Developments in quantum information science rely critically on entanglement—a fundamental aspect of quantum mechanics that causes parts of a composite system to show correlations stronger than can be explained classically. In particular, scalable quantum networks require the capability to create, store and distribute entanglement among distant matter nodes by means of photonic channels. Atomic ensembles can play the role of such nodes. So far, in the photon-counting regime, heralded entanglement between atomic ensembles has been successfully demonstrated through probabilistic protocols. But an inherent drawback of this approach is the compromise between the amount of entanglement and its preparation probability, leading to intrinsically low count rates for high entanglement. Here we report a protocol where entanglement between two atomic ensembles is created by coherent mapping of an entangled state of light. By splitting a single photon and performing subsequent state transfer, we separate the generation of entanglement and its storage. After a programmable delay, the stored entanglement is mapped back into photonic modes with overall efficiency of 17%. Together with improvements in single-photon sources, our protocol will allow ‘on-demand’ entanglement of atomic ensembles, a powerful resource for quantum information science.

http://absimage.aps.org/image/MAR08/MWS_MAR08-2007-007122.pdf

Mapping photonic entanglement into and out of a quantum memory

We demonstrate slow light via population oscillation in semiconductor quantum-well structures for the first time. A group velocity as low as 9600 m/s is inferred from the experimentally measured dispersive characteristics. The transparency window exhibits a bandwidth as large as 2 GHz.

Slow-light in semiconductor quantum wells

We experimentally demonstrate coherent amplification of probe field in a tripod-type atoms driven by strong coupling, signal and weak probe fields. We suppress linear and nonlinear atomic absorptions for resonant and near resonant probe via double electromagnetically induced transparency (DEIT). Combining these advantages of suppressed absorption along with temperature- or atomic-density-controlled transfer of population(ToP) between hyperfine ground states, we can induce near-resonant amplification of probe through stimulated Raman scattering(SRS) pumped by low-intensity signal field. The increased population difference of initial and final states of SRS due to increased ToP rate, together with reduced absorption at the second EIT window in an optically thick Cesium vapor, gives rise to highly effective coherent amplification.

/pdf/strong-coherent-light-amplification-with-double-57i493ipki.pdf

Strong Coherent Light Amplification with Double Electromagnetically Induced Transparency Coherences.

We demonstrate experimentally a procedure to obtain the maximum efficiency for the storage and retrieval of light pulses in atomic media. The procedure uses time-reversal to obtain optimal input signal pulse shapes. Experimental results in warm Rb vapor are in good agreement with theoretical predictions and demonstrate a substantial improvement of efficiency. This optimization procedure is applicable to a wide range of systems.

http://absimage.aps.org/image/DAMOP08/MWS_DAMOP08-2008-000192.pdf

Optimal control of light pulse storage and retrieval

We report on the observation of slow light induced by transient spectral hole-burning in a solid, that is based on excited-state population storage. Experiments were conducted in the R1-line (2E←4A2 transition) of a 2.3 mm thick pink ruby (Al2O3:Cr(III) 130 ppm). Importantly, the pulse delay can be controlled by the application of a low external magnetic field B||c≤9 mT and delays of up to 11 ns with minimal pulse distortion are observed for ~55 ns Gaussian pulses. The delay corresponds to a group velocity value of ~c/1400. The experiment is very well modelled by linear spectral filter theory and the results indicate the possibility of using transient hole-burning based slow light experiments as a spectroscopic technique.

Slowing light down by low magnetic fields: pulse delay by transient spectral hole-burning in ruby.

We present observations of self induced ultraslow light in a persistent spectral hole-burning rare-earth doped crystal. The observed group delay (velocity) is as long as 40 µs (75 m/s), which is comparable to that obtained using electromagnetically induced transparency or coherent population oscillations. We analyze the observed ultraslow light as a function of frequency detuning, light intensity, and atom population (oscillator strength). The present observation of ultraslow light in a persistent spectral hole-burning medium gives potentials to all-optical information processing such as on-demand all-optical buffer memories.

Observations of self-induced ultraslow light in a persistent spectral hole burning medium.

Using an ultraslow light-based double-Λ-type configuration we demonstrate atomic coherence swing between two different frequencies in a nondegenerate four-wave mixing scheme. A short control pulse applied to the middle of an ultraslow light envelope results in coherence conversion between two ground states, causing both coherence depletion and recovery, resulting in a temporal hole and amplification in the ultraslow light envelope. This outcome holds potential for temporally and spatially localized coherence control of ultraslow light in such applications as a selective photon trap.

Atomic coherence swing in a double-Λ-type system using ultraslow light

Coherent dynamics of slow light for all-optical switching is investigated in a multilevel system of solids for an understanding of self-induced ultraslow light. In an optical population shelving system of a rare-earth doped solid, dynamics of the slow light are presented by using a third optical field controlling shelved atom population. Unlike two-photon coherence-based delayed all-optical switching utilizing electromagnetically induced transparency, the present method relies on one-photon coherence controlling shelved atom population.

Coherent dynamics of self-induced ultraslow light for all-optical switching.

We present transmission enhancement of ultraslow light in an inhomogeneously broadened spectral hole-burning solid medium by using precedent dummy light The function of the dummy light is to burn a half-depth narrow spectral hole in an optically shelved solid system and to maintain the system optically transparent to the probe light, where the probe must experiences ultraslow group velocity due to the narrow spectral hole The observed transmission increase is as high as 7 times compared with self-induced ultraslow light [J Hahn and B S Ham, Opt Express 16, 16723 (2008)], where the transmission enhancement is equivalent to 105 amplification considering an optical depth of d = 10

Transmission enhancement of ultraslow light in an atom shelved model of spectral hole burning solids.

Using ultraslow light phenomenon, we report two-orders of magnitude enhanced photon echo efficiency in a rare-earth doped solid medium, where the enhancement is due to lengthened photon-atom interaction time in a dilute optical medium.

J. Hahn

Papers

Observations of self-induced ultraslow light in a persistent spectral hole burning medium.

Atomic coherence swing in a double-Λ-type system using ultraslow light

Coherent dynamics of self-induced ultraslow light for all-optical switching.

Transmission enhancement of ultraslow light in an atom shelved model of spectral hole burning solids.

Enhanced Echo Retrieval Efficiency Using Ultraslow Light