Mpemba effects occur after a sudden quench of control parameters if, for “far” (or “hot”) initial states with respect to a final target state, the relaxation time toward the target state is shorter than for “close” (or “cold”) initial states. Following a strategy of fishermen in Pontus described by Aristotle, we introduce the Pontus-Mpemba effect as a two-step protocol that includes the time needed for preparing the system in the “far” initial state that can now be an arbitrary nonequilibrium state. Our protocol needs no parameter distance concept and applies to general (classical or quantum) systems. We find that all possible Pontus-Mpemba effects fall into three classes and illustrate the theory for open Markovian two-state quantum systems.

We utilize the symmetry groups of regular tessellations on two-dimensional surfaces of different constant curvatures, including spheres, Euclidean planes, and hyperbolic planes to encode a qubit or qudit into the physical degrees of freedom on these surfaces, which we call tessellation codes. We show that tessellation codes exhibit decent error correction properties by analysis via geometric considerations and the representation theory of the isometry groups on the corresponding surfaces. Interestingly, we demonstrate how this formalism enables the implementation of certain logical operations through geometric rotations of surfaces in real space, opening a new approach to logical quantum computation. We provide a variety of concrete constructions of such codes associated with different tessellations, which give rise to different logical groups. This formalism sheds a new light on quantum code and logical operation construction.

We study correlations in the prepare-and-measure scenario when quantum communication is constrained by photon-number statistics. Such constraints are natural and practical control parameters for semi-device-independent certification in optical platforms. To analyse these scenarios, we show how semidefinite programming relaxations for noncommutative polynomial optimization can be used to bound the set of quantum correlations under restrictions on the photon-number distribution. The practicality of this method is demonstrated by computing optimal performance bounds on several well-known communication tasks. We then apply the method to the certification of semi-device-inpependent random number generation protocols and show how to bound the conditional Shannon entropy. We showcase this versatile tool by improving randomness extraction in established protocols based on coherent states and homodyne measurements.

We present a novel approach to investigating axions and axionlike particles by studying their potential conversion into x-rays within the Sun’s atmospheric magnetic field. Utilizing high-sensitivity data from the nuclear spectroscopic telescope array (NuSTAR) collected during the 2020 solar minimum, along with advanced solar atmospheric magnetic field models, we establish a new limit on the axion-photon coupling strength $g_{a\gamma }\lesssim 7.3\times {10}^{-12}{\mathrm{GeV}}^{-1}$ at 95% CL for axion masses $m_a\lesssim 4\times {10}^{-7}\mathrm{eV}$. This constraint surpasses current ground-based experimental limits, studying previously unexplored regions of the axion-photon coupling parameter space up to masses of $m_a\lesssim 3.4\times {10}^{-4}\mathrm{eV}$. These findings mark a significant advancement in our ability to probe axion properties and strengthen indirect searches for dark matter candidates.

We interpret holographic entropy inequalities in terms of erasure correction. The nonsaturation of an inequality is a necessary condition for certain schemes of holographic erasure correction, manifested in the bulk as nonempty overlaps of corresponding entanglement wedges.

Understanding the equation of state (EOS) of pure neutron matter is necessary for interpreting multimessenger observations of neutron stars. Reliable data analyses of these observations require well-quantified uncertainties for the EOS input, ideally propagating uncertainties from nuclear interactions directly to the EOS. This, however, requires calculations of the EOS for a prohibitively larger number of nuclear Hamiltonians, solving the nuclear many-body problem for each one. Quantum Monte Carlo methods, such as auxiliary-field diffusion Monte Carlo (AFDMC), provide precise and accurate results for the neutron matter EOS, but they are very computationally expensive, making them unsuitable for the fast evaluations necessary for uncertainty propagation. Here, we employ parametric matrix models to develop fast emulators for AFDMC calculations of neutron matter and use them to directly propagate uncertainties of coupling constants in the Hamiltonian to the EOS. As these uncertainties include estimates of the effective field theory truncation uncertainty, this approach provides robust uncertainty estimates for use in astrophysical data analyses. This Letter will enable novel applications such as using astrophysical observations to put constraints on coupling constants for nuclear interactions.

The shapes of the beta spectra of ${}^{92}\mathrm{Rb}$ and ${}^{142}\mathrm{Cs}$, two of the beta decays most relevant for the prediction of the antineutrino spectrum in reactors, have been measured. A new setup composed of two $\mathrm{\Delta }E\text{−}E$ telescopes has been used. High-purity radioactive beams of the isotopes of interest were provided by the IGISOL facility using the JYFLTRAP double Penning trap. The resulting beta spectra have been compared with model predictions using beta decay feedings from total absorption gamma spectroscopy measurements and shape corrections employed in the calculation of the antineutrino spectrum, corroborating both further. The procedure can be extended to other relevant nuclei in the future, providing solid ground for the prediction of the antineutrino spectrum in reactors.

