Decoherence-avoiding spin qubits in optically active quantum dot molecules

TL;DR

This paper demonstrates a method to significantly extend the coherence time of spin qubits in quantum dot molecules by using two exchange-coupled spins to avoid decoherence from magnetic and charge fluctuations.

Contribution

The authors introduce a decoherence-avoiding qubit in quantum dot molecules using two exchange-coupled spins, surpassing previous coherence time limitations.

Findings

T2* coherence time exceeds 200 nanoseconds

Coherent superposition of singlet and triplet states achieved

Simultaneous mitigation of magnetic and charge fluctuation effects

Abstract

In semiconductors, the T2* coherence time of a single confined spin is limited either by the fluctuating magnetic environment (via the hyperfine interaction), or by charge fluctuations (via the spin-orbit interaction). We demonstrate that both limitations can be overcome simultaneously by using two exchange-coupled electron spins that realize a single decoherence-avoiding qubit. Using coherent population trapping, we generate a coherent superposition of the singlet and triplet states of an optically active quantum-dot molecule, and show that the corresponding T2* may exceed 200 nanoseconds.