We observe a dramatic difference in optical line shapes of a ^{4}He Bose-Einstein condensate and a ^{3}He degenerate Fermi gas by measuring the 1557-nm 2 ^{3}S-2 ^{1}S magnetic dipole transition ...(8 Hz natural linewidth) in an optical dipole trap. The 15 kHz FWHM condensate line shape is only broadened by mean field interactions, whereas the degenerate Fermi gas line shape is broadened to 75 kHz FWHM due to the effect of Pauli exclusion on the spatial and momentum distributions. The asymmetric optical line shapes are observed in excellent agreement with line shape models for the quantum degenerate gases. For ^{4}He a triplet-singlet s-wave scattering length a=+50(10)_{stat}(43)_{syst}a_{0} is extracted. The high spectral resolution reveals a doublet in the absorption spectrum of the BEC, and this effect is understood by the presence of a weak optical lattice in which a degeneracy of the lattice recoil and the spectroscopy photon recoil leads to Bragg-like scattering.
Improvements in both theory and frequency metrology of few-electron systems such as hydrogen and helium have enabled increasingly sensitive tests of quantum electrodynamics, as well as ever more ...accurate determinations of fundamental constants and the size of the nucleus. At the same time, advances in cooling and trapping of neutral atoms have revolutionized the development of increasingly accurate atomic clocks. Here, we combine these fields to reach very high precision on an optical transition in the helium atom by employing a 4He Bose–Einstein condensate confined in a magic wavelength optical dipole trap. The measured transition accurately connects the ortho- and parastates of helium and constitutes a stringent test of quantum electrodynamics theory. In addition, we test polarizability calculations and ultracold scattering properties of the helium atom. Finally, our measurement lays the foundation for a determination of the 3He–4He nuclear charge radius difference with an accuracy exceeding that of muonic helium measurements currently being performed in the context of the proton radius puzzle.
A robust, high-flux source of laser-cooled ytterbium atoms Wodey, E; Rengelink, R J; Meiners, C ...
Journal of physics. B, Atomic molecular and optical physics/Journal of physics. B, Atomic, molecular and optical physics,
02/2021, Letnik:
54, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present a high-flux source of cold ytterbium atoms that is robust, lightweight and low-maintenance. Our apparatus delivers 1 × 109 atoms s−1 into a 3D magneto-optical trap without requiring water ...cooling or high current power supplies. We achieve this by employing a Zeeman slower and a 2D magneto-optical trap fully based on permanent magnets in Halbach configurations. This strategy minimizes mechanical complexity, stray magnetic fields, and heat production while requiring little to no maintenance, making it applicable to both embedded systems that seek to minimize electrical power consumption, and large scale experiments to reduce the complexity of their subsystems.
High-precision spectroscopy on the
2
3
S
→
2
1
S
transition is possible in ultracold optically trapped helium, but the accuracy is limited by the ac-Stark shift induced by the optical dipole trap. To ...overcome this problem, we have built a trapping laser system at the predicted magic wavelength of 319.8 nm. Our system is based on frequency conversion using commercially available components and produces over 2 W of power at this wavelength. With this system, we show trapping of ultracold atoms, both thermal (~0.2 μk) and in a Bose–Einstein condensate, with a trap lifetime of several seconds, mainly limited by off-resonant scattering .
We report on interference studies in the internal and external degrees of freedom of metastable triplet helium atoms trapped near quantum degeneracy in a
1.5
μ
m
optical dipole trap. Applying a ...single
π
/
2
rf pulse we demonstrate that 50% of the atoms initially in the
m
=
+
1
state can be transferred to the magnetic field insensitive
m
=
0
state. Two
π
/
2
pulses with varying time delay allow a Ramsey-type measurement of the Zeeman shift for a high precision measurement of the
2
3
S
1
–
2
1
S
0
transition frequency. We show that this method also allows strong suppression of mean-field effects on the measurement of the Zeeman shift, which is necessary to reach the accuracy goal of 0.1 kHz on the absolute transition frequencies. Theoretically the feasibility of using metastable triplet helium atoms in the
m
=
0
state for atom interferometry is studied demonstrating favorable conditions, compared to the alkali atoms that are used traditionally, for a non-QED determination of the fine structure constant.
