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Compounds of polyatomic anions are investigated theoretically as hosts for thorium in nuclear clock devices. 

The population dynamics of the ${}^{229}\mathrm{Th}$isomeric state is studied in a solid-state host under laser illumination. A photoquenching process is observed, where off-resonant vacuum-ultraviolet (VUV) radiation leads to relaxation of the isomeric state. The cross-section for this photoquenching process is measured, and a model for the decay process, where photoexcitation of electronic states within the material band gap opens an internal conversion decay channel, is presented and appears to reproduce the measured cross-section. By engineering defects into ${}^{229}\mathrm{Th}$-doped solid-state hosts, this previously unrecognized photoquenching process may be used to reduce the clock transition readout time and thereby increase the stability of the nuclear clock. Published by the American Physical Society2025 

Running Median Subtraction Filter (RMSF) is a robust statistical tool for removing slowly varying baselines in data streams containing transients (short-duration signals) of interest. In this work, we explore the RMSF performance and properties using simulated time series and analytical methods. We study the RMSF fidelity in preserving the signal of interest in the data using (i) a Gaussian pulse and (ii) a transient oscillatory signal. Such signals may be generated by hypothetical exotic low-mass fields (ELFs) associated with intense astrophysical events like binary black hole or neutron star mergers. We consider and assess RMSF as a candidate method to extract transient ELF signals. RMSF operates by sliding a window across the data and subtracting the median value within each window from the data points. With a suitable choice of running window size, RMSF effectively filters out baseline variations without compromising the integrity of transients. The RMSF window width is a critical parameter: it must be wide enough to encompass a short transient but narrow enough to remove the slowly varying baseline. We show that the RMSF removes the mean of a normally distributed white noise while preserving its variance and higher-order moments in the limit of large windows. In addition, RMSF does not color the white noise stream, that is, it does not induce any significant correlation in the filtered data. Ideally, a filter would preserve both the signal of interest and the statistical characteristics of the stochastic component of the data, while removing the background clutter and outliers. We find the RMSF to satisfy these practical criteria for data preprocessing. While we rigorously prove several RMSF properties, the paper is organized as a tutorial with multiple illustrations of RMSF applications. 

The recent laser excitation of the 229Th isomeric transition in a solid-state host opens the door for a portable solid-state nuclear optical clock. However, at present, the vacuum-ultraviolet laser systems required for clock operation are not conducive to a fieldable form factor. Here, we propose a possible solution to this problem by using 229Th-doped nonlinear optical crystals, which would allow clock operation without a vacuum-ultraviolet laser system and without the need of maintaining the crystal under vacuum. We investigate electronic properties and thorium doping in BaMgF4 and BaZnF4 with density functional theory, predicting BaMgF4 to be the superior material, and evaluate the performance of a Th:BaMgF4 clock. 

We explore a novel, exotic physics, modality in multi-messenger astronomy. We are interested in exotic fields emitted by the mergers and theirdirectdetection with a network of atomic clocks. We specifically focus on the rubidium clocks onboard satellites of the Global Positioning System. Bursts of exotic fields may be produced during the coalescence of black hole singularities, releasing quantum gravity messengers. To be detectable such fields must be ultralight and ultra-relativistic and we refer to them as exotic low-mass fields (ELFs). Since such fields possess non-zero mass, the ELF bursts lag behind the gravitational waves emitted by the very same merger. Then the gravitational wave observatories provide a detection trigger for the atomic clock networks searching for the feeble ELF signals. ELFs would imprint an anti-chirp transient across the sensor network. ELFs can be detectable by atomic clocks if they cause variations in fundamental constants. We report our progress in the development of techniques to search for ELF bursts with clocks onboard GPS satellites. We focus on the binary neutron star merger GW170817 of August 17, 2017. We find an intriguing excess in the clock noise post LIGO gravitational wave trigger. Potentially the excess noise could be explained away by the increased solar electron flux post LIGO trigger. 

This document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more kilometer--scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions.