Inductively-shunted transmon for driven-dissipative operations with superconducting circuits

The transmon, a remarkably versatile superconducting qubit, consists of a small Josephson junction shunted by a large capacitance. This capacitance reduces the susceptibility of the qubit to offset charge fluctuations by localizing the superconducting phase across the junction near zero. However, the finite-height potential well of the transmon Hamiltonian renders higher excited states unstable due to their non-negligible running-state component. The effect associated with the non-fully-confining nature of the transmon potential may include the experimentally observed limitations on the transmon ac Stark shift, which limits the efficacy of pumping schemes for driven-dissipative operation such as error correction. We propose modifying the transmon by additionally shunting the junction with a linear inductance approximated by multiple larger junctions. The loop that is formed is maintained at zero flux. In this circuit, the Josephson energy is comparable to the inductive energy of the shunt inductance. Progress on circuit design and experimental results testing these ideas will be reported.