Coherent preparation by laser light of quantum states of atoms and molecules can lead to quantum interference in the amplitudes of optical transitions. In this way the optical properties of a medium can be dramatically modified, leading to electromagnetically induced transparency and related effects, which have placed gas-phase systems at the center of recent advances in the development of media with radically new optical properties. This article reviews these advances and the new possibilities they offer for nonlinear optics and quantum information science. As a basis for the theory of electromagnetically induced transparency the authors consider the atomic dynamics and the optical response of the medium to a continuous-wave laser. They then discuss pulse propagation and the adiabatic evolution of field-coupled states and show how coherently prepared media can be used to improve frequency conversion in nonlinear optical mixing experiments. The extension of these concepts to very weak optical fields in the few-photon limit is then examined. The review concludes with a discussion of future prospects and potential new applications.

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Electromagnetically induced transparency : Optics in coherent media

We review the field of cavity optomechanics, which explores the interaction between electromagnetic radiation and nano- or micromechanical motion This review covers the basics of optical cavities and mechanical resonators, their mutual optomechanical interaction mediated by the radiation pressure force, the large variety of experimental systems which exhibit this interaction, optical measurements of mechanical motion, dynamical backaction amplification and cooling, nonlinear dynamics, multimode optomechanics, and proposals for future cavity quantum optomechanics experiments In addition, we describe the perspectives for fundamental quantum physics and for possible applications of optomechanical devices

Cavity Optomechanics

The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed and updated. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eotvos experiment, tests of local Lorentz invariance and clock experiments. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and a growing family of other binary pulsar systems is yielding new tests, especially of strong-field effects. Current and future tests of relativity will center on strong gravity and gravitational waves.

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The Confrontation Between General Relativity and Experiment

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation in photonic crystal fiber

Electromagnetically induced transparency is a technique for eliminating the effect of a medium on a propagating beam of electromagnetic radiation EIT may also be used, but under more limited conditions, to eliminate optical self‐focusing and defocusing and to improve the transmission of laser beams through inhomogeneous refracting gases and metal vapors, as figure 1 illustrates The technique may be used to create large populations of coherently driven uniformly phased atoms, thereby making possible new types of optoelectronic devices

Electromagnetically Induced Transparency

Coherent population trapping (CPT) resonances usually exhibit contrasts below 10 % when interrogated with frequency modulated lasers. We discuss a relatively simple way to increase the resonance contrast to nearly 100 % generating an additional light field through a nonlinear four-wave mixing interaction in the atomic vapor 1 . A similar method can also be used to create a beat signal at the CPT resonance frequency that can injection-lock a low-power microwave oscillator at 3.4 GHz directly to the atomic resonance 2 . This could lead to chip-scale atomic clocks (CSACs) with improved performance. Furthermore, we introduce a miniature microfabricated saturated absorption spectrometer 3 that produces a signal for locking a laser frequency to optical transitions in alkali atoms. The Rb absorption spectra are comparable to signals obtained with standard table-top setups, although the rubidium vapor cell has an interior volume of only 1 mm 3 and the volume of the entire spectrometer is around 0.1 cm 3 .

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Advances in Chip-Scale Atomic Frequency References at NIST

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Tunable UV generation at 283 nm by frequency doubling and sum frequency mixing of two semiconductor lasers for the detection of Pb

Characteristics of an optically pumped Cs frequency standard developed at the National Research Laboratory of Metrology (NRLM) are reported. The short-term frequency stability was estimated to be 1.1*10/sup -12// square root pi when the optical feedback technique was used for laser diode stabilization. Frequency shifts due to microwave power and pumping conditions were measured and their characteristics are described. >

Characteristics of an optically pumped Cs frequency standard at the NRLM

The Primary Atomic Reference Clock in Space (PARCS) project is a joint NIST-JPL-University of Colorado venture aimed at placing a Cs atomic clock aboard the International Space Station (ISS). This orbiting clock will achieve high accuracy, in part due to the long Ramsey times afforded by the microgravity environment, and allow for precision tests of fundamental physics including relativity theory. As part of this effort, we are evaluating the characteristics of a prototype cold Cs source based on launching atoms from an optical molasses. Experimental results, in conjunction with theoretical modeling of atom flux requirements, will be applied to the design and construction of a robust, space-qualified device. The apparatus described here will be used to develop other PARCS components such as the microwave cavity structure and detection systems, and to investigate two-dimensional cooling schemes for future Cs fountains and space clocks.

Characterization of a cold cesium source for PARCS: Primary Atomic Reference Clock in Space

This paper describes the fabrication of chip-scale alkali atom vapor cells, for use in highly miniaturized atomic frequency references, using silicon micromachining and anodic bonding technology. The cells consist of silicon cavities with internal volume ranging from a few mm/sup 3/ to less than 1 mm/sup 3/. The cells were filled with cesium and nitrogen buffer gas either by chemical reaction of cesium chloride and barium azide, or by direct injection of elemental cesium within a controlled anaerobic environment. Cesium optical absorption spectra were obtained from the cells, and coherent population trapping resonances with linewidths of about 1 kHz were measured.

Leo W. Hollberg

Papers

Advances in Chip-Scale Atomic Frequency References at NIST

Tunable UV generation at 283 nm by frequency doubling and sum frequency mixing of two semiconductor lasers for the detection of Pb

Characteristics of an optically pumped Cs frequency standard at the NRLM

Characterization of a cold cesium source for PARCS: Primary Atomic Reference Clock in Space

Micromachined alkali atom vapor cells for chip-scale atomic clocks