Scientists Produce ‘Schrödinger Cats’ from Light Waves

Erwin Schrödinger famously related the idea of a cat simultaneously dead and alive to the idea that particles behaving according to quantum physics can occupy simultaneously two opposite states. Now researchers at Université Paris-Sud in Palaiseau, France, and at the University of Queensland in Brisbane, Australia, have generated light waves that simultaneously have two opposite phases and are thus optical Schrödinger cats.

Side view of experimental results, showing Schrödinger cat photons. Reprinted with permission of Nature.

The scientists said that the ability to generate particles with simultaneous opposite states can be applied to building more powerful quantum computers, to making ultraprecise measurements and even to quantum teleportation, which could take teleportation from the pages of science fiction to reality.

To generate the Schrödinger cats, they produced laser pulses with two photons. They employed a laser that delivered pulses at 180 fs, which became frequency-doubled via second-harmonic generation and traveled through a nondegenerate optical parametric amplifier, resulting in the two-photon state. Two avalanche photon detectors were used to determine whether the optical parametric amplifier had successfully produced the two-photon state. The pulses in the two-photon state were randomly separated by a beamsplitter. Homodyne detection established whether the result was an optical Schrödinger cat.

There was an ~7.5 percent probability of opposite-phase Schrödinger cats once the two-photon state was produced. Statistical analysis indicated that the cat state was generated with amplitudes of ±√2.6, as reported in the Aug. 16 issue of Nature.

The researchers said that their protocol also enables production of beams of any intensity (cats of any size) and totally even or odd photon numbers. They also said that improvements in the setup will enable a higher probability of Schrödinger cats, and that this will hasten quantum information processing, for example.