arXiv subjects

S. Eckel

Publications and source records attributed to S. Eckel.

At least 19 recordsLinked to original sources

arXiv2023

Grating magneto-optical traps with complicated level structures

We study the forces and optical pumping within grating magneto-optical traps (MOTs) operating on transitions with non-trivial level structure. In contrast to the standard six-beam MOT configuration, rate equation modelling predicts that the asymmetric laser geometry of a grating MOT will produce spin-polarized atomic samples. Furthermore, the Land\'e $g$-factors and total angular momenta of the trapping transition strongly influence both the confinement and equilibrium position of the trap. Using the intuition gained from the rate equation model, we realize a grating MOT of fermionic $^{87}$Sr and observe that it forms closer to the center of the trap's quadrupole magnetic field than its bosonic counterpart. We also explore the application of grating MOTs to molecule laser cooling, where the rate equations suggest that dual-frequency operation is necessary, but not sufficient, for stable confinement for type-II level structures. To test our molecule laser cooling models, we create grating MOTs using the $D_1$ line of $^7$Li and see that only two of the four possible six-beam polarization configurations operate in the grating geometry. Our results will aid the development of portable atom and molecule traps for time keeping, inertial navigation, and precision measurement.

physics.atom-ph↗

arXiv2021

A constant pressure flowmeter for extreme-high vacuum

We demonstrate operation of a constant-pressure flowmeter capable of generating and accurately measuring flows as low as $2\times10^{-13}$ mol/s. Generation of such small flows is accomplished by using a small conductance element with $C\approx 50$ nL/s. Accurate measurement then requires both low outgassing materials ($<10^{-15}$ mol/s) and small volume changes ($\approx 70$ $\mu$L). We outline the present flowmeter's construction, detail its operation, and quantify its uncertainty. The type-B uncertainty is $<0.2$ % ($k=1$) over the entire operating range. In particular, we present an analysis of its hydraulic system, and quantify the shift and uncertainty due to the slightly compressible oil. Finally, we compare our flowmeter against a NIST standard flowmeter, and find agreement to within 0.5 % ($k=2$).

physics.ins-det↗

arXiv2021

$\Lambda$-enhanced gray molasses in a tetrahedral laser beam geometry

We report observation of sub-Doppler cooling of lithium using an irregular-tetrahedral laser beam arrangement, which is produced by a nanofabricated diffraction grating. We are able to capture 11(2) % of the lithium atoms from a grating magneto-optical trap into $\Lambda$-enhanced $D_1$ gray molasses. The molasses cools the captured atoms to a radial temperature of 60(9) $\mu$K and an axial temperature of 23(3) $\mu$K. In contrast to results from conventional counterpropagating beam configurations, we do not observe cooling when our optical fields are detuned from Raman resonance. An optical Bloch equation simulation of the cooling dynamics agrees with our data. Our results show that grating magneto-optical traps can serve as a robust source of cold atoms for tweezer-array and atom-chip experiments, even when the atomic species is not amenable to sub-Doppler cooling in bright optical molasses.

physics.atom-ph↗

arXiv2021

Accurate Determination of Hubble Attenuation and Amplification in Expanding and Contracting Cold-Atom Universes

In the expanding universe, relativistic scalar fields are thought to be attenuated by "Hubble friction", which results from the dilation of the underlying spacetime metric. By contrast, in a contracting universe this pseudo-friction would lead to amplification. Here, we experimentally measure with five-fold better accuracy, both Hubble attenuation and amplification in expanding and contracting toroidally-shaped Bose-Einstein condensates, in which phonons are analogous to cosmological scalar fields. We find that the observed attenuation or amplification depends on the temporal phase of the phonon field, which is only possible for non-adiabatic dynamics. The measured strength of the Hubble friction disagrees with recent theory [J. M. Gomez Llorente and J. Plata, {\it Phys. Rev. A} {\bf 100} 043613 (2019) and S. Eckel and T. Jacobson, {\it SciPost Phys.} {\bf 10} 64 (2021)]; because our experiment probes physics outside the scope of this theory -- with large excitations in rings of intermediate thickness -- this indicates the presence of new physics.

quant-ph↗

arXiv2020

PyLCP: A python package for computing laser cooling physics

We present a python object-oriented computer program for simulating various aspects of laser cooling physics. Our software is designed to be both easy to use and adaptable, allowing the user to specify the level structure, magnetic field profile, or the laser beams' geometry, detuning, and intensity. The program contains three levels of approximation for the motion of the atom, applicable in different regimes offering cross checks for calculations and computational efficiency depending on the physical situation. We test the software by reproducing well-known phenomena, such as damped Rabi flopping, electromagnetically induced transparency, stimulated Raman adiabatic passage, and optical molasses. We also use our software package to quantitatively simulate recoil-limited magneto-optical traps, like those formed on the narrow $^1$S$_0\rightarrow ^3$P$_1$ transition in $^{88}$Sr and $^{87}$Sr.