We have measured the angular correlation function, $w(\theta)$, of radio sources in the 1.4 GHz NVSS and FIRST radio surveys. Below ~$6\arcmin$ the signal is dominated by the size distribution of ...classical double radio galaxies, an effect underestimated in some previous studies. We model the physical size distribution of FRII radio galaxies to account for this excess signal in $w(\theta)$. The amplitude of the true cosmological clustering of radio sources is roughly constant at $A\simeq1\times10^{-3}$ for flux limits of 3–40 mJy, but has increased to $A\simeq7\times10^{-3}$ at 200 mJy. This can be explained if powerful (FRII) radio galaxies probe significantly more massive structures compared to radio galaxies of average power at $z\sim1$. This is consistent with powerful high-redshift radio galaxies generally having massive (forming) elliptical hosts in rich (proto-)cluster environments. For FRIIs we derive a spatial (comoving) correlation length of $r_0=14\pm3$ h-1 Mpc. This is remarkably close to that measured for extremely red objects (EROs) associated with a population of old elliptical galaxies at $z\sim1$ by CITE. Based on their similar clustering properties, we propose that EROs and powerful radio galaxies may be the same systems seen at different evolutionary stages. Their r0 is ~$2\times$ higher than that of QSOs at a similar redshift, and comparable to that of bright ellipticals locally. This suggests that r0 (comoving) of these galaxies has changed little from $z\sim1$ to $z=0$, in agreement with current ΛCDM hierarchical merging models for the clustering evolution of massive early-type galaxies. Alternatively, the clustering of radio galaxies can be explained by the galaxy conservation model. This then implies that radio galaxies of average power are the progenitors of the local field population of early-types, while the most powerful radio galaxies will evolve into a present-day population with r0 comparable to that of local rich clusters.
1 We studied the performance of 17 Dutch populations of the perennial Succisa pratensis, in relation to population size, genetic variation and habitat quality. We used a path-analytical model to ...analyse the possible relationships between these variables and performance. 2 Plants in smaller populations produced fewer seeds per flower head. Their seeds had lower germination rates and higher seedling mortality, and more seeds were dormant or non-viable. 3 Population size was also correlated with genetic measures. Small populations had higher inbreeding coefficients than large populations and observed heterozygosity was positively correlated with population size. The mean genetic diversity (expected heterozygosity) was relatively high ($\text{H}_{\text{exp}}$= 0.42), but not correlated with population size. 4 Less eutrophic habitats appeared to support larger populations. High concentrations of NH4and NO3in the soil were significantly negatively correlated with population size. 5 Path-analysis showed that Succisa pratensis is vulnerable to habitat deterioration (eutrophication). Population size was strongly influenced by habitat quality. Reduced performance, however, was better explained by direct genetic effects and by habitat deterioration rather than by effects of population size per se. Both habitat quality and genetic effects are thus important for population persistence, even in the short term. The results suggest that there will be a continuing decline of the small populations, due to deteriorating habitat conditions, decreased genetic variation and a reduced reproductive capacity.
We present a high-flux source of cold ytterbium atoms that is robust, lightweight and low-maintenance. Our apparatus delivers \(10^9\) atoms/s into a 3D magneto-optical trap without requiring ...water-cooling or high current power supplies. We achieve this by employing a Zeeman slower and a 2D magneto-optical trap fully based on permanent magnets in Halbach configurations. This strategy minimizes mechanical complexity, stray magnetic fields, and heat production while requiring little to no maintenance, making it applicable to both embedded systems that seek to minimize electrical power consumption, and large scale experiments to reduce the complexity of their subsystems.
High precision spectroscopy on the \(2 \ ^3 S \rightarrow 2 \ ^1 S\) transition is possible in ultracold optically trapped helium but the accuracy is limited by the ac-Stark shift induced by the ...optical dipole trap. To overcome this problem, we have built a trapping laser system at the predicted magic wavelength of 319.8 nm. Our system is based on frequency conversion using commercially available components and produces over 2 W of power at this wavelength. With this system, we show trapping of ultracold atoms, both thermal (\(\sim0.2 \ \mathrm{\mu K}\)) and in a Bose-Einstein condensate, with a trap lifetime of several seconds, mainly limited by off-resonant scattering.
PDF
