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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

Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

Feshbach resonances are the essential tool to control the interaction between atoms in ultracold quantum gases. They have found numerous experimental applications, opening up the way to important breakthroughs. This review broadly covers the phenomenon of Feshbach resonances in ultracold gases and their main applications. This includes the theoretical background and models for the description of Feshbach resonances, the experimental methods to find and characterize the resonances, a discussion of the main properties of resonances in various atomic species and mixed atomic species systems, and an overview of key experiments with atomic Bose-Einstein condensates, degenerate Fermi gases, and ultracold molecules.

Feshbach resonances in ultracold gases

Rydberg atoms with principal quantum number $n⪢1$ have exaggerated atomic properties including dipole-dipole interactions that scale as ${n}^{4}$ and radiative lifetimes that scale as ${n}^{3}$. It was proposed a decade ago to take advantage of these properties to implement quantum gates between neutral atom qubits. The availability of a strong long-range interaction that can be coherently turned on and off is an enabling resource for a wide range of quantum information tasks stretching far beyond the original gate proposal. Rydberg enabled capabilities include long-range two-qubit gates, collective encoding of multiqubit registers, implementation of robust light-atom quantum interfaces, and the potential for simulating quantum many-body physics. The advances of the last decade are reviewed, covering both theoretical and experimental aspects of Rydberg-mediated quantum information processing.

Quantum information with Rydberg atoms

We report the observation of dipole-forbidden, but quadrupole-allowed, one-photon transitions to high Rydberg states in Rb. Using pulsed UV excitation of ultracold atoms in a magneto-optical trap, we excite $5s \to nd$ transitions over a range of principal quantum numbers $n=27-59$. Compared to dipole-allowed (E1) transitions from $5s \to np$, these E2 transitions are weaker by a factor of approximately 2000. We also report measurements of the anomalous $np_{3/2} : np_{1/2}$ fine-structure transition strength ratio for $n=28-75$. Both results are in agreement with theoretical predictions.

Observation of Electric Quadrupole Transitions to Rydberg nd States of Ultracold Rubidium Atoms

We give a brief overview of some basic concepts in quantum information processing, and discuss various systems considered to implement these ideas. We focus our attention on one particular system, ultracold Rydberg atoms, and show how the strong interaction between such atoms can be used to implement an universal quantum logic gate, namely a phase gate. We also describe how quantum information can be stored and manipulated in mesoscopic ensembles of such atoms. We present some experimental results on the effects of strong interactions between Rydberg atoms.

Quantum computing with Rydberg atoms

Pushing the Frontiers of Atomic Physics

We compute the formation rate of a polar molecule, LiH, into the lowest triplet electronic state, a {sup 3{Sigma}+}, via population of the intermediate excited electronic state, b {sup 3{Pi}}, followed by radiative decay. We find large formation rates into the single rovibrational bound state (v=0,J=0) of the a {sup 3{Sigma}+}, which can be explained by the unusually large overlap of its wave function with those of the two upper-most bound levels of the b {sup 3{Pi}}. With conservative parameters, we estimate that over 10{sup 4} molecules/s could be produced in the single rovibrational level of the a {sup 3{Sigma}+} state. We also discuss scattering properties of LiH triplet molecules and their relevance to ultracold chemical reactions.

Formation of ultracold polar molecules in a single quantum state

Calculations of the coefficients of viscosity and thermal conductivity of lithium, sodium, and potassium gases are performed using accurate potential curves Comparison with previous calculations and measurements is made, and simple expressions are given for the viscosity and thermal conductivity as functions of temperature

Robin Côté

Papers

Observation of Electric Quadrupole Transitions to Rydberg nd States of Ultracold Rubidium Atoms

Quantum computing with Rydberg atoms

Pushing the Frontiers of Atomic Physics

Formation of ultracold polar molecules in a single quantum state

Viscosity and Thermal Conductivity of Li, Na, and K Gases