Magneto-optic trap using a reversible, solid-state alkali-metal source

In-Plane Porous Graphene: A Promising Anode Material with High Ion Mobility and Energy Storage for Rubidium-Ion Batteries

Rubidium-ion batteries (RIBs) have received a lot of attention in the quantum field because of their fast release and reversible advantages as alkali sources. However, the anode material of RIBs still follows graphite, whose layer spacing can greatly restrict the diffusion and storage capability of Rb-ions, posing a significant barrier to RIB development. Herein, using first-principles calculations, the potential performance of three kinds of in-plane porous graphene with pore sizes of 5.88 Å (HG588), 10.39 Å (HG1039), and 14.20 Å (HG1420) as anode materials for RIBs was explored. The results indicate that HG1039 appears to be an appropriate anode material for RIBs. HG1039 has excellent thermodynamic stability and a volume expansion of <25% during charge and discharge. The theoretical capacity of HG1039 is up to 1810 mA h g^-1, which is ∼5 times higher than that of the existing graphite-based lithium-ion batteries. Importantly, not only HG1039 enables the diffusion of Rb-ions at the three-dimensional level but also the electrode-electrolyte interface formed by HG1039 and Rb-β-Al₂O₃ facilitates the arrangement and transfer of Rb-ions. In addition, HG1039 is metallic, and its outstanding ionic conductivity (diffusion energy barrier of only 0.04 eV) and electronic conductivity indicates superior rate capability. These characteristics make HG1039 an appealing anode material for RIBs.

A chip-scale atomic beam clock

Atomic beams are a longstanding technology for atom-based sensors and clocks with widespread use in commercial frequency standards. Here, we report the demonstration of a chip-scale microwave atomic beam clock using coherent population trapping (CPT) interrogation in a passively pumped atomic beam device. The beam device consists of a hermetically sealed vacuum cell fabricated from an anodically bonded stack of glass and Si wafers in which lithographically defined capillaries produce Rb atomic beams and passive pumps maintain the vacuum environment. A prototype chip-scale clock is realized using Ramsey CPT spectroscopy of the atomic beam over a 10 mm distance and demonstrates a fractional frequency stability of ≈1.2 × 10^-9/[Formula: see text] for integration times, τ, from 1 s to 250 s, limited by detection noise. Optimized atomic beam clocks based on this approach may exceed the long-term stability of existing chip-scale clocks, and leading long-term systematics are predicted to limit the ultimate fractional frequency stability below 10^-12.

Monolayer H-MoS2 with high ion mobility as a promising anode for rubidium (cesium)-ion batteries

Secondary ion batteries rely on two-dimensional (2D) electrode materials with high energy density and outstanding rate capability. Rb- and Cs-ion batteries (RIBs and CIBs) are late-model batteries. Herein, using first-principles calculations, the potential performance of H-MoS₂ as a 2D electrode candidate in RIBs and CIBs has been investigated. The M-top site on 2D H-MoS₂ possesses the most stable metal atom binding sites, and after adsorbing Rb and Cs atoms, its Fermi level goes up to the conduction band, indicating a semiconductor-to-metal transition. The maximal theoretical capacities of RIBs and CIBs are 372.05 (comparable to those of commercial graphite-based LIBs) and 223.23 mA h g^-1, respectively, due to the strong adsorption capability of H-MoS₂ for Rb and Cs ions. Noticeably, the diffusion barriers of Rb and Cs on H-MoS₂ are 0.037 and 0.036 eV, respectively. Such a low diffusion barrier gives MoS₂-based RIBs and CIBs high rate capability. In addition, H-MoS₂ also has the characteristics of suitable open-circuit voltage, low expansion, good cycle stability, low cost, and easy experimental realization. These results indicate that MoS₂-based RIBs and CIBs are innovative batteries with great potential, and may provide opportunities for cross-application of energy storage and multiple disciplines.

Micro-fabricated components for cold atom sensors

Laser cooled atoms have proven transformative for precision metrology, playing a pivotal role in state-of-the-art clocks and interferometers and having the potential to provide a step-change in our modern technological capabilities. To successfully explore their full potential, laser cooling platforms must be translated from the laboratory environment and into portable, compact quantum sensors for deployment in practical applications. This transition requires the amalgamation of a wide range of components and expertise if an unambiguously chip-scale cold atom sensor is to be realized. We present recent developments in cold-atom sensor miniaturization, focusing on key components that enable laser cooling on the chip-scale. The design, fabrication, and impact of the components on sensor scalability and performance will be discussed with an outlook to the next generation of chip-scale cold atom devices.

Enhanced observation time of magneto-optical traps using micro-machined non-evaporable getter pumps

We show that micro-machined non-evaporable getter pumps (NEGs) can extend the time over which laser cooled atoms can be produced in a magneto-optical trap (MOT), in the absence of other vacuum pumping mechanisms. In a first study, we incorporate a silicon-glass microfabricated ultra-high vacuum (UHV) cell with silicon etched NEG cavities and alumino-silicate glass (ASG) windows and demonstrate the observation of a repeatedly-loading MOT over a 10 min period with a single laser-activated NEG. In a second study, the capacity of passive pumping with laser activated NEG materials is further investigated in a borosilicate glass-blown cuvette cell containing five NEG tablets. In this cell, the MOT remained visible for over 4 days without any external active pumping system. This MOT observation time exceeds the one obtained in the no-NEG scenario by almost five orders of magnitude. The cell scalability and potential vacuum longevity made possible with NEG materials may enable in the future the development of miniaturized cold-atom instruments.

Optical characterisation of micro-fabricated Fresnel zone plates for atomic waveguides

We optically assess Fresnel zone plates (FZPs) that are designed to guide cold atoms. Imaging of various ring patterns produced by the FZPs gives an average RMS error in the brightest part of the ring of 3% with respect to trap depth. This residue is attributed to the imaging system, incident beam shape and FZP manufacturing tolerances. Axial propagation of the potentials is presented experimentally and through numerical simulations, illustrating prospects for atom guiding without requiring light sheets.