Search

Xenon oscillations in pressurized water reactors were analyzed, using linear stability analysis and weak nonlinear analysis based on the multiple time-scales method. The dynamics are described by a spatio-temporal nonlinear model, which includes feedback processes of xenon absorption, as well as fuel and coolant temperature changes. It is shown that the homogeneous steady-state solution that describes nominal operation of a large reactor can go through uniform Hopf bifurcations at several values of the neutron flux, and the long-wavelength modes that can grow beyond the instability thresholds are identified. In order to study the dynamics beyond the Hopf bifurcation, a nonlinear equation for the amplitude of the growing oscillatory mode is derived. The amplitude equation is used to identify parameter ranges of bounded periodic oscillations and of oscillations with diverging amplitudes. The approach described may be used to broaden the operational limits required to suppress xenon oscillations for safe operation.

The AMS setup at the Maier-Leibnitz-Laboratory (MLL) in Garching features a 14 MV tandem accelerator and two dedicated beam lines for high-sensitivity measurements of isotopes in all mass ranges. Especially in the medium mass range (70 A 120), AMS sensitivity is often limited by isobaric and isotopic background with only small relative difference in Z and/or A. Here, we present recent developments and upgrades at the MLL with special focus on improved sensitivity and new techniques for challenging AMS isotopes such as 93 Zr and 99 Tc. Upgrades of the measurement setup as well as radiopurity studies for AMS samples, which could be altered by atmospheric neutrons during transportation by aircraft, are discussed.

In this work, a first cryogenic characterization of a scintillating $$\hbox {LiAlO}_{2}$$ LiAlO 2 single crystal is presented. The results achieved show that this material holds great potential as a target for direct dark matter search experiments. Three different detector modules obtained from one crystal grown at the Leibniz-Institut für Kristallzüchtung (IKZ) have been tested to study different properties at cryogenic temperatures. Firstly, two 2.8 g twin crystals were used to build different detector modules which were operated in an above-ground laboratory at the Max Planck Institute for Physics (MPP) in Munich, Germany. The first detector module was used to study the scintillation properties of $$\hbox {LiAlO}_{2}$$ LiAlO 2 at cryogenic temperatures. The second achieved an energy threshold of ($$213.02\pm 1.48$$ 213.02 ± 1.48 ) eV which allows setting a competitive limit on the spin-dependent dark matter particle-proton scattering cross section for dark matter particle masses between $$350\,\hbox {MeV/c}^{2}$$ 350 MeV/c 2 and $$1.50\,\hbox {GeV/c}^{2}$$ 1.50 GeV/c 2 . Secondly, a detector module with a 373 g $$\hbox {LiAlO}_{2}$$ LiAlO 2 crystal as the main absorber was tested in an underground facility at the Laboratori Nazionali del Gran Sasso (LNGS): from this measurement it was possible to determine the radiopurity of the crystal and study the feasibility of using this material as a neutron flux monitor for low-background experiments.

The development of low-threshold detectors for the study of coherent elastic neutrino-nucleus scattering and for the search for light dark matter necessitates methods of low-energy calibration. We suggest this can be provided by the nuclear recoils resulting from the $\gamma$ emission following thermal neutron capture. In particular, several MeV-scale single-$\gamma$ transitions induce well-defined nuclear recoil peaks in the 100 eV range. Using the FIFRELIN code, complete schemes of $\gamma$-cascades for various isotopes can be predicted with high accuracy to determine the continuous background of nuclear recoils below the calibration peaks. We present a comprehensive experimental concept for the calibration of CaWO$_4$ and Ge cryogenic detectors at a research reactor. For CaWO$_4$ the simulations show that two nuclear recoil peaks at 112.5 eV and 160.3 eV should be visible above background simply in the spectrum of the cryogenic detector. Then we discuss how the additional tagging for the associated $\gamma$ increases the sensitivity of the method and extends its application to a wider energy range and to Ge cryogenic detectors., Comment: 21 pages, 8 figures

