Here we describe how, utilizing a time-dependent optomechanical interaction, a mechanical probe can provide an amplified measurement of the virtual photons dressing the quantum ground state of an ultrastrongly coupled light-matter system. We calculate the thermal noise tolerated by this measurement scheme and discuss an experimental setup in which it could be realized.

In excitable media, chaotic dynamics governed by spiral or scroll waves is often not persistent but transient. Using extensive simulations employing different mathematical models we identify a specific type-II supertransient by an exponential increase of transient lifetimes with the system size in 2D and an investigation of the dynamics (number and lifetime of spiral waves, Kaplan-Yorke dimension). In 3D, simulations exhibit an increase of transient lifetimes and filament lengths only above a critical thickness. Finally, potential implications for understanding cardiac arrhythmias are discussed.

The Adam-Gibbs (AG) relation connects the dynamics of a glass-forming liquid to its thermodynamics via the configurational entropy and is of fundamental importance in descriptions of glassy behavior. The breakdown of the Stokes-Einstein relation (SEB) between the diffusion coefficient and the viscosity (or structural relaxation times) in glass formers raises the question as to which dynamical quantity the AG relation describes. By performing molecular dynamics simulations, we show that the AG relation is valid over the widest temperature range for the diffusion coefficient and not for the viscosity or relaxation times. Studying relaxation times defined at a given wavelength, we find that SEB and the deviation from the AG relation occur below a temperature at which the correlation length of dynamical heterogeneity equals the wavelength probed.

We investigate the self-dissociation of water that is nanoconfined between the sheets of a realistic layered mineral, FeS mackinawite, as well as between Lennard-Jones walls via ab initio simulations. By comparing it with the same reaction in bulk water under various thermodynamic conditions, we show that such strong two-dimensional confinement between hard surfaces greatly enhances the self-dissociation process of water—thus increasing its ionic product $K_w$ due to nanoconfinement. In addition to providing free energies, we analyze in detail the underlying dielectric properties in terms of dipole moment distributions, and thus the polarity of the liquid, as well as local polarization fluctuations as quantified by dielectric tensor profiles perpendicular to the lamella.

We report the first 3D spin liquid state of isotropic organic spins. Structural analysis, and magnetic and heat–capacity measurements were carried out for a chiral organic radical salt, ${(\mathrm{TBA})}_{1.5}[(-)\text{−}\mathrm{NDI}\text{−}\mathrm{\Delta }]$ (TBA denotes tetrabutylammonium and NDI denotes naphthalene diimide), in which $(-)\text{−}\mathrm{NDI}\text{−}\mathrm{\Delta }$ forms a $K_4$ structure due to its triangular molecular structure and an intermolecular $\pi \text{−}\pi$ overlap between the NDI moieties. This lattice was identical to the hyperkagome lattice of $S=1/2$ Mott dimers, and should exhibit 3D spin frustration. In fact, even though the high-temperature magnetic susceptibility followed the Curie-Weiss law with a negative Weiss constant of $\theta =-15\mathrm{K}$, the low-temperature magnetic measurements revealed no long-range magnetic ordering down to 70 mK, and suggested the presence of a spin liquid state with a large residual paramagnetism ${\chi }_0$ of $8.5\times {10}^{-6}\mathrm{emu}{\mathrm{g}}^{-1}$ at the absolute zero temperature. This was supported by the ${}^{14}\mathrm{N}$ NMR measurements down to 0.38 K. Further, the low-temperature heat capacities $c_p$ down to 68 mK clearly indicated the presence of $c_p$ for the spin liquid state, which can be fitted to the power law of $T^{0.62}$ in the wide temperature range 0.07–4.5 K.

