105 research outputs found
Optical trapping of anti-hydrogen towards an atomic anti-clock
The Anti-Matter Factory at CERN is gearing up, commissioning of the Extra Low
ENergy Antiprotons (ELENA) ring is ongoing and the first anti-protons are
foreseen to circulate in the decelerator very soon. The unprecedented flux of
low energy antiprotons delivered by ELENA will open a new era for precision
tests with antimatter including laser and microwave spectroscopy and tests of
its gravitational behaviour. Here we propose a scheme to load the ultra cold
anti-hydrogen atoms that will be produced by the GBAR experiment in an optical
lattice tuned at the magic wavelength of the 1S-2S transition in order to
measure this interval at a level comparable or even better than its matter
counter part. This will provide the most sensitive test of CPT symmetry
parametrised in the framework of the Standard Model Extension.Comment: 7 pages, 2 Figure
Pressure Shifts in High-Precision Hydrogen Spectroscopy: II. Impact Approximation and Monte-Carlo Simulations
We investigate collisional shifts of spectral lines involving excited
hydrogenic states, where van der Waals coefficients have recently been shown to
have large numerical values when expressed in atomic units. Particular emphasis
is laid on the recent hydrogen 2S-4P experiment (and an ongoing 2S-6P
experiment) in Garching, but numerical input data are provided for other
transitions (e.g., involving S states), as well. We show that the frequency
shifts can be described, to sufficient accuracy, in the impact approximation.
The pressure related effects were separated into two parts, (i) related to
collisions of atoms inside of the beam, and (ii) related to collisions of the
atoms in the atomic beam with the residual background gas. The latter contains
both atomic as well as molecular hydrogen. The dominant effect of intra-beam
collisions is evaluated by a Monte-Carlo simulation, taking the geometry of the
experimental apparatus into account. While, in the Garching experiment, the
collisional shift is on the order of 10 Hz, and thus negligible, it can
decisively depend on the experimental conditions. We present input data which
can be used in order to describe the effect for other transitions of current
and planned experimental interest.Comment: 26 pages; 2 figures; this is part 2 of a series of two papers; part 1
carries article number 075005, while part 2 carries article number 075006 in
the journal (online journal version has been rectified
Pressure Shifts in High-Precision Hydrogen Spectroscopy: I. Long-Range Atom-Atom and Atom-Molecule Interactions
We study the theoretical foundations for the pressure shifts in
high-precision atomic beam spectrosopy of hydrogen, with a particular emphasis
on transitions involving higher excited P states. In particular, the long-range
interaction of an excited hydrogen atom in a 4P state with a ground-state and
metastable hydrogen atom is studied, with a full resolution of the hyperfine
structure. It is found that the full inclusion of the 4P_1/2 and 4P_3/2
manifolds becomes necessary in order to obtain reliable theoretical
predictions, because the 1S ground state hyperfine frequency is commensurate
with the 4P fine-structure splitting. An even more complex problem is
encountered in the case of the 4P-2S interaction, where the inclusion of
quasi-degenerate 4S-2P_1/2 state becomes necessary in view of the dipole
couplings induced by the van der Waals Hamiltonian. Matrices of dimension up to
40 have to be treated despite all efforts to reduce the problem to irreducible
submanifolds within the quasi-degenerate basis. We focus on the
phenomenologically important second-order van der Waals shifts, proportional to
1/R^6 where R is the interatomic distance, and obtain results with full
resolution of the hyperfine structure. The magnitude of van der Waals
coefficients for hydrogen atom-atom collisions involving excited P states is
drastically enhanced due to energetic quasi-degeneracy; we find no such
enhancement for atom-molecule collisions involving atomic nP states, even if
the complex molecular spectrum involving ro-vibrational levels requires a
deeper analysis.Comment: 32 pages; 2 figures; this is part 1 of a series of two papers; part 1
carries article number 075005, while part 2 carries article number 075006 in
the journal (online journal version has been rectified). arXiv admin note:
text overlap with arXiv:1711.1003
Sub-Hz line width diode lasers by stabilization to vibrationally and thermally compensated ULE Fabry-Perot cavities
We achieved a 0.5 Hz optical beat note line width with ~ 0.1 Hz/s frequency
drift at 972 nm between two external cavity diode lasers independently
stabilized to two vertically mounted Fabry-Perot (FP) reference cavities.
