Microwave-Activated Controlled-Z Gate for Fixed-Frequency Fluxonium Qubits

  1. Konstantin N. Nesterov,
  2. Ivan V. Pechenezhskiy,
  3. Chen Wang,
  4. Vladimir E. Manucharyan,
  5. and Maxim G. Vavilov
The superconducting fluxonium circuit is an artificial atom with a strongly anharmonic spectrum: when biased at a half flux quantum, the lowest qubit transition is an order of magnitude
smaller in frequency than those to higher levels. Similar to conventional atomic systems, such a frequency separation between the computational and noncomputational subspaces allows independent optimizations of the qubit coherence and two-qubit interactions. Here we describe a controlled-Z gate for two fluxoniums connected either capacitively or inductively, with qubit transitions fixed near 500 MHz. The gate is activated by a microwave drive at a resonance involving the second excited state. We estimate intrinsic gate fidelities over 99.9% with gate times below 100 ns.