We develop a framework for matrix product quantum channels, a one-dimensional tensor-network description of completely positive, trace-preserving maps. We focus on translation-invariant channels, generated by a single repeated tensor, that admit a local purification. We show that their purifying isometry can always be implemented by a constant-depth brickwork quantum circuit, implying that such channels generate only short-range correlations when applied on product states. In contrast to the unitary setting, where one-dimensional quantum cellular automata (in one-to-one correspondence with matrix product unitaries) carry a nontrivial index, we prove that all locally purified channels belong to a single phase, that is, they can be continuously deformed into one another. Then, we extend the framework to a broader class of translation-invariant channels capable of generating long-range entanglement and show that these remain deterministically implementable in constant depth using two rounds of measurements and feedforward.

We study error-correction protocols in which a quantum channel encodes logical information into an enlarged Hilbert space through a one-dimensional random circuit with local gates. We consider both noise acting after the encoding step and noise affecting the encoding circuit itself. Using the coherent information, we show that in both settings the infinite-depth limit is governed by a universal random-matrix transition at a critical noise rate, separating a recoverable phase from one where information is lost. We then characterize the leading finite-depth deviations from this universal regime. When noise acts only after a unitary encoder, convergence to perfect encoding is exponential in circuit depth, although boundary effects can delay saturation beyond the design time. When the encoder itself is noisy, the relevant control parameter becomes the circuit fidelity, which replaces the Hashing bound, and convergence is only polynomial in depth.

Quantum many-body systems coupled to out-of-equilibrium reservoirs can behave as active matter and exhibit signs of flocking. However, the resulting steady states are highly mixed and carry only weak quantum signatures. We show that signatures of active matter also arise in ensembles of pure states undergoing monitored quantum dynamics. We consider a spinful Luttinger liquid subject to measurement processes that shuffle spin-up particles to the left and spin-down particles to the right. For weak monitoring strengths and ferromagnetic spin interactions, we find power-law quantum correlations between spin density and charge current, which we identify as a hallmark of active quantum matter. The monitoring plays a dual role, generating the quantum active correlations for weak strengths while driving a Berezinskii-Kosterlitz-Thouless phase transition to a short-range correlated state at larger strengths.

Much like the aerodynamic deflection of a spinning curveball, a rotating secondary in an extreme-mass-ratio inspiral (EMRI) experiences Magnus and lift forces, in addition to the standard drag force, when traversing a gaseous environment. We present the first framework that incorporates these specific spin-coupled environmental effects (EEs) into the evolution of EMRI. Over the multiyear observation windows of space-based gravitational wave (GW) detectors, these interactions imprint a unique, distinguishable dephasing signature on the signal. Crucially, a Fisher matrix analysis reveals that gas drag breaks the fundamental vacuum-projection degeneracy between the secondary’s spin magnitude and inclination, thereby tightening parameter constraints. Thus, accounting for EEs is not merely a modeling necessity, but could potentially be a powerful tool for enhancing the detectability of the secondary’s intrinsic spin, and could serve as a novel probe of accretion flows harboring massive black holes.

Ground states of $1+1d$ conformal field theories (CFTs) satisfy a local entropic condition called the vector fixed point equation. This condition is surprisingly well satisfied by ground states of quantum critical lattice models even at small system sizes. We perform a search in the space of states of very small systems (4 qubits and 4 qutrits) and examine the states that satisfy this condition. By reconstructing a local Hamiltonian from each state, we are able to identify many of these solutions with known CFTs; others are gapped fixed points or involve large relevant perturbations, and others are CFTs we have not yet identified. These ideas are also useful for identifying continuous quantum phase transitions in a given family of Hamiltonians and for identifying the nature of the critical theory in small systems.

We propose a novel factorization theorem for $N$-jettiness at hadron colliders, which incorporates coherence-violating effects induced by Glauber gluons and several new momentum modes. Their interplay generates coherence-violating logarithms starting at four-loop ($N\ge 1$) or five-loop order ($N=0$). We calculate the anomalous dimensions required for the resummation of coherence-violating logarithms and establish a general framework for the systematic treatment of coherence violation. Our findings imply that most existing factorization formulas for global LHC observables must be revised.

We develop a self-consistent approach that provides an explicit potential for a Rydberg electron whose ionic core consists of a polarizable medium, typically realized with superfluid droplets. The electron’s motion remains separable in spherical coordinates, but the radial force exerted by the droplet breaks degeneracy of the angular momentum states nonperturbatively. The ensuing electron spectrum reveals intriguing properties dependent on droplet size and electron excitation. Deviations of the polarizable medium from the continuous spherical distribution can be taken into account as a perturbation of this redefined Rydberg dynamics. We discuss specific but paradigmatic examples for superfluid helium and also propose a way to probe droplet properties, including its possible crystallized fraction through stimulated transitions of the Rydberg electron.