Vertical FP reference cavities are suspended in mid-plane such that the
influence of vertical vibrations to the mirror separation is significantly
suppressed. This makes the setup virtually immune for vertical vibrations that
are more difficult to isolate than the horizontal vibrations. To compensate for
thermal drifts the FP spacers are made from Ultra-Low-Expansion (ULE) glass
which possesses a zero linear expansion coefficient. A new design using Peltier
elements in vacuum allows operation at an optimal temperature where the
quadratic temperature expansion of the ULE could be eliminated as well. The
measured linear drift of such ULE FP cavity of 63 mHz/s was due to material
aging and the residual frequency fluctuations were less than 40 Hz during 16
hours of measurement. Some part of the temperature-caused drift is attributed
to the thermal expansion of the mirror coatings. High-frequency thermal
fluctuations that cause vibrations of the mirror surfaces limit the stability
of a well designed reference cavity. By comparing two similar laser systems we
obtain an Allan instability of 2*10-15 between 0.1 and 10 s averaging time,
which is close to the theoretical thermal noise limit.Comment: submitted to Applied Physics
High-Precision Optical Measurement of the 2S Hyperfine Interval in Atomic Hydrogen
We have applied an optical method to the measurement of the 2S hyperfine
interval in atomic hydrogen. The interval has been measured by means of
two-photon spectroscopy of the 1S-2S transition on a hydrogen atomic beam
shielded from external magnetic fields. The measured value of the 2S hyperfine
interval is equal to 177 556 860(15) Hz and represents the most precise
measurement of this interval to date. The theoretical evaluation of the
specific combination of 1S and 2S hyperfine intervals D_21 is in moderately
good agreement with the value for D_21 deduced from our measurement
2S hyperfine structure of atomic deuterium
We have measured the frequency splitting between the and hyperfine sublevels in atomic deuterium by an optical differential
method based on two-photon Doppler-free spectroscopy on a cold atomic beam. The
result Hz is the most precise value for
this interval to date. In comparison to the previous radio-frequency
measurement we have improved the accuracy by the factor of three.
The specific combination of hyperfine frequency intervals for metastable- and
ground states in deuterium atom derived from our measurement is in a good agreement with
calculated from quantum-electrodynamics theory.Comment: 7 pages, 7 figure
Long-Range Interactions of Hydrogen Atoms in Excited States. II. Hyperfine-Resolved 2S-2S Systems
The interaction of two excited hydrogen atoms in metastable states constitutes a theoretically interesting problem because of the quasidegenerate 2P1/2 levels that are removed from the 2S states only by the Lamb shift. The total Hamiltonian of the system is composed of the van der Waals Hamiltonian, the Lamb shift, and the hyperfine effects. The van der Waals shift becomes commensurate with the 2S-2P3/2 fine-structure splitting only for close approach (R \u3c 100a0, where a0 is the Bohr radius) and one may thus restrict the discussion to the levels with n = 2 and J = 1/2 to a good approximation. Because each S or P state splits into an F = 1 triplet and an F = 0 hyperfine singlet (eight states for each atom), the Hamiltonian matrix a priori is of dimension 64. A careful analysis of the symmetries of the the problem allows one to reduce the dimensionality of the most involved irreducible submatrix to 12. We determine the Hamiltonian matrices and thleading-order van der Waals shifts for states that are degenerate under the action of the unperturbed Hamiltonian (Lamb shift plus hyperfine structure). The leading first- and second-order van der Waals shifts lead to interaction energies proportional to 1/R3 and 1/R6 and are evaluated within the hyperfine manifolds. When both atoms are metastable 2S states, we find an interaction energy of order EhΧ(a0/R)6, where Eh and L are the Hartree and Lamb shift energies, respectively, and Χ = Eh/L â 6.22 x 106 is their ratio
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