Coherent elastic neutrino–nucleus scattering ($$\hbox {CE}\nu \hbox {NS}$$CEνNS) offers a unique way to study neutrino properties and to search for new physics beyond the Standard Model. Nuclear reactors are promising sources to explore this process at low energies since they deliver large fluxes of anti-neutrinos with typical energies of a few MeV. In this paper, a new-generation experiment to study$$\hbox {CE}\nu \hbox {NS}$$CEνNSis described. The NUCLEUS experiment will use cryogenic detectors which feature an unprecedentedly low-energy threshold and a time response fast enough to be operated under above-ground conditions. Both sensitivity to low-energy nuclear recoils and a high event rate tolerance are stringent requirements to measuring$$\hbox {CE}\nu \hbox {NS}$$CEνNSof reactor anti-neutrinos. A new experimental site, the Very-Near-Site (VNS), at the Chooz nuclear power plant in France is described. The VNS is located between the two 4.25 $$\hbox {GW}_{\mathrm {th}}$$GWthreactor cores and matches the requirements of NUCLEUS. First results of on-site measurements of neutron and muon backgrounds, the expected dominant background contributions, are given. In this paper a preliminary experimental set-up with dedicated active and passive background reduction techniques and first background estimations are presented. Furthermore, the feasibility to operate the detectors in coincidence with an active muon veto at shallow overburden is studied. The paper concludes with a sensitivity study pointing out the physics potential of NUCLEUS at the Chooz nuclear power plant.

Cryogenic Rare Event Search with Superconducting Thermometers (CRESST) is a long-standing direct dark matter detection experiment with cryogenic detectors located at the underground facility Laboratori Nazionali del Gran Sasso in Italy. CRESST-III, the third generation of CRESST, was specifically designed to have a world-leading sensitivity for low-mass dark matter (DM) (less than 2 GeV/$$\hbox {c}^{2}$$c2) to probe the spin-independent DM-nucleus cross section. At present, a large part of the parameter space for spin-independent scattering off nuclei remains untested for dark matter particles with masses below few GeV/$$\hbox {c}^{2}$$c2 although many motivated theoretical models having been proposed. The CRESST-III experiment employs scintillating $$\hbox {CaWO}_{{4}}$$CaWO4 crystals of $$\sim$$∼ 25 g as target material for dark matter interactions operated as cryogenic scintillating calorimeters at $$\sim$$∼ 10 mK. CRESST-III first data taking was successfully completed in 2018, achieving an unprecedented energy threshold for nuclear recoils. This result extended the present sensitivity to DM particles as light as $$\sim$$∼ 160 MeV/$$\hbox {c}^{2}$$c2. In this paper, an overview of the CRESST-III detectors and results will be presented.

A precise measurement of the radio-purity levels of the CaWO4 crystals used for both the CRESST and the NUCLEUS experiment, is fundamental for a better background understanding. The sensitivity of HPGe detectors is not sufficient to the excellent radio-purity levels of the CaWO4 crystals produced in-house at the Technische Universität München (TUM). We report on a cryogenic α-screening facility which will provide a method to determine the radio-purity of this crystals by measuring the alpha-decays with a high precision, taking advantage of the unique experimental environment of the shallow underground laboratory (UGL) of the TUM.

The CRESST experiment is a direct dark matter search which aims to measure interactions of potential dark matter particles in an earth-bound detector. With the current stage, CRESST-III, we focus on a low energy threshold for increased sensitivity towards light dark matter particles. In this manuscript we describe the analysis of one detector operated in the first run of CRESST-III (05/2016-02/2018) achieving a nuclear recoil threshold of 30.1eV. This result was obtained with a 23.6g CaWO$_4$ crystal operated as a cryogenic scintillating calorimeter in the CRESST setup at the Laboratori Nazionali del Gran Sasso (LNGS). Both the primary phonon/heat signal and the simultaneously emitted scintillation light, which is absorbed in a separate silicon-on-sapphire light absorber, are measured with highly sensitive transition edge sensors operated at ~15mK. The unique combination of these sensors with the light element oxygen present in our target yields sensitivity to dark matter particle masses as low as 160MeV/c$^2$., 9 pages, 9 figures

