Communications Physics最新文献

Understanding how time-reversal symmetry (TRS) breaks in quantum materials is key to uncovering new states of matter and advancing quantum technologies. However, unraveling the interplay between TRS breaking, charge order, and superconductivity in kagome metals continues to be a compelling challenge. Here, we investigate the kagome metal Cs(V_1-x Nb _x )₃Sb₅ with x = 0.07 using muon spin rotation (μSR), alternating current (AC) magnetic susceptibility, and scanning tunneling microscopy (STM), under combined tuning by chemical doping, hydrostatic pressure, magnetic field, and depth from the surface. We find that TRS breaking in the bulk emerges below 40 K-lower than the charge order onset at 58 K-while near the surface, TRS breaking onsets at 58 K and is twice as strong. Niobium doping raises the superconducting critical temperature from 2.5 K to 4.4 K. Under pressure, both the critical temperature and superfluid density double, with TRS-breaking superconductivity appearing above 0.85 GPa. These findings reveal a depth-tunable TRS-breaking state and unconventional superconducting behavior in kagome systems.

Neural networks have shown to be a powerful tool to represent the ground state of quantum many-body systems, including fermionic systems. However, efficiently integrating lattice symmetries into neural representations remains a significant challenge. In this work, we introduce a framework for embedding lattice symmetries in fermionic wavefunctions and demonstrate its ability to target both ground states and low-lying excitations. Using group-equivariant neural backflow transformations, we study the t-V model on a square lattice away from half-filling. Our symmetry-aware backflow significantly improves ground-state energies and yields accurate low-energy excitations for lattices up to 10 × 10. We also compute accurate two-point density-correlation functions and the structure factor to identify phase transitions and critical points. These findings introduce a symmetry-aware framework important for studying quantum materials and phase transitions.

Phase-sensitive measurements usually utilize interferometric techniques to retrieve the optical phase. However, when the feature space of an electromagnetic field is inherently low dimensional, most field parameters can be extracted from intensity measurements only. However, even the fastest of the previously published intensity-only methods have too high a computational complexity to be applicable at high data rates and, most importantly, require data from CCD cameras, which are generally slow. This paper shows how a few intensity measurements taken from properly placed photodetectors can be used to reconstruct the complex-valued field fully in systems with low-dimensional feature space. The presented method allows full-field characterization in few-mode fibers and does not employ a reference beam. This result is 3 orders of magnitude faster than the fastest previously published result and uses 3 orders of magnitude fewer photodetectors, allowing retrieval of mode amplitudes and phases relative to the fundamental mode using only several photodetectors. This approach enables ultrafast applications of intensity-only mode decomposition method, including pulse-to-pulse laser beam characterization, providing an essential tool for experimental exploration of the modal dynamics in spatiotemporal modelocked systems. It can also be applied to ultrafast sensing in few-mode fibers and for coherent mode division-multiplexed receivers using quadratic detectors only.

High-order phenomena are pervasive across complex systems, yet their formal characterisation remains a formidable challenge. The literature provides various information-theoretic quantities that capture high-order interdependencies, but their conceptual foundations and mutual relationships are not well understood. The lack of unifying principles underpinning these quantities impedes a principled selection of appropriate analytical tools for guiding applications. Here we introduce entropic conjugation as a formal principle to investigate the space of possible high-order measures, which clarifies the nature of the existent high-order measures while revealing gaps in the literature. Additionally, entropic conjugation leads to notions of symmetry and skew-symmetry which serve as key indicators ensuring a balanced account of high-order interdependencies. Our analyses highlight the O-information as the unique skew-symmetric measure whose estimation cost scales linearly with system size, which spontaneously emerges as a natural axis of variation among high-order quantities in real-world and simulated systems.

"Electron-only" reconnection, which is both uncoupled from the surrounding ions and much faster than standard reconnection, is arguably ubiquitous in turbulence. One critical step to understanding the rate in this novel regime is to model the outflow speed that limits the transport of the magnetic flux, which is super ion Alfvénic but significantly lower than the electron Alfvén speed based on the asymptotic reconnecting field. Here we develop a simple model to determine this limiting speed by taking into account the multiscale nature of reconnection, the Hall-mediated electron outflow speed, and the pressure buildup within the small system. The predicted scalings of rates and various key quantities compare well with fully kinetic simulations and can be useful for interpreting the observations of NASA's Magnetospheric-Multiscale (MMS) mission and other ongoing missions.

