Search for: All records

We demonstrate a neutral atom networking node that combines high photon collection efficiency with high atom-photon entanglement fidelity in a compact, fiber-integrated platform. A parabolic mirror is used both to form the trap and to collect fluorescence from a single rubidium atom, intrinsically mode-matching $\sigma$ polarized emitted photons to the fiber and rendering the system largely insensitive to small imperfections or drifts. The core optics consist of millimeter-scale components that are pre-aligned, rigidly bonded on a monolithic in-vacuum assembly, and interfaced entirely via optical fibers. With this design, we measure an overall photon collection and detection efficiency of 5%, from which we infer an overall collection efficiency of 9% after the single-mode fiber coupling. We generate atom-photon entangled states with a raw Bell-state fidelity of 0.93 and an inferred fidelity of 0.98 after correcting for atom readout errors. The same node design has been realized in two independent setups with comparable performance and is compatible with adding high-NA objective lenses to create and control atomic arrays at each node. Our results establish a robust, cavity-free neutral atom interface that operates near the limit set by the collection optics numerical aperture and provides a practical building block for scalable quantum network nodes and repeaters. 

The seismic performance of acceleration-sensitive mechanical equipment is a major area of interest within the field of nonstructural components and systems (NCSs). To save indoor space, conserve energy, or meet functional requirements, such equipment is often installed on building rooftops, where higher acceleration demands during earthquakes make rooftop-mounted units more susceptible to damage. Floor-mounted mechanical equipment is typically supported by vibration and noise isolation devices to reduce the transmission of unwanted motion to the supporting structure. However, limited attention has been given to understanding under what conditions, and to what extent, vibration and acoustical design strategies may enhance, or potentially compromise, the seismic performance of lightweight NCSs. To investigate this issue, five lightweight air-conditioning condenser units, each weighing no more than 1,500 N, including three with a slender aspect ratio of 3.7 and two with a squat aspect ratio of 1.1, were installed on the rooftop of a full-scale, ten-story cold-formed steel (CFS) building tested on a six-degree-of-freedom outdoor shake table. Different base attachment strategies were employed. All three slender units were screwmounted at four manufacturer-provided feet to the CFS studs. Two of the units had a modified base boundary condition, with neoprene pads and spring isolators respectively added under the base feet. Both squat units were screw-mounted using four steel angles connected to the CFS studs, with one additionally supported by neoprene pads placed beneath the equipment. This paper presents the first release of preliminary results from the recently completed experimental program, focusing on rooftop mechanical equipment responses under service-level, design-level, and maximum-considered earthquake motions. Results presented include measured floor acceleration amplification factors, peak component accelerations, and component amplification factors. These findings are compared with code-based provisions to evaluate the adequacy of current design coefficients in capturing the acceleration demands on lightweight components. 

Stair systems, which provide the primary means of egress in and out of a building during and after an earthquake, play a critical role in seismic resiliency. Often, these systems are detailed with fixed flight-tolanding connections. However, previous experimental studies and field reconnaissance have shown that such configurations are prone to severe damage. To mitigate this damage to both the stair systems and the supporting structural members, as well as to avoid the ensuing potential to stiffen the lateral force resisting system of the building, stair connections are often detailed to release drift demands. Referred to as driftrelease, these approaches generally focus on releasing inter-story drift at the flight-to-landing connections. Findings from a recent shake table test of a 10-story prefabricated stair system within a mass timber building showed that stair systems with drift-release connections result in a seismically resilient egress solution. However, due to the free movement of stair flights, handrail connections received damage at multiple levels. In a complementary follow-on study, a 9-story stair system with refined connection details was integrated into a 10-story cold-formed steel (CFS10) building recently tested at NHERI@UC San Diego. Numerical analyses have indicated that stair systems with fixed flight-to-landing connections can influence the dynamic characteristics of the supporting structure due to strut action. As such, stairs in the CFS10 building system were designed to allow for easy modification between fixed and drift-release connections by installing or removing locking bolts at the flight to mid-landing interfaces. In the CFS10 building, white noise tests were conducted in each orthogonal direction under two configurations: first, with the stair connections fixed, and then with the locking bolts removed. This study aims to determine the impact of stair connection detailing on the modal characteristics of the building. In addition, complementary numerical simulations were carried out for both fixed and drift-release stair configurations. Based on both experimental and numerical studies, it is found that, under low-amplitude excitation, the impact of stair flexibility on the building vibration period is not significant because the drift-release connection is not appreciably engaged under small lateral loading. However, the impact of stair strut action under large-amplitude excitation still needs to be investigated.