Cold Atoms Physics

The term 'laser cooling' is applied to the use of optical means to cool the motional energies of either atoms and molecules, or micromirrors. In the literature, these two strands are kept largely separate; both, however suffer from severe limitations. Laser cooling of atoms and molecules largely relies on the internal level structure of the species being cooled. As a result, only a small number of elements and a tiny number of molecules can be cooled this way. In the case of micromirrors, the problem lies in the engineering of micromirrors that need to satisfy a large number of constraints-these include a high mechanical Q-factor, high reflectivity and very good optical quality, weak coupling to the substrate, etc.-in order to enable efficient cooling.

We report on an absolute frequency measurement of the hydrogen 1S-2S two-photon transition in a cold atomic beam with an accuracy of 1.8 parts in 10 14 . Our experimental result of 2 466 061 413 187 103(46) Hz has been obtained by phase coherent comparison of the hydrogen transition frequency with an atomic cesium fountain clock. Both frequencies are linked with a comb of laser frequencies emitted by a mode locked laser. 06.30.Ft, 06.20.Jr, 42.62.Fi The 1S-2S two-photon transition in atomic hydrogen has played a central role in the progress of high resolution laser spectroscopy and optical frequency metrology . It provides a cornerstone for the determination of fundamental constants such as the Rydberg constant, which has become the most precisely measured constant in physics, and the 1S-Lamb shift to yield the most stringent test of quantum electrodynamics in an atom .

Deep eutectic solvents (DESs) are considered as potential alternatives for ionic liquids (ILs). The evaluation of DESs as new generation of solvents for various practical application requires enough knowledge about some main physical, chemical, and thermodynamic properties. In this study, due to lack of data for DESs' refractive indices, the refractive indices of twenty four DESs based on ammonium and phosphonium salts were measured and predicted using atomic contribution method. The atomic contributions data for molar refraction proposed by Wildman and Crippen which was developed for neutral compounds were employed to calculate the molar refractions of DESs. Subsequently, the refractive indices of DESs were predicted using Lorentz-Lorenz equation through the calculated DESs' molar refractions and experimental DESs' densities values. The absolute relative percentage error (ARPE) value of 0.56% and a regression coefficient (R 2 ) value of 0.9822 both confirmed the highly possible application of the proposed method for predicting the refractive indices. In addition, the effect of DESs' composition on refractive index of DESs was investigated and it was found that the refractive index of the DESs lies between that of the salt and HBD. Moreover, the densities of DESs were also predicted using Lorentz-Lorenz equation employing the calculated molar refraction and values of experimental DESs' refractive indices. The ARPE of 1.43% shows that this method for prediction of densities of the synthesized DESs is applicable as well.

The main theme of this review is the many-body physics of vortices in quantum droplets of bosons or fermions, in the limit of small particle numbers. Systems of interest include cold atoms in traps as well as electrons confined in quantum dots. When set to rotate, these in principle very different quantum systems show remarkable analogies. The topics reviewed include the structure of the finite rotating many-body state, universality of vortex formation and localization of vortices in both bosonic and fermionic systems, and the emergence of particle-vortex composites in the quantum Hall regime. An overview of the computational many-body techniques sets focus on the configuration interaction and density-functional methods. Studies of quantum droplets with one or several particle components, where vortices as well as coreless vortices may occur, are reviewed, and theoretical as well as experimental challenges are discussed.

Deep eutectic solvents (DESs) are considered as potential alternatives for ionic liquids (ILs). The evaluation of DESs as new generation of solvents for various practical application requires enough knowledge about some main physical, chemical, and thermodynamic properties. In this study, due to lack of data for DESs' refractive indices, the refractive indices of twenty four DESs based on ammonium and phosphonium salts were measured and predicted using atomic contribution method. The atomic contributions data for molar refraction proposed by Wildman and Crippen which was developed for neutral compounds were employed to calculate the molar refractions of DESs. Subsequently, the refractive indices of DESs were predicted using Lorentz-Lorenz equation through the calculated DESs' molar refractions and experimental DESs' densities values. The absolute relative percentage error (ARPE) value of 0.56% and a regression coefficient (R 2 ) value of 0.9822 both confirmed the highly possible application of the proposed method for predicting the refractive indices. In addition, the effect of DESs' composition on refractive index of DESs was investigated and it was found that the refractive index of the DESs lies between that of the salt and HBD. Moreover, the densities of DESs were also predicted using Lorentz-Lorenz equation employing the calculated molar refraction and values of experimental DESs' refractive indices. The ARPE of 1.43% shows that this method for prediction of densities of the synthesized DESs is applicable as well.

