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Full-Text Articles in Physics

Scheme For The Protective Measurement Of A Single Photon Using A Tunable Quantum Zeno Effect, Maximilian Schlosshauer Jan 2018

Scheme For The Protective Measurement Of A Single Photon Using A Tunable Quantum Zeno Effect, Maximilian Schlosshauer

Physics Faculty Publications and Presentations

This paper presents a proof-of-principle scheme for the protective measurement of a single photon. In this scheme, the photon is looped arbitrarily many times through an optical stage that implements a weak measurement of a polarization observable followed by a strong measurement protecting the state. The ability of this scheme to realize a large number of such interaction{protection steps means that the uncertainty in the measurement result can be drastically reduced while maintaining a sufficient probability for the photon to survive the measurement.


Quantum Fidelity Approach To The Ground-State Properties Of The One-Dimensional Axial Next-Nearest-Neighbor Ising Model In A Transverse Field, Oz De Alcantara Bonfim, B. Boechat, J. Florencio Oct 2017

Quantum Fidelity Approach To The Ground-State Properties Of The One-Dimensional Axial Next-Nearest-Neighbor Ising Model In A Transverse Field, Oz De Alcantara Bonfim, B. Boechat, J. Florencio

Physics Faculty Publications and Presentations

In this work we analyze the ground-state properties of the s =1/2 one-dimensional axial next-nearest-neighbor Ising model in a transverse field using the quantum fidelity approach. We numerically determined the fidelity susceptibility as a function of the transverse field Bx and the strength of the next-nearest-neighbor interaction J2, for systems of up to 24 spins. We also examine the ground-state vector with respect to the spatial ordering of the spins. The ground-state phase diagram shows ferromagnetic, floating, and ⟨2,2⟩ phases, and we predict an infinite number of modulated phases in the thermodynamic limit (L→∞). Paramagnetism only ...


Structure Of Local Quantum Operations And Classical Communication: Finite Versus Infinite Rounds, Scott M. Cohen Apr 2015

Structure Of Local Quantum Operations And Classical Communication: Finite Versus Infinite Rounds, Scott M. Cohen

Physics Faculty Publications and Presentations

Every measurement that can be implemented by local quantum operations and classical communication (LOCC) using an infinite number of rounds is the limit of a sequence of measurements, where each measurement in the sequence requires only a finite number of rounds. This rather obvious and well-known fact is nonetheless of interest as it shows that these infinite-round measurements can be approximated arbitrarily closely simply by using more and more rounds of communication. Here we demonstrate the perhaps less obvious result that (at least) for bipartite systems, the reverse relationship also holds. Specifically, we show that every finite-round bipartite LOCC measurement ...


Dynamical Properties Of An Harmonic Oscillator Impacting A Vibrating Wall, O. F. De Alcantara Bonfim May 2009

Dynamical Properties Of An Harmonic Oscillator Impacting A Vibrating Wall, O. F. De Alcantara Bonfim

Physics Faculty Publications and Presentations

The dynamics of a spring-mass system under repeated impact with a vibrating wall is investigated using the static wall approximation. The evolution of the harmonic oscillator is described by two coupled difference equations. These equations are solved numerically, and in some cases exact analytical expressions have also been found. For a periodically vibrating wall, Fermi acceleration is only found at resonance. There, the average rebounding velocity increases linearly with the number of collisions. Near resonance, the average rebounding velocity grows initially with the number of collisions and eventually reaches a plateau. In the vicinity of resonance, the motion of the ...


Quantum Phase Transitions In The Transverse One-Dimensional Ising Model With Four-Spin Interactions, O. F. De Alcantara Bonfim, J. Florencio Jan 2006

Quantum Phase Transitions In The Transverse One-Dimensional Ising Model With Four-Spin Interactions, O. F. De Alcantara Bonfim, J. Florencio

Physics Faculty Publications and Presentations

In this work we investigate the quantum phase transitions at zero temperature of the one-dimensional transverse Ising model with an extra term containing four-spin interactions. The competition between the energy couplings of the model leads to an interesting zero-temperature phase diagram. We use a modified Lanczos method to determine the ground state and the first excited state energies of the system, with sizes of up to 20 spins. We apply finite size scaling to the energy gap to obtain the boundary region where ferromagnetic to paramagnetic transition takes place. We also find the critical exponent associated with the correlation length ...


Dynamical Behavior Of The Random·Bond Transverse Ising Model With Four-Spin Interactions, Beatriz Boechat, Claudette Cordeiro, J. Florencio, F. C. Sá Barreto, O. F. De Alcantara Bonfim Jun 2000

Dynamical Behavior Of The Random·Bond Transverse Ising Model With Four-Spin Interactions, Beatriz Boechat, Claudette Cordeiro, J. Florencio, F. C. Sá Barreto, O. F. De Alcantara Bonfim

Physics Faculty Publications and Presentations

We study the effect of random bonds and fields on the dynamical behavior of the one-dimensional transverse Ising model with four-spin interactions. We consider finite chains of increasing size to determine the time-dependent correlation function and the longitudinal relaxation function of the infinite chain. In this fully disordered system we observe a crossover from a collective modetype of dynamics to that of a central regime.


Quantum Chaos In A Double Square-Well: An Approach Based On Bohm's View Of Quantum Mechanics, O. F. De Alcantara Bonfim, J. Florencio, F. C. Sá Barreto Nov 1998

Quantum Chaos In A Double Square-Well: An Approach Based On Bohm's View Of Quantum Mechanics, O. F. De Alcantara Bonfim, J. Florencio, F. C. Sá Barreto

Physics Faculty Publications and Presentations

We study the dynamics of a quantum particle in a double square-well potential within a deterministic framework using Bohm’s quantum mechanics. Phase portraits, Fourier spectral analysis, Poincaré sections, and Lyapunov exponents clearly indicate that the particle undergoes periodic, quasiperiodic, and chaotic motions depending on the initial form of the wave packet. We also make a detailed comparison between the predictions of the present approach and those of conventional quantum mechanics for the same problem.


Chaotic Dynamics In Billiards Using Bohm’S Quantum Mechanics, O. F. De Alcantara Bonfim, J. Florencio, F. C. Sá Barreto Sep 1998

Chaotic Dynamics In Billiards Using Bohm’S Quantum Mechanics, O. F. De Alcantara Bonfim, J. Florencio, F. C. Sá Barreto

Physics Faculty Publications and Presentations

The dynamics of a particle in square and circular billiards is studied within the framework of Bohm’s quantum mechanics. While conventional quantum mechanics predicts that the system shows no indication of chaotic behavior for these geometries from either the eigenvalue spectra distribution or the structure of the eigenfunctions, we find that in Bohm’s quantum mechanics these systems exhibit both regular and chaotic behavior, depending on the form of the initial wave packet and on the particle’s initial position.


Critical Behavior Of The One-Dimensional S = 1 Xy Model With Single-Ion Anisotropy, O. F. De Alcantara Bonfim, T. Schneider Aug 1984

Critical Behavior Of The One-Dimensional S = 1 Xy Model With Single-Ion Anisotropy, O. F. De Alcantara Bonfim, T. Schneider

Physics Faculty Publications and Presentations

We study the quantum critical behavior of the one-dimensional, S = 1 XY model in the presence of a single-ion anisotropy. Using a path-integral approach, we obtain, at T = 0 and for a positive anisotropy constant, a classical free-energy functional that allows discussion of the critical properties. The rescaling of frequencies is governed by the critical exponent z = 1. Renormalization-group arguments reveal that at criticality the system belongs to the same universality class as the isotropic 2-d XY model.