Catalytic colloidal swimmers that propel due to self-generated fluid flows exhibit strong affinity for surfaces. Here, we report experimental measurements of a significant dependence of such microswimmers’ speed on the nearby substrate material. We find that speeds scale with the solution contact angle $\theta$ on the substrate, which relates to the associated hydrodynamic substrate slip length, as $V\propto (\cos \theta +1{)}^{-3/2}$. We show that such dependence can be attributed to osmotic coupling between swimmers and substrate. Our work points out that hydrodynamic slip at nearby walls, though often unconsidered, can significantly impact microswimmer self-propulsion.

Microbial cells generally leak various metabolites including those necessary to grow. Why cells secrete even essential chemicals so often is, however, still unclear. Based on analytical and numerical calculations, we show that if the intracellular metabolism includes multibody (e.g., catalytic) reactions, leakage of essential metabolites can promote the leaking cell’s growth. This advantage is typical for most metabolic networks via “flux control” and “growth-dilution” mechanisms, as a general consequence of the balance between synthesis and growth-induced dilution with autocatalytic reactions. We further argue that this advantage may lead to a novel form of symbiosis among diverse cells.

We uncover a topological classification applicable to open fermionic systems governed by a general class of Lindblad master equations. These “quadratic Lindbladians” can be captured by a non-Hermitian single-particle matrix which describes internal dynamics as well as system-environment coupling. We show that this matrix must belong to one of ten non-Hermitian Bernard-LeClair symmetry classes which reduce to the Altland-Zirnbauer classes in the closed limit. The Lindblad spectrum admits a topological classification, which we show results in gapless edge excitations with finite lifetimes. Unlike previous studies of purely Hamiltonian or purely dissipative evolution, these topological edge modes are unconnected to the form of the steady state. We provide one-dimensional examples where the addition of dissipators can either preserve or destroy the closed classification of a model, highlighting the sensitivity of topological properties to details of the system-environment coupling.

Events in mesoscopic systems often take place at first-passage times, as is for instance the case for a colloidal particle that escapes a metastable state. An interesting question is how much work an external agent has done on a particle when it escapes a metastable state. We develop a thermodynamic theory for processes in mesoscopic systems that terminate at stopping times, which generalize first-passage times. This theory implies a thermodynamic bound, reminiscent of the second law of thermodynamics, for the work exerted by an external protocol on a mesoscopic system at a stopping time. As an illustration, we use this law to bound the work required to stretch a polymer to a certain length or to let a particle escape from a metastable state.

We show that the chiral Dirac and Majorana hinge modes in three-dimensional higher-order topological insulators (HOTIs) and superconductors (HOTSCs) can be gapped while preserving the protecting ${\mathsf{C}}_{2n}\mathcal{T}$ symmetry upon the introduction of non-Abelian surface topological order. In both cases, the topological order on a single side surface breaks time-reversal symmetry, but appears with its time-reversal conjugate on alternating sides in a ${\mathsf{C}}_{2n}\mathcal{T}$ preserving pattern. In the absence of the HOTI/HOTSC bulk, such a pattern necessarily involves gapless chiral modes on hinges between ${\mathsf{C}}_{2n}\mathcal{T}$-conjugate domains. However, using a combination of $K$-matrix and anyon condensation arguments, we show that on the boundary of a 3D HOTI/HOTSC these topological orders are fully gapped and hence “anomalous.” Our results suggest that new patterns of surface and hinge states can be engineered by selectively introducing topological order only on specific surfaces.

Echo chambers and opinion polarization recently quantified in several sociopolitical contexts and across different social media raise concerns on their potential impact on the spread of misinformation and on the openness of debates. Despite increasing efforts, the dynamics leading to the emergence of these phenomena remain unclear. We propose a model that introduces the dynamics of radicalization as a reinforcing mechanism driving the evolution to extreme opinions from moderate initial conditions. Inspired by empirical findings on social interaction dynamics, we consider agents characterized by heterogeneous activities and homophily. We show that the transition between a global consensus and emerging radicalized states is mostly governed by social influence and by the controversialness of the topic discussed. Compared with empirical data of polarized debates on Twitter, the model qualitatively reproduces the observed relation between users’ engagement and opinions, as well as opinion segregation in the interaction network. Our findings shed light on the mechanisms that may lie at the core of the emergence of echo chambers and polarization in social media.

