Cat state

In quantum computing, the cat state, named after Schrödinger's cat, is a quantum state that is composed of two diametrically opposed conditions at the same time, such as the possibilities that a cat be alive and dead at the same time. In quantum computing, the cat state, named after Schrödinger's cat, is a quantum state that is composed of two diametrically opposed conditions at the same time, such as the possibilities that a cat be alive and dead at the same time. Generalizing Schrödinger's gedanken experiment, any other quantum superposition of two macroscopically distinct states is also referred to as a cat state. A cat state could be of one or more modes or particles, therefore it is not necessarily an entangled state. This is in contrast to the more specific concept of a Greenberger–Horne–Zeilinger state, which by definition consists of multiple distinct particles or modes and their entanglement. Schrödinger's cat is sometimes connected to the many worlds hypothesis by its proponents. Concretely, a cat state can refer to the possibilities that six atoms be spin up and spin down, as published by a team led by David Wineland at NIST, December 1, 2005. Large cat states have also been experimentally created using photons by a team led by Pan Jianwei at University of Science and Technology of China, for instance, four-photon entanglement, five-photon entanglement, six-photon entanglement, eight-photon entanglement, and five-photon ten-qubit cat state. This spin up/down formulation was proposed by David Bohm, who conceived of spin as an observable in a version of thought experiments formulated in the 1935 EPR paradox. In quantum optics, a cat state is defined as the coherent superposition of two coherent states with opposite phase: