57 research outputs found
Observation of Aubry transition in finite atom chains via friction
The highly nonlinear many-body physics of a chain of mutually interacting
atoms in contact with a periodic substrate gives rise to complex static and
dynamical phenomena, such as structural phase transitions and friction. In the
limit of an infinite chain incommensurate with the substrate, Aubry predicted a
structural transition with increasing substrate potential, from the chain's
intrinsic arrangement free to slide on the substrate, to a pinned arrangement
favoring the substrate pattern. To date, the Aubry transition has not been
observed. Here, using a chain of cold ions subject to a periodic optical
potential we qualitatively and quantitatively establish a close relation
between Aubry's sliding-to-pinned transition and superlubricity breaking in
stick-slip friction. Using friction measurements with high spatial resolution
and individual ion detection, we experimentally observe the Aubry transition
and the onset of its hallmark fractal atomic arrangement. Notably, the observed
critical lattice depth for a finite chain agrees well with the Aubry prediction
for an infinite chain. Our results elucidate the connection between competing
ordering patterns and superlubricity in nanocontacts - the elementary building
blocks of friction.Comment: 5 pages, 4 figure
Squeezing on momentum states for atom interferometry
We propose and analyse a method that allows for the production of squeezed
states of the atomic center-of-mass motion that can be injected into an atom
interferometer. Our scheme employs dispersive probing in a ring resonator on a
narrow transition of strontium atoms in order to provide a collective
measurement of the relative population of two momentum states. We show that
this method is applicable to a Bragg diffraction-based atom interferometer with
large diffraction orders. The applicability of this technique can be extended
also to small diffraction orders and large atom numbers by inducing atomic
transparency at the frequency of the probe field, reaching an interferometer
phase resolution scaling , where is the atom
number. We show that for realistic parameters it is possible to obtain a 20 dB
gain in interferometer phase estimation compared to the Standard Quantum Limit.Comment: 5 pages, 4 figure
Tuning friction atom-by-atom in an ion-crystal simulator
Friction between ordered, atomically smooth surfaces at the nanoscale
(nanofriction) is often governed by stick-slip processes. To test long-standing
atomistic models of such processes, we implement a synthetic nanofriction
interface between a laser-cooled Coulomb crystal of individually addressable
ions as the moving object, and a periodic light-field potential as the
substrate. We show that stick-slip friction can be tuned from maximal to nearly
frictionless via arrangement of the ions relative to the substrate. By varying
the ion number, we also show that this strong dependence of friction on the
structural mismatch, as predicted by many-particle models, already emerges at
the level of two or three atoms. This model system enables a microscopic and
systematic investigation of friction, potentially even into the quantum
many-body regime.Comment: 10 pages, 5 figure
Multislip Friction with a Single Ion
A trapped ion transported along a periodic potential is studied as a
paradigmatic nanocontact frictional interface. The combination of the periodic
corrugation potential and a harmonic trapping potential creates a
one-dimensional energy landscape with multiple local minima, corresponding to
multistable stick-slip friction. We measure the probabilities of slipping to
the various minima for various corrugations and transport velocities. The
observed probabilities show that the multislip regime can be reached
dynamically at smaller corrugations than would be possible statically, and can
be described by an equilibrium Boltzmann model. While a clear microscopic
signature of multislip behavior is observed for the ion motion, the frictional
force and dissipation are only weakly affected by the transition to multistable
potentials.Comment: 8 pages, 7 figure
Producing Squeezed Input States for an Atomic Clock Using an Optical Cavity
Spin squeezing, the generation of collective states of atomic ensembles with reduced spin noise by exploiting non-classical correlations between particles, is a promising approach to overcoming the standard quantum limit set by projection noise of independent atoms. We present two implementations of spin squeezing in ensembles of [superscript 87]Rb confined within an optical resonator, and discuss some of the decoherence mechanisms, both technical and fundamental, that we encounter.Harvard University - MIT Center for Ultracold AtomsDefense Advanced Research Projects AgencyNational Science Foundatio
Single-atom heat machines enabled by energy quantization
Quantization of energy is a quintessential characteristic of quantum systems.
Here we analyze its effects on the operation of Otto cycle heat machines and
show that energy quantization alone may alter and increase machine performance
in terms of output power, efficiency, and even operation mode. Our results
demonstrate that quantum thermodynamics enable the realization of classically
inconceivable Otto machines, such as those with an incompressible working
fluid. We propose to measure these effects experimentally using a laser-cooled
trapped ion as a microscopic heat machine
- …