382 research outputs found
Radiative and collisional processes in translationally cold samples of hydrogen Rydberg atoms studied in an electrostatic trap
Supersonic beams of hydrogen atoms, prepared selectively in Rydberg-Stark
states of principal quantum number in the range between 25 and 35, have
been deflected by 90, decelerated and loaded into off-axis electric
traps at initial densities of atoms/cm and translational
temperatures of 150 mK. The ability to confine the atoms spatially was
exploited to study their decay by radiative and collisional processes. The
evolution of the population of trapped atoms was measured for several
milliseconds in dependence of the principal quantum number of the initially
prepared states, the initial Rydberg-atom density in the trap, and the
temperature of the environment of the trap, which could be varied between 7.5 K
and 300 K using a cryorefrigerator. At room temperature, the population of
trapped Rydberg atoms was found to decay faster than expected on the basis of
their natural lifetimes, primarily because of absorption and emission
stimulated by the thermal radiation field. At the lowest temperatures
investigated experimentally, the decay was found to be multiexponential, with
an initial rate scaling as and corresponding closely to the natural
lifetimes of the initially prepared Rydberg-Stark states. The decay rate was
found to continually decrease over time and to reach an almost -independent
rate of more than (1 ms) after 3 ms. To analyze the experimentally
observed decay of the populations of trapped atoms, numerical simulations were
performed which included all radiative processes, i.e., spontaneous emission as
well as absorption and emission stimulated by the thermal radiation. These
simulations, however, systematically underestimated the population of trapped
atoms observed after several milliseconds by almost two orders of magnitude,
although they reliably predicted the decay rates of the remaining atoms in the
trap. TheComment: 36 pages, 18 figure
Slow and velocity-tunable beams of metastable He by multistage Zeeman deceleration
Metastable helium molecules (He) have been generated by striking a
discharge in a supersonic expansion of helium gas from a pulsed valve. When
operating the pulsed valve at room temperature, 77K, and 10K, the mean velocity
of the supersonic beam was measured to be 1900m/s, 980m/s, and 530m/s,
respectively. A 55-stage Zeeman decelerator operated in a phase-stable manner
was then used to further reduce the beam velocity and tune it in the range
between 100 and 150m/s. The internal-state distribution of the decelerated
sample was established by photoionization spectroscopy.Comment: 10 pages, 7 figure
Fluorescence-lifetime-limited trapping of Rydberg helium atoms on a chip
Metastable (1s)(2s) helium atoms produced in a supersonic beam
were excited to Rydberg-Stark states (with in the range) in a
cryogenic environment and subsequently decelerated by, and trapped above, a
surface-electrode decelerator. In the trapping experiments, the Rydberg atoms
were brought to rest in 75~s and over a distance of 33~mm and kept
stationary for times in the ~s range, before
being re-accelerated for detection by pulsed field ionization. The use of a
home-built valve producing short gas pulses with a duration of about 20~s
enabled the reduction of losses arising from collisions with atoms in the
trailing part of the gas pulses. Cooling the decelerator to 4.7~K further
suppressed losses by transitions induced by blackbody radiation and by
collisions with atoms desorbing from the decelerator surface. The main
contribution (60\%) to the atom loss during deceleration is attributed to the
escape out of the decelerator moving traps of atoms having energies higher than
the trap saddle point, spontaneous emission and collisions with atoms in the
trailing part of the gas pulses causing each only about 20\% of the atom loss.
At 4.7 K, the atom losses in the trapping phase of the experiments were found
to be almost exclusively caused by spontaneous emission and the trap lifetimes
were found to correspond to the natural lifetimes of the Rydberg-Stark states.
Increasing the temperature to 100 K enhanced the trap losses by transitions
stimulated by blackbody radiation
Driving Rydberg-Rydberg transitions from a co-planar microwave waveguide
The coherent interaction between ensembles of helium Rydberg atoms and
microwave fields in the vicinity of a solid-state co-planar waveguide is
reported. Rydberg-Rydberg transitions, at frequencies between 25 GHz and 38
GHz, have been studied for states with principal quantum numbers in the range
30 - 35 by selective electric-field ionization. An experimental apparatus
cooled to 100 K was used to reduce effects of blackbody radiation.
