Trap Loss Research Articles

Controlling collisional loss and scattering lengths of ultracold dipolar molecules with static electric fields

Trapped samples of ultracold molecules are often short-lived because close collisions between them result in trap loss. We investigate the use of shielding with static electric fields to create repulsive barriers between polar molecules to prevent such loss. Shielding is very effective even for RbCs, with a relatively low dipole moment, and even more effective for molecules such as NaK, NaRb, and NaCs, with progressively larger dipoles. Varying the electric field allows substantial control over the scattering length, which will be crucial for the stability or collapse of molecular Bose-Einstein condensates. This arises because the dipole-dipole interaction creates a long-range attraction that is tunable with electric field. For RbCs, the scattering length is positive across the range where shielding is effective because the repulsion responsible for shielding dominates. For NaK, the scattering length can be tuned across zero to negative values. For NaRb and NaCs, the attraction is strong enough to support tetra-atomic bound states, and the scattering length passes through resonant poles where these states cross threshold. For KAg and CsAg, there are multiple bound states and multiple poles. For each molecule, we calculate the variation of the scattering length with field and comment on the possibilities for exploring new physics. Published by the American Physical Society 2024

Ultrahigh vacuum pressure measurement using magneto-optical trap on atom chip

In this work, the UHV background pressure as low as 1.1×10−10 Torr has been measured using the loss rate characteristics of a vapor-loaded magneto-optical trap (MOT) formed on an atom chip in a UHV chamber. The loss rate due to non-rubidium (Rb) gases in the background in the chamber has been estimated by operating the MOT in low cooling beam intensities and low Rb pressure regimes simultaneously. Using this approach, we minimized the contributions of the intra-trap collisions as well as background MOT species collisions to the measured trap loss rate in our setup. These results can be useful for development of cold-atom based UHV pressure standards.

Environmental and economic impacts of retrieved abandoned, lost, and discarded fishing gear in Southwest Nova Scotia, Canada

Abandoned, lost, and discarded fishing gear (ALDFG), negatively impacts marine environments. Managing ALDFG in Atlantic Canada is challenging due to knowledge gaps on loss rates, locations, data availability/accuracy, impacts, and regulatory barriers for retrieval. This study removed ALDFG in Southwest Nova Scotia in collaboration with local fishers (with local knowledge and practical ALDFG removal expertise), government, non-profit organizations, and academia. A total of 29,298 kg of ALDFG was retrieved, including 24,630 kg using towed grapples covering ~3986 km of seafloor and 4668 kg from shorelines (comprising, 68 % lobster traps and 12 % dragger cable by weight). Traps ranged from <1 to 37 years old (median, 10 years). Traps continued to catch target and non-target species with 25 species released, including 652 individual lobsters (82 % were market-sized) and 57 fish (42 were species-at-risk). Based on estimated 2 % trap losses, annual commercial losses from ALDFG were $155,836 CAD in Lobster Fishing Area 34.

Understanding the drivers, scale and impact of abandoned, lost and otherwise discarded fishing gear in small-scale fisheries: an Eastern Caribbean perspective

