Until very recently, it was generally believed that the (approximate) 2-design property is strictly stronger than anticoncentration of random quantum circuits, mainly because it was shown that the latter anticoncentrate in logarithmic depth, while the former generally need linear depth circuits. This belief was disproven by recent results that show that so-called relative-error approximate unitary designs can, in fact, be generated in logarithmic depth, implying anticoncentration. Their result does not, however, apply to ordinary local random circuits, a gap that we close in this Letter, at least for 2-designs. More precisely, we show that anticoncentration of local random quantum circuits already implies that they form relative-error approximate state 2-designs, making them equivalent properties for these ensembles. Our result holds more generally for any random circuit that is invariant under local (single-qubit) unitaries, independent of the architecture.

Orbital angular momentum (OAM) entanglement gives access to multiple qubit and high dimensional Hilbert spaces but is unfortunately susceptible to disturbance, decaying in real-world noisy channels. Here, we show that an underlying topology arising from OAM entanglement remains robust to such channels, which we demonstrate using atmospheric turbulence—exemplary of stochastic or chaotic media. Using a quantum channel with various turbulence strengths, we find that the OAM topological observable is preserved even though the OAM itself is shown to be highly sensitive to the turbulence. We show this is true for mixed states too, with the OAM topology intact even as the purity of the state decreases due to decoherence. Our Letter offers a new perspective on harnessing OAM entanglement in noisy channels, and may easily be extended to other spatial bases, degrees of freedom, and complex channels.

The dynamics of quantum correlations are central to understanding many physical properties of quantum systems. Here we experimentally study the correlation dynamics via two-particle quantum walks in superconducting Bose-Hubbard qutrit arrays, with tunable on-site interaction $U$ realized by Floquet engineering. Quantum walks show the characteristic change from bosonic bunching to fermionic antibunching with increasing $U$. The two-site entanglement and quantum correlation dynamics, as measured by negativity and quantum discord, are investigated. We find that, depending on the initial state, the propagation of entanglement can be strongly suppressed with increasing $U$, while that of quantum discord exhibits considerably larger amplitude, or both appear insensitive to $U$. Furthermore, the forms of entanglement are found to persist throughout particle walks for $U=0$, and it is generally not the case when $U$ increases. Our Letter highlights the role of interaction in shaping quantum dynamics and extends the realm of simulating correlated quantum systems with superconducting circuits.

We realize a nanoscale accelerometer with a levitated nanoparticle near the ground state, exploiting its dynamical behavior triggered by the abrupt quench of its trapping potential. We find that rapid quenching provides a readout time at which the sensitivity is enhanced by 2 orders of magnitude with a favorable combination of a large acceleration-induced displacement and a reduced position uncertainty, enabling us to detect a weak acceleration obscured by the zero-point fluctuation in the initial potential. With rapid quenching, the observed sensitivity is in good agreement with a numerical simulation based on the quantum Langevin equation. Our results provide a step toward inertial sensing with levitated nanoparticles through time-optimal quench dynamics in the quantum regime.

Nickel, one of the most tightly bound nuclei alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE’s excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of cosmic-ray nickel spectrum from 10 GeV/n to 2 TeV/n with nine years of flight data. The nickel spectrum is consistent with a single power law with spectral index $-2.60\pm 0.03$ from 40 GeV/n to 1 TeV/n. This Letter provides an accurate measurement of differential flux of nickel with kinetic energy extending to TeV/n for the first time.

