2,707 research outputs found
Direct measurement of the van der Waals interaction between two Rydberg atoms
We report on the direct measurement of the van der Waals interaction between
two isolated, single Rydberg atoms separated by a controlled distance of a few
micrometers. By working in a regime where the single-atom Rabi frequency of the
laser used for excitation to the Rydberg state is comparable to the interaction
energy, we observe a \emph{partial} Rydberg blockade, whereby the
time-dependent populations of the various two-atom states exhibit coherent
oscillations with several frequencies. A quantitative comparison of the data
with a simple model based on the optical Bloch equations allows us to extract
the van der Waals energy, and to observe its characteristic
dependence. The magnitude of the measured coefficient agrees well with an
\emph{ab-initio} theoretical calculation, and we observe its dramatic increase
with the principal quantum number of the Rydberg state. Our results not
only allow to test an important physical law, but also demonstrate a degree of
experimental control which opens new perspectives in quantum information
processing and quantum simulation using long-range interactions between the
atoms.Comment: 4 pages, 3 figures, published versio
Coherent dipole-dipole coupling between two single atoms at a F\"orster resonance
Resonant energy transfers, i.e. the non-radiative redistribution of an
electronic excitation between two particles coupled by the dipole-dipole
interaction, lie at the heart of a variety of chemical and biological
phenomena, most notably photosynthesis. In 1948, F\"orster established the
theoretical basis of fluorescence resonant energy transfer (FRET), paving the
ground towards the widespread use of FRET as a "spectroscopic ruler" for the
determination of nanometer-scale distances in biomolecules. The underlying
mechanism is a coherent dipole-dipole coupling between particles, as already
recognized in the early days of quantum mechanics, but this coherence was not
directly observed so far. Here, we study, both spectroscopically and in the
time domain, the coherent, dipolar-induced exchange of electronic excitations
between two single Rydberg atoms separated by a controlled distance as large as
15 microns, and brought into resonance by applying a small electric field. The
coherent oscillation of the system between two degenerate pair states occurs at
a frequency that scales as the inverse third power of the distance, the
hallmark of dipole-dipole interactions. Our results not only demonstrate, at
the most fundamental level of two atoms, the basic mechanism underlying FRET,
but also open exciting prospects for active tuning of strong, coherent
interactions in quantum many-body systems.Comment: 4 pages, 3 figure
Single-Atom Addressing in Microtraps for Quantum-State Engineering using Rydberg Atoms
We report on the selective addressing of an individual atom in a pair of
single-atom microtraps separated by m. Using a tunable light-shift, we
render the selected atom off-resonant with a global Rydberg excitation laser
which is resonant with the other atom, making it possible to selectively block
this atom from being excited to the Rydberg state. Furthermore we demonstrate
the controlled manipulation of a two-atom entangled state by using the
addressing beam to induce a phase shift onto one component of the wave function
of the system, transferring it to a dark state for the Rydberg excitation
light. Our results are an important step towards implementing quantum
information processing and quantum simulation with large arrays of Rydberg
atoms.Comment: 4 pages, 3 figure
Single-atom trapping in holographic 2D arrays of microtraps with arbitrary geometries
We demonstrate single-atom trapping in two-dimensional arrays of microtraps
with arbitrary geometries. We generate the arrays using a Spatial Light
Modulator (SLM), with which we imprint an appropriate phase pattern on an
optical dipole trap beam prior to focusing. We trap single
atoms in the sites of arrays containing up to microtraps separated by
distances as small as m, with complex structures such as triangular,
honeycomb or kagome lattices. Using a closed-loop optimization of the
uniformity of the trap depths ensures that all trapping sites are equivalent.
This versatile system opens appealing applications in quantum information
processing and quantum simulation, e.g. for simulating frustrated quantum
magnetism using Rydberg atoms.Comment: 9 pages, 10 figure
Frictional velocity-weakening in landslides on Earth and on other planetary bodies
One of the ultimate goals in landslide hazard assessment is to predict maximum landslide
extension and velocity. Despite much work, the physical processes governing energy
dissipation during these natural granular flows remain uncertain. Field observations show that
large landslides travel over unexpectedly long distances, suggesting low dissipation.
Numerical simulations of landslides require a small friction coefficient to reproduce the
extension of their deposits. Here, based on analytical and numerical solutions for granular
flows constrained by remote-sensing observations, we develop a consistent method to
estimate the effective friction coefficient of landslides. This method uses a constant basal
friction coefficient that reproduces the first-order landslide properties. We show that friction
decreases with increasing volume or, more fundamentally, with increasing sliding velocity.
Inspired by frictional weakening mechanisms thought to operate during earthquakes, we
propose an empirical velocity-weakening friction law under a unifying phenomenological
framework applicable to small and large landslides observed on Earth and beyond
Slippery sliding on icy Iapetus
Enigmatically, some landslides flow farther than normal frictional resistance allows. Cassini images of Saturnâs icy
moon Iapetus reveal a multitude of long-runout landslides that may have been enabled by flash heating along the
sliding surface
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