We provide proof-of-principle illustration of lasing in a two-dimensional polariton topological insulator. Topological edge states may arise in a structured polariton microcavity under the combined action of spin-orbit coupling and Zeeman splitting in the magnetic field. Their properties and lifetime are strongly affected by gain. Thus, gain concentrated along the edge of the insulator can counteract intrinsic losses in such a selective way that the topologically protected edge states become amplified, while bulk modes remain damped. When gain is compensated by nonlinear absorption the metastable nonlinear edge states are formed. Taking a triangular structure instead of an infinite edge we observed persistent topological currents accompanied by the time-periodic oscillations of the polariton density.

In nonexcitable cells, global ${\mathrm{Ca}}^{2+}$ spikes emerge from the collective dynamics of clusters of ${\mathrm{Ca}}^{2+}$ channels that are coupled by diffusion. Current modeling approaches have opposed stochastic descriptions of these systems to purely deterministic models, while both paradoxically appear compatible with experimental data. Combining fully stochastic simulations and mean-field analyses, we demonstrate that these two approaches can be reconciled. Our fully stochastic model generates spike sequences that can be seen as noise-perturbed oscillations of deterministic origin, while displaying statistical properties in agreement with experimental data. These underlying deterministic oscillations arise from a phenomenological spike nucleation mechanism.

The cellular uptake of nanoparticles or viruses requires that the gain of adhesion energy overcomes the cost of plasma membrane bending. It is well known that this leads to a minimal particle size for uptake. Using a simple deterministic theory for this process, we first show that, for the same radius and volume, cylindrical particles should be taken up faster than spherical particles, both for normal and parallel orientations. We then address stochastic effects, which are expected to be relevant due to small system size, and show that, now, spherical particles can have a faster uptake because the mean first passage time profits from the multiplicative noise induced by the spherical geometry. We conclude that stochastic effects are strongly geometry dependent and may favor spherical shapes during adhesion-driven particle uptake.

When a quantum system is driven slowly through a parametric cycle in a degenerate Hilbert space, the state would acquire a non-Abelian geometric phase, which is stable and forms the foundation for holonomic quantum computation (HQC). However, in the adiabatic limit, the environmental decoherence becomes a significant source of errors. Recently, various nonadiabatic holonomic quantum computation (NHQC) schemes have been proposed, but all at the price of increased sensitivity to control errors. Alternatively, there exist theoretical proposals for speeding up HQC by the technique of “shortcut to adiabaticity” (STA), but no experimental demonstration has been reported so far, as these proposals involve a complicated control of four energy levels simultaneously. Here, we propose and experimentally demonstrate that HQC via shortcut to adiabaticity can be constructed with only three energy levels, using a superconducting qubit in a scalable architecture. With this scheme, all holonomic single-qubit operations can be realized nonadiabatically through a single cycle of state evolution. As a result, we are able to experimentally benchmark the stability of $\mathrm{STA}+\mathrm{HQC}$ against NHQC in the same platform. The flexibility and simplicity of our scheme makes it also implementable on other systems, such as nitrogen-vacancy center, quantum dots, and nuclear magnetic resonance. Finally, our scheme can be extended to construct two-qubit holonomic entangling gates, leading to a universal set of STAHQC gates.

We have realized a new interaction between superconducting qubits and a readout cavity that results in the displacement of a coherent state in the cavity, conditioned on the state of the qubit. This conditional state, when it reaches the cavity-following, phase-sensitive amplifier, matches its measured observable, namely, the in phase quadrature. In a setup where several qubits are coupled to the same readout resonator, we show it is possible to measure the state of a target qubit with minimal dephasing of the other qubits. Our results suggest novel directions for faster readout of superconducting qubits and implementations of bosonic quantum error-correcting codes.

