Analysis of quantum coherence in bismuth-doped silicon: a system of strongly coupled spin qubits

TL;DR

This paper investigates the quantum coherence properties of bismuth-doped silicon, highlighting its strong hyperfine coupling and potential for faster quantum gates, while analyzing decoherence effects and optimal operating points.

Contribution

It provides a detailed analysis of the hyperfine interactions and decoherence mechanisms in Si:Bi, identifying optimal working points for quantum coherence enhancement.

Findings

Identification of regions with minimized dephasing at $df/dB=0$

Demonstration of potential for faster quantum gates using EPR forbidden transitions

Modeling of decoherence effects using a Markovian master equation

Abstract

There is growing interest in bismuth-doped silicon (Si:Bi) as an alternative to the well-studied proposals for silicon based quantum information processing (QIP) using phosphorus-doped silicon (Si:P). We focus here on the implications of its anomalously strong hyperfine coupling. In particular, we analyse in detail the regime where recent pulsed magnetic resonance experiments have demonstrated the potential for orders of magnitude speedup in quantum gates by exploiting transitions that are electron paramagnetic resonance (EPR) forbidden at high fields. We also present calculations using a phenomenological Markovian master equation which models the decoherence of the electron spin due to Gaussian temporal magnetic field perturbations. The model quantifies the advantages of certain "optimal working points" identified as the $df/dB=0$ regions, where $f$ is the transition frequency, which come in the form of frequency minima and maxima. We show that at such regions, dephasing due to the interaction of the electron spin with a fluctuating magnetic field in the $z$ direction (usually adiabatic) is completely removed.