64 research outputs found
Measuring entanglement entropy through the interference of quantum many-body twins
Entanglement is one of the most intriguing features of quantum mechanics. It
describes non-local correlations between quantum objects, and is at the heart
of quantum information sciences. Entanglement is rapidly gaining prominence in
diverse fields ranging from condensed matter to quantum gravity. Despite this
generality, measuring entanglement remains challenging. This is especially true
in systems of interacting delocalized particles, for which a direct
experimental measurement of spatial entanglement has been elusive. Here, we
measure entanglement in such a system of itinerant particles using quantum
interference of many-body twins. Leveraging our single-site resolved control of
ultra-cold bosonic atoms in optical lattices, we prepare and interfere two
identical copies of a many-body state. This enables us to directly measure
quantum purity, Renyi entanglement entropy, and mutual information. These
experiments pave the way for using entanglement to characterize quantum phases
and dynamics of strongly-correlated many-body systems.Comment: 14 pages, 12 figures (6 in the main text, 6 in supplementary
material
Realization of a Laughlin state of two rapidly rotating fermions
We realize a Laughlin state of two rapidly rotating fermionic atoms in an
optical tweezer. By utilizing a single atom and spin resolved imaging
technique, we sample the Laughlin wavefunction, thereby revealing its
distinctive features, including a vortex distribution in the relative motion,
correlations in the particles' relative angle, and suppression of the
inter-particle interactions. Our work lays the foundation for atom-by-atom
assembly of fractional quantum Hall states in rotating atomic gases
Fracture behavior of metallic thin films as evaluated by bulge-tests and in situ TEM deformation experiments
Metallic thin films generally show a fracture toughness which is considerably lower than that of bulk samples. Although this has been evidenced by several groups, a conclusive understanding of this low fracture toughness is still missing and open questions related with the difficulty of reliably testing very thin films often remain. Bulge testing is a very suitable method allowing reliable investigations of the fracture toughness of thin films by introducing a slit in a freestanding membrane by focused ion beam (FIB) milling. With such tests the fracture toughness of silver and gold films in the thickness range of 100 nm have been determined to be around 2 MPa m1/2 confirming earlier results obtained with other testing techniques on similar metallic thin films. Recent investigations by Preiss et al. [1] gave an explanation for this extremely low fracture toughness based on in-situ observations of the crack tip region by atomic force microscopy (AFM). The AFM scans show stable crack growth mainly along grain boundaries and sliding of grains. Plastic deformation is localized in a very narrow corridor in front of the crack tip and a large plastic zone, as one would typically expect under plane stress, is not observed. We conclude that the spatial confinement of the plastic deformation is the primary reason for the low fracture toughness of metallic thin films.
More detailed observations of the deformation mechanisms are of particular interest and are enabled by in situ transmission electron microscopy (TEM). For this a new flexible method for the preparation of thin film samples for in situ mechanical testing in a TEM has been developed [2], which is based on a combination of focused ion beam (FIB) shadow milling and electron-beam-assisted etching with Xenon difluoride precursor gas. Loading of the specimens is performed by a TEM Nanoindenter combined with a Push-to-Pull conversion device. In contrast to existing FIB-based preparation approaches, the area of interest is never exposed to ion beam irradiation and a pristine microstructure is preserved.
With this method nanotwinned Cu and Cu-Al thin films were tested in situ in the TEM. Al is an effective element to reduce the stacking fault energy in Cu alloys and leads to increased amount of twinning and detwinning events. The films are tested until final fracture and different deformation mechanism as sliding of grains, twinning and dislocation activity can be correlated with the captured stress-strain curves from the experiment. The fracture behavior of these films will be discussed in the presentation and compared to the bulge-test results.
References
[1] E. I. Preiß, B. Merle, M. Göken; Understanding the extremely low fracture toughness of freestanding gold thin films by in-situ bulge testing in an AFM; Mat. Sci. Eng. A691 (2017) 2018-2025
[2] J.P. Liebig, M. Göken, G. Richter, M. Mačković, T. Przybilla, E. Spiecker, O.N. Pierron, B. Merle; A flexible method for the preparation of thin film samples for in situ TEM characterization combining shadow-FIB milling and electron-beam-assisted etching; Ultramicroscopy 171 (2016) 82–8
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Photon-Assisted Tunneling in a Biased Strongly Correlated Bose Gas
We study the impact of coherently generated lattice photons on an atomic Mott insulator subjected to a uniform force. Analogous to an array of tunnel-coupled and biased quantum dots, we observe sharp, interaction-shifted photon-assisted tunneling resonances corresponding to tunneling one and two lattice sites either with or against the force and resolve multiorbital shifts of these resonances. By driving a Landau-Zener sweep across such a resonance, we realize a quantum phase transition between a paramagnet and an antiferromagnet and observe quench dynamics when the system is tuned to the critical point. Direct extensions will produce gauge fields and site-resolved spin flips, for topological physics and quantum computing.Physic
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