Integrated photonic sensors have advanced significantly in the past decade for an ever-increasing range of applications, driven by the inherent scalability of integrated photonics combined with the precision of nanofabrication. Robust and ruggedized photonic fiber-to-chip bonding solutions are needed to develop photonic sensors that can operate in extreme environments. Here, we demonstrate a robust and high-efficiency method for photonic packaging that can operate in extreme environments ranging from cryogenic temperatures and high vacuum to high-dose radiation environments. Our packaging solution is also readily adaptable to high-temperature applications. In contrast to traditional polymer-based photonics packaging, we utilize direct chemical bonding of a V-groove optical fiber array to a photonic chip via hydroxide catalysis bonding to ensure operation across a wide range of extreme operating environments. The packaged chip is characterized from 360 K down to 3.8 K, demonstrating successful operation at cryogenic temperatures with 1 dB bandwidth of 50 nm per grating coupler in the telecom wavelength range, withstanding a cryogenic thermal shock of rapid submerging from ambient room temperature into a liquid nitrogen bath at 77 K. High-dose ionizing radiation testing is achieved by exposing the packaged chip to an electron beam corresponding to a cumulative radiation dose of 1.1 MGy. After irradiation, we do not observe degradation in insertion loss across the measured wavelength range from 1510 nm to 1630 nm. We bond several test dies and confirm the high-temperature compatibility of our bonding approach by measuring mechanical bond strength after annealing at 973 K. The annealed chips withstand 1 N/mm2 axial stress. Finally, we conduct a preliminary outgassing study to demonstrate high vacuum compatibility. Our packaging methodology can be readily adapted to different photonics applications, ranging from cryogenic circuits to extreme-environment in situ sensors. (c) 2026 Chinese Laser Press

We demonstrate a Doppler thermometer based on direct optical frequency comb spectroscopy of an ^85Rb vapor with a chirped electro-optic frequency comb (EOFC). The direct EOFC Doppler thermometer is accurate to within its approximately 1 K statistical uncertainty. We experimentally compare direct EOFC spectroscopy with conventional Doppler spectroscopy using a single-frequency, step-scanned laser probe. Our results show that direct EOFC spectroscopy mitigates transit-induced optical pumping distortion of the atomic lineshape, which is the dominant systematic temperature shift in alkali atom Doppler thermometry. Optical Bloch equation simulations of conventional and direct EOFC Doppler spectroscopy confirm that EOFC spectroscopy can use higher optical power to reduce statistical noise without optical pumping distortion. Our results indicate that EOFC Doppler thermometry is a promising approach to realizing a primary thermometer with size and measurement rate sufficient for applications including pharmaceutical manufacturing and nuclear waste monitoring.

We demonstrate Doppler-broadening thermometry based on direct optical frequency comb spectroscopy of an 85Rb vapor with a chirped electro-optic frequency comb (EOFC). The direct EOFC Doppler-broadening thermometry measurements are accurate to within their approximately 1 K statistical uncertainty. We experimentally compare direct EOFC spectroscopy with conventional Doppler spectroscopy using a single-frequency, step-scanned laser probe. Our results show that direct EOFC spectroscopy mitigates transit-induced optical pumping distortion of the atomic lineshape, which is the dominant systematic temperature shift in alkali atom Doppler-broadening thermometry. Optical Bloch equation simulations of conventional and direct EOFC Doppler spectroscopy confirm that EOFC spectroscopy can use higher optical power to reduce statistical noise without optical pumping distortion. Our results indicate that EOFC Doppler-broadening thermometry is a promising approach to realizing a primary thermometer with size and measurement rate sufficient for applications including pharmaceutical manufacturing and nuclear waste monitoring.

