https://doi.org/10.1140/epjp/i2014-14266-0
Regular Article
Experimental heat-bath cooling of spins
1
Département IRO, Université de Montréal, H3C 3J7, Montréal, QC, Canada
2
The Canadian Institute for Advanced Research, Toronto, Canada
3
Institute for Theoretical Studies at ETH, Zürich, Switzerland
4
Department of Computer Science, Technion, 32000, Haifa, Israel
5
Département de génie informatique, École Polytechnique de Montréal, H3C 3A7, Montréal, QC, Canada
6
Department of Chemistry, Technion, 32000, Haifa, Israel
7
Centre for Quantum Computation, Clarendon Laboratory, University of Oxford, Parks Road, OX13PU, Oxford, UK
* e-mail: yossiv@technion.ac.il
Received:
3
May
2014
Accepted:
9
November
2014
Published online:
16
December
2014
Algorithmic cooling (AC) is a method to purify quantum systems, such as ensembles of nuclear spins, or cold atoms in an optical lattice. When applied to spins, AC produces ensembles of highly polarized spins, which enhance the signal strength in nuclear magnetic resonance (NMR). According to this cooling approach, spin-half nuclei in a constant magnetic field are considered as bits, or more precisely quantum bits, in a known probability distribution. Algorithmic steps on these bits are then translated into specially designed NMR pulse sequences using common NMR quantum computation tools. The algorithmic cooling of spins is achieved by alternately combining reversible, entropy-preserving manipulations (borrowed from data compression algorithms) with selective reset, the transfer of entropy from selected spins to the environment. In theory, applying algorithmic cooling to sufficiently large spin systems may produce polarizations far beyond the limits due to conservation of Shannon entropy. Here, only selective reset steps are performed, hence we prefer to call this process “heat-bath” cooling, rather than algorithmic cooling. We experimentally implemented two consecutive steps of selective reset, thus transferring entropy from two selected spins to the environment. We performed such cooling experiments, with commercially available labeled molecules, on standard liquid-state NMR spectrometers. We report in particular on our original experiment, unpublished until now except on the arXiv (quant-ph/0511156) in 2005, which was, to the best of our knowledge, the world’s first experiment that yielded polarizations results that bypassed Shannon’s entropy-conservation bound, so that the entire spin-system was cooled.
© Società Italiana di Fisica and Springer-Verlag Berlin Heidelberg, 2014