Communication in a network generally takes place through a sequence of intermediate nodes connected by communication channels. In the standard theory of communication, it is assumed that the communication network is embedded in a classical spacetime, where the relative order of different nodes is well defined. In principle, a quantum theory of spacetime could allow the order of the intermediate points between sender and receiver to be in a coherent superposition. Here we experimentally realize a tabletop simulation of this exotic possibility on a photonic system, demonstrating high-fidelity transmission of quantum information over two noisy channels arranged in a superposition of two alternative causal orders.

Using a total of $11.0{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data with center-of-mass energies between 4.009 and 4.6 GeV and collected with the BESIII detector at BEPCII, we measure fifteen exclusive cross sections and effective form factors for the process $e^{+}{e}^{-}\to {\mathrm{\Xi }}^{-}{\overline{\mathrm{\Xi }}}^{+}$ by means of a single baryon-tag method. After performing a fit to the dressed cross section of $e^{+}{e}^{-}\to {\mathrm{\Xi }}^{-}{\overline{\mathrm{\Xi }}}^{+}$, no significant $\psi (4230)$ or $\psi (4260)$ resonance is observed in the ${\mathrm{\Xi }}^{-}{\overline{\mathrm{\Xi }}}^{+}$ final states, and upper limits at the 90% confidence level on ${\mathrm{\Gamma }}_{ee}\mathcal{B}$ for the processes $\psi (4230)/\psi (4260)\to {\mathrm{\Xi }}^{-}{\overline{\mathrm{\Xi }}}^{+}$ are determined. In addition, an excited $\mathrm{\Xi }$ baryon at $1820\mathrm{MeV}/c^2$ is observed with a statistical significance of $6.2–6.5\sigma$ by including the systematic uncertainty, and the mass and width are measured to be $M=(1825.5\pm 4.7\pm 4.7)\mathrm{MeV}/c^2$ and $\mathrm{\Gamma }=(17.0\pm 15.0\pm 7.9)\mathrm{MeV}$, which confirms the existence of the $J^P={\frac{3}{2}}^{-}$ state $\mathrm{\Xi }(1820)$.

Radioactive ${}^{129}\mathrm{Sb}$, which can be treated as a proton plus semimagic ${}^{128}\mathrm{Sn}$ core within the particle-core coupling scheme, was studied by Coulomb excitation. Reduced electric quadrupole transition probabilities, $B(E2)$, for the $2^{+}\otimes \pi g_{7/2}$ multiplet members and candidate $\pi d_{5/2}$ state were measured. The results indicate that the total electric quadrupole strength of ${}^{129}\mathrm{Sb}$ is a factor of 1.39(11) larger than the ${}^{128}\mathrm{Sn}$ core, which is in stark contrast to the expectations of the empirically successful particle-core coupling scheme. Shell-model calculations performed with two different sets of nucleon-nucleon interactions suggest that this enhanced collectivity is due to constructive quadrupole coherence in the wave functions stemming from the proton-neutron residual interactions, where adding one nucleon to a core near a double-shell closure can have a pronounced effect. The enhanced electric quadrupole strength is an early signal of the emerging nuclear collectivity that becomes dominant away from the shell closure.

Researchers routinely sense molecules by their infrared vibrational “fingerprint” absorption resonances. In addition, the dominant handedness of chiral molecules can be detected by circular dichroism (CD), the normalized difference between their optical response to incident left- and right- handed circularly polarized light. Here, we introduce a cavity composed of two parallel arrays of helicity-preserving silicon disks that allows one to enhance the CD signal by more than 2 orders of magnitude for a given molecule concentration and given thickness of the cell containing the molecules. The underlying principle is first-order diffraction into helicity-preserving modes with large transverse momentum and long lifetimes. In sharp contrast, in a conventional Fabry-Perot cavity, each reflection flips the handedness of light, leading to large intensity enhancements inside the cavity, yet to smaller CD signals than without the cavity.

We present an entanglement scheme for Rydberg atoms using the van der Waals interaction phase induced by Ramsey-type pulsed interactions. This scheme realizes not only controlled phase operations between atoms at a distance larger than Rydberg blockade distance, but also various counterintuitive entanglement examples, including two-atom entanglement in the presence of a closer third atom and $W$-state generation for three partially blockaded atoms. Experimental realization is conducted with single rubidium atoms in optical tweezer dipole traps, to demonstrate the proposed entanglement generations with an entanglement fidelity of $\mathcal{F}=0.59\pm 0.11$.