A first-order phase transition could occur in the late Universe when vacuum energy begins dominating the energy density ($z\lesssim 0.3$) and convert some latent heat into other forms such as invisible radiation. This generic possibility also has concrete motivation in particle physics models, which invoke a multitude of vacua to address theoretical puzzles. The naïve constraint on such an event comes from measurements of the Hubble expansion rate, but this can only probe transitions involving $\mathcal{O}(10)\%$ of the dark energy. In this Letter, we show that significantly tighter constraints appear when accounting for phase transition fluctuations affecting CMB photon propagation anisotropically. For instance, if a completed phase transition has $\beta /H_{\star }\lesssim 25$, current CMB data limit the associated vacuum energy released to less than 1% of the dark energy. A transition to negative vacuum energy (quasi-anti–de Sitter) is allowed only for $\beta /H_{\star }\gtrsim 300$. For $\beta /H_{\star }\lesssim 500$, the Universe will not crunch for at least 14 Gyr.

We perform fully relativistic general-relativistic magnetohydrodynamics simulations of magnetized, self-gravitating black hole disk (BHD) systems in which the black hole spin is misaligned with the disk angular momentum. Massive disks (disk to black hole mass ratios of 16%–28%) around rapidly rotating black holes ($\chi \lesssim 0.97$) develop a nonaxisymmetric instability for tilt angles from 0° to 180°. Magnetic stresses damp, but do not completely suppress, the nonaxisymmetric instability, and corresponding gravitational wave emission, in aligned systems, while they enhance it in antialigned BHDs: magnetorotational instability (MRI) driven turbulence enhances angular momentum transport and accelerates nonlinear instability evolution in misaligned configurations. All models launch magnetically driven jets consistent with the Blandford-Znajek mechanism, with collimation depending on spin orientation. The gravitational waves reflect strong nonaxisymmetric structure from a persistent $m=1$ mode. The coupling between fast MRI and the slower nonaxisymmetric instability growth governs the outcome, with tilt controlling how MRI modifies the global mode. These simulations provide the first self-consistent general-relativistic magnetohydrodynamics treatment of tilted, self-gravitating BHD systems and support their role as multimessenger sources.

We analyze the expectation value of the energy-momentum tensor and its fluctuations in quantum field theory on curved spacetimes. A generally accepeted condition for the conceptual consistency of semiclassical gravity is that the fluctuations of the energy momentum tensor remain small compared to its expectation value. We study the renormalization of both the energy-momentum tensor $⟨T_{ab}(x){⟩}_{\mathrm{ren}}$ and the fluctuation tensor $⟨T_{ab}(x)T_{cd}(x){⟩}_{\mathrm{ren}}$ for suitably well behaved states, using the operator product expansion for a free scalar field on a fixed curved background. We show that states (usually referred to as “squeezed vacua”)—arising naturally in black hole evaporation and in inflationary cosmology—fail to satisfy the natural semiclassicality criterion.

The two-dimensional $\mathrm{O}(\mathrm{N})$ nonlinear sigma model (NLSM) is asymptotically free for $N>2$: it exhibits neither a nontrivial fixed point nor spontaneous symmetry breaking. Here, we show that a nontrivial fixed point generically does exist in the complex coupling plane and is described by a complex conformal field theory (CCFT). This CCFT fixed point is generic in the sense that it has a single relevant singlet operator, and is thus expected to arise in any non-Hermitian model with $\mathrm{O}(\mathrm{N})$ symmetry upon tuning a single complex parameter. We confirm this prediction numerically by locating the CCFT at $N=3$ in two non-Hermitian spin-1 antiferromagnetic Heisenberg chains, and in a non-Hermitian spin-$1/2$ ladder, finding good agreement between the complex central charge and scaling dimensions and those obtained by analytic continuation of real fixed points from $N\le 2$. The low-energy spectra also reveal a noninvertible symmetry inherited from the $\mathrm{O}(\mathrm{N})$ loop model, realized as an emergent symmetry at the NLSM fixed point and exactly in the spin-1/2 ladder. We further construct a realistic Lindbladian for a spin-1 chain whose no-click dynamics are governed by the non-Hermitian Hamiltonian realizing the CCFT. Since the CCFT vacuum is the eigenstate with the smallest decay rate, the system naturally relaxes under dissipative dynamics toward a conformal field theory state, thus providing a route to preparing long-range entangled states through engineered dissipation.

