10 research outputs found
A hybrid model for Rydberg gases including exact two-body correlations
A model for the simulation of ensembles of laser-driven Rydberg-Rydberg
interacting multi-level atoms is discussed. Our hybrid approach combines an
exact two-body treatment of nearby atom pairs with an effective approximate
treatment for spatially separated pairs. We propose an optimized evolution
equation based only on the system steady state, and a time-independent Monte
Carlo technique is used to efficiently determine this steady state. The hybrid
model predicts features in the pair correlation function arising from
multi-atom processes which existing models can only partially reproduce. Our
interpretation of these features shows that higher-order correlations are
relevant already at low densities. Finally, we analyze the performance of our
model in the high-density case.Comment: significantly expanded and revised version (more observables,
high-density regime); 9 pages, 8 figure
Ab initio quantum models for thin-film x-ray cavity QED
We develop two ab initio quantum approaches to thin-film x-ray cavity quantum
electrodynamics with spectrally narrow x-ray resonances, such as those provided
by M\"ossbauer nuclei. The first method is based on a few-mode description of
the cavity, and promotes and extends existing phenomenological few-mode models
to an ab initio theory. The second approach uses analytically-known Green's
functions to model the system. The two approaches not only enable one to ab
initio derive the effective few-level scheme representing the cavity and the
nuclei in the low-excitation regime, but also provide a direct avenue for
studies at higher excitation, involving non-linear or quantum phenomena. The ab
initio character of our approaches further enables direct optimizations of the
cavity structure and thus of the photonic environment of the nuclei, to tailor
the effective quantum optical level scheme towards particular applications. To
illustrate the power of the ab initio approaches, we extend the established
quantum optical modeling to resonant cavity layers of arbitrary thickness,
which is essential to achieve quantitative agreement for cavities used in
recent experiments. Further, we consider multi-layer cavities featuring
electromagnetically induced transparency, derive their quantum optical
few-level systems ab initio, and identify the origin of discrepancies in the
modeling found previously using phenomenological approaches as arising from
cavity field gradients across the resonant layers.Comment: 41 pages, 20 figures, added clarifications and minor correction
Coherent X-ray−optical control of nuclear excitons
Coherent control of quantum dynamics is key to a multitude of fundamental studies and applications. In the visible or longer-wavelength domains, near-resonant light fields have become the primary tool with which to control electron dynamics. Recently, coherent control in the extreme-ultraviolet range was demonstrated, with a few-attosecond temporal resolution of the phase control. At hard-X-ray energies (above 5–10 kiloelectronvolts), Mössbauer nuclei feature narrow nuclear resonances due to their recoilless absorption and emission of light, and spectroscopy of these resonances is widely used to study the magnetic, structural and dynamical properties of matter. It has been shown that the power and scope of Mössbauer spectroscopy can be greatly improved using various control techniques. However, coherent control of atomic nuclei using suitably shaped near-resonant X-ray fields remains an open challenge. Here we demonstrate such control, and use the tunable phase between two X-ray pulses to switch the nuclear exciton dynamics between coherent enhanced excitation and coherent enhanced emission. We present a method of shaping single pulses delivered by state-of-the-art X-ray facilities into tunable double pulses, and demonstrate a temporal stability of the phase control on the few-zeptosecond timescale. Our results unlock coherent optical control for nuclei, and pave the way for nuclear Ramsey spectroscopy and spin-echo-like techniques, which should not only advance nuclear quantum optics, but also help to realize X-ray clocks and frequency standards. In the long term, we envision time-resolved studies of nuclear out-of-equilibrium dynamics, which is a long-standing challenge in Mössbauer science
Spectral narrowing of x-ray pulses for precision spectroscopy with nuclear resonances
Spectroscopy of nuclear resonances offers a wide range of applications due to the remarkable energy resolution afforded by their narrow linewidths. However, progress toward higher resolution is inhibited at modern x-ray sources because they deliver only a tiny fraction of the photons on resonance, with the remainder contributing to an off-resonant background. We devised an experimental setup that uses the fast mechanical motion of a resonant target to manipulate the spectrum of a given x-ray pulse and to redistribute off-resonant spectral intensity onto the resonance. As a consequence, the resonant pulse brilliance is increased while the off-resonant background is reduced. Because our method is compatible with existing and upcoming pulsed x-ray sources, we anticipate that this approach will find applications that require ultranarrow x-ray resonances
Analysis of Outcomes in Ischemic vs Nonischemic Cardiomyopathy in Patients With Atrial Fibrillation A Report From the GARFIELD-AF Registry
IMPORTANCE Congestive heart failure (CHF) is commonly associated with nonvalvular atrial fibrillation (AF), and their combination may affect treatment strategies and outcomes