In quantum computing, the cat state, named after Schrödinger's cat,[1] is the special quantum state where the qubits are in an equal superposition of all being |0> and all being |1>, i.e. (in Bra-ket notation): |00...0> +|11...1>.
In other quantum mechanics contexts, according to The New York Times for example, physicists view the cat state as composed of two diametrically opposed conditions at the same time,[2] such as the possibilities that a cat be alive and dead at the same time. This is sometimes called the many worlds hypothesis. More prosaically, a cat state might be the possibilities that six atoms be spin up and spin down, as published by a team at NIST, December 1, 2005.[3] 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.[4] David Bohm and Yakir Aharonov later attained recognition for the Aharonov-Bohm effect, 1959.
Erwin Schrödinger formulated this concept by positing a condition in which one intrinsically does not know something, and that only by performing an observation could one know it. He dramatized the situation by positing a moral choice (bestowing life or death on a cat). Later formulations have de-emphasized the life/death choice by showing the possibility of a cat state which is independent of human action.[3]
The reading list contained in Incompleteness of quantum physics.