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Quantum physics

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Articles 61 - 90 of 93

Full-Text Articles in Physics

Damping And Decoherence Of A Nanomechanical Resonator Due To A Few Two-Level Systems, Laura G. Remus, Miles P. Blencowe, Yukihiro Tanaka Nov 2009

Damping And Decoherence Of A Nanomechanical Resonator Due To A Few Two-Level Systems, Laura G. Remus, Miles P. Blencowe, Yukihiro Tanaka

Dartmouth Scholarship

We consider a quantum model of a nanomechanical flexing beam resonator interacting with a bath comprising a few damped tunneling two-level systems. In contrast with a resonator interacting bilinearly with an ohmic free oscillator bath (modeling clamping loss, for example), the mechanical resonator damping is amplitude dependent, while the decoherence of quantum superpositions of mechanical position states depends only weakly on their spatial separation.


Dynamical Quantum Error Correction Of Unitary Operations With Bounded Controls, Kaveh Khodjasteh, Lorenza Viola Sep 2009

Dynamical Quantum Error Correction Of Unitary Operations With Bounded Controls, Kaveh Khodjasteh, Lorenza Viola

Dartmouth Scholarship

Dynamically corrected gates were recently introduced [K. Khodjasteh and L. Viola, Phys. Rev. Lett. 102, 080501 (2009)] as a tool to achieve decoherence-protected quantum gates based on open-loop Hamiltonian engineering. Here, we further expand the framework of dynamical quantum error correction, with emphasis on elucidating under what conditions decoherence suppression can be ensured while performing a generic target quantum gate, using only available bounded-strength control resources. Explicit constructions for physically relevant error models are detailed, including arbitrary linear decoherence and pure dephasing on qubits. The effectiveness of dynamically corrected gates in an illustrative non-Markovian spin-bath setting is investigated numerically, …


Anomalous Nonergodic Scaling In Adiabatic Multicritical Quantum Quenches, Shusa Deng, Gerardo Ortiz, Lorenza Viola Sep 2009

Anomalous Nonergodic Scaling In Adiabatic Multicritical Quantum Quenches, Shusa Deng, Gerardo Ortiz, Lorenza Viola

Dartmouth Scholarship

We investigate non-equilibrium dynamical scaling in adiabatic quench processes across quantum multi critical points. Our analysis shows that the resulting power-law scaling depends sensitively on the control path, and that anomalous critical exponents may emerge depending on the universality class. We argue that the observed anomalous behavior originates in the fact that the dynamical excitation process takes place asymmetrically with respect to the static multicritical point, and that non-critical energy modes may play a dominant role. As a consequence, dynamical scaling requires introducing new non-static exponents.


Analogue Hawking Radiation In A Dc-Squid Array Transmission Line, P D. Nation, M. P. Blencowe, A. J. Rimberg, E. Buks Aug 2009

Analogue Hawking Radiation In A Dc-Squid Array Transmission Line, P D. Nation, M. P. Blencowe, A. J. Rimberg, E. Buks

Dartmouth Scholarship

We propose the use of a superconducting transmission line formed from an array of dc-SQUID’s for investigating analogue Hawking radiation. Biasing the array with a space-time varying flux modifies the propagation velocity of the transmission line, leading to an effective metric with an horizon. Being a fundamentally quantum mechanical device, this setup allows for investigations of quantum effects such as back-reaction and analogue space-time fluctuations on the Hawking process.


Dynamically Error-Corrected Gates For Universal Quantum Computation, Kaveh Khodjasteh, Lorenza Viola Feb 2009

Dynamically Error-Corrected Gates For Universal Quantum Computation, Kaveh Khodjasteh, Lorenza Viola

Dartmouth Scholarship

Scalable quantum computation in realistic devices requires that precise control can be implemented efficiently in the presence of decoherence and operational errors. We propose a general constructive procedure for designing robust unitary gates on an open quantum system without encoding or measurement overhead. Our results allow for a low-level err or correction strategy solely based on Hamiltonian engineering using realistic bounded-strength controls and may substantially reduce implementation requirements for fault-tolerant quantum computing architectures.


