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Quantum physics

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Articles 61 - 72 of 72

Full-Text Articles in Quantum Physics

Quantum Analysis Of A Linear Dc Squid Mechanical Displacement Detector, M. P. Blencowe, E. Buks Jul 2007

Quantum Analysis Of A Linear Dc Squid Mechanical Displacement Detector, M. P. Blencowe, E. Buks

Dartmouth Scholarship

We provide a quantum analysis of a dc SQUID mechanical displacement detector within the subcritical Josephson current regime. A segment of the SQUID loop forms the mechanical resonator and motion of the latter is transduced inductively through changes in the flux threading the loop. Expressions are derived for the detector signal response and noise, which are used to evaluate the position and force detection sensitivity. We also investigate cooling of the mechanical resonator due to detector back reaction.

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The E.P.R. Paradox, George Levesque Jan 2007

The E.P.R. Paradox, George Levesque

Undergraduate Review

No abstract provided.

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Decoherence And Recoherence In A Vibrating Rf Squid, Eyal Buks, M. P. Blencowe Nov 2006

Decoherence And Recoherence In A Vibrating Rf Squid, Eyal Buks, M. P. Blencowe

Dartmouth Scholarship

We study an rf SQUID, in which a section of the loop is a freely suspended beam that is allowed to oscillate mechanically. The coupling between the rf SQUID and the mechanical resonator originates from the dependence of the total magnetic flux threading the loop on the displacement of the resonator. Motion of the latter affects the visibility of Rabi oscillations between the two lowest energy states of the rf SQUID. We address the feasibility of experimental observation of decoherence and recoherence, namely decay and rise of the visibility, in such a system.

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Casimir Forces And Non-Newtonian Gravitation, Roberto Onofrio Oct 2006

Casimir Forces And Non-Newtonian Gravitation, Roberto Onofrio

Dartmouth Scholarship

The search for non-relativistic deviations from Newtonian gravitation can lead to new phenomena signalling the unification of gravity with the other fundamental interactions. Various recent theoretical frameworks indicate a possible window for non-Newtonian forces with gravitational coupling strength in the micrometre range. The major expected background in the same range is attributable to the Casimir force or variants of it if dielectric materials, rather than conducting ones, are considered. Here we review the measurements of the Casimir force performed so far in the micrometre range and how they determine constraints on non-Newtonian gravitation, also discussing the dominant sources of false …

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Generalized Entanglement As A Natural Framework For Exploring Quantum Chaos, Y. S. Weinstein, L Viola Oct 2006

Generalized Entanglement As A Natural Framework For Exploring Quantum Chaos, Y. S. Weinstein, L Viola

Dartmouth Scholarship

We demonstrate that generalized entanglement (Barnum et al., Phys. Rev. A, 68 (2003) 032308) provides a natural and reliable indicator of quantum chaotic behavior. Since generalized entanglement depends directly on a choice of preferred observables, exploring how generalized entanglement increases under dynamical evolution is possible without invoking an auxiliary coupled system or decomposing the system into arbitrary subsystems. We find that, in the chaotic regime, the long-time saturation value of generalized entanglement agrees with random matrix theory predictions. For our system, we provide physical intuition into generalized entanglement within a single system by invoking the notion of extent …

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Enhanced Convergence And Robust Performance Of Randomized Dynamical Decoupling, Lea F. Santos, Lorenza Viola Oct 2006

Enhanced Convergence And Robust Performance Of Randomized Dynamical Decoupling, Lea F. Santos, Lorenza Viola

Dartmouth Scholarship

We demonstrate the advantages of randomization in coherent quantum dynamical control. For systems which are either time-varying or require decoupling cycles involving a large number of operations, we find that simple randomized protocols offer superior convergence and stability as compared to deterministic counterparts. In addition, we show how randomization may allow us to outperform purely deterministic schemes at long times, including combinatorial and concatenated methods. General criteria for optimally interpolating between deterministic and stochastic design are proposed and illustrated in explicit decoupling scenarios relevant to quantum information storage.

