Extending the coherence of a quantum dot hybrid qubit

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 ( $$T_2^*$$ T 2 * ) and the Rabi decay rate (ΓRabi) 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 $$T_2^*$$ T 2 * of 177 ns and a Rabi decay time 1/ΓRabi exceeding 1 μs. We find that the slowest ΓRabi is limited by fluctuations in the Rabi frequency induced by charge noise and not by fluctuations in the qubit energy itself. Researchers in the United States demonstrate high tunability of spin qubits in silicon-based quantum dots. Mark Eriksson at the University of Wisconsin-Madison and colleagues have achieved more than a tenfold improvement in the performance of these three-electron double dot qubits by tuning the electric fields used to confine electrons to quantum dots to a regime where the qubit was predicted to be much less susceptible to the effects of charge noise. Since charge noise limits the performance of many such qubits, these findings provide a path toward the fabrication of electrically gated qubits in silicon quantum dots with very high fidelities.