335 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
Probing the Superfluid to Mott Insulator Transition at the Single Atom Level
Quantum gases in optical lattices offer an opportunity to experimentally
realize and explore condensed matter models in a clean, tunable system. We
investigate the Bose-Hubbard model on a microscopic level using single
atom-single lattice site imaging; our technique enables space- and
time-resolved characterization of the number statistics across the
superfluid-Mott insulator quantum phase transition. Site-resolved probing of
fluctuations provides us with a sensitive local thermometer, allows us to
identify microscopic heterostructures of low entropy Mott domains, and enables
us to measure local quantum dynamics, revealing surprisingly fast transition
timescales. Our results may serve as a benchmark for theoretical studies of
quantum dynamics, and may guide the engineering of low entropy phases in a
lattice
Cold Matter Assembled Atom-by-Atom
The realization of large-scale fully controllable quantum systems is an
exciting frontier in modern physical science. We use atom-by-atom assembly to
implement a novel platform for the deterministic preparation of regular arrays
of individually controlled cold atoms. In our approach, a measurement and
feedback procedure eliminates the entropy associated with probabilistic trap
occupation and results in defect-free arrays of over 50 atoms in less than 400
ms. The technique is based on fast, real-time control of 100 optical tweezers,
which we use to arrange atoms in desired geometric patterns and to maintain
these configurations by replacing lost atoms with surplus atoms from a
reservoir. This bottom-up approach enables controlled engineering of scalable
many-body systems for quantum information processing, quantum simulations, and
precision measurements.Comment: 12 pages, 9 figures, 3 movies as ancillary file
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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
Modern Feynman Diagrammatic One-Loop Calculations
In this talk we present techniques for calculating one-loop amplitudes for
multi-leg processes using Feynman diagrammatic methods in a semi-algebraic
context. Our approach combines the advantages of the different methods allowing
for a fast evaluation of the amplitude while monitoring the numerical stability
of the calculation. In phase space regions close to singular kinematics we use
a method avoiding spurious Gram determinants in the calculation. As an
application of our approach we report on the status of the calculation of the
amplitude for the process .Comment: 10 pages, 2 figures; contribution to the proceedings of the CPP2010
Workshop, 23-25 Sep. 2010, KEK, Tsukuba, Japa
Increases in norepinephrine release and ovarian cyst formation during ageing in the rat
<p>Abstract</p> <p>Background</p> <p>Depletion of ovarian follicles is associated with the end of reproductive function in ageing females. Recently, it has been described that this process parallels increases in the concentration of norepinephrine (NE) in the rat ovary. In sexually mature rats, experimentally-induced increases in the sympathetic tone of the ovary is causally related to ovarian cyst formation and deranged follicular development. Thus, there is a possibility that increased ovarian NE concentrations represent changes in the activity of sympathetic nerves, which consequently participate in the process of ovarian cyst formation observed during ageing in the human and experimental animal models.</p> <p>Methods</p> <p>Sprague-Dawley rats between 6 and 14 months old were used to analyse the capacity of the ovary to release <sup>3</sup>H-NE recently incorporated under transmural depolarisation in relation to changes in the ovarian follicular population. Morphometric analysis of ovarian follicles and real time PCR for Bcl2 and Bax mRNA were used to assess follicular atresia.</p> <p>Results</p> <p>From 8 months old, the induced release of recently incorporated <sup>3</sup>H-norepinephrine (<sup>3</sup>H-NE) from the ovary and ovarian NE concentrations increased, reaching their peak values at 12 months old and remained elevated up to 14 months old. Increases in sympathetic nerve activity paralleled changes in the follicular population, as well as disappearance of the corpus luteum. In contrast, luteinised follicles, precystic follicles, and cystic follicles increased. During this period, the relationship between Bax and Bcl2 mRNAs (the proapoptotic/antiapoptotic signals) increased, suggesting atresia as the principal mechanism contributing to the decreased follicular population. When NE tone was increased, the mRNA ratio favoured Bcl2 to Bax and antiapoptotic signals dominated this period of development. Thus, these changing ratios could be responsible for the increase in luteinised follicles, as well as precystic and cystic follicles.</p> <p>Conclusion</p> <p>These data suggest that the ageing process in the ovary of the Sprague-Dawley rat is accompanied by an increased sympathetic tone of the ovary. Consequently, this sympathetic change could be related to a neuroendocrine-driven formation of a polycystic condition similar to that observed in the sympathetic-activated adult ovary.</p
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