1,485 research outputs found
Dynamics of quartz tuning fork force sensors used in scanning probe microscopy
We have performed an experimental characterization of the dynamics of
oscillating quartz tuning forks which are being increasingly used in scanning
probe microscopy as force sensors. We show that tuning forks can be described
as a system of coupled oscillators. Nevertheless, this description requires the
knowledge of the elastic coupling constant between the prongs of the tuning
fork, which has not yet been measured. Therefore tuning forks have been usually
described within the single oscillator or the weakly coupled oscillators
approximation that neglects the coupling between the prongs. We propose three
different procedures to measure the elastic coupling constant: an
opto-mechanical method, a variation of the Cleveland method and a thermal noise
based method. We find that the coupling between the quartz tuning fork prongs
has a strong influence on the dynamics and the measured motion is in remarkable
agreement with a simple model of coupled harmonic oscillators. The precise
determination of the elastic coupling between the prongs of a tuning fork
allows to obtain a quantitative relation between the resonance frequency shift
and the force gradient acting at the free end of a tuning fork prong.Comment: 16 pages, 6 figures, 2 Table
Current rectification in a single molecule diode: the role of electrode coupling
We demonstrate large rectification ratios (> 100) in single-molecule
junctions based on a metal-oxide cluster (polyoxometalate), using a scanning
tunneling microscope (STM) both at ambient conditions and at low temperature.
These rectification ratios are the largest ever observed in a single-molecule
junction, and in addition these junctions sustain current densities larger than
10^5 A/cm^2. By following the variation of the I-V characteristics with
tip-molecule separation we demonstrate unambiguously that rectification is due
to asymmetric coupling to the electrodes of a molecule with an asymmetric level
structure. This mechanism can be implemented in other type of molecular
junctions using both organic and inorganic molecules and provides a simple
strategy for the rational design of molecular diodes
Measuring out-of-time-order correlations and multiple quantum spectra in a trapped ion quantum magnet
Controllable arrays of ions and ultra-cold atoms can simulate complex
many-body phenomena and may provide insights into unsolved problems in modern
science. To this end, experimentally feasible protocols for quantifying the
buildup of quantum correlations and coherence are needed, as performing full
state tomography does not scale favorably with the number of particles. Here we
develop and experimentally demonstrate such a protocol, which uses time
reversal of the many-body dynamics to measure out-of-time-order correlation
functions (OTOCs) in a long-range Ising spin quantum simulator with more than
100 ions in a Penning trap. By measuring a family of OTOCs as a function of a
tunable parameter we obtain fine-grained information about the state of the
system encoded in the multiple quantum coherence spectrum, extract the quantum
state purity, and demonstrate the buildup of up to 8-body correlations. Future
applications of this protocol could enable studies of many-body localization,
quantum phase transitions, and tests of the holographic duality between quantum
and gravitational systems.Comment: main text: 7 pages, 4 figures; supplement: 9 pages, 4 figure
Observation of a parity oscillation in the conductance of atomic wires
Using a scanning tunnel microscope or mechanically controlled break
junctions, atomic contacts of Au, Pt and Ir are pulled to form chains of atoms.
We have recorded traces of conductance during the pulling process and averaged
these for a large amount of contacts. An oscillatory evolution of conductance
is observed during the formation of the monoatomic chain suggesting a
dependence on even or odd numbers of atoms forming the chain. This behaviour is
not only present in the monovalent metal Au, as it has been previously
predicted, but is also found in the other metals which form chains suggesting
it to be a universal feature of atomic wires
On linearity of separating multi-particle differential Schr\"odinger operators for identical particles
We show that hierarchies of differential Schroedinger operators for identical
particles which are separating for the usual (anti-)symmetric tensor product,
are necessarily linear, and offer some speculations on the source of quantum
linearity.Comment: As accepted by Journal of Mathematical Physics. Original title
"Separating multi-particle differential Schroedinger operators for identical
particles are necessarily linear". Some new discussion and references. Main
result unchanged. Uses RevTeX 4, 9 page
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