Probing relaxation times in graphene quantum dots

TL;DR

This paper reports on the measurement of relaxation times in graphene quantum dots using advanced pulsed-gate spectroscopy, revealing lower limits of charge relaxation times around 60-100 nanoseconds, which is crucial for quantum computing applications.

Contribution

The study introduces an improved device design enabling precise control of tunnelling barriers and measurement of relaxation dynamics in graphene quantum dots.

Findings

Charge relaxation times estimated at 60-100 ns

Device design allows tuning tunnelling barriers to low MHz regime

Monitoring of barrier asymmetry with integrated charge sensors

Abstract

Graphene quantum dots are attractive candidates for solid-state quantum bits. In fact, the predicted weak spin-orbit and hyperfine interaction promise spin qubits with long coherence times. Graphene quantum dot devices have been extensively investigated with respect to their excitation spectrum, spin-filling sequence, and electron-hole crossover. However their relaxation dynamics remain largely unexplored. This is mainly due to challenges in device fabrication, in particular regarding the control of carrier confinement and the tunability of the tunnelling barriers, both crucial to experimentally investigate decoherence times. Here, we report on pulsed-gate transient spectroscopy and relaxation time measurements of excited states in graphene quantum dots. This is achieved by an advanced device design, allowing to tune the tunnelling barriers individually down to the low MHz regime and to monitor their asymmetry with integrated charge sensors. Measuring the transient currents through electronic excited states, we estimate lower limit of charge relaxation times on the order of 60-100 ns.