We demonstrate sawtooth wave adiabatic passage (SWAP) in a grating magneto-optical trap (MOT) operating on the ^1S_0 → ^3P_1 transition of neutral ^88Sr. From numerical simulations of SWAP using our laser beam geometry, we find that SWAP provides greater cooling than triangle wave frequency modulation despite the complex polarization environment of a grating MOT. The simulation is confirmed by our experimental results, where we demonstrate a factor of two improvement in transfer efficiency between our ^1S_0 → ^1P_1 grating MOT and our ^1S_0 → ^3P_1 grating MOT. We trap up to 3×10^6 ^88Sr atoms in the ^1S_0 → ^3P_1 grating MOT, at an average temperature of 4.9 μK with a lifetime of approximately 0.7 s. Our results show that SWAP is effective in non-orthogonal laser beam geometries, allowing greater duty cycles or higher atom number in sensors based on narrow-line grating MOTs.

We theoretically investigate the effect of "glancing" collisions on the ultra-high vacuum (UHV) pressure readings of the cold atom vacuum standard (CAVS), based on either ultracold 7Li or 87Rb atoms. Here, glancing collisions are those collisions between ultracold atoms and room-temperature background atoms or molecules in the vacuum that do not impart enough kinetic energy to eject an ultracold atom from its trap. Our model is wholly probabilistic and shows that the number of the ultracold atoms remaining in the trap as a function of time is non-exponential. We update the recent results of a comparison between a traditional pressure standard-a combined flowmeter and dynamic expansion system-to the CAVS [D.S. Barker, et al., AVS Quantum Science 5 035001 (2023)] to reflect the results of our model. We find that the effect of glancing collisions shifts the theoretical predictions of the total loss rate coefficients for 7Li colliding with noble gases or N2 by up to 0.6 %. Likewise, we find that in the limit of zero trap depth the experimentally extracted loss rate coefficients for 87Rb colliding with noble gases or N2 shift by as much as 2.2 %.

We show that optomechanical pressure sensors with characterized density and thickness can achieve uncertainty as low as 1.1 % via comparison with a secondary pressure standard. The agreement between the secondary standard and our optomechanical sensors is a necessary step toward using optomechanical devices as primary pressure sensors. Our silicon nitride and silicon carbide sensors are short-term and long-term stable, displaying Allan deviations compatible with better than 1 % precision and baseline drift significantly lower than the secondary standard. Our measurements also yield the in situ thin-film density of our sensors with 1 % total uncertainty or lower, aiding development of other optomechanical sensors. Our results demonstrate that optomechanical pressure sensors can achieve accuracy, precision, and drift sufficient to replace high-performance legacy pressure gauges.

Heat and pressure are ultimately transmitted via quantized degrees of freedom, like gas particles and phonons. While a continuous Brownian description of these noise sources is adequate to model measurements with relatively long integration times, sufficiently precise measurements can resolve the detailed time dependence coming from individual bath-system interactions. We propose the use of nanomechanical devices operated with impulse readout sensitivity around the ``standard quantum limit'' to sense ultra-low gas pressures by directly counting the individual collisions of gas particles on a sensor. We illustrate this in two paradigmatic model systems: an optically levitated nanobead and a tethered membrane system in a phononic bandgap shield.

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 modeling predicts that the asymmetric laser geometry of a grating MOT will produce spin-polarized atomic samples. Furthermore, the Landé 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.

We simulate the capture process of MgF molecules into a frequency-chirped molecular MOT. Our calculations show that by chirping the frequency, the MOT capture velocity is increased by about of factor of 4 to 80 m/s, allowing for direct loading from a two-stage cryogenic buffer gas beam source. Moreover, we simulate the effect of this frequency chirp for molecules already present in the MOT. We find that the MOT should be stable with little to no molecule loss. The chirped MOT should thus allow loading of multiple molecule pulses to increase the number of trapped molecules

