Essential for building quantum networks over remote independent nodes, the indistinguishability of photons has been extensively studied by observing the coincidence dip in the Hong-Ou-Mandel interferometer. However, indistinguishability is not limited to the same type of bosons. For the first time, we hereby observe quantum interference between flying photons and a single quantum of stored atomic coherence (magnon) in an atom-light beam splitter interface. We demonstrate that the Hermiticity of this interface determines the type of quantum interference between photons and magnons. Consequently, not only the bunching behavior that characterizes bosons is observed, but counterintuitively, fermionlike antibunching as well. The hybrid nature of the demonstrated magnon-photon quantum interface can be applied to versatile quantum memory platforms, and can lead to fundamentally different photon distributions from those occurring in boson sampling.

While the heat transfer and the flow dynamics in a cylindrical Rayleigh-Bénard (RB) cell are rather independent of the aspect ratio $\mathrm{\Gamma }$ (diameter/height) for large $\mathrm{\Gamma }$, a small-$\mathrm{\Gamma }$ cell considerably stabilizes the flow and thus affects the heat transfer. Here, we first theoretically and numerically show that the critical Rayleigh number for the onset of convection at given $\mathrm{\Gamma }$ follows ${\mathrm{Ra}}_{c,\mathrm{\Gamma }}\sim {\mathrm{Ra}}_{c,\infty }(1+C{\mathrm{\Gamma }}^{-2}{)}^2$, with $C\lesssim 1.49$ for Oberbeck-Boussinesq (OB) conditions. We then show that, in a broad aspect ratio range $(1/32)\le \mathrm{\Gamma }\le 32$, the rescaling $\mathrm{Ra}\to {\mathrm{Ra}}_{\ell }\equiv \mathrm{Ra}[{\mathrm{\Gamma }}^2/(C+{\mathrm{\Gamma }}^2){]}^{3/2}$ collapses various OB numerical and almost-OB experimental heat transport data $\mathrm{Nu}(\mathrm{Ra},\mathrm{\Gamma })$. Our findings predict the $\mathrm{\Gamma }$ dependence of the onset of the ultimate regime ${\mathrm{Ra}}_{u,\mathrm{\Gamma }}\sim [{\mathrm{\Gamma }}^2/(C+{\mathrm{\Gamma }}^2){]}^{-3/2}$ in the OB case. This prediction is consistent with almost-OB experimental results (which only exist for $\mathrm{\Gamma }=1$, $1/2$, and $1/3$) for the transition in OB RB convection and explains why, in small-$\mathrm{\Gamma }$ cells, much larger Ra (namely, by a factor ${\mathrm{\Gamma }}^{-3}$) must be achieved to observe the ultimate regime.

Nanoscale surface curvatures, either convex or concave, strongly influence the charging behavior of supercapacitors. Rationalizing individual influences of electrode atoms to the capacitance is possible by interpreting distinct elements of the charge-charge covariance matrix derived from individual charge variations of the electrode atoms. An ionic liquid solvated in acetonitrile and confined between two electrodes, each consisting of three undulated graphene layers, serves as a demonstrator to illustrate pronounced and nontrivial features of the capacitance with respect to the electrode curvature. In addition, the applied voltage determines whether a convex or concave surface contributes to increased capacitance. While at lower voltages capacitance variations are in general correlated with ion number density variations in the double layer formed in the concave region of the electrode, for certain electrode designs a surprisingly strong contribution of the convex part to the differential capacitance is found both at higher and lower voltages.

How irreversibility arises in a universe with time-reversal symmetric laws is a central problem in physics. In this Letter, we discuss a radically different take on the emergence of irreversibility, adopting the recently proposed constructor theory framework. Irreversibility is expressed as the requirement that a task is possible, while its inverse is not. We prove the compatibility of such irreversibility with quantum theory’s time-reversal symmetric laws, using a dynamical model based on the universal quantum homogenizer. We also test the physical realizability of this model by means of an experimental demonstration with high-quality single-photon qubits.

