Physics Commons^™

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 …

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 …

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, …

Thermodynamical Approaches To Efficient Sympathetic Cooling In Ultracold Fermi-Bose Atomic Mixtures, Michael Brown-Hayes, Qun Wei, Carlo Presilla, Roberto Onofrio

Dartmouth Scholarship

We discuss the cooling efficiency of ultracold Fermi-Bose mixtures in species-selective traps using a thermodynamical approach. The dynamics of evaporative cooling trajectories is analyzed in the specific case of bichromatic optical dipole traps also taking into account the effect of partial spatial overlap between the Fermi gas and the thermal component of the Bose gas. We show that large trapping frequency ratios between the Fermi and the Bose species allow for the achievement of a deeper Fermi degeneracy, consolidating in a thermodynamic setting earlier arguments based on more restrictive assumptions. In particular, we confirm that the minimum temperature of the …

Plasticity In Current-Driven Vortex Lattices, Panayotis Benetatos, M. Cristina Marchetti

Physics - All Scholarship

We present a theoretical analysis of recent experiments on current-driven vortex dynamics in the Corbino disk geometry. This geometry introduces controlled spatial gradients in the driving force and allows the study of the onset of plasticity and tearing in clean vortex lattices. We describe plastic slip in terms of the stress-driven unbinding of dislocation pairs, which in turn contribute to the relaxation of the shear, yielding a nonlinear response. The steady state density of free dislocations induced by the applied stress is calculated as a function of the applied current and temperature. A criterion for the onset of plasticity at …

Driven Depinning Of Strongly Disordered Media And Anisotropic Mean-Field Limits, M. Cristina Marchetti, Alan Middleton, Karl Saunders, J. M. Schwarz

Physics - All Scholarship

Extended systems driven through strong disorder are modeled generically using coarse-grained degrees of freedom that interact elastically in the directions parallel to the driving force and that slip along at least one of the directions transverse to the motion. A realization of such a model is a collection of elastic channels with transverse viscous couplings. In the infinite range limit this model has a tricritical point separating a region where the depinning is continuous, in the universality class of elastic depinning, from a region where depinning is hysteretic. Many of the collective transport models discussed in the literature are special …

Patterned Geometries And Hydrodynamics At The Vortex Bose Glass Transition, M. Cristina Marchetti, David R. Nelson

Physics - All Scholarship

Patterned irradiation of cuprate superconductors with columnar defects allows a new generation of experiments which can probe the properties of vortex liquids by confining them to controlled geometries. Here we show that an analysis of such experiments that combines an inhomogeneous Bose glass scaling theory with the hydrodynamic description of viscous flow of vortex liquids can be used to infer the critical behavior near the Bose glass transition. The shear viscosity is predicted to diverge as

|T − TBG|−z at the Bose glass transition, with z ≃

6 the dynamical critical exponent.

Vortex Physics In Confined Geometries, M. Cristina Marchetti, David R. Nelson

Physics - All Scholarship

Patterned irradiation of cuprate superconductors with columnar defects allows a new generation of experiments which can probe the properties of vortex liquids by forcing them to flow in confined geometries. Such experiments can be used to distinguish experimentally between continuous disorder-driven glass transitions of vortex matter, such as the vortex glass or the Bose glass transition, and nonequilibrium polymer-like glass transitions driven by interaction and entanglement. For continuous glass transitions, an analysis of such experiments that combines an inhomogeneous scaling theory with the hydrodynamic description of viscous flow of vortex liquids can be used to infer the critical behavior. After …

A Hydrodynamic Approach To The Bose-Glass Transition, Panayotis Benetatos, M. Cristina Marchetti

Physics - All Scholarship

Nonlinear hydrodynamics is used to evaluate disorder-induced corrections to the vortex liquid tilt modulus for finite screening length and arbitrary disorder geometry. Explicit results for aligned columnar defects yield a criterion for locating the Bose glass transition line at all fields.

Hydrodynamics Of Liquids Of Arbitrarily Curved Flux-Lines And Vortex Loops, Panayotis Benetatos, M. Cristina Marchetti

Physics - All Scholarship

We derive a hydrodynamic model for a liquid of arbitrarily curved flux-lines and vortex loops using the mapping of the vortex liquid onto a liquid of relativistic charged quantum bosons in 2+1 dimensions recently suggested by Tesanovic and by Sudbo and collaborators. The loops in the flux-line system correspond to particle-antiparticle fluctuations in the bosons. We explicitly incorporate the externally applied magnetic field which in the boson model corresponds to a chemical potential associated with the conserved charge density of the bosons. We propose this model as a convenient and physically appealing starting point for studying the properties of the …

Picovoltmeter For Probing Vortex Dynamics In A Single Weak-Pinning Corbino Channel, T. W. Heitmann, Kang Yu, C. Song, M P. Defeo, B.L.T. Plourde

Physics - All Scholarship

We have developed a picovoltmeter using a Nb dc Superconducting QUantum Interference Device (SQUID) for measuring the flux-flow voltage from a small number of vortices moving through a submicron weak-pinning superconducting channel. We have applied this picovoltmeter to measure the vortex response in a single channel arranged in a circle on a Corbino disk geometry. The circular channel allows the vortices to follow closed orbits without encountering any sample edges, thus eliminating the influence of entry barriers.

Superconductivity Close To Magnetic Instability In Fe(Se1−Xtex)0.82, M H. Fang, H M. Pham, B Qian, T J. Liu, E K. Vehstedt, Y Liu, L Spinu, Z Q. Mao

Physics Faculty Publications

We report our study of the evolution of superconductivity and the phase diagram of the ternary Fe(Se_1−xTe_x)_0.82 (0≤x≤1.0) system. We discovered a superconducting phase with T_c,max=14 K in the 0.30.82, which exhibits an incommensurate antiferromagnetic order. We discuss the relationship between the superconductivity and magnetism of this material system in terms of recent results from neutron-scattering measurements. Our results and analyses suggest that superconductivity in this class of Fe-based compounds is associated with magnetic fluctuations and therefore may be unconventional in nature.