Since the first atom interferometry experiments in 1991, measurements of rotation through the Sagnac effect in open-area atom interferometers has been studied. These studies have demonstrated very high sensitivity which can compete with state-of-the-art optical Sagnac interferometers. Since the early 2000s, these developments have been motivated by possible applications in inertial guidance and geophysics. Most matter-wave interferometers that have been investigated
since then are based on two-photon Raman transitions for the manipulation of atomic wave packets. Results from the two most studied configurations, a space-domain interferometer
with atomic beams and a time-domain interferometer with cold atoms, are presented and compared. Finally, the latest generation of cold atom interferometers and their preliminary results are presented.

We investigate the feasibility of simulating different model Hamiltonians used in high-temperature superconductivity. We briefly discuss the most common models and then focus on the simulation of the so-called t-J-U Hamiltonian using ultra-cold atoms in optical lattices. For this purpose, previous simulation schemes to realize the spin interaction term J are extended. We especially overcome the condition of a filling factor of exactly one, which otherwise would restrict the phase of the simulated system to a Mott-insulator. Using ultra-cold atoms in optical lattices allows simulation of the discussed models for a very wide range of parameters. The time needed to simulate the Hamiltonian is estimated and the accuracy of the simulation process is numerically investigated for small systems.

We explore the trap profiles of a two-dimensional atomic Fermi gas in the presence of a Rashba spin-orbit coupling and under an adiabatic rotation. We first consider a noninteracting gas and show that the competition between the effects of Rashba coupling on the local density of single-particle states and the Coriolis effects caused by rotation gives rise to a characteristic ring-shaped density profile that survives at experimentally accessible temperatures. Furthermore, Rashba splitting of the Landau levels gives the density profiles a ziggurat shape in the rapid-rotation limit. We then consider an interacting gas under the BCS mean-field approximation for local pairing, and study the pair-breaking mechanism that is induced by the Coriolis effects on superfluidity, where we calculate the critical rotation frequencies both for the onset of pair breaking and for the complete destruction of superfluidity in the system. In particular, by comparing the results of a fully-quantum-mechanical Bogoliubov–de Gennes approach with those of a semiclassical local-density approximation, we construct extensive phase diagrams for a wide range of parameter regimes in the trap where the aforementioned competition may, e.g., favor an outer normal edge that is completely phase separated from the central superfluid core by vacuum.

In this review, we discuss the impact of the development of lasers on ultracold atoms and molecules and their applications. After a brief historical review of laser cooling and Bose-Einstein condensation, we present important applications of ultra cold atoms, including time and frequency metrology, atom interferometry and inertial sensors, atom lasers, simulation of condensed matter systems, production and study of strongly correlated systems, and production of ultracold molecules.

We consider a family of tight-binding models based on kagome lattice with local fluxes, which have a lowest flat band in the single particle spectrum. The flat band is spanned by eigenstates forming localized loops on the lattice, with the maximally compact loop states typically breaking the discrete rotational symmetry of the lattice.  When populated by locally-interacting particles, the close packing of such maximally compact loop states leads to a nematic Wigner crystal ground state. If particles are bosons, increasing filling beyond the close packing filling fraction, at the mean field level, leads to formation of a nematic supersolid and a nematic superfluid phases with broken lattice rotation and $U(1)$ symmetry.

Strongly correlated quantum systems can exhibit exotic behaviour called topological order which is characterized by non-local correlations that depend on the system topology. Such systems can exhibit remarkable phenomena such as quasiparticles with anyonic statistics and have been proposed as candidates for naturally error-free quantum computation. However, anyons have never been observed in nature directly. Here, we describe how to unambiguously detect and characterize such states in recently proposed spinlattice realizations using ultracold atoms or molecules trapped in an optical lattice. We propose an experimentally feasible technique to access non-local degrees of freedom by carrying out global operations on trapped spins mediated by an optical cavity mode. We show how to reliably read and write topologically protected quantum memory using an atomic or photonic qubit. Furthermore, our technique can be used to probe statistics and dynamics of anyonic excitations.