In two-dimensional Floquet systems, many-body localized dynamics in the bulk may give rise to a chaotic evolution at the one-dimensional edges that is characterized by a nonzero chiral topological index. Such anomalous dynamics is qualitatively different from local-Hamiltonian evolution. Here we show how the presence of a nonzero index affects entanglement generation and the spreading of local operators, focusing on the coarse-grained description of generic systems. We tackle this problem by analyzing exactly solvable models of random quantum cellular automata (QCA) that generalize random circuits. We find that a nonzero index leads to asymmetric butterfly velocities with different diffusive broadening of the light cones and to a modification of the order relations between the butterfly and entanglement velocities. We propose that these results can be understood via a generalization of the recently introduced entanglement membrane theory, by allowing for a spacetime entropy current, which in the case of a generic QCA is fixed by the index. We work out the implications of this current on the entanglement “membrane tension” and show that the results for random QCA are recovered by identifying the topological index with a background velocity for the coarse-grained entanglement dynamics.

The formation of ultrarare supermassive black holes (SMBHs), with masses of $\mathcal{O}({10}^9{M}_{\odot })$, in the first billion years of the Universe remains an open question in astrophysics. At the same time, ultralight dark matter (DM) with mass in the vicinity of $\mathcal{O}({10}^{-20}\mathrm{eV})$ has been motivated by small scale DM distributions. Though this type of DM is constrained by various astrophysical considerations, certain observations could be pointing to modest evidence for it. We present a model with a confining first order phase transition at $\sim 10\mathrm{keV}$ temperatures, facilitating production of $\mathcal{O}(10^9{M}_{\odot })$ primordial SMBHs. Such a phase transition can also naturally lead to the implied mass for a motivated ultralight axion DM candidate, suggesting that SMBHs and ultralight DM may be two sides of the same cosmic coin. We consider constraints and avenues to discovery from superradiance and a modification to $N_{\mathrm{eff}}$. On general grounds, we also expect primordial gravitational waves—from the assumed first order phase transition—characterized by frequencies of $\mathcal{O}({10}^{-12}–{10}^{-9}\mathrm{Hz})$. This frequency regime is largely uncharted, but could be accessible to pulsar timing arrays if the primordial gravitational waves are at the higher end of this frequency range, as could be the case in our assumed confining phase transition.

We present a new infinite class of gravitational observables in asymptotically anti–de Sitter space living on codimension-one slices of the geometry, the most famous of which is the volume of the maximal slice. We show that these observables display universal features for the thermofield-double state: they grow linearly in time at late times and reproduce the switchback effect in shock wave geometries. We argue that any member of this class of observables is an equally viable candidate as the extremal volume for a gravitational dual of complexity.

One of the outstanding problems in physics is to explain the baryon–antibaryon asymmetry observed in nature. According to the well-known Sakharov criterion for explaining the observed asymmetry, it is essential that $CP$ violation exist. Even though $CP$ violation has been observed in meson decays and is an integral part of the standard model (SM), measurements in meson decays indicate that $CP$ violation in the SM is insufficient to explain the observed baryon–antibaryon asymmetry. The SM predicts the existence of yet to be observed $CP$ violation in baryon decays. A critical test of the SM requires that $CP$ violation be measured in baryon decays as well, in order to verify that it agrees with the measurement using meson decays. In this Letter we propose a new method to measure the $CP$ violating phase in $b$ baryons, using interference arising implicitly due to Bose symmetry considerations of the decaying amplitudes.

