Levitated nanodiamonds hosting a single nitrogen-vacancy (NV) center provide an ultralow-frequency mechanical mode with widely tunable dissipation and spin backaction under microwave dressing and optical pumping. We demonstrate that the driven NV spin can be tuned to act as an inverted gain medium for the center-of-mass motion, thereby stabilizing an autonomous phonon maser. In the timescale-separation regime where the spin dynamics is fast, adiabatic elimination yields a reduced mechanical master equation with closed-form detuning-dependent transition rates and a sharp threshold given by the sign change of the phonon-number damping. For representative levitated NV parameters, we find that a percent-level dressed-basis inversion is sufficient to reach the threshold and the small-signal gain can exceed the intrinsic mechanical loss by orders of magnitude. Full master-equation simulations confirm above-threshold self-oscillation and a phase-diffusing coherent steady state whose saturation follows the Maxwell-Bloch prediction.

Fano resonances are a fundamental physical phenomenon that occurs when an open channel couples with a closed one, resulting in a resonant cancellation of transmission. In this Letter, we introduce a photonic waveguide device designed to observe multiorbital Fano resonances. The system consists of a homogeneous lattice, which includes a plane-wave generator, and an atomlike impurity that supports first-order ($S$) and second-order ($P$) modes. We derive a two-impurity Fano-Anderson model to describe this system and fit the experimental results accordingly, demonstrating a remarkable agreement between our experimental measurements and theoretical predictions. A comprehensive experimental characterization reveals clear double resonances for the $S$ and $P$ states, which depend on the properties of the atom and the excitation wavelength. Our results illustrate how the transport of a propagating beam on a lattice can be effectively controlled by simply adjusting the properties of a single external atomlike impurity, which works as an efficient energy valve.

Fusing small resource states into a larger-scale, highly connected graph state is essential for scalable photonic quantum computing. Theoretical analysis reveals that this can only be achieved when the success probability of the fusion gate surpasses a specific percolation threshold of 58.98% by using three-photon Greenberger-Horne-Zeilinger states as resource states. However, such an implementation of a fusion gate has never been experimentally realized before. Here, we successfully demonstrate a boosted fusion gate with a theoretical success probability of 75%, using deterministically generated auxiliary states. The success probability is experimentally measured to be 71.0(7)%. We further demonstrate the effectiveness of the boosted fusion gate by fusing two Bell states with a fidelity of 67(2)%. Our work paves a crucial path toward scalable linear optical quantum computing.

We investigate a “quantum microscope” for qubits based on nonlinear discrete-time chaotic dynamics, which exponentially amplifies the initially small fidelity of a pair of states to a large saturation value ($\sim 1/2$), thereby pushing the Helstrom bound to more accessible values. We show that Bell-type temporal correlations can capture even the minutest differences between two initial states, thus enabling their distinguishability. The cost of distinguishability is quantified in terms of the characteristic waiting time of the evolution, defined as the time after which the temporal correlation of a given initial state begins to diverge exponentially from that of a nearby state. The closer the two states are, the longer this waiting time becomes. By combining chaos with Bell-type temporal correlations, this approach opens unexplored avenues for pushing the limits of precision in quantum metrology.

We demonstrate polarization-entangled biphotons in a cold-atom double-$\mathrm{\Lambda }$ system by coherently mapping a selected two-dimensional orbital-angular-momentum (OAM) subspace onto the polarization basis. In a standard double-$\mathrm{\Lambda }$ configuration, atomic selection rules often suppress direct polarization correlations and favor OAM entanglement. Our approach bypasses this constraint through external mode conversion and postselection without modifying the atomic level structure or the underlying four-wave-mixing dynamics. Quantum state tomography confirms that the mapping preserves the biphoton coherence. The four polarization Bell states are generated with fidelities of $92\%–94\%$ with few-percent statistical uncertainties. An average Clauser-Horne-Shimony-Holt parameter of $S=2.44$ verifies the survival of nonlocal correlations. This work presents the demonstration of OAM-to-polarization entanglement transfer in a cold-atom spontaneous four-wave-mixing platform and establishes a coherent interface between atomic OAM resources and polarization-based quantum communication networks.

Attosecond electron dynamics driven by strong laser fields are a cornerstone of strong-field physics. However, quantum many-body correlations have prevented the resolution of ionization and rescattering dynamics from specific valence subshells. Here, we present a theoretical framework that integrates time-dependent density functional theory with Bohmian mechanics, enabling us to track the attosecond dynamics of electrons from individual quantum orbitals in real time. Applying this to the many-electron argon atom uncovers a pronounced orientation-dependent effect. For $p$-orbital electrons, ionization occurs earlier for the perpendicular ($m=\pm 1$) alignment than for the parallel ($m$ = 0), yet the subsequent rescattering is delayed. This orientation-dependent dynamics persists even when the total ionization yield is lower. Our work provides an attosecond-resolved, orbital-specific picture of strong-field processes and establishes a foundation for future explorations of orbital-selective control with tailored waveforms.

