As stated in the text, Figs. 3 and 4 (transmission versus probe laser detuning) were taken at an energy of 10 nJ in a 0.5-mm-diam beam. We should have noted that when the probe energy is increased to 150 n3 (— 10" W/cm ) the absorption cross section at the transmission maximum increases by a factor of approximately 2. At this energy density, with or without the coupling laser present, transmitted probe energy is no longer linear with incident probe energy.

Observation of Electromagnetically Induced Transparency in Collisionally Broadened Lead Vapor

We propose and analyze a scheme to enhance optomechanically-induced-transparency (OMIT) based on parity-time-symmetric optomechanical system. Our results predict that an OMIT window which does not exist originally can appear in weak optomechanical coupling and driving system via coupling an auxiliary active cavity with optical gain. This phenomenon is quite different from these reported in previous works in which the gain is considered just to damage OMIT phenomenon even leads to electromagnetically induced absorption or inverted-OMIT. Such enhanced OMIT effects are ascribed to the additional gain which can increase photon number in cavity without reducing effective decay. We also discuss the scheme feasibility by analyzing recent experiment parameters. Our work provide a promising platform for the coherent manipulation and slow light operation, which has potential applications for quantum information processing and quantum optical device.

/pdf/parity-time-symmetry-enhanced-optomechanically-induced-18nokdm4xr.pdf

Parity-time-symmetry enhanced optomechanically-induced-transparency

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 report the measurement of the inhomogeneous linewidth, homogeneous linewidth, and spin-state lifetime of Pr3+ ions in a novel waveguide architecture. The TeO2 slab waveguide deposited on a bulk Pr3+∶Y2SiO5 crystal allows the 3H4↔1D2 transition of Pr3+ ions to be probed by the optical evanescent field that extends into the substrate. The 2-GHz inhomogeneous linewidth, the optical coherence time of 70±5  μs, and the spin-state lifetime of 9.8±0.3  s indicate that the properties of ions interacting with the waveguide mode are consistent with those of bulk ions. This result establishes the foundation for large, integrated, and high performance rare-earth-ion quantum systems based on a waveguide platform.

/pdf/observation-of-photon-echoes-from-evanescently-coupled-rare-45g9u91sx8.pdf

Observation of Photon Echoes From Evanescently Coupled Rare-Earth Ions in a Planar Waveguide.

We propose to use a five-level cascade system to enhance self-Kerr nonlinearity under an electromagnetically induced transparency (EIT) condition. Using density-matrix theory, an expression of the self-Kerr nonlinear coefficient for a weak probe light is derived. Variations of the self-Kerr coefficient with respect to the frequency and intensity of a strong coupling light are investigated. The Kerr nonlinearity is basically modified and enhanced greatly in the spectral regions corresponding to EIT transparent windows. Furthermore, the sign, slope, and magnitude of the self-Kerr coefficient can be controlled with the frequency and intensity of the coupling light. Such a controllable Kerr nonlinearity can find interesting applications in optoelectronic devices working with low light intensity at multiple frequencies.

Enhancement of self-Kerr nonlinearity via electromagnetically induced transparency in a five-level cascade system: an analytical approach

A four-level inverted-Y scheme with an electromagnetically induced transparency (EIT) core is investigated for the enhancement of cross-Kerr effect in rubidium atoms. When detunings of the coupling and control fields are appropriately set, an enhanced EIT window is observed, and the induced phase shift of the probe field due to cross-phase modulation (XPM) is obtained by measuring the dispersive property of the probe transition. The maximal XPM phase shift is about 12° under the current experimental conditions. The experimental measurements agree well with the theoretical calculations. The enhanced XPM phase shift in such an atomic system has applications in quantum nonlinear optics and quantum information science.

EIT-assisted large cross-Kerr nonlinearity in a four-level inverted-Y atomic system

The effect of Doppler broadening on the gain spectrum is theoretically investigated in a hot N-type active Raman gain atomic system. It is found that the gain peak in the spectrum can be extremely narrowed and amplified by two orders at room temperature as compared with that in the cold atomic system. This remarkable result originates from the shift of the dressed levels and the modification to the transition probability between dressed states when the Doppler effect is considered in the hot atomic system. The enhanced subluminal and superluminal pulse propagation for the probe field in the hot atomic system has also been obtained by numerical simulation; the probe pulse undergoes no absorption and little pulse distortion.

Extremely narrowed and amplified gain spectrum induced by the Doppler effect

We experimentally demonstrate a three-channel all-optical routing based on light storage in a Pr3+:Y2SiO5 crystal. By switching off the control field under the condition of electromagnetically induced transparency, the optical information of the probe light pulse can be stored in the crystal. When three retrieve control fields are switched on in the release process, the stored optical information from one light channel can be transferred (or distributed) into three different light channels. Also we show that this all-optical routing can be time-delayed. Such a multichannel all-optical routing in solids may have practical applications in quantum information and all-optical network.

Three-channel all-optical routing in a Pr3+:Y2SiO5 crystal.

We propose a new scheme for achieving the complete population transfer and the optimal coherence generation between the ground state and the Rydberg state in a four-level ladder system by combining the STIRAP or fractional STIRAP technique and the π pulse technique. We consider, in particular, two different situations where spontaneous emission from the two highest states are neglected or not. Our numerical calculations show that the time width and the delay time of the π pulse are two critical parameters for attaining the maximal population transfer and coherence generation in this scheme.

Coherence generation and population transfer by stimulated Raman adiabatic passage and π pulse in a four-level ladder system

We experimentally investigate the transfer of orbital angular momentum (OAM) of light in a solid driven by electromagnetically induced transparency (EIT). Under the condition of dynamical EIT, the OAM of the probe pulse is stored and retrieved in the experimental medium. By using a four-level double-lambda system to control the retrieval process of EIT storage, we show that OAM can be transferred from the probe field or the second control field to the newly generated signal field, which has a new spatial-frequency mode compared with the input mode. Furthermore, we use EIT-based four-wave mixing to investigate the direct OAM transfer without experiencing the storage, where we do not need to switch off and back on the control field.

Xiao-Jun Zhang

Papers

EIT-assisted large cross-Kerr nonlinearity in a four-level inverted-Y atomic system

Extremely narrowed and amplified gain spectrum induced by the Doppler effect

Three-channel all-optical routing in a Pr3+:Y2SiO5 crystal.

Coherence generation and population transfer by stimulated Raman adiabatic passage and π pulse in a four-level ladder system

Transfer of orbital angular momentum of light using electromagnetically induced transparency