Thermal Cloud Research Articles

Composite pulses for interferometry in a thermal cold atom cloud

Atom interferometric sensors and quantum information processors must maintain coherence while the evolving quantum wavefunction is split, transformed and recombined, but suffer from experimental inhomogeneities and uncertainties in the speeds and paths of these operations. Several error-correction techniques have been proposed to isolate the variable of interest. Here we apply composite pulse methods to velocity-sensitive Raman state manipulation in a freely-expanding thermal atom cloud. We compare several established pulse sequences, and follow the state evolution within them. The agreement between measurements and simple predictions shows the underlying coherence of the atom ensemble, and the inversion infidelity in an 80 micro-Kelvin atom cloud is halved. Composite pulse techniques, especially if tailored for atom interferometric applications, should allow greater interferometer areas, larger atomic samples and longer interaction times, and hence improve the sensitivity of quantum technologies from inertial sensing and clocks to quantum information processors and tests of fundamental physics.

Evaporative cooling of cold atoms at surfaces

We theoretically investigate the evaporative cooling of cold rubidium atoms that are brought close to a solid surface. The dynamics of the atom cloud are described by coupling a dissipative Gross-Pitaevskii equation for the condensate with a quantum Boltzmann description of the thermal cloud (the Zaremba-Nikuni-Griffin method). We have also performed experiments to allow for a detailed comparison with this model and find that it can capture the key physics of this system provided the full collisional dynamics of the thermal cloud are included. In addition, we suggest how to optimize surface cooling to obtain the purest and largest condensates.

Self-localized state and solitons in a Bose-Einstein-condensate–impurity mixture at finite temperature

We study the properties of a Bose-Einstein-condensate (BEC)--impurity mixture at finite temperature employing the time-dependent Hartree-Fock Bogoliubov (TDHFB) theory which is a set of coupled nonlinear equations of motion for the condensate and its normal and anomalous fluctuations on the one hand and for impurity on the other. The numerical solutions of these equations in the static quasi-one-dimensional regime show that the thermal cloud and the anomalous density are deformed as happens to the condensate and the impurity becomes less localized at nonzero temperatures. Effects of the BEC fluctuations on the self-trapping state are studied in homogeneous weakly interacting BEC-impurity at low temperature. The self-trapping threshold is also determined in such a system. The formation of solitons in the BEC-impurity mixture at finite temperature is investigated.

Vortex reconnections in atomic condensates at finite temperature

The study of vortex reconnections is an essential ingredient of understanding superfluid turbulence, a phenomenon recently also reported in trapped atomic Bose-Einstein condensates. In this work we show that, despite the established dependence of vortex motion on temperature in such systems, vortex reconnections are actually temperature independent on the typical length/time scales of atomic condensates. Our work is based on a dissipative Gross-Pitaevskii equation for the condensate, coupled to a semiclassical Boltzmann equation for the thermal cloud (the Zaremba-Nikuni-Griffin formalism). Comparison to vortex reconnections in homogeneous condensates further show reconnections to be insensitive to the inhomogeneity in the background density.

Periodic array of Bose-Einstein condensates in a magnetic lattice

We report the realization of a periodic array of Bose-Einstein condensates of 87Rb |F = 1; mF = -1> atoms trapped in a one-dimensional magnetic lattice close (8 micrometres) to the surface of an atom chip. A clear signature for the onset of BEC in the magnetic lattice is provided by in-situ site-resolved radiofrequency (RF) spectra, which exhibit a pronounced bimodal distribution consisting of a narrow component characteristic of a BEC together with a broad thermal cloud component. Similar bimodal distributions are found for various sites across the magnetic lattice. The realization of a periodic array of multiple BECs in a magnetic lattice represents a major advance towards the implementation of magnetic lattices to simulate many-body condensed matter phenomena in lattices of complex geometry and arbitrary period.

Dynamics of matter-wave condensates with time-dependent two- and three-body interactions trapped by a linear potential in the presence of atom gain or loss.

