132 research outputs found
Noise thermometry and electron thermometry of a sample-on-cantilever system below 1 Kelvin
We have used two types of thermometry to study thermal fluctuations in a
microcantilever-based system below 1 K. We measured the temperature of a
cantilever's macroscopic degree-of-freedom (via the Brownian motion of its
lowest flexural mode) and its microscopic degrees-of-freedom (via the electron
temperature of a metal sample mounted on the cantilever). We also measured both
temperatures' response to a localized heat source. We find it possible to
maintain thermal equilibrium between these two temperatures and a refrigerator
down to at least 300 mK. These results are promising for ongoing experiments to
probe quantum effects using micromechanical devices
Analytic and Numerical Aspects of the Nonsingular Laplacian Representation of the Asymptotic Part of the Layered-Medium Green Function in the Mixed Potential Formulation
We report on developments in the evaluation of matrix elements of the electric and magnetic field operators involving the asymptotic (large transverse wave-number or small transverse distances) components of the mixed-potential Green's function of a layered medium. Subtracting these asymptotic terms significantly accelerates numerical computation of the Sommerfeld-type integrals required in constructing Green's function and then the matrix elements [1]
New Simplified Analytic Expressions for the Matrix Elements of the Asymptotic Part of the Layered Medium Green Function in the Mixed Potential Formulation
We report new developments in the analytical evaluation of the near-field contribution to the matrix elements of the electric and magnetic field operators for planar conducting structures embedded in a layered medium. The method is applicable to Rao-Wilton-Glisson (RWG) basis functions supported on parallel interfaces in the medium. Our method is an extension of the approach described in [1] of representing a Green function as a two-dimensional Laplacian of an auxiliary function. Such Laplacian representations can be obtained for the asymptotic forms of the Green functions, which are being subtracted in order to regularize the behavior of the Sommerfeld-type integrals. Matrix elements resulting from these asymptotic forms, given originally as quadruple surface integrals with singular integrands, are then reduced to double contour integrals over the perimeters of the surface elements, involving simple closed-form non-singular auxiliary functions
Mesoscopic persistent currents in a strong magnetic field
Recent precision measurements of mesoscopic persistent currents in
normal-metal rings rely on the interaction between the magnetic moment
generated by the current and a large applied magnetic field. Motivated by this
technique, we extend the theory of mesoscopic persistent currents to include
the effect of the finite thickness of the ring and the resulting penetration of
the large magnetic field. We discuss both the sample-specific typical current
and the ensemble-averaged current which is dominated by the effects of
electron-electron interactions. We find that the magnetic field strongly
suppresses the interaction-induced persistent current and so provides direct
access to the independent-electron contribution. Moreover, the technique allows
for measurements of the entire distribution function of the persistent current.
We also discuss the consequences of the Zeeman splitting and spin-orbit
scattering, and include a detailed and quantitative comparison of our
theoretical results to experimental data.Comment: 12 pages, 7 figure
Measuring mechanical motion with a single spin
We study theoretically the measurement of a mechanical oscillator using a
single two level system as a detector. In a recent experiment, we used a single
electronic spin associated with a nitrogen vacancy center in diamond to probe
the thermal motion of a magnetized cantilever at room temperature {Kolkowitz et
al., Science 335, 1603 (2012)}. Here, we present a detailed analysis of the
sensitivity limits of this technique, as well as the possibility to measure the
zero point motion of the oscillator. Further, we discuss the issue of
measurement backaction in sequential measurements and find that although
backaction heating can occur, it does not prohibit the detection of zero point
motion. Throughout the paper we focus on the experimental implementation of a
nitrogen vacancy center coupled to a magnetic cantilever; however, our results
are applicable to a wide class of spin-oscillator systems. Implications for
preparation of nonclassical states of a mechanical oscillator are also
discussed.Comment: 17 pages, 6 figure
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