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

The performance and prospects for neutral-atom optical frequency standards are discussed based on our recent progress with a calcium optical frequency star~dard. Second stage narrow-line cooling to microkelvin (and even 300 nK) temperatures, combined with launched atoms, should reduce Doppler frequency errors to about 1x10 1 6 . Advanced femtosecond optical frequency combs allow direct comparisons between the Ca optical standard, the Hg* optical standard and the Cs primary standard. These comparisons provide independent "reality checks" on both the stability and accuracy. Relative frequency measurements also constrain the possible time variation of atomic energy levels and fundamental constants.

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Optical Clocks with Cold Atoms and Stable Lasers

The goal this work was to study the limitations imposed on frequency stability of synthesised optical signal by intrinsic fluctuations of the femtosecond laser as well as fluctuations in the optical readout system.

Experimental Study of Noise Properties of a TI-Sapphire Mode-Locked Laser

The need for an accurate time and position reference on orbiting platforms motivates the study of time transfer over satellite optical communication links. The transfer of precise optical clock signals to space would benefit many fields in fundamental science and applications. However, the precise role of atmospheric turbulence during the optical time transfer process is not well-known and documented. In free-space optical links, atmospheric turbulence represents a major impairment, since it causes degradation of the spatial and temporal coherence of the optical signals. We present possible link scenarios in which the atmospheric channel behavior for time transfer between ground and space can be investigated, and have identified the major challenges to be overcome. We found in our analysis that, despite the limited reciprocity in uplink and downlink propagation, partial two-way cancellation of atmospheric effects still occurs. We established that laser communication links make possible high-quality time transfer in most practical propagation scenarios and over a single satellite visibility period. Our results demonstrate that sharing of optical communication resources for optical time transfer and range determination is an effective and relevant scheme for space clock developments and enabling for future space missions.

Impact of atmospheric anisoplanaticity on earth-to-satellite time transfer over laser communication links

Summary form only given. We report here measurements of electromagnetically induced transparency (EIT) in a sample of cold trapped Rb/sup 87/ atoms. By using cold atoms, we avoid complications associated with Doppler broadening, which often exist in similar experiments performed with room-temperature vapors. The measurements were made on an 2mm-diameter sample of -10/sup 8/ laser-cooled Rb/sup 87/ atoms collected in a standard magnetooptic trap.

Electromagnetically induced transparency in cold atoms

We report on our recent evaluations of stability and accuracy of the JILA Sr optical lattice clock. We discuss precision tools for the lattice clock, including a stabilized clock laser with sub-Hz linewidth, fs-comb based technology allowing accurate clock comparison in both the microwave and optical domains, and clock transfer over optical fiber in an urban environment. High resolution spectroscopy (Q > 2 × 10) of lattice-confined, spin-polarized strontium atoms is used for both a high-performance optical clock and atomic structure measurement. Using a Ca optical standard for comparison, the overall systematic uncertainty of the Sr clock is reduced to < 2 × 10.

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Leo W. Hollberg

Papers

Optical Clocks with Cold Atoms and Stable Lasers

Experimental Study of Noise Properties of a TI-Sapphire Mode-Locked Laser

Impact of atmospheric anisoplanaticity on earth-to-satellite time transfer over laser communication links

Electromagnetically induced transparency in cold atoms

Sr Optical Clock with High Stability and Accuracy