‘Schrödinger Kittens’ Studied

In pursuit of practical quantum information and computation systems, a team of scientists at Laboratoire Charles Fabry de l’Institut d’Optique in Orsay, France, is investigating so-called Schrödinger kitten states created using photons spontaneously emitted by an optical parametric amplifier. A report of the experiments appeared in the April 7 issue of Science.

These quantum superpositions of classical states take the name “kittens” in reference to the imaginary half-dead/half-alive oddity known as Schrödinger’s cat and to the relatively small amplitude of the states involved. The kittens can be used to investigate phenomena such as decoherence that affect the viability of quantum information processing and computing.

The researchers frequency-doubled the output of a cavity-dumped femtosecond Ti:sapphire laser from Time-Bandwidth Products of Zurich, Switzerland, in a 100 µm-thick KNbO₃ crystal from FEE GmbH of Idar-Oberstein, Germany. The resulting pulses then pumped another KNbO₃crystal in a frequency-degenerate optical parametric amplifier configuration to produce pulses of squeezed light, which yielded high-fidelity kitten states upon the subtraction of a photon from a pulse using filters and an avalanche photodiode.