Nonclassical phenomena tied to entangled states are the focus of foundational studies and powerful resources in many applications. By contrast, the counterparts on quantum measurements are still poorly understood. Notably, genuine multipartite nonclassicality is barely discussed, let alone its experimental realization. Here we experimentally demonstrate the power of genuine tripartite nonclassicality in quantum measurements based on a simple estimation problem. To this end we realize an optimal genuine three-copy collective measurement via a nine-step two-dimensional photonic quantum walk with 30 elaborately designed coin operators. Then we realize an optimal estimation protocol and achieve an unprecedented high estimation fidelity, which can beat all strategies based on restricted collective measurements by more than 11 standard deviations. These results clearly demonstrate that genuine collective measurements can extract more information than local measurements and restricted collective measurements. Our Letter opens the door for exploring genuine multipartite nonclassical measurements and their power in quantum information processing.

High-dimensional entangled states offer higher information capacity and stronger resilience to noise compared with two-dimensional systems. However, the large number of modes and sensitivity to random rotations complicate experimental entanglement certification. Here, we experimentally certify three-dimensional entanglement in a five-dimensional two-photon state using 800 Haar-random measurements implemented via a ten-plane programmable light converter. We further demonstrate the robustness of this approach against random rotations, certifying high-dimensional entanglement despite arbitrary phase randomization of the optical modes. This method, which requires no common reference frame between parties, opens the door for high-dimensional entanglement distribution through long-range random links.

Quantum scars are nonthermal eigenstates that prevent thermalization of initial states with weight on the scars. When the scar states are equally spaced in energy, superpositions of scars show oscillating local observables that can be detected in experiments. However, we note that scarred models in the literature show fundamentally different scar entanglement dynamics: some show entanglement oscillations while others are completely frozen. We explain this freezing through a no-go theorem which we apply to more than a dozen scarred models in the literature. We also discuss a method for evading the no-go theorem by deforming the scarred models with frozen scar entanglement dynamics.

Quantum random access memory (QRAM) promises simultaneous data queries at multiple memory locations, with data retrieved in coherent superpositions, essential for achieving quantum speedup in many quantum algorithms. We introduce a transmon-controlled phonon router and propose a QRAM implementation by connecting these routers in a treelike architecture. The router controls the motion of itinerant surface acoustic wave phonons based on the state of the control transmon, implementing the core functionality of conditional routing for QRAM. Our QRAM design is compact, supports fast routing operations, and avoids frequency crowding. Additionally, we propose a hybrid dual-rail encoding method to detect dominant loss errors without additional hardware, a versatile approach applicable to other QRAM platforms. Our estimates indicate that the proposed QRAM platform can achieve high heralding rates using current device parameters, with heralding fidelity primarily limited by transmon dephasing.

It is commonly believed that logical states of quantum error-correcting codes have to be highly entangled such that codes capable of correcting more errors require more entanglement to encode a qubit. Here, we show that the validity of this belief depends on the specific code and the choice of entanglement measure. To this end, we characterize a tradeoff between the code distance $d$ quantifying the number of correctable errors, and the geometric entanglement measure of logical states quantifying their maximal overlap with product states or more general “topologically trivial” states. The maximum overlap is shown to be exponentially small in $d$ for three families of codes: (1) low-density parity check codes with commuting check operators, (2) stabilizer codes, and (3) codes with a constant encoding rate. Equivalently, the geometric entanglement of any logical state of these codes grows at least linearly with $d$. On the opposite side, we also show that this distance-entanglement tradeoff does not hold in general. For any constant $d$ and $k$ (number of logical qubits), we show there exists a family of codes such that the geometric entanglement of some logical states approaches zero in the limit of large code length.

Sensors for mapping the trajectory of an incoming particle find important utility in experimental high energy physics and searches for dark matter. For a quantum sensing protocol that uses projective measurements on a multiqubit sensor array to infer the trajectory of an incident particle, we establish that entanglement can dramatically reduce the particle-qubit interaction strength $\theta$ required for perfect trajectory discrimination. Within an interval of $\theta$ above this reduced threshold, any unentangled sensor requires $\mathrm{\Theta }[\log (1/\epsilon )]$ repetitions of the protocol to estimate a previously unknown particle trajectory with $\epsilon$ error probability, whereas an entangled sensor can succeed with zero error in a single shot. Furthermore, entanglement can enhance trajectory sensing in realistic scenarios where $\theta$ varies continuously over the sensor qubits, exemplified by a Gaussian-profile laser pulse propagating through an array of atoms.

