Decoherence of spin qubits due to a nearby charge fluctuator in gate-defined double dots

TL;DR

This paper theoretically investigates how a nearby charge fluctuator causes decoherence in spin qubits within double quantum dots, identifying key coupling mechanisms and potential mitigation strategies.

Contribution

It provides a detailed calculation of Coulomb couplings between charge fluctuators and spin qubits, revealing how environmental charge noise impacts qubit coherence and control.

Findings

Charge environment can significantly affect qubit performance.

Identifies optimal working points to minimize decoherence.

Suggests using an ancillary double-dot for better qubit control.

Abstract

The effects of a nearby two-level charge fluctuator on a double-dot two-spin qubit are studied theoretically. Assuming no direct tunneling between the charge fluctuator and the qubit quantum dots, the Coulomb couplings between the qubit orbital states and the fluctuator are calculated within the Hund-Mulliken framework to quadrupole-quadrupole order in a multipole expansion. We identify and quantify the coupling term that entangles the qubit to the fluctuator and analyze qubit decoherence effects that result from the decay of the fluctuator to its reservoir. Our results show that the charge environment can severely impact the performance of spin qubits, and indicate working points at which this decoherence channel is minimized. Our analysis also suggests that an ancillary double-dot can provide a convenient point for single-qubit operations and idle position, adding flexibility in the quantum control of the two-spin qubit.