On the survival of the quantum depletion of a condensate after release from a magnetic trap.

We present observations of the high momentum tail in expanding Bose-Einstein condensates of metastable Helium atoms released from a harmonic trap. The far-field density profile exhibits features that support identification of the tails of the momentum distribution as originating in the in-situ quantum depletion prior to release. Thus, we corroborate recent observations of slowly-decaying tails in the far-field beyond the thermal component.

Trap frequency measurement with a pulsed atom laser.

We describe a novel method of single-shot trap frequency measurement for a confined Bose-Einstein Condensate, which uses an atom laser to repeatedly sample the mean velocity of trap oscillations as a function of time. The method is able to determine the trap frequency to an accuracy of 39 ppm (16 mHz) in a single experimental realization, improving on the literature by a factor of three. Further, we show that by employing a reconstructive aliasing approach our method can be applied to trap frequencies more than a factor of 3 greater than the sampling frequency.

Measurement of a helium tune-out frequency: an independent test of quantum electrodynamics.

Despite quantum electrodynamics (QED) being one of the most stringently tested theories underpinning modern physics, recent precision atomic spectroscopy measurements have uncovered several small discrepancies between experiment and theory. One particularly powerful experimental observable that tests QED independently of traditional energy level measurements is the "tune-out" frequency, where the dynamic polarizability vanishes and the atom does not interact with applied laser light. In this work, we measure the tune-out frequency for the 2 state of helium between transitions to the 2 and 3 manifolds and compare it with new theoretical QED calculations.

Development and validation of a measure of organizational capacity for implementing youth development programs.

Accumulating evidence indicates that incorporating youth development (YD) principles, strategies, and supports into an organization promotes positive adult and youth outcomes. However, few validated measures assess this type of capacity. The YMCA commissioned a study to validate its Capacity Assessment for Youth Development Programming (Y-CAP), which examines the organizational infrastructure required to implement YD programs and processes in seven areas.

Direct Measurement of the Forbidden 2^{3}S_{1}→3^{3}S_{1} Atomic Transition in Helium.

We present the detection of the highly forbidden 2^{3}S_{1}→3^{3}S_{1} atomic transition in helium, the weakest transition observed in any neutral atom. Our measurements of the transition frequency, upper state lifetime, and transition strength agree well with published theoretical values and can lead to tests of both QED contributions and different QED frameworks. To measure such a weak transition, we develop two methods using ultracold metastable (2^{3}S_{1}) helium atoms: low background direct detection of excited then decayed atoms for sensitive measurement of the transition frequency and lifetime, and a pulsed atom laser heating measurement for determining the transition strength.

Bell correlations between spatially separated pairs of atoms.

Bell correlations are a foundational demonstration of how quantum entanglement contradicts the classical notion of local realism. Rigorous validation of quantum nonlocality have only been achieved between solid-state electron spins, internal states of trapped atoms, and photon polarisations, all weakly coupling to gravity. Bell tests with freely propagating massive particles, which could provide insights into the link between gravity and quantum mechanics, have proven to be much more challenging to realise.

Higher-Order Quantum Ghost Imaging with Ultracold Atoms.

Ghost imaging is a quantum optics technique that uses correlations between two beams to reconstruct an image from photons that do not interact with the object being imaged. While pairwise (second-order) correlations are usually used to create the ghost image, higher-order correlations can be utilized to improve the performance. In this Letter, we demonstrate higher-order atomic ghost imaging, using entangled ultracold metastable helium atoms from an s-wave collision halo.

Approaching the adiabatic timescale with machine learning.

The control and manipulation of quantum systems without excitation are challenging, due to the complexities in fully modeling such systems accurately and the difficulties in controlling these inherently fragile systems experimentally. For example, while protocols to decompress Bose-Einstein condensates (BECs) faster than the adiabatic timescale (without excitation or loss) have been well developed theoretically, experimental implementations of these protocols have yet to reach speeds faster than the adiabatic timescale. In this work, we experimentally demonstrate an alternative approach based on a machine-learning algorithm which makes progress toward this goal.