In the context of quantum chaos, both theory and numerical analysis predict large fluctuations of the tunneling transition probabilities when irregular dynamics is present at the classical level. Here we consider the nondissipative quantum evolution of cold atoms trapped in a time-dependent modulated periodic potential generated by two laser beams. We give some precise guidelines for the observation of chaos-assisted tunneling between invariant phase space structures paired by time-reversal symmetry.

We study the diffusive propagation of multiply scattered light in an optically thick cloud of cold rubidium atoms illuminated by a quasiresonant laser beam. In the vicinity of a sharp atomic resonance, the energy transport velocity of the scattered light is almost 5 orders of magnitude smaller than the vacuum speed of light, reducing strongly the diffusion constant. We verify the theoretical prediction of a frequency-independent transport time around the resonance. We also observe the effect of the residual velocity of the atoms at long times.

Topological insulators are a broad class of unconventional materials that are insulating in the interior but conduct along the edges. This edge transport is topologically protected and dissipationless. Until recently, all existing topological insulators, known as quantum Hall states, violated time-reversal symmetry. However, the discovery of the quantum spin Hall effect demonstrated the existence of novel topological states not rooted in time-reversal violations. Here, we lay out an experiment to realize time-reversal topological insulators in ultra-cold atomic gases subjected to synthetic gauge fields in the near-field of an atom-chip. In particular, we introduce a feasible scheme to engineer sharp boundaries where the "edge states" are localized. Besides, this multi-band system has a large parameter space exhibiting a variety of quantum phase transitions between topological and normal insulating phases. Due to their unprecedented controllability, cold-atom systems are ideally suited to realize topological states of matter and drive the development of topological quantum computing.

We study theoretically, numerically, and experimentally the relaxation of a collisionless gas in a quadrupole trap after a momentum kick. The non-separability of the potential enables a quasi thermalization of the single particle distribution function even in the absence of interactions. Suprinsingly, the dynamics features an effective decoupling between the strong trapping axis and the weak trapping plane. The energy delivered during the kick is redistributed according to the symmetries of the system and satisfies the Virial theorem, allowing for the prediction of the final temperatures. We show that this behaviour is formally equivalent to the relaxation of massless relativistic Weyl fermions after a sudden displacement from the center of a harmonic trap.

An effective field theory developed for systems interacting through short-range interactions can be applied to systems of cold atoms with a large scattering length and to nucleons at low energies. It is therefore the ideal tool to analyze the universal properties associated with the Efimov effect in three- and four-body systems. In this progress report, we will discuss recent results obtained within this framework and report on progress regarding the inclusion of higher order corrections associated with the finite range of the underlying interaction.

Istituto Elettrotecnico Nazionale Galileo Ferraris (IEN), National and Physikalisch-Technische Bundesanstalt (PTB) operate cold-atom based primary frequency standards which are capable of realizing the SI second with a relative uncertainty of 1 × 10 −15 or even below. These institutes performed an intense comparison campaign of selected frequency references maintained in their laboratories during about 25 days in October/November 2004. Active hydrogen maser reference standards served as frequency references for the institutes' fountain frequency standards. Three techniques of frequency (and time) comparisons were employed. Two-way satellite time and frequency transfer (TWSTFT) was performed in an intensified measurement schedule of 12 equally spaced measurements per day. The data of dual-frequency geodetic Global Positioning System (GPS) receivers were processed to yield an ionosphere-free linear combination of the code observations from both GPS frequencies, typically referred to as GPS TAI P3 analysis. Last but not least, the same GPS raw data were separately processed, allowing GPS carrier-phase (GPS CP) based frequency comparisons to be made. These showed the lowest relative frequency instability at short averaging times of all the methods. The instability was at the level of 1 part in 10 15 at one-day averaging time using TWSTFT and GPS CP. The GPS TAI P3 analysis is capable of giving a similar quality of data after averaging over two days or longer. All techniques provided the same mean frequency difference between the standards involved within the 1σ measurement uncertainty of a few parts in 10 16 . The frequency differences between the three fountains of IEN (IEN-CsF1), NPL (NPL-CsF1) and OP (OP-FO2) were evaluated. Differences lower than the 1σ measurement uncertainty were observed between NPL and OP, whereas the IEN fountain deviated by about 2σ from the other two fountains.

