9 research outputs found
A robust, high-flux source of laser-cooled ytterbium atoms
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
A magic wavelength optical dipole trap for high-precision spectroscopy of utracold metastable helium
Vassen, W. [Promotor]Ubachs, W.M.G. [Copromotor
A simple 2 W continuous-wave laser system for trapping ultracold metastable helium atoms at the 319.8 nm magic wavelength
High-precision spectroscopy on the
Comparison of spectral linewidths for quantum degenerate bosons and fermions
We observe a dramatic difference in optical line shapes of a
Bose-Einstein condensate and a degenerate Fermi gas by measuring
the 1557-nm magnetic dipole transition ( natural
linewidth) in an optical dipole trap. The FWHM condensate line
shape is only broadened by mean field interactions, whereas the degenerate
Fermi gas line shape is broadened to 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 He a triplet-singlet s-wave
scattering length 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.Comment: 5 pages, 4 figures, 5 pages supplemental informatio
The spatial clustering of radio sources in NVSS and FIRST; implications for galaxy clustering evolution
We have measured the angular correlation function of radio sources in the 1.4
GHz NVSS and FIRST surveys. Below ~6 arcminutes w(theta) is dominated by the
size distribution of radio galaxies. A model of the size distribution of radio
galaxies can account for this excess signal in w(theta). The amplitude of the
cosmological clustering of radio sources is roughly constant at A~0.001 from 3
to 40 mJy, but has increased to A~0.007 at 200 mJy. This can be explained if
powerful (FRII) radio galaxies probe more massive structures at z~1 compared to
average power radio galaxies, consistent with powerful high-z radio galaxies
generally having massive (forming) elliptical hosts in rich cluster
environments. For FRIIs we derive a spatial (comoving) correlation length of
r_0=14\pm3 h^{-1} Mpc. This is close to that measured for extremely red objects
(EROs) associated with a population of old elliptical galaxies at z~1 by Daddi
et al. (2001). 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 r_0 is ~2 times higher than that of QSOs at a
similar redshift, and comparable to that of bright ellipticals locally. This
suggests that r_0 (comoving) of these galaxies has changed little from z~1 to
z=0, in agreement with current LCDM hierarchical models for 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
early-type field population, while the most powerful radio galaxies will evolve
into a present-day population with r_0 similar to that of local rich clusters.Comment: 21 pages, 17 figures. Accepted for publication in A&
Magic wavelengths for the 2 3 S→2 1 S transition in helium
We have calculated ac polarizabilities of the 23S and 21S states of both He4 and He3 in the range 318 nm to 2.5 μm and determined the magic wavelengths at which these polarizabilities are equal for either isotope. The calculations, only based on available ab initio tables of level energies and Einstein A coefficients, do not require advanced theoretical techniques. The polarizability contribution of the continuum is calculated using a simple extrapolation beyond the ionization limit, yet the results agree to better than 1% with such advanced techniques. Several promising magic wavelengths are identified around 320 nm with sufficient accuracy to design an appropriate laser system. The extension of the calculations to He3 is complicated due to the additional hyperfine structure, but we show that the magic wavelength candidates around 320 nm are predominantly shifted by the isotope shift
Ultracold metastable helium: Ramsey fringes and atom interferometry
We report on interference studies in the internal and external degrees of freedom of metastable triplet helium atoms trapped near quantum degeneracy in a 1.5μm 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 23S1–21S0 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
The effect of magnetic field on the intrinsic detection efficiency of superconducting single-photon detectors
We experimentally investigate the effect of a magnetic field on photon
detection in superconducting single-photon detectors. At low fields, the effect
of a magnetic field is through the direct modification of the quasiparticle
density of states of the superconductor, and magnetic field and bias current
are interchangable, as is expected for homogeneous dirty-limit superconductors.
At the field where a first vortex enters the detector, the effect of the
magnetic field is reduced, up until the point where the critical current of the
detector starts to be determined by flux flow. From this field on, increasing
the magnetic field does not alter the detection of photons anymore, whereas it
does still change the rate of dark counts. This result points at an intrinsic
difference in dark and light counts, and also shows that no enhancement of the
intrinsic detection efficiency of a straight SSPD wire is achievable in a
magnetic field