78 research outputs found
Quantum Test of the Universality of Free Fall
We simultaneously measure the gravitationally-induced phase shift in two
Raman-type matter-wave interferometers operated with laser-cooled ensembles of
Rb and K atoms. Our measurement yields an E\"otv\"os ratio of
. We briefly estimate possible
bias effects and present strategies for future improvements
Creating nearly Heisenberg-limited matter-waves exploiting tunable interactions
The wave nature of matter implies wavepackets with minimal combined
uncertainty in position and momentum, a limit which can hardly be reached for
clouds of large atom numbers of interacting particles. Here, we report on a
high-flux source of ultra-cold atoms realizing near-Heisenberg-limited
expansion rates upon release from the trap. Depending on the value of the
scattering length, we model our system either with a scaling approach based on
the Thomas-Fermi approximation, or with a variational approach based on a
Gaussian atomic density approximation, observing the transition between the
weak and strong interaction regimes. Finally, we discuss applications of our
methods to test foundational principles of quantum mechanics such as the
superposition principle or their extension to other atomic species
Matter-wave collimation to picokelvin energies with scattering length and potential shape control
We study the impact of atomic interactions on an in-situ collimation method
for matter-waves. Building upon an earlier study with Rb, we apply a
lensing protocol to K where the atomic scattering length can be tailored
by means of magnetic Feshbach resonances. Minimizing interactions, we show an
enhancement of the collimation compared to the strong interaction regime,
realizing ballistic 2D expansion energies of 438(77) pK in our experiment. Our
results are supported by an accurate simulation, describing the ensemble
dynamics, which we further use to study the behavior of various trap
configurations for different interaction strengths. Based on our findings we
propose an advanced scenario which allows for 3D expansion energies below 16 pK
by implementing an additional pulsed delta-kick collimation directly after
release from the trapping potential. Our results pave the way to achieve
state-of-the-art quantum state in typical dipole trap setups required to
perform ultra-precise measurements without the need of complex micro-gravity or
long baselines environments
All-optical matter-wave lens using time-averaged potentials
The precision of matter-wave sensors benefits from interrogating large-particle-number atomic ensembles at high cycle rates. Quantum-degenerate gases with their low effective temperatures allow for constraining systematic errors towards highest accuracy, but their production by evaporative cooling is costly with regard to both atom number and cycle rate. In this work, we report on the creation of cold matter-waves using a crossed optical dipole trap and shaping them by means of an all-optical matter-wave lens. We demonstrate the trade off between lowering the residual kinetic energy and increasing the atom number by reducing the duration of evaporative cooling and estimate the corresponding performance gain in matter-wave sensors. Our method is implemented using time-averaged optical potentials and hence easily applicable in optical dipole trapping setups. © 2022, The Author(s)
Optomechanical resonator-enhanced atom interferometry
Matter-wave interferometry and spectroscopy of optomechanical resonators offer complementary advantages. Interferometry with cold atoms is employed for accurate and long-term stable measurements, yet it is challenged by its dynamic range and cyclic acquisition. Spectroscopy of optomechanical resonators features continuous signals with large dynamic range, however it is generally subject to drifts. In this work, we combine the advantages of both devices. Measuring the motion of a mirror and matter waves interferometrically with respect to a joint reference allows us to operate an atomic gravimeter in a seismically noisy environment otherwise inhibiting readout of its phase. Our method is applicable to a variety of quantum sensors and shows large potential for improvements of both elements by quantum engineering. © 2020, The Author(s)
Of tennis courts and fireplaces: Neurath's internment on the Isle of Man and his politics of design
Otto Neurath’s version of functionalism is one that begins with people “as we find them,” a proposition first set out in his 1917 essay “The Converse Taylor System.” Any attempt to redesign the existing furnishings of everyday life must take into account “functions” that go beyond the obvious purpose of objects: functions that are to do with sociability, happiness, familiarity, the love of “coziness,” and that address the diversity and contradictoriness of people. This essay considers how Neurath applied and made use of these ideas about design in 1940s Britain, during and after his internment on the Isle of Man between 1940–1941 and in talks, papers and correspondence from this period. It does not focus on the Isotype Institute, which would usually be considered his principal intervention in design, but on his commentary on everyday objects and practices. In particular it centres on four items – tennis courts, fireplaces, chairs and shoes – and through these elaborates some of the connections between Neurath’s ideas about the design of everyday life, and the significance of everyday practices, and his logical empiricism
Effectiveness of an intensive care telehealth programme to improve process quality (ERIC): a multicentre stepped wedge cluster randomised controlled trial
Zeitlich-gemittelte optische Potentiale zur Erzeugung und Manipulation von Bose-Einstein Kondensaten
The precision of atom interferometers, targeted for example in the Hannover Very
Long Baseline Atom Interferometer (VLBAI) facility, imposes stringent requirements
in several respects. They concern the control of center-of-mass motion and expansion
of the wave packets by the matter-wave source as well as the number of atoms.
By reducing the expansion, systematic errors, appearing e.g. through wavefront
aberrations, can be lowered. These requirements can be matched by employing
ultracold quantum gases or even quantum degenerate gases. A promising method
to create those ensembles is evaporative cooling in a spatially modulated optical
dipole trap. Here, the utilization of time-averaged potentials enables the fast creation
of ultracold atomic ensembles with large number of atoms. Both, the higher
number of atoms and the increased repetition rate, enhance the performance of the
interferometer due to a lower quantum projection noise, which scales with 1/sqrt(N),
and a larger bandwidth of the sensor due to faster sampling. The shaping of the
matter-waves by techniques such as matter-wave lensing or Delta-Kick collimation
is also feasible due to the dynamic control of the trapping potential.
In this thesis the implementation and application of dynamic time-averaged optical
potentials created via center position modulation of dipole trap beams is
demonstrated. By evaporative cooling in these potentials, 1.9(0.4) x 10^5 condensed
atoms with an expansion temperature of 29.2(1.3) nK were achieved after 3 s of
evaporation. Up to 4.2(0.1) x 10^5 condensed atoms could be observed with slower
evaporation of 5 s. Subsequent matter-wave lensing is carried out yielding expansion
rates as low as 553(49) μms^-1 resulting in an effective temperature of 3.2(0.6) nK in
two dimensions. This lens can be applied at any stage of evaporative cooling, thus
short-cutting the generation of ultracold effective temperatures. In this thesis the
limitations of optical matter-wave lensing in the current setup are revealed and
ways to improve the performance are discussed.
The fast generation of ultracold atomic ensembles will enhance the performance of
the dual-species atom interferometer, which represents the experiment apparatus
for this thesis and strives for a test of the Universality of Free Fall with an uncertainty
on the order of 10^-9. The results of this thesis were used to test numerical
simulations which were utilized to show the perspective of generating up to 10^6
collimated condensed atoms within 1 s of cycle time in the rubidium source system
of Hannover’s VLBAI
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