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Published April 1, 2005 | public
Journal Article Open

Physical Limits of Heat-Bath Algorithmic Cooling


Simultaneous near-certain preparation of qubits (quantum bits) in their ground states is a key hurdle in quantum computing proposals as varied as liquid-state NMR and ion traps. "Closed-system" cooling mechanisms are of limited applicability due to the need for a continual supply of ancillas for fault tolerance, and to the high initial temperatures of some systems. "Open-system" mechanisms are therefore required. We describe a new, efficient initialization procedure for such open systems. With this procedure, an n-qubit device that is originally maximally mixed, but is in contact with a heat bath of bias epsilon>>2-n, can be almost perfectly initialized. This performance is optimal due to a newly discovered threshold effect: for bias epsilon<<2-n no cooling procedure can, even in principle (running indefinitely without any decoherence), significantly initialize even a single qubit.

Additional Information

©2005 The American Physical Society (Received 30 March 2004; revised 20 October 2004; published 1 April 2005) Thanks to R. Laflamme and J. Fernandez for helpful discussions. L.S. was supported in part by the NSF, the Mathematical Sciences Research Institute, and the Okawa Foundation. T.M. and Y.W. were supported in part by the Israel Ministry of Defense.


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