Inhomogeneous, stray electric fields emanating from the surface of the
waveguide have been characterized in frequency- and time-resolved measurements
and coherence times of the Rydberg atoms on the order of 250 ns have been
determined.Comment: 5 pages, 5 figure
Imaging electric fields in the vicinity of cryogenic surfaces using Rydberg atoms
The ability to characterize static and time-dependent electric fields in situ
is an important prerequisite for quantum-optics experiments with atoms close to
surfaces. Especially in experiments which aim at coupling Rydberg atoms to the
near field of superconducting circuits, the identification and subsequent
elimination of sources of stray fields is crucial. We present a technique that
allows the determination of stray-electric-field distributions
at distances of less than from (cryogenic) surfaces using
coherent Rydberg-Stark spectroscopy in a pulsed supersonic beam of metastable
helium atoms. We demonstrate the
capabilities of this technique by characterizing the electric stray field
emanating from a structured superconducting surface. Exploiting coherent
population transfer with microwave radiation from a coplanar waveguide, the
same technique allows the characterization of the microwave-field distribution
above the surface.Comment: 6 pages, 4 figure
Measuring the dispersive frequency shift of a rectangular microwave cavity induced by an ensemble of Rydberg atoms
In recent years the interest in studying interactions of Rydberg atoms or
ensembles thereof with optical and microwave frequency fields has steadily
increased, both in the context of basic research and for potential applications
in quantum information processing. We present measurements of the dispersive
interaction between an ensemble of helium atoms in the 37s Rydberg state and a
single resonator mode by extracting the amplitude and phase change of a weak
microwave probe tone transmitted through the cavity. The results are in
quantitative agreement with predictions made on the basis of the dispersive
Tavis-Cummings Hamiltonian. We study this system with the goal of realizing a
hybrid between superconducting circuits and Rydberg atoms. We measure maximal
collective coupling strengths of 1 MHz, corresponding to 3*10^3 Rydberg atoms
coupled to the cavity. As expected, the dispersive shift is found to be
inversely proportional to the atom-cavity detuning and proportional to the
number of Rydberg atoms. This possibility of measuring the number of Rydberg
atoms in a nondestructive manner is relevant for quantitatively evaluating
scattering cross sections in experiments with Rydberg atoms
Vacuum-ultraviolet frequency-modulation spectroscopy
Frequency-modulation (FM) spectroscopy has been extended to the
vacuum-ultraviolet (VUV) range of the electromagnetic spectrum. Coherent VUV
laser radiation is produced by resonance-enhanced sum-frequency mixing
() in Kr and Xe using two
near-Fourier-transform-limited laser pulses of frequencies
and . Sidebands generated in the output of the second laser ()
using an electro-optical modulator operating at the frequency
are directly transfered to the VUV and used to record FM
spectra. Demodulation is demonstrated both at and
. The main advantages of the method are that its
sensitivity is not reduced by pulse-to-pulse fluctuations of the VUV laser
intensity, compared to VUV absorption spectroscopy is its background-free
nature, the fact that its implementation using table-top laser equipment is
straightforward and that it can be used to record VUV absorption spectra of
cold samples in skimmed supersonic beams simultaneously with
laser-induced-fluorescence and photoionization spectra. To illustrate these
advantages we present VUV FM spectra of Ar, Kr, and N in selected regions
between 105000cm and 122000cm.Comment: 23 pages, 10 figure
Metrology of Rydberg states of the hydrogen atom
We present a method to precisly measure the frequencies of transitions to
high- Rydberg states of the hydrogen atom which are not subject to
uncontrolled systematic shifts caused by stray electric fields. The method
consists in recording Stark spectra of the field-insensitive Stark states
and the field-sensitive Stark states, which are used to calibrate the
electric field strength. We illustrate this method with measurements of
transitions from the hyperfine levels in the
presence of intentionally applied electric fields with strengths in the range
between and Vcm. The slightly field-dependent level
energies are corrected with a precisely calculated shift to obtain the
corresponding Bohr energies . The energy
difference between and obtained with our method agrees with
Bohr's formula within the kHz experimental uncertainty. We also
determined the hyperfine splitting of the state by taking the
difference between transition frequencies from the levels to the Stark states. Our results demonstrate the
possibility of carrying out precision measurements in high- hydrogenic
quantum states
Multistage Zeeman deceleration of metastable neon
A supersonic beam of metastable neon atoms has been decelerated by exploiting
the interaction between the magnetic moment of the atoms and time-dependent
inhomogeneous magnetic fields in a multistage Zeeman decelerator. Using 91
deceleration solenoids, the atoms were decelerated from an initial velocity of
580m/s to final velocities as low as 105m/s, corresponding to a removal of more
than 95% of their initial kinetic energy. The phase-space distribution of the
cold, decelerated atoms was characterized by time-of-flight and imaging
measurements, from which a temperature of 10mK was obtained in the moving frame
of the decelerated sample. In combination with particle-trajectory simulations,
these measurements allowed the phase-space acceptance of the decelerator to be
quantified. The degree of isotope separation that can be achieved by multistage
Zeeman deceleration was also studied by performing experiments with pulse
sequences generated for Ne and Ne.Comment: 16 pages, 15 figure
Measurements of AMPs in stratum corneum of atopic dermatitis and healthy skin-tape stripping technique
Abstract Decreased levels of antimicrobial peptides (AMPs) in atopic dermatitis (AD) have previously been reported and have been linked to the increased susceptibility to skin infections found in AD patients. This study intents to identify AMPs: hBD-2, hBD-3, RNase7, psoriasin and LL-37 in AD patients and healthy controls, and determine concentrations in consecutive depths of the outer most skin layers. Tape stripping was used on lesional and non-lesional skin. From each skin site, 35 consecutive tape strips were collected and pooled in groups of 5. Commercially available ELISA kits were used to determine AMP concentration in stratum corneum samples. hBD-2, hBD-3, RNase7 and psoriasin were identified in stratum corneum samples. hBD-3-level was markedly higher in AD non-lesional skin compared to healthy controls, and a similar trend was observed for RNase7. Most AMPs were distributed evenly through 35 tape strips, implying a homogeneous distribution of antimicrobial defense in the outer most skin layers. The findings indicate that AD patients may not suffer from a general baseline deficiency in AMPs, and that the innate immune defense is present throughout the stratum corneum, both insights of importance for understanding the role of AMPs in AD
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