Physical Society Colloquium

Implementing cat-codes in superconducting quantum circuits

Michel Devoret

Department of Applied Physics
Yale University

Physical systems usually exhibit quantum phenomena, such as state superposition and entanglement, only when they are sufficiently decoupled from a lossy environment. Paradoxically, a specially engineered interaction with the environment can become a resource for the generation and protection of quantum states. Moreover, this notion can be generalized to a manifold of quantum states that consists of all coherent superpositions of multiple stable steady states. In particular, it has now become practically feasible to confine the state of an harmonic oscillator to the quantum manifold spanned by two coherent states of opposite phases. In a recent experiment [1], we have observed a superposition of two such coherent states, also known as a Schrodinger cat state, spontaneously squeeze out of vacuum, before decaying into a classical mixture. The dynamical protection of logical qubits built from Schrodinger cat states is based on an engineered driven-dissipative process in which photon pairs are exchanged rather than single photons. The recent class of experiments in which qubits are encoded using cat states opens a new avenue in quantum information processing with superconducting circuits.

[1] Leghtas et al., Science 347, 853 (2015)