Single-Shot Spin Readout in Graphene Quantum Dots

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 a 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 perform single-shot readout of our two-level system with a signal-to-noise ratio of about 7 and find relaxation times up to 50 ms for the spin-excited state, with a strong magnetic field dependence, promising even higher values for smaller magnetic fields. This is an important step for developing a quantum-information processor in graphene.