We propose the microscopic origin of the pole inflation from the scalar fields of broken noncompact isometry in Weyl gravity. We show that the $SO(1,N)$ isometry in the field space in combination with the Weyl symmetry relates the form of the nonminimal couplings to the one of the potential in the Jordan frame. In the presence of an explicit breaking of the $SO(1,N)$ symmetry in the coefficient of the potential, we realize the pole inflation near the pole of the inflaton kinetic term. Applying our results to the Higgs or Peccei-Quinn (PQ) inflation models, we find that there is one parameter family of the solutions for the pole inflation, depending on the overall coefficient of the Weyl covariant derivatives for scalar fields. The same coefficient not only makes the predictions of the pole inflation varying, being compatible with the Planck data, but also determines the mass of the Weyl gauge field. We also show that the isocurvature perturbations of the axion can be suppressed sufficiently during the PQ pole inflation, and the massive Weyl gauge field produced during reheating serves as a dark matter candidate.

Strong gravitational lensing occurs when photons pass through the vicinity of a black hole. We investigate this phenomenon in the context of a gravitational-wave event, specifically when a black hole is settling into its final state. The deflection angle of photons mimics the ringdown pattern of the gravitational wave at intermediate times. At late times it has an inverse cubic dependence on observation time. The deviation angle increases exponentially as photons approach the photon ring orbit, reflecting its unstable nature. Our findings are directly applicable to imaging scenarios involving stars against the background of compact binaries or circumbinary accretion disks, particularly during the merger of two black holes.

Future gravitational wave observatories open a unique avenue to study the environments surrounding black holes. Intermediate or extreme mass ratio inspirals will spend thousands to millions of cycles in the sensitivity range of detectors, allowing subtle environmental effects to accumulate in the gravitational waveform. Working in Lorenz gauge and considering equatorial circular orbits, we present the first self-consistent, fully relativistic calculation of a perturbation to a black hole environment due to an inspiraling secondary in the Kerr geometry. As an example case, we consider the environment to be that of a superradiantly grown scalar cloud, though our framework is generalizable to other scenarios. We demonstrate that the scalar field develops a rich wake structure induced by the secondary and compute scalar fluxes emitted to infinity and through the horizon. Relative differences in the fluxes compared to Schwarzschild are tens of percent on large intervals of parameter space, underscoring the importance of modeling in Kerr.

We present a full Batalin-Vilkovisky action in the component field formalism for $\mathcal{N}=1$ supergravity in ten dimensions coupled to Yang-Mills multiplets.

Nuclear halos are exotic quantal structures observed far from stability. They are mostly studied through reactions. The ratio of angular cross sections for breakup and scattering is predicted to be independent of the reaction process and to be very sensitive to the halo structure. We test this new observable experimentally for the first time on the collision of ${}^{11}\mathrm{Be}$ on C at $22.8\mathrm{MeV}/\mathrm{nucleon}$ and using existing data on Pb at $19.1\mathrm{MeV}/\mathrm{nucleon}$. The theoretical predictions are verified, which offers the possibility of developing a new spectroscopic tool to study nuclear structure far from stability.

Quantum states of light, particularly at optical frequencies, are considered necessary to realize a host of important quantum technologies and applications, spanning Heisenberg-limited metrology, continuous-variable quantum computing, and quantum communications. Nevertheless, a wide variety of important quantum light states are currently challenging to deterministically generate at optical frequencies. In part, this is due to a relatively small number of schemes that prepare target quantum states given nonlinear interactions. Here, we present an especially simple concept for deterministically generating and stabilizing important quantum states of light, using only third-order optical nonlinearities and engineered dissipation. We show how, by considering either a nonlinear cavity with frequency-dependent outcoupling or a chain of nonlinear waveguides, one can induce high loss for all but some desired light intensities. Specifically, we find that the stabilized intensities can correspond to an evenly spaced pattern of stablilized photon numbers. This is shown to produce important quantum states with coherent superpositions between various photon numbers. As examples of this phenomenon, we show cavities which can stabilize squeezed states, as well as produce “photon-number-comb” states. Moreover, in these types of filter cavities, Glauber coherent states will deterministically evolve into Schrodinger cat states of a desired order. We discuss potential realizations in quantum nonlinear optics. More broadly, we expect that combining the techniques introduced here with additional “phase-sensitive” nonlinearities (such as second-order nonlinearity) should enable passive stabilization and generation of a wider variety of states than shown here.

