342 research outputs found
Entanglement interferometry for precision measurement of atomic scattering properties
We report on a two-particle matter wave interferometer realized with pairs of
trapped 87Rb atoms. Each pair of atoms is confined at a single site of an
optical lattice potential. The interferometer is realized by first creating a
coherent spin-mixture of the two atoms and then tuning the inter-state
scattering length via a Feshbach resonance. The selective change of the
inter-state scattering length leads to an entanglement dynamics of the
two-particle state that can be detected in a Ramsey interference experiment.
This entanglement dynamics is employed for a precision measurement of atomic
interaction parameters. Furthermore, the interferometer allows to separate
lattice sites with one or two atoms in a non-destructive way.Comment: 4 pages, 5 figure
Quantum Spin Dynamics of Mode-Squeezed Luttinger Liquids in Two-Component Atomic Gases
We report on the observation of the phase dynamics of interacting
one-dimensional ultracold bosonic gases with two internal degrees of freedom.
By controlling the non-linear atomic interactions close to a Feshbach resonance
we are able to induce a phase diffusive many-body spin dynamics. We monitor
this dynamical evolution by Ramsey interferometry, supplemented by a novel,
many-body echo technique. We find that the time evolution of the system is well
described by a Luttinger liquid initially prepared in a multimode squeezed
state. Our approach allows us to probe the non-equilibrium evolution of
one-dimensional many-body quantum systems.Comment: 4 pages, 3 figures Updated version, minor change
Spin squeezing of high-spin, spatially extended quantum fields
Investigations of spin squeezing in ensembles of quantum particles have been
limited primarily to a subspace of spin fluctuations and a single spatial mode
in high-spin and spatially extended ensembles. Here, we show that a wider range
of spin-squeezing is attainable in ensembles of high-spin atoms, characterized
by sub-quantum-limited fluctuations in several independent planes of
spin-fluctuation observables. Further, considering the quantum dynamics of an
ferromagnetic spinor Bose-Einstein condensate, we demonstrate
theoretically that a high degree of spin squeezing is attained in multiple
spatial modes of a spatially extended quantum field, and that such squeezing
can be extracted from spatially resolved measurements of magnetization and
nematicity, i.e.\ the vector and quadrupole magnetic moments, of the quantum
gas. Taking into account several experimental limitations, we predict that the
variance of the atomic magnetization and nematicity may be reduced as far as 20
dB below the standard quantum limits.Comment: 18 pages, 5 figure
Coherent collisional spin dynamics in optical lattices
We report on the observation of coherent, purely collisionally driven spin
dynamics of neutral atoms in an optical lattice. For high lattice depths, atom
pairs confined to the same lattice site show weakly damped Rabi-type
oscillations between two-particle Zeeman states of equal magnetization, induced
by spin changing collisions. This paves the way towards the efficient creation
of robust entangled atom pairs in an optical lattice. Moreover, measurement of
the oscillation frequency allows for precise determination of the spin-changing
collisional coupling strengths, which are directly related to fundamental
scattering lengths describing interatomic collisions at ultracold temperatures.Comment: revised version; 4 pages, 5 figure
Bayesian feedback control of a two-atom spin-state in an atom-cavity system
We experimentally demonstrate real-time feedback control of the joint
spin-state of two neutral Caesium atoms inside a high finesse optical cavity.
The quantum states are discriminated by their different cavity transmission
levels. A Bayesian update formalism is used to estimate state occupation
probabilities as well as transition rates. We stabilize the balanced two-atom
mixed state, which is deterministically inaccessible, via feedback control and
find very good agreement with Monte-Carlo simulations. On average, the feedback
loops achieves near optimal conditions by steering the system to the target
state marginally exceeding the time to retrieve information about its state.Comment: 4 pages, 4 figure
Precision measurement of spin-dependent interaction strengths for spin-1 and spin-2 87Rb atoms
We report on precision measurements of spin-dependent interaction-strengths
in the 87Rb spin-1 and spin-2 hyperfine ground states. Our method is based on
the recent observation of coherence in the collisionally driven spin-dynamics
of ultracold atom pairs trapped in optical lattices. Analysis of the Rabi-type
oscillations between two spin states of an atom pair allows a direct
determination of the coupling parameters in the interaction hamiltonian. We
deduce differences in scattering lengths from our data that can directly be
compared to theoretical predictions in order to test interatomic potentials.
