77 research outputs found
Hydrogen molecular ions for improved determination of fundamental constants
The possible use of high-resolution rovibrational spectroscopy of the
hydrogen molecular ions H + 2 and HD + for an independent determination of
several fundamental constants is analyzed. While these molecules had been
proposed for metrology of nuclear-to-electron mass ratios, we show that they
are also sensitive to the radii of the proton and deuteron and to the Rydberg
constant at the level of the current discrepancies colloquially known as the
proton size puzzle. The required level of accuracy, in the 10 --12 range, can
be reached both by experiments, using Doppler-free two-photon spectroscopy
schemes, and by theoretical predictions. It is shown how the measurement of
several well-chosen rovibrational transitions may shed new light on the
proton-radius puzzle, provide an alternative accurate determination of the
Rydberg constant, and yield new values of the proton-to-electron and
deuteron-to-proton mass ratios with one order of magnitude higher precision
Measurement of optical to electrical and electrical to optical delays with ps-level uncertainty
We present a new measurement principle to determine the absolute time delay
of a waveform from an optical reference plane to an electrical reference plane
and vice versa. We demonstrate a method based on this principle with 2 ps
uncertainty. This method can be used to perform accurate time delay
determinations of optical transceivers used in fibre-optic time-dissemination
equipment. As a result the time scales in optical and electrical domain can be
related to each other with the same uncertainty. We expect this method to break
new grounds in high-accuracy time transfer and absolute calibration of
time-transfer equipment
Proton-electron mass ratio from HD revisited
We present a new derivation of the proton-electron mass ratio from the
hydrogen molecular ion, HD. The derivation entails the adjustment of the
mass ratio in highly precise theory so as to reproduce accurately measured
ro-vibrational frequencies. This work is motivated by recent improvements of
the theory, as well as the more accurate value of the electron mass in the
recently published CODATA-14 set of fundamental constants, which justifies
using it as input data in the adjustment, rather than the proton mass value as
done in previous works. This leads to significantly different sensitivity
coefficients and, consequently, a different value and larger uncertainty margin
of the proton-electron mass ratio as obtained from HD
Two-photon spectroscopy of trapped HD ions in the Lamb-Dicke regime
We study the feasibility of nearly-degenerate two-photon rovibrational
spectroscopy in ensembles of trapped, sympathetically cooled hydrogen molecular
ions using a resonance-enhanced multiphoton dissociation (REMPD) scheme. Taking
advantage of quasi-coincidences in the rovibrational spectrum, the excitation
lasers are tuned close to an intermediate level to resonantly enhance
two-photon absorption. Realistic simulations of the REMPD signal are obtained
using a four-level model that takes into account saturation effects, ion
trajectories, laser frequency noise and redistribution of population by
blackbody radiation. We show that the use of counterpropagating laser beams
enables optical excitation in an effective Lamb-Dicke regime. Sub-Doppler lines
having widths in the 100 Hz range can be observed with good signal-to-noise
ratio for an optimal choice of laser detunings. Our results indicate the
feasibility of molecular spectroscopy at the accuracy level for
improved tests of molecular QED, a new determination of the proton-to-electron
mass ratio, and studies of the time (in)dependence of the latter.Comment: 16 pages, 17 figure
Precision Spectroscopy of Molecular Hydrogen Ions: Towards Frequency Metrology of Particle Masses
We describe the current status of high-precision ab initio calculations of
the spectra of molecular hydrogen ions (H_2^+ and HD^+) and of two experiments
for vibrational spectroscopy. The perspectives for a comparison between theory
and experiment at a level of 1 ppb are considered.Comment: 26 pages, 13 figures, 1 table, to appear in "Precision Physics of
Simple Atomic Systems", Lecture Notes in Physics, Springer, 200
Frequency Comparison of Two High-Accuracy Al+ Optical Clocks
We have constructed an optical clock with a fractional frequency inaccuracy
of 8.6e-18, based on quantum logic spectroscopy of an Al+ ion. A simultaneously
trapped Mg+ ion serves to sympathetically laser-cool the Al+ ion and detect its
quantum state. The frequency of the 1S0->3P0 clock transition is compared to
that of a previously constructed Al+ optical clock with a statistical
measurement uncertainty of 7.0e-18. The two clocks exhibit a relative stability
of 2.8e-15/ sqrt(tau), and a fractional frequency difference of -1.8e-17,
consistent with the accuracy limit of the older clock.Comment: 4 pages, 2 tables, 3 figure
Bounds on fifth forces from precision measurements on molecules
Highly accurate results from frequency measurements on neutral hydrogen
molecules H_2, HD and D_2 as well as the HD^+ ion can be interpreted in terms
of constraints on possible fifth-force interactions. Where the hydrogen atom is
a probe for yet unknown lepton-hadron interactions, and the helium atom is
sensitive for lepton-lepton interactions, molecules open the domain to search
for additional long-range hadron-hadron forces. First principles calculations
in the framework of quantum electrodynamics have now advanced to the level that
hydrogen molecules and hydrogen molecular ions have become calculable systems,
making them a search-ground for fifth forces. Following a phenomenological
treatment of unknown hadron-hadron interactions written in terms of a Yukawa
potential of the form V_5(r)=\beta exp(-r/\lambda)/r current precision
measurements on hydrogenic molecules yield a constraint \beta < 1 \times
10^{-7} eV\AA for long-range hadron-hadron interactions at typical force ranges
commensurate with separations of a chemical bond, i.e. \lambda ~1 \AA and
beyond.Comment: 7 pages, 3 figures, 1 tabl
Observation of the 1S0 - 3P0 clock transition in 27Al+
We report for the first time, laser spectroscopy of the 1S0 - 3P0 clock
transition in 27Al+. A single aluminum ion and a single beryllium ion are
simultaneously confined in a linear Paul trap, coupled by their mutual Coulomb
repulsion. This coupling allows the beryllium ion to sympathetically cool the
aluminum ion, and also enables transfer of the aluminum's electronic state to
the beryllium's hyperfine state, which can be measured with high fidelity.
These techniques are applied to a measurement of the clock transition
frequency, \nu = 1 121 015 393 207 851(8) Hz. They are also used to measure the
lifetime of the metastable clock state, \tau = 20.6 +/- 1.4 s, the ground state
1S0 g-factor, g_S = -0.00079248(14), and the excited state 3P0 g-factor, g_P =
-0.00197686(21), in units of the Bohr magneton.Comment: 4 pages, 2 figures; updated author lis
Prospects for measurement and control of the scattering length of metastable helium using photoassociation techniques
A numerical investigation of two-laser photoassociation (PA) spectroscopy on
spin-polarized metastable helium (He*) atoms is presented within the context of
experimental observation of the least-bound energy level in the scattering
potential and subsequent determination of the s-wave scattering length.
Starting out from the model developed by Bohn and Julienne [Phys. Rev. A
\textbf{60}, (1999) 414], PA rate coefficients are obtained as a function of
the parameters of the two lasers. The rate coefficients are used to simulate
one- and two-laser PA spectra. The results demonstrate the feasibility of a
spectroscopic determination of the binding energy of the least-bound level. The
simulated spectra may be used as a guideline when designing such an experiment,
whereas the model may also be employed for fitting experimentally obtained PA
spectra. In addition, the prospects for substantial modification of the He*
scattering length by means of optical Feshbach resonances are considered.
Several experimental issues relating to the numerical investigation presented
here are discussed.Comment: 9 pages, 7 figure
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