Bose-Einstein condensates with time varying two- and three-body interatomic interactions, confined in a linear potential and exchanging atoms with the thermal cloud are investigated. Using the extended tanh-function method with an auxiliary equation, i.e., the Lenard equation, many exact solutions describing the dynamics of matter-wave condensates are derived. An important issue is the time management of the cubic and the quintic nonlinearities by tuning the rate of exchange of atoms between the condensate and the thermal background. In addition, adjusting the strength of the linear potential, the rate of exchange of atoms, and many other free parameters allow one to control many features of the condensate such as its height, width, position, velocity, acceleration, and its direction, respectively. Full numerical solutions corroborate the analytical predictions.

Measurement of Critical correlations in an ultracold Bose gas by means of a temporal Talbot-Lau interferometery

We report the results of a study of measuring the correlation length at the Lambda critical phase transition point in an ultra-cold Bose gas with a temporal Talbot-Lau (TL) interferometery. Near the critical temperature, the correlation length increase exponentially and its critical exponent factor is measured around 0.67, which is a universal value in quantum gas. In the experiment we filtered the fraction of condensate from the thermal cloud at the Lambda critical phase transition point by means of the TL interferometer technique.

Atmospheric thermal structure and cloud features in the southern hemisphere of Venus as retrieved from VIRTIS/VEX radiation measurements

Thermal structure and cloud features in the atmosphere of Venus are investigated using spectroscopic nightside measurements recorded by the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) aboard ESA’s Venus Express mission in the moderate resolution infrared mapping channel (M-IR, 1–5μm). New methodical approaches and retrieval results for the northern hemisphere have been recently described by Haus et al. (Haus, R., Kappel, D., Arnold, G. [2013]. Planet. Space Sci. 89, 77–101. http://dx.doi.org/10.1016/j.pss.2013.09.020). Now, southern hemisphere maps of mesospheric temperature and cloud parameter fields are presented that cover variations with altitude, latitude, local time, and mission time. Measurements from the entire usable data archive are utilized comprising radiation spectra recorded during eight Venus solar days between April 2006 and October 2008.Zonal averages of retrieved temperature altitude profiles in both hemispheres are very similar and give evidence of global N–S axial symmetry of atmospheric temperature structure. Cold collar and warmer polar vortex regions exhibit the strongest temperature variability with standard deviations up to 8.5K at 75°S and 63km altitude compared with about 1.0K at low and mid latitudes above 75km. The mesospheric temperature field strongly depends on local time. At altitudes above about 75km, the atmosphere is warmer in the second half of night, while the dawn side at lower altitudes is usually colder than the dusk side by about 8K. Local minimum temperature of 220K occurs at 03:00h local time at 65km and 60°S. Temperature standard deviation at polar latitudes is particularly large near midnight. Temperature variability with solar longitude is forced by solar thermal tides with a dominating diurnal component. The influence of observed cloud parameter changes on retrieved mesospheric zonal average temperature structure is moderate and does not exceed 2–3K at altitudes between 60 and 75km. The mesospheric thermal structure was essentially stable with Julian date between 2006 and 2008.Global N–S axial symmetry is also observed in cloud structures. Cloud top altitude at 1μm slowly decreases from 71km at the equator to 70km at 45–50° and rapidly drops poleward of 50°. It reaches 61km over both poles. Average particle size in the vertical cloud column increases from mid latitudes toward the poles and also toward the equator resulting in minimum and maximum zonal average cloud opacities of about 32 and 42 and a planetary average of 36.5 at 1μm. Zonal averages of cloud features are similar at different solar days, but variations with local time are very complex and inseparably associated with the superrotation of the clouds.