We investigate the polarization selection rules of sharp zero-phonon lines (ZPLs) from isolated defects in hexagonal boron nitride (HBN) and compare our findings with the predictions of a Huang-Rhys model involving two electronic states. Our survey, which spans the spectral range $\sim 550–740\mathrm{nm}$, reveals that, in disagreement with a two-level model, the absorption and emission dipoles are often misaligned. We relate the dipole misalignment angle ($\mathrm{\Delta }\theta$) of a ZPL to its energy shift from the excitation energy ($\mathrm{\Delta }E$) and find that $\mathrm{\Delta }\theta \approx 0°$ when $\mathrm{\Delta }E$ corresponds to an allowed HBN phonon frequency and that $0°\le \mathrm{\Delta }\theta \le 90°$ when $\mathrm{\Delta }E$ exceeds the maximum allowed HBN phonon frequency. Consequently, a two-level Huang-Rhys model succeeds at describing excitations mediated by the creation of one optical phonon but fails at describing excitations that require the creation of multiple phonons. We propose that direct excitations requiring the creation of multiple phonons are inefficient due to the low Huang-Rhys factors in HBN and that these ZPLs are instead excited indirectly via an intermediate electronic state. This hypothesis is corroborated by polarization measurements of an individual ZPL excited with two distinct wavelengths that indicate a single ZPL may be excited by multiple mechanisms. These findings provide new insight on the nature of the optical cycle of novel defect-based single-photon sources in HBN.

The nanodomain pattern in ferroelectric-dielectric superlattices transforms to a uniform polarization state under above-band-gap optical excitation. $X$-ray scattering reveals a disappearance of domain diffuse scattering and an expansion of the lattice. The reappearance of the domain pattern occurs over a period of seconds at room temperature, suggesting a transformation mechanism in which charge carriers in long-lived trap states screen the depolarization field. A Landau-Ginzburg-Devonshire model predicts changes in lattice parameter and a critical carrier concentration for the transformation.

Azobenzene-embedded liquid crystal polymers can undergo mechanical deformation in response to ultraviolet (UV) light. The natural rodlike trans state azobenzene absorbs UV light and isomerizes to a bentlike cis state, which disturbs the order of the polymer network, leading to an anisotropic deformation. The current consensus is that the magnitude of the photoinduced deformation is related to the statistical building up of molecules in the cis state. However, a recent experimental study [Liu and Broer, Nat. Commun. 6 8334 (2015).] shows that a drastic (fourfold) increase of the photoinduced deformation can be generated by exposing the samples simultaneously to 365 nm (UV) and 455 nm (visible) light. To elucidate the physical mechanism that drives this increase, we develop a two-light attenuation model and an optomechanical constitutive relation that not only accounts for the statistical accumulation of cis azobenzenes, but also for the dynamic trans-cis-trans oscillatory isomerization process. Our experimentally calibrated model predicts that the optimal single-wavelength exposure is 395 nm light, a pronounced shift towards the visible spectrum. In addition, we identify a range of optimal combinations of two-wavelength lights that generate a favorable response for a given amount of injected energy. Our model provides mechanistic insight into the different (multi)wavelength exposures used in experiments and, at the same time, opens new avenues towards enhanced, multiwavelength optomechanical behavior.

We find that embedded active colloids increase the ensemble-averaged mean squared displacement of particles in otherwise passively fluctuating fractal cluster gels. The enhancement in dynamics occurs by a mechanism in which the active colloids contribute to the average dynamics both directly through their own active motion and indirectly through their excitation of neighboring passive colloids in the fractal network. Fractal cluster gels are synthesized by addition of magnesium chloride to an initially stable suspension of $1.0\mu \mathrm{m}$ polystyrene colloids in which a dilute concentration of platinum coated Janus colloids has been dispersed. The Janus colloids are thereby incorporated into the fractal network. We measure the ensemble-averaged mean squared displacement of all colloids in the gel before and after the addition of hydrogen peroxide, a fuel that drives diffusiophoretic motion of the Janus particles. The gel mean squared displacement increases by up to a factor of 3 for an active to passive particle ratio of $1:20$ and inputted active energy—defined based on the hydrogen peroxide’s effect on colloid swim speed and run length—that is up to 9.5 times thermal energy, on a per particle basis. We model the enhancement in gel particle dynamics as the sum of a direct contribution from the displacement of the Janus particles themselves and an indirect contribution from the strain field that the active colloids induce in the surrounding passive particles.