We theoretically propose and experimentally implement a method of measuring a qubit by driving it close to the frequency of a dispersively coupled bosonic mode. The separation of the bosonic states corresponding to different qubit states begins essentially immediately at maximum rate, leading to a speedup in the measurement protocol. Also the bosonic mode can be simultaneously driven to optimize measurement speed and fidelity. We experimentally test this measurement protocol using a superconducting qubit coupled to a resonator mode. For a certain measurement time, we observe that the conventional dispersive readout yields close to 100% higher average measurement error than our protocol. Finally, we use an additional resonator drive to leave the resonator state to vacuum if the qubit is in the ground state during the measurement protocol. This suggests that the proposed measurement technique may become useful in unconditionally resetting the resonator to a vacuum state after the measurement pulse.

We present the first measurements of absolute branching fractions of ${\mathrm{\Xi }}_c^0$ decays into ${\mathrm{\Xi }}^{-}{\pi }^{+}$, $\mathrm{\Lambda }{K}^{-}{\pi }^{+}$, and $p{K}^{-}{K}^{-}{\pi }^{+}$ final states. The measurements are made using a dataset comprising $(772\pm 11)\times {10}^6$ $B\overline{B}$ pairs collected at the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. We first measure the absolute branching fraction for $B^{-}\to {\overline{\mathrm{\Lambda }}}_c^{-}{\mathrm{\Xi }}_c^0$ using a missing-mass technique; the result is $\mathcal{B}(B^{-}\to {\overline{\mathrm{\Lambda }}}_c^{-}{\mathrm{\Xi }}_c^0)=(9.51\pm 2.10\pm 0.88)\times {10}^{-4}$. We subsequently measure the product branching fractions $\mathcal{B}(B^{-}\to {\overline{\mathrm{\Lambda }}}_c^{-}{\mathrm{\Xi }}_c^0)\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+})$, $\mathcal{B}(B^{-}\to {\overline{\mathrm{\Lambda }}}_c^{-}{\mathrm{\Xi }}_c^0)\mathcal{B}({\mathrm{\Xi }}_c^0\to \mathrm{\Lambda }{K}^{-}{\pi }^{+})$, and $\mathcal{B}(B^{-}\to {\overline{\mathrm{\Lambda }}}_c^{-}{\mathrm{\Xi }}_c^0)\mathcal{B}({\mathrm{\Xi }}_c^0\to p{K}^{-}{K}^{-}{\pi }^{+})$ with improved precision. Dividing these product branching fractions by the result for $B^{-}\to {\overline{\mathrm{\Lambda }}}_c^{-}{\mathrm{\Xi }}_c^0$ yields the following branching fractions: $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+})=(1.80\pm 0.50\pm 0.14)\%$, $\mathcal{B}({\mathrm{\Xi }}_c^0\to \mathrm{\Lambda }{K}^{-}{\pi }^{+})=(1.17\pm 0.37\pm 0.09)\%$, and $\mathcal{B}({\mathrm{\Xi }}_c^0\to p{K}^{-}{K}^{-}{\pi }^{+})=(0.58\pm 0.23\pm 0.05)\%$. For the above branching fractions, the first uncertainties are statistical and the second are systematic. Our result for $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+})$ can be combined with ${\mathrm{\Xi }}_c^0$ branching fractions measured relative to ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}$ to yield other absolute ${\mathrm{\Xi }}_c^0$ branching fractions.

We explore proximity-induced ferromagnetism on transition metal dichalcogenides (TMDs), focusing on molybdenum ditelluride ribbons with zigzag edges, deposited on ferromagnetic europium oxide (EuO). A tight-binding model incorporates exchange and Rashba fields induced by proximity to EuO or similar substrates. For in-gap Fermi levels, electronic modes in the nanoribbon are localized along the edges, acting as one-dimensional (1D) conducting channels with tunable spin-polarized currents. TMDs on magnetic substrates can become very useful in spintronics, providing versatile platforms to study the proximity effects and electronic interactions in complex 1D systems.

