"Schrödinger Kittens" and other quantum states of light with negative Wigner functions

Philippe Grangier

Alexei Ourjoumtsev, Aurélien Dantan, Rosa Tualle-Brouri +1 more

We describe recent progress in the experimental realization of propagating light fields with observed negative Wigner functions, measured by pulsed homodyne quantum tomography. This includes in particular Schrödinger cat states with small amplitudes ("Schrödinger kittens") [1], and n=2 Fock states [2]. Quantum information applications of such states will be discussed, such as loophole-free tests of Bell's inequalities [3].

David Vitali

Brian R. La Cour

Alexei Ourjoumtsev, Rosa Tualle-Brouri, Julien Laurat +1 more

We present a detailed experimental analysis of a free-propagating light pulse prepared in a "Schrödinger kitten" state, which is defined as a quantum superposition of "classical" coherent states with small amplitudes. This kitten state is generated by subtracting one photon from a squeezed vacuum beam, and it clearly presents a negative Wigner function. The predicted influence of the experimental parameters is in excellent agreement with the experimental results. The amplitude of the coherent states can be amplified to transform our "Schrödinger kittens" into bigger Schrödinger cats, providing an essential tool for quantum information processing.

Brian R. La Cour