Suppressing Counter-Rotating Errors for Fast Single-Qubit Gates with Fluxonium

In order to mitigate error from decoherence and reduce the runtime of quantum algorithms, it is desirable to implement quantum operations that are as fast as possible. The fluxonium qubit, featuring high coherence times and low typical qubit frequencies (less than 1 gigahertz), has become a promising alternate to the transmon qubit for gate-based quantum computing. However, the fluxonium’s low transition frequency leads to single-qubit gate errors when gate times approach the qubit Larmor period due to the breakdown of the rotating-wave approximation (RWA) for strong, linearly polarized Rabi drives. In this talk, we detail two complementary strategies for mitigating such counter-rotating errors. The first strategy comprises the implementation of a co-rotating drive which natively contains no counter-rotating component, via simultaneous charge and flux control. The second strategy, referred to as commensurate pulses, comprises timing restrictions that homogenize counter-rotating errors for all pulses, enabling their correction with conventional Rabi gate calibration protocols. Commensurate pulses, requiring no calibration overhead relative to conventional Rabi gates, can be readily applied in any platform leveraging fast resonant control. With our methods, we demonstrate single-qubit gates as fast as one Larmor period (~ 4 ns) with fidelities reliably exceeding 99.997%.

In addition, we will discuss recent results exploring decoherence signatures related to the anisotropy of transverse noise, which may provide a means to disentangle charge and flux noise in superconducting circuits.