Abandoned, lost and otherwise discarded fishing gear (ALDFG) presents a significant and complex challenge which can result in severe deleterious impacts to habitats, marine wildlife, and fishing and coastal communities the world over. Small island states like the countries of the Eastern Caribbean are highly vulnerable to a range of external stressors, therefore it is essential to gain an understanding of the threat posed by all forms of marine debris including ALDFG to the sub-region. To gain an understanding of the drivers, scale and impact of the threat associated with small-scale fisheries of the Eastern Caribbean, interviews with 49 fish trap and line fishers as well as 14 divers in Antigua and Barbuda, and Dominica were conducted. Interviews were completed over the course of two months (July – August 2022) at landing sites around all three islands. Fish traps continue to be a major contributor to ALDFG in the study area, with an estimated 2, 273 traps and 2, 567 being lost on Antigua and Barbuda, and Dominica respectively, based on the most recent estimates of the fishing fleet. Severe weather and snagging of benthic obstructions have emerged as the most significant contributors to fish trap loss in both countries while towing of fishing lines was the most frequently identified cause in the countries’ line fisheries. Observed variabilities in drivers of loss between both countries may be attributed to a number of factors including diversities in the fishing sectors, differences in local practices and heterogeneity in the biogeography of the marine environment. Further, evidence shows that the challenge of ALDFG within the Eastern Caribbean context, goes beyond local drivers of loss and may be influenced by transboundary inputs from both within and outside the region. Divers reported encountering not only ALDFG originating from within the two countries but some forms of ALDFG that may have drifted into the area from neighbouring islands (MFAD components) or further afield (polypropylene netting). Managing this challenge effectively will require not only fisheries specific interventions but the cooperation and collaboration of pool of stakeholders both nationally and beyond.

Trap-loss spectroscopy of Rydberg states in ytterbium

We present an experimental study of the Rydberg - and - series of ytterbium for principal quantum numbers in the range of n = 70–90. The study is performed using trap loss spectroscopy in a magneto-optical trap operating on the transition at 399 nm. Compared to the commonly used Rydberg spectroscopy method using field-ionization and ion detection, trap loss spectroscopy is significantly simpler and requires a less sophisticated experimental setup. Using this method we determine relative values of the scalar and tensor electric polarizabilities of both, - and - Rydberg states.

Dephasing effect of Rydberg states on trap loss spectroscopy of cold atoms

In this paper, we investigate the asymmetry of trap loss spectra of ultracold atoms during the excitation of Rydberg states. It is shown that the profile of a trap loss spectrum is affected by the density of Rydberg atoms as well as the dephasing rate of Rydberg states. The splitting of a trap loss spectrum is shown at the higher dephasing rates of Rydberg states. A three-level model, where the dephasing rates can be ascribed mainly to a random collision of Rydberg atoms, reasonably explains the experimental results.

Mitigating camera trap loss using permanent security posts: 10 years of development

Camera traps provide a valuable tool for surveying wildlife, but theft and vandalism can be costly and pose a constant threat to image data integrity and continuity. Permanent, secure posts represent one solution, but they need constant innovation to account for the persistence and ingenuity of camera trap vandals and thieves. Here we outline the progression of designs for a bollard-style housing used to mitigate theft and damage of camera traps placed for continuous monitoring of predators and other wildlife along tracks. The evolving design process over a 10 year period was driven by ongoing attacks on the posts and finally our endeavours to counter what we considered might be the next attack on our design. The current security posts have not been breached to date, producing a design that we consider the most formidable.

Laser-induced frequency shift in a spin-1 Bose–Einstein condensate of sodium

Experimental measurement and analysis of the laser-induced frequency shifts (LIFSs) of photoassociation (PA) spectra in a spinor Bose–Einstein condensate (BEC) of sodium is reported. The trap loss spectra of the atoms in the BEC were recorded at different PA laser intensities. Linear variations of the frequency shift for different spin components were demonstrated. The analogous linear dependence on the intensity of the full width at half maximum (FWHM) of the spectra was also shown. The slopes of the linear relationships of the shift and broadening are both independent of spin component within the error range of the experiment. A theoretical model, considering the interactions of three channels (a scattering continuum state, a single bound level near the scattering state, and an optically excited light-dressed level), explains the linear dependence of the LIFSs and the FWHM broadening on the PA laser power. The experimental results are consistent with the theoretical calculations.

