arXiv subjects

Sean S. Hodgman

Publications and source records attributed to Sean S. Hodgman.

11 recordsLinked to original sources

arXiv2023

A matter wave Rarity-Tapster interferometer to demonstrate non-locality

We present an experimentally viable approach to demonstrating quantum non-locality in a matter wave system via a Rarity-Tapster interferometer using two $s$-wave scattering halos generated by colliding helium Bose-Einstein condensates. The theoretical basis for this method is discussed, and its suitability is experimentally quantified. As a proof of concept, we demonstrate an interferometric visibility of $V=0.42(9)$, corresponding to a maximum CSHS-Bell parameter of $S=1.1(1)$, for the Clauser-Horne-Shimony-Holt (CHSH) version of the Bell inequality, between atoms separated by $\sim 4$ correlation lengths. This constitutes a significant step towards a demonstration of a Bell inequality violation for motional degrees of freedom of massive particles and possible measurements of quantum effects in a gravitationally sensitive system.

quant-ph↗

arXiv2022

Production of a highly degenerate Fermi gas of metastable helium-3 atoms

We report on the achievement of quantum degeneracy in both components of a Bose-Fermi mixture of metastable helium atoms, $^4$He* and $^3$He*. Degeneracy is achieved via Doppler cooling and forced evaporation for $^4$He*, and sympathetically cooling $^3$He* with $^4$He*. We discuss our simplified implementation, along with the high versatility of our system. This technique is able to produce a degenerate Fermi gas with a minimum reduced temperature of $T/T_F=0.14(1)$, consisting of $2.5 \times 10^4$ $^3$He* atoms. Due to the high internal energy of both isotopes single atom detection is possible, opening the possibility of a large number of experiments into Bose-Fermi mixtures.

cond-mat.quant-gas↗

arXiv2020

Frequency measurements of transitions from the $2^{3\!}P_2$ state to the $5^{1\!}D_2$, $5^{3\!}S_1$, and $5^{3\!}D$ states in ultracold helium

We perform laser absorption spectroscopy with ultracold $^4$He atoms to measure the energy intervals between the $2^{3\!} P_2$ level and five levels in the n = 5 manifold. The laser light perturbs the cold atomic cloud during the production of Bose-Einstein condensates and decreases the phase space density, causing a measurable decrease in the number of atoms in the final condensate. We improve on the precision of previous measurements by at least an order of magnitude, and report the first observation of the spin-forbidden $2^{3\!}P_2 - 5^{1\!}D_2$ transition in helium. Theoretical transition energies agree with the observed values within our experimental uncertainty.

physics.atom-ph↗

arXiv2019

Higher Order Quantum Ghost Imaging with Ultra-Cold Atoms

Ghost imaging is a quantum optics technique that uses correlations between two beams to reconstruct an image in one beam from photons that do not interact with the object being imaged. While pairwise (second order) correlations are usually used to create the image, higher order correlations can be utilized to improve the performance of ghost imaging. In this paper, we demonstrate higher order atomic ghost imaging, using entangled ultracold metastable helium atoms from an s-wave collision halo. We construct higher order ghost images up to 5th order and show that using higher order correlations can improve the visibility of the images without impacting the resolution. This is the first demonstration of higher order ghost imaging with massive particles and the first higher order ghost imaging protocol of any type using a quantum source.

cond-mat.quant-gas↗

arXiv2018

Approaching the adiabatic timescale with machine-learning

The control and manipulation of quantum systems without excitation is 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 (BEC) 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 towards this goal. The algorithm is given control of the coupled decompression and transport of a metastable helium condensate, with its performance determined after each experimental iteration by measuring the excitations of the resultant BEC. After each iteration the algorithm adjusts its internal model of the system to create an improved control output for the next iteration. Given sufficient control over the decompression, the algorithm converges to a novel solution that sets the current speed record in relation to the adiabatic timescale, beating out other experimental realizations based on theoretical approaches. This method presents a feasible approach for implementing fast state preparations or transformations in other quantum systems, without requiring a solution to a theoretical model of the system. Implications for fundamental physics and cooling are discussed.

quant-ph↗

arXiv2016

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

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 (7.8 GHz) without mode-hopping and modulated with bandwidths up to 3 kHz (piezo) and 37(3) kHz (current). The spectral linewidth of the free-running ECL was measured to be 22(2) kHz (Gaussian) and 4.2(3) kHz (Lorentzian) over 22.5 ms, while a long-term frequency stability better than 40(20) kHz over 11 hours was observed when locked to an atomic reference.

physics.ins-det↗

arXiv2016

Signatures of Many-Body Localization in a Controlled Open Quantum System

In the presence of disorder, an interacting closed quantum system can undergo many-body localization (MBL) and fail to thermalize. However, over long times even weak couplings to any thermal environment will necessarily thermalize the system and erase all signatures of MBL. This presents a challenge for experimental investigations of MBL, since no realistic system can ever be fully closed. In this work, we experimentally explore the thermalization dynamics of a localized system in the presence of controlled dissipation. Specifically, we find that photon scattering results in a stretched exponential decay of an initial density pattern with a rate that depends linearly on the scattering rate. We find that the resulting susceptibility increases significantly close to the phase transition point. In this regime, which is inaccessible to current numerical studies, we also find a strong dependence on interactions. Our work provides a basis for systematic studies of MBL in open systems and opens a route towards extrapolation of closed system properties from experiments.

cond-mat.quant-gas↗

arXiv2016

Coupling Identical 1D Many-Body Localized Systems

We experimentally study the effects of coupling one-dimensional Many-Body Localized (MBL) systems with identical disorder. Using a gas of ultracold fermions in an optical lattice, we artifically prepare an initial charge density wave in an array of 1D tubes with quasi-random onsite disorder and monitor the subsequent dynamics over several thousand tunneling times. We find a strikingly different behavior between MBL and Anderson Localization. While the non-interacting Anderson case remains localized, in the interacting case any coupling between the tubes leads to a delocalization of the entire system.

cond-mat.quant-gas↗

arXiv2015

Observation of many-body localization of interacting fermions in a quasi-random optical lattice

We experimentally observe many-body localization of interacting fermions in a one-dimensional quasi-random optical lattice. We identify the many-body localization 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 remnants of the initial order. In contrast, above a critical disorder strength a significant portion of the initial ordering persists, thereby serving as an effective order parameter for localization. The stationary density wave order and the critical disorder value show a distinctive dependence on the interaction strength, in agreement with numerical simulations. We connect this dependence to the ubiquitous logarithmic growth of entanglement entropy characterizing the generic many-body localized phase.

cond-mat.quant-gas↗

arXiv2013

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 non-equilibrium 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. For strongly interacting bosons, we observe a dimensional crossover of the dynamics from ballistic in the one-dimensional hard-core case to diffusive in two dimensions, as well as a similar crossover when higher occupancies are introduced into the system.

cond-mat.quant-gas↗

arXiv2012

Negative Absolute Temperature for Motional Degrees of Freedom

Absolute temperature, the fundamental temperature scale in thermodynamics, is usually bound to be positive. Under special conditions, however, negative temperatures - where high-energy states are more occupied than low-energy states - are also possible. So far, such states have been demonstrated in localized systems with finite, discrete spectra. Here, we were able to prepare a negative temperature state for motional degrees of freedom. By tailoring the Bose-Hubbard Hamiltonian we created an attractively interacting ensemble of ultracold bosons at negative temperature that is stable against collapse for arbitrary atom numbers. The quasi-momentum distribution develops sharp peaks at the upper band edge, revealing thermal equilibrium and bosonic coherence over several lattice sites. Negative temperatures imply negative pressures and open up new parameter regimes for cold atoms, enabling fundamentally new many-body states and counterintuitive effects such as Carnot engines above unity efficiency.

cond-mat.quant-gas↗