We search for a light Higgs boson ($A^0$) decaying into a ${\tau }^{+}{\tau }^{-}$ or ${\mu }^{+}{\mu }^{-}$ pair in the radiative decays of $\mathrm{\Upsilon }(1S)$. The production of $\mathrm{\Upsilon }(1S)$ mesons is tagged by $\mathrm{\Upsilon }(2S)\to {\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }(1S)$ transitions, using $158\times {10}^6$ $\mathrm{\Upsilon }(2S)$ events accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant $A^0$ signals in the mass range from the ${\tau }^{+}{\tau }^{-}$ or ${\mu }^{+}{\mu }^{-}$ threshold to $9.2\mathrm{GeV}/c^2$ are observed. We set the upper limits at 90% credibility level (C.L.) on the product branching fractions for $\mathrm{\Upsilon }(1S)\to \gamma A^0$ and $A^0\to {\tau }^{+}{\tau }^{-}$ varying from $3.8\times {10}^{-6}$ to $1.5\times {10}^{-4}$. Our results represent an approximately twofold improvement on the current world best upper limits for the $\mathrm{\Upsilon }(1S)\to \gamma A^0(\to {\tau }^{+}{\tau }^{-})$ production. For $A^0\to {\mu }^{+}{\mu }^{-}$, the upper limits on the product branching fractions for $\mathrm{\Upsilon }(1S)\to \gamma A^0$ and $A^0\to {\mu }^{+}{\mu }^{-}$ are at the same level as the world average limits, and vary from $3.1\times {10}^{-7}$ to $1.6\times {10}^{-5}$. The upper limits at 90% credibility level on the Yukawa coupling $f_{\mathrm{\Upsilon }(1S)}$ and mixing angle $\sin {\theta }_{A^0}$ are also given.

Measurements of the inclusive and differential fiducial cross sections of the Higgs boson are presented, using the $\tau$ lepton decay channel. The differential cross sections are measured as functions of the Higgs boson transverse momentum, jet multiplicity, and transverse momentum of the leading jet in the event, if any. The analysis is performed using proton-proton collision data collected with the CMS detector at the LHC at a center-of-mass energy of $13\mathrm{TeV}$ and corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. These are the first differential measurements of the Higgs boson cross section in the final state of two $\tau$ leptons. In final states with a large jet multiplicity or with a Lorentz-boosted Higgs boson, these measurements constitute a significant improvement over measurements performed in other final states.

We detail our discovery of a chiral enhancement in the production cross sections of massive spin-2 gravitons, below the electroweak symmetry breaking scale, that makes them ideal dark matter candidates for the freeze-in mechanism. The result is independent of the physics at high scales and points toward masses in the keV–MeV range. The graviton is, therefore, a sub-MeV dark matter particle, as favored by the small scale galaxy structures. We apply the novel calculation to a Randall-Sundrum model with multiple branes, showing a significant parameter space where the first two massive gravitons saturate the dark matter relic density.

We examine the possibility that dark matter (DM) consists of a gapped continuum, rather than ordinary particles. A weakly interacting continuum (WIC) model, coupled to the standard model via a $Z$ portal, provides an explicit realization of this idea. The thermal DM relic density in this model is naturally consistent with observations, providing a continuum counterpart of the “WIMP miracle.” Direct detection cross sections are strongly suppressed compared to ordinary $Z$-portal WIMP, thanks to a unique effect of the continuum kinematics. Continuum DM states decay throughout the history of the Universe, and observations of cosmic microwave background place constraints on potential late decays. Production of WICs at colliders can provide a striking cascade-decay signature. We show that a simple $Z$-portal WIC model provides a fully viable DM candidate consistent with all current experimental constraints.

The interpretation of the emergent collective behavior of atomic nuclei in terms of deformed intrinsic shapes is at the heart of our understanding of the rich phenomenology of their structure, ranging from nuclear energy to astrophysical applications across a vast spectrum of energy scales. A new window into the deformation of nuclei has been recently opened with the realization that nuclear collision experiments performed at high-energy colliders, such as the CERN Large Hadron Collider (LHC), enable experimenters to identify the relative orientation of the colliding ions in a way that magnifies the manifestations of their intrinsic deformation. Here we apply this technique to LHC data on collisions of ${}^{129}\mathrm{Xe}$ nuclei to exhibit the first evidence of nonaxiality in the ground state of ions collided at high energy. We predict that the low-energy structure of ${}^{129}\mathrm{Xe}$ is triaxial (a spheroid with three unequal axes) and show that such deformation can be determined from high-energy data. This result demonstrates the unique capabilities of precision collider machines such as the LHC as new means to perform imaging of the collective structure of atomic nuclei.

