55 research outputs found
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
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
A hybrid optical-wireless network for decimetre-level terrestrial positioning
Global navigation satellite systems (GNSS) are widely used for navigation and
time distribution, features indispensable for critical infrastructure such as
mobile communication networks, as well as emerging technologies like automated
driving and sustainable energy grids. While GNSS can provide centimetre-level
precision, GNSS receivers are prone to many-metre errors due to multipath
propagation and obstructed view of the sky, which occur especially in urban
areas where accurate positioning is needed most. Moreover, the vulnerabilities
of GNSS, combined with the lack of a back-up system, pose a severe risk to
GNSS-dependent technologies. Here, we demonstrate a terrestrial positioning
system which is independent of GNSS and offers superior performance through a
constellation of radio transmitters, connected and time-synchronised at the
sub-nanosecond level through a fibre-optic Ethernet network. Employing optical
and wireless transmission schemes similar to those encountered in mobile
communication networks, and exploiting spectrally efficient virtual wideband
signals, the detrimental effects of multipath propagation are mitigated, thus
enabling robust decimetre-level positioning and sub-nanosecond timing in a
multipath-prone outdoor environment. This work provides a glimpse of a future
in which telecommunication networks provide not only connectivity, but also
GNSS-independent timing and positioning services with unprecedented accuracy
and reliability.Comment: 38 pages, 9 figures, 3 table
Quantum control, quantum information processing, and quantum-limited metrology with trapped ions
We briefly discuss recent experiments on quantum information processing using
trapped ions at NIST. A central theme of this work has been to increase our
capabilities in terms of quantum computing protocols, but we have also applied
the same concepts to improved metrology, particularly in the area of frequency
standards and atomic clocks. Such work may eventually shed light on more
fundamental issues, such as the quantum measurement problem.Comment: Proceedings of the International Conference on Laser Spectroscopy
(ICOLS), 10 pages, 5 figure
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
Magneto-optical trap for metastable helium at 389 nm
We have constructed a magneto-optical trap (MOT) for metastable triplet
helium atoms utilizing the 2 3S1 -> 3 3P2 line at 389 nm as the trapping and
cooling transition. The far-red-detuned MOT (detuning Delta = -41 MHz)
typically contains few times 10^7 atoms at a relatively high (~10^9 cm^-3)
density, which is a consequence of the large momentum transfer per photon at
389 nm and a small two-body loss rate coefficient (2 * 10^-10 cm^3/s < beta <
1.0 * 10^-9 cm^3/s). The two-body loss rate is more than five times smaller
than in a MOT on the commonly used 2 3S1 -> 2 3P2 line at 1083 nm. Furthermore,
we measure a temperature of 0.46(1) mK, a factor 2.5 lower as compared to the
1083 nm case. Decreasing the detuning to Delta= -9 MHz results in a cloud
temperature as low as 0.25(1) mK, at small number of trapped atoms. The 389 nm
MOT exhibits small losses due to two-photon ionization, which have been
investigated as well.Comment: 11 page
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