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Experimental demonstration of quantum memory for light

Brian Julsgaard·Jacob Sherson·J. Ignacio Cirac·Jaromir Fiurasek·Eugene S. Polzik
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Abstract

The information carrier of today's communications, a weak pulse of light, is an intrinsically quantum object. As a consequence, complete information about the pulse cannot, even in principle, be perfectly recorded in a classical memory. In the field of quantum information this has led to a long standing challenge: how to achieve a high-fidelity transfer of an independently prepared quantum state of light onto the atomic quantum state? Here we propose and experimentally demonstrate a protocol for such quantum memory based on atomic ensembles. We demonstrate for the first time a recording of an externally provided quantum state of light onto the atomic quantum memory with a fidelity up to 70%, significantly higher than that for the classical recording. Quantum storage of light is achieved in three steps: an interaction of light with atoms, the subsequent measurement on the transmitted light, and the feedback onto the atoms conditioned on the measurement result. Density of recorded states 33% higher than that for the best classical recording of light on atoms is achieved. A quantum memory lifetime of up to 4 msec is demonstrated.

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Brian Julsgaard, Jacob Sherson, J. Ignacio Cirac, Jaromir Fiurasek, Eugene S. Polzik. 2004-10-11. Experimental demonstration of quantum memory for light. https://doi.org/10.1038/nature03064

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