Critical correlations in an ultra-cold Bose gas revealed by means of a temporal Talbot–Lau interferometer

The transition from a thermal cloud to a Bose–Einstein condensate (BEC) in an interacting ultra-cold Bose gas is a prototype in a universality class of diverse phase transitions. For a trapped ultra-cold Bose gas, we were able to study the critical regime both above and below the critical temperature with a Talbot–Lau interferometer, observing a peak in the correlation length. From this peak, we managed to determine the universal critical exponents for this phase transition as well as the finite-size and interaction corrections to the critical temperature. The results are all in quantitative agreement with theory. This work demonstrates the potential application of the Talbot–Lau interferometer to a wide range of critical phase transitions in ultra-cold atomic gases.

Self-consistent retrieval of temperature profiles and cloud structure in the northern hemisphere of Venus using VIRTIS/VEX and PMV/VENERA-15 radiation measurements

Improved radiative transfer simulation and multi-window retrieval procedures (MWR) are described that are applied to investigate thermal structure and cloud features in the nightside atmosphere of Venus over the northern hemisphere. Comparative analyses of spectroscopic data, which were recorded independently in different parts of the infrared spectrum by the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS-M-IR) aboard ESA's Venus Express space probe and the Profile Measuring Instrument for Venus (PMV, Fourier spectrometer FS-1/4) during the earlier Soviet Venera-15 experiment, are combined with self-consistent temperature profile and cloud parameter retrievals. MWR performance is studied using synthetic spectra at different latitudes and for different atmospheric temperature profiles and cloud parameters. VIRTIS and PMV retrieval result comparisons are used to determine constraints on physical state parameter variations, especially on applicability of different cloud models. An analytically parameterized initial model of four-modal cloud altitude distributions is proposed. Together with retrieved cloud parameters, which encompass individual mode factors and cloud upper altitude boundary, it permits optimum fits of measured radiances and brightness temperatures in the 4.3 and 15µm CO2 bands utilized for atmospheric temperature profile retrievals. A new multi-spectrum retrieval (MSR) method (Kappel et al., 2012, Kappel, in press) provides deep atmosphere CO2 opacity correction parameters, which affect cloud parameter retrievals from short-wavelength emission windows.The main features of retrieved latitude and altitude-dependent temperature fields (zonal averages) are in good quantitative accordance with earlier obtained results. Prominent structures like ‘cold collar’ and ‘hot dipole’ are re-examined. The cold inversion layer is centered at about 62–66km and 55 and 75°N. Below the collar, temperature usually decreases with latitude at the same altitude, while it typically increases toward the pole above 70km. Absolute temperature differences between zonal averages of VIRTIS and PMV results are usually below 3K between 58 and 80km, while a 9K lower VIRTIS temperature is only observed at 75°N near 60km. Both VIRTIS and PMV retrievals reveal a slow decrease of cloud top altitude from about 71km at the equator to about 70km at mid latitudes. Northward of 55°N, it quickly descends down to about 61.5km at polar latitudes in accordance with earlier results. Cloud particle size and total cloud optical depth exhibit a minimum at 50°N and increase towards the equator and the North Pole. The hemispheric average of cloud opacity derived from VIRTIS data is 34.7 at 1µm.

Collective modes and generation of a new vortex in a trapped Bose gas at finite temperature

The dynamics of Bose-Einstein condensate (BEC) is studied at nonzero temperatures using our variational time-dependent-Hartree-Fock-Bogoliubov formalism. We have shown that this approach is an efficient tool to study the expansion and collective excitations of the condensate, the thermal cloud, and the anomalous correlation function at nonzero temperatures. We have found that the condensate and the anomalous density have the same breathing oscillations. We have investigated, on the other hand, the behavior of a single quantized vortex in a harmonically trapped BEC at nonzero temperatures. Generalized expressions for vortex excitations, vortex core size, and Kelvin modes have been derived. An important and somehow surprising result is that the numerical solution of our equations predicts that the vortex core is partially filled by the thermal atoms at nonzero temperatures. We have shown that the effect of thermal fluctuations is important and it may lead to enhancing the size of the vortex core. The behavior of the singly anomalous vortex has also been studied at nonzero temperatures.