Spectral collapse in the two-photon quantum Rabi model (tpQRM) has long been regarded as insufficient to establish quantum criticality because, under generic conditions, the lowest excitation gap remains finite. We show that, at a special qubit frequency, spectral collapse in the anisotropic tpQRM constitutes a continuous quantum phase transition governed by a single soft mode. The same-parity gap, set by the vanishing effective oscillator frequency, closes with exponent $z\nu =1/2$, whereas the lower different-parity gap arises from symmetry-induced splitting. Parity symmetry excludes the different-parity excitation from the quantum Fisher information response and restricts Kibble-Zurek dynamics to excitations within the ground-state parity sector. Together, these results identify the same-parity excitation as the soft mode and its gap as the characteristic energy scale. The corresponding critical exponents, $\nu =1/4$ and $z=2$, place the anisotropic tpQRM in the same universality class as the standard quantum Rabi model. Our results establish spectral collapse as a potential route to experimentally accessible quantum criticality in a few-body system and show that universality is determined by the soft-mode structure rather than by the closing of the lowest excitation gap.

Fractional Chern insulators are interaction-driven topological states that realize the lattice analog of the fractional quantum Hall effect without external magnetic fields. Here we propose a programmable platform for engineering topological flat bands by combining a Zeeman field with a tunable electrostatic superlattice potential in a Rashba spin-orbit-coupled thin film. The Zeeman field generates a nearly flat segment of the Rashba band, which is isolated by the superlattice potential into a flat band with Chern number $\mathcal{C}=1$. Using many-body exact diagonalization, we show that this band supports fractional Chern insulators at filling factors $n=1/3$ and $2/3$, both of which remain robust over broad parameter ranges. We further identify realistic material candidates and the corresponding device conditions that enable experimental realization. These results establish a versatile and experimentally accessible platform for engineering topological flat bands and exploring correlated topological phases.

We report direct spectroscopic evidence of antimagnons, i.e., negative-energy spin waves identified by their signature inverted dispersion and left-handed precession with Brillouin light scattering (BLS) spectroscopy. We investigate an ultrathin BiYIG film with a perpendicular magnetic anisotropy that compensates the demagnetizing field. By injecting a spin-orbit torque, the magnetization is driven into auto-oscillation and eventually into a nonequilibrium reversed state above a secondary current threshold ($\sim 1.2\times {10}^7\mathrm{A}/{\mathrm{cm}}^2$). The dispersion is measured by wave-vector-resolved BLS and exhibits a sharp change from an upward dispersion to a downward one, in agreement with theoretical predictions and micromagnetic simulations. Around the threshold current, we observe the coexistence of conventional magnons and antimagnons. Our Letter establishes antimagnons with inverted dispersion and is a first step toward exploring novel phenomena and applications due to magnon-antimagnon coupling, such as magnon amplification and magnon-antimagnon entanglement, which are part of the emerging field of antimagnonics.

A recent study reporting interferencelike patterns in nonlocal spin-wave measurements on hematite [Sheng et al., Control of spin currents by magnon interference in a canted antiferromagnet, Nat. Phys. 21, 740 (2025).] suggested the existence of a hidden ultrafast spin-wave mode at tens of gigahertz. This hidden mode lies beyond the scope of conventional spin-wave theory in hematite, and its origin remains unexplained. In this Letter, we show that two mechanisms—crosstalk-induced spin-orbit torque and the antenna-generated Oersted field—quantitatively account for all observed interferencelike features, eliminating the need for a hypothetical hidden mode. We find that the spin-orbit torque generates both out-of-plane local magnetization dynamics and in-plane polarized propagating spin waves. While the former, combined with the antenna-generated propagating spin waves, leads to a frequency-dependent sign in the detected spin pumping signal, the latter gives rise to a finite Brillouin light scattering signal at twice the microwave frequency. Meanwhile, the Oersted field, which possesses both in-plane and out-of-plane components, produces the spatial oscillation profile previously observed in Brillouin light scattering at the excitation frequency. Such a spatial modulation is found to persist even in the absence of the crosstalk-induced spin-orbit torque, indicating that it arises from a conventional excitation effect. Our results not only elucidate the roles of spin-orbit torque and Oersted field in the magnetization dynamics of easy-plane antiferromagnets but also highlight the significance of crosstalk effects in nonlocal spin-wave measurements using microwave excitation and heavy-metal detectors.

