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1. Deconvolving Pulsar Signals with Cyclic Spectroscopy: A Systematic Evaluation

   https://doi.org/10.3847/1538-4357/abf48b  

   Dolch, Timothy; Stinebring, Dan R.; Jones, Glenn; Zhu, Hengrui; Lynch, Ryan S.; Cohen, Tyler; Demorest, Paul B.; Lam, Michael T.; Levin, Lina; McLaughlin, Maura A.; et al (May 2021, The Astrophysical Journal)

   Abstract Radio pulsar signals are significantly perturbed by their propagation through the ionized interstellar medium. In addition to the frequency-dependent pulse times of arrival due to dispersion, pulse shapes are also distorted and shifted, having been scattered by the inhomogeneous interstellar plasma, affecting pulse arrival times. Understanding the degree to which scattering affects pulsar timing is important for gravitational-wave detection with pulsar timing arrays (PTAs), which depend on the reliability of pulsars as stable clocks with an uncertainty of ∼100 ns or less over ∼10 yr or more. Scattering can be described as a convolution of the intrinsic pulse shape with an impulse response function representing the effects of multipath propagation. In previous studies, the technique of cyclic spectroscopy has been applied to pulsar signals to deconvolve the effects of scattering from the original emitted signals, increasing the overall timing precision. We present an analysis of simulated data to test the quality of deconvolution using cyclic spectroscopy over a range of parameters characterizing interstellar scattering and pulsar signal-to-noise ratio (S/N). We show that cyclic spectroscopy is most effective for high S/N and/or highly scattered pulsars. We conclude that cyclic spectroscopy could play an important role in scattering correction to distant populations of highly scattered pulsars not currently included in PTAs. For future telescopes and for current instruments such as the Green Bank Telescope upgraded with the ultrawide bandwidth receiver, cyclic spectroscopy could potentially double the number of PTA-quality pulsars. 

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2. The fluctuation–dissipation measurement instrument at the Linac Coherent Light Source

   https://doi.org/10.1063/5.0091297  

   Assefa, T. A.; Seaberg, M. H.; Reid, A. H.; Shen, L.; Esposito, V.; Dakovski, G. L.; Schlotter, W.; Holladay, B.; Streubel, R.; Montoya, S. A.; et al (August 2022, Review of Scientific Instruments)

   The development of new modes at x-ray free electron lasers has inspired novel methods for studying fluctuations at different energies and timescales. For closely spaced x-ray pulses that can be varied on ultrafast time scales, we have constructed a pair of advanced instruments to conduct studies targeting quantum materials. We first describe a prototype instrument built to test the proof-of-principle of resonant magnetic scattering using ultrafast pulse pairs. This is followed by a description of a new endstation, the so-called fluctuation–dissipation measurement instrument, which was used to carry out studies with a fast area detector. In addition, we describe various types of diagnostics for single-shot contrast measurements, which can be used to normalize data on a pulse-by-pulse basis and calibrate pulse amplitude ratios, both of which are important for the study of fluctuations in materials. Furthermore, we present some new results using the instrument that demonstrates access to higher momentum resolution. 

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3. Parametric study of the polarization dependence of nonlinear Breit–Wheeler pair creation process using two laser pulses

   https://doi.org/10.1063/5.0165788  

   Qian, Qian; Seipt, Daniel; Vranic, Marija; Grismayer, Thomas E; Blackburn, Thomas G; Ridgers, Christopher P; Thomas, Alexander_G R (October 2023, Physics of Plasmas)

   With the rapid development of high-power petawatt class lasers worldwide, exploring physics in the strong field QED regime will become one of the frontiers for laser–plasma interactions research. Particle-in-cell codes, including quantum emission processes, are powerful tools for predicting and analyzing future experiments where the physics of relativistic plasma is strongly affected by strong field QED processes. The spin/polarization dependence of these quantum processes has been of recent interest. In this article, we perform a parametric study of the interaction of two laser pulses with an ultrarelativistic electron beam. The first pulse is optimized to generate high-energy photons by nonlinear Compton scattering and efficiently decelerate electron beam through the quantum radiation reaction. The second pulse is optimized to generate electron–positron pairs by the nonlinear Breit–Wheeler decay of photons with the maximum polarization dependence. This may be experimentally realized as a verification of the strong field QED framework, including the spin/polarization rates. 

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4. Temporally Localized Quantum Operations on Continuous-Wave Thermal Light

   https://doi.org/10.1103/y4v8-1wgm  

   Wang, Yunkai; Zhang, Yujie; Lorenz, Virginia O (September 2025, Physical Review Letters)

   Previous work showed that thermal light with a blackbody spectrum cannot be decomposed into a mixture of independent localized pulses. However, we find that in the weak-source limit and under the assumption of a flat spectrum, the first nonvacuum term in the state expansion does form a mixture of such pulses. This decomposition is essential for quantum-enhanced astronomical interferometry, which typically operates on localized pulses even though stellar light is inherently continuous-wave. We present a quantum derivation of the van Cittert–Zernike theorem that incorporates finite bandwidth, thereby justifying the operations on localized pulses while processing continuous-wave thermal light. For general spectra in the weak-source limit, we establish a criterion under which correlations between pulses can be safely neglected. When this criterion is not met, we provide a corrected strategy that accurately accounts for both the spectral profile and the detector-defined pulse shape. 

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5. First demonstration of 30 eVee ionization energy resolution with Ricochet germanium cryogenic bolometers

   https://doi.org/10.1140/epjc/s10052-024-12433-1  

   Augier, C.; Baulieu, G.; Belov, V.; Bergé, L.; Billard, J.; Bres, G.; Bret, J. -.; Broniatowski, A.; Calvo, M.; Cazes, A.; et al (February 2024, The European Physical Journal C)

   Abstract The futureRicochetexperiment aims to search for new physics in the electroweak sector by measuring the Coherent Elastic Neutrino-Nucleus Scattering process from reactor antineutrinos with high precision down to the sub-100 eV nuclear recoil energy range. While theRicochetcollaboration is currently building the experimental setup at the reactor site, it is also finalizing the cryogenic detector arrays that will be integrated into the cryostat at the Institut Laue Langevin in early 2024. In this paper, we report on recent progress from the Ge cryogenic detector technology, called the CryoCube. More specifically, we present the first demonstration of a 30 eVee (electron equivalent) baseline ionization resolution (RMS) achieved with an early design of the detector assembly and its dedicated High Electron Mobility Transistor (HEMT) based front-end electronics with a total input capacitance of about 40 pF. This represents an order of magnitude improvement over the best ionization resolutions obtained on similar phonon-and-ionization germanium cryogenic detectors from the EDELWEISS and SuperCDMS dark matter experiments, and a factor of three improvement compared to the first fully-cryogenic HEMT-based preamplifier coupled to a CDMS-II germanium detector with a total input capacitance of 250 pF. Additionally, we discuss the implications of these results in the context of the futureRicochetexperiment and its expected background mitigation performance. 

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