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Latest articles for Reports on Progress in Physics
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Even-denominator fractional quantum Hall states with spontaneously broken rotational symmetry
The interplay between the fractional quantum Hall effect and nematicity is intriguing as it links emerging topological order and spontaneous symmetry breaking. Anisotropic fractional quantum Hall states (FQHSs) have indeed been reported in GaAs quantum wells but only in tilted magnetic fields, where the in-plane field explicitly breaks the rotational symmetry. Here we report the observation of FQHSs with highly anisotropic longitudinal resistances in purely perpendicular magnetic fields at even-denominator Landau level (LL) fillings and 7/2 in ultrahigh-quality GaAs two-dimensional hole systems. The coexistence of FQHSs and spontaneous symmetry breaking at half fillings signals the emergence of nematic FQHSs which also likely harbor non-Abelian quasiparticle excitations. By gate tuning the hole density, we observe a phase transition from an anisotropic, developing FQHS to an isotropic composite fermion Fermi sea at . Our calculations suggest that the mixed orbital components in the partially occupied LL play a key role in the competition and interplay between topological and nematic orders.
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Quantum metrology with a continuous-variable system
As one of the main pillars of quantum technologies, quantum metrology aims to improve measurement precision using techniques from quantum information. The two main strategies to achieve this are the preparation of nonclassical states and the design of optimized measurement observables. We discuss precision limits and optimal strategies in quantum metrology and sensing with a single mode of quantum continuous variables. We focus on the practically most relevant cases of estimating displacements and rotations and provide the sensitivities of the most important classes of states that includes Gaussian states and superpositions of Fock states or coherent states. Fundamental precision limits that are obtained from the quantum Fisher information are compared to the precision of a simple moment-based estimation strategy based on the data obtained from possibly sub-optimal measurement observables, including homodyne, photon number, parity and higher moments. Finally, we summarize some of the main experimental achievements and present emerging platforms for continuous-variable sensing. These results are of particular interest for experiments with quantum light, trapped ions, mechanical oscillators, and microwave resonators.
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Topological phases in discrete stochastic systems
Topological invariants have proved useful for analyzing emergent function as they characterize a property of the entire system, and are insensitive to local details, disorder, and noise. They support boundary states, which reduce the system response to a lower dimensional space and, in two-dimensional (2D) systems, offer a mechanism for the emergence of global cycles within a large phase space. Topological invariants have been heavily studied in quantum electronic systems and have been observed in other classical platforms such as mechanical lattices. However, this framework largely describes equilibrium systems within an ordered crystalline lattice, whereas biological systems are often strongly non-equilibrium with stochastic components. We review recent developments in topological states in discrete stochastic models in one-dimensional and 2D systems, and initial progress in identifying testable signatures of topological states in molecular systems and ecology. These models further provide simple principles for targeted dynamics in synthetic systems and in the engineering of reconfigurable materials. Lastly, we describe novel theoretical properties of these systems such as the necessity for non-Hermiticity in permitting edge states, as well as new analytical tools to reveal these properties. The emerging developments shed light on fundamental principles for non-equilibrium systems and topological protection enabling robust biological function.
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Plasmonic photoelectric detection engineering: basic principle, design strategies and challenges
Surface plasmonics (SP) studies the collective oscillations of electrons in materials following excitation by light and related evanescent wave properties under near-field coupling. Due to the advantages of near-field enhancement, wavelength tunability, and overcoming the band gap limitation on the absorption wavelength, SPs is considered promising for broad developments in optoelectronics. Over the past decade, SP phenomena have been used in various technologies, for example photodetectors. This review discusses the physical models, role of waveguides, carrier dynamics and energy transfer modes of plasmons, particularly the structure and working principle of state-of-the-art plasmon photodetectors, with the aim of delving into the underlying mechanisms. In addition, we summarize recent developments in simulation techniques and detection methods in plasmonic photoelectric detection engineering. Finally, we present the latest progress, future prospects and remaining challenges associated with plasmon enhanced photodetection.
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New expansion rate anomalies at characteristic redshifts geometrically determined using DESI-DR2 BAO and DES-SN5YR observations
We perform a model-independent reconstruction of the cosmic distances using the multi-task Gaussian process framework as well as knot-based spline techniques with Dark Energy Spectroscopic Instrument (DESI)-DR2 baryon acoustic oscillation (BAO) and DES-SN5YR datasets. We calibrate the comoving sound horizon at the baryon drag epoch to the Planck value, ensuring consistency with early-Universe physics. With the reconstructed cosmic distances and their derivatives, we obtain seven characteristic redshifts in the range . We derive the normalized expansion rate of the Universe E(z) at these redshifts. Our findings reveal a significant deviations of approximately 4–5σ from the Planck 2018 cold dark matter Λcold dark matter predictions, particularly pronounced in the redshift range –0.55. These anomalies are consistently observed across both reconstruction methods and combined datasets, indicating robust late-time tensions in the expansion rate of the Universe and which are distinct from the existing ‘Hubble Tension’. This could signal new physics beyond the standard cosmological framework at this redshift range. Our findings underscore the role of characteristic redshifts as sensitive indicators of expansion rate anomalies and motivate further scrutiny with forthcoming datasets from DESI-5YR BAO, Euclid, and LSST. These future surveys will tighten constraints and will confirm whether these late-time anomalies arise from new fundamental physics or unresolved systematics in the data.