We present the ground and excited state spectra of ${\mathrm{\Omega }}_c^0$ baryons with spin up to $7/2$ from lattice quantum chromodynamics with dynamical quark fields. Based on our lattice results, we predict the quantum numbers of five ${\mathrm{\Omega }}_c^0$ baryons, which have recently been observed by the LHCb Collaboration. Our results strongly indicate that the observed states ${\mathrm{\Omega }}_c(3000{)}^0$ and ${\mathrm{\Omega }}_c(3050{)}^0$ have spin-parity $J^P=1/2^{-}$, the states ${\mathrm{\Omega }}_c(3066{)}^0$ and ${\mathrm{\Omega }}_c(3090{)}^0$ have $J^P=3/2^{-}$, whereas ${\mathrm{\Omega }}_c(3119{)}^0$ is possibly a $5/2^{-}$ state.

We demonstrate that the magnetic nano-Skyrmion lattice on the Fe monolayer on Ir(111) and the positions of the Fe atoms can be resolved simultaneously using magnetic exchange force microscopy. Thus, the relation between magnetic and atomic structure can be determined straightforwardly by evaluating the Fourier transformation of the real space image data. We further show that the magnetic contrast can be mapped on a Heisenberg-like magnetic interaction between tip and sample spins. Since our imaging technique is based on measuring forces, our observation paves the way to study Skyrmions or other complex spin textures on insulating sample systems with atomic resolution.

We generalize the hierarchy construction to generic $2+1\mathrm{D}$ topological orders (which can be non-Abelian) by condensing Abelian anyons in one topological order to construct a new one. We show that such construction is reversible and leads to a new equivalence relation between topological orders. We refer to the corresponding equivalence class (the orbit of the hierarchy construction) as “the non-Abelian family.” Each non-Abelian family has one or a few root topological orders with the smallest number of anyon types. All the Abelian topological orders belong to the trivial non-Abelian family whose root is the trivial topological order. We show that Abelian anyons in root topological orders must be bosons or fermions with trivial mutual statistics between them. The classification of topological orders is then greatly simplified, by focusing on the roots of each family: those roots are given by non-Abelian modular extensions of representation categories of Abelian groups.

The surface code is a many-body quantum system, and simulating it in generic conditions is computationally hard. While the surface code is believed to have a high threshold, the numerical simulations used to establish this threshold are based on simplified noise models. We present a tensor-network algorithm for simulating error correction with the surface code under arbitrary local noise. We use this algorithm to study the threshold and the subthreshold behavior of the amplitude damping and systematic rotation channels. We also compare these results to those obtained by making standard approximations to the noise models.

We investigate a cavity quantum electrodynamic effect, where the alignment of two-dimensional freely rotating optical dipoles is driven by their collective coupling to the cavity field. By exploiting the formal equivalence of a set of rotating dipoles with a polymer we calculate the partition function of the coupled light-matter system and demonstrate that it exhibits a second order phase transition between a bunched state of isotropic orientations and a stretched one with all the dipoles aligned. Such a transition manifests itself as an intensity-dependent shift of the polariton mode resonance. Our work, lying at the crossroad between cavity quantum electrodynamics and quantum optomechanics, is a step forward in the ongoing quest to understand how strong coupling can be exploited to influence matter internal degrees of freedom.

Evaporating droplets are known to show complex motion that has conventionally been explained by the Marangoni effect (flow induced by the gradient of surface tension). Here, we show that the droplet motion can be induced even in the absence of the Marangoni effect due to the gradient of the evaporation rate. We derive an equation for the velocity of a droplet subject to the nonuniform evaporation rate and nonuniform surface tension placed on an inert substrate, where the wettability is uniform and unchanged. The equation explains the previously observed attraction-repulsion-chasing behaviors of evaporating droplets.