Aircraft Measurements of Atmospheric Aerosol over North China in Autumn

Using an aircraft equipped with Passive Cavity Aerosol Spectrum Probe (PCASP-100X) and streamwise thermal gradient cloud condensation nuclei (CCN) counter, six flight measurements of atmospheric aerosol and CCN were conducted over North China in autumn. Five flight observations over Shijiazhuang urban area show that there is great difference of aerosol microphysical character between clear day and haze day. Vertical distributions show that aerosols mainly concentrated on the levels from near surface to the low level of troposphere and the concentration generally decreased with height increasing. The max aerosol concentration was 8110 cm-3on haze day and 1614 cm-3on clear day. There was more than 4 times difference in concentration of aerosol in boundary layer between haze day and clear day. CCN has the similar vertical distributions as aerosol. Most CCN concentrated on the boundary layer suggesting that the main source of CCN is from surface. Observation over Bohai Bay shows that the marine aerosol and CCN were greatly influenced by anthropogenic emissions.

Planck Distribution of Phonons in a Bose-Einstein Condensate

The Planck distribution of photons emitted by a blackbody led to the development of quantum theory. An analogous distribution of phonons should exist in a Bose-Einstein condensate. We observe this Planck distribution of thermal phonons in a 3D condensate. This observation provides an important confirmation of the basic nature of the condensate's quantized excitations. In contrast to the bunching effect, the density fluctuations are seen to increase with increasing temperature. This is due to the nonconservation of the number of phonons. In the case of rapid cooling, the phonon temperature is out of equilibrium with the surrounding thermal cloud. In this case, a Bose-Einstein condensate is not as cold as previously thought. These measurements are enabled by our in situ k-space technique.

Chaotic dynamics of dilute thermal atom clouds on stationary optical Bessel beams

We characterize the semiclassical dynamics of dilute thermal atom clouds located in three-dimensional optical lattices generated by stationary optical Bessel beams. The dynamics of the cold atoms is explored in the quasi-Hamiltonian regime that arises using laser beams with far-off resonance detuning. Although the transverse structure of Bessel beams exhibits a complex topological structure, it is found that the longitudinal motion along the main propagation axis of the beam is the detonator of a high sensitivity of the atoms' motion to the initial conditions. This effect would not be properly described by bidimensional models. We show that an experimental implementation can be highly simplified by an analysis of the behaviour of the dynamical system under scale transformations. Experimentally feasible signatures of the chaotic dynamics of the atom clouds are also identified.

Dark-soliton dynamics in a two-species Bose–Einstein condensate with the external potential and thermal cloud effects

Considering the time-dependent external potential and thermal cloud effects, this paper investigates via symbolic computation the dark-soliton dynamics in a two-species Bose–Einstein condensate (BEC), which can be described by the quasi-one-dimensional coupled Gross–Pitaevskii equations. Under the balance between the harmonic potential and thermal cloud effects, dark multi-soliton solutions are derived for the two-species BEC through the Hirota bilinear method. Regions of the s-wave scattering lengths are ascertained for the existence of the dark solitons in two species. Influence of the scattering lengths and external potential on the background density, soliton width and velocity is examined. Graphical analysis demonstrates that the harmonic and linear potentials can change the propagation paths, collision positions and collision time of the dark solitons, and that the thermal cloud effects can affect the number of atoms in the two-species BEC.

Interaction of atomic quantum gases with a single carbon nanotube

We study inelastic processes in the hybrid quantum system constituted by a carbon nanotube (CNT) in contact with an ultracold quantum gas, such as a cloud of thermal atoms or a Bose-Einstein condensate (BEC). We present a parameter-free ab initio approach for the loss rate based on the underlying scattering process, considering the two-dimensional character of the system as well as the exact Casimir-Polder potential. The predicted loss rates are in perfect agreement with recent experimental results, obtained both for a thermal cloud of rubidium atoms and for a BEC. For the trap loss of a thermal cloud, we find that retardation effects become important and contribute significantly, which emphasises the crucial role of the exact interaction potential.

