Single-shot readout in graphene quantum dots

TL;DR

This paper demonstrates single-shot readout of spin states in graphene quantum dots, showing long excited state decay times and high readout visibility, advancing graphene-based quantum computing.

Contribution

It introduces two experimental methods for measuring excited state decay times in graphene quantum dots, achieving millisecond relaxation times and high readout fidelity.

Findings

Excited state decay time is on the order of milliseconds.

Single-shot readout visibility reaches 87.1%.

Two measurement approaches successfully characterize quantum dot dynamics.

Abstract

Electrostatically defined quantum dots in bilayer graphene offer a promising platform for spin qubits with presumably long coherence times due to low spin-orbit coupling and low nuclear spin density. We demonstrate two different experimental approaches to measure the decay times of excited states. The first is based on direct current measurements through the quantum device. Pulse sequences are applied to control the occupation of ground and excited states. We observe a lower bound for the excited state decay on the order of hundred microseconds. The second approach employs a capacitively coupled charge sensor to study the time dynamics of the excited state using the Elzerman technique. We find that the relaxation time of the excited state is of the order of milliseconds. We perform single-shot readout of our two-level system with a visibility of $87.1\%$, which is an important step for developing a quantum information processor in graphene.