41 research outputs found
xSIM++: An Improved Proxy to Bitext Mining Performance for Low-Resource Languages
We introduce a new proxy score for evaluating bitext mining based on
similarity in a multilingual embedding space: xSIM++. In comparison to xSIM,
this improved proxy leverages rule-based approaches to extend English sentences
in any evaluation set with synthetic, hard-to-distinguish examples which more
closely mirror the scenarios we encounter during large-scale mining. We
validate this proxy by running a significant number of bitext mining
experiments for a set of low-resource languages, and subsequently train NMT
systems on the mined data. In comparison to xSIM, we show that xSIM++ is better
correlated with the downstream BLEU scores of translation systems trained on
mined bitexts, providing a reliable proxy of bitext mining performance without
needing to run expensive bitext mining pipelines. xSIM++ also reports
performance for different error types, offering more fine-grained feedback for
model development.Comment: The first two authors contributed equally; ACL 2023 short; Code and
data are available at https://github.com/facebookresearch/LASE
Resonant Processes in a Frozen Gas
We present a theory of resonant processes in a frozen gas of atoms
interacting via dipole-dipole potentials that vary as , where is
the interatomic separation. We supply an exact result for a single atom in a
given state interacting resonantly with a random gas of atoms in a different
state. The time development of the transition process is calculated both on-
and off-resonance, and the linewidth with respect to detuning is obtained as a
function of time . We introduce a random spin Hamiltonian to model a dense
system of resonators and show how it reduces to the previous model in the limit
of a sparse system. We derive approximate equations for the average effective
spin, and we use them to model the behavior seen in the experiments of Anderson
et al. and Lowell et al. The approach to equilibrium is found to be
proportional to ), where the constant is explicitly related to the system's parameters.Comment: 30 pages, 6 figure
Millimeter-Wave Spectroscopy of Cold Rb Rydberg Atoms in a Magneto-Optical Trap: Quantum Defects of the \u3ci\u3ens\u3c/i\u3e, \u3ci\u3enp\u3c/i\u3e, and \u3ci\u3end\u3c/i\u3e Series
By using a magneto-optical trap we have measured the Rb ns-(n+1)s and nd(j)-(n+1)d(j) two-photon millimeter-wave transitions for 32less than or equal tonless than or equal to37, observing 100-kHz-wide resonances, in spite of the trap\u27s 10 G/cm magnetic-field gradient, in which one might expect to observe resonances 5 MHz wide. This resolution is possible because of the similarity of the g(j) factors in the initial and final states. Under the same conditions, the single-photon ns-np resonances are similar to5 MHz wide. To make useful measurements of these intervals, we turned off the trap field and used the 300-K atoms of the background Rb vapor. Together these measurements improve the accuracy of the s, p, and d quantum defects by an order of magnitude
High Resolution Rydberg Spectroscopy of ultracold Rubidium Atoms
We present experiments on two-photon excitation of Rb atoms to
Rydberg states. For this purpose, two continuous-wave (cw)-laser systems for
both 780 nm and 480 nm have been set up. These systems are optimized to a small
linewidth (well below 1 MHz) to get both an efficient excitation process and
good spectroscopic resolution. To test the performance of our laser system, we
investigated the Stark splitting of Rydberg states. For n=40 we were able to
see the hyperfine levels splitting in the electrical field for different
finestructure states. To show the ability of spatially selective excitation to
Rydberg states, we excited rubidium atoms in an electrical field gradient and
investigated both linewidths and lineshifts. Furthermore we were able to excite
the atoms selectively from the two hyperfine ground states to Rydberg states.