An automated vision-based method for rapid 3D energy performance modeling of existing buildings using thermal and digital imagery

Modeling the energy performance of existing buildings enables quick identification and reporting of potential areas for building retrofit. However, current modeling practices of using energy simulation tools do not model the energy performance of buildings at their element level. As a result, potential retrofit candidates caused by construction defects and degradations are not represented. Furthermore, due to manual modeling and calibration processes, their application is often time-consuming. Current application of 2D thermography for building diagnostics is also facing several challenges due to a large number of unordered and non-geo-tagged images. To address these limitations, this paper presents a new computer vision-based method for automated 3D energy performance modeling of existing buildings using thermal and digital imagery captured by a single thermal camera. First, using a new image-based 3D reconstruction pipeline which consists of Graphic Processing Unit (GPU)-based Structure-from-Motion (SfM) and Multi-View Stereo (MVS) algorithms, the geometrical conditions of an existing building is reconstructed in 3D. Next, a 3D thermal point cloud model of the building is generated by using a new 3D thermal modeling algorithm. This algorithm involves a one-time thermal camera calibration, deriving the relative transformation by forming the Epipolar geometry between thermal and digital images, and the MVS algorithm for dense reconstruction. By automatically superimposing the 3D building and thermal point cloud models, 3D spatio-thermal models are formed, which enable the users to visualize, query, and analyze temperatures at the level of 3D points. The underlying algorithms for generating and visualizing the 3D spatio-thermal models and the 3D-registered digital and thermal images are presented in detail. The proposed method is validated for several interior and exterior locations of a typical residential building and an instructional facility. The experimental results show that inexpensive digital and thermal imagery can be converted into ubiquitous reporters of the actual energy performance of existing buildings. The proposed method expedites the modeling process and has the potential to be used as a rapid and robust building diagnostic tool.

Long-Lived Rogue Waves and Inelastic Interaction in Binary Mixtures of Bose—Einstein Condensates

We investigate bright, dark and two rogue waves in two-component Bose—Einstein condensates. It is found that one rogue wave of a new structure that contains two humps and two valleys around one center in the temporal-spatial distribution interacts with the conventional rogue wave. We present an effective way to obtain long-lived rogue waves through managing the nonlinear interaction with modulating trapping frequency and interchange atoms between thermal clouds and condensates. The results provide many possibilities to manipulate rogue waves experimentally in the condensate system.

Fluid description of the cooperative scattering of light by spherical atomic clouds

AbstractWhen a cold atomic gas is illuminated by a quasi-resonant laser beam, light-induced dipole–dipole correlations make the scattering of light a cooperative process. Once a fluid description is adopted for the atoms, many scattering properties are captured by the definition of a complex refractive index. The solution of the scattering problem is here presented for spherical atomic clouds of arbitrary density profiles, such as parabolic densities characteristic of ultra-cold clouds. A new solution for clouds with infinite boundaries is derived, which is particularly useful for the Gaussian densities of thermal atomic clouds. The presence of Mie resonances, a signature of the cloud acting as a cavity for the light, is discussed. These resonances leave their fingerprint in various observables such as the scattered intensity or in the radiation pressure force, and can be observed by tuning the frequency of the incident laser field or the atom number.

Inverse Energy Cascade in Forced Two-Dimensional Quantum Turbulence

We demonstrate an inverse energy cascade in a minimal model of forced 2D quantum vortex turbulence. We simulate the Gross-Pitaevskii equation for a moving superfluid subject to forcing by a stationary grid of obstacle potentials, and damping by a stationary thermal cloud. The forcing injects large amounts of vortex energy into the system at the scale of a few healing lengths. A regime of forcing and damping is identified where vortex energy is efficiently transported to large length scales via an inverse energy cascade associated with the growth of clusters of same-circulation vortices, a Kolmogorov scaling law in the kinetic energy spectrum over a substantial inertial range, and spectral condensation of kinetic energy at the scale of the system size. Our results provide clear evidence that the inverse energy cascade phenomenon, previously observed in a diverse range of classical systems, can also occur in quantum fluids.