The Physics Department of the Technical University of Munich operates a shallow underground detector laboratory in Garching, Germany. It provides $$\sim 160\,{\mathrm{m}^2}$$ of laboratory space which is shielded from cosmic radiation by $$\sim 6\,\mathrm{m}$$ of gravel and soil, corresponding to a shielding of $$\sim 15\,{\mathrm{m.w.e.}}$$ . The laboratory also houses a cleanroom equipped with work- and wetbenches, a chemical fumehood as well as a spin-coater and a mask-aligner for photolithographic processing of semiconductor detectors. Furthermore, the shallow underground laboratory runs two high-purity germanium detector screening stations, a liquid argon cryostat and a $$^3$$ He– $$^4$$ He dilution refrigerator with a base temperature of $$\le 12-14\,\mathrm{mK}$$ . The infrastructure provided by the shallow laboratory is particularly relevant for the characterization of $$\hbox {CaWO}_4$$ target crystals for the CRESST-III experiment, detector fabrication and assembly for rare event searches. Future applications of the laboratory include detector development in the framework of coherent neutrino nucleus scattering experiments ( $$\nu $$ -cleus) and studying its potential as a site to search for MeV-scale dark matter with gram-scale cryogenic detectors.

Zusammenfassung Hintergrund Die Mobilitat des 1 Strahls in transversaler Richtung fand bisher wenig Beachtung. Methoden Die Messungen (n= 50) des Intermetatarsalwinkels IM° im ap Rontgenbild vergleichen die Messungen im Stehen und beim praoperativen Varus- und Valgusstress und nach Release der Kapsel vom M 1 Kopf. Resultate Der praoperative Valgusstresstest im Liegen zeigt IM°, die den IM° im Stehen entsprechen (IM°16°). Nach Release der medialen und lateralen Kapsel werden vergroserte IM° bei 2 Drittel der Fusse gemessen. Schlussfolgerungen Der transversale Hypermobilitats-Stress-Test ermoglicht die intraoperative Testung und Vermessung der Mobilitat des 1. Metatarsale gegenuber dem 2. Metatarsale. Der Valgusstresstest mit maximaler Varisierung des M1 entspricht dem Intermetatarsal-Winkel, der im Stehen gemessen wird. Die maximale Varisierung des M 1 beim Valgusstresstest nach dem Release des Metatarsale 1 Kopfes zeigt in diesem Patientenkollektiv zu einem Drittel stabile Verhaltnisse im metatarso-tarsalen Ubergang, einem Drittel massig mobile IM° 4-5° und zu einem Drittel hypermobile IM° > 5° Verhaltnisse.

The NUCLEUS experiment aims for the detection of coherent elastic neutrino-nucleus scattering at a nuclear power reactor with gram-scale, ultra-low-threshold cryogenic detectors. This technology leads to a miniaturization of neutrino detectors and allows to probe physics beyond the Standard Model of particle physics. A 0.5 g NUCLEUS prototype detector, operated above ground in 2017, reached an energy threshold for nuclear recoils of below 20 eV. This sensitivity is achieved with tungsten transition edge sensors which are operating at temperatures of 15 mK and are mainly sensitive to non-thermal phonons. These small recoil energies become accessible for the first time with this technology, which allows collecting large-statistics neutrino event samples with a moderate detector mass. A first-phase cryogenic detector array with a total mass of 10 g enables a 5-sigma observation of coherent scattering within several weeks. We identified a suitable experimental site at the Chooz Nuclear Power Plant and performed muon and neutron background measurements there. The operation of a NUCLEUS cryogenic detector array at such a site requires highly efficient background suppression. NUCLEUS plans to use an innovative technique consisting of separate cryogenic anticoincidence detectors against surface backgrounds and penetrating (gamma, neutron) radiation. We present first results from prototypes of these veto detectors and their operation in coincidence with a NUCLEUS target detector.

In this work, we want to highlight the potential of lithium as a target for spin-dependent dark matter search in cryogenic experiments, with a special focus on the low-mass region of the parameter space. We operated a prototype detector module based on a $$\hbox {Li}_2\hbox {MoO}_4$$ target crystal in an above-ground laboratory. Despite the high background environment, the detector sets a competitive limit on spin-dependent interactions of dark matter particles with protons and neutrons for masses between $$0.8~\hbox {GeV/c}^2$$ and $$1.5~\hbox {GeV/c}^2$$ .

The CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) dark matter search experiment aims for the detection of dark matter particles via elastic scattering off nuclei in $\mathrm{CaWO_4}$ crystals. To understand the CRESST electromagnetic background due to the bulk contamination in the employed materials, a model based on Monte Carlo simulations was developed using the Geant4 simulation toolkit. The results of the simulation are applied to the TUM40 detector module of CRESST-II phase 2. We are able to explain up to $(68 \pm 16)\,\mathrm{\%}$ of the electromagnetic background in the energy range between $1\,\mathrm{keV}$ and $40\,\mathrm{keV}$., Comment: 19 pages, 12 figures

In the current direct dark matter search landscape, the leading experiments in the sub-GeV mass region mostly rely on cryogenic techniques which employ crystalline targets. One attractive type of crystals for these experiments is those containing lithium, due to the fact that $$^7\hbox {Li}$$7Li is an ideal candidate to study spin-dependent dark matter interactions in the low mass region. Furthermore, $$^6\hbox {Li}$$6Li can absorb neutrons, a challenging background for dark matter experiments, through a distinctive signature which allows the monitoring of the neutron flux directly on site. In this work, we show the results obtained with three different detectors based on $$\hbox {LiAlO}_2$$LiAlO2, a target crystal never used before in cryogenic experiments.

Weakly nonlinear stability analysis is applied to study xenon oscillations in nuclear reactors using the approach of multiple time-scales method. This approach allows to characterize the dynamics of the system beyond the Hopf instability point. It provides important insight on the characteristics of the oscillations, namely if they diverge with time, or converge into a bounded limit cycle. Detailed derivation of the amplitude equation is presented. This equation is used to identify parameter ranges of bounded periodic oscillations, which may be allowed for safe operation. The influence of neutron generation time and the power feedback coefficients on the amplitude of limit cycles, as well as on convergence times, is discussed. The described method may be used to extend the safety margins required to prevent xenon unstable oscillations in reactor cores.

The CRESST-III experiment searches for direct interactions of dark matter with ordinary matter. The main event signature would be a nuclear recoil inside one of the scintillating CaWO4 crystals. Operating the crystals as cryogenic calorimeters provides a phonon signal as measure of the deposited energy. The simultaneous readout of both signals is used to actively discriminate backgrounds. CRESST-III focuses on the sub-GeV/c2 mass region where the sensitivity is driven by the threshold. In the first data taking campaign of CRESST-III from 2016-2018 an unprecedented low threshold of 30.1 eV for nuclear recoils was obtained. In this contribution, we will report the status of the experiment and the latest results.

The original version of this article unfortunately contains mistakes.

We demonstrate light-pulse atom interferometry with large-momentum-transfer atom optics based on stimulated Raman transitions and frequency-swept adiabatic rapid passage. Our atom optics have produced momentum splittings of up to 30 photon recoil momenta in an acceleration-sensitive interferometer for laser cooled atoms. We experimentally verify the enhancement of phase shift per unit acceleration and characterize interferometer contrast loss. By forgoing evaporative cooling and velocity selection, this method lowers the atom shot-noise-limited measurement uncertainty and enables large-area atom interferometry at higher data rates.

We present a method for robust timekeeping in which alkali-metal atoms are interrogated in a Ramsey sequence based on stimulated Raman transitions with optical photons. To suppress systematic effects introduced by differential ac Stark shifts and optical intensity gradients, we employ atom optics derived from Raman adiabatic rapid passage (ARP). Raman ARP drives coherent transfer between the alkali-metal hyperfine ground states via a sweep of the Raman detuning through the two-photon resonance. Our experimental implementation of Raman ARP reduced the phase sensitivity of Ramsey sequences to Stark shifts in $^{133}\mathrm{Cs}$ atoms by about two orders of magnitude, relative to fixed-frequency Raman transitions. This technique also preserved Ramsey fringe contrast for cloud displacements reaching the $1/{e}^{2}$ intensity radius of the laser beam. In a magnetically unshielded apparatus, second-order Zeeman shifts limited the fractional frequency uncertainty to $\ensuremath{\sim}3.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ after about 2500 s of averaging.

