Cat state

In quantum computing, the cat state, named after Schrödinger's cat, [John Gribbin (1984), "In Search of Schrödinger's Cat", ISBN 0-552-12555-5, 22nd February 1985, Transworld Publishers, Ltd, 318 pages.] 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 time", [Dennis Overbye, " [http://www.nytimes.com/2005/12/27/science/27eins.html?ex=1293339600&en=caf5d835203c3500&ei=5090 Quantum Trickery: Testing Einstein's Strangest Theory] ". "New York Times" Tuesday ("Science Times"), December 27, 2005 pages D1,D4.] 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.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.] 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. [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.] 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.

ee also

The reading list contained in Incompleteness of quantum physics.

Notes