A density matrix (DM) approach has been successfully developed for modeling the dissociative sequential double ionization of molecules driven by ultrashort intense infrared laser pulses. Here, we extend the DM method to theoretically study the dissociative sequential triple ionization of nitrogen molecules. We first calculate potential-energy curves of the ${\mathrm{N}}_2^{3+}$ states and the transition dipole moments between these ${\mathrm{N}}_2^{3+}$ states using the complete active state self-consistent field method. Using the DM method, we calculate the kinetic-energy release (KER) spectra for the ${\mathrm{N}}_2^{3+}$ dissociating through the ${\mathrm{N}}^{2+}+{\mathrm{N}}^{+}$ channel. We find that our simulated KER spectra agree well with the experimental data by Wu et al. [Phys. Chem. Chem. Phys. 13, 18398 (2011)]. This Letter provides a simple model for theoretically investigating the molecular dissociative sequential triple ionization.

We report observation of self-oscillating supersonic flows in a two-dimensional atomic superfluid. By imposing a local particle sink with strong loss, we induce a convergent radial flow with a spatially bounded supersonic region, forming an acoustic analog of a black-hole horizon and an inner horizon around the sink. The observed superflow appears to be modulated by quasiperiodic bursts of superluminal signals. We measure their frequencies and find agreement with numerical simulations of the frequencies of ring soliton oscillations within the black-hole horizon. The solitons seen in the simulations are emitted from the region between the two horizons in a process that we attribute to the Landau instability. The presented experