Training Schrodinger's cat: Controlling the quantum properties of light

Constructing quantum computers and other quantum devices requires the ability to leverage quantum properties such as superposition and entanglement – but these effects are fragile and therefore hard to maintain. Recently, scientists at Ecole Normale Supérieure in Paris demonstrated a novel method for controlling the quantum properties of light by probing a superconducting circuit in a cavity with microwave photons to control the energy levels that photon quanta can occupy. Specifically, the scientists prevented access to a single energy level corresponding to a number of photons N, and thereby confined the dynamics of the field to levels 0 to N -1. In so doing, the intracavity field changed from a classical wave to a Schrödinger cat of light – a superposition between two waves of opposite phases instead of a single one. As a result, this new technique could apply to the development of quantum computers by protecting qubits from decoherence as well as enhancing quantum error correction and quantum systems measurement.