Thiolated gold nanointerfaces play a key role in numerous fields of science, technology, as well as modern medicine to coat, functionalize, and protect. Our computational study reveals that the mechanical vs thermal stabilities of aliphatic thiolates on gold surfaces are strikingly different from those of aromatic thiolates. The aliphatic thiolates feature, at the same time, a higher thermal desorption energy but a lower mechanical rupture force than thiophenolates. Our analysis discloses that this most counterintuitive property is due to different mechanochemical detachment mechanisms. Electronic structure analyses along the detachment pathways trace this back to the distinct electronic properties of the $\mathrm{S}─\mathrm{Au}$ bond in stretched nanojunctions. The discoveries that it is a higher thermal stability that entails a lower mechanical stability and that mechanical loads generate different local nanostructures depending on the nature of the thiolate are highly relevant for the rational design of improved thiol-gold nanocontacts.

Superconductivity in the iron pnictides emerges from metallic parent compounds exhibiting intertwined stripe-type magnetic order and nematic order, with itinerant electrons suggested to be essential for both. Here we use x-ray and neutron scattering to show that a similar intertwined state is realized in semiconducting ${\mathrm{KFe}}_{0.8}{\mathrm{Ag}}_{1.2}{\mathrm{Te}}_2$ (${\mathrm{K}}_5{\mathrm{Fe}}_4{\mathrm{Ag}}_6{\mathrm{Te}}_{10}$) without itinerant electrons. We find that Fe atoms in ${\mathrm{KFe}}_{0.8}{\mathrm{Ag}}_{1.2}{\mathrm{Te}}_2$ form isolated $2\times 2$ blocks, separated by nonmagnetic Ag atoms. Long-range magnetic order sets in below $T_N\approx 35\mathrm{K}$, with magnetic moments within the $2\times 2$ Fe blocks ordering into the stripe-type configuration. A nematic order accompanies the magnetic transition, manifest as a structural distortion that breaks the fourfold rotational symmetry of the lattice. The nematic orders in ${\mathrm{KFe}}_{0.8}{\mathrm{Ag}}_{1.2}{\mathrm{Te}}_2$ and iron pnictide parent compounds are similar in magnitude and in how they relate to the magnetic order, indicating a common origin. Since ${\mathrm{KFe}}_{0.8}{\mathrm{Ag}}_{1.2}{\mathrm{Te}}_2$ is a semiconductor without itinerant electrons, this indicates that local-moment magnetic interactions are integral to its magnetic and nematic orders, and such interactions may play a key role in iron-based superconductivity.

We reconsider the isothermal equation of state (EOS) for linear homopolymers in good solvents, $p=p(c,T)$, which relates the osmotic pressure $p$ of polymers with the bulk concentration $c$ and the temperature $T$. The classical scaling theory predicts the EOS in dilute and semidilute regimes. We suggest a generalized EOS that extends the universal behavior of polymer solutions up to the highly concentrated state and confirm it by molecular dynamics simulations and available experimental data. Our conjecture implies that properties of polymer chains dominate the EOS in the presence of many-body interactions. Our theoretical approach is based on a viral expansion in terms of concentration blobs leading to a superposition of two power laws in the regime of concentrated solutions.

A key ingredient within theories focusing on the rheology of entangled polymers is the way how the topological constraints of an entangled chain are lifted by unconstrained segments, i.e., how the constraining tube is dilated. This important question has been addressed by directly measuring the tube diameter $d$ at the scale of the tube by neutron spin echo spectroscopy. The tube diameter $d$ and plateau modulus $G_N^0$ of highly entangled polyethylene oxide (PEO) chains of volume fraction $c$ that are diluted by low molecular PEO show a concentration dependence $d\propto c^{a/2}$ and $G_N^0\propto c^{1+a}$ with an exponent $a$ close to $4/3$. This result allows the clear discrimination between different theoretical models that predict $4/3$ or other values between 1 and 2 and provides an important ingredient to tube model theories.