Refining the cold atom pressure standard

In our previous work (Shen et al 2020 Metrologia 57 025015; Booth et al 2019 New J. Phys. 21 102001), we have reported the first primary quantum pressure standard based on the loss rate of cold rubidium atoms from a magnetic trap. We have shown that this standard is self-calibrating. That is, the single parameter required to quantify the pressure or particle flux impinging on the sensor atoms, , can be determined experimentally. In this paper, we refine our procedure to extract the trap loss rate coefficient by expressing the measured trap loss rate of the rubidium atoms as a convolution of the universal loss rate expression from Shen et al (2020 Metrologia 57 025015) and Booth et al (2019 New J. Phys. 21 102001) with the energy distribution of the rubidium atoms in the trap. We report improved values for 87Rb–X (X = He, Ar, Xe, H2, N2, and CO2) collision pairs. All are systematically higher than our previously reported values, although the differences are less than 2%. The calibration factor of an ionization gauge for nitrogen obtained using the cold atom standard, i g = 0.950 (19), agrees with the value obtained by NIST, i g = 0.940 (26) calibrated against their orifice flow standard.

Photoassociation spectroscopy of weakly bound Rb287 molecules near the 5P1/2+5S1/2 threshold by optical Bragg scattering in Bose-Einstein condensates

We report the high resolution photoassociation (PA) spectroscopy of a $^{87}Rb$ Bose-Einstein condensate (BEC) to excited molecular states near the dissociation limit of $5P_{1/2} +5S_{1/2}$ by optical Bragg scattering. Since the detection of optical Bragg scattering in BEC has a high signal-noise ratio, we obtain the high resolution PA spectrum of excited molecular states in the range of $\pm1$ GHz near the dissociation limit of $5P_{1/2} +5S_{1/2}$. We compare the results with the conventional method of trap loss and show that the results agree each other very well. Many interesting phenomena of excited molecular states are observed, such as light-induced frequency shift and the anomalous strong bound molecular lines at the atomic transition from $|F=1\rangle$ to $|F^{\prime}=2\rangle$. The observed excited molecular states in the range of $\pm1$ GHz near the dissociation limit of $5P_{1/2} +5S_{1/2}$ are never reported before, which will help to further improve the long range bound state models near the dissociation limit.

Controlling the ac Stark effect of RbCs with dc electric and magnetic fields

We investigate the effects of static electric and magnetic fields on the differential ac Stark shifts for microwave transitions in ultracold bosonic $^{87}$Rb$^{133}$Cs molecules, for light of wavelength $\lambda = 1064~\mathrm{nm}$. Near this wavelength we observe unexpected two-photon transitions that may cause trap loss. We measure the ac Stark effect in external magnetic and electric fields, using microwave spectroscopy of the first rotational transition. We quantify the isotropic and anisotropic parts of the molecular polarizability at this wavelength. We demonstrate that a modest electric field can decouple the nuclear spins from the rotational angular momentum, greatly simplifying the ac Stark effect. We use this simplification to control the ac Stark shift using the polarization angle of the trapping laser.

Inverted-ladder-type optical excitation of potassium Rydberg states with hot and cold ensembles

We present experimental results on the sub-Doppler Rydberg spectroscopy of potassium in a hot cell and cold atoms, performed with two counter-propagating laser beams of 405 nm and 980 nm in the inverted ladder-type system (4S1/2-5P3/2-nS1/2 and nD3/2;5/2). Such an inverted ladder-type scheme is predicted to be without sub-Doppler electromagnetically induced transparency (EIT) feature in a thermal ensemble under the weak-probe approximation. Instead, we utilized a strong probe field and successfully observed a transparency window with a width narrower than 50~MHz. Our all-order numerical simulation is in satisfactory agreement with the experimental results. This narrow linewidth allows us to measure the energy levels of the Rydberg levels from $n$=20-70 with improved accuracy. The deduced ionization energy agrees with the previous measurements. Furthermore, the two-photon Rydberg excitation scheme was applied to the cold ensembles to study the ground-state atoms population decrease in the MOT for various Rydberg states. Our experimental observations suggested two distinct regimes of the trap losses under different probe detuning conditions. While the far off-resonance case (\delta p>>0) can be described by the picture of dressed atom, the on-resonance case (\delta p~0) reveals more interesting results. The higher Rydberg states suffer larger trap loss. Besides, even with similar level energies, the excitation to nD states result in faster escape of the ground-state atom from trap than nearby nS states.

