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Copenhagen, Denmark

Zeuner J.M.,Friedrich - Schiller University of Jena | Rechtsman M.C.,Pennsylvania State University | Plotnik Y.,Technion - Israel Institute of Technology | Lumer Y.,Technion - Israel Institute of Technology | And 4 more authors.
Physical Review Letters | Year: 2015

We present the first experimental observation of a topological transition in a non-Hermitian system. In contrast to standard methods for examining topological properties, which involve probing edge (or surface) states, we monitor the topological transition by employing bulk dynamics only. The system is composed of a lattice of evanescently coupled optical waveguides, and non-Hermitian behavior is engineered by inducing bending loss by spatially "wiggling" every second waveguide. © 2015 American Physical Society. Source

Rudner M.S.,Niels Bohr International Academy | Rudner M.S.,Ohio State University | Rudner M.S.,Austrian Academy of Sciences | Levitov L.S.,Massachusetts Institute of Technology
Physical Review Letters | Year: 2013

Early experiments on spin-blockaded double quantum dots revealed robust, large-amplitude current oscillations in the presence of a static (dc) source-drain bias. Despite experimental evidence implicating dynamical nuclear polarization, the mechanism has remained a mystery. Here we introduce a minimal albeit realistic model of coupled electron and nuclear spin dynamics which supports self-sustained oscillations. Our mechanism relies on a nuclear spin analog of the tunneling magnetoresistance phenomenon (spin-dependent tunneling rates in the presence of an inhomogeneous Overhauser field) and nuclear spin diffusion, which governs dynamics of the spatial profile of nuclear polarization. The proposed framework naturally explains the differences in phenomenology between vertical and lateral quantum dot structures as well as the extremely long oscillation periods. © 2013 American Physical Society. Source

Kastoryano M.J.,Niels Bohr Institute | Kastoryano M.J.,Niels Bohr International Academy | Reiter F.,Niels Bohr Institute | Sorensen A.S.,Niels Bohr Institute
Physical Review Letters | Year: 2011

We propose a novel scheme for the preparation of a maximally entangled state of two atoms in an optical cavity. Starting from an arbitrary initial state, a singlet state is prepared as the unique fixed point of a dissipative quantum dynamical process. In our scheme, cavity decay is no longer undesirable, but plays an integral part in the dynamics. As a result, we get a qualitative improvement in the scaling of the fidelity with the cavity parameters. Our analysis indicates that dissipative state preparation is more than just a new conceptual approach, but can allow for significant improvement as compared to preparation protocols based on coherent unitary dynamics. © 2011 American Physical Society. Source

Greensite J.,Niels Bohr International Academy | Langfeld K.,University of Plymouth
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We apply the relative weights method [J. Greensite, Phys. Rev. D 86, 114507 (2012)] to determine the effective Polyakov line action for SU(2) lattice gauge theory in the confined phase, at lattice coupling β=2.2 and N t=4 lattice spacings in the time direction. The effective action turns out to be bilinear in the fundamental representation Polyakov line variables, with a rather simple expression for the finite range kernel. The validity of this action is tested by computing Polyakov line correlators, via Monte Carlo simulation, in both the effective action and the underlying lattice theory. It is found that the correlators in each theory are in very close agreement. © 2013 American Physical Society. Source

Cremon J.C.,Lund University | Kavoulakis G.M.,Technological Educational Institute of Crete | Mottelson B.R.,Niels Bohr International Academy | Reimann S.M.,Lund University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

For a weakly interacting Bose gas rotating in a harmonic trap we relate the yrast states of small systems (that can be treated exactly) to the thermodynamic limit (derived within the mean-field approximation). For a few dozens of atoms, the yrast line shows distinct quasiperiodic oscillations with increasing angular momentum that originate from the internal structure of the exact many-body states. These finite-size effects disappear in the thermodynamic limit, where the Gross-Pitaevskii approximation provides the exact energy to leading order in the number of particles N. However, the exact yrast states reveal significant structure not captured by the mean-field approximation: Even in the limit of large N, the corresponding mean-field solution accounts for only a fraction of the total weight of the exact quantum state. © 2013 American Physical Society. Source

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