Electrometry using coherent exchange oscillations in a singlet-triplet qubit

Two level systems that can be reliably controlled and measured hold promise as qubits both for metrology and for quantum information science (QIS). Since a fluctuating environment limits the performance of qubits in both capacities, understanding the environmental coupling and dynamics is key to improving qubit performance. We show measurements of the level splitting and dephasing due to voltage noise of a GaAs singlet-triplet qubit during exchange oscillations. Unexpectedly, the voltage fluctuations are non-Markovian even at high frequencies and exhibit a strong temperature dependence. The magnitude of the fluctuations allows the qubit to be used as a charge sensor with a sensitivity of 2 × 10−8e/ √ Hz, two orders of magnitude better than a quantum-limited RF single electron transistor (RF-SET). Based on these measurements we provide recommendations for improving qubit coherence, allowing for higher fidelity operations and improved charge sensitivity.