Hyperfine structure of the NaCs b3Π2 state near the dissociation limit 3S1/2 + 6P3/2 observed with ultracold atomic photoassociation.

We report new observations of the hyperfine structure in three ro-vibrational levels of the b3Π2 state of NaCs near the dissociation limit 3S1/2 + 6P3/2. The experiment was done via photoassociation of ultracold atoms in a dual-species dark-spot magneto-optical trap, and the spectra were measured as atomic trap losses. The simulation of the hyperfine structure showed that the greater part of the observed structure belongs to almost isolated levels of the b3Π2 state, but there are other parts of mixed character where the contribution from the 1Σ symmetry dominates.

Effect of measurement frequency on admittance characteristics in Al/p-Si structures with interfacial native oxide layer

Al/p-Si/Al diodes with interfacial native oxide layer were formed. Their frequency induced admittance-voltage measurements were made. The frequency-dependent density distribution of interface states has been determined from the corrected characteristics by considering the series resistance effect which masks the interface trap loss. The majority carrier density corresponding to the depletion and inversion parts of the C-2-V curve, was determined 1.82 x 1014 and 4.48 x 1014 cm-3 at 1000 kHz, respectively. The fact that the carrier density obtained from the inversion part of the plot is higher than that obtained from the depletion part can be related to the increase in the density of negative space charge in the depletion region.The value of was determined as 0.95 eV from the same plot. Interface state density decreased from 4.31 x 1012 eV-1cm-2 at 100 kHz to 7.30 x 1011 eV-1 cm-2 at 1000 kHz, because the interface charges do not follow the ac signal and do not contribute to capacitance values in high frequencies.

Ultrashort nonautonomous similariton solutions and the cascade tunneling of interacting similaritons

Similarity transformation and Hirota bilinearization are deployed to derive exact bright and dark ultrashort one- and two-similariton solutions of a nonautonomous cubic–quintic nonlinear Schrödinger equation. Such wave packets may emerge when group-velocity dispersion and cubic–quintic self-phase modulations are balanced by Raman self-frequency shift in the presence of an external harmonic trap and linear gain or loss. The solutions presented here can be used to investigate the compression, amplification and interaction phenomena associated with bright and dark similaritons in inhomogeneous fiber systems. Furthermore, the dynamics of the characteristic parameters of the similaritons are studied analytically, and similariton stability in a distributed system is tested through extensive computations. As an example application, the tunneling behavior of bright and dark similaritons through cascade dispersion barriers and dispersion wells on an exponential background is investigated, and some interesting novel features are uncovered which are expected to facilitate the control of bright and dark ultrashort similariton in experimental scenarios.

Review of fish trap fisheries from tropical and subtropical reefs: Main features, threats and management solutions

Fish traps are extensively used in tropical and subtropical reef fisheries. Despite this, there is a significant lack of extensive and consecutive research concerning the basic aspects of trap fishing. We herein compile the available information from the main coral and rocky reef fish trap fisheries, and compared their main aspects (i.e., mesh size, CPUE, catch composition, ghost fishing, and management) to assess the dynamics of these fisheries and their environmental impact. The analysis revealed that most fish stocks showed declining trends, with only few species under heavy management being capable of withstanding high fishing pressure. In other fisheries, due to fishing down the web, miscellaneous reef fish comprised the bulk of the catch, while the proportion of high-value landed species was insignificant. Gear restrictions remain the most common management method in trap fisheries; however, even the minimum mesh size has not been ubiquitously enforced, while due to great variability of targeted fish species, use of a uniform mesh size is highly unlikely. Other management tools, such as, restrictions in effort, size, and species, temporal and spatial closures were also widely used, but effective only when well enforced and interconnected. Rates of trap loss widely differed as well as the reported rates of ghost fishing mortality. In most cases, incorporation of escape panels resulted in almost complete elimination of ghost fishing. However, further research is required concerning these issues.

