17 research outputs found
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.Comment: 7 pages main text, 2 pages supporting informatio
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.Comment: 6 pages, 6 figures + supplementary informatio
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, He* and He*. Degeneracy
is achieved via Doppler cooling and forced evaporation for He*, and
sympathetically cooling He* with 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
, consisting of 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.Comment: 13 pages, 8 figure
N-body antibunching in a degenerate Fermi gas of ^{3}He^{*} atoms
A key set of observables for investigating quantum systems are the n-body correlation functions, which provide a powerful tool for experimentally determining coherence and directly probing the many-body wave function. While the (bosonic) correlations of photonic systems are well explored, the correlations present in matter-wave systems, particularly for fermionic atoms, are still an emerging field. In this work, we use the unique single-atom detection properties of ^{3}He^{*} atoms to perform simultaneous measurements of the n-body quantum correlations, up to the fifth order, of a degenerate Fermi gas. In a direct demonstration of the Pauli exclusion principle, we observe clear antibunching at all orders and find good agreement with predicted correlation volumes. Our results pave the way for using correlation functions to probe some of the rich physics associated with fermionic systems
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. While the noninteracting Anderson case remains localized, in the interacting case any coupling between the tubes leads to a delocalization of the entire system.We acknowledge financial support by the European Commision (UQUAM, AQuS) and the Nanosystems Initiative Munich (NIM).This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevLett.116.14040