Probing relaxation times in graphene quantum dots

Area of Science:

• Quantum computing
• Materials science
• Condensed matter physics

Background:

• Graphene quantum dots (GQDs) are promising for solid-state quantum bits due to predicted long coherence times from weak spin-orbit and hyperfine interactions.
• Previous research explored GQDs' excitation spectra and spin properties, but relaxation dynamics remain understudied.
• Fabrication challenges, including carrier confinement and tunable tunneling barriers, have hindered experimental investigation of decoherence times.

Purpose of the Study:

• To experimentally investigate the relaxation dynamics of excited states in graphene quantum dots.
• To overcome fabrication challenges and enable precise control over quantum dot properties for decoherence studies.

Main Methods:

• Utilized pulsed-gate transient current spectroscopy to measure relaxation times.
• Developed an advanced device design for individually tunable tunneling barriers in the megahertz regime.
• Monitored tunneling barrier asymmetry during measurements.

Main Results:

• Successfully measured transient currents through electronic excited states in GQDs.
• Estimated a lower bound for charge relaxation times in the range of 60-100 nanoseconds.
• Demonstrated a method to probe decoherence in GQDs.

Conclusions:

• The study provides crucial experimental data on charge relaxation times in GQDs, a key parameter for qubit performance.
• The developed device design and measurement technique pave the way for further investigations into GQD decoherence.
• These findings advance the understanding of GQDs as viable candidates for solid-state quantum bits.