12,372 research outputs found
Lieb-Robinson Bounds in Quantum Many-Body Physics
We give an overview of recent results on Lieb-Robinson bounds and some of
their applications in the study of quantum many-body models in condensed matter
physics.Comment: Lecture Notes for the school "Entropy and the Quantum", 16-20 March
2009, Tucson, Arizona
Locality Estimates for Quantum Spin Systems
We review some recent results that express or rely on the locality properties
of the dynamics of quantum spin systems. In particular, we present a slightly
sharper version of the recently obtained Lieb-Robinson bound on the group
velocity for such systems on a large class of metric graphs. Using this bound
we provide expressions of the quasi-locality of the dynamics in various forms,
present a proof of the Exponential Clustering Theorem, and discuss a
multi-dimensional Lieb-Schultz-Mattis Theorem.Comment: Contribution for the proceedings of ICMP XV, Rio de Janeiro, 200
On the dynamics of lattice systems with unbounded on-site terms in the Hamiltonian
We supply the mathematical arguments required to complete the proofs of two
previously published results: Lieb-Robinson bounds for the dynamics of quantum
lattice systems with unbounded on-site terms in the Hamiltonian and the
existence of the thermodynamic limit of the dynamics of such systems
Pulsed source of spectrally uncorrelated and indistinguishable photons at telecom wavelengths
We report on the generation of indistinguishable photon pairs at telecom
wavelengths based on a type-II parametric down conversion process in a
periodically poled potassium titanyl phosphate (PPKTP) crystal. The phase
matching, pump laser characteristics and coupling geometry are optimised to
obtain spectrally uncorrelated photons with high coupling efficiencies. Four
photons are generated by a counter- propagating pump in the same crystal and
anlysed via two photon interference experiments between photons from each pair
source as well as joint spectral and g^(2) measurements. We obtain a spectral
purity of 0.91 and coupling efficiencies around 90% for all four photons
without any filtering. These pure indistinguishable photon sources at telecom
wavelengths are perfectly adapted for quantum network demonstrations and other
multi-photon protocols
Tracking ancient beach-lines inland: 2600-year-old dentate-stamped ceramics at Hopo, Vailala River region, Papua New Guinea
The Lapita expansion took Austronesian seafaring peoples with distinctive pottery eastward from the Bismarck Archipelago to western Polynesia during the late second millennium BC, marking the first stage in the settlement of Oceania. Here it is shown that a parallel process also carried Lapita pottery and people many hundreds of kilometres westward along the southern shore of Papua New Guinea. The key site is Hopo, now 4.5km inland owing to the progradation of coastal sand dunes, but originally on the sea edge. Pottery and radiocarbon dates indicate Lapita settlement in this location c.600 BC, and suggest that the long-distance maritime networks linking the entire southern coast of Papua New Guinea in historical times may trace their origin to this period
Testing Optimal Punishment Mechanisms under Price Regulation: the Case of the Retail Market for Gasoline
We analyse the effects of a price floor on price wars (or deep price cuts) in the retail market for gasoline. Bertrand supergame oligopoly models predict that price wars should last longer in the presence of price floors. In 1996, the introduction of a price floor in the Quebec retail market for gasoline serves as a natural experiment with which to test this prediction. We use a Markov Switching Model with two latent states to simultaneously identify the periods of price-collusion/price-war and estimate the parameters characterizing each state. Results support the prediction that price floors reduce the intensity of price wars but increase their expected duration.price regulation, oligopoly supergame, Markov switching model, gasoline
Political Predation and Economic Development
We analyze a game between citizens and governments, whose type (benevolent or predatory) is unknown to the public. Opportunistic governments mix between predation and restraint. As long as restraint is observed, political expectations improve, people enter the modern sector, and the economy grows. Once there is predation, the reputation of the government is ruined and the economy collapses. If citizens are unable to overthrow this government, the collapse is durable. Otherwise, a new government is drawn and the economy can rebound. Consistent with stylized facts, equilibrium political and economic histories are random, unstable, and exhibit long-term divergence.
Entanglement Dynamics of Disordered Quantum XY Chains
We consider the dynamics of the quantum XY chain with disorder under the
general assumption that the expectation of the eigenfunction correlator of the
associated one-particle Hamiltonian satisfies a decay estimate typical of
Anderson localization. We show that, starting from a broad class of product
initial states, entanglement remains bounded for all times. For the XX chain,
we also derive bounds on the particle transport which, in particular, show that
the density profile of initial states that consist of fully occupied and empty
intervals, only have significant dynamics near the edges of those intervals,
uniformly for all times.Comment: 22 pages, final version, to appear in Lett. Math. Phy
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