Fast Gates for Slow Fluxonium Qubits Using Single Flux Quantum Control

The single flux quantum (SFQ) method for superconducting qubit control is a promising technology for next-generation quantum processors. [1] This method was originally proposed for a transmon qubit [2] and subsequently experimentally realized. [3] The fluxonium is another type of superconducting qubit that is compatible with SFQ control, and is of particular interest due to its high anharmonicity and long coherence times. However, the fluxonium has a long qubit period, which would result in unacceptably slow gates for a simple SFQ sequence. We propose a new family of sequences that provides faster gates. We examine the gate time and fidelity for these SFQ structures as applied to slow fluxonium qubits. We demonstrate sequences that provide gate times below 50 ns with slow fluxonium qubits of a broad range of physical parameters and fidelities greater than 99.99%.

[1] R. McDermott et al, Quantum-classical interface based on single flux quantum digital logic, Quantum Sci. Technol. 3, 024004 (2018).

[2] R. McDermott and M. G. Vavilov, Accurate Qubit Control with Single Flux Quantum Pulses, Phys. Rev. Appl. 2, 014007 (2014).

[3] E. Leonard Jr. et al, Digital coherent control of a superconducting qubit, Phys. Rev. Appl. 11, 014009 (2018).