We develop a Fokker-Planck theory of tissue growth with three types of cells (symmetrically dividing, asymmetrically dividing, and nondividing) as main agents to study the growth dynamics of human cerebral organoids. Fitting the theory to lineage tracing data obtained in next generation sequencing experiments, we show that the growth of cerebral organoids is a critical process. We derive analytical expressions describing the time evolution of clonal lineage sizes and show how power-law distributions arise in the limit of long times due to the vanishing of a characteristic growth scale. We discuss that the independence of critical growth on initial conditions could be biologically advantageous.

Single quantum emitters embedded in solid-state hosts are an ideal platform for realizing quantum information processors and quantum network nodes. Among the currently investigated candidates, ${\mathrm{Er}}^{3+}$ ions are particularly appealing due to their $1.5\mathrm{\mu }\mathrm{m}$ optical transition in the telecom band as well as their long spin coherence times. However, the long lifetimes of the excited state—generally in excess of 1 ms—along with the inhomogeneous broadening of the optical transition result in significant challenges. Photon emission rates are prohibitively small, and different emitters generally create photons with distinct spectra, thereby preventing multiphoton interference—a requirement for building large-scale, multinode quantum networks. Here we solve this challenge by demonstrating for the first time linear Stark tuning of the emission frequency of a single ${\mathrm{Er}}^{3+}$ ion. Our ions are embedded in a lithium niobate crystal and couple evanescently to a silicon nanophotonic crystal cavity that provides a strong increase of the measured decay rate. By applying an electric field along the crystal $c$ axis, we achieve a Stark tuning greater than the ion’s linewidth without changing the single-photon emission statistics of the ion. These results are a key step towards rare earth ion-based quantum networks.

Coating thermal noise is one of the dominant noise sources in current gravitational wave detectors and ultimately limits their ability to observe weaker or more distant astronomical sources. This Letter presents investigations of ${\mathrm{TiO}}_2$ mixed with ${\mathrm{SiO}}_2$ (${\mathrm{TiO}}_2:{\mathrm{SiO}}_2$) as a coating material. We find that, after heat treatment for 100 h at $850°\mathrm{C}$, thermal noise of a highly reflective coating comprising of ${\mathrm{TiO}}_2:{\mathrm{SiO}}_2$ and ${\mathrm{SiO}}_2$ reduces to 76% of the current levels in the Advanced LIGO and Advanced Virgo detectors—with potential for reaching 45%, if we assume the mechanical loss of state-of-the-art ${\mathrm{SiO}}_2$ layers. Furthermore, those coatings show low optical absorption of $<1\mathrm{ppm}$ and optical scattering of $\lesssim 5\mathrm{ppm}$. Notably, we still observe excellent optical and thermal noise performance following crystallization in the coatings. These results show the potential to meet the parameters required for the next upgrades of the Advanced LIGO and Advanced Virgo detectors.

The quest for complete observables in general relativity has been a long-standing open problem. We employ methods from descriptive set theory to show that no complete observable on rich enough collections of spacetimes is Borel definable. In fact, we show that it is consistent with the Zermelo-Fraenkel and dependent choice axioms that no complete observable for rich collections of spacetimes exists whatsoever. In a nutshell, this implies that the problem of observables is to “analysis” what the Delian problem was to “straightedge and compass.” Our results remain true even after restricting the space of solutions to vacuum solutions. In other words, the issue can be traced to the presence of local degrees of freedom. We discuss the next steps in a research program that aims to further uncover this novel connection between theoretical physics and descriptive set theory.

We introduce a modification to the standard expression for tree-level $CP$ violation in scattering processes at the LHC, which is important when the initial state is not self-conjugate. Based on that, we propose a generic and model-independent search strategy for probing tree-level $CP$ violation in inclusive multilepton signals. We then use TeV-scale 4-fermion operators of the form $tu\ell \ell$ and $tc\ell \ell$ with complex Wilson coefficients as an illustrative example and show that it may generate $\mathcal{O}(10\%)$ $CP$ asymmetries that should be accessible at the LHC with an integrated luminosity of $\mathcal{O}(1000){\mathrm{fb}}^{-1}$.

A flavor-tagged time-dependent angular analysis of the decay $B_s^0\to \varphi \varphi$ is performed using $pp$ collision data collected by the LHCb experiment at the center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$. The $CP$-violating phase and direct $CP$-violation parameter are measured to be ${\varphi }_s^{s\overline{s}s}=-0.042\pm 0.075\pm 0.009\mathrm{rad}$ and $|\lambda |=1.004\pm 0.030\pm 0.009$, respectively, assuming the same values for all polarization states of the $\varphi \varphi$ system. In these results, the first uncertainties are statistical and the second systematic. These parameters are also determined separately for each polarization state, showing no evidence for polarization dependence. The results are combined with previous LHCb measurements using $pp$ collisions at center-of-mass energies of 7 and 8 TeV, yielding ${\varphi }_s^{s\overline{s}s}=-0.074\pm 0.069\mathrm{rad}$ and $|\lambda |=1.009\pm 0.030$. This is the most precise study of time-dependent $CP$ violation in a penguin-dominated $B$ meson decay. The results are consistent with $CP$ symmetry and with the standard model predictions.