Exp Astron (2009) 23:573-610 575 reference frame for the Earth's gravitational potential and will allow a new approach to mapping Earth's gravity field with very high spatial resolution. The mission was proposed as a class-M mission to ESA's Cosmic Vision Program 2015-2025.

We theoretically investigate a tight binding model of fermions hopping on the square-octagon lattice which consists of a square lattice with plaquette corners themselves decorated by squares. Upon the inclusion of second neighbor spin-orbit coupling or non-Abelian gauge fields, time-reversal symmetric topological Z2 band insulators are realized. Additional insulating and gapless phases are also realized via the non-Abelian gauge fields. Some of the phase transitions involve topological changes to the Fermi surface. The stability of the topological phases to various symmetry breaking terms is investiaged via the entanglement spectrum. Our results enlarge the number of known exactly solvable models of Z2 band insulators, and are potentially relevant to the realization and identification of topological phases in both the solid state and cold atomic gases.

We investigate the properties of the Lieb lattice, i.e a face-centered square lattice, subjected to external gauge fields. We show that an Abelian gauge field leads to a peculiar quantum Hall effect, which is a consequence of the single Dirac cone and the flat band characterizing the energy spectrum. Then we explore the effects of an intrinsic spin-orbit term -a non-Abelian gauge fieldand demonstrate the occurrence of the quantum spin Hall effect in this model. Besides, we obtain the relativistic Hamiltonian describing the Lieb lattice at low energy and derive the Landau levels in the presence of external Abelian and non-Abelian gauge fields. Finally, we describe concrete schemes for realizing these gauge fields with cold fermionic atoms trapped in an optical Lieb lattice. In particular, we provide a very efficient method to reproduce the intrinsic (Kane-Mele) spin-orbit term with assisted-tunneling schemes. Consequently, our model could be implemented in order to produce a variety of topological states with cold-atoms.

We describe two experimental tests of the Equivalence Principle that are based on frequency measurements between precision oscillators and/or highly accurate atomic frequency standards. Based on comparisons between the hyperfine frequencies of 87 Rb and 133 Cs in atomic fountains, the first experiment constrains the stability of fundamental constants. The second experiment is based on a comparison between a cryogenic sapphire oscillator and a hydrogen maser. It tests Local Lorentz Invariance. In both cases, we report recent results which improve significantly over previous experiments.

We analyze and experimentally demonstrate a new (temporal) Talbot effect, where a pulsed phase grating is applied to a cloud of cold atoms (Bose-Einstein condensate). In contrast to the usual (spatial) Talbot effect, our atoms gain kinetic energy when diffracted by the pulsed grating. The energy gain and the matter-wave-dispersion relation result in an exact (no paraxial approximation) Talbot effect where the initial wave front is reconstructed at multiples of a "Talbot time" T T . We demonstrate the Talbot effect by applying a second pulsed phase grating after a variable delay. When this second grating is applied at even (odd) multiples of T T ͞2, it doubles (cancels) the effect of the first pulsed grating.

This article describes the work performed at BNM-SYRTE (Observatoire de Paris) in the past few years, toward the improvement and the use of microwave frequency standards using laser-cooled atoms. First, recent improvements of the 133 Cs and 87 Rb atomic fountains are described. An important advance is the achievement of a fractional frequency instability of 1.6 × 10 −14 τ −1/2 where τ is the measurement time in seconds, thanks to the routine use of a cryogenic sapphire oscillator as an ultra-stable local frequency reference. The second advance is a powerful method to control the frequency shift due to cold collisions. These two advances lead to a fractional frequency in stability of 2 × 10 −16 at 50 000 s between two independent primary standards. In addition, these clocks realize the SI second with an accuracy of 7 × 10 −16 , one order of magnitude below that of uncooled devices. Tests of fundamental physical laws constitute an important field of application for highly accurate atomic clocks. In a second part, we describe tests of possible variations of fundamental constants using 87 Rb and 133 Cs fountains. The third part is an update on the cold atom space clock PHARAO developed in collaboration with CNES. This clock is one of the main instruments of the ACES/ESA mission which will fly on board the International Space Station in 2007-2008, enabling a new generation of relativity tests. To cite this article: S. Bize et al., C. R. Physique 5 (2004).  2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.