Saturation of photoassociation in NaCs dark magneto-optical trap

We report the production of ultracold heteronuclear NaCs molecules in excited electronic states by photoassociation (PA) of ultracold Na and Cs atoms. The saturation of the photoassociation scattering probability is observed from the dependence of the trap loss probability on the photoassociation laser intensity. Based on the scattering theory, we estimate the saturation intensity of photoassociation, which is deduced by fitting the experimental data to a saturation model.

Collaborative research reveals cryptic declines within the multispecies California rock crab fishery

The southern California rock crab fishery targets stocks comprised of three species: red (Cancer productus), yellow (Metacarcinus anthonyi), and brown rock crab (Romaleon antennarium). Fishers have expressed concern about the sustainability of the fishery due to increased fishing effort over the past decade, and because it is managed as one assemblage despite distinct life history differences among the species. We collaborated with fishers to test for stock-specific declines in key fishery-dependent indicators by replicating a 2008 study in 2016–2017 and comparing indicator values between years using multiple regression techniques. Indicators included spatially explicit species-level data for size, catch-per-unit-effort (CPUE), discard rate, sex composition, and trap location and depth across the heavily fished Santa Barbara Channel and Northern Channel Islands. Results showed significant declines in male size, overall CPUE, and proportion of crab landed versus discarded for heavily targeted stocks, translating to fewer pounds per trap and potential financial losses for fishers. Fishing and environmental conditions may have both contributed to stock declines. Evidence of decline differed substantially across space, species, and sex. We suggest that a spatially explicit and adaptive approach to empirically managing southern California rock crab may help to protect fishers from financial loss and avoid continued depletion of certain stocks, and we show that relatively simple collaborative approaches can provide defensible insight into complex systems.

Optical Dipole Trap for Laser-Cooled Lithium-7 Atoms

In this work, we discuss a far-off resonance optical dipole trap for cold lithium-7 atoms. A single optical trapping beam was produced by a continuous-wave fiber laser. Using our experimental data, we obtained important parameters of the trap, such as size of the cold atomic cloud, and evaluate the dipole potential and the rate of the trap losses. Information on temperature is acquired from observation of parametric resonances. We investigate the parametric resonances obtained with strong modulation of the trap potential and record superharmonics. We plan to prepare ultra-cold gas of highly-excited lithium atoms and study interactions between Rydberg atoms.

Fluorescence-lifetime-limited trapping of Rydberg helium atoms on a chip

Metastable (1s)(2s) helium atoms produced in a supersonic beam were excited to Rydberg-Stark states (with n in the 27–30 range) in a cryogenic environment and subsequently decelerated by, and trapped above, a surface-electrode decelerator. In the trapping experiments, the Rydberg atoms were brought to rest in 75 μs and over a distance of 33 mm and kept stationary for times in the 0–525 μs range, before being re-accelerated for detection by pulsed field ionisation. The use of a home-built valve producing short gas pulses with a duration of about 20 μs enabled the reduction of losses arising from collisions with atoms in the trailing part of the gas pulses. Cooling the decelerator to 4.7 K further suppressed losses by transitions induced by blackbody radiation and by collisions with atoms desorbing from the decelerator surface. The main contribution (60%) to the atom loss during deceleration is attributed to the escape out of the decelerator moving traps of atoms having energies higher than the trap saddle point, spontaneous emission and collisions with atoms in the trailing part of the gas pulses causing each only about 20% of the atom loss. At 4.7 K, the atom losses in the trapping phase of the experiments were found to be almost exclusively caused by spontaneous emission and the trap lifetimes were found to correspond to the natural lifetimes of the Rydberg-Stark states. Increasing the temperature to 100 K enhanced the trap losses by transitions stimulated by blackbody radiation.