A quadrupolar exchange-only spin qubit

TL;DR

The paper introduces a new quadrupolar exchange-only spin (QUEX) qubit in quantum dots that is highly resistant to charge noise and nuclear spin dephasing, with controllable energy splitting suitable for microwave integration.

Contribution

It presents the design of a novel QUEX qubit operating in a decoherence-free subspace with extended charge noise sweet spots for enhanced stability.

Findings

Qubit operates at a charge noise sweet spot, reducing decoherence.

Qubit energy splitting can reach several GHz, enabling microwave compatibility.

The design is robust against charge noise and nuclear spin dephasing.

Abstract

We propose a quadrupolar exchange-only spin (QUEX) qubit that is highly robust against charge noise and nuclear spin dephasing, the dominant decoherence mechanisms in quantum dots. The qubit consists of four electrons trapped in three quantum dots, and operates in a decoherence-free subspace to mitigate dephasing due to nuclear spins. To reduce sensitivity to charge noise, the qubit can be completely operated at an extended charge noise sweet spot that is first-order insensitive to electrical fluctuations. Due to on-site exchange mediated by the Coulomb interaction, the qubit energy splitting is electrically controllable and can amount to several GHz even in the ``off" configuration, making it compatible with conventional microwave cavities.