Identifying and ameliorating dominant sources of decoherence are important steps in understanding and improving quantum systems. Here we show that the free induction decay time (T * 2 ) and the Rabi decay rate (Γ Rabi ) of the quantum dot hybrid qubit can be increased by more than an order of magnitude by appropriate tuning of the qubit parameters and operating points. By operating in the spin-like regime of this qubit, and choosing parameters that increase the qubit's resilience to charge noise (which we show is presently the limiting noise source for this qubit), we achieve a Ramsey decay time T * 2 of 177 ns and a Rabi decay time 1/Γ Rabi exceeding 1 µs. We find that the slowest Γ Rabi is limited by fluctuations in the Rabi frequency induced by charge noise and not by fluctuations in the qubit energy itself.

100s 21 a) Value calculated using the noise spectrum (Equation (1)); b) A transition is observed between α = 1 and α = 2; c) Device implanted with P donors; d) Spin-orbit qubit; e) Singlet-triplet qubit formed between Si-MOS quantum dot and a P donor.

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