60 research outputs found
Fast simulation of a quantum phase transition in an ion-trap realisable unitary map
We demonstrate a method of exploring the quantum critical point of the Ising
universality class using unitary maps that have recently been demonstrated in
ion trap quantum gates. We reverse the idea with which Feynman conceived
quantum computing, and ask whether a realisable simulation corresponds to a
physical system. We proceed to show that a specific simulation (a unitary map)
is physically equivalent to a Hamiltonian that belongs to the same universality
class as the transverse Ising Hamiltonian. We present experimental signatures,
and numerical simulation for these in the six-qubit case.Comment: 12 pages, 6 figure
Measurement-Based Teleportation Along Quantum Spin Chains
We consider teleportation of an arbitrary spin-1/2 target quantum state along
the ground state of a quantum spin chain. We present a decomposition of the
Hilbert space of the many body quantum state into 4 vector spaces. Within each
of these subspaces, it is possible to take any superposition of states, and use
projective measurements to perform unit fidelity teleportation. Any such
superposition is necessarily a spin liquid state. We also show that all total
spin-0 quantum states belong in the same space, so that it is possible to
perform unit fidelity teleportation over any one-dimensional spin-0 many body
quantum state. We generalise to -Bell states, and present some general
bounds on fidelity of teleportation given a general state of a quantum spin
chain.Comment: 5 pages, 2 figures, presented as posters at "Quantum entanglement in
physical and information sciences", Pisa, 2004 and at the AIP Congress,
Canberra, 200
Ground state fidelity and quantum phase transitions in free Fermi systems
We compute the fidelity between the ground states of general quadratic
fermionic hamiltonians and analyze its connections with quantum phase
transitions. Each of these systems is characterized by a real
matrix whose polar decomposition, into a non-negative and a unitary
, contains all the relevant ground state (GS) information. The boundaries
between different regions in the GS phase diagram are given by the points of,
possibly asymptotic, singularity of . This latter in turn implies a
critical drop of the fidelity function. We present general results as well as
their exemplification by a model of fermions on a totally connected graph.Comment: 4 pages, 2 figure
From density-matrix renormalization group to matrix product states
In this paper we give an introduction to the numerical density matrix
renormalization group (DMRG) algorithm, from the perspective of the more
general matrix product state (MPS) formulation. We cover in detail the
differences between the original DMRG formulation and the MPS approach,
demonstrating the additional flexibility that arises from constructing both the
wavefunction and the Hamiltonian in MPS form. We also show how to make use of
global symmetries, for both the Abelian and non-Abelian cases.Comment: Numerous small changes and clarifications, added a figur
New Spirometry Indices for Detecting Mild Airflow Obstruction.
The diagnosis of chronic obstructive pulmonary disease (COPD) relies on demonstration of airflow obstruction. Traditional spirometric indices miss a number of subjects with respiratory symptoms or structural lung disease on imaging. We hypothesized that utilizing all data points on the expiratory spirometry curves to assess their shape will improve detection of mild airflow obstruction and structural lung disease. We analyzed spirometry data of 8307 participants enrolled in the COPDGene study, and derived metrics of airflow obstruction based on the shape on the volume-time (Parameter D), and flow-volume curves (Transition Point and Transition Distance). We tested associations of these parameters with CT measures of lung disease, respiratory morbidity, and mortality using regression analyses. There were significant correlations between FEV1/FVC with Parameter D (r = -0.83; p < 0.001), Transition Point (r = 0.69; p < 0.001), and Transition Distance (r = 0.50; p < 0.001). All metrics had significant associations with emphysema, small airway disease, dyspnea, and respiratory-quality of life (p < 0.001). The highest quartile for Parameter D was independently associated with all-cause mortality (adjusted HR 3.22,95% CI 2.42-4.27; p < 0.001) but a substantial number of participants in the highest quartile were categorized as GOLD 0 and 1 by traditional criteria (1.8% and 33.7%). Parameter D identified an additional 9.5% of participants with mild or non-recognized disease as abnormal with greater burden of structural lung disease compared with controls. The data points on the flow-volume and volume-time curves can be used to derive indices of airflow obstruction that identify additional subjects with disease who are deemed to be normal by traditional criteria
Phase diagram of a Bose-Fermi mixture in a one-dimensional optical lattice in terms of fidelity and entanglement
We study the ground-state phase diagram of a Bose-Fermi mixture loaded in a
one-dimensional optical lattice by computing the ground-state fidelity and
quantum entanglement. We find that the fidelity is able to signal quantum phase
transitions between the Luttinger liquid phase, the density-wave phase, and the
phase separation state of the system; and the concurrence can be used to signal
the transition between the density-wave phase and the Ising phase.Comment: 4 pages 3 figure
Ground-state fidelity of Luttinger liquids: A wave functional approach
We use a wave functional approach to calculate the fidelity of ground states
in the Luttinger liquid universality class of one-dimensional gapless quantum
many-body systems. The ground-state wave functionals are discussed using both
the Schrodinger (functional differential equation) formulation and a path
integral formulation. The fidelity between Luttinger liquids with Luttinger
parameters K and K' is found to decay exponentially with system size, and to
obey the symmetry F(K,K')=F(1/K,1/K') as a consequence of a duality in the
bosonization description of Luttinger liquids.Comment: 13 pages, IOP single-column format. Sec. 3 expanded with discussion
of short-distance cut-off. Some typos corrected. Ref. 44 in v2 is now
footnote 2 (moved by copy editor). Published versio
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Clinical Significance of Bronchodilator Responsiveness Evaluated by Forced Vital Capacity in COPD: SPIROMICS Cohort Analysis.
ObjectiveBronchodilator responsiveness (BDR) is prevalent in COPD, but its clinical implications remain unclear. We explored the significance of BDR, defined by post-bronchodilator change in FEV1 (BDRFEV1) as a measure reflecting the change in flow and in FVC (BDRFVC) reflecting the change in volume.MethodsWe analyzed 2974 participants from a multicenter observational study designed to identify varying COPD phenotypes (SPIROMICS). We evaluated the association of BDR with baseline clinical characteristics, rate of prospective exacerbations and mortality using negative binomial regression and Cox proportional hazards models.ResultsA majority of COPD participants exhibited BDR (52.7%). BDRFEV1 occurred more often in earlier stages of COPD, while BDRFVC occurred more frequently in more advanced disease. When defined by increases in either FEV1 or FVC, BDR was associated with a self-reported history of asthma, but not with blood eosinophil counts. BDRFVC was more prevalent in subjects with greater emphysema and small airway disease on CT. In a univariate analysis, BDRFVC was associated with increased exacerbations and mortality, although no significance was found in a model adjusted for post-bronchodilator FEV1.ConclusionWith advanced airflow obstruction in COPD, BDRFVC is more prevalent in comparison to BDRFEV1 and correlates with the extent of emphysema and degree of small airway disease. Since these associations appear to be related to the impairment of FEV1, BDRFVC itself does not define a distinct phenotype nor can it be more predictive of outcomes, but it can offer additional insights into the pathophysiologic mechanism in advanced COPD.Clinical trials registrationClinicalTrials.gov: NCT01969344T4
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