1,635 research outputs found
Decoherence suppression for oscillator-assisted geometric quantum gates via symmetrization
We propose a novel symmetrization procedure to beat decoherence for
oscillator-assisted quantum gate operations. The enacted symmetry is related to
the global geometric features of qubits transformation based on ancillary
oscillator modes, e.g. phonons in an ion-trap system. It is shown that the
devised multi-circuit symmetrized evolution endows the system with a two-fold
resilience against decoherence: insensitivity to thermal fluctuations and
quantum dissipation.Comment: 4 pages, 2 figure
Error Avoiding Quantum Codes
The existence is proved of a class of open quantum systems that admits a
linear subspace of the space of states such that the restriction of
the dynamical semigroup to the states built over is unitary. Such
subspace allows for error-avoiding (noiseless) enconding of quantum
information.Comment: 9 pages, LaTe
The global chilling effects of antidumping.
Advocates of antidumping (AD) laws downplay their effects by arguing that the trade flows that are subject to AD are small and their distortions negligible. This paper is the first to counter that notion by quantifying the worldwide effect of AD laws on aggregate trade flows. The recent proliferation of AD laws across countries provides us with a natural experiment to estimate the trade effects of adopting versus using AD laws; differences in the intensity of use among countries with older AD laws allow us to investigate reputation effects. For this purpose, we estimate worldwide trade flows using a gravity equation spanning 21 years (1980-2000) of annual observations. Our estimates confirm that AD effects are not small. Among other findings, new tough users have their aggregate imports depressed by 15.7 billion US on top of the cumulative negative effect of reputation. For some countries, the dampening effects of AD laws on trade flows are found to nearly offset the gains from trade liberalization.Behavior; Control; Power; Law; Intensity; Trade liberalization;
Does Antidumping Use Contribute to Trade Liberalization? An Empirical Analysis
Some supporters of antidumping have argued that this procedure serves as a kind of "safety valve" for protectionist pressure.This paper examines whether there is any empirical evidence that the use of antidumping actions has contributed to tariff reductions in a sample of 35 developing and developed countries.There is very little evidence that such a relationship might exist among the 27 developing countries in the sample.We do find some weak but inconsistent evidence for antidumping helping liberalization efforts in the experience of developed countries, which have been the traditional users of antidumping.Antidumping;Trade Liberalization;Commercial Policy
The Global Chilling Effects of Antidumping Proliferation
Advocates of antidumping (AD) laws downplay their effects by arguing that the trade flows that are subject to AD are small and their distortions negligible.This paper is the first to counter that notion by quantifying the worldwide effect of AD laws on aggregate trade flows.The recent proliferation of AD laws across countries provides us with a natural experiment to estimate the trade effects of adopting versus using AD laws; differences in the intensity of use among countries with older AD laws allow us to investigate reputation effects.For this purpose, we estimate worldwide trade flows using a gravity equation spanning 21 years (1980-2000) of annual observations.Our estimates confirm that AD effects are not small.Among other findings, new tough users have their aggregate imports depressed by 15.7 billion US on top of the cumulative negative effect of reputation.For some countries, the dampening effects of AD laws on trade flows are found to nearly offset the gains from trade liberalization.antidumping;gravity equation;trade liberalization;trade flows
Bures metric over thermal state manifolds and quantum criticality
We analyze the Bures metric over the manifold of thermal density matrices for
systems featuring a zero temperature quantum phase transition. We show that the
quantum critical region can be characterized in terms of the temperature
scaling behavior of the metric tensor itself. Furthermore, the analysis of the
metric tensor when both temperature and an external field are varied, allows to
complement the understanding of the phase diagram including cross-over regions
which are not characterized by any singular behavior. These results provide a
further extension of the scope of the metric approach to quantum criticality.Comment: 9 pages, 4 figures, LaTeX problems fixed, references adde
Quantum fidelity and quantum phase transitions in matrix product states
Matrix product states, a key ingredient of numerical algorithms widely
employed in the simulation of quantum spin chains, provide an intriguing tool
for quantum phase transition engineering. At critical values of the control
parameters on which their constituent matrices depend, singularities in the
expectation values of certain observables can appear, in spite of the
analyticity of the ground state energy. For this class of generalized quantum
phase transitions we test the validity of the recently introduced fidelity
approach, where the overlap modulus of ground states corresponding to slightly
different parameters is considered. We discuss several examples, successfully
identifying all the present transitions. We also study the finite size scaling
of fidelity derivatives, pointing out its relevance in extracting critical
exponents.Comment: 7 pages, 3 figure
Quantum phase transitions and quantum fidelity in free fermion graphs
In this paper we analyze the ground state phase diagram of a class of
fermionic Hamiltonians by looking at the fidelity of ground states
corresponding to slightly different Hamiltonian parameters. The Hamiltonians
under investigation can be considered as the variable range generalization of
the fermionic Hamiltonian obtained by the Jordan-Wigner transformation of the
XY spin-chain in a transverse magnetic field. Under periodic boundary
conditions, the matrices of the problem become circulant and the models are
exactly solvable. Their free-ends counterparts are instead analyzed
numerically. In particular, we focus on the long range model corresponding to a
fully connected directed graph, providing asymptotic results in the
thermodynamic limit, as well as the finite-size scaling analysis of the second
order quantum phase transitions of the system. A strict relation between
fidelity and single particle spectrum is demonstrated, and a peculiar gapful
transition due to the long range nature of the coupling is found. A comparison
between fidelity and another transition marker borrowed from quantum
information i.e., single site entanglement, is also considered.Comment: 14 pages, 5 figure
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