Our measurements agree with the predictions within 20%. The knowledge of these
coupling parameters allows one to determine the nature of the magnetic ground
state. Our data imply a ferromagnetic ground state for 87Rb in the f=1
manifold, in agreement with earlier experiments performed without the optical
lattice. For 87Rb in the f=2 manifold the data points towards an
antiferromagnetic ground state, however our error bars do not exclude a
possible cyclic phase.Comment: 11 pages, 5 figure
Quantum Walk in Position Space with Single Optically Trapped Atoms
The quantum walk is the quantum analogue of the well-known random walk, which
forms the basis for models and applications in many realms of science. Its
properties are markedly different from the classical counterpart and might lead
to extensive applications in quantum information science. In our experiment, we
implemented a quantum walk on the line with single neutral atoms by
deterministically delocalizing them over the sites of a one-dimensional
spin-dependent optical lattice. With the use of site-resolved fluorescence
imaging, the final wave function is characterized by local quantum state
tomography, and its spatial coherence is demonstrated. Our system allows the
observation of the quantum-to-classical transition and paves the way for
applications, such as quantum cellular automata.Comment: 7 pages, 4 figure
Correlated hopping of bosonic atoms induced by optical lattices
In this work we analyze a particular setup with ultracold atoms trapped in
state-dependent lattices. We show that any asymmetry in the contact interaction
translates into one of two classes of correlated hopping. After deriving the
effective lattice Hamiltonian for the atoms, we obtain analytically and
numerically the different phases and quantum phase transitions. We find for
weak correlated hopping both Mott insulators and charge density waves, while
for stronger correlated hopping the system transitions into a pair superfluid.
We demonstrate that this phase exists for a wide range of interaction
asymmetries and has interesting correlation properties that differentiate it
from an ordinary atomic Bose-Einstein condensate.Comment: 24 pages with 9 figures, to appear in New Journal of Physic
Nearest-Neighbor Detection of Atoms in a 1D Optical Lattice by Fluorescence Imaging
We overcome the diffraction limit in fluorescence imaging of neutral atoms in
a sparsely filled one-dimensional optical lattice. At a periodicity of 433 nm,
we reliably infer the separation of two atoms down to nearest neighbors. We
observe light induced losses of atoms occupying the same lattice site, while
for atoms in adjacent lattice sites, no losses due to light induced
interactions occur. Our method points towards characterization of correlated
quantum states in optical lattice systems with filling factors of up to one
atom per lattice site.Comment: 4 pages, 4 figure
Simple method for sub-diffraction resolution imaging of cellular structures on standard confocal microscopes by three-photon absorption of quantum dots
This study describes a simple technique that improves a recently developed 3D sub-diffraction imaging method based on three-photon absorption of commercially available quantum dots. The method combines imaging of biological samples via tri-exciton generation in quantum dots with deconvolution and spectral multiplexing, resulting in a novel approach for multi-color imaging of even thick biological samples at a 1.4 to 1.9-fold better spatial resolution. This approach is realized on a conventional confocal microscope equipped with standard continuous-wave lasers. We demonstrate the potential of multi-color tri-exciton imaging of quantum dots combined with deconvolution on viral vesicles in lentivirally transduced cells as well as intermediate filaments in three-dimensional clusters of mouse-derived neural stem cells (neurospheres) and dense microtubuli arrays in myotubes formed by stacks of differentiated C2C12 myoblasts
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