Dynamical Non-Ergodic Scaling In Continuous Finite-Order Quantum Phase Transitions, S. Deng, G. Ortiz, L. Viola Jan 2009

Dynamical Non-Ergodic Scaling In Continuous Finite-Order Quantum Phase Transitions, S. Deng, G. Ortiz, L. Viola

Dartmouth Scholarship

We investigate the emergence of universal dynamical scaling in quantum critical spin systems adiabatically driven out of equilibrium, with emphasis on quench dynamics which involves non-isolated critical points (i.e., critical regions) and cannot be a priori described through standard scaling arguments nor time-dependent perturbative approaches. Comparing to the case of an isolated quantum critical point, we find that non-equilibrium scaling behavior of a large class of physical observables may still be explained in terms of equilibrium critical exponents. However, the latter are in general non-trivially path-dependent, and detailed knowledge about the time-dependent excitation process becomes essential. In particular, …


Anomalies In Electrostatic Calibrations For The Measurement Of The Casimir Force In A Sphere-Plane Geometry, W. J. Kim, M. Brown-Hayes, D. A.R. Dalvit, J. H. Brownell, R. Onofrio Dec 2008

Anomalies In Electrostatic Calibrations For The Measurement Of The Casimir Force In A Sphere-Plane Geometry, W. J. Kim, M. Brown-Hayes, D. A.R. Dalvit, J. H. Brownell, R. Onofrio

Dartmouth Scholarship

We have performed precision electrostatic calibrations in the sphere-plane geometry, and observed anomalous behavior. Namely, the scaling exponent of the electrostatic signal with distance was found to be smaller than expected on the basis of the pure Coulombian contribution, and the residual potential found to be distance dependent. We argue that these findings affect the accuracy of the electrostatic calibrations and invite reanalysis of previous determinations of the Casimir force.


Parameters Of Pseudorandom Quantum Circuits, Yaakov S. Weinstein, Winton G. Brown, Lorenza Viola Nov 2008

Parameters Of Pseudorandom Quantum Circuits, Yaakov S. Weinstein, Winton G. Brown, Lorenza Viola

Dartmouth Scholarship

Pseudorandom circuits generate quantum states and unitary operators which are approximately distributed according to the unitarily invariant Haar measure. We explore how several design parameters affect the efficiency of pseudorandom circuits, with the goal of identifying relevant tradeoffs and optimizing convergence. The parameters we explore include the choice of single- and two-qubit gates, the topology of the underlying physical qubit architecture, the probabilistic application of two-qubit gates, as well as circuit size, initialization, and the effect of control constraints. Building on the equivalence between pseudorandom circuits and approximate t-designs, a Markov matrix approach is employed to analyze asymptotic convergence properties …


Probing The Quantum Coherence Of A Nanomechanical Resonator Using A Superconducting Qubit: Ii. Implementation, M. P. Blencowe, A. D. Armour Sep 2008

Probing The Quantum Coherence Of A Nanomechanical Resonator Using A Superconducting Qubit: Ii. Implementation, M. P. Blencowe, A. D. Armour

Dartmouth Scholarship

We describe a possible implementation of the nanomechanical quantum superposition generation and detection scheme described in the preceding, companion paper (Armour A D and Blencowe M P 2008 New. J. Phys. 10 095004). The implementation is based on the circuit quantum electrodynamics (QED) set-up, with the addition of a mechanical degree of freedom formed out of a suspended, doubly-clamped segment of the superconducting loop of a dc SQUID located directly opposite the centre conductor of a coplanar waveguide (CPW). The relative merits of two SQUID based qubit realizations are addressed, in particular a capacitively coupled charge qubit and inductively coupled …


Probing The Quantum Coherence Of A Nanomechanical Resonator Using A Superconducting Qubit: I. Echo Scheme, A. D. Armour, M. P. Blencowe Sep 2008

