Fast single qubit gates in a capacitively shunted fluxonium

A capacitively shunted fluxonium circuit has among the longest lifetimes seen in cQED due to the exponential suppression of the charge transition matrix element from the extra capacitance. The suppressed matrix elements however make it challenging to perform fast fluxon gates via charge coupling, requiring the use of excited fluxonium levels and Raman transitions [1]. Here, we present and characterize new protocols for performing fast single-qubit gates near half flux quantum, using fast flux modulation. The low transition frequencies near half flux quantum allow for adiabatic gates, and direct synthesis of flux pulses. These approaches increase the ease of control of fluxonium circuit at its highest coherence point, and thereby its feasibility as a building block for future quantum information processors.


[1] N. Earnest et al., Physical review letters 120.15 (2018)