91 research outputs found
A Modified Approach to Single-Spin Detection Using Magnetic Resonance Force Microscopy
The magnetic moment of a single spin interacting with a cantilever in
magnetic resonance force microscopy (MRFM) experiences quantum jumps in
orientation rather than smooth oscillations. These jumps cannot be detected by
a conventional MRFM based on observation of driven resonant oscillations of a
cantilever. In this paper, we propose a method which will allow detection of
the magnetic signal from a single spin using a modification of a conventional
MRFM. We estimate the opportunity to detect the magnetic signal from a single
proton.Comment: 4 pages LaTex, 4 figures in GIF forma
Digital control of force microscope cantilevers using a field programmable gate array
This report describes a cantilever controller for magnetic resonance force
microscopy (MRFM) based on a field programmable gate array (FPGA), along with
the hardware and software used to integrate the controller into an experiment.
The controller is assembled from a low-cost commercially available software
defined radio (SDR) device and libraries of open-source software. The
controller includes a digital filter comprising two cascaded second-order
sections ("biquads"), which together can implement transfer functions for
optimal cantilever controllers. An appendix in this report shows how to
calculate filter coefficients for an optimal controller from measured
cantilever characteristics. The controller also includes an input multiplexer
and adder used in calibration protocols. Filter coefficients and multiplexer
settings can be set and adjusted by control software while an experiment is
running. The input is sampled at 64 MHz; the sampling frequency in the filters
can be divided down under software control to achieve a good match with filter
characterisics. Data reported here were sampled at 500 kHz, chosen for acoustic
cantilevers with resonant frequencies near 8 kHz. Inputs are digitized with 12
bits resolution, outputs with 14 bits. The experiment software is organized as
a client and server to make it easy to adapt the controller to different
experiments. The server encapusulates the details of controller hardware
organization, connection technology, filter architecture, and number
representation. The same server could be used in any experiment, while a
different client encodes the particulars of each experiment.Comment: submitted to Review of Scientific Instrument
The Magnetic Casimir Effect
The Casimir effect results from alterations of the zero-point electromagnetic
energy introduced by boundary-conditions. For ferromagnetic layers separated by
vacuum (or a dielectric) such boundary-conditions are influenced by the
magneto-optical Kerr effect. We will show that this gives rise to a long-range
magnetic interaction and discuss the effect for two different configurations
(magnetization parallel and perpendicular to the layers). Analytical
expressions are derived for two models and compared to numerical calculations.
Numerical calculations of the effect for Fe are also presented and the
possibility of an experimental observation of the Casimir magnetic interaction
is discussed
Phonon Squeezed States Generated by Second Order Raman Scattering
We study squeezed states of phonons, which allow a reduction in the quantum
fluctuations of the atomic displacements to below the zero-point quantum noise
level of coherent phonon states. We investigate the generation of squeezed
phonon states using a second order Raman scattering process. We calculate the
expectation values and fluctuations of both the atomic displacement and the
lattice amplitude operators, as well as the effects of the phonon squeezed
states on macroscopically measurable quantities, such as changes in the
dielectric constant. These results are compared with recent experiments.Comment: 4 pages, REVTE
Spin-drift transport and its applications
We study the generation of non-equilibrium spin currents in systems with
spatially-inhomogeneous magnetic potentials. For sufficiently high current
densities, the spin polarization can be transported over distances
significantly exceeding the intrinsic spin-diffusion length. This enables
applications that are impossible within the conventional spin-diffusion regime.
Specifically, we propose dc measurement schemes for the carrier spin relaxation
times, and , as well as demonstrate the possibility of spin species
separation by driving current through a region with an inhomogeneous magnetic
potential.Comment: 4 pages, 2 eps figure
Quantum Phonon Optics: Coherent and Squeezed Atomic Displacements
In this paper we investigate coherent and squeezed quantum states of phonons.
The latter allow the possibility of modulating the quantum fluctuations of
atomic displacements below the zero-point quantum noise level of coherent
states. The expectation values and quantum fluctuations of both the atomic
displacement and the lattice amplitude operators are calculated in these
states---in some cases analytically. We also study the possibility of squeezing
quantum noise in the atomic displacement using a polariton-based approach.Comment: 6 pages, RevTe
- …