We discuss the importance of the fermion nodes for the quantum Monte Carlo (QMC) methods and find two cases of the exact nodes. We describe the structure of the generalized pairing wave functions in Pfaffian antisymmetric form and demonstrate their equivalency with certain class of configuration interaction wave functions. We present the QMC calculations of a model fermion system at unitary limit. We find the system to have the energy of E = 0.425E free and the condensate fraction of α = 0.48. Further we also perform the QMC calculations of the potential energy surface and the electric dipole moment along that surface of the LiSr molecule. We estimate the vibrationally averaged dipole moment to be D

This article describes the work performed at BNM-SYRTE (Observatoire de Paris) in the past few years, toward the improvement and the use of microwave frequency standards using laser-cooled atoms. First, recent improvements of the 133 Cs and 87 Rb atomic fountains are described. An important advance is the achievement of a fractional frequency instability of 1.6 × 10 −14 τ −1/2 where τ is the measurement time in seconds, thanks to the routine use of a cryogenic sapphire oscillator as an ultra-stable local frequency reference. The second advance is a powerful method to control the frequency shift due to cold collisions. These two advances lead to a fractional frequency in stability of 2 × 10 −16 at 50 000 s between two independent primary standards. In addition, these clocks realize the SI second with an accuracy of 7 × 10 −16 , one order of magnitude below that of uncooled devices. Tests of fundamental physical laws constitute an important field of application for highly accurate atomic clocks. In a second part, we describe tests of possible variations of fundamental constants using 87 Rb and 133 Cs fountains. The third part is an update on the cold atom space clock PHARAO developed in collaboration with CNES. This clock is one of the main instruments of the ACES/ESA mission which will fly on board the International Space Station in 2007-2008, enabling a new generation of relativity tests. To cite this article: S. Bize et al., C. R. Physique 5 (2004).  2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.

We analyze the interplay of adiabatic rotation and Rashba spin-orbit coupling on the BCS-BEC evolution of a harmonically trapped Fermi gas in two dimensions under the assumption that vortices are not excited. First, by taking the trapping potential into account via both the semiclassical and exact quantum-mechanical approaches, we firmly establish the parameter regime where the noninteracting gas forms a ring-shaped annulus. Then, by taking the interactions into account via the BCS mean-field approximation, we study the pair-breaking mechanism that is induced by rotation, i.e., the Coriolis effects. In particular, we show that the interplay allows for the possibility of creating either an isolated annulus of rigidly rotating normal particles that is disconnected from the central core of nonrotating superfluid pairs or an intermediate mediator phase where the superfluid pairs and normal particles coexist as a partially rotating gapless superfluid.

Limits on the long-term stability and accuracy of a second generation cold atom gravimeter are investigated. We demonstrate a measurement protocol based on four interleaved measurement configurations, which allows rejection of most of the systematic effects, but not those related to Coriolis acceleration and wave-front distortions. Both are related to the transverse motion of the atomic cloud. Carrying out measurements with opposite orientations with respect to the Earth's rotation vector direction allows us to separate the effects and correct for the Coriolis shift. Finally, measurements at different atomic temperatures are presented and analyzed. In particular, we show the difficulty of extrapolating these measurements to zero temperature, which is required in order to correct for the bias due to wave-front distortions.

This paper describes advances in microwave frequency standards using laser-cooled atoms at BNM-SYRTE. First, recent improvements of the 133 Cs and 87 Rb atomic fountains are described. Thanks to the routine use of a cryogenic sapphire oscillator as an ultra-stable local frequency reference, a fountain frequency instability of 1.6 × 10 −14 τ −1/2 where τ is the measurement time in seconds is measured. The second advance is a powerful method to control the frequency shift due to cold collisions. These two advances lead to a frequency stability of 2 × 10 −16 at 50 000 s for the first time for primary standards. In addition, these clocks realize the SI second with an accuracy of 7 × 10 −16 , one order of magnitude below that of uncooled devices. In a second part, we describe tests of possible variations of fundamental constants using 87 Rb and 133 Cs fountains. Finally we give an update on the cold atom space clock PHARAO developed in collaboration with CNES. This clock is one of the main instruments of the ACES/ESA mission which is scheduled to fly on board the International Space Station in 2008, enabling a new generation of relativity tests.

We describe the operation of a light pulse interferometer using cold 87Rb atoms in reduced gravity. Using a series of two Raman transitions induced by light pulses, we have obtained Ramsey fringes in the low gravity environment achieved during parabolic flights. With our compact apparatus, we have operated in a regime which is not accessible on ground. In the much lower gravity environment and lower vibration level of a satellite, our cold atom interferometer could measure accelerations with a sensitivity orders of magnitude better than the best ground based accelerometers and close to proven spaced-based ones.