We use all-optical methods to produce a highly-degenerate, Fermi gas of 6Li atoms near a Feshbach resonance, where strong interactions are predicted. In this regime, the zero-energy scattering length is larger than the interparticle spacing, and both the mean field energy and the collision rate take on universal forms as a consequence of unitarity and many-body interactions. Our experiments study universal hydrodynamic expansion of the gas and universal mean field interactions. By measuring the cloud radii of the trapped gas, we determine a universal parameter for strongly interacting two-component Fermi systems, the ratio of the mean field energy to the kinetic energy.

In this paper we review the crystal chemistry and structure data from the literature and our results reported in the last decade for natural and synthetic samples of the tantalite-columbite series. Order-disorder transitions and oxidation reactions on the ixiolite-columbite-wodginite system are reported for one Brazilian sample. It is shown that reports on these subjects are sometimes dubious and incomplete. In addition to the reaction atmosphere (air or vacuum), order-disorder and oxidation are strongly dependent on the physical state of the samples (powdered or crystal). Structure and chemical composition have been investigated in our laboratory using X-ray diffraction (XRD), electron probe microanalysis (EPMA) and Mossbauer spectroscopy (MS).

Practical atom interferometric sensors may benefit from robust atom optics based on Raman chirped adiabatic passage (RCAP). We demonstrate coherent transfer and interference using RCAP, and discuss expected enhancement of interferometer stability.

Raman pulse atom interferometry is an important modality for precision measurements of inertial forces and tests of fundamental physics. Typical Raman atom optics use two coherent laser fields applied at gigahertz-scale detunings from optical resonance, so that spontaneous emission produces a minor or negligible source of decoherence. An additional consequence of spontaneous emission is coherent population trapping (CPT). We show that CPT produces coherences and population differences which induce systematic effects in Raman pulse atom interferometers. We do not believe that CPT has been previously identified as an error mechanism in Raman pulse atom interferometry. We present an experimental characterization of CPT coherences and population differences induced in laser-cooled cesium atoms by application of Raman pulses at detunings near 1 GHz, commensurate with detunings used in several precision measurement experiments. We are not aware of previous demonstrations of CPT-induced population difference. We argue that CPT effects could induce phase shifts of several milliradians in magnitude for typical experimental parameters and stipulate that these errors can be suppressed by propagation direction reversal in Raman interferometer-based precision measurements.

Sound waves are excited in an optically trapped degenerate Fermi gas of spin-up and spin-down atoms with magnetically tunable interactions. Measurements are made throughout the crossover region, from a weakly interacting Fermi gas through the resonant Fermi superfluid regime to a Bose condensate of dimer molecules. The measured sound velocities test theories of hydrodynamic wave propagation and predictions of the equation of state. At resonance, the sound velocity exhibits universal scaling with the Fermi velocity, to within 1.8% over a factor of 30 in density.

We report a model-independent measurement of the entropy, energy, and critical temperature of a degenerate, strongly interacting Fermi gas of atoms. The total energy is determined from the mean square cloud size in the strongly interacting regime, where the gas exhibits universal behavior. The entropy is measured by sweeping a bias magnetic field to adiabatically tune the gas from the strongly interacting regime to a weakly interacting regime, where the entropy is known from the cloud size after the sweep. The dependence of the entropy on the total energy quantitatively tests predictions of the finite-temperature thermodynamics., 16 pages, 3 figures

We use all-optical methods to produce a highly-degenerate Fermi gas of spin-1/2 $^6$Li atoms. A magnetic field tunes the gas near a collisional (Feshbach) resonance, producing strong interactions between spin-up and spin-down atoms. This atomic gas is a paradigm for strong interactions in nature, and provides tests of current quantum many-body calculational methods for diverse systems, including very high temperature superconductors, nuclear matter in neutron stars, and the quark-gluon plasma of the Big Bang. We have measured properties of a breathing mode over a wide range of temperatures. At temperatures both below and well above the superfluid transition, the frequency of the mode is nearly constant and very close to the hydrodynamic value. However, explaining both the frequency and the damping rate in the normal collisional regime has not been achieved. Our measurements of the damping rate as a function of the energy of the gas are used to estimate an upper bound on the viscosity. Using our new measurements of the entropy of the gas, we estimate the ratio of the shear viscosity to the entropy density, and compare the result with the lower bound for quantum viscosity recently predicted using string theory methods., Comment: 10 pages, 5 figures

Optical traps provide tight confinement and very long storage times for atomic gases. Using a single focused beam from a CO 2 laser, we confine a mixture of spin-up and spin-down fermionic 6 Li atoms, achieving storage times of ten minutes, and evaporative cooling to quantum degeneracy in seconds. A bias magnetic field tunes the gas to a collisional (Feshbach) resonance, producing extremely strong spin-pairing. This system now tests current many-body predictions for high-temperature superconductors, universal interactions in neutron stars, and hydrodynamic flow of quark-gluon plasmas, a state of matter that existed microseconds after the Big Bang.