The set of all qubit states that can be steered to by measurements on a correlated qubit is predicted to form an ellipsoid—called the quantum steering ellipsoid—in the Bloch ball. This ellipsoid provides a simple visual characterization of the initial two-qubit state, and various aspects of entanglement are reflected in its geometric properties. We experimentally verify these properties via measurements on many different polarization-entangled photonic qubit states. Moreover, for pure three-qubit states, the volumes of the two quantum steering ellipsoids generated by measurements on the first qubit are predicted to satisfy a tight monogamy relation, which is strictly stronger than the well-known monogamy of entanglement for concurrence. We experimentally verify these predictions, using polarization and path entanglement. We also show experimentally that this monogamy relation can be violated by a mixed entangled state, which nevertheless satisfies a weaker monogamy relation.

Tensor network methods have become a powerful class of tools to capture strongly correlated matter, but methods to capture the experimentally ubiquitous family of models at finite temperature beyond one spatial dimension are largely lacking. We introduce a tensor network algorithm able to simulate thermal states of two-dimensional quantum lattice systems in the thermodynamic limit. The method develops instances of projected entangled pair states and projected entangled pair operators for this purpose. It is the key feature of this algorithm to resemble the cooling down of the system from an infinite temperature state until it reaches the desired finite-temperature regime. As a benchmark, we study the finite-temperature phase transition of the Ising model on an infinite square lattice, for which we obtain remarkable agreement with the exact solution. We then turn to study the finite-temperature Bose-Hubbard model in the limits of two (hard-core) and three bosonic modes per site. Our technique can be used to support the experimental study of actual effectively two-dimensional materials in the laboratory, as well as to benchmark optical lattice quantum simulators with ultracold atoms.

The dark matter density distribution in small-scale astrophysical objects may indicate that dark matter is self-interacting, while observations from clusters of galaxies suggest that the corresponding cross section depends on the velocity. Using a model-independent approach, we show that resonant self-interacting dark matter can naturally explain such a behavior. In contrast to what is often assumed, this does not require a light mediator. We present explicit realizations of this mechanism and discuss the corresponding astrophysical constraints.

Using a $3.19{\mathrm{fb}}^{-1}$ data sample collected at an $e^{+}{e}^{-}$ center-of-mass energy of $E_{\mathrm{cm}}=4.178\mathrm{GeV}$ with the BESIII detector, we measure the branching fraction of the leptonic decay $D_s^{+}\to {\mu }^{+}{\nu }_{\mu }$ to be ${\mathcal{B}}_{D_s^{+}\to {\mu }^{+}{\nu }_{\mu }}=(5.49\pm 0.16_{\text{stat}}\pm 0.15_{\text{syst}})\times {10}^{-3}$. Combining our branching fraction with the masses of the $D_s^{+}$ and ${\mu }^{+}$ and the lifetime of the $D_s^{+}$, we determine $f_{D_s^{+}}|V_{cs}|=246.2\pm 3.6_{\text{stat}}\pm 3.5_{\text{syst}}\mathrm{MeV}$. Using the $c\to s$ quark mixing matrix element $|V_{cs}|$ determined from a global standard model fit, we evaluate the $D_s^{+}$ decay constant $f_{D_s^{+}}=252.9\pm 3.7_{\text{stat}}\pm 3.6_{\text{syst}}\mathrm{MeV}$. Alternatively, using the value of $f_{D_s^{+}}$ calculated by lattice quantum chromodynamics, we find $|V_{cs}|=0.985\pm 0.014_{\text{stat}}\pm 0.014_{\text{syst}}$. These values of ${\mathcal{B}}_{D_s^{+}\to {\mu }^{+}{\nu }_{\mu }}$, $f_{D_s^{+}}|V_{cs}|$, $f_{D_s^{+}}$ and $|V_{cs}|$ are each the most precise results to date.