This colloquium gives an overview of recent theoretical and experimental progress in the area of nonequilibrium dynamics of isolated quantum systems. We particularly focus on quantum quenches: the temporal evolution following a sudden or slow change of the coupling constants of the system Hamiltonian. We discuss several aspects of the slow dynamics in driven systems and emphasize the universality of such dynamics in gapless systems with specific focus on dynamics near continuous quantum phase transitions. We also review recent progress on understanding thermalization in closed systems through the eigenstate thermalization hypothesis and discuss relaxation in integrable systems. Finally we overview key experiments probing quantum dynamics in cold atom systems and put them in the context of our current theoretical understanding.

We introduce novel schemes for quantum computing based on local measurements on entangled resource states. This work elaborates on the framework established in [Phys. Rev. Lett. 98, 220503 (2007), quant-ph/0609149]. Our method makes use of tools from many-body physics -matrix product states, finitely correlated states or projected entangled pairs states -to show how measurements on entangled states can be viewed as processing quantum information. This work hence constitutes an instance where a quantum information problem -how to realize quantum computation -was approached using tools from many-body theory and not vice versa. We give a more detailed description of the setting, and present a large number of new examples. We find novel computational schemes, which differ from the original one-way computer for example in the way the randomness of measurement outcomes is handled. Also, schemes are presented where the logical qubits are no longer strictly localized on the resource state. Notably, we find a great flexibility in the properties of the universal resource states: They may for example exhibit non-vanishing long-range correlation functions or be locally arbitrarily close to a pure state. We discuss variants of Kitaev's toric code states as universal resources, and contrast this with situations where they can be efficiently classically simulated. This framework opens up a way of thinking of tailoring resource states to specific physical systems, such as cold atoms in optical lattices or linear optical systems.

Dynamics of vortex clusters is essential for understanding diverse superfluid phenomena. In this paper, we examine the dynamics of vortex quadrupoles in a trapped two-dimensional (2D) Bose-Einstein condensate. We find that the movement of these vortex-clusters fall into three distinct regimes which are fully described by the radial positions of the vortices in a 2D isotropic harmonic trap, or by the major radius (minor radius) of the elliptical equipotential lines decided by the vortex positions in a 2D anisotropic harmonic trap. In the " recombination " and " exchange " regimes the quadrupole structure maintains, while the vortices annihilate each other permanently in the " annihilation " regime. We find that the mechanism of the charge flipping in the " exchange " regime and the disappearance of the quadrupole structure in the " annihilation " regime are both through an intermediate state where two vortex dipoles connected through a soliton ring. We give the parameter ranges for these three regimes in coordinate space for a specific initial configuration and phase diagram of the vortex positions with respect to the Thomas-Fermi radius of the condensate. We show that the results are also applicable to systems with quantum fluctuations for the short-time evolution. Vortices could be observed in most realm of physics such as hydrodynamics, superfluids, optical fields and even cosmology. The dynamics of quantized vortices is essential for understanding diverse superfluid phenomena such as critical-current densities in superconductors 1 , quantum turbulence 2–6 and novel quantum phases 7–11 in superfluids. Vortices are also topological defects that play key roles in transport, dissipative and coherent properties 12–16 of superfluid systems. The pioneering work of Yarmchuk et al. in 1979 successfully located the ends of parallel vortex lines in superfluid Helium 17. The real-time dynamics of vortex lattice in type II super conductors was observed in 1992 18. Until 2006, direct observation of quantized vortex lines in superfluid Helium in arbitrary three-dimensional configurations has been achieved 19. The realization of Bose-Einstein condensates (BECs) provides an accessible and highly controllable platform for fundamental studies of superfluid vortex dynamics, and has been followed by various theoretical investigations and numerical analyses. It is remarkable that, comparing with other systems ruled by nonlinear Schrödinger equations , BECs are the ideal laboratory for finding these nonlinear excitations due to larger interaction strengths and easier tunable parameters. The size of vortex cores in a BEC is proportional to the healing length of the condensate,  ζ ρ = mg / 2 , where m is the mass of atoms, ρ is the density of the condensate in the absence of vortex, and g is the interatomic interaction strength. For given trap frequencies, g is proportional to the scattering length between atoms, which can be easily adjusted by using magnetic or optical Feshbach resonances 20–22. Due to the matter wave nature of condensates 23 , vortices can be detected in atomic interference. Matthews et al. 24 firstly demonstrated vortex production through an interference measurement, and later, Inouye et al. observed vortex phase singular-ities as dislocations in the interference fringes in BECs 25. As the size of the vortex cores in a trapped condensate is ordinarily several times smaller than the wavelength of light used for imaging, in experiments the condensates are usually allowed to expand to a point at which the vortex cores are large compared to the imaging resolution 24–30. Many works have been done to develop the vortex detection techniques and to understand vortex dynamics during the interference of BECs 25,31–36 , which is important for the applications of matter-wave interferometry. However, the direct, in situ observation of vortices in a trapped condensate without expansion was wachieved