physics.atom-ph↗

arXiv2020

A Bitter-type electromagnet for complex atomic trapping and manipulation

We create a pair of symmetric Bitter-type electromagnet assemblies capable of producing multiple field configurations including uniform magnetic fields, spherical quadruple traps, or Ioffe-Pritchard magnetic bottles. Unlike other designs, our coil allows both radial and azimuthal cooling water flows by incorporating an innovative 3D-printed water distribution manifold. Combined with a double-coil geometry, such orthogonal flows permit stacking of non-concentric Bitter coils. We achieve a low thermal resistance of 4.2(1) K/kW and high water flow rate of 10.0(3) L/min at a pressure of 190(10) kPa.

physics.ins-det↗

arXiv2020

Confinement of an alkaline-earth element in a grating magneto-optical trap

We demonstrate a compact magneto-optical trap (MOT) of alkaline-earth atoms using a nanofabricated diffraction grating chip. A single input laser beam, resonant with the broad $^1$S$_0\,\rightarrow \,^1$P$_1$ transition of strontium, forms the MOT in combination with three diffracted beams from the grating chip and a magnetic field produced by permanent magnets. A differential pumping tube limits the effect of the heated, effusive source on the background pressure in the trapping region. The system has a total volume of around 2.4 L. With our setup, we have trapped up to $5 \times 10^6$ $^{88}$Sr atoms, at a temperature of approximately $6$ mK, and with a trap lifetime of approximately 1 s. Our results will aid the effort to miniaturize optical atomic clocks and other quantum technologies based on alkaline-earth atoms.

physics.atom-ph↗

arXiv2020

A radiofrequency voltage-controlled current source for quantum spin manipulation

We present a design for a wide-bandwidth, voltage-controlled current source that is easily integrated with radiofrequency magnetic field coils. Our design uses current feedback to compensate for the frequency-dependent impedance of a radiofrequency antenna. We are able to deliver peak currents greater than 100 mA over a 300 kHz to 54 MHz frequency span. The radiofrequency current source fits onto a printed circuit board smaller than $4~\text{cm}^2$ and consumes less than 1.3 W of power. It is suitable for use in deployable quantum sensors and nuclear-magnetic-resonance systems.

physics.ins-det↗

arXiv2019

A flexible, open-source radio-frequency driver for acousto-optic and electro-optic devices

We present a design for a radio-frequency driver that leverages telecom amplifiers to achieve high power output and wide bandwidth. The design consists of two compact printed circuit boards (total area $< 255$ cm), which incorporate power (turn-on) and thermal management to prevent accidental damage to the amplifier circuitry. Our driver provides $>1$ W of output power over a $10$ MHz to $1.1$ GHz frequency range, and $\geq 5$ W from $20$ MHz to $100$ MHz. The driver circuit includes auxiliary components for analog frequency and amplitude modulation ($\approx 70$ kHz bandwidth), as well as digital power switching ($> 30$ dB of extinction within $40$ ns and final extinction $> 90$ dB). The radio-frequency source can also be digitally switched between an external input and an integrated voltage-controlled oscillator. Our design is motivated by the need for flexible, inexpensive drivers of optically active devices, such as acousto-optic and electro-optic modulators.

physics.ins-det↗

arXiv2018

Single-beam Zeeman slower and magneto-optical trap using a nanofabricated grating

We demonstrate a compact (0.25 L) system for laser cooling and trapping atoms from a heated dispenser source. Our system uses a nanofabricated diffraction grating to generate a magneto-optical trap (MOT) using a single input laser beam. An aperture in the grating allows atoms from the dispenser to be loaded from behind the chip, increasing the interaction distance of atoms with the cooling light. To take full advantage of this increased distance, we extend the magnetic field gradient of the MOT to create a Zeeman slower. The MOT traps approximately $10^6$ $^7$Li atoms emitted from an effusive source with loading rates in excess of $10^6$ s$^{-1}$. Our design is portable to a variety of atomic and molecular species and could be a principal component of miniaturized cold-atom-based technologies.

physics.atom-ph↗

arXiv2018

Light-induced atomic desorption of lithium

We demonstrate loading of a Li magneto-optical trap using light-induced atomic desorption. The magneto-optical trap confines up to approximately $4\times10^{4}$ $^{7}\text{Li}$ atoms with loading rates up to approximately $4\times10^{3}$ atoms per second. We study the Li desorption rate as a function of the desorption wavelength and power. The extracted wavelength threshold for desorption of Li from fused silica is approximately $470$ nm. In addition to desorption of lithium, we observe light-induced desorption of background gas molecules. The vacuum pressure increase due to the desorbed background molecules is $\lesssim50$ % and the vacuum pressure decreases back to its base value with characteristic timescales on the order of seconds when we extinguish the desorption light. By examining both the loading and decay curves of the magneto-optical trap, we are able to disentangle the trap decay rates due to background gases and desorbed lithium. Our results show that light-induced atomic desorption can be a viable Li vapor source for compact devices and sensors.

physics.atom-ph↗

arXiv2017

A rapidly expanding Bose-Einstein condensate: an expanding universe in the lab

We study the dynamics of a supersonically expanding ring-shaped Bose-Einstein condensate both experimentally and theoretically. The expansion redshifts long-wavelength excitations, as in an expanding universe. After expansion, energy in the radial mode leads to the production of bulk topological excitations -- solitons and vortices -- driving the production of a large number of azimuthal phonons and, at late times, causing stochastic persistent currents. These complex nonlinear dynamics, fueled by the energy stored coherently in one mode, are reminiscent of a type of "preheating" that may have taken place at the end of inflation.

