42 research outputs found
Experimental Demonstration of a Synthetic Lorentz Force by Using Radiation Pressure
Synthetic magnetism in cold atomic gases opened the doors to many exciting
novel physical systems and phenomena. Ubiquitous are the methods used for the
creation of synthetic magnetic fields. They include rapidly rotating
Bose-Einstein condensates employing the analogy between the Coriolis and the
Lorentz force, and laser-atom interactions employing the analogy between the
Berry phase and the Aharonov-Bohm phase. Interestingly, radiation pressure -
being one of the most common forces induced by light - has not yet been used
for synthetic magnetism. We experimentally demonstrate a synthetic Lorentz
force, based on the radiation pressure and the Doppler effect, by observing the
centre-of-mass motion of a cold atomic cloud. The force is perpendicular to the
velocity of the cold atomic cloud, and zero for the cloud at rest. Our novel
concept is straightforward to implement in a large volume, for a broad range of
velocities, and can be extended to different geometries.Comment: are welcom
Synthetic Lorentz force in classical atomic gases via Doppler effect and radiation pressure
We theoretically predict a novel type of synthetic Lorentz force for
classical (cold) atomic gases, which is based on the Doppler effect and
radiation pressure. A fairly uniform and strong force can be constructed for
gases in macroscopic volumes of several cubic millimeters and more. This opens
the possibility to mimic classical charged gases in magnetic fields, such as
those in a tokamak, in cold atom experiments.Comment: are welcom
Absolute frequency measurement of the 5s5p - 5s5d transition in strontium
We report on the absolute frequency determination of the 5s5p - 5s5d
transition in atomic strontium, achieved through frequency
comb-referenced laser-induced-fluorescence (LIF) spectroscopy. We excite the
5s - 5s5p transition using an on-resonance laser at
461 nm, and then measure the variation in the LIF signal while
scanning the laser at 767 nm across the 5s5p - 5s5d
transition. We determine the absolute frequency of MHz,
with an accuracy that surpasses the previous most accurate measurement by two
orders of magnitude. This measurement technique can be readily applied for
precision spectroscopy of high-lying states not only in strontium, but also in
other atomic species
Two-photon transitions driven by a combination of diode and femtosecond lasers
We report on the combined action of a cw diode laser and a train of
ultrashort pulses when each of them drives one step of the 5S-5P-5D two-photon
transition in rubidium vapor. The fluorescence from the 6P_{3/2} state is
detected for a fixed repetition rate of the femtosecond laser while the
cw-laser frequency is scanned over the rubidium D_{2} lines. This scheme allows
for a velocity selective spectroscopy in a large spectral range including the
5D_{3/2} and 5D_{5/2} states. The results are well described in a simplified
frequency domain picture, considering the interaction of each velocity group
with the cw laser and a single mode of the frequency comb.Comment: 4 pages, 4 figure
Frequency-comb-induced radiative force on cold rubidium atoms
We experimentally investigate the radiative force and laser-induced fluorescence (LIF) in cold rubidium atoms induced by pulse-train (frequency-comb) excitation. Three configurations are studied: (i) single-pulse-train excitation, (ii) two in-phase counterpropagating pulse trains, and (iii) two out-of-phase counterpropagating pulse trains. In all configurations, measured LIF is in agreement with calculations based on the optical Bloch equations. The observed forces in the first two configurations are in qualitative agreement with the model(s) used for calculating mechanical action of a pulse train on atoms; however, this is not the case for the third configuration. Possible resolution of the discrepancy is discussed
Comparative study of light storage in antirelaxation-coated and buffer-gas-filled alkali vapor cells
We perform a comparative study of light storage in antirelaxation-coated and
buffer-gas-filled alkali vapor cells using electromagnetically induced
transparency (EIT) in warm rubidium vapor. The use of a buffer-gas-filled cell
resulted in 10-fold improvement in storage time and efficiency
compared to antirelaxation-coated cells. We achieve up to sixfold enhancement
in buffer-gas-filled memory efficiency, while maintaining a similar memory
lifetime, by employing a near-resonant EIT -scheme instead of a
resonant one. Our findings contribute to the development of field-deployable
quantum memories. quantum memories.Comment: 8 pages, 6 figure
Frequency-comb-induced radiation pressure force in dense atomic clouds
We investigate the frequency comb induced radiation pressure force acting on
a cloud of cold Rb atoms. Reduction and spectral broadening of the
frequency comb force are observed as the cloud's optical thickness is
increased. Since the radiation pressure force is uniquely determined by light
scattered by an atomic cloud, we discuss different scattering mechanisms, and
point to the shadow effect as the dominant mechanism affecting FC-induced force
in resonantly excited dense atomic clouds. Our results improve the
understanding of the interaction of frequency comb light with many-atom
ensembles, which is essential for novel frequency comb applications in
simultaneous multi-species cooling, multi-mode quantum memories, and multi-mode
atom-light interfaces.Comment: 8 pages, 4 figure
Simultaneous dual-species laser cooling using an optical frequency comb
We demonstrate 1D simultaneous laser cooling of Rb and Rb atoms
using an optical frequency comb. By adjusting the pulse repetition frequency
and the offset frequency, the frequency comb spectrum is tuned to ensure that
two distinct frequency comb modes are simultaneously red-detuned from the
cooling transitions, one mode for each species. Starting from a pre-cooled
cloud of Rb atoms at above-Doppler temperatures, we show simultaneous
cooling of both species down to the Doppler temperature using two
counter-propagating /-polarized beams from the
frequency comb. The results indicate that simultaneous dual-species frequency
comb cooling does not affect the cooling characteristics of individual atomic
species. The results of this work imply that several atomic species could be
cooled simultaneously using a single frequency comb source. This comb-based
multi-channel laser cooling could bring significant advances in multi-species
atom interferometers for space applications and in the study of multi-species
interactions
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Cobra-IE Evaluation by Simulation of the NUPEC BWR Full-Size Fine-Mesh Bundle Test (BFBT)
The COBRA-IE computer code is a thermal-hydraulic subchannel analysis program capable of simulating phenomena present in both PWRs and BWRs. As part of ongoing COBRA-IE assessment efforts, the code has been evaluated against experimental data from the NUPEC BWR Full-Size Fine-Mesh Bundle Tests (BFBT). The BFBT experiments utilized an 8 x 8 rod bundle to simulate BWR operating conditions and power profiles, providing an excellent database for investigation of the capabilities of the code. Benchmarks performed included steady-state and transient void distribution, single-phase and two-phase pressure drop, and steady-state and transient critical power measurements. COBRA-IE effectively captured the trends seen in the experimental data with acceptable prediction error. Future sensitivity studies are planned to investigate the effects of enabling and/or modifying optional code models dealing with void drift, turbulent mixing, rewetting, and CHF