Condensation of atom pairs with finite total momentum is expected in a portion of the phase diagram of a two-component fermionic cold-atom system. This unusual condensate can be identified by detecting the exotic higher-Landau-level ͑HLL͒ vortex lattice states it can form when rotated. With this motivation, we have solved the linearized gap equations of a polarized cold-atom system in a Landau-level basis to predict experimental circumstances under which HLL vortex lattice states occur.

We report on the study of the noise properties of laser light propagating through a cold 87 Rb atomic sample held in a magneto-optical trap. The laser is tuned around the Fg = 2 → Fe = 1, 2 D 1 transitions of 87 Rb. We observe quadrature-dependent noise in the light signal, an indication that it may be possible to produce squeezed states of light. We measure the minimum and maximum phase-dependent noise as a function of detuning and compare these results to theoretical predictions to explore the best conditions for light squeezing using cold atomic Rb.

We propose a new possibility to form ultracold molecules, via photoassociation of a pair of cold atoms into vibrational levels of the external well of an excited electronic state located at intermediate interatomic distance (≈ 20 Bohr radii), and embedded in the dissociation continuum above its dissociation limit. The existence of such a well is demonstrated by conventional free-free absorption spectroscopy at thermal energies. Estimation for cold atom photoassociation and cold molecule formation rates are obtained within a perturbative approach [Drag et al., IEEE J. Quant. Electr. 36, 1378], and are found observable for usual conditions of photoassociation experiments.

We present a general analysis of two-dimensional optical lattice models that give rise to topologically non-trivial insulating states. We identify the main ingredients of the lattice models that are responsible for the non-trivial topological character and argue that such states can be realized within a large family of realistic optical lattice Hamiltonians with cold atoms. We focus our quantitative analysis on the properties of topological states with broken time-reversal symmetry specific to cold-atom settings. In particular, we analyze finite-size effects, multi-orbital phenomena that give rise to a variety of distinct topological states and transitions between them, the dependence on the trap geometry, and most importantly, the behavior of the edge states for different types of soft and hard boundaries. Furthermore, we demonstrate the possibility of experimentally detecting the topological states through light Bragg scattering of the edge and bulk states.

We present a new experimental system (the "atom-optics billiard") and demonstrate chaotic and regular dynamics of cold, optically trapped atoms. We show that the softness of the walls and additional optical potentials can be used to manipulate the structure of phase space.

The role of synchronization on the current of particles in periodically-forced overdamped ratchets is studied. The main goal is to explain the mean velocity and diffusion on the basis of synchronization between the individual particles motion and the driving force. Both normal and anomalous diffusion are considered. Three cases are studied: (1) a perfect lattice with a sinusoidal driving force, (2) a lattice with quenched disorder, and (3) a perfect lattice with a square driving force. In case (1) synchronization is guaranteed over the whole parameter space and the diffusion coefficient is zero. In case (2) a trapping mechanism appears due to partial loss of synchronization. The mean velocity of the particles and the diffusion coefficient are found to have a non-monotonic dependence on the quenched noise strength. These non-trivial results are explained on the basis of the synchronized motion of case (1). Finally, in case (3), the system has neither temporal nor quenched noise but the strong nonlinearity of the driving force produces a very rich bifurcation pattern with synchronized as well as chaotic regions. This unexpected behavior is produced by the strong nonlinearity produced by the switching between two exactly solvable subsystems, each with its own characteristic transit time, so that the ratio between the period of the driving force and the transit times can be analyzed. Our results can be experimentally confirmed in a number of systems, including the three-junction superconducting quantum interference devices ratchet, the rocking ratchet effect for cold atoms, and the Josephson vortex ratchet.

