One Hundred Second Bit-Flip Time in a Two-Photon Dissipative Oscillator

Abstract

Current implementations of quantum bits (qubits) continue to undergo too many\nerrors to be scaled into useful quantum machines. An emerging strategy is to\nencode quantum information in the two meta-stable pointer states of an\noscillator exchanging pairs of photons with its environment, a mechanism shown\nto provide stability without inducing decoherence. Adding photons in these\nstates increases their separation, and macroscopic bit-flip times are expected\neven for a handful of photons, a range suitable to implement a qubit. However,\nprevious experimental realizations have saturated in the millisecond range. In\nthis work, we aim for the maximum bit-flip time we could achieve in a\ntwo-photon dissipative oscillator. To this end, we design a Josephson circuit\nin a regime that circumvents all suspected dynamical instabilities, and employ\na minimally invasive fluorescence detection tool, at the cost of a two-photon\nexchange rate dominated by single-photon loss. We attain bit-flip times of the\norder of 100 seconds for states pinned by two-photon dissipation and containing\nabout 40 photons. This experiment lays a solid foundation from which the\ntwo-photon exchange rate can be gradually increased, thus gaining access to the\npreparation and measurement of quantum superposition states, and pursuing the\nroute towards a logical qubit with built-in bit-flip protection.\n