cond-mat.quant-gas↗

arXiv2016

Subwavelength-width optical tunnel junctions for ultracold atoms

We propose a new method for creating far-field optical barrier potentials for ultracold atoms with widths that are narrower than the diffraction limit and can approach tens of nanometers. The reduced widths stem from the nonlinear atomic response to control fields that create spatially varying dark resonances. The subwavelenth barrier is the result of the geometric scalar potential experienced by an atom prepared in such a spatially varying dark state. The performance of this technique, as well as its applications to the study of many-body physics and to the implementation of quantum information protocols with ultracold atoms, are discussed, with a focus on the implementation of tunnel junctions.

cond-mat.quant-gas↗

arXiv2016

Minimally destructive, Doppler measurement of a quantized, superfluid flow

The Doppler effect, the shift in the frequency of sound due to motion, is present in both classical gases and quantum superfluids. Here, we perform an in-situ, minimally destructive measurement, of the persistent current in a ring-shaped, superfluid Bose-Einstein condensate using the Doppler effect. Phonon modes generated in this condensate have their frequencies Doppler shifted by a persistent current. This frequency shift will cause a standing-wave phonon mode to be "dragged" along with the persistent current. By measuring this precession, one can extract the background flow velocity. This technique will find utility in experiments where the winding number is important, such as in emerging `atomtronic' devices.

cond-mat.quant-gas↗

arXiv2016

Contact resistance and phase slips in mesoscopic superfluid atom transport

We have experimentally measured transport of superfluid, bosonic atoms in a mesoscopic system: a small channel connecting two large reservoirs. Starting far from equilibrium (superfluid in a single reservoir), we observe first resistive flow transitioning at a critical current into superflow, characterized by oscillations. We reproduce this full evolution with a simple electronic circuit model. We compare our fitted conductance to two different microscopic phenomenological models. We also show that the oscillations are consistent with LC oscillations as estimated by the kinetic inductance and effective capacitance in our system. Our experiment provides an attractive platform to begin to probe the mesoscopic transport properties of a dilute, superfluid, Bose gas.

cond-mat.quant-gas↗

arXiv2015

Resonant wavepackets and shock waves in an atomtronic SQUID

The fundamental dynamics of ultracold atomtronic devices are reflected in their phonon modes of excitation. We probe such a spectrum by applying a harmonically driven potential barrier to a $^{23}$Na Bose-Einstein condensate in a ring-shaped trap. This perturbation excites phonon wavepackets. When excited resonantly, these wavepackets display a regular periodic structure. The resonant frequencies depend upon the particular configuration of the barrier, but are commensurate with the orbital frequency of a Bogoliubov sound wave traveling around the ring. Energy transfer to the condensate over many cycles of the periodic wavepacket motion causes enhanced atom loss from the trap at resonant frequencies. Solutions of the time-dependent Gross-Pitaevskii equation exhibit quantitative agreement with the experimental data. We also observe the generation of supersonic shock waves under conditions of strong excitation, and collisions of two shock wavepackets.

cond-mat.quant-gas↗

arXiv2014

Interferometric measurement of the current-phase relationship of a superfluid weak link

Weak connections between superconductors or superfluids can differ from classical links due to quantum coherence, which allows flow without resistance. Transport properties through such weak links can be described with a single function, the current-phase relationship, which serves as the quantum analog of the current-voltage relationship. Here, we present a technique for inteferometrically measuring the current-phase relationship of superfluid weak links. We interferometrically measure the phase gradient around a ring-shaped superfluid Bose-Einstein condensate (BEC) containing a rotating weak link, allowing us to identify the current flowing around the ring. While our BEC weak link operates in the hydrodynamic regime, this technique can be extended to all types of weak links (including tunnel junctions) in any phase-coherent quantum gas. Moreover, it can also measure the current-phase relationships of excitations. Such measurements may open new avenues of research in quantum transport.

cond-mat.quant-gas↗

arXiv2014

Resistive flow in a weakly interacting Bose-Einstein condensate

We report the direct observation of resistive flow through a weak link in a weakly interacting atomic Bose-Einstein condensate. Two weak links separate our ring-shaped superfluid atomtronic circuit into two distinct regions, a source and a drain. Motion of these weak links allows for creation of controlled flow between the source and the drain. At a critical value of the weak link velocity, we observe a transition from superfluid flow to superfluid plus resistive flow. Working in the hydrodynamic limit, we observe a conductivity that is 4 orders of magnitude larger than previously reported conductivities for a Bose-Einstein condensate with a tunnel junction. Good agreement with zero-temperature Gross-Pitaevskii simulations and a phenomenological model based on phase slips indicate that the creation of excitations plays an important role in the resulting conductivity. Our measurements of resistive flow elucidate the microscopic origin of the dissipation and pave the way for more complex atomtronic devices.

cond-mat.quant-gas↗