The optical clock states of alkaline earth and alkaline earthlike atoms are the fundament of state-of-the-art optical atomic clocks. An important prerequisite for the operation of optical clocks is the magic trapping conditions where electronic and motional dynamics decouple. Here, we identify and experimentally demonstrate simultaneous magic trapping for two clock transitions in ${}^{88}\mathrm{Sr}$, realizing so-called triple-magic conditions at a specially chosen magic angle. Under these conditions, we operate an all-optical qutrit comprising the ground state ${}^1{S}_0$, and the two metastable clock states ${}^3{P}_0$ and ${}^3{P}_2$. We demonstrate fast optical control in an atom array using two- and three-photon couplings to realize high-fidelity manipulation between all qutrit states. At the magic angle, we probe the coherence achievable in magic-angle-tuned traps and find atom-atom coherence times between the metastable states as long as 715(30) ms. Our work opens several new directions, including qutrit-based quantum metrology on optical transitions and high-fidelity and high-coherence manipulation on the ${}^{88}\mathrm{Sr}$ fine-structure qubit.

Correlation between the propagation direction of light and spin can be induced via the spin-orbit interaction and has been proven to be the workhorse in the emerging field of chiral quantum optics and in the spin-related Hall effects of light. Photonic orbital angular momentum (OAM) provides a high-dimensional degree of freedom in classical and quantum information processing. However, integrated OAM-based information technology is an open challenge, because OAM modes are always generated in pairs with opposite topological charges due to their degeneracy. Here, we observe locking of the OAM and linear momentum of light by using a chiral optical waveguide with an Archimedean cross section to induce the orbit-orbit interaction. This OAM-momentum locking enables the deterministic and robust generation of on-demand OAM vortex light beam in a photonic chip. This new correlation paves the way toward exotic high-dimensional chiral physical effects and also provides the capability of on-chip manipulation of light in high-dimensional space.

Quantum Monte Carlo is a powerful tool for studying quantum many-body physics, yet its efficacy is often curtailed by the notorious sign problem. In this Letter, we introduce a novel criterion for the “intrinsic” sign problem in two-dimensional bosonic topological orders, which cannot be resolved by local basis transformations or adiabatic deformations of the Hamiltonian. Specifically, we find that the positivity of higher Gauss sums is a necessary condition for a two-dimensional bosonic topological order to be realized by a stoquastic Hamiltonian, and hence “sign-problem-free.” Equivalently, a nonpositive higher Gauss sum for a given topological order indicates the presence of an intrinsic sign problem. This condition not only aligns with prior findings but significantly broadens their scope. Using this new criterion, we examine the Gauss sums of all 405 bosonic topological orders classified up to rank 12, and strikingly find that 398 of them exhibit intrinsic sign problems. We also uncover intriguing links between the intrinsic sign problem, the gappability of boundary theories, and time-reversal symmetry, suggesting that sign-problem-free quantum Monte Carlo simulation may fundamentally rely on both time-reversal symmetry and gapped boundaries. These results highlight the deep connection between the intrinsic sign problem and fundamental properties of topological phases, offering valuable insights into their classical simulability.

Surface polaritons (SPs) are electromagnetic waves bound to a surface through their interaction with charge carriers in the surface material. Hyperbolic SPs can be supported by optically anisotropic materials where the in-plane and out-of-plane permittivities have opposite signs. Here we report what we believe to be the first experimental study of hyperbolic surface exciton polaritons (HSEPs). We study the intensity and phase response of HSEPs in the J-aggregate TDBC (a type-II natural hyperbolic material). HSEPs can be used to generate phase singularities; the behavior of these phase singularities is a consequence of the hyperbolic nature of TDBC. The combined intensity and phase response of nonhyperbolic and hyperbolic SPs suggests that they are topologically distinct. We predict analogous effects for hyperbolic surface phonon polaritons in hexagonal boron nitride. Our Letter suggests that organic materials can provide a new platform for the exploration of hyperbolic surface polaritonics at visible frequencies.

Using a mechanical cantilever submitted to electrostatic feedback control, we investigate the thermodynamic properties of an information engine that extracts work from thermal fluctuations. The cantilever position is rapidly sampled and the feedback is triggered by the first passage of the system across a fixed threshold. The information ΔI associated with the feedback is based on the first-passage-time distribution. In this setting, we derive and experimentally verify two distinct fluctuation theorems that involve $\mathrm{\Delta }I$ and give a tight bound on the work produced by the engine. Our results extend beyond the specific application to our experiment: we develop a general framework for obtaining fluctuation theorems and work bounds, formulated in terms of probability distributions of protocols rather than underlying measurement outcomes.

We investigate energy diffusion in long-range interacting spin systems, where the interaction decays algebraically as $V(r)\propto r^{-\alpha }$ with the distance $r$ between the sites. We consider prototypical spin systems, the transverse Ising model, and the XYZ model in the $D$-dimensional lattice with a finite exponent $\alpha >D$ which guarantees the thermodynamic extensivity. In one dimension, both normal and anomalous diffusion are observed, where the anomalous diffusion is attributed to anomalous enhancement of the amplitude of the equilibrium current correlation. We prove the power-law clustering property of arbitrary orders of joint cumulants in general dimensions. Applying this theorem to equal-time current correlations, we further prove several theorems leading to the statement that the sufficient condition for normal diffusion in one dimension is $\alpha >3/2$ regardless of the models. The fluctuating hydrodynamics approach consistently explains Lévy diffusion for $\alpha <3/2$, which implies that the condition is optimal. In higher dimensions of $D\ge 2$, normal diffusion is indicated as long as $\alpha >D$.

