Encoding a cat-qubit in a 3D millisecond lifetime superconducting cavity

In this talk on experimental superconducting circuits, we implement a cat-qubit in a millisecond lifetime cavity. The cat-qubit encodes quantum information in an oscillator endowed with a special mechanism that dissipates photons in pairs. This pins down two coherent states of opposite phase that play the role of logical states. Remarkably, as the number of photons in each coherent state is increased, bit-flips between the two are exponentially suppressed. This comes at the cost of a linear increase of the phase flip rate, that is augmented, for each added photon, by twice the oscillator energy dissipation rate. Therefore, minimizing oscillator losses is crucial to maintain low phase-flip rates. The lowest dissipation rates have been reported in 3D superconducting cavities, routinely reaching single photon lifetimes up to several milliseconds. In this experiment, we embed a two-photon dissipation apparatus in a 3D cavity, and address the several technological challenges associated to combining a millisecond lifetime superconducting cavity, flux tunability, and a strongly driven-dissipative mode.