The quantum Rabi model (QRM) is a cornerstone in the study of light-matter interactions within cavity and circuit quantum electrodynamics (QED). It effectively captures the dynamics of a two-level system coupled to a single-mode resonator, serving as a foundation for understanding quantum optical phenomena in a great variety of systems. However, this model may produce inaccurate results for large coupling strengths, even in systems with high anharmonicity. Moreover, issues of gauge invariance further undermine its reliability. In this work, we introduce a renormalized QRM that incorporates the effective influence of higher atomic energy levels, providing a significantly more accurate representation of the system while still maintaining a two-level description. To demonstrate the versatility of this approach, we present two different examples: an atom in a double-well potential and a superconducting artificial atom (fluxonium qubit). This procedure opens new possibilities for precisely engineering and understanding cavity and circuit QED systems, which are highly sought-after, especially for quantum information processing.

Additive-free electroformed copper has emerged as the material of choice in exceptionally radiopure detectors for rare-event searches, based on its radiopurity, physical properties, and affordability. However, copper is ductile and of limited mechanical strength posing challenges for its use in future experiments. Electroformed copper-based alloys have been identified as a promising solution. However, their synthesis needs refining by exploring a complex parameter space of compositions and strengthening mechanisms. Here we show how a materials design approach may address current challenges and optimize alloy synthesis and processing. Alloy properties are predicted following thermal processing, using computational thermodynamics. The findings suggest a methodology to design high-performance, radiopure copper-based alloys suitable for next-generation rare-event experiments, while minimizing lengthy and expensive trial-and-error approaches. The impact on future experiments is exemplified through case-studies of the DarkSPHERE and XLZD experiments.

In many multiferroics, rare-earth and transition-metal orders coexist. For analyzing their interaction and its consequences for the multiferroic state, the domain patterns and their spatial correlation give valuable insight. Unfortunately, this is often hampered by the lack of access to the domains of the rare-earth order. Here, we uncover such a domain pattern for the multiferroic Dy_0.7Tb_0.3FeO₃. Optical second harmonic generation reveals columnar Dy/Tb domains. The columns arrange perpendicular to the magnetically induced electric polarization. Hence, the antiferromagnetic rare-earth order forces the ferroelectric domains to form nominally charged domain walls. In turn, to reduce energy, the ferroelectric order causes a diminished rare-earth domain-wall density along the polarization direction. This interplay highlights the multiferroic character of the Dy_0.7Tb_0.3FeO₃ domain pattern and the important role of the rare-earth order. We position Dy_0.7Tb_0.3FeO₃ within the broader landscape of rare-earth multiferroics identifying three distinct scenarios for the role of rare-earth order.

Atomic nuclei serve as prime laboratories for investigations of complex quantum phenomena, where minor nucleon rearrangements cause significant structural changes. ¹⁹⁰Pb is the heaviest known neutron-deficient Pb isotope that can exhibit three distinct shapes: prolate, oblate, and spherical, with nearly degenerate excitation energies. Here we report on the combined results from three state-of-the-art measurements to directly observe these deformations in ¹⁹⁰Pb. Contrary to earlier interpretations, we associate the collective yrast band as predominantly oblate, while the non-yrast band with higher collectivity follows characteristics of more deformed, predominantly prolate bands. Direct measurement of the $E0\left(0_2^{+}\to 0_1^{+}\right)$ transition and γ-e ^- coincidence relations allowed us to locate and firmly assign the $0_2^{+}$ state in the level scheme and to discover a spherical $2_3^{+}$ state at 1281(1) keV with $B\left(E2;2_3^{+}\to 0_1^{+}\right)=1.2\left(3\right)$ W.u. These assignments are based purely on observed transition probabilities and monopole strength values, and do not rely on model calculations for their interpretation.

The study of quantum reference frames (QRFs) is motivated by the idea of taking into account the quantum properties of the reference frames used, explicitly or implicitly, in our description of physical systems. Like classical reference frames, QRFs can be used to define physical quantities relationally. Unlike their classical analogue, they relativise the notions of superposition and entanglement. Here, we explain this feature by examining how configurations or locations are identified across different branches in superposition. We show that, in the presence of symmetries, whether a system is in "the same" or "different" configurations across the branches depends on the choice of QRF. Hence, sameness and difference - and thus superposition and entanglement - lose their absolute meaning. We apply these ideas to the context of semi-classical spacetimes in superposition and use coincidences of four scalar fields to construct a comparison map between spacetime points in the different branches. This reveals that the localisation of an event is frame-dependent. We discuss the implications for indefinite causal order and the locality of interaction and conclude with a generalisation of Einstein's hole argument to the quantum context.