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

(b) Write out the equations for the time dependence of ρ11, ρ22, ρ12 and ρ21 assuming that a light field interaction V = -μ12Ee iωt + c.c. couples only levels |1> and |2>, and that the excited levels exhibit spontaneous decay. (8 marks) (c) Under steady-state conditions, find the ratio of populations in states |2> and |3>. (3 marks) (d) Find the slowly varying amplitude ̃ ρ 12 of the polarization ρ12 = ̃ ρ 12e iωt . (6 marks) (e) In the limiting case that no decay is possible from intermediate level |3>, what is the ground state population ρ11(∞)? (2 marks) 2. (15 marks total) In a 2-level atom system subjected to a strong field, dressed states are created in the form |D1(n)> = sin θ |1,n> + cos θ |2,n-1> |D2(n)> = cos θ |1,n> sin θ |2,n-1>

The Quantum Theory of Light

This paper presents a review of the current state of the art in the research field of cold and ultracold molecules. It serves as an introduction to the focus issue of New Journal of Physics on Cold and Ultracold Molecules and describes new prospects for fundamental research and technological development. Cold and ultracold molecules may revolutionize physical chemistry and few-body physics, provide techniques for probing new states of quantum matter, allow for precision measurements of both fundamental and applied interest, and enable quantum simulations of condensed-matter phenomena. Ultracold molecules offer promising applications such as new platforms for quantum computing, precise control of molecular dynamics, nanolithography and Bose-enhanced chemistry. The discussion is based on recent experimental and theoretical work and concludes with a summary of anticipated future directions and open questions in this rapidly expanding research field.

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Cold and ultracold molecules: science, technology and applications

Photoassociation is the process in which two colliding atoms absorb a photon to form an excited molecule. The development of laser-cooling techniques for producing gases at ultracold !!1 mK" temperatures allows photoassociation spectroscopy to be performed with very high spectral resolution. Of particular interest is the investigation of molecular states whose properties can be related, with high precision, to the properties of their constituent atoms with the “complications” of chemical binding accounted for by a few parameters. These include bound long-range or purely long-range vibrational states in which two atoms spend most or all of their time at large internuclear separations. Low-energy atomic scattering states also share this characteristic. Photoassociation techniques have made important contributions to the study of all of these. This review describes what is special about photoassociation spectroscopy at ultracold temperatures, how it is performed, and a sampling of results including the determination of scattering lengths, their control via optical Feshbach resonances, precision determinations of atomic lifetimes from molecular spectra, limits on photoassociation rates in a Bose-Einstein condensate, and briefly, production of cold molecules. Discussions are illustrated with examples on alkali-metal atoms as well as other species. Progress in the field is already past the point where this review can be exhaustive, but an introduction is provided on the capabilities of photoassociation spectroscopy and the techniques presently in use.

/pdf/ultracold-photoassociation-spectroscopy-long-range-molecules-31d6x6vqxx.pdf

Ultracold photoassociation spectroscopy: Long-range molecules and atomic scattering

We demonstrate the production of ultracold polar RbCs molecules in their vibronic ground state, via photoassociation of laser-cooled atoms followed by a laser-stimulated state transfer process. The resulting sample of X1Sigma+ (nu = 0) molecules has a translational temperature of approximately 100 microK and a narrow distribution of rotational states. With the method described here it should be possible to produce samples even colder in all degrees of freedom, as well as other bialkali species.

/pdf/optical-production-of-ultracold-polar-molecules-37eufc9smm.pdf

Optical production of ultracold polar molecules.

We propose a new compact and reliable laser system for rubidium laser cooling in onboard experiments like atomic clocks or atomic inertial sensors The system is based on the frequency doubling of a telecom fiber bench at 1560 nm Fiber components at 1560 nm allow us to generate the repumping laser and to control dynamically the power and the frequency of the 780 nm laser With this laser system, we obtain a magneto-optical trap of 85Rb even in the presence of mechanical vibrations and strong thermal variations (12 °C in 30 min)

Compact and robust laser system for rubidium laser cooling based on the frequency doubling of a fiber bench at 1560 nm

