11,458 research outputs found
Large deviations in quantum lattice systems: one-phase region
We give large deviation upper bounds, and discuss lower bounds, for the
Gibbs-KMS state of a system of quantum spins or an interacting Fermi gas on the
lattice. We cover general interactions and general observables, both in the
high temperature regime and in dimension one.Comment: 30 pages, LaTeX 2
Foreclosing Competition through Access Charges and Price Discrimination
This article analyzes competition between two asymmetric networks, an incumbent and a new entrant. Networks compete in non-linear tariffs and may charge different prices for on-net and off-net calls. Departing from cost-based access pricing allows the incumbent to foreclose the market in a profitable way. If the incumbent benefits from customer inertia, then it has an incentive to insist in the highest possible access markup even if access charges are reciprocal and even in the absence of actual switching costs. If instead the entrant benefits from customer activism, then foreclosure is profitable only when switching costs are large enough.Access Pricing, Entry Deterrence, Interconnection, Network Competition, Two-way Access
Quantum lattice models at intermediate temperatures
We analyze the free energy and construct the Gibbs-KMS states for a class of
quantum lattice systems, at low temperatures and when the interactions are
almost diagonal in a suitable basis. We study systems with continuous symmetry,
but our results are valid for discrete symmetry breaking only. Such phase
transitions occur at intermediate temperatures where the continuous symmetry is
not broken, while at very low temperature continuous symmetry breaking may
occur.Comment: 25 pages, 6 figure
Foreclosing competition through access charges and price discrimination
This article analyzes competition between two asymmetric networks, an incumbent and a new entrant. Networks compete in non-linear tariffs and may charge different prices for on-net and off-net calls. Departing from cost-based access pricing allows the incumbent to foreclose the market in a profitable way. If the incumbent benefits from customer inertia, then it has an incentive to insist on the highest possible access markup even if access charges are reciprocal and even in the absence of actual switching costs. If instead the entrant benefits from customer activism, then foreclosure is profitable only when switching costs are large enough.Networks; benefits; costs; customer;
Quantum limited measurements of atomic scattering properties
We propose a method to perform precision measurements of the interaction
parameters in systems of N ultra-cold spin 1/2 atoms. The spectroscopy is
realized by first creating a coherent spin superposition of the two relevant
internal states of each atom and then letting the atoms evolve under a
squeezing Hamiltonian. The non-linear nature of the Hamiltonian decreases the
fundamental limit imposed by the Heisenberg uncertainty principle to N^(-2), a
factor of N smaller than the fundamental limit achievable with non-interacting
atoms. We study the effect of decoherence and show that even with decoherence,
entangled states can outperform the signal to noise limit of non-entangled
states. We present two possible experimental implementations of the method
using Bose-Einstein spinor condensates and fermionic atoms loaded in optical
lattices and discuss their advantages and disadvantages.Comment: 7 pages, 5 figures. References adde
Simulating generic spin-boson models with matrix product states
The global coupling of few-level quantum systems ("spins") to a discrete set
of bosonic modes is a key ingredient for many applications in quantum science,
including large-scale entanglement generation, quantum simulation of the
dynamics of long-range interacting spin models, and hybrid platforms for force
and spin sensing. We present a general numerical framework for treating the
out-of-equilibrium dynamics of such models based on matrix product states. Our
approach applies for generic spin-boson systems: it treats any spatial and
operator dependence of the two-body spin-boson coupling and places no
restrictions on relative energy scales. We show that the full counting
statistics of collective spin measurements and infidelity of quantum simulation
due to spin-boson entanglement, both of which are difficult to obtain by other
techniques, are readily calculable in our approach. We benchmark our method
using a recently developed exact solution for a particular spin-boson coupling
relevant to trapped ion quantum simulators. Finally, we show how decoherence
can be incorporated within our framework using the method of quantum
trajectories, and study the dynamics of an open-system spin-boson model with
spatially non-uniform spin-boson coupling relevant for trapped atomic ion
crystals in the presence of molecular ion impurities.Comment: 13 pages+refs. 13 figure
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