10,006 research outputs found
Bond Order via Light-Induced Synthetic Many-body Interactions of Ultracold Atoms in Optical Lattices
We show how bond order emerges due to light mediated synthetic interactions
in ultracold atoms in optical lattices in an optical cavity. This is a
consequence of the competition between both short- and long-range interactions
designed by choosing the optical geometry. Light induces effective many-body
interactions that modify the landscape of quantum phases supported by the
typical Bose-Hubbard model. Using exact diagonalization of small system sizes
in one dimension, we present the many-body quantum phases the system can
support via the interplay between the density and bond (or matter-wave
coherence) interactions. We find numerical evidence to support that dimer
phases due to bond order are analogous to valence bond states. Different
possibilities of light-induced atomic interactions are considered that go
beyond the typical atomic system with dipolar and other intrinsic interactions.
This will broaden the Hamiltonian toolbox available for quantum simulation of
condensed matter physics via atomic systems.Comment: Accepted in New Journal of Physic
Non-Hermitian Dynamics in the Quantum Zeno Limit
Measurement is one of the most counter-intuitive aspects of quantum physics.
Frequent measurements of a quantum system lead to quantum Zeno dynamics where
time evolution becomes confined to a subspace defined by the projections.
However, weak measurement performed at a finite rate is also capable of locking
the system into such a Zeno subspace in an unconventional way: by Raman-like
transitions via virtual intermediate states outside this subspace, which are
not forbidden. Here, we extend this concept into the realm of non-Hermitian
dynamics by showing that the stochastic competition between measurement and a
system's own dynamics can be described by a non-Hermitian Hamiltonian. We
obtain an analytic solution for ultracold bosons in a lattice and show that a
dark state of the tunnelling operator is a steady state in which the
observable's fluctuations are zero and tunnelling is suppressed by destructive
matter-wave interference. This opens a new venue of investigation beyond the
canonical quantum Zeno dynamics and leads to a new paradigm of competition
between global measurement backaction and short-range atomic dynamics.Comment: Accepted in Phys. Rev.
Multipartite Entangled Spatial Modes of Ultracold Atoms Generated and Controlled by Quantum Measurement
We show that the effect of measurement back-action results in the generation
of multiple many-body spatial modes of ultracold atoms trapped in an optical
lattice, when scattered light is detected. The multipartite mode entanglement
properties and their nontrivial spatial overlap can be varied by tuning the
optical geometry in a single setup. This can be used to engineer quantum states
and dynamics of matter fields. We provide examples of multimode generalizations
of parametric down-conversion, Dicke, and other states, investigate the
entanglement properties of such states, and show how they can be transformed
into a class of generalized squeezed states. Further, we propose how these
modes can be used to detect and measure entanglement in quantum gases.Comment: 6 Pages, 3 Figures, Supplemental Material include
Langevin equations for reaction-diffusion processes
For reaction-diffusion processes with at most bimolecular reactants, we
derive well-behaved, numerically tractable, exact Langevin equations that
govern a stochastic variable related to the response field in field theory.
Using duality relations, we show how the particle number and other quantities
of interest can be computed. Our work clarifies long-standing conceptual issues
encountered in field-theoretical approaches and paves the way for systematic
numerical and theoretical analyses of reaction-diffusion problems.Comment: 5 pages + 6 pages supplemental materia
Detailed Modeling and Reliability Analysis of Fault-Tolerant Processor Arrays
Recent advances in VLSI/WSI technology have led to the design of processor arrays with a large number of processing elements confined in small areas. The use of redundancy to increase fault-tolerance has the effect of reducing the ratio of area dedicated to processing elements over the area occupied by other resources in the array. The assumption of fault-free hardware support (switches, buses, interconnection links, etc.,), leads at best to conservative reliability estimates. However, detailed modeling entails not only an explosive growth in the model state space but also a difficult model construction process. To address the latter problem, a systematic method to construct Markov models for the reliability evaluation of processor arrays is proposed. This method is based on the premise that the fault behavior of a processor array can be modeled by a Stochastic Petri Net (SPN). However, in order to obtain a more compact representation, a set of attributes is associated with each transition in the Petri net model. This representation is referred to as a Modified Stochastic Petri Net (MSPN) model. A MSPN allows the construction of the corresponding Markov model as the reachability graph is being generated. The Markov model generated can include the effect of failures of several different components of the array as well as the effect of a peculiar distribution of faults when the reconfiguration occurs. Specific reconfiguration schemes such as Successive Row Elimination (SRE), Alternate Row-Column Elimination (ARCE) and Direct Reconfiguration (DR), are analyze
On the 2-point function of the O(N) model
The self-energy of the critical 3-dimensional O(N) model is calculated. The
analysis is performed in the context of the Non-Perturbative Renormalization
Group, by exploiting an approximation which takes into account contributions of
an infinite number of vertices. A very simple calculation yields the 2-point
function in the whole range of momenta, from the UV Gaussian regime to the
scaling one. Results are in good agreement with best estimates in the
literature for any value of N in all momenta regimes. This encourages the use
of this simple approximation procedure to calculate correlation functions at
finite momenta in other physical situations
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