In this Letter, we study pole skipping in nonmaximally quantum chaotic systems. Using Rindler conformal field theories and the large-$q$ Sachdev-Ye-Kitaev chain as illustrative examples, we argue that the pole skipping points of few-body operators organize into trajectories in the complex frequency-momentum plane, with the leading trajectory encoding the quantum Lyapunov exponent. We further propose that these trajectories admit a natural interpretation as Regge trajectories of stringy excitations in a dual stringy black-hole geometry. From this perspective, pole skipping for an individual operator can be viewed as tracking the stringy horizon through the response of a single excitation. Our results suggest that pole skipping reflects intrinsic properties of quantum chaotic systems and may be deeply connected to the structure of horizons in the stringy regime.

A search for the rare decay $B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-}$ is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of $m(\overline{\mathrm{\Lambda }}p)<2.8\mathrm{GeV}/c^2$. The branching fraction is measured to be ${\mathcal{B}}_{\mathrm{low}}(B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-})=(1.70_{-0.56}^{+0.65}(\mathrm{stat})\pm 0.17(\mathrm{syst})\pm 0.14(\mathrm{ext}))\times {10}^{-8}$, where the last uncertainty is due to external inputs on $\mathcal{B}(B^{+}\to J/\psi \overline{\mathrm{\Lambda }}p)\times \mathcal{B}(J/\psi \to {\mu }^{+}{\mu }^{-})$. With no significant signal observed in the high $m(\overline{\mathrm{\Lambda }}p)$ region above $2.8\mathrm{GeV}/c^2$, an upper limit is set to be ${\mathcal{B}}_{\mathrm{high}}(B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-})<2.8(3.7)\times {10}^{-9}$ at the 90% (95%) confidence level.

In a search for potential signals of neutron ($n$) to mirror-neutron $(n^{\prime })$ oscillations, a collaboration centered at the Paul Scherrer Institute investigated the remaining parameter space claimed by anomalies with a dedicated high-sensitivity apparatus. An elaborate magnetic-field-mapping analysis and Monte Carlo simulation of the cumulative $n-n^{\prime }$ oscillation probabilities along the neutron trajectories inside the storage vessel complemented the neutron data analysis. Magnetic fields were scanned in the range $5<B<109\mathrm{\mu }\mathrm{T}$. No evidence of anomalous neutron losses was found. Consequently, new limits for the $n-n^{\prime }$ oscillation time constant were set. The parameter space, previously claimed for potential signals, has been excluded to 99.98%.

Muon-electron universality is tested in $B^0\to K^{*0}{\ell }^{+}{\ell }^{-}$ decays, in the dilepton-invariant-mass region above the $\psi (2S)$ resonance. The analysis uses beauty mesons produced in proton-proton collisions recorded by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. The ratio of branching fractions between the muon and electron channels $R_{K^{*0}}$ is measured to be ${1.08}_{-0.12}^{+0.14}(\mathrm{stat})\pm 0.07(\mathrm{syst})$ for a dilepton-invariant-mass squared above $14.0{\mathrm{GeV}}^2/c^4$, consistent with the standard model prediction. This result represents the most precise measurement of $R_{K^{*0}}$ in this region and the first such measurement performed at a hadron collider.

Our understanding of the origin of heavy elements beyond iron relies on the rapid neutron capture process ($r$ process), which accounts for roughly half of their cosmic abundance. However, the extreme neutron-rich conditions required for the $r$ process involve many nuclei that remain experimentally inaccessible, making theoretical predictions essential. We explore the impact of nuclear masses calculated with the ab initio valence-space in-medium similarity renormalization group, focusing on the region around the $N=82$ shell closure. We show for the first time that such ab initio mass calculations can be used to refine $r$-process predictions compared to global, but more phenomenological mass models. With the ab initio masses, the waiting point of the second $r$-process peak is strengthened, which leads to an overall slower nucleosynthesis flow, lower abundances of nuclei beyond the peak, and a stronger shift of the third $r$-process peak.

