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Latest articles for Reports on Progress in Physics
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Bayesian frequency metrology with optimal Ramsey interferometry in optical atomic clocks
Frequency metrology is a cornerstone of modern precision measurements and optical atomic clocks have emerged as one of the most precise measurement devices. In this progress report, we explore various Ramsey interrogation schemes tailored to optical atomic clocks primarily limited by laser noise. To incorporate frequency fluctuations directly into the theoretical model, we consider a Bayesian framework. In this context, we review fundamental bounds arising in Bayesian estimation theory, which serve as a benchmark throughout this work. We investigate the trade-off between entanglement–enhanced sensitivity and robustness against laser noise in order to identify optimal initial states, measurement schemes and estimation strategies. Beside standard protocols based on coherent spin states, spin-squeezed states and Greenberger–Horne–Zeilinger states, we consider variational Ramsey protocols implemented via low-depth quantum circuits based on one-axis twisting operations to approach optimal stability. In particular, we review known and identify new optimal Ramsey interrogation schemes for a variety of scenarios, including different experimental platforms, ensemble sizes and regimes characterized by a wide range of interrogation durations and dead times. Hence, this work establishes a comprehensive theoretical framework for optimizing Ramsey interrogation schemes, providing guidance for the development of next-generation optical atomic clocks.
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Search for heavy pseudoscalar and scalar bosons decaying to a top quark pair in proton–proton collisions at s ...
A search for pseudoscalar or scalar bosons decaying to a top quark pair ( ) in final states with one or two charged leptons is presented. The analyzed proton–proton collision data was recorded at by the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 138 . The invariant mass of the reconstructed system and variables sensitive to its spin and parity are used to discriminate against the standard model background. Interference between pseudoscalar or scalar boson production and the standard model continuum is included, leading to peak-dip structures in the distribution. An excess of the data above the background prediction, based on perturbative quantum chromodynamics (QCD) calculations, is observed near the kinematic production threshold, while good agreement is found for high . The data are consistent with the background prediction if the contribution from a simplified model of a color-singlet quasi-bound state , inspired by nonrelativistic QCD, is added. Upper limits at 95% confidence level are set on the coupling between the pseudoscalar or scalar bosons and the top quark for boson masses in the range 365–1000 GeV, relative widths between 0.5% and 25%, and two background scenarios with or without contribution.
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Kolmogorov modes and linear response of jump-diffusion models
We present a generalization of linear response theory(LRT) for mixed jump-diffusion models—which combine both Gaussian and Lévy noise forcings that interact with the nonlinear dynamics—by deriving a comprehensive response formulas that accounts for perturbations to both the drift term and the jumps law. This class of models is particularly relevant for parameterizing the effects of unresolved scales in complex systems. Our formulas help thus quantifying uncertainties in either what needs to be parameterized (e.g. the jumps law), or measuring dynamical changes due to perturbations of the drift term (e.g. parameter variations). By generalizing the concepts of Kolmogorov operators and Green’s functions, we obtain new forms of fluctuation-dissipation relations. The resulting response is decomposed into contributions from the eigenmodes of the Kolmogorov operator, providing a fresh look into the intimate relationship between a system’s natural and forced variability. We demonstrate the theory’s predictive power with two distinct climate-centric applications. First, we apply our framework to a paradigmatic El Niño-Southern Oscillation model subject to state-dependent jumps and additive white noise, showing how the theory accurately predicts the system’s response to perturbations and how Kolmogorov modes can be used to diagnose its complex time variability. In a second, more challenging application, we use our LRT to perform accurate climate change projections in the Ghil–Sellers energy balance climate model, which is a spatially-extended model forced here by a spatio-temporal α-stable process. This work provides a comprehensive approach to climate modeling and prediction that enriches Hasselmann’s program, with implications for understanding climate sensitivity, detection and attribution of climate change, and assessing the risk of climate tipping points. Our results may find applications beyond the realm of climate, and seem of relevance for epidemiology, biology, finance, and quantitative social sciences, among others.
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Hierarchical topological states without dimension reduction
Topological insulators exhibit boundary states protected by bulk band topology, a principle first established in quantum systems and later extended to classical waves, including phononics. Conventionally, an n-dimensional bulk with nontrivial topology hosts -dimensional topologically protected boundary states, which may be further gapped out by breaking the symmetry that protects them, potentially leading to the emergence of -dimensional, or even lower-dimensional topological states, as in higher-order topological insulators. In this work, we introduce an alternative mechanism for gapping out topological states and forming new topological modes within the resulting gap without further unit-cell symmetry breaking or dimension reduction. Using one- and two-dimensional Su–Schrieffer–Heeger models, we show that controlled repositioning of topological domain walls enables the construction of hierarchical unit cells that gap out the original domain-wall states while preserving the underlying symmetry. This process produces higher-hierarchical-level topological states, characterized by a generalized winding number, and can be iterated to realize multiple—potentially infinite—hierarchical levels of topological states. Our approach expands the conventional topological classification and offers a versatile route for engineering complex networks of protected modes in higher dimensions.
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Order parameter for non-equilibrium dissipation and ideal glass
Glass materials, as quintessential non-equilibrium systems, exhibit properties such as energy dissipation that are highly sensitive to their preparation histories. A key challenge has been identifying a unified order parameter to rationalize these properties. Here, we demonstrate that a configurational distance metric can effectively collapse energy dissipation data across diverse preparation histories and testing protocols, including varying cooling rates, aging processes, probing times, and the amplitudes of mechanical excitation, as long as the temperature remains above the kinetic ideal glass transition temperature (where the extrapolated structural relaxation time diverges). Our results provide a unified description of the non-equilibrium dissipation and suggest that the putative concept of the kinetic ideal glass transition is imprinted in material characteristics.