Confining the state of light to a quantum manifold by engineered two-photon loss

TL;DR

This paper demonstrates how engineered two-photon loss can confine a harmonic oscillator's quantum state to a manifold of superpositions, enabling the creation of Schrödinger cat states and advancing quantum information processing.

Contribution

The authors experimentally realize confinement of a harmonic oscillator to a quantum manifold using engineered two-photon loss in a superconducting resonator, enabling new quantum state control methods.

Findings

Successfully confined the oscillator to a superposition of two coherent states.

Observed spontaneous squeezing of a Schrödinger cat state from vacuum.

Demonstrated potential for error correction in quantum computing.

Abstract

Physical systems usually exhibit quantum behavior, such as superpositions 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. This notion can be generalized to the confinement of a system into a manifold of quantum states, consisting of all coherent superpositions of multiple stable steady states. We have experimentally confined the state of a harmonic oscillator to the quantum manifold spanned by two coherent states of opposite phases. In particular, we have observed a Schrodinger cat state spontaneously squeeze out of vacuum, before decaying into a classical mixture. This was accomplished by designing a superconducting microwave resonator whose coupling to a cold bath is dominated by photon pair exchange. This experiment opens new avenues in the fields of nonlinear quantum optics and quantum information, where systems with multi-dimensional steady state manifolds can be used as error corrected logical qubits.