By measuring the cyclotron frequency ratio of ${}^4{\mathrm{He}}^{+}$ to ${{}^{12}\mathrm{C}}^{3+}$ in a Penning trap the mass of ${}^4\mathrm{He}$ has been determined to be 4.002 603 254 665(36) u. [The corresponding mass of the alpha particle is 4.001 506 179 662 (36) u]. This opens the possibility of deriving the atomic mass of the electron at a relative precision of $1\times {10}^{-11}$ from proposed measurements of the Landé $g$-factor of ${}^4{\mathrm{He}}^{+}$.

Ultrafast charge transfer (CT) lies at the heart of molecular and electronic functionality. We develop a Fano-based core-hole clock (FCHC) method that captures coherent coupling between localized excitons and the directly populated delocalized CT continua in resonant Auger scattering. Applied to sulfur $KLL$ Auger spectra of a conductive organic polymer, FCHC reveals clear Fano interference and a CT time of $27\pm 1.8\mathrm{fs}$, demonstrating that the conventional core-hole clock model underestimates the CT dynamics timescale. We establish FCHC as a robust method for probing ultrafast CT in complex molecular systems.

We calculate the bound and scattering properties of a system of two neutral atoms and an ion near an ion-atom Feshbach resonance. Our results indicate that long-range ion-atom interactions lead to significant deviations from universal behavior derived from contact or van der Waals potentials. We find that ionic systems display an overall suppression of inelastic transitions leading to recombination rates and lifetimes of Efimov state orders of magnitude larger with respect to those for neutral atoms. We further characterize the dense spectra of triatomic molecular ions with extended lifetimes. Our results provide a deeper insight into the universality and structure of three-body ionic systems and establish them as a promising platform for exploring novel few- and many-body phenomena with long-range interactions.

Although they enabled several advances in the field of optomechanics, optomechanical disk resonators have not yet been qualified for operation in the quantum regime of motion. We present the experimental demonstration of an optomechanical disk resonator prepared in the quantum ground state. With a gigahertz frequency, the mechanical breathing mode of the investigated semiconductor disk reaches a level of excitation below a single phonon when cooled in a dilution refrigerator. We quantify the phonon occupancy by performing sideband thermometry: a conical optical fiber is evanescently coupled to the disk optical whispering-gallery mode, and Stokes and anti-Stokes photons scattered by phonon emission and absorption are counted on a single-photon detector. We measure a suppression of the absorption process corresponding to a mean phonon occupancy of $0.66\pm 0.20$. Beyond ground-state cooling, we experimentally investigate the mechanisms ruling laser-induced heating, which ultimately limits the lowest measurable phonon occupancy, and witness both intracavity and extracavity heating.

We experimentally investigate resonance fluorescence from a two-level system in a novel configuration where a strong laser drives an optical Rabi oscillation while an acoustic field parametrically modulates the frequency of the two-level system. We observe emission spectra that deviate markedly from the standard Mollow triplet, including dynamical cancellation of the central peak. A doubly dressed state model incorporating hybridization among the emitter, optical field, and acoustic field captures these features. Guided by this model, we experimentally validate the condition for optimal cooling of acoustic phonons in an emitter-optomechanical system. These results reveal new regimes of strongly driven quantum nonlinear interactions.

Two-photon light-matter interactions exhibit distinctive features such as spectral collapse. The two-photon Dicke model has been reported to exhibit a superradiant phase which could be useful in quantum applications. Here we show that this superradiant phase is not a genuine thermodynamic phase but a finite-size effect. Combining analytical and numerical analyses, we demonstrate that the superradiant region shrinks with increasing system size and disappears in the thermodynamic limit, while spectral collapse remains. Our results clarify the nature of superradiant conditions in two-photon systems and constrain its realization in quantum platforms.