We propose and demonstrate the appearance of an effective attractive three-body interaction in coherently driven two-component Bose-Einstein condensates. It originates from the spinor degree of freedom that is affected by a two-body mean-field shift of the driven transition frequency. Importantly, its strength can be controlled with the Rabi-coupling strength and it does not come with additional losses. In the experiment, the three-body interactions are adjusted to play a predominant role in the equation of state of a cigar-shaped trapped condensate. This is confirmed through two striking observations: a downshift of the radial breathing mode frequency and the radial collapses for positive values of the dressed-state scattering length.

We show that an open quantum system in a non-Markovian environment can reach steady states that it cannot reach in a Markovian environment. As these steady states are unique for the non-Markovian regime, they could offer a simple way of detecting non-Markovianity, as no information about the system’s transient dynamics is necessary. In particular, we study a driven two-level system (TLS) in a semi-infinite waveguide. Once the waveguide has been traced out, the TLS sees an environment with a distinct memory time. The memory time enters the equations as a time delay that can be varied to compare a Markovian to a non-Markovian environment. We find that some non-Markovian states show exotic behaviors such as population inversion and steady-state coherence beyond $1/\sqrt{8}$, neither of which is possible for a driven TLS in the Markovian regime, where the time delay is neglected. Additionally, we show how the coherence of quantum interference is affected by time delays in a driven system by extracting the effective Purcell-modified decay rate of a TLS in front of a mirror.

We propose an all-optical approach to achieve optical nonreciprocity on a chip by quantum squeezing one of two coupled resonator modes. By parametric pumping a ${\chi }^{(2)}$-nonlinear resonator unidirectionally with a classical coherent field, we squeeze the resonator mode in a selective direction due to the phase-matching condition, and induce a chiral photon interaction between two resonators. Based on this chiral interresonator coupling, we achieve an all-optical diode and a three-port quasicirculator. By applying a second squeezed-vacuum field to the squeezed resonator mode, our nonreciprocal device also works for single-photon pulses. We obtain an isolation ratio of $>40\mathrm{dB}$ for the diode and fidelity of $>98\%$ for the quasicirculator, and insertion loss of $<1\mathrm{dB}$ for both. We also show that nonreciprocal transmission of strong light can be switched on and off by a relative weak pump light. This achievement implies a nonreciprocal optical transistor. Our protocol opens up a new route to achieve integrable all-optical nonreciprocal devices permitting chip-compatible optical isolation and nonreciporcal quantum information processing.

We reveal that finite-size solid acoustic resonators can support genuine bound states in the continuum (BICs) completely localized inside the resonator. The developed theory provides the multipole classification of such BICs in the resonators of various shapes. It is shown how breaking of the resonator’s symmetry turns BICs into quasi-BICs manifesting themselves in the scattering spectra as high-$Q$ Fano resonances. We believe that the revealed novel states will push the performance limits of acoustic devices and will serve as high-$Q$ building blocks for acoustic sensors, antennas, and topological acoustic structures.

A new type of self-sustained divertor oscillation is discovered in the Large Helical Device stellarator, where the peripheral plasma is detached from material diverters by means of externally applied perturbation fields. The divertor oscillation is found to be a self-regulation of an isolated magnetic field structure (the magnetic island) width induced by a drastic change in a poloidal inhomogeneity of the plasma radiation across the detachment-attachment transitions. A predator-prey model between the magnetic island width and a self-generated local plasma current (the bootstrap current) is introduced to describe the divertor oscillation, which successfully reproduces the experimental observations.

The plasma exit flow speed at the sheath entrance is constrained by the Bohm criterion. The so-called Bohm speed regulates the plasma particle and power exhaust fluxes to the wall, and it is commonly deployed as a boundary condition to exclude the sheath region in quasineutral plasma modeling. Here the Bohm criterion analysis is performed in the intermediate plasma regime away from the previously known limiting cases of adiabatic laws and the asymptotic limit of infinitesimal Debye length in a finite-size system, using the transport equations of an anisotropic plasma. The resulting Bohm speed has explicit dependence on local plasma heat flux, temperature isotropization, and thermal force. Comparison with kinetic simulations demonstrates its accuracy over the plasma-sheath transition region in which quasineutrality is weakly perturbed and the Bohm criterion applies.