We present the measurements of thermalized collisional rate coefficients for ultra-cold 7Li and 87Rb colliding with room-temperature He, Ne, N2, Ar, Kr, and Xe. In our experiments, a combined flowmeter and dynamic expansion system, a vacuum metrology standard, is used to set a known number density for the room-temperature background gas in the vicinity of the magnetically trapped 7Li or 87Rb clouds. Each collision with a background atom or molecule removes a 7Li or 87Rb atom from its trap, and the change in the atom loss rate with background gas density is used to determine the thermalized loss rate coefficients with fractional standard uncertainties better than 1.6% for 7Li and 2.7% for 87Rb. We find consistency—a degree of equivalence of less than one—between the measurements and recent quantum-scattering calculations of the loss rate coefficients [Kłos and Tiesinga, J. Chem. Phys. 158, 014308 (2023)], with the exception of the loss rate coefficient for both 7Li and 87Rb colliding with Ar. Nevertheless, the agreement between theory and experiment for all other studied systems provides validation that a quantum-based measurement of vacuum pressure using cold atoms also serves as a primary standard for vacuum pressure, which we refer to as the cold-atom vacuum standard.

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Received 20 January 2022DOI:https://doi.org/10.1103/PhysRevA.105.029902©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtomic & molecular collisionsChemical bindingElectronic structure of atoms & moleculesInteratomic & molecular potentialsVan der Waals interactionAtomic, Molecular & Optical

In this paper, the stability of bakeable capacitance diaphragm gauges is studied. In particular, an investigation of their stability before and after a controlled series of bakes is undertaken. It is found that baking results in appreciable shifts of the zero offset, but that these can easily be corrected at time of use. However, sensitivity, linearity and higher order calibration factors cannot be corrected at time of use. So it is essential to understand the effect of baking if one wishes to use similar gauges in a system that requires heat treatment. For the gauges in this study, baking introduces a minimal additional uncertainty, and the total uncertainty can be kept to below about 0.3% at the k=2 confidence level (95%).

We demonstrate operation of a constant-pressure flowmeter capable of generating and accurately measuring flows as low as 2 × 10-13 mol/s. Generation of such small flows is accomplished by using a small conductance element with C ≈ 50 nL/s. Accurate measurement then requires both low outgassing materials (< 1 × 10-15 mol/s) and small volume changes (≈ 70 μL). 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).

Here we report measured and calculated values of decay rates of the 3d(4)(D-5)4s4p(P-3(0)) y(7)P(2,3,4)(0) states of Cr I. The decay rates are measured using time-correlated single-photon counting with roughly 1% total uncertainty. In addition, the isotope shifts for transitions between these states and the ground state are measured by laser induced fluorescence to roughly 0.5% uncertainty. The decay rate calculations are carried out by a hybrid approach that combines configuration interaction and the linearized coupled-cluster method (CI+all-order method). The measurements provide a much needed precision benchmark for testing the accuracy of the CI-Pall-order approach for such complicated systems with six valence electrons, allowing us to significantly expand its applicability. These measurements also demonstrate operation of a cryogenic buffer gas beam source for future cold molecule experiments.

Received 10 March 2022DOI:https://doi.org/10.1103/PhysRevA.105.039903©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtomic & molecular collisionsElectronic structure of atoms & moleculesInteratomic & molecular potentialsPotential energy surfacesUltracold collisionsAtomic, Molecular & Optical

We compare the vacuum measured by two portable cold-atom vacuum standards (pCAVSs) based on ultracold 7Li atoms. pCAVSs are quantum-based standards that use a priori scattering calculations to convert a measured loss rate of cold atoms from a conservative trap into a background gas pressure. Our pCAVS devices share the same laser system and measure the vacuum concurrently. The two pCAVSs together detected a leak with a rate on the order of 10−6 Pa l/s. After fixing the leak, the pCAVS measured pressure of about 40 nPa with 2.6% uncertainty. The two pCAVSs agree within their uncertainties, even when swapping some of their component parts. Operation of the pCAVS was found to cause some additional outgassing, on the order of 10−8 Pa l/s, which can be mitigated in the future by better thermal management.

We report the 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 Λ-enhanced D1 gray molasses. The molasses cools the captured atoms to a radial temperature of 60(9) μK and an axial temperature of 23(3) μK. 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.