We study the properties of an optically-trapped, Fermi gas of 6Li atoms, near the center of a broad Feshbach resonance, where strong interactions are observed. Strongly interacting Fermi gases exhibit universal behavior, and are of interest as models of exotic systems ranging from high temperature superconductors to neutron stars and quark-gluon plasmas. We measure the frequency and damping rate of the radial breathing mode of the trapped gas and consider quantum viscosity as a damping mechanism. We also demonstrate that the virial theorem holds and measure the heat capacity. In the experiments, energy is precisely added to the gas and an empirical temperature is determined from the spatial profiles of the cloud. Transitions are observed in both the damping rate and the heat capacity, measured as functions of the empirical temperature. Recent theory, using a pseudogap formalism, enables the first temperature calibration, and shows that the observed transition temperatures are close to that predicted for the onset of superfluidity in a strongly attractive Fermi gas.

Unitary Fermi gases, where the scattering length is large compared to the interparticle spacing, can have universal properties, which are independent of the details of the interparticle interactions when the range of the scattering potential is negligible. We prepare an optically-trapped, unitary Fermi gas of $^6$Li, tuned just above the center of a broad Feshbach resonance. In agreement with the universal hypothesis, we observe that this strongly-interacting many-body system obeys the virial theorem for an ideal gas over a wide range of temperatures. Based on this result, we suggest a simple volume thermometry method for unitary gases. We also show that the observed breathing mode frequency, which is close to the unitary hydrodynamic value over a wide range of temperature, is consistent with a universal hydrodynamic gas with nearly isentropic dynamics., Comment: 5 pages and 2 figures

We measure the temperature dependence of the radial breathing mode in an optically trapped, unitary Fermi gas of 6Li, just above the center of a broad Feshbach resonance. The damping rate reveals a clear change in behavior which we interpret as arising from a superfluid transition. We suggest pair breaking as a mechanism for an increase in the damping rate which occurs at temperatures well above the transition. In contrast to the damping, the frequency varies smoothly and remains close to the unitary hydrodynamic value. At low temperature T, the damping depends on the atom number only through the reduced temperature, and extrapolates to 0 at T = 0.

We have measured the heat capacity of an optically trapped, strongly interacting Fermi gas of atoms. A precise addition of energy to the gas is followed by single-parameter thermometry, which determines the empirical temperature parameter of the gas cloud. Our measurements reveal a clear transition in the heat capacity. The energy and the spatial profile of the gas are computed using a theory of the crossover from Fermi to Bose superfluids at finite temperatures. The theory calibrates the empirical temperature parameter, yields excellent agreement with the data, and predicts the onset of superfluidity at the observed transition point.

We observe collective oscillations of a trapped, degenerate Fermi gas of $^6$Li atoms at a magnetic field just above a Feshbach resonance, where the two-body physics does not support a bound state. The gas exhibits a radial breathing mode at a frequency of 2837(05) Hz, in excellent agreement with the frequency of $\nu_H\equiv\sqrt{10\nu_x\nu_y/3}=2830(20)$ Hz predicted for a {\em hydrodynamic} Fermi gas with unitarity limited interactions. The measured damping times and frequencies are inconsistent with predictions for both the collisionless mean field regime and for collisional hydrodynamics. These observations provide the first evidence for superfluid hydrodynamics in a resonantly interacting Fermi gas., Comment: 5 pages, ReVTeX4, 2 eps figs. Resubmitted to PRL in response to referees' comments. Title and abstract changed. Corrected error in Table 1, atom numbers for 0.33 TF and 0.5 TF data were interchanged. Corrected typo in ref 3. Added new figure of damping time versus temperature