Solving the Quantum Many-Body Problem via Correlations Measured with a Momentum Microscope.

In quantum many-body theory, all physical observables are described in terms of correlation functions between particle creation or annihilation operators. Measurement of such correlation functions can therefore be regarded as an operational solution to the quantum many-body problem. Here, we demonstrate this paradigm by measuring multiparticle momentum correlations up to third order between ultracold helium atoms in an s-wave scattering halo of colliding Bose-Einstein condensates, using a quantum many-body momentum microscope.

Widely tunable, narrow linewidth external-cavity gain chip laser for spectroscopy between 1.0 - 1.1 µm.

We have developed and characterised a stable, narrow linewidth external-cavity laser (ECL) tunable over 100 nm around 1080 nm, using a single-angled-facet gain chip. We propose the ECL as a low-cost, high-performance alternative to fibre and diode lasers in this wavelength range and demonstrate its capability through the spectroscopy of metastable helium. Within the coarse tuning range, the wavelength can be continuously tuned over 30 pm (7.

Ghost imaging with atoms.

Ghost imaging is a counter-intuitive phenomenon-first realized in quantum optics-that enables the image of a two-dimensional object (mask) to be reconstructed using the spatio-temporal properties of a beam of particles with which it never interacts. Typically, two beams of correlated photons are used: one passes through the mask to a single-pixel (bucket) detector while the spatial profile of the other is measured by a high-resolution (multi-pixel) detector. The second beam never interacts with the mask.

Coupling Identical one-dimensional Many-Body Localized Systems.

We experimentally study the effects of coupling one-dimensional many-body localized systems with identical disorder. Using a gas of ultracold fermions in an optical lattice, we artificially prepare an initial charge density wave in an array of 1D tubes with quasirandom on-site disorder and monitor the subsequent dynamics over several thousand tunneling times. We find a strikingly different behavior between many-body localization and Anderson localization.

Dynamical Quasicondensation of Hard-Core Bosons at Finite Momenta.

Long-range order in quantum many-body systems is usually associated with equilibrium situations. Here, we experimentally investigate the quasicondensation of strongly interacting bosons at finite momenta in a far-from-equilibrium case. We prepare an inhomogeneous initial state consisting of one-dimensional Mott insulators in the center of otherwise empty one-dimensional chains in an optical lattice with a lattice constant d.

QUANTUM GASES. Observation of many-body localization of interacting fermions in a quasirandom optical lattice.

Many-body localization (MBL), the disorder-induced localization of interacting particles, signals a breakdown of conventional thermodynamics because MBL systems do not thermalize and show nonergodic time evolution. We experimentally observed this nonergodic evolution for interacting fermions in a one-dimensional quasirandom optical lattice and identified the MBL transition through the relaxation dynamics of an initially prepared charge density wave. For sufficiently weak disorder, the time evolution appears ergodic and thermalizing, erasing all initial ordering, whereas above a critical disorder strength, a substantial portion of the initial ordering persists.

Emergence of coherence and the dynamics of quantum phase transitions.

The dynamics of quantum phase transitions pose one of the most challenging problems in modern many-body physics. Here, we study a prototypical example in a clean and well-controlled ultracold atom setup by observing the emergence of coherence when crossing the Mott insulator to superfluid quantum phase transition. In the 1D Bose-Hubbard model, we find perfect agreement between experimental observations and numerical simulations for the resulting coherence length.

Observation of transverse Bose-Einstein condensation via Hanbury Brown-Twiss correlations.

A fundamental property of a three-dimensional Bose-Einstein condensate is long-range coherence; however, in systems of lower dimensionality, not only is the long-range coherence destroyed but additional states of matter are predicted to exist. One such state is a "transverse condensate," first predicted by van Druten and Ketterle [Phys. Rev.

Expansion dynamics of interacting bosons in homogeneous lattices in one and two dimensions.