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Dynamics Of A Nanomechanical Resonator Coupled To A Superconducting Single-Electron Transistor, M. P. Blencowe, J. Imbers, A. D. Armour Nov 2005

Dynamics Of A Nanomechanical Resonator Coupled To A Superconducting Single-Electron Transistor, M. P. Blencowe, J. Imbers, A. D. Armour

Dartmouth Scholarship

We present an analysis of the dynamics of a nanomechanical resonator coupled to a superconducting single-electron transistor (SSET) in the vicinity of Josephson quasi-particle (JQP) and double Josephson quasi-particle (DJQP) resonances. For weak coupling and wide separation of dynamical timescales, we find that for either superconducting resonances the dynamics of the resonator are given by a Fokker–Planck equation, i.e. the SSET behaves effectively as an equilibrium heat bath, characterized by an effective temperature, which also damps the resonator and renormalizes its frequency. Depending on the gate and drain–source voltage bias points with respect to the superconducting resonance, the SSET can …

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Shape Invariance In Supersymmetric Quantum Mechanics And Its Application To Selected Special Functions Of Modern Physics, Chad Husko, Brenton Knuffman, Asim Gangopadhyaya, Jeffrey Mallow Feb 2005

Shape Invariance In Supersymmetric Quantum Mechanics And Its Application To Selected Special Functions Of Modern Physics, Chad Husko, Brenton Knuffman, Asim Gangopadhyaya, Jeffrey Mallow

Physics: Faculty Publications and Other Works

We applied the methods of supersymmetric quantum mechanics to differential equations that generate well-known special functions of modern physics. This application provides new insight into these functions and generates recursion relations among them. Some of these recursion relations are apparently new (or forgotten), as they are not available in commonly used texts and handbooks. This method can be easily extended to explore other special functions of modern physics.

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Exactly Solvable Systems And The Quantum Hamilton Jacobi Formalism, C. Rasinariu, John J. Dykla, Asim Gangopadhyaya, Jeffrey Mallow Jan 2005

Exactly Solvable Systems And The Quantum Hamilton Jacobi Formalism, C. Rasinariu, John J. Dykla, Asim Gangopadhyaya, Jeffrey Mallow

Physics: Faculty Publications and Other Works

We connect Quantum Hamilton-Jacobi Theory with supersymmetric quantum mechanics (SUSYQM). We show that the shape invariance, which is an integrability condition of SUSYQM, translates into fractional linear relations among the quantum momentum functions.

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Casimir Force Between Eccentric Cylinders, D. A. R. Dalvit, F. C. Lombardo, F. D D. Mazzitelli, R Onofrio Aug 2004

Casimir Force Between Eccentric Cylinders, D. A. R. Dalvit, F. C. Lombardo, F. D D. Mazzitelli, R Onofrio

Dartmouth Scholarship

We consider the Casimir interaction between a cylinder and a hollow cylinder, both conducting, with parallel axis and slightly different radii. The Casimir force, which vanishes in the coaxial situation, is evaluated for both small and large eccentricities using the proximity approximation. The cylindrical configuration offers various experimental advantages with respect to the parallel planes or the plane-sphere geometries, leading to favourable conditions for the search of extra-gravitational forces in the micrometer range and for the observation of finite-temperature corrections.

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Exact Solutions Of The Schroedinger Equation: Connection Between Supersymmetric Quantum Mechanics And Spectrum Generating Algebras, Asim Gangopadhyaya, Jeffrey Mallow, C. Rasinariu, Uday P. Sukhatne Apr 2001

Exact Solutions Of The Schroedinger Equation: Connection Between Supersymmetric Quantum Mechanics And Spectrum Generating Algebras, Asim Gangopadhyaya, Jeffrey Mallow, C. Rasinariu, Uday P. Sukhatne

Physics: Faculty Publications and Other Works

Using supersymmetric quantum mechanics, one can obtain analytic expressions for the eigenvalues and eigenfunctions for all nonrelativistic shape invariant Hamiltonians. These Hamiltonians also possess spectrum generating algebras and are hence solvable by an independent, group theoretical method. In this paper, we demonstrate the equivalence of the two methods of solution, and review related progress in this field.

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Wannier-Stark Localization In Modulation-Doped Multiple-Quantum-Well Structures, Roger H. Yu Feb 1994

Wannier-Stark Localization In Modulation-Doped Multiple-Quantum-Well Structures, Roger H. Yu

All Faculty Scholarship for the College of the Sciences

The external-electric-field effect and the doping effect on a modulation-doped finite-length GaAs/AlxGa1−xAs superlattice have been studied by solving the Schrödinger-Kohn-Sham equation and the Poisson equation self-consistently. In the heavy-doping case, the external electric field makes electrons sequentially tunnel through several potential barriers, and accumulates electrons near one side of the finite-length superlattice. The collective motion of the electrons results in high- and low-field domains in the superlattice. We have found that Wannier-Stark localization exists only in the high-field domain, and that the electronic states are not evenly spaced. The electric-field-induced (doping induced) depopulation (population) of subbands …

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