Finally, we investigated the Autler-Townes splitting of the
5S5P transition via a Rydberg state to determine the Rabi
frequency of this excitation step.Comment: 9 pages, 7 figure
Radiative charge transfer lifetime of the excited state of (NaCa)
New experiments were proposed recently to investigate the regime of cold
atomic and molecular ion-atom collision processes in a special hybrid
neutral-atom--ion trap under high vacuum conditions. The collisional cooling of
laser pre-cooled Ca ions by ultracold Na atoms is being studied. Modeling
this process requires knowledge of the radiative lifetime of the excited
singlet A state of the (NaCa) molecular system. We calculate
the rate coefficient for radiative charge transfer using a semiclassical
approach. The dipole radial matrix elements between the ground and the excited
states, and the potential curves were calculated using Complete Active Space
Self-Consistent field and M\"oller-Plesset second order perturbation theory
(CASSCF/MP2) with an extended Gaussian basis, 6-311+G(3df). The semiclassical
charge transfer rate coefficient was averaged over a thermal Maxwellian
distribution. In addition we also present elastic collision cross sections and
the spin-exchange cross section. The rate coefficient for charge transfer was
found to be cm/sec, while those for the elastic and
spin-exchange cross sections were found to be several orders of magnitude
higher ( cm/sec and cm/sec,
respectively). This confirms our assumption that the milli-Kelvin regime of
collisional cooling of calcium ions by sodium atoms is favorable with the
respect to low loss of calcium ions due to the charge transfer.Comment: 4 pages, 5 figures; v.2 - conceptual change
Observation of Nonspreading Wave Packets in an Imaginary Potential
We propose and experimentally demonstrate a method to prepare a nonspreading
atomic wave packet. Our technique relies on a spatially modulated absorption
constantly chiseling away from an initially broad de Broglie wave. The
resulting contraction is balanced by dispersion due to Heisenberg's uncertainty
principle. This quantum evolution results in the formation of a nonspreading
wave packet of Gaussian form with a spatially quadratic phase. Experimentally,
we confirm these predictions by observing the evolution of the momentum
distribution. Moreover, by employing interferometric techniques, we measure the
predicted quadratic phase across the wave packet. Nonspreading wave packets of
this kind also exist in two space dimensions and we can control their amplitude
and phase using optical elements.Comment: 4 figure
Formation of Giant Quasibound Cold Diatoms by Strong Atom-Cavity Coupling
We show that giant quasi-bound diatomic complexes, whose size is typically
hundreds of nm, can be formed by intra-cavity cold diatom photoassociation or
photodissociation in the strong atom-cavity coupling regime.Comment: 4 pages, 3 figure
Macrodimers: ultralong range Rydberg molecules
We study long range interactions between two Rydberg atoms and predict the
existence of ultralong range Rydberg dimers with equilibrium distances of many
thousand Bohr radii. We calculate the dispersion coefficients ,
and for two rubidium atoms in the same excited level , and find
that they scale like , and , respectively. We show that
for certain molecular symmetries, these coefficients lead to long range
potential wells that can support molecular bound levels. Such macrodimers would
be very sensitive to their environment, and could probe weak interactions. We
suggest experiments to detect these macrodimers.Comment: 4 pages, submitted to PR
Dipole Blockade and Quantum Information Processing in Mesoscopic Atomic Ensembles
We describe a technique for manipulating quantum information stored in
collective states of mesoscopic ensembles. Quantum processing is accomplished
by optical excitation into states with strong dipole-dipole interactions. The
resulting ``dipole blockade'' can be used to inhibit transitions into all but
singly excited collective states. This can be employed for a controlled
generation of collective atomic spin states as well as non-classical photonic
states and for scalable quantum logic gates. An example involving a cold
Rydberg gas is analyzed
Findings of the WMT'22 Shared Task on Large-Scale Machine Translation Evaluation for African Languages
We present the results of the WMT'22 Shared Task on Large-Scale Machine Translation Evaluation for African Languages. The shared task included both a data and a systems track, along with additional innovations, such as a focus on African languages and extensive human evaluation of submitted systems. We received 14 system submissions from 8 teams, as well as 6 data track contributions. We report a large progress in the quality of translation for African languages since the last iteration of this shared task: there is an increase of about 7.5 BLEU points across 72 language pairs, and the average BLEU scores went from 15.09 to 22.60