Atomic coherence

About: Atomic coherence is a research topic. Over the lifetime, 877 publications have been published within this topic receiving 29395 citations.

Experimental Observation of Partial Parity-Time Symmetry and Its Phase Transition with a Laser-Driven Cesium Atomic Gas

Abstract: Realization and manipulation of parity-time (PT) symmetry in multidimensional systems are highly desirable for exploring nontrivial physics and uncovering exotic phenomena in non-Hermitian systems. Here, we report the first experimental observation of partial PT (pPT) symmetry in a cesium atomic gas coupled with laser fields, where a two-dimensional pPT-symmetric optical potential for probe laser beam is created. A transition of the pPT symmetry from an unbroken phase to a broken one is observed through changing the beam-waist ratio of the control and probe laser beams, and the domains of unbroken, broken, and non-pPT phases are also discriminated unambiguously. Moreover, we develop a technique to precisely determine the location of the exceptional point of the pPT symmetry breaking by measuring the asymmetry degree of the probe-beam intensity distribution. The findings reported here pave the way for controlling multidimensional laser beams in non-Hermitian systems via laser-induced atomic coherence, and have potential applications for designing new types of light amplifiers and attenuators

Optical Isolation with Optical Parametric Amplification in an Atomic System

Abstract: Magnet‐free active optical nonreciprocal (AON) devices free from insertion loss help to establish optical information processing networks involving weak signals without introducing external magnetic fields. However, considering the necessary resonant condition for amplification or the presence of optical resonators for most demonstrated magnet‐free AON schemes, it remains a challenge to broaden the AON bandwidth. Here the optical isolation based on optical parametric amplification is demonstrated experimentally in a coherent three‐level atomic configuration. With the phase‐matching condition satisfied or not by oppositely launching the probe beams, they can pass through the medium experiencing parametric amplification or strong resonant absorption. Such magnet‐ and cavity‐free optical isolation exhibits a maximum isolation ratio of 46.5 dB and a broad bandwidth of over 0.85 GHz for the isolation ratio ≥30 dB. The demonstrated results arising from atomic‐coherence‐based optical parametric process with quantum nature pave the way to achieve high‐performance nonreciprocal quantum information processing.

Optical pumping and coherence effects in fluorescence from a four level system

Abstract: An effective four-level system around the D2 line of 85Rb at room temperature, is experimentally investigated by fluorescent studies under the action of two driving fields L1 and L2. This system exhibits unique features in fluorescence as a function of frequency separation between L1 and L2. In particular, at two-photon resonance, when the Rabi frequency of L1 exceeds that of L2, signatures of Electromagnetically Induced Transperancy effect (EIT) arising from the three-level Λ sub-system is present as a sub-natural dip in fluorescence from the fourth level. At comparable strengths of L1 and L2 the fluorescence features indicate a regime, where the effects arising from optical pumping and EIT effect due to ground hyperfine level coherence coexist. We see in the coexistence regime, saturation effects arising from difference frequency crossing (DFC) resonances and optical pumping around the EIT window. At low strengths of L1, all signs of coherence vanishes from the system and the fluorescent features result from incoherent optical pumping through the Autler-Townes split states of the excited state hyperfine levels, which are split due to the stronger L2 laser. The dominant role of the L1 laser in creating a robust transparency signal even in the presence of an off-resonant excitation is brought out. The results are supported by density matrix calculations.

Observation of spontaneous coherence grating transfer in cold cesium atoms

Abstract: We report on the direct observation of spontaneous coherence grating transfer between different pairs of Zeeman sublevels belonging to different cesium hyperfine states. Coherent Bragg diffraction is employed as a signature of the transfer mechanism; this spectrum shows a subnatural linewidth. Theoretically we model the observed effect using a tensorial density matrix formalism to describe the light interaction with a pair of degenerate two-level systems coupled by spontaneous emission. The possibility of transferring a short-lived atomic coherence into a long-lived one might be of considerable importance for the growing field of quantum-information processing.

Optical phase information writing and storage in populations of metastable quantum states

Abstract: We propose a scheme for robust writing and storage of optical phase information in populations of metastable states of the atoms with a tripod structure of levels by using frequency-chirped laser pulses. The method provides much longer storage times compared with the schemes based on the collective atomic spin coherences. A negligible excitation of the atom provides immunity to decoherence induced by decay of the excited states. The method is robust against small-to-medium variations in the laser pulse intensity and speed of the chirp and, being insensitive to resonance conditions, it is effective both in homogeneously and inhomogeneously broadened media.