Probing The Quantum Coherence Of A Nanomechanical Resonator Using A Superconducting Qubit: I. Echo Scheme, A. D. Armour, M. P. Blencowe

Dartmouth Scholarship

We propose a scheme in which the quantum coherence of a nanomechanical resonator can be probed using a superconducting qubit. We consider a mechanical resonator coupled capacitively to a Cooper pair box and assume that the superconducting qubit is tuned to the degeneracy point so that its coherence time is maximized and the electro-mechanical coupling can be approximated by a dispersive Hamiltonian. When the qubit is prepared in a superposition of states, this drives the mechanical resonator progressively into a superposition which in turn leads to apparent decoherence of the qubit. Applying a suitable control pulse to the qubit allows …


Quantum Analysis Of A Nonlinear Microwave Cavity-Embedded Dc Squid Displacement Detector, P. D. Nation, M. P. Blencowe, E. Buks Sep 2008

Quantum Analysis Of A Nonlinear Microwave Cavity-Embedded Dc Squid Displacement Detector, P. D. Nation, M. P. Blencowe, E. Buks

Dartmouth Scholarship

We carry out a quantum analysis of a dc superconducting quantum interference device (SQUID) mechanical displacement detector, comprising a SQUID with mechanically compliant loop segment, which is embedded in a microwave transmission line resonator. The SQUID is approximated as a nonlinear current-dependent inductance, inducing an external flux tunable nonlinear Duffing self-interaction term in the microwave resonator mode equation. Motion of the compliant SQUID loop segment is transduced inductively through changes in the external flux threading SQUID loop, giving a ponderomotive radiation pressure-type coupling between the microwave and mechanical resonator modes. Expressions are derived for the detector signal response and noise, …


Advantages Of Randomization In Coherent Quantum Dynamical Control, Lea F. Santos, Lorenza Viola Aug 2008

Advantages Of Randomization In Coherent Quantum Dynamical Control, Lea F. Santos, Lorenza Viola

Dartmouth Scholarship

Control scenarios have been identified where the use of randomized design may substantially improve the performance of dynamical decoupling methods (Santos and Viola 2006 Phys. Rev. Lett. 97 150501). Here, by focusing on the suppression of internal unwanted interactions in closed quantum systems, we review and further elaborate on the advantages of randomization at long evolution times. By way of illustration, special emphasis is devoted to isolated Heisenberg chains of coupled spin-1/2 particles. In particular, for nearest-neighbor interactions, two types of decoupling cycles are contrasted: inefficient averaging, whereby the number of control actions increases exponentially with the system size, and …


Quantum Pseudorandomness From Cluster-State Quantum Computation, Winton G. Brown, Yaakov S. Weinstein, Lorenza Viola Apr 2008

Quantum Pseudorandomness From Cluster-State Quantum Computation, Winton G. Brown, Yaakov S. Weinstein, Lorenza Viola

Dartmouth Scholarship

We show how to efficiently generate pseudorandom states suitable for quantum information processing via cluster-state quantum computation. By reformulating pseudorandom algorithms in the cluster-state picture, we identify a strategy for optimizing pseudorandom circuits by properly choosing single-qubit rotations. A Markov chain analysis provides the tool for analyzing convergence rates to the Haar measure and finding the optimal single-qubit gate distribution. Our results may be viewed as an alternative construction of approximate unitary 2-designs.


Shape Invariance And The Exactness Of Quantum Hamilton-Jacobi Formalism, Charles Cherqui, Yevgeny Binder, Asim Gangopadhyaya Sep 2007

Shape Invariance And The Exactness Of Quantum Hamilton-Jacobi Formalism, Charles Cherqui, Yevgeny Binder, Asim Gangopadhyaya

Physics: Faculty Publications and Other Works

Quantum Hamilton-Jacobi Theory and supersymmetric quantum mechanics (SUSYQM) are two parallel methods to determine the spectra of a quantum mechanical systems without solving the Schr ̈odinger equation. It was recently shown that the shape invariance, which is an integrability condition in SUSYQM formalism, can be utilized to develop an iterative algorithm to determine the quantum momentum functions. In this paper, we show that shape invariance also suffices to determine the eigenvalues in Quantum Hamilton-Jacobi Theory.