We present a scheme for the quantum teleportation of the polarization state of a photon employing a cross-Kerr medium. The experimental feasibility of the scheme is discussed and we show that, using the recently demonstrated ultraslow light propagation in cold atomic media, our proposal can be realized with presently available technology. PACS numbers: 03.67Hk, 42.65.-k, 03.65.Bz, 42.50.Gy Quantum entanglement is a powerful resource at the basis of the extraordinary development of quantum information. Among the most fascinating examples of the possibilities offered by sharing quantum entanglement are quantum teleportation [1], quantum dense coding [2], entanglement swapping [3], quantum cryptography [4]

The HORACE device is a compact cold atom clock where about 10 8 cesium atoms are laser cooled at a few µK, then interrogated and detected directly in a 20 cm 3 spherical microwave cavity. The optimization of the short term stability with the cooling and interrogation durations is presented, leading to an estimation of the Allan deviation of σy(τ ) = 1 10 −13 τ −1/2 on earth and σy(τ ) = 7 10 −14 τ −1/2 in space. The quantum projection noise, the Dick effect and the detection laser noises are taken into account. The calculations are based on a preliminary model for the recapture of cold atoms, in reasonable agreement with measurements.

We explain the dynamics of cold atoms, initially trapped and cooled in a magneto-optic trap, in a monochromatic stationary standing electromagnetic wave field. In the large-detuning limit, the system is modeled as a nonlinear quantum pendulum. We show that the wavepacket evolution of the quantum particle probes parametric regimes in the quantum pendulum that support the classical period and quantum-mechanical revival and superrevival phenomena. Interestingly, complete reconstruction, in particular the parametric regime at quantum revival times, is independent of the potential height.

Space-based experiments today can uniquely address important questions related to the fundamental laws of Nature. In particular, high-accuracy physics experiments in space can test relativistic gravity and probe the physics beyond the Standard Model; they can perform direct detection of gravitational waves and are naturally suited for precision investigations in cosmology and astroparticle physics. In addition, atomic physics has recently shown substantial progress in the development of optical clocks and atom interferometers. If placed in space, these instruments could turn into powerful high-resolution quantum sensors greatly benefiting fundamental physics. We discuss the current status of space-based research in fundamental physics, its discovery potential, and its importance for modern science. We offer a set of recommendations to be considered by the upcoming National Academy of Sciences' Decadal Survey in Astronomy and Astrophysics. In our opinion, the Decadal Survey shoul...

We study the properties of an ultracold Fermi gas loaded in an optical square lattice and subjected to an external and classical non-Abelian gauge field. We show that this system can be exploited as an optical analogue of relativistic quantum electrodynamics, offering a remarkable route to access the exotic properties of massless Dirac fermions with cold atoms experiments. In particular we show that the underlying Minkowski space-time can also be modified, reaching anisotropic regimes where a remarkable anomalous quantum Hall effect and a squeezed Landau vacuum could be observed.

Quantum dots in photonic crystals are interesting because of their potential in quantum information processing and as a testbed for cavity quantum electrodynamics. Recent advances in controlling and coherent probing of such systems open the possibility of realizing quantum networks originally proposed for atomic systems. Here, we demonstrate that non-classical states of light can be coherently generated using a quantum dot strongly coupled to a photonic crystal resonator. We show that the capture of a single photon into the cavity affects the probability that a second photon is admitted. This probability drops when the probe is positioned at one of the two energy eigenstates corresponding to the vacuum Rabi splitting, a phenomenon known as photon blockade, the signature of which is photon antibunching. In addition, we show that when the probe is positioned between the two eigenstates, the probability of admitting subsequent photons increases, resulting in photon bunching. We call this process photon-induced tunnelling. This system represents an ultimate limit for solid-state nonlinear optics at the single-photon level. Along with demonstrating the generation of non-classical photon states, we propose an implementation of a single-photon transistor in this system.

We discuss the suitability of holographically generated optical potentials for the investigation of superfluidity in ultracold atoms. By using a spatial light modulator and a feedback enabled algorithm we generate a smooth ring with variable bright regions that can be dynamically rotated to stir ultracold atoms and induce superflow. We also comment on its future integration into a cold atoms experiment.