Abstract
Just as classical information systems require buffers and memory, the same is true for quantum information systems. The potential that optical quantum information processing holds for revolutionizing computation and communication is therefore driving significant research into developing optical quantum memory. A practical optical quantum memory must be able to store and recall quantum states on demand with high efficiency and low noise. Ideally, the platform for the memory would also be simple and inexpensive. Here, we present a complete tomographic reconstruction of quantum states that have been stored in the ground states of rubidium in a vapour cell operating at around 80 °C. Without conditional measurements, we show recall fidelity up to 98% for coherent pulses containing around one photon. To unambiguously verify that our memory beats the quantum no-cloning limit we employ state-independent verification using conditional variance and signal-transfer coefficients.
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Acknowledgements
The authors thank J. Bernu for providing us with a Matlab code to carry out maximum-likelihood reconstruction and G. Hétet, M. Sellars and T. Ralph for discussions. This research was conducted by the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (project number CE110001027).
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Experiments, measurements and data analysis were carried out by M.H. with the assistance of B.M.S. and G.C. for data collection and experimental preparation. The project was planned and supervised by B.C.B. and P.K.L. The manuscript was written by M.H., B.C.B. and G.C. with the assistance of all other authors.
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Hosseini, M., Campbell, G., Sparkes, B. et al. Unconditional room-temperature quantum memory. Nature Phys 7, 794–798 (2011). https://doi.org/10.1038/nphys2021
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DOI: https://doi.org/10.1038/nphys2021
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