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1. Spin Echo, Fidelity, and the Quantum Critical Fan in ${\mathrm{TmVO}}_4$

   https://doi.org/10.1103/PhysRevLett.132.216502  

   Nian, Y-H; Vinograd, I; Green, T; Chaffey, C; Massat, P; Singh, R_R P; Zic, M P; Fisher, I R; Curro, N J (May 2024, Physical Review Letters)

   Using spin-echo nuclear magnetic resonance in the model transverse field Ising system TmVO4, we show that low frequency quantum fluctuations at the quantum critical point have a very different effect on 51V nuclear spins than classical low-frequency noise or fluctuations that arise at a finite temperature critical point. Spin echoes filter out the low-frequency classical noise but not the quantum fluctuations. This allows us to directly visualize the quantum critical fan and demonstrate the persistence of quantum fluctuations at the critical coupling strength in TmVO4 to high temperatures in an experiment that remains transparent to finite temperature classical phase transitions. These results show that while dynamical decoupling schemes can be quite effective in eliminating classical noise in a qubit, a quantum critical environment may lead to rapid entanglement and decoherence. 

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2. Quantum effects in $3+1$ Schwarzschild–de Sitter spacetime: Properties of the Hadamard function

   https://doi.org/10.1103/PhysRevD.111.L021702  

   Newsome, Ian M; Pla, Silvia; Anderson, Paul R (January 2025, Physical Review D)

   In a four-dimensional Schwarzschild–de Sitter background, the spherically symmetric (l = 0) contribution to the Hadamard two-point correlation function is computed for a massless minimally coupled scalar field in the Unruh state. Consideration is given to spacetime points located between the black hole and cosmological horizons. Previously it was found in two dimensions at late times for spatially separated points that the Hadamard function exhibits unbounded linear growth in time, with a rate of growth proportional to the sum of the black hole and cosmological surface gravities. Here it is shown numerically that this instability persists in four dimensions, but with a modification of the two-dimensional result due to scattering effects associated with the scalar field modes. An analytic approximation is derived for the growth rate in four dimensions and, in the limit that the black hole vanishes, is found to be equivalent to the rate of growth for the Hadamard function found previously for de Sitter space in cosmological coordinates. 

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3. Apparatus-dependent corrections to the electron $g-2$ revisited

   https://doi.org/10.1103/PhysRevD.107.076014  

   Jentschura, Ulrich D (April 2023, Physical Review D)

   We revisit the derivation of the apparatus-dependent correction to the energy levels of quantum cyclotron states, as previously outlined [Boulware et al., Phys. Rev. D 32, 729 (1985)]. We evaluate the leading corrections to the axial, magnetron, cyclotron, and spin-projection-dependent energy levels due to the altered photon field quantization in the vicinity of a conducting wall. Our work significantly extends previous considerations. Quantum cyclotron states are used for the determination of the electron g factor in Penning traps. Our calculations show that the numerically largest apparatus-dependent corrections can be expected for the axial and magnetron frequencies, where they can be as large as 10−8 in relative units. For the cyclotron frequency, one can expect corrections on the order of 10−12 , which can affect the determination of the anomalous magnetic moment of the electron. 

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4. Revisiting $C$ and $CP$ violation in $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ decay

   https://doi.org/10.1103/PhysRevD.110.055039  

   Shi, Jun; Liang, Jian; Gardner, Susan (September 2024, Physical Review D)

   The decay $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$is an ideal process in which to study flavor-conserving $C$and $CP$violation beyond the Standard Model. We deduce the $C$- and $CP$-odd quark operators that contribute to $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$originating from the mass-dimension-six Standard Model effective field theory. The corresponding hadron-level operators that generate a nonvanishing $I=0$amplitude at order $p^6$in the chiral effective theory are presented for the first time, to the best of our knowledge, in addition to the leading-order operators ascribed to the $I=2$final state. By fitting the KLOE-2 and the most recent BESIII experimental data, we determine the coefficients of the lowest-order $I=0$and $I=2$amplitudes and estimate the potential new physics energy scale. We also perform an impact study of the future $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$experiments. Published by the American Physical Society2024 

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5. New 4D lattice QCD equation of state: Extended density coverage from a generalized $T^{\prime }$ expansion

   https://doi.org/10.1103/2dmh-26yh  

   Abuali, Ahmed; Borsányi, Szabolcs; Fodor, Zoltán; Jahan, Johannes; Kahangirwe, Micheal; Parotto, Paolo; Pásztor, Attila; Ratti, Claudia; Shah, Hitansh; Trabulsi, Seth A (September 2025, Physical Review D)

   We present a new equation of state for QCD in which the temperature $T$and the three chemical potentials for baryon number ${\mu }_B$, electric charge ${\mu }_Q$, and strangeness ${\mu }_S$can be varied independently. This result is based on a generalization of the $T^{\prime }$expansion scheme, thanks to which the diagonal ${\mu }_B$extrapolation was pushed up to a baryo-chemical potential ${\mu }_B/T\sim 3.5$for the first time. This considerably extended the coverage of the Taylor expansion, limited to ${\mu }_B/T<2.5–3$. As a consequence, we are able to offer a substantially larger coverage of the four-dimensional QCD phase diagram as well, compared to previously available Taylor expansion results. Our findings are based on new continuum estimated lattice data on the full set of second- and fourth-order fluctuations. 

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