650 research outputs found
Landau Levels in Strained Optical Lattices
We propose a hexagonal optical lattice system with spatial variations in the
hopping matrix elements. Just like in the valley Hall effect in strained
Graphene, for atoms near the Dirac points the variations in the hopping matrix
elements can be described by a pseudo-magnetic field and result in the
formation of Landau levels. We show that the pseudo-magnetic field leads to
measurable experimental signatures in momentum resolved Bragg spectroscopy,
Bloch oscillations, cyclotron motion, and quantization of in-situ densities.
Our proposal can be realized by a slight modification of existing experiments.
In contrast to previous methods, pseudo-magnetic fields are realized in a
completely static system avoiding common heating effects and therefore opening
the door to studying interaction effects in Landau levels with cold atoms.Comment: 5 pages, 3 figure
Probing correlated quantum many-body systems at the single-particle level
The detection of correlation and response
functions plays a crucial role in the experimental characterization of quantum many-body systems. In this thesis, we present novel techniques for the measurement of such functions at the single-particle level. Specifically, we show the single-atom- and single-site-resolved detection of an ultracold quantum gas in an optical lattice. The quantum gas is described by the Bose-Hubbard model, which features a zero temperature phase transition from a superfluid to a Mott-insulating state, a paradigm example of a quantum phase transition. We used the aforementioned detection techniques to study correlation and response properties across the superfluid-Mott-insulator transition.
The single-atom sensitivity of our method is achieved by fluorescence detection of individual atoms with a high signal-to-noise ratio. A high-resolution objective collects the fluorescence light and yields in situ `snapshots' of the quantum gas that allow for a single-site-resolved reconstruction of the atomic distribution.
This allowed us to measure two-site and non-local correlation-functions across the superfluid-Mott-insulator transition. Non-local correlation functions are based on the information of an extended region of the system and play an important role for the characterization of low-dimensional quantum phases. While non-local correlation functions were so far only theoretical tools, our results show that they are actually experimentally accessible.
Furthermore, we used a new thermometry scheme, based on the counting of individual thermal excitations, to measure the response of the system to lattice modulation. Using this method, we studied the excitation spectrum of the system across the two-dimensional superfluid-Mott-insulator transition. In particular, we detected a `Higgs' amplitude mode in the strongly-interacting superfluid close to the transition point where the system is described by an effectively Lorentz-invariant low-energy theory. Our experimental results helped to resolve a debate about the observability of Higgs modes in two-dimensional systems
Detecting two-site spin-entanglement in many-body systems with local particle-number fluctuations
We derive experimentally measurable lower bounds for the two-site
entanglement of the spin-degrees of freedom of many-body systems with local
particle-number fluctuations. Our method aims at enabling the spatially
resolved detection of spin-entanglement in Hubbard systems using
high-resolution imaging in optical lattices. A possible application is the
observation of entanglement generation and spreading during spin impurity
dynamics, for which we provide numerical simulations. More generally, the
scheme can simplify the entanglement detection in ion chains, Rydberg atoms, or
similar atomic systems
Non-local order in Mott insulators, Duality and Wilson Loops
It is shown that the Mott insulating and superfluid phases of bosons in an
optical lattice may be distinguished by a non-local 'parity order parameter'
which is directly accessible via single site resolution imaging. In one
dimension, the lattice Bose model is dual to a classical interface roughening
problem. We use known exact results from the latter to prove that the parity
order parameter exhibits long range order in the Mott insulating phase,
consistent with recent experiments by Endres et al. [Science 334, 200 (2011)].
In two spatial dimensions, the parity order parameter can be expressed in terms
of an equal time Wilson loop of a non-trivial U(1) gauge theory in 2+1
dimensions which exhibits a transition between a Coulomb and a confining phase.
