60 research outputs found
Measurement of the Angular Dependence of the Dipole-Dipole Interaction Between Two Individual Rydberg Atoms at a F\"orster Resonance
We measure the angular dependence of the resonant dipole-dipole interaction
between two individual Rydberg atoms with controlled relative positions. By
applying a combination of static electric and magnetic fields on the atoms, we
demonstrate the possibility to isolate a single interaction channel at a
F\"orster resonance, that shows a well-defined angular dependence. We first
identify spectroscopically the F\"orster resonance of choice and we then
perform a direct measurement of the interaction strength between the two atoms
as a function of the angle between the internuclear axis and the quantization
axis. Our results show good agreement with the expected angular dependence
, and represent an important step towards quantum
state engineering in two-dimensional arrays of individual Rydberg atoms.Comment: 5 pages, 4 figure
Realizing quantum Ising models in tunable two-dimensional arrays of single Rydberg atoms
Spin models are the prime example of simplified manybody Hamiltonians used to
model complex, real-world strongly correlated materials. However, despite their
simplified character, their dynamics often cannot be simulated exactly on
classical computers as soon as the number of particles exceeds a few tens. For
this reason, the quantum simulation of spin Hamiltonians using the tools of
atomic and molecular physics has become very active over the last years, using
ultracold atoms or molecules in optical lattices, or trapped ions. All of these
approaches have their own assets, but also limitations. Here, we report on a
novel platform for the study of spin systems, using individual atoms trapped in
two-dimensional arrays of optical microtraps with arbitrary geometries, where
filling fractions range from 60 to 100% with exact knowledge of the initial
configuration. When excited to Rydberg D-states, the atoms undergo strong
interactions whose anisotropic character opens exciting prospects for
simulating exotic matter. We illustrate the versatility of our system by
studying the dynamics of an Ising-like spin-1/2 system in a transverse field
with up to thirty spins, for a variety of geometries in one and two dimensions,
and for a wide range of interaction strengths. For geometries where the
anisotropy is expected to have small effects we find an excellent agreement
with ab-initio simulations of the spin-1/2 system, while for strongly
anisotropic situations the multilevel structure of the D-states has a
measurable influence. Our findings establish arrays of single Rydberg atoms as
a versatile platform for the study of quantum magnetism.Comment: This is the version of the manuscript as initially submitted to
Natur
Engineering Gaussian states of light from a planar microcavity
Quantum fluids of light in a nonlinear planar microcavity can exhibit
antibunched photon statistics at short distances due to repulsive polariton
interactions. We show that, despite the weakness of the nonlinearity, the
antibunching signal can be amplified orders of magnitude with an appropriate
free-space optics scheme to select and interfere output modes. Our results are
understood from the unconventional photon blockade perspective by analyzing the
approximate Gaussian output state of the microcavity. In a second part, we
illustrate how the temporal and spatial profile of the density-density
correlation function of a fluid of light can be reconstructed with free-space
optics. Also here the nontrivial (anti)bunching signal can be amplified
significantly by shaping the light emitted by the microcavity
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
Nonlinear optics in the fractional quantum Hall regime
Engineering strong interactions between optical photons is a great challenge
for quantum science. Envisioned applications range from the realization of
photonic gates for quantum information processing to synthesis of photonic
quantum materials for investigation of strongly-correlated driven-dissipative
systems. Polaritonics, based on the strong coupling of photons to atomic or
electronic excitations in an optical resonator, has emerged as a promising
approach to implement those tasks. Recent experiments demonstrated the onset of
quantum correlations in the exciton-polariton system, showing that strong
polariton blockade could be achieved if interactions were an order of magnitude
stronger. Here, we report time resolved four-wave mixing experiments on a
two-dimensional electron system embedded in an optical cavity, demonstrating
that polariton-polariton interactions are strongly enhanced when the electrons
are initially in a fractional quantum Hall state. Our experiments indicate that
in addition to strong correlations in the electronic ground state,
exciton-electron interactions leading to the formation of polaron polaritons
play a key role in enhancing the nonlinear optical response. Besides potential
applications in realization of strongly interacting photonic systems, our
findings suggest that nonlinear optical measurements could provide information
about fractional quantum Hall states that is not accessible in linear optical
response
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
Orbital angular momentum bistability in a microlaser
Light's orbital angular momentum (OAM) is an unbounded degree of freedom
emerging in helical beams that appears very advantageous technologically. Using
a chiral microlaser, i.e. an integrated device that allows generating an
emission carrying a net OAM, we demonstrate a regime of bistability involving
two modes presenting distinct OAM (L = 0 and L = 2). Furthermore, thanks to an
engineered spin-orbit coupling of light in the device, these modes also exhibit
distinct polarization patterns, i.e. cirular and azimuthal polarizations. Using
a dynamical model of rate euqations, we show that this bistability arises from
polarization-dependent saturation of the gain medium. Such a bistable regime
appears very promising for implementing ultrafast optical switches based on the
OAM of light. As well, it paves the way to the exploration of dynamical
processes involving phase and polarization vortices
Phase diagram of one-dimensional driven-dissipative exciton-polariton condensates
We consider a one-dimensional driven-dissipative exciton-polariton condensate
under incoherent pump, described by the stochastic generalized Gross-Pitaevskii
equation. It was shown that the condensate phase dynamics maps under some
assumptions to the Kardar-Parisi-Zhang (KPZ) equation, and the temporal
coherence of the condensate follows a stretched exponential decay characterized
by KPZ universal exponents. In this work, we determine the main mechanisms
which lead to the departure from the KPZ phase, and identify three possible
other regimes: (i) a soliton-patterned regime at large interactions and weak
noise, populated by localized structures analogue to dark solitons; (ii) a
vortex-disordered regime at high noise and weak interactions, dominated by
point-like phase defects in space-time; (iii) a defect-free reservoir-textured
regime where the adiabatic approximation breaks down. We characterize each
regime by the space-time maps, the first-order correlations, the momentum
distribution and the density of topological defects. We thus obtain the phase
diagram at varying noise, pump intensity and interaction strength. Our
predictions are amenable to observation in state-of-art experiments with
exciton-polaritons
- …