The first observation and study of two new baryonic structures in the final state ${\mathrm{\Xi }}_b^0{\pi }^{+}{\pi }^{-}$ and the confirmation of the ${\mathrm{\Xi }}_b{(6100)}^{-}$ state in the ${\mathrm{\Xi }}_b^{-}{\pi }^{+}{\pi }^{-}$ decay mode are reported using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. In addition, the properties of the known ${\mathrm{\Xi }}_b^{*0}$, ${\mathrm{\Xi }}_b^{\prime -}$ and ${\mathrm{\Xi }}_b^{*-}$ resonances are measured with improved precision. The new decay mode of the ${\mathrm{\Xi }}_b^0$ baryon to the ${\mathrm{\Xi }}_c^{+}$ ${\pi }^{-}$ ${\pi }^{+}$ ${\pi }^{-}$ final state is observed and exploited for the first time in these measurements.

This letter presents a measurement of the nuclear modification factor of large-radius jets in $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ $\mathrm{Pb}+\mathrm{Pb}$ collisions by the ATLAS experiment. The measurement is performed using $1.72{\mathrm{nb}}^{-1}$ and $257{\mathrm{pb}}^{-1}$ of $\mathrm{Pb}+\mathrm{Pb}$ and $pp$ data, respectively. The large-radius jets are reconstructed with the anti-$k_t$ algorithm using a radius parameter of $R=1.0$, by reclustering anti-$k_t$ $R=0.2$ jets, and are measured over the transverse momentum ($p_T$) kinematic range of $158<p_T<1000\mathrm{GeV}$ and absolute pseudorapidity $|y|<2.0$. The large-radius jet constituents are further reclustered using the $k_t$ algorithm in order to obtain the splitting parameters, $\sqrt{d_{12}}$ and $\mathrm{\Delta }{R}_{12}$, which characterize the transverse momentum scale and angular separation for the hardest splitting in the jet, respectively. The nuclear modification factor, $R_{AA}$, obtained by comparing the $\mathrm{Pb}+\mathrm{Pb}$ jet yields to those in $pp$ collisions, is measured as a function of jet transverse momentum ($p_T$) and $\sqrt{d_{12}}$ or $\mathrm{\Delta }{R}_{12}$. A significant difference in the quenching of large-radius jets having single subjet and those with more complex substructure is observed. Systematic comparison of jet suppression in terms of $R_{AA}$ for different jet definitions is also provided. Presented results support the hypothesis that jets with hard internal splittings lose more energy through quenching and provide a new perspective for understanding the role of jet structure in jet suppression.

Nonclassical states of light, such as number-squeezed light, with fluctuations below the classical shot noise level, have important uses in metrology, communication, quantum information processing, and quantum simulation. However, generating these nonclassical states of light, especially with high intensity and a high degree of squeezing, is challenging. To address this problem, we introduce a new concept which uses gain to generate intense sub-Poissonian light at optical frequencies. It exploits a strongly nonlinear gain for photons which arises from a combination of frequency-dependent gain and Kerr nonlinearity. In this laser architecture, the interaction between the gain medium and Kerr nonlinearity suppresses the spontaneous emission at high photon number states, leading to a strong “negative feedback” that suppresses photon-number fluctuations. We discuss realistic implementations of this concept based on the use of solid-state gain media in laser cavities with Kerr nonlinear materials, showing how 90% squeezing of photon number fluctuations below the shot noise level can be realized.

The theory of topological phases of matter predicts invariants protected only by crystalline symmetry, yet it has been unclear how to extract these from microscopic calculations in general. Here, we show how to extract a set of many-body invariants $\{{\mathrm{\Theta }}_o^{\pm }\}$, where $o$ is a high symmetry point, from partial rotations in $(2+1)\mathrm{D}$ invertible fermionic states. Our results apply in the presence of magnetic field and Chern number $C\ne 0$, in contrast to previous work. $\{{\mathrm{\Theta }}_o^{\pm }\}$ together with $C$, chiral central charge $c_{-}$, and filling $\nu$ provide a complete many-body characterization of the topological state with symmetry group $G=U(1){\times }_{\varphi }[{\mathbb{Z}}^2⋊{\mathbb{Z}}_M]$. Moreover, all these many-body invariants can be obtained from a single bulk ground state, without inserting additional defects. We perform numerical computations on the square lattice Hofstadter model. Remarkably, these match calculations from conformal and topological field theory, where $G$-crossed modular $S$, $T$ matrices of symmetry defects play a crucial role. Our results provide additional colorings of Hofstadter’s butterfly, extending recently discovered colorings by the discrete shift and quantized charge polarization.