We present our the construction of an atom interferometer for inertial sensing in microgravity, as part of the I.C.E. (Interferometrie Coherente pour l'Espace) collaboration. On-board laser systems have been devel- oped based on fibre-optic components, which are insen- sitive to mechanical vibrations and acoustic noise, have sub-MHz linewidth, and remain frequency stabilised for weeks at a time. A compact, transportable vacuum sys- tem has been built, and used for laser cooling and magneto- optical trapping. We will use a mixture of quantum de- generate gases, bosonic 87 Rb and fermionic 40 K, in or- der to find the optimal conditions for precision and sen- sitivity of inertial measurements. Microgravity will be realised in parabolic flights lasting up to 20s in an Air- bus. We show that the factors limiting the sensitivity of a long-interrogation-time atomic inertial sensor are the phase noise in reference frequency generation for Raman- pulse atomic beam-splitters and acceleration fluctuations during free fall.

https://hal.archives-ouvertes.fr/hal-00023609/document

I.C.E.: a transportable atomic inertial sensor for test in microgravity

We report on the spectra of the long-range attractive molecular states of the Cs/sub 2/ dimer below the dissociation limits 6s+6p/sub 1/2/ and 6s+6p/sub 3/2/ which are accessible by molecular photoassociation of cold Cs atoms. For the states O/sub u//sup +/ and O/sub g//sup -/(6s+6p/sub 3/2/), we have performed trap-loss measurements, which are in good agreement with the theoretical calculations, performed in a perturbative approach. For the O/sub g//sup -/ and 1/sub u/(6s+6p/sub 3/2/) states, we observe, after spontaneous decay of the electronically excited molecules, the formation of translationally cold molecules. A rate of formation of cold molecules of the order of /spl sim/10/sup 6/ molecules per second is obtained in the case of the state O/sub g//sup $/.

Experimental versus theoretical rates for photoassociation and for formation of ultracold molecules

OBJECTIVE: To evaluate the most recent transport ventilators' operational performance regarding volume delivery in controlled mode, trigger function, and the quality of pressurization in pressure support mode.

METHODS: Eight recent transport ventilators were included in a bench study in order to evaluate their accuracy to deliver a set tidal volume under normal resistance and compliance conditions, ARDS conditions, and obstructive conditions. The performance of the triggering system was assessed by the measure of the decrease in pressure and the time delay required to open the inspiratory valve. The quality of pressurization was obtained by computing the integral of the pressure-time curve for the first 300 ms and 500 ms after the onset of inspiration.

RESULTS: For the targeted tidal volumes of 300, 500, and 800 mL the errors ranged from –3% to 48%, –7% to 18%, and –5% to 25% in the normal conditions, –4% to 27%, –2% to 35%, and –3% to 35% in the ARDS conditions, and −4% to 53%, −6% to 30%, and −30% to 28% in the obstructive conditions. In pressure support mode the pressure drop range was 0.4–1.7 cm H2O, the trigger delay range was 68–198 ms, and the pressurization performance (percent of ideal pressurization, as measured by pressure-time product at 300 ms and 500 ms) ranges were –9% to 44% at 300 ms and 6%–66% at 500 ms ( P < .01).

CONCLUSIONS: There were important differences in the performance of the tested ventilators. The most recent turbine ventilators outperformed the pneumatic ventilators. The best performers among the turbine ventilators proved comparable to modern ICU ventilators.

http://rc.rcjournal.com/content/respcare/58/11/1911.full.pdf

Evaluation of ventilators used during transport of critically ill patients: a bench study.

The intensity and the phase of ultrashort pulses from a self-mode-locked Ti:sapphire laser operating in the vicinity of zero group-delay dispersion (GDD) have been completely characterized by the technique of frequency-resolved optical gating (FROG). For small values of negative GDD, the appearance of a dispersive wave in the pulse spectrum is manifested in the measured FROG trace, and pulse retrieval directly shows its association with a broad leading-edge pedestal. For positive GDD, we confirm previous experimental observations of picosecond pulses with large positive chirp and report a new operating regime in which the output pulses are of picosecond duration but are intensity modulated at 20 THz. The physical origin of this modulation is discussed by analogy with similar effects observed during pulse propagation in optical fibers, and the experimental results are compared with a model of intracavity four-wave mixing about the cavity zero GDD wavelength.

Salah Boussen

Papers

Compact and robust laser system for rubidium laser cooling based on the frequency doubling of a fiber bench at 1560 nm

I.C.E.: a transportable atomic inertial sensor for test in microgravity

Experimental versus theoretical rates for photoassociation and for formation of ultracold molecules

Evaluation of ventilators used during transport of critically ill patients: a bench study.

Complete characterization of a self-mode-locked Ti:sapphire laser in the vicinity of zero group-delay dispersion by frequency-resolved optical gating