Variational quantum control for single- and two-qubit transmon gates

Transmon are among the most successful qubits in the superconducting world, enabling the largest gate-based quantum computations to-date. In this talk I will present a new set of techniques to design single-qubit and two-qubit gates for transmon qubits, which can be used to tune qubit frequencies, implement direct or cavity mediated CZ interactions [1], and √SWAP gates with tuneable couplers. The technique is based on variational estimates of the transmon qubit state dynamics, and provides semi-analytical controls that can be further tuned to develop more robust protocols. With minor efforts, methods provide various orders of magnitude improvement in fidelity over earlier techniques based on fast-quasi-adiabatic passages or conventional square or segmented pulses, as used in current experiments.

[1] L. DiCarlo et al, Nature 467, 574 (2010)
[2] R. Barends et al. Nature 508, 500 (2014)
[3] Y. Chen et al. Physical Review Letters 113,220502 (2014)