Single-shot readout in graphene quantum dots

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.

Gate‐Controlled Quantum Dots Based on 2D Materials

“…This results in a transport current below 1 pA, which is very difficult to be precisely measured. [192][193][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.…”

“…tunneling event happens in the dot, it will be reflected by a current jump/peak of the detector, even when direct transport current through the dot is no longer measurable (Figure 13b). Such a charging detecting scheme has been demonstrated in both etched [128,138,143,145,224] and gate-defined [194,225] graphene quantum dots. Another possible solution to the readout problem is using the radio-frequency reflectometry technique.…”

“…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][193][194] provides great potential along this approach.…”

“…[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][193][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][236][237][238] and controlled rotations on the Bloch sphere, [239][240][241][242][243][244][245][246][247][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][193][194] A spin relaxation time exceeding 200 μs has been extracted. [193] In addition to using an electric field to induce a bandgap in bilayer graphene, other strategies are also considered and experimentally demonstrated to form quantum dots in graphene without employing the etching process.…”