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  • Tunable magnetic states and spin dynamics in van der Waals crystal Fe x NbS2
    The manipulation of magnetic states in van der Waals (vdW) materials through stoichiometric engineering holds significant promise for spintronic applications. In FexNbS2 (0.15 ⩽ x ⩽ 0.5), a prototypical vdW magnet exhibiting tunable behaviors including giant exchange bias and spin-glass dynamics, the interplay between iron concentration, magnetic ground states, and electronic states remains unresolved. Through combined magnetization studies and 57Fe Mössbauer spectroscopy, we unravel atomic-scale correlations between hyperfine interactions, lattice symmetry, and spin dynamics. Our results reveal a rich phase diagram governed by Fe stoichiometry: ideal x = 1/4 and 1/3 compositions stabilize long-range antiferromagnetic (AFM) order, while deviations induce structural disorder and phonon softening, triggering bi-magnetic phases with coexisting AFM and spin-glass states. Critical dimensionality crossover emerges, where Fe0.25/0.33/0.5NbS2 exhibit 2D magnetism via RKKY interaction modulation, whereas Fe0.15/0.4NbS2 transition to 3D behavior through frustrated interlayer coupling. Mössbauer analysis further uncovers Fe2+ 3d orbital splitting and electric field gradient reorientation tune electronic states. These findings establish FexNbS2 as a tunable platform for engineering magnetic dimensionality and frustration in vdW magnet, offering design principles for next-generation spintronic devices.

  • Generation of polarization-entangled counter-propagating photons with high orbital angular momentum
    Spin and orbital angular momenta of light are attractive resources to harness for encoding, and manipulating information, with applications in various quantum photonic technologies. However, to fully harness that potential, we require robust sources of high-order angular momentum photons exhibiting nonclassical correlations. Here, we propose a fiber-based source of polarization-entangled photons in high-order orbital angular momentum (OAM) modes. In our setup the pairs of photons are generated in a cylindrical fiber through a four-wave mixing process, which induces polarization, or spin entanglement. The photons are then converted to modes exhibiting large OAM by two helical gratings inscribed in the core of the fiber. We present a complete theoretical framework used to consistently describe this process, and demonstrate a robust control over the joint spectral amplitude of the generated photons.

  • Dislocations and fibrations: the topological structure of knotted defects in smectic liquid crystals
    In this work, we investigate the topological properties of knotted defects in smectic liquid crystals. Our story begins with screw dislocations, whose radial surface structure can be smoothly accommodated on S3 for fibred knots by using the corresponding knot fibration. To understand how a smectic texture may take on a screw dislocation in the shape of a knot without a fibration, we study first knotted edge defects. Unlike screw defects, knotted edge dislocations force singular points in the system for any non-trivial knot. We provide a lower bound on the number of such point defects required for a given edge dislocation knot and draw an analogy between the point defect structure of knotted edge dislocations and that of focal conic domains. By showing that edge dislocations, too, are sensitive to knot fibredness, we reinterpret the so-called Morse–Novikov points required for non-fibred screw dislocation knots as analogous smectic defects. Our methods are then applied to and negative-charge disclinations in the smectic phase, furthering the analogy between knotted smectic defects and focal conic domains and uncovering an intricate relationship between point and line defects in smectic liquid crystals. The connection between smectic defects and knot theory not only unravels the uniquely topological knotting of smectic defects but also provides a mathematical and experimental playground for modern questions in knot and Morse–Novikov theory.

  • Observation of high partial-wave Feshbach resonances in 39K Bose–Einstein condensates
    We report the new observation of several high partial-wave (HPW) magnetic Feshbach resonances (FRs) in 39K atoms of the hyperfine substate . These resonances locate at the region between two broad s-wave FRs from 32.6 G to 162.8 G, in which Bose–Einstein condensates can be produced with tunable positive scattering length obtained by magnetic FRs. These HPW FRs are induced by the dipolar spin–spin interaction with s-wave in the open channel and HPW in the closed channel. Therefore, these HPW FRs have distinct characteristics in temperature dependence and loss line shape from that induced by spin–exchange interaction with HPWs in both open and closed channels. Among these resonances, one d-wave and two g-wave FRs are confirmed by the multichannel quantum-defect theory calculation. The HPW FRs have significant applications in many-body physics dominated by HPW pairing.

  • Quantum mutual information in time
    While the quantum mutual information is a fundamental measure of quantum information, it is only defined for spacelike separated quantum systems. Such a limitation is not present in the theory of classical information, where the mutual information between two random variables is well-defined irrespective of whether or not the variables are separated in space or separated in time. Motivated by this disparity between the classical and quantum mutual information, we employ the pseudo-density matrix formalism to define a simple extension of quantum mutual information into the time domain. As in the spatial case, we show that such a notion of quantum mutual information in time serves as a natural measure of correlation between timelike separated systems, while also highlighting ways in which quantum correlations distinguish between space and time. We also show how such quantum mutual information is time-symmetric with respect to quantum Bayesian inversion, and then we conclude by showing how quantum mutual information in time yields a Holevo bound for the amount of classical information that may be extracted from sequential measurements on an ensemble of quantum states.