The negative logarithm of the parity order parameter obeys a perimeter law in
the Mott insulator and is enhanced by a logarithmic factor in the superfluid.Comment: published versio
2000-times repeated imaging of strontium atoms in clock-magic tweezer arrays
We demonstrate single-atom resolved imaging with a survival probability of
and a fidelity of , enabling us to perform repeated
high-fidelity imaging of single atoms in tweezers for thousands of times. We
further observe lifetimes under laser cooling of more than seven minutes, an
order of magnitude longer than in previous tweezer studies. Experiments are
performed with strontium atoms in tweezer arrays, which is at
a magic wavelength for the clock transition. Tuning to this wavelength is
enabled by off-magic Sisyphus cooling on the intercombination line, which lets
us choose the tweezer wavelength almost arbitrarily. We find that a single not
retro-reflected cooling beam in the radial direction is sufficient for
mitigating recoil heating during imaging. Moreover, this cooling technique
yields temperatures below K, as measured by release and recapture.
Finally, we demonstrate clock-state resolved detection with average survival
probability of and average state detection fidelity of .
Our work paves the way for atom-by-atom assembly of large defect-free arrays of
alkaline-earth atoms, in which repeated interrogation of the clock transition
is an imminent possibility.Comment: 6 pages, 5 figures, 1 vide
Destruction of string order after a quantum quench
We investigate the evolution of string order in a spin-1 chain following a
quantum quench. After initializing the chain in the Affleck-Kennedy-Lieb-Tasaki
state, we analyze in detail how string order evolves as a function of time at
different length scales. The Hamiltonian after the quench is chosen either to
preserve or to suddenly break the symmetry which ensures the presence of string
order. Depending on which of these two situations arises, string order is
either preserved or lost even at infinitesimal times in the thermodynamic
limit. The fact that non-local order may be abruptly destroyed, what we call
string-order melting, makes it qualitatively different from typical order
parameters in the manner of Landau. This situation is thoroughly characterized
by means of numerical simulations based on matrix product states algorithms and
analytical studies based on a short-time expansion for several simplified
models.Comment: 14 pages, 6 figures. Changes after publication on PR
Berry electrodynamics: Anomalous drift and pumping from a time-dependent Berry connection
The Berry curvature of a Bloch band can be interpreted as a local magnetic field in reciprocal space. This analogy can be extended by defining an electric field analog in reciprocal space which arises from the time-dependent Berry connection. We explore the term in the semiclassical equation of motion that gives rise to this phenomenon, and show that it can lead to anomalous drift in wave-packet motion. A similar effect arises from changes in the band population due to periodic driving, where the resulting drift depends on the nature of the drive and can be expressed in terms of a shift vector. Finally, these effects can be combined to build a pump with a net anomalous drift during a cyclic evolution in momentum space
Coherent light scattering from a two-dimensional Mott insulator
We experimentally demonstrate coherent light scattering from an atomic Mott
insulator in a two-dimensional lattice. The far-field diffraction pattern of
small clouds of a few hundred atoms was imaged while simultaneously laser
cooling the atoms with the probe beams. We describe the position of the
diffraction peaks and the scaling of the peak parameters by a simple analytic
model. In contrast to Bragg scattering, scattering from a single plane yields
diffraction peaks for any incidence angle. We demonstrate the feasibility of
detecting spin correlations via light scattering by artificially creating a
one-dimensional antiferromagnetic order as a density wave and observing the
appearance of additional diffraction peaks.Comment: 4 pages, 4 figure
Spatially Resolved Detection of a Spin-Entanglement Wave in a Bose-Hubbard Chain
Entanglement is an essential property of quantum many-body systems. However,
its local detection is challenging and was so far limited to spin degrees of
freedom in ion chains. Here we measure entanglement between the spins of atoms
located on two lattice sites in a one-dimensional Bose-Hubbard chain which
features both local spin- and particle-number fluctuations. Starting with an
initially localized spin impurity, we observe an outwards propagating
entanglement wave and show quantitatively how entanglement in the spin sector
rapidly decreases with increasing particle-number fluctuations in the chain.Comment: 6 pages, 4 figure
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