We measure the magnetic field dependence of the frequency and damping time for the radial breathing mode of an optically trapped, Fermi gas of $^6$Li atoms near a Feshbach resonance. The measurements address the apparent discrepancy between the results of Kinast et al., [Phys. Rev. Lett. {\bf 92}, 150402 (2004)] and those of Bartenstein et al., [Phys. Rev. Lett. {\bf 92}, 203201 (2004)]. Over the range of magnetic field from 770 G to 910 G, the measurements confirm the results of Kinast et al. Close to resonance, the measured frequencies are in excellent agreement with predictions for a unitary hydrodynamic gas. At a field of 925 G, the measured frequency begins to decrease below predictions. For fields near 1080 G, we observe a breakdown of hydrodynamic behavior, which is manifested by a sharp increase in frequency and damping rate. The observed breakdown is in qualitative agreement with the sharp transition observed by Bartenstein et al., at 910 G., Comment: 4 pages, 2 figures, 1 table. Revised in response to referees' Comments. Published in PRA(R)

We report a demonstration of composite Raman pulses that achieve broadband population inversion and are used to increase the momentum splitting of an atom interferometer up to 18ℏk (corresponding to an increase in the inertial signal by a factor of nine). Composite Raman pulses suppress the effects of pulse length and detuning errors, providing higher transfer efficiency and velocity acceptance than single square pulses. We implement two composite pulse sequences, π/20°−π90°−π/20° and π/20°−π180°−3π/20°, and use the latter composite pulse to demonstrate large-area atom interferometry with stimulated Raman transitions. In addition to enabling larger momentum transfer and higher sensitivity, we argue that composite pulses can improve the robustness of atom interferometers operating in dynamic environments.

High-precision inertial sensing demonstrations with light pulse atom interferometry have typically used Raman pulses having durations orders of magnitude shorter than the dwell time between interferometer pulses. Environmentally robust sensors operating at high-bandwidth will be required to operate at short (millisecond scale) dwell times between Raman pulses. In such an operational mode, the Raman pulse duration becomes an appreciable fraction of the dwell time between pulses. In addition, high-precision inertial sensing applications have typically been demonstrated in mildly dynamic or nondynamic environments having low rate of change of inertial input, ensuring that applied Raman pulses satisfy the Raman resonance condition. Application of nonresonant pulses will be inevitable in sensors registering time-varying inertial input. We present a diagrammatic technique for calculation of atomic output state populations for multipulse atom optics manipulations that explicitly account for the effects of finite pulse duration and finite Raman detuning effects on the laser-induced atomic phase. We analyze several atom interferometer sequences. We report accelerometer and gyroscope phase evolution for fixed Raman laser frequency difference incorporating corrections in powers of the ratio of pulse duration to time interval between interferometer pulses. Our accelerometer result agrees with other published results.

We measure the scaling laws for the number of atoms and the cloud size as a function of trap depth for evaporative cooling of a unitary Fermi gas in an optical trap. A unitary Fermi gas comprises a trapped mixture of atoms in two hyperfine states which is tuned to a collisional (Feshbach) resonance using a bias magnetic field. Near resonance, the zero energy s-wave scattering length diverges, and the s-wave scattering cross-section is limited by unitarity to be 4?/k2, where k is the relative wavevector of the colliding particles. In this case, the collision cross-section for evaporation scales inversely with the trap depth, enabling runaway evaporation under certain conditions. We demonstrate high evaporation efficiency, which is achieved by maintaining a high ratio ? of trap depth to thermal energy as the trap depth is lowered. We derive and demonstrate a trap lowering curve which maintains ? constant for a unitary gas. This evaporation curve yields a quantum degenerate sample from a classical gas in a fraction of a second, with only a factor of three loss in atom number.

Es wird die Stromung einer einfachen viskoelastischen Flussigkeit zwischen zwei ebenen festen Wanden, die einen Winkel miteinander bilden und langs deren Schnittgeraden Senken verteilt sind, untersucht. Eine konvergierende Stromung dieser Art wird naherungsweise in der Einlaufzone von Keilspaltdusen realisiert. Es wird gezeigt, das je nachdem, ob die Scherentzahung im Stoffverhalten uberwiegt oder nicht, die Sekundarstromung aus zwei an den Kanalwanden anliegenden Zonen besteht, oder aus einer Zone in der Kanalmitte.