Cat state

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In quantum computing, the cat state, named after Schrödinger's cat¹, is the special state where the qubits are in an equal superposition of all being |0> and all being |1>, i.e. |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 time², 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 paradox⁴. 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 action³.

[edit] See also

The reading list contained in Incompleteness of quantum physics.

[edit] Notes

• Note 1: John Gribbin (1984), In Search of Schrödinger's Cat, ISBN 0-552-12555-5, 22nd February 1985, Transworld Publishers, Ltd, 318 pages.

• Note 2: Dennis Overbye, "Quantum Trickery: Testing Einstein's Strangest Theory". New York Times Tuesday (Science Times), December 27, 2005 pages D1,D4.

• Note 3: D. Leibfried, E. Knill, S. Seidelin, J. Britton, R.B. Blakestad, J. Chiaverini, D. Hume, W.M. Itano, J.D. Jost, C. Langer, R. Ozeri, R. Reichle, and D.J. Wineland. "Creation of a six atom 'Schrödinger cat' state". Nature. Dec. 1, 2005, 639-642.

• Note 4: Amir D. Aczel (2001), Entanglement: the unlikely story of how scientists, mathematicians, and philosophers proved Einstein's spookiest theory. ISBN 0-452-28457-0 Penguin: paperback, 284 pages, index.