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arXiv:1004.0980

Analysis of Controlled Photon Storage Time Using Phase Locking by Atomic Population Transfer

Byoung Seung HAM

Published Apr 6, 2010• 2 citations
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Abstract

Atomic population transfer in an inhomogeneously broadened optical medium is analyzed for on-demand photon storage-time control in both atomic frequency comb (AFC) and phase locked echoes. In AFC the photon storage mechanism belongs to the conventional three-pulse photon echoes, while the storage time control is limited by conventional two-pulse photon echoes.

DOI
10.48550/arxiv.1004.0980

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Atomic population transfer in an inhomogeneously broadened optical medium is analyzed for on-demand photon storage-time control in both atomic frequency comb (AFC) and phase locked echoes. In AFC the photon storage mechanism belongs to the conventional three-pulse photon echoes, while the storage time control is limited by conventional two-pulse photon echoes.
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Using on-demand coherence conversion via optical locking, a dynamic coherent control of the collective atom phase has been demonstrated for longer photon storage beyond the critical constraint of spin phase decay time, where the storage time can be extended up to hours in a rare-earth-doped solid. Coherent transient phenomena such as photon echoes have been investigated for frozen phase decay via coherent population transfer using a simple deshelving optical pulse pair. Unlike the rephasing halt applied to two-pulse photon echoes, where optical decoherence is accelerated by spin inhomogeneous broadening, a completely atom phase-locked coherence conversion has been observed in three-pulse photon echoes, resulting in spin dephasing-free coherence control. Here, the mechanism of the atom phase-locked coherence conversion via optical locking has been investigated in a solid medium whose optical transition is imperfect, where partial coherence is lost via optical depth-dependent imperfect population transfer. The relationship between coherence loss and optical depth is analyzed, where nearly perfect photon echo efficiency can be obtained for ultralong photon storage in an optically thick medium.
Quantum coherence control of two-pulse photon echoes has been demonstrated for a rephasing halt, resulting in storage-time extension using atom phase-controlled optical deshelving (optical locking) in a backward propagation scheme for the additional benefit of echo intensity enhancement. Compared with conventional forward two-pulse photon echoes, the backward two-pulse photon echo efficiency is enhanced by 15-fold even in a dilute sample, and the storage time is lengthened by spin dephasing time accelerated by spin inhomogeneous broadening. The mechanism of delayed photon echoes via optical locking is due to the temporal hold of the rephasing process by coherent population transfer to a robust spin state.
A photon echo storage-time extension protocol is presented by using a phase locking method in a three-level backward propagation scheme, where phase locking serves as a conditional stopper of the rephasing process in conventional two-pulse photon echoes. The backward propagation scheme solves the critical problems of extremely low retrieval efficiency and pi rephasing pulse-caused spontaneous emission noise in photon echo based quantum memories. The physics of the storage time extension lies in the imminent population transfer from the excited state to an auxiliary spin state by a phase locking control pulse. We numerically demonstrate that the storage time is lengthened by spin dephasing time.
For the last decade quantum memories have been intensively studied for potential applications to quantum information and communications using atomic and ionic ensembles. With the importance of a multimode storage capability in quantum memories, on-demand control of reversible inhomogeneous broadening of an optical medium has been broadly investigated recently. However, the photon storage time in these researches is still too short to apply for long-distance quantum communications. In this paper, we demonstrate new physics of spin population decay dependent ultralong photon storage method, where spin population decay time is several orders of magnitude longer than the conventional constraint of spin phase decay time.