We report a proof-of-principle experiment for a new method of temperature measurements in waveguide quantum electrodynamics experiments, allowing one to measure separately the temperature of global and local baths. The method takes advantage of collective states of two transmons located in the center of a waveguide. The Hilbert space of such a system forms two separate subspaces (bright and dark) that are coupled differently to external noise sources. Measuring transmission through the waveguide allows one to extract separately the temperatures of the baths responsible for global and local excitations in the system. Such a system would allow for building a new type of primary temperature sensor capable of addressing both local and global baths.

We propose the use of collective states of matter as a resource for the deterministic generation of quantum states of light, which are fundamental for quantum information technologies. Our minimal model consists of three emitters coupled to a half-waveguide, i.e., a one-dimensional waveguide terminated by a mirror. Photon-mediated interactions between the emitters result in the emergence of bright and dark states. The dark states form a decoherence-free subspace, protected from dissipation. Local driving of the emitters and control of their resonance frequencies allows us to perform arbitrary quantum gates within the decoherence-free subspace. Coupling to bright states facilitates photon emission, thereby enabling the realization of quantum gates between light and matter. We demonstrate that sequential application of these gates leads to the generation of photonic entangled states, such as Greenberger-Horne-Zeilinger and one- and two-dimensional cluster states.

Locality is a transversal principle that governs quantum dynamics of many-body systems. However, for cavity-embedded systems, such a fundamental notion is hindered by the presence of nonlocal cavity modes, leaving space for new possible dynamical behavior. Here, we investigate the real-time dynamics of low-energy excitations in one-dimensional Rydberg atom arrays coupled to a global cavity mode. We derive an effective description in terms of a Tavis-Cummings–Ising model, whose phase diagram features ordered and disordered phases. The nonlocal nature of the cavity mode drastically affects the emergent meson and string dynamics. Mesons hybridize coherently with the cavity photons, leading to composite meson-polariton excitations. Strings, differently from local interacting theories, acquire a finite kinetic energy thanks to nonlocal cavity-mediated interactions between the underlying domain walls. We then conclude by presenting a new concrete experimental blueprint for a cavity QED Rydberg atom array simulator where the physics outlined in this Letter can be realized.

A major limitation of laser interferometers using continuous wave lasers are parasitic light fields, such as ghost beams, scattered or stray light, that can cause nonlinear noise. This is especially relevant for laser interferometric ground-based gravitational wave detectors. Increasing their sensitivity, particularly at frequencies below 10 Hz, is threatened by the influence of parasitic photons. These can up-convert low-frequency disturbances into phase and amplitude noise inside the relevant measurement band. By artificially tuning the coherence of the lasers, using pseudo-random-noise (PRN) phase modulations, this influence of parasitic fields can be suppressed. As it relies on these fields traveling different paths, it does not sacrifice the coherence for the intentional interference. We demonstrate the feasibility of this technique experimentally, achieving noise suppression levels of 40 dB in a Michelson interferometer with an artificial coherence length below 30 cm. We probe how the suppression depends on the delay mismatch and length of the PRN sequence. We also prove that optical resonators can be operated in the presence of PRN modulation by measuring the behavior of a linear cavity with and without such a modulation. By matching the resonators round-trip length and the PRN sequence repetition length, the classic response is recovered.

Spontaneous symmetry breaking (SSB) is a significant topic in particle physics, condensed matter physics, fluid dynamics, etc. In nonlinear optics, polarization is a crucial degree of freedom that enables novel SSB dynamics in coherently pumped Kerr platforms, yet to be explored in laser systems with self-organized localized structure—dissipative soliton. In this study, a special kind of SSB—polarization symmetry breaking (PSB) of GHz dissipative solitons is demonstrated in a mini fiber laser. First, we establish a bidirectional model of the Fabry-Pérot (FP) mini fiber laser with orthogonally polarized counterpropagating light fields. This bidirectional model theoretically predicts the onset of PSB by merely increasing the soliton energy, which manifests as a Hopf bifurcation. Then, experimental validation is performed by implementing a FP mini fiber laser operating at a GHz repetition rate. An abrupt change of the polarization dynamics from the fixed-point attractor to the limit cycle is observed as the soliton energy increases. To verify these findings in real time, specialized polarization-resolved ultrafast techniques are developed for the analysis of high-repetition-rate vectorial signals. The measurements, including the full-Stokes characterization, not only confirm the presence of PSB but also elucidate the underlying physical mechanism associated with the polarization rotation of vector solitons. Our results suggest that the mini fiber laser can potentially become a promising platform for studying the physics of SSB by exploring the nonlinear dynamics of dissipative optical solitons.