Estimating the properties of quantum states is a fundamental task in both theoretical and experimental quantum physics. While numerous Pauli-based measurement strategies have been proposed, none explicitly exploit prior knowledge of structural features such as symmetry. Here, we introduce a compact measurement scheme that exploits symmetry to speed up quantum measurements. By incorporating symmetry into the measurement design, our approach can rigorously reduce sample complexity for symmetric states and suitable observables. We provide a theoretical analysis showing that, for specific observables, the variance of our estimator admits polynomial or even exponential improvements in the required number of state copies. To demonstrate practicality, we implement the scheme on photonic quantum platforms, preparing high-fidelity Greenberger-Horne-Zeilinger (GHZ) and $W$ states. The experimental results confirm substantial gains in estimation accuracy for both linear and nonlinear properties. Our work suggests that symmetry and other structural properties of quantum states can be systematically exploited as algorithmic resources, opening new avenues for scalable characterization and verification of complex quantum systems on near-term and fault-tolerant devices.

Non-Hermitian physics has attracted significant interest due to its exotic phenomena. However, non-Hermitian effects at topological interfaces and their potential applications remain largely unexplored. Here, based on an interface skin-effect model, we theoretically propose a non-Hermitian topological beam splitter (NHTBS) and experimentally demonstrate it as a proof of principle in a photonic spatiotemporal lattice using coupled fiber loops. By tuning the nonreciprocal parameters of the interface lattice, we demonstrate amplification of the wave packets at the output ports of the NHTBS and achieve fully tunable splitting ratios. Moreover, we carry out 4-bit temporal beam encoding using cascaded NHTBS units and also observe the amplification phenomenon. The output ports of the encoded beam exhibit high stability even in the presence of disorder perturbations on the asymmetric interactions. This work reveals the potential of non-Hermitian interface physics for enabling future multifunctional photonic information processors.

We present a classical algorithm for approximating the expectation values of observables in linear optical circuits with arbitrary product input states, achieving additive-error accuracy. This result indicates that current applications of photonic systems aimed at demonstrating practical quantum advantage through expectation value estimation, such as photonic variational algorithms, may face challenges in attaining the computational advantage. It also implies the output probabilities of boson sampling with arbitrary product input states can be efficiently approximated by our method, so that boson sampling becomes efficiently simulable when its output probability distribution is polynomially sparse. We also develop an efficient classical algorithm for estimating transition amplitudes of arbitrary product states in linear optical circuits. This provides additive-error approximation algorithms for matrix functions associated with linear optical circuits, such as the (loop-)Hafnian, which are of independent interest. As an application, it solves the generalized molecular vibronic spectra problem [C. Oh et al., Nat. Phys. 20, 225 (2024)], previously suggested as a candidate for practical quantum advantage. Finally, we extend our framework to near-Clifford circuits, enabling classical approximation of their expectation values.

Magnetic fields between a supernova (SN) and Earth convert axions into gamma rays. The absence of such a signal in coincidence with SN 1987A neutrinos, using the coherent Milky Way field, provides well-studied constraints on $g_{ap}\times g_{a\gamma }$ (axion-proton times axion-photon couplings) and on $g_{a\gamma }$ alone. We show that the small-scale power of the turbulent magnetic field component boosts axion-photon conversion and, crucially, extends sensitivity to larger masses. The turbulent field components of the Milky Way and of the Large Magellanic Cloud (hosting SN 1987A) yield improvements of up to 2 orders of magnitude in $g_{ap}\times g_{a\gamma }$. Turbulence should likely impact the sensitivity of other searches based on other axion-photon conversion sites, such as starburst galaxies.

We present greyring, a new model for the postmerger signal in black-hole binary coalescences based on the graybody factor of the remnant. The model accurately reproduces the full frequency-domain ringdown signal for a large set of comparable-mass, aligned-spin numerical relativity waveforms, including the $(\ell ,m)=(2,2)$, (3,3), and (4,4) modes. It achieves mismatches of order $\mathcal{O}({10}^{-6})$ for the dominant (2,2) mode, demonstrating that the graybody-factor parametrization provides a very accurate phenomenological description of the postmerger signal. Building on this model, we introduce a novel consistency test of strong gravity based on the graybody factor: the remnant mass and spin inferred from greyring can be compared with those obtained through standard black-hole spectroscopy. This agnostic test relies exclusively on the postmerger signal and does not require the inclusion of overtones or the choice of very early ringdown starting times, combining the advantages of inspiral-merger-ringdown consistency tests and traditional black-hole spectroscopy. We apply the test to GW250114 and find that the remnant mass and spin inferred from greyring are consistent with those measured from the full signal. Remarkably, the inferred parameters can be measured with a precision comparable to, or slightly better than, that achieved with standard black-hole spectroscopy. Our graybody-factor waveform model allows for new precision tests of strong gravity using the ringdown signal.