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M. P. Blencowe

Publications and source records attributed to M. P. Blencowe.

49 records · Page 3Linked to original sources
arXiv2005

Nanoelectromechanical Systems

Nanoelectromechanical systems (NEMS) are nano-to-micrometer scale mechanical resonators coupled to electronic devices of similar dimensions. NEMS show promise for fast, ultrasensitive force microscopy and for deepening our understanding of how classical dynamics arises by approximation to quantum dynamics. This article begins with a survey of NEMS and then describes certain aspects of their classical dynamics. In particular, we show that for weak coupling the action of the electronic device on the mechanical resonator can be effectively that of a thermal bath, this despite the device being a driven, far-from-equilibrium system.

cond-mat.mes-hall↗
arXiv2003

Classical dynamics of a nano-mechanical resonator coupled to a single-electron transistor

We analyze the dynamics of a nano-mechanical resonator coupled to a single-electron transistor (SET) in the regime where the resonator behaves classically. A master equation is derived describing the dynamics of the coupled system which is then used to obtain equations of motion for the average charge state of the SET and the average position of the resonator. We show that the action of the SET on the resonator is very similar to that of a thermal bath, as it leads to a steady-state probability-distribution for the resonator which can be described by mean values of the resonator position, a renormalized frequency, an effective temperature and an intrinsic damping constant. Including the effects of extrinsic damping and finite temperature, we find that there remain experimentally accessible regimes where the intrinsic damping of the resonator still dominates its behavior. We also obtain the average current through the SET as a function of the coupling to the resonator.

cond-mat.mes-hall↗
arXiv2001

Entanglement and decoherence of a micromechanical resonator via coupling to a Cooper box

We analyse the quantum dynamics of a micromechanical resonator capacitively coupled to a Cooper box. With appropriate quantum state control of the Cooper box, the resonator can be driven into a superposition of spatially separated states. The Cooper box can also be used to probe the environmentally-induced decoherence of the resonator superposition state.

cond-mat.mes-hall↗
arXiv2001

Dephasing and thermal smearing in an electromechanical which-path device

In an electromechanical which-path device electrons travelling through an Aharonov-Bohm ring with a quantum dot in one of the arms are dephased by an interaction with the fundamental flexural mode of a radio-frequency cantilever, leading to a reduction in the visibilty of the interference fringes. However, at finite temperatures time-averaged measurement of the current leads to a fringe visibility which is reduced partly by dephasing of the electrons and partly by a thermal smearing effect. The balance between thermal smearing and dephasing predicted by a calculation depends very strongly on the choice of cantilever basis states used. The interaction between the cantilever and its environment is expected to select the coherent state basis for the cantilever and hence lead to a dephasing rate which is substantially lower than that which would arise if instead the Fock states were selected.

cond-mat.mes-hall↗
arXiv2001

Mechanical Lamb-shift analogue for the Cooper-pair box

We estimate the correction to the Cooper-pair box energy level splitting due to the quantum motion of a coupled micromechanical gate electrode. While the correction due to zero-point motion is very small, it should be possible to observe thermal motion-induced corrections to the photon-assisted tunneling current.

cond-mat.mes-hall↗
arXiv2001

An Electromechanical Which-Path Interferometer

We investigate the possibility of an electromechanical which-path interferometer, in which electrons travelling through an Aharonov-Bohm ring incorporating a quantum dot in one of the arms are dephased by an interaction with the fundamental flexural mode of a radio frequency cantilever. The cantilever is positioned so that its tip lies just above the dot and a bias is applied so that an electric field exists between the dot and the tip. This electric field is modified when an additional electron hops onto the dot, coupling the flexural mode of the cantilever and the microscopic electronic degrees of freedom. We analyze the transmission properties of this system and the dependence of interference fringe visibility on the cantilever-dot coupling and on the mechanical properties of the cantilever. The fringes are progressively destroyed as the interaction with the cantilever is turned up, in part due to dephasing arising from the entanglement of the electron and cantilever states and also due to the thermal smearing that results from fluctuations in the state of the cantilever. When the dwell time of the electron on the dot is comparable to or longer than the cantilever period, we find coherent features in the transmission amplitude. These features are washed out when the cantilever is decohered by its coupling to the environment.

cond-mat.mes-hall↗
arXiv1998

Quantum squeezing micron-sized cantilevers

We show that substantial quantum squeezing of mechanical motion can be achieved for micron-sized cantilever devices fabricated using available techniques. A method is also described for measuring the cantilever fluctuation magnitudes in the squeezing regime.

cond-mat.mes-hall↗
arXiv1998

Acoustoconductance of quantum contacts

We describe theoretically the acoustoconductance (AC) of quantum contacts. One characteristic of a contact which distinguishes it from a long, uniform wire is a strong, energy-dependent transmission probability. This has several consequences for AC. Electrons which are forward scattered by phonons can contribute to AC and, furthermore, AC can have positive sign (i.e. a conductance-increase under the influence of phonons). By contrast, for uniform wires only backscattered electrons contribute to AC which always has negative sign.

cond-mat.mes-hall↗
arXiv1998

Quantum energy flow, dissipation and decoherence in mesoscopic dielectric structures

We first present a summary of recent results concerning the phononic energy transport properties of mesoscopic, suspended dielectric wires. We then discuss some related open problems concerning the fundamental lower limits on the vibrational damping rates of submicron-sized cantilever structures and also the possibility to create and detect quantum superpositions of spatially separated states for such structures.

cond-mat.mes-hall↗
arXiv1998

Quantum energy flow in mesoscopic dielectric structures

We investigate the phononic energy transport properties of mesoscopic, suspended dielectric wires. The Landauer formula for the thermal conductance is derived and its universal aspects discussed. We then determine the variance of the energy current in the presence of a steady state current flow. In the final part, some initial results are presented concerning the nature of the temperature fluctuations of a mesoscopic electron gas thermometer due to the absorption and emission of wire phonons.

cond-mat.mes-hall↗
arXiv1997

Applying the linear delta expansion to `i phi^3'

The linear $δ$ expansion (LDE) is applied to the Hamiltonian $H=(p^2 +m^2 x^2)/2 + igx^3$, which arises in the study of Lee-Yang zeros in statistical mechanics. Despite being non-Hermitian, this Hamiltonian appears to possess a real, positive spectrum. In the LDE, as in perturbation theory, the eigenvalues are naturally real, so a proof of this property devolves on the convergence of the expansion. A proof of convergence of a modified version of the LDE is provided for the $ix^3$ potential in zero dimensions. The methods developed in zero dimensions are then extended to quantum mechanics, where we provide numerical evidence for convergence.

hep-th↗
arXiv1997

Applying the linear δ-expansion to disordered systems

We apply the linear $δ$-expansion (LDE), originally developed as a nonperturbative, analytical approximation scheme in quantum field theory, to problems involving noninteracting electrons in disordered solids. The initial idea that the LDE method might be applicable to disorder is suggested by the resemblance of the supersymmetric field theory formalism for quantities such as the disorder-averaged density of states and conductance to the path integral expressions for the n-point functions of $λϕ^4$ field theory, where the LDE has proved a successful method of approximation. The field theories relevant for disorder have several unusual features which have not been considered before, however, such as anticommuting fields with Faddeev-Popov (FP) rather than Dirac-type kinetic energy terms, imaginary couplings and Minkowskian field coordinate metric.Nevertheless we show that the LDE method can be successfully generalized to such field systems.

cond-mat.dis-nn↗