Phonons and magnons are engineered by periodic potential landscapes in phononic and magnonic crystals, and their combined studies may enable valley phonon transport tunable by the magnetic field. Through nonreciprocal surface acoustic wave transmission, we demonstrate valley-selective phonon-magnon scattering in magnetoelastic superlattices. The lattice symmetry and the out-of-plane magnetization component control the sign of nonreciprocity. The phonons in the valleys play a crucial role in generating nonreciprocal transmission by inducing circularly polarized strains that couple with the magnons. The transmission spectra show a nonreciprocity peak near a transmission gap, matching the phononic band structure. Our results open the way for manipulating valley phonon transport through periodically varying magnon-phonon coupling.

The rainbow trapping phenomenon of graded metamaterials can be combined with the fractal spectra of quasiperiodic waveguides to give a metamaterial that performs fractal rainbow trapping. This is achieved through a graded cut-and-project algorithm that yields a geometry for which the effective projection angle is graded along its length. As a result, the fractal structure of local band gaps varies with position, leading to broadband “fractal” rainbow trapping. We demonstrate this principle by designing an acoustic waveguide, which is characterised using theory, simulation and experiments.

In order to unitarily evolve a quantum system, an agent requires knowledge of time, a parameter that no physical clock can ever perfectly characterize. In this Letter, we study how limitations on acquiring knowledge of time impact controlled quantum operations in different paradigms. We show that the quality of timekeeping an agent has access to limits the circuit complexity they are able to achieve within circuit-based quantum computation. We do this by deriving an upper bound on the average gate fidelity achievable under imperfect timekeeping for a general class of random circuits. Another area where quantum control is relevant is quantum thermodynamics. In that context, we show that cooling a qubit can be achieved using a timer of arbitrary quality for control: timekeeping error only impacts the rate of cooling and not the achievable temperature. Our analysis combines techniques from the study of autonomous quantum clocks and the theory of quantum channels to understand the effect of imperfect timekeeping on controlled quantum dynamics.

Considering non-Hermitian systems implemented by utilizing enlarged quantum systems, we determine the fundamental limits for the sensitivity of non-Hermitian sensors from the perspective of quantum information. We prove that non-Hermitian sensors do not outperform their Hermitian counterparts (directly couple to the parameter) in the performance of sensitivity, due to the invariance of the quantum information about the parameter. By scrutinizing two concrete non-Hermitian sensing proposals, which are implemented using full quantum systems, we demonstrate that the sensitivity of these sensors is in agreement with our predictions. Our theory offers a comprehensive and model-independent framework for understanding the fundamental limits of non-Hermitian quantum sensors and builds the bridge over the gap between non-Hermitian physics and quantum metrology.

Despite impressive advances in the ${\mathrm{AdS}}_3/{\mathrm{CFT}}_2$ correspondence, the setup involving Ramond-Ramond backgrounds, which is related to the D1–D5 system of branes, remained relatively poorly understood. We use the mirror thermodynamic Bethe ansatz (TBA) equations recently constructed by Frolov and Sfondrini to study the spectrum of pure Ramond-Ramond ${\mathrm{AdS}}_3\times {\text{S}}^3\times {\text{T}}^4$ strings. We find that the leading-order contribution to the anomalous dimensions at small tension is due to the gapless world-sheet excitations, i.e., to the ${\text{T}}^4$ bosons and their superpartners, whose interactions are nontrivial.

We construct a representation for the first anti–de Sitter curvature correction to the Virasoro-Shapiro amplitude, as an integral over the Riemann sphere. The integrand is that of the Virasoro-Shapiro amplitude in flat space, with the extra insertion of a linear combination of single-valued multiple polylogarithms of weight three. The integral representation implies an elegant, manifestly single-valued representation for the Wilson coefficients of the low-energy expansion.

Molecular simulations discover a new mode of dynamic wetting that manifests itself in the very earliest stages of spreading, after a droplet contacts a solid. The observed mode is a “rolling” type of motion, characterized by a contact angle lower than the classically assumed value of 180°, and precedes the conventional “sliding” mode of spreading. This motivates the development of a novel continuum framework that captures all modes of motion, allows the dominant physical mechanisms to be understood, and permits the study of larger droplets.