Spin relaxation in a single-electron graphene quantum dot

Abstract

The relaxation time of a single-electron spin is an important parameter for solid-state spin qubits, as it directly limits the lifetime of the encoded information. Thanks to the low spin-orbit interaction and low hyperfine coupling, graphene and bilayer graphene (BLG) have long been considered promising platforms for spin qubits. Only recently, it has become possible to control single-electrons in BLG quantum dots (QDs) and to understand their spin-valley texture, while the relaxation dynamics have remained mostly unexplored. Here, we report spin relaxation times (T1) of single-electron states in BLG QDs. Using pulsed-gate spectroscopy, we extract relaxation times exceeding 200 μs at a magnetic field of 1.9 T. The T1 values show a strong dependence on the spin splitting, promising even longer T1 at lower magnetic fields, where our measurements are limited by the signal-to-noise ratio. The relaxation times are more than two orders of magnitude larger than those previously reported for carbon-based QDs, suggesting that graphene is a potentially promising host material for scalable spin qubits.

Elektronen auf den Punkt gebracht

“…Experimentell wird nun der Strom durch den Quantenpunkt, gemittelt über etwa 10 000 Pulszyklen, gemessen. In Abbildung 9 ist die gemessene Relaxationsrate 1/ T 1 als Funktion des Magnetfeldes B , beziehungsweise der Energieaufspaltung, dargestellt (violette Datenpunkte) [9]. Relaxationsraten unterhalb 5 kHz können wir nicht nachweisen, wegen des Rauschniveaus mit der von uns verwendeten Methode der Mittelung über viele Pulszyklen.…”

Gate‐Controlled Quantum Dots Based on 2D Materials

“…Moreover, due to the weak spin–orbit coupling and hyperfine interaction, graphene is expected to be a promising material for hosting spin qubits. [ 111 ] The long spin relaxation time in graphene quantum dots reported recently [ 192–194 ] provides great potential along this approach.…”

“…This results in a transport current below 1 pA, which is very difficult to be precisely measured. [ 192–194 ] Meanwhile, particular electron state manipulations require that the electron tunneling can only happen through single‐side barrier. [ 222 ] In these cases, no transport current can be detected.…”

“…[ 34,42,233,234 ] Thus, the devices’ response to microwaves and pulse sequences needs to be investigated to reveal the coherency of the system. Although charge pumping [ 131 ] and relaxation time measurements [ 132,192–194 ] have been realized, other typical microwave manipulation experiments, which are widely studied in quantum dots based on other material systems, such as photon‐assisted tunneling, [ 235–238 ] and controlled rotations on the Bloch sphere, [ 239–248 ] are still in lack of demonstration in 2D material systems.…”

“…Furthermore, the dynamics of excited states are also studied using pulsed‐gate spectroscopy. [ 192–194 ] A spin relaxation time exceeding 200 $$\umu {\rm s}$$ has been extracted. [ 193 ]…”