Quantum physics: Finding a quantum Cheshire Cat

The first experimental demonstration of the recently predicted “quantum Cheshire Cat” is reported this week in Nature Communications.

The quantum Cheshire Cat consists of the separation of a particle, such as a photon or neutron, from one of its physical properties, like polarization or magnetic moment. Just as the disembodied smile is a property of the Cheshire Cat, so polarisation is a property of a photon.

Yuji Hasegawa and colleagues demonstrated the quantum Cheshire Cat using neutron interferometry-a procedure allowing the investigation of the properties of neutrons. They showed the separation of a neutron and its magnetic moment when neutrons went through one arm of the interferometer, with their magnetic moment travelling along the other one.

Researchers also confirmed that “weak measurements” of neutron properties, which do not significantly perturb the system, are essential for the observation of the phenomenon, as conventional measurements are too invasive.

While the quantum Cheshire Cat has only been observed with neutrons, it should be possible to test it in other physical scenarios and these may prove useful for high precision metrology and quantum information technology.