Multiphoton-added cat states are constructed by repeatedly applying the creation operator to a cat state. We study in detail their photon-number distribution, $Q$ parameter, squeezing properties, and Wigner function. We show that photon addition induces a $\pi$ phase shift in the original parity configuration whenever an odd number of photons is added, reflected as swapped vanishing probabilities and phase-space displacements at the origin. Remarkably, the same process drives these states into a sub-Poissonian regime regardless of the relative phase between their coherent state components, making them valuable resources for quantum imaging, at the cost of losing quadrature squeezing, but gaining amplitude-squared one. We also discuss how these states can be generated using existing hardware.

We demonstrate that linear and nonlinear Thouless pumping can be realized in two-component elongated Bose-Einstein condensates using helicoidal spin-orbit coupling that slides with respect to a static optical lattice, identical for both spinor components. Stable quantized transport is found for solitons in semi-infinite and finite gaps, within certain intervals of chemical potentials and numbers of atoms. In the semi-infinite gap, the transport is arrested for solitons with sufficiently large number of atoms. We elucidate the important role of Zeeman splitting in the control of quantized transport, which disappears when the longitudinal component of the Zeeman field is removed.

Today's most advanced ion-trap quantum computers have significant overhead due to the need for dual-species operation. Looking ahead, logical qubit register sizes will be limited by the encoding rate needed to correct generic Pauli errors. We address both of these issues by establishing high-fidelity control of metastable qubits, a key component of omg or dual-type architectures, which enables converting a significant fraction of gate errors to erasures. We first implement an erasure conversion scheme which enables detection of $\sim 94\%$ of spontaneous Raman scattering errors during logic gates and nearly all errors from qubit decay. Second, we perform a two-ion geometric phase gate using far-detuned (−44 THz) stimulated Raman transitions to produce an entangled state with a raw Bell-state fidelity of 97.73% and a state preparation and measurement-corrected Bell-state fidelity of 98.61%. When subtracting erasure errors, this fidelity becomes 99.16%. These results, along with projections based on our detailed error budget, demonstrate metastable trapped-ion qubits as a platform for low-overhead, fault-tolerant quantum computing.

When a metastable state decays into radiation, there must be entanglement between the radiation and the decaying system, as well as between radiation collected at late and early times. We study the interplay between these two types of entanglement in simple Gaussian models in the Markov approximation. We define, via a windowed Fourier transform, multimode quantum states associated with radiation fragments produced at different times and compute the corresponding entanglement entropy increments. On the basis of these results, we argue that such entropy increments are useful entanglement measures, especially in cases such as Hawking radiation, where one wishes to separate the radiation into “old” and “new.”

Absorption profiles of vector light upon interaction with atomic vapor carries distinct signatures of an external magnetic field vector. However, this signature becomes ambiguous for antiparallel magnetic field vectors of equal magnitude, which makes their absorption profiles visually indistinguishable. To resolve this ambiguity, we present a theoretical analysis of the interaction of vector light with optically polarized atoms immersed in reference and test magnetic fields. Furthermore, we demonstrate the complete characterization of the arbitrarily oriented test magnetic field via a Fourier analysis of the absorption profile. This analysis reveals a one-to-one correspondence between the magnetic field properties and the profile's contrast and rotational angle. Our findings open an avenue to design an optical vector atomic magnetometer based on structured light fields.

We investigate the Casimir effect in a system of two twisted photonic gratings made of uniaxially anisotropic materials. Two distinct configurations are explored: a stack of symmetric gratings and a stack of in-plane chiral grating, with the latter realized by choosing a specific orientation of the anisotropy axis relative to stripes. We apply the reflection-matrix-based Casimir-Lifshitz formalism to explore how twist angle, material anisotropy, and the separation between gratings influence Casimir energy, force, and torque. Our calculations reveal that the equilibrium orientation of the gratings is governed by the anisotropy rotation angles, leading to a chiral configuration where the anisotropy axes of the upper and lower gratings are mutually parallel. These findings demonstrate that material anisotropy provides a powerful mechanism for controlling rotational alignment forces in nanophotonic systems.

We investigate a two-color scheme for tabletop high-order harmonic generation (HHG) that combines a mid-infrared (MIR) driving field with an ultrashort ultraviolet (UV) pulse that could be generated via resonant dispersive wave emission in gas-filled hollow-core fibers. This configuration enables the generation of bright, isolated, and tunable attosecond x-ray pulses. In contrast to single-color driving schemes, which suffer from low conversion efficiency, unfavorable wavelength scaling, and limited spectral control, the $\mathrm{MIR}+\mathrm{UV}$ approach provides a practical and controllable route for advancing tabletop ultrafast spectroscopy and real-time molecular imaging within current experimental capabilities.

