Nature 438, 470-473 (24 November 2005) | doi:10.1038/nature04272; Received 14 July 2005; Accepted 22 September 2005

Experimental implementation of heat-bath algorithmic cooling using solid-state nuclear magnetic resonance

J. Baugh1, O. Moussa1, C. A. Ryan1, A. Nayak1,2,3 & R. Laflamme1,3

  1. Institute for Quantum Computing,
  2. Department of Combinatorics and Optimization, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
  3. Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada

Correspondence to: J. Baugh1 Correspondence and requests for materials should be addressed to J.B. (Email: baugh@iqc.ca).

The counter-intuitive properties of quantum mechanics have the potential to revolutionize information processing by enabling the development of efficient algorithms with no known classical counterparts1, 2. Harnessing this power requires the development of a set of building blocks3, one of which is a method to initialize the set of quantum bits (qubits) to a known state. Additionally, fresh ancillary qubits must be available during the course of computation to achieve fault tolerance4, 5, 6, 7. In any physical system used to implement quantum computation, one must therefore be able to selectively and dynamically remove entropy from the part of the system that is to be mapped to qubits. One such method is an 'open-system' cooling protocol in which a subset of qubits can be brought into contact with an external system of large heat capacity. Theoretical efforts8, 9, 10 have led to an implementation-independent cooling procedure, namely heat-bath algorithmic cooling. These efforts have culminated with the proposal of an optimal algorithm, the partner-pairing algorithm, which was used to compute the physical limits of heat-bath algorithmic cooling11. Here we report the experimental realization of multi-step cooling of a quantum system via heat-bath algorithmic cooling. The experiment was carried out using nuclear magnetic resonance of a solid-state ensemble three-qubit system. We demonstrate the repeated repolarization of a particular qubit to an effective spin-bath temperature, and alternating logical operations within the three-qubit subspace to ultimately cool a second qubit below this temperature. Demonstration of the control necessary for these operations represents an important step forward in the manipulation of solid-state nuclear magnetic resonance qubits.


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