Extensive research has been dedicated to the asymptotic theory of quantum metrology, where the goal is to determine the ultimate precision limit of quantum channel estimation when many accesses to the channel are allowed. The ultimate limit has been well established, but in general, a noiseless and controllable ancilla is required for attaining it. Little is known about the metrological performance without noiseless ancillae, which is more relevant in practical circumstances. In this Letter, we present a novel theoretical framework to address this problem, bridging quantum metrology and the asymptotic theory of quantum channels. Leveraging this framework, we prove sufficient conditions for achieving the Heisenberg limit with repeated applications of the channel to be estimated both with and without applying interleaved unitary control operations. For the latter case, we design an algorithm to identify the control operation explicitly.

Classically, the causal order of two timelike separated events $A$ and $B$ is fixed—either $A$ before $B$ or $B$ before $A$. This is no longer true in quantum theory, where it is possible to encounter superpositions of causal orders. The quantum switch is one of the most prominent processes with indefinite causal order. Optical realizations of the quantum switch have been successfully implemented in experiments, but some argue that this merely simulates a process with indefinite causal order and that a superposition of spacetime metrics is required for a true realization. Here, we provide a relativistic definition of causal order between operationally defined events that defines a meaningful observable in both the general relativistic and quantum mechanical sense. Importantly, this observable does not distinguish between the indefinite causal order implemented on an optical bench and the gravitational quantum switch, a gedanken experiment where the indefinite causal order is achieved by a quantum superposition of gravitational fields. Therefore, our results support the thesis that the optical quantum switch is just as much a realization of indefinite causal order as its gravitational counterpart, which makes use of the quantum mechanical behavior of spacetime.

We investigate the tidal resonance of the fundamental ($f$) mode in spinning neutron stars, robustly tracing the onset of the excitation to its saturation, using numerical relativity for the first time. We performed long-term ($\approx 15$ orbits) fully relativistic simulations of a merger of two highly and retrogradely spinning neutron stars. The resonance window of the $f$ mode is extended by self-interaction, and the nonlinear resonance continues up to the final plunging phase. We observe that the quasicircular orbit is maintained throughout since the dissipation of orbit motion due to the resonance is coherent with that due to gravitational waves. The $f$-mode resonance causes a variation in the stellar spin of $\gtrsim 6.3\%$ in the linear regime and much more as $\sim 33\%$ during the later nonlinear regime. At the merger, a phase shift of $\lesssim 40\mathrm{rad}$ is rendered in the gravitational waveform as a consequence of the angular momentum and energy transfers into the neutron star oscillations.

A stringent test of $CP$ symmetry in hyperon decays is performed using $1.0\times {10}^{10}J/\psi$ events and $2.7\times {10}^9\psi (3686)$ events collected by the BESIII experiment. The $CP$ asymmetry in the two-body nonleptonic weak decays ${\mathrm{\Sigma }}^{+}\to p{\pi }^0$ and ${\overline{\mathrm{\Sigma }}}^{-}\to \overline{p}{\pi }^0$ is determined to be $A_{CP}=-0.0118\pm 0.0083(\mathrm{stat})\pm 0.0028(\mathrm{syst})$, consistent with $CP$ conservation. The average decay parameter $⟨{\alpha }_0⟩=-0.9869\pm 0.0011(\mathrm{stat})\pm 0.0016(\mathrm{syst})$ represents the most precise measurement in the baryon sector to date. A model-independent analysis of the hyperon polarization is performed for the first time at $J/\psi$ and $\psi (3686)$ resonances, revealing a clear sign reversal and offering new insight into SU(3) symmetry breaking and baryon internal structure. These results provide the most stringent constraints on $CP$ violation in $\mathrm{\Sigma }$ decays and establish a benchmark for future precision studies.

We predict collective free-space lasing in a dense nanoscopic emitter arrangement where dipole-dipole coupled atomic emitters synchronize their emission and exhibit lasing behavior without the need for an optical resonator. At the example of a subwavelength-spaced linear emitter chain with varying fractions of pumped and unpumped emitters, we present a comprehensive study of this mirrorless lasing phenomenon. The total radiated power transitions from subradiant suppression under weak pumping to superradiant enhancement at stronger pumping, while exhibiting directional emission confined to a narrow spatial angle. At the same time multiple independent spectral emission lines below the lasing threshold merge toward a single narrow spectral line at high pump power. The most substantial enhancement and line narrowing occur when a fraction of unpumped atoms is present. We show that this leads to superradiant lasing near the bare atomic frequency, making the system a promising candidate for a minimalist active optical frequency reference.