8,429 research outputs found
Fermionic Coset Models as Topological Models
By considering the fermionic realization of coset models, we show that
the partition function for the model defines a Topological Quantum
Field Theory and coincides with that for a 2-dimensional Abelian BF system. In
the non-Abelian case, we prove the topological character of coset models
by explicit computation, also finding a natural extension of 2-dimensional BF
systems with non-Abelian symmetry.Comment: 14p
Quasiadiabatic dynamics of ultracold bosonic atoms in a one-dimensional optical superlattice
We study the quasiadiabatic dynamics of a one-dimensional system of ultracold
bosonic atoms loaded in an optical superlattice. Focusing on a slow linear
variation in time of the superlattice potential, the system is driven from a
conventional Mott insulator phase to a superlattice-induced Mott insulator,
crossing in between a gapless critical superfluid region. Due to the presence
of a gapless region, a number of defects depending on the velocity of the
quench appear. Our findings suggest a power-law dependence similar to the
Kibble-Zurek mechanism for intermediate values of the quench rate. For the
temporal ranges of the quench dynamics that we considered, the scaling of
defects depends nontrivially on the width of the superfluid region.Comment: 6 Pages, 4 Figure
Optimal correlations in many-body quantum systems
Information and correlations in a quantum system are closely related through
the process of measurement. We explore such relation in a many-body quantum
setting, effectively bridging between quantum metrology and condensed matter
physics. To this aim we adopt the information-theory view of correlations, and
study the amount of correlations after certain classes of
Positive-Operator-Valued Measurements are locally performed. As many-body
system we consider a one-dimensional array of interacting two-level systems (a
spin chain) at zero temperature, where quantum effects are most pronounced. We
demonstrate how the optimal strategy to extract the correlations depends on the
quantum phase through a subtle interplay between local interactions and
coherence.Comment: 5 pages, 5 figures + supplementary material. To be published in PR
Non-Abelian fractional quantum Hall states and chiral coset conformal field theories
We propose an effective Lagrangian for the low energy theory of the Pfaffian
states of the fractional quantum Hall effect in the bulk in terms of
non-Abelian Chern-Simons (CS) actions. Our approach exploits the connection
between the topological Chern-Simons theory and chiral conformal field
theories. This construction can be used to describe a large class of
non-Abelian FQH states.Comment: Revised manuscript, 17 pages; new section discusses parafermion
state
Diagnosing order by disorder in quantum spin systems
In this paper we study the frustrated J1-J2 quantum Heisenberg model on the
square lattice for J2 > 2J1, in a magnetic field. In this regime the classical
system is known to have a degenerate manifold of lowest energy configurations,
where standard thermal order by disorder occurs. In order to study its quantum
version we use a path integral formulation in terms of coherent states. We show
that the classical degeneracy in the plane transverse to the magnetic field is
lifted by quantum fluctuations. Collinear states are then selected, in a
similar pattern to that set by thermal order by disorder, leaving a Z2
degeneracy. A careful analysis reveals a purely quantum mechanical effect given
by the tunneling between the two minima selected by fluctuations. The effective
description contains two planar (XY -like) fields conjugate to the total
magnetization and the difference of the two sublattice magnetizations. Disorder
in either or both of these fields produces the locking of their conjugate
observables. Furthermore, within this scenario we argue that the quantum state
is close to a product state.Comment: 8 pages, 3 figure
Lean supply chain planning: Simulation of lean techniques integration
Lean Supply Chain (LSC) has become a strategic configuration in order to satisfy customer's expectations efficiently and effectively. LSC concept is the implementation of Lean principles and techniques outside single company boundaries, creating the flow and making SC reacting instead of foreseeing. Supply Chain Planning (SCP) is a part of SCM management strategy that allows managers to align operations of different companies and so improve operations efficiency and effectiveness. Lean Supply Chain Planning (LSCP) is a new SCP model that is growing interest among both academics and practitioners, but it is not well studied yet. This paper aims at providing a theoretical and practical guidelines about Lean techniques implementations impact in SCP. To reach it, a Discret-event-simulation (DES) simulation model of a three-echelon and multi-product supply chain has been set. This research focuses on three principles of Lean production: identifying the value, creating flow to the customer and pull. The results achieved demonstrate that LSCP techniques have a positive impact on inventories levels and in particular, they demonstrate synergy among techniques so that total benefit is greater than the sum of benefits of single technique implementations
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