The interplay between nonlinear and topological physics has led to intriguing emergent phenomena, such as quantized and fractionally quantized Thouless pumping of solitons dictated by the topological invariants of the underlying band structure. Unlike linear Thouless pumping, which requires excitation of a Wannier function of a uniformly filled band, quantized soliton pumping is observed even with localized excitations that do not represent Wannier functions. Here, we show that similar solitonlike quantized pumping can be observed in the Aubry-André-Harper model by introducing a synthetic nonlinearity in the form of a cutoff on the coupling strengths between lattice sites. More importantly, we reveal that the localized excitations driving quantized soliton pumping are precisely the Wannier functions of the uniformly filled bands of the effectively nonlinear lattice, thus restoring consistency with linear Thouless pumping. We extend this approach to multiband systems and show that the nonlinearity introduces a degeneracy between bands, subsequently leading to the observation of fractionally quantized pumping. Our approach of introducing a synthetic nonlinearity is general and could be extended to reveal soliton dynamics in other nonlinear topological systems.

We investigate the fully quantum evolution of the population imbalance in a perfectly symmetric Bose-Josephson junction modeled by a two-mode Bose-Hubbard Hamiltonian, focusing on the validity of macroscopic quantum self-trapping beyond the mean-field theory. We show that for any finite number of particles, the exact quantum dynamics leads to the breakdown of macroscopic quantum self-trapping after a finite time, regardless of the initial state. Using the symmetries of the Bose-Hubbard Hamiltonian, we provide a mathematical demonstration of this result and analyze the spectral properties governing the dynamics. We identify a branching behavior in the eigenvalue differences and a nontrivial structure of the population-imbalance amplitudes. These features allow us to distinguish two clearly different dynamical regimes and to elucidate the mechanism leading to the emergence of a quasi–macroscopic quantum self-trapping regime for large particle numbers. These findings bridge the gap between mean-field predictions and exact quantum dynamics and provide insight into the emergence of classical nonlinear behavior from finite quantum many-body systems.

Typically, quantum phases of many-body systems fit either the Landau-Ginzburg paradigm or topological classifications, with the intertwined emergence of spontaneous symmetry breaking and topological order being experimentally challenging. We present an experimentally accessible spin-orbit-coupled Lieb lattice platform for magnetic topological states. Remarkably, we observe topological characteristics, quantified by Chern number and Bott index, coexisting with spontaneous symmetry-breaking orders (like ferrimagnetism) in the many-body ground states. Computational analyses reveal a pronounced parameter regime where magnetic topological insulators emerge even under weak interactions. This unconventional coexistence stems from the Lieb lattice's unique band structure, enabling synergy between interaction-driven symmetry breaking and spin-orbit coupling-induced band inversion. Crucially, spin polarization and spin winding coemerge as coupled phenomena originating from identical degrees of freedom. We propose an implementation using ultracold atoms with existing Raman lattice techniques. Our findings pave the way for exploring the interplay between symmetry-broken states and topological order in strongly correlated systems.

We provide the ultimate precision attainable in spectroscopy of a quantum emitter using single-photon pulses. We find that the maximum precision of linewidth estimation is independent of the details of the emitter's bare Hamiltonian, though this is not true for the detunings. We also identify optimal pulse shapes attaining these precisions.

We present a quantum averaging theory (QAT) for analytically modeling unitary gate dynamics in driven quantum systems beyond the rotating wave approximation. QAT addresses the simultaneous presence of distinct timescales by generating a rotating frame with a dynamical phase operator that toggles with the high-frequency dynamics and yields an effective Hamiltonian for the slow degree of freedom. By accounting for the fast-varying effects, we demonstrate that high-fidelity two-qubit gates in strongly driven systems are achievable by going beyond the validity of first-order approximations. The QAT results rapidly converge with numerical calculations of a fast-entangling Mølmer-Sørensen trapped-ion-qubit gate in the strong-coupling regime, illustrating QAT's ability to simultaneously provide both an intuitive, effective Hamiltonian model and high accuracy.

We consider coherently coupled bosonic mixtures scattering at low energies in the presence of an external confinement along either one or two directions. We exactly solve the two-body scattering problem, showing that for large Rabi coupling the confinement-induced resonance can be displaced towards scattering lengths much smaller than the oscillator length. Our results make the observation of confinement-induced resonances more tunable and accessible, offering yet another handle for the efficient control of strong interactions in ultracold quantum gases.

Supersolidity—the simultaneous superfluid flow and crystalline order—has been realized in quantum atomic systems, but remains widely unexplored in photonic platforms operating at weak light-matter coupling. We predict a supersolid phase of light in a plasma-filled optical microcavity, where photons acquire effective mass and interact via nonlocal, plasma-mediated nonlinearities. By deriving a Gross-Pitaevskii equation with a tunable photon-photon interaction kernel, we show that the light field can spontaneously crystallize into a supersolid lattice via modulational instability. Crucially, this supersolid arises from a weak photon-electron coupling enabled by virtual electronic transitions and it does not require hybrid polariton formation. Using doped semiconductor microcavities, we identify accessible conditions (electron densities $\sim {10}^{10}–{10}^{11}{\mathrm{cm}}^{-2}$ and optical intensities $\sim {10}^3–{10}^5\mathrm{W}/{\mathrm{cm}}^2$) for experimental realization. This work establishes plasmonic cavities as a platform for correlated photonic matter with emergent quantum order.