114 research outputs found
Scanning electron microscopy of Rydberg-excited Bose-Einstein condensates
We report on the realization of high resolution electron microscopy of
Rydberg-excited ultracold atomic samples. The implementation of an ultraviolet
laser system allows us to excite the atom, with a single-photon transition, to
Rydberg states. By using the electron microscopy technique during the Rydberg
excitation of the atoms, we observe a giant enhancement in the production of
ions. This is due to -changing collisions, which broaden the Rydberg level
and therefore increase the excitation rate of Rydberg atoms. Our results pave
the way for the high resolution spatial detection of Rydberg atoms in an atomic
sample
Engineering long-range molecular potentials by external drive
We report the engineering of molecular potentials at large interatomic
distances. The molecular states are generated by off-resonant optical coupling
to a highly excited, long-range Rydberg molecular potential. The coupling
produces a potential well in the low-lying molecular potential, which supports
a bound state. The depth of the potential well, and thus the binding energy of
the molecule, can be tuned by the coupling parameters. We characterize these
molecules and find good agreement with a theoretical model based on the
coupling of the two involved adiabatic potential energy curves. Our results
open numerous possibilities to create long-range molecules between ultracold
ground state atoms and to use them for ultracold chemistry and applications
such as Feshbach resonances, Efimov physics or the study of halo molecules
All-optical measurement of magnetic fields for quantum gas experiments
We present an all-optical method to measure and compensate for residual
magnetic fields present in a cloud of ultracold atoms trapped in an optical
dipole trap. Our approach leverages the increased loss from the trapped atomic
sample through electromagnetically induced absorption. Modulating the
excitation laser provides coherent sidebands, resulting in {\Lambda}-type
pump-probe scheme. Scanning an additional magnetic offset field leads to pairs
of sub-natural linewidth resonances, whose positions encode the magnetic field
in all three spatial directions. Our measurement scheme is readily implemented
in a typical quantum gas experiments and has no particular hardware
requirements
Griffiths Phase in a Facilitated Rydberg Gas at Low Temperature
The spread of excitations by Rydberg facilitation bears many similarities to
epidemics. Such systems can be modeled with Monte-Carlo simulations of
classical rate equations to great accuracy as a result of high dephasing. In
this paper, we analyze the dynamics of a Rydberg many-body system in the
facilitation regime in the limits of high and low temperatures. While in the
high-temperature limit a homogeneous mean-field behaviour is recovered,
characteristic effects of heterogeneity can be seen in a frozen gas. At large
temperatures the system displays an absorbing-state phase transition and, in
the presence of an additional loss channel, self-organized criticality. In a
frozen or low-temperature gas, excitations are constrained to a network
resembling an Erd\"os-Renyi graph. We show that the absorbing-state phase
transition is replaced with an extended Griffiths phase, which we accurately
describe by a susceptible-infected-susceptible model on the Erd\"os-Renyi
network taking into account Rydberg blockade. Furthermore, we expand upon an
existing macroscopic Langevin equation to more accurately describe the density
of Rydberg atoms in the frozen and finite temperature regimes.Comment: 14 pages, 11 figure
Experimental realization of a 3D long-range random hopping model
Randomness and disorder have strong impact on transport processes in quantum
systems and give rise to phenomena such as Anderson localization [1-3],
many-body localization [4] or glassy dynamics [5]. Their characteristics
thereby depend on the strength and type of disorder. An important class are
hopping models, where particles or excitations move through a system which has
randomized couplings. This includes, e.g., spin glasses [5], coupled optical
waveguides [6], or NV center arrays [7]. They are also key to understand
excitation transport in molecular and biological systems, such as light
harvesting complexes [8]. In many of those systems, the microscopic coupling
mechanism is provided by the dipole-dipole interaction. Rydberg systems [9] are
therefore a natural candidate to study random hopping models. Here, we
experimentally study a three-dimensional many-body Rydberg system with random
dipole-dipole couplings. We measure the spectrum of the many-body system and
find good agreement with an effective spin model. We also find spectroscopic
signatures of a localization-delocalization transition. Our results pave the
way to study transport processes and localization phenomena in random hopping
models in detail. The inclusion of strong correlations is experimentally
straightforward and will allow to study the interplay between random hopping
and localization in strongly interacting systems.Comment: 7 pages, 4 figure
Competing Interactions in Strongly Driven Multi-Level Systems
We experimentally study the level mixing, splitting and repulsion of an
optically driven atomic multi-level system under two competing interactions.
The strength of the optical coupling is increased until it surpasses the atomic
hyperfine interaction responsible for mixing the magnetic substates. Due to the
multi-level character of the coupled state space, the level shifts exhibit
complex behavior reminiscent of the Paschen-Back effect. Our results show that
multi-level effects can have significant influence for strong external drive,
differing from a simple model of effective non-interacting two-level systems.
These results highlight the relevance of imperfections of the light
polarization or initial state preparation in strongly optically driven systems
Continuous Coupling of Ultracold Atoms to an Ionic Plasma via Rydberg Excitation
We characterize the two-photon excitation of an ultracold gas of Rubidium
atoms to Rydberg states analysing the induced atomic losses from an optical
dipole trap. Extending the duration of the Rydberg excitation to several ms,
the ground state atoms are continuously coupled to the formed positively
charged plasma. In this regime we measure the -dependence of the blockade
effect and we characterise the interaction of the excited states and the ground
state with the plasma. We also investigate the influence of the
quasi-electrostatic trapping potential on the system, confirming the validity
of the ponderomotive model for states with
- …