We experimentally and numerically investigate the expansion of initially localized ultracold bosons in homogeneous one- and two-dimensional optical lattices. We find that both dimensionality and interaction strength crucially influence these nonequilibrium dynamics. While the atoms expand ballistically in all integrable limits, deviations from these limits dramatically suppress the expansion and lead to the appearance of almost bimodal cloud shapes, indicating diffusive dynamics in the center surrounded by ballistic wings.

Negative absolute temperature for motional degrees of freedom.

Absolute temperature is usually bound to be positive. Under special conditions, however, negative temperatures-in which high-energy states are more occupied than low-energy states-are also possible. Such states have been demonstrated in localized systems with finite, discrete spectra.

Correlations in amplified four-wave mixing of matter waves.

The coherence properties of amplified matter waves generated by four-wave mixing (FWM) are studied using the Hanbury-Brown-Twiss method. We examine two limits. In the first case stimulated processes lead to the selective excitation of a pair of spatially separated modes, which we show to be second order coherent, while the second occurs when the FWM process is multimode, due to spontaneous scattering events which leads to incoherent matter waves.

Observation of atomic speckle and Hanbury Brown-Twiss correlations in guided matter waves.

Speckle patterns produced by multiple independent light sources are a manifestation of the coherence of the light field. Second-order correlations exhibited in phenomena such as photon bunching, termed the Hanbury Brown-Twiss effect, are a measure of quantum coherence. Here we observe for the first time atomic speckle produced by atoms transmitted through an optical waveguide, and link this to second-order correlations of the atomic arrival times.

Observation of the first excited transverse mode in guided matter waves.

In direct analogy to the textbook example of light guided in a few-mode fiber (FMF), we report the observation of the first excited mode of an optically guided atomic beam. We selectively excite the atomic analog of the LP₀₁ optical mode by controlling the energy distribution of ultracold atoms loaded into the guide, resulting in a modal structure dominated by a 47(2)% population in the first excited transverse mode. The ability to guide lower-order modes has been essential to demonstrating optical effects such as multimode interferometry, slow light, and entanglement, and an atomic analog to a FMF may lead to similarly useful applications.

Direct measurement of long-range third-order coherence in Bose-Einstein condensates.

A major advance in understanding the behavior of light was to describe the coherence of a light source by using correlation functions that define the spatio-temporal relationship between pairs and larger groups of photons. Correlations are also a fundamental property of matter. We performed simultaneous measurement of the second- and third-order correlation functions for atoms.

The Hanbury Brown-Twiss effect in a pulsed atom laser.

We have used the Hanbury Brown-Twiss effect to directly compare the density correlations of a pulsed atom laser and a pulsed ultracold thermal source of metastable helium. It was found that the isotropic RF outcoupling of atoms from a Bose-Einstein condensate does not result in decoherence, while the 'bunching' typical of incoherent sources was observed for thermal atoms. This new method significantly increases data acquisition rates compared to previous measurements, and also permits future novel experiments which may allow us to probe processes such as the birth and death of a condensate by monitoring correlation effects.

Metastable helium: a new determination of the longest atomic excited-state lifetime.

Exited atoms may relax to the ground state by radiative decay, a process which is usually very fast (of order nanoseconds). However, quantum-mechanical selection rules can prevent such rapid decay, in which case these "metastable" states can have lifetimes of order seconds or longer. In this Letter, we determine experimentally the lifetime of the longest-lived neutral atomic state-the first excited state of helium (the 2(3)S1 metastable state)-to the highest accuracy yet measured.

Predictive modeling & outcomes.

Purpose/objectives: The intent of this article is to explain predictive modeling-a statistical tool-as it applies to the practice of case management. While actuaries and financial experts focus on the statistical relevance of predictive risk scores, case managers will benefit from knowing what these scores mean and how interpreting and applying them into meaningful action can lead to improved patient outcomes.

Primary Practice Setting(s): Predictive modeling can be used by physician practice groups, managed care organizations, worksite wellness programs, and any organization desiring to identify the most actionable population for targeted outreach, education, and management.