The Development Of A Quantum Dot Solar Concentrator, Brenda Rowan Sep 2007

The Development Of A Quantum Dot Solar Concentrator, Brenda Rowan

Doctoral

The aim of this study was to investigate the feasibility of Quantum Dot Solar Concentrators (QDSCs). Quantum Dots offer the advantages of having broad absorption specr4a, tunable emission and improved stability. A range of Cadmium Selenide/|Zince Sulphide Quantum Dots were characterized in solution and composite form using time-resolved and steady state spectroscopie techniques and the stability of the composite samples was investigated over a 6 month period. A number of matrix materials were compared and the most suitable type for fabrication of QDSCs were identified. Techniques for fabrication and characterization of QDSCs were developed and a range of different QDSC …


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.


Strokes Of Existence: The Connection Of All Things, Mari Gorman Jan 2007

Strokes Of Existence: The Connection Of All Things, Mari Gorman

Graduate Student Publications and Research

Acted or real—and all life is real whether one is acting or not—the common denominator and consistent, ubiquitous reality of life and all behavior is that it manifests in the form of relationships on all scales. But what is a relationship? Until now, the answer to this question has not been sufficiently known. As a result of many years of empirical research that began with the aim of discovering what is going on in a gifted actor when s/he is playing a character that can be observed and experienced as a living, intuitive being, and based on the knowledge that …


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

The E.P.R. Paradox, George Levesque

Undergraduate Review

No abstract provided.


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.


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 …


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 …


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.


Multivalued Logic, Neutrosophy And Schrodinger Equation, Florentin Smarandache, Victor Christianto Dec 2005

Multivalued Logic, Neutrosophy And Schrodinger Equation, Florentin Smarandache, Victor Christianto

Branch Mathematics and Statistics Faculty and Staff Publications

This book was intended to discuss some paradoxes in Quantum Mechanics from the viewpoint of Multi-Valued-logic pioneered by Lukasiewicz, and a recent concept Neutrosophic Logic. Essentially, this new concept offers new insights on the idea of ‘identity’, which too often it has been accepted as given. Neutrosophy itself was developed in attempt to generalize Fuzzy-Logic introduced by L. Zadeh. While some aspects of theoretical foundations of logic are discussed, this book is not intended solely for pure mathematicians, but instead for physicists in the hope that some of ideas presented herein will be found useful. The book is motivated by …


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 …


The Dyad Theory Of Classical And Quantum Physics, Preston Jones Feb 2005

The Dyad Theory Of Classical And Quantum Physics, Preston Jones

Publications

The 4-space equations of hydrodynamics, electrodynamics, and quantum mechanics are developed using the dyad calculus. Gravity is found to couple hydrodynamics, electrodynamics, and quantum mechanics through the 4- space metric and differential operator. Expanding the 4-space equations of electrodynamics a time varying metric is shown to dissipate electromagnetic energy.


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.


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.


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.


Mutually Unbiased Binary Observable Sets On N Qubits, Jay Lawrence, Časlav Brukner, Anton Zeilinger Feb 2002

Mutually Unbiased Binary Observable Sets On N Qubits, Jay Lawrence, Časlav Brukner, Anton Zeilinger

Dartmouth Scholarship

The Pauli operators (tensor products of Pauli matrices) provide a complete basis of operators on the Hilbert space of N qubits. We prove that the set of 4N−1 Pauli operators may be partitioned into 2N+1 distinct subsets, each consisting of 2N−1 internally commuting observables. Furthermore, each such partitioning defines a unique choice of 2N+1 mutually unbiased basis sets in the N-qubit Hilbert space. Examples for 2 and 3 qubit systems are discussed with emphasis on the nature and amount of entanglement that occurs within these basis sets.


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.