Jiteng Sheng

Two-Photon Dynamics in Coherent Rydberg Atomic Ensemble

We study the interaction of two photons in a Rydberg atomic ensemble under the condition of electromagnetically induced transparency, combining a semiclassical approach for pulse propagation and a complete quantum treatment for quantum state evolution. We find that the blockade regime is not suitable for implementing photon-photon cross-phase modulation due to pulse absorption and dispersion. However, approximately ideal cross-phase modulation can be realized based on relatively weak interactions, with counterpropagating and transversely separated pulses.

Observation of Parity-Time Symmetry in Optically Induced Atomic Lattices.

We experimentally demonstrate PT-symmetric optical lattices with periodical gain and loss profiles in a coherently prepared four-level N-type atomic system. By appropriately tuning the pertinent atomic parameters, the onset of PT-symmetry breaking is observed through measuring an abrupt phase-shift jump between adjacent gain and loss waveguides. The experimental realization of such a readily reconfigurable and effectively controllable PT-symmetric waveguide array structure sets a new stage for further exploiting and better understanding the peculiar physical properties of these non-Hermitian systems in atomic settings.

PT-symmetric optical potentials in a coherent atomic medium

We demonstrate that a coherently-prepared four-level atomic medium can provide a versatile platform for realizing parity-time (PT) symmetric optical potentials. Different types of PT-symmetric potentials are proposed by appropriately tuning the exciting optical fields and the pertinent atomic parameters. Such reconfigurable and controllable systems can open up new avenues in observing PT-related phenomena with appreciable gain/loss contrast in coherent atomic media.

All-optical switching in an N-type four-level atom-cavity system

We report an experimental observation of all-optical switching in an N-type atom-cavity system with a rubidium atomic vapor cell inside an optical ring cavity. Both absorptive and dispersive switching can be realized on dark- or bright-polariton peaks by a weak switching laser beam (with the extinction ratio better than 20:1). The switching mechanism can be explained as the combination of quantum interference and intracavity dispersion properties.

Atom-Based Sensing of Weak Radio Frequency Electric Fields Using Homodyne Readout

We utilize a homodyne detection technique to achieve a new sensitivity limit for atom-based, absolute radio-frequency electric field sensing of 5 μV cm−1 Hz−1/2. A Mach-Zehnder interferometer is used for the homodyne detection. With the increased sensitivity, we investigate the dominant dephasing mechanisms that affect the performance of the sensor. In particular, we present data on power broadening, collisional broadening and transit time broadening. Our results are compared to density matrix calculations. We show that photon shot noise in the signal readout is currently a limiting factor. We suggest that new approaches with superior readout with respect to photon shot noise are needed to increase the sensitivity further.

Observation of discrete diffraction patterns in an optically induced lattice

We have experimentally observed the discrete diffraction of light in a coherently prepared multi-level atomic medium. This is achieved by launching a probe beam into an optical lattice induced from the interference of two coupling beams. The diffraction pattern can be controlled through the atomic parameters such as two-photon detuning and temperature, as well as orientations of the coupling and probe beams. Clear diffraction patterns occur only near the two-photon resonance.

Amplification of the intracavity dark-state field by a four-wave mixing process

We demonstrate both experimentally and theoretically that the intracavity electromagnetically induced transparency dark-state field can be significantly amplified with the characteristic three-peak structure unchanged by a four-wave mixing process in an optical ring cavity containing four-level double-Λ Doppler-broadened rubidium atoms. The intracavity dispersion and absorption/gain properties are used to qualitatively explain this cavity resonance structure. The amplification is saturated at a relatively high pump laser power, and the dark-state peak position is shifted due to the ac-Stark effect.

Spatial Domain Interactions between Ultraweak Optical Beams

We have observed spatial interactions between two ultraweak optical beams that are initially collinear and nonoverlapping. The weak beams are steered towards each other by a spatially varying cross-Kerr refractive index waveguide written by a strong laser beam in a three-level coherently prepared atomic medium. After fusing together, the combined beam shows controllable phase-dependent behaviors. This is the first observation of solitonlike interactions between weak beams and can be useful for all-optically tunable beam combining, switching, and gating for weak photonic signals.

Intracavity Rydberg-atom electromagnetically induced transparency using a high-finesse optical cavity

We present an experimental study of cavity assisted Rydberg atom electromagnetically induced transparency (EIT) using a high-finesse optical cavity (

Observation of electromagnetically induced Talbot effect in an atomic system

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