in electron energy. The improved understanding of which decoherence process is dominant will improve the optimisation of future designs.