We present a scheme, based on the delocalized heralded addition of a single photon, to entangle two or more distinct field modes, each containing arbitrary light states. A high degree of entanglement can in principle endure light states of macroscopic intensities and is expected to be particularly robust against losses. We experimentally establish and measure significant entanglement between two identical weak laser pulses containing up to 60 photons each.

Bubble nucleation in water induced by boiling, gas supersaturation, or cavitation usually originates from preexisting gas cavities trapped into solid defects. Even though the destabilization of such gas pockets, called nuclei, has been extensively studied, little is known on the nuclei dynamic. Here, nuclei of water-particle suspensions are excited by acoustic cavitation, and their dynamic is investigated by monitoring the cavitation probability over several thousand pulses. A stable and reproducible cavitation probability emerges after a few thousand pulses and depends on particle concentration, hydrophobicity, and dissolved gas content. Our observations indicate that a stable nuclei distribution is reached at a later time, different from previously reported nuclei depletion in early time. This apparent paradox is elucidated by varying the excitation rate, where the cavitation activity increases with the repetition period, indicating that the nuclei depletion is balanced by spontaneous nucleation or growth of nuclei. A model of this self-supporting generation of nuclei suggests an origin from dissolved gas adsorption on surfaces. The method developed can be utilized to further understand the spontaneous formation and distribution of nanosized bubbles on heterogeneous surfaces.

Fast isochoric laser heating is a scheme to heat matter with a relativistic intensity ($>{10}^{18}\mathrm{W}/{\mathrm{cm}}^2$) laser pulse for producing an ultrahigh-energy-density (UHED) state. We have demonstrated an efficient fast isochoric heating of a compressed dense plasma core with a multipicosecond kilojoule-class petawatt laser and an assistance of externally applied kilotesla magnetic fields for guiding fast electrons to the dense plasma. A UHED state of 2.2 PPa is achieved experimentally with 4.6 kJ of total laser energy that is one order of magnitude lower than the energy used in the conventional implosion scheme. A two-dimensional particle-in-cell simulation confirmed that diffusive heating from a laser-plasma interaction zone to the dense plasma plays an essential role to the efficient creation of the UHED state.

Platinum ditelluride (${\mathrm{PtTe}}_2$), a type-II Dirac semimetal, remains semimetallic in ultrathin films down to just two triatomic layers (TLs) with a negative gap of $-0.36\mathrm{eV}$. Further reduction of the film thickness to a single TL induces a Lifshitz electronic transition to a semiconductor with a large positive gap of $+0.79\mathrm{eV}$. This transition is evidenced by experimental band structure mapping of films prepared by layer-resolved molecular beam epitaxy, and by comparing the data to first-principles calculations using a hybrid functional. The results demonstrate a novel electronic transition at the two-dimensional limit through film thickness control.

Tensor-network states (TNS) are a promising but numerically challenging tool for simulating two-dimensional (2D) quantum many-body problems. We introduce an isometric restriction of the TNS ansatz that allows for highly efficient contraction of the network. We consider two concrete applications using this ansatz. First, we show that a matrix-product state representation of a 2D quantum state can be iteratively transformed into an isometric 2D TNS. Second, we introduce a 2D version of the time-evolving block decimation algorithm for approximating of the ground state of a Hamiltonian as an isometric TNS—which we demonstrate for the 2D transverse field Ising model.

The mechanical response of packings of purely repulsive, spherical particles to athermal, quasistatic simple shear near jamming onset is highly nonlinear. Previous studies have shown that, at small pressure $p$, the ensemble-averaged static shear modulus $⟨G-G_0⟩$ scales with $p^{\alpha }$, where $\alpha \approx 1$, but above a characteristic pressure $p^{**}$, $⟨G-G_0⟩\sim p^{\beta }$, where $\beta \approx 0.5$. However, we find that the shear modulus $G^i$ for an individual packing typically decreases linearly with $p$ along a geometrical family where the contact network does not change. We resolve this discrepancy by showing that, while the shear modulus does decrease linearly within geometrical families, $⟨G⟩$ also depends on a contribution from discontinuous jumps in $⟨G⟩$ that occur at the transitions between geometrical families. For $p>p^{**}$, geometrical-family and rearrangement contributions to $⟨G⟩$ are of opposite signs and remain comparable for all system sizes. $⟨G⟩$ can be described by a scaling function that smoothly transitions between two power-law exponents $\alpha$ and $\beta$. We also demonstrate the phenomenon of compression unjamming, where a jammed packing unjams via isotropic compression.