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1. Two-Photon Vibrational Transitions in 16O2+ as Probes of Variation of the Proton-to-Electron Mass Ratio

   https://doi.org/10.3390/atoms7010001  

   Carollo, Ryan; Frenett, Alexander; Hanneke, David (March 2019, Atoms)

   Vibrational overtones in deeply-bound molecules are sensitive probes for variation of the proton-to-electron mass ratio μ . In nonpolar molecules, these overtones may be driven as two-photon transitions. Here, we present procedures for experiments with 16 O 2 + , including state-preparation through photoionization, a two-photon probe, and detection. We calculate transition dipole moments between all X 2 Π g vibrational levels and those of the A 2 Π u excited electronic state. Using these dipole moments, we calculate two-photon transition rates and AC-Stark-shift systematics for the overtones. We estimate other systematic effects and statistical precision. Two-photon vibrational transitions in 16 O 2 + provide multiple routes to improved searches for μ variation. 

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2. Assessing the stability of azopolymer nanotopography during live-cell fluorescence imaging

   https://doi.org/10.3389/fbioe.2024.1409735  

   Abdelrahman, Mona H; Shen, Jerry; Fisher, Nicholas C; Losert, Wolfgang; Fourkas, John T (August 2024, Frontiers in Bioengineering and Biotechnology)

   IntroductionPhotomodifiable azopolymer nanotopographies represent a powerful means of assessing how cells respond to rapid changes in the local microenvironment. However, previous studies have suggested that azopolymers are readily photomodified under typical fluorescence imaging conditions over much of the visible spectrum. Here we assess the stability of azopolymer nanoridges under 1-photon and 2-photon imaging over a broad range of wavelengths. MethodsAzopolymer nanoridges were created via microtransfer molding of master structures that were created using interference lithography. The effects of exposure to a broad range of wavelengths of light polarized parallel to the ridges were assessed on both a spinning-disk confocal microscope and a 2-photon fluorescence microscope. Experiments with liveDictyostelium discoideumcells were also performed using alternating cycles of 514-nm light for photomodification and 561-nm light for fluorescence imaging. Results and DiscussionWe find that for both 1-photon and 2-photon imaging, only a limited range of wavelengths of light leads to photomodification of the azopolymer nanotopography. These results indicate that nondestructive 1-photon and 2-photon fluorescence imaging can be performed over a considerably broader range of wavelengths than would be suggested by previous research. 

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3. The Born Versus Heisenberg Quantum-Vacuum Controversy and Beyond

   https://doi.org/10.1007/978-3-031-55463-6_8  

   Roso, Luis; Lera, Roberto; Ravichandran, Smrithan; Longman, Andrew; He, Calvin Z; Pérez-Hernández, José Antonio; Apiñaniz, Jon I; Mahnot, Rohan; Mateu, Vicent; Fedosejevs, Robert; et al (May 2024, Springer Nature Switzerland)

   Yamanouchi, K; DiMauro, L F; Hill_III, W T (Ed.)

   Photon-photon collisions, as one of the fundamental processes in quantum physics, have attracted a lot of attention. However, most effort has been focused on photons energetic enough to create particle-antiparticle pairs. The low energy limit—e.g., optical photons—has attracted less attention because of their extremely low collision cross section. By optical photons we mean UV, visible and infrared, although the cutting edge of extreme lasers is in the near infrared. The Schwinger critical field for pair generation seems not possible, at least directly, with the current laser technology. This often is considered as a problem, but we view this as an asset; the near impossibility of pair production via photon-photon scattering in the infrared is a perfect scenario to study virtual pairs that characterize Dirac’s quantum vacuum. Moreover, it is remarkable that this scenario of photon-photon collisions was already studied in the 1930s by two of the fathers of Quantum Mechanics, among others, at the dawn of this theory. In their respective papers, however, Born and Heisenberg arrived to different conclusions regarding the birefringence of vacuum. This controversy is still an open question that will be solved soon, we hope, with upcoming experiments. Here, we discuss a possible photon-photon collision experiment with extreme lasers, and will show that it can provide measurable effects, allowing fundamental information about the essence of Quantum Electrodynamics and its Lagrangian to be extracted. A possible experimental scenario with two ultra-intense pulses for detecting photon-photon scattering is analyzed. This would need a high-precision measurement, with control of temporal and spatial jitter, and noise. We conclude that such an experiment is barely feasible at $$10^{23}$$ W/cm$^2$ (today’s intensity record) and very promising at 1$$0^{24}$$ W/cm$^2$. 

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4. Non-Gaussian and Gottesman–Kitaev–Preskill state preparation by photon catalysis

   https://doi.org/10.1088/1367-2630/ab5330  

   Eaton, Miller; Nehra, Rajveer; Pfister, Olivier (November 2019, New Journal of Physics)

   Abstract Continuous-variable quantum-computing is the most scalable implementation of QC to date but requires non-Gaussian resources to allow exponential speedup and quantum correction, using error encoding such as Gottesman–Kitaev–Preskill (GKP) states. However, GKP state generation is still an experimental challenge. We show theoretically that photon catalysis, the interference of coherent states with single-photon states followed by photon-number-resolved detection, is a powerful enabler for non-Gaussian quantum state engineering such as exactly displaced single-photon states andM-symmetric superpositions of squeezed vacuum (SSV), including squeezed cat states (M= 2). By including photon-counting based state breeding, we demonstrate the potential to enlarge SSV states and produce GKP states. 

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5. Search for a diffuse flux of photons with energies above tens of PeV at the Pierre Auger Observatory

   https://doi.org/10.1088/1475-7516/2025/05/061  

   Abdul_Halim, A; Abreu, P; Aglietta, M; Allekotte, I; Almeida_Cheminant, K; Almela, A; Aloisio, R; Alvarez-Muñiz, J; Ambrosone, A; Ammerman_Yebra, J; et al (May 2025, Journal of Cosmology and Astroparticle Physics)

   Abstract Diffuse photons of energy above 0.1 PeV, produced through the interactions between cosmic rays and either interstellar matter or background radiation fields, are powerful tracers of the distribution of cosmic rays in the Galaxy. Furthermore, the measurement of a diffuse photon flux would be an important probe to test models of super-heavy dark matter decaying into gamma-rays. In this work, we search for a diffuse photon flux in the energy range between 50 PeV and 200 PeV using data from the Pierre Auger Observatory. For the first time, we combine the air-shower measurements from a 2 km²surface array consisting of 19 water-Cherenkov surface detectors, spaced at 433 m, with the muon measurements from an array of buried scintillators placed in the same area. Using 15 months of data, collected while the array was still under construction, we derive upper limits to the integral photon flux ranging from 13.3 to 13.8 km^-2sr^-1yr^-1above tens of PeV. We extend the Pierre Auger Observatory photon search program towards lower energies, covering more than three decades of cosmic-ray energy. This work lays the foundation for future diffuse photon searches: with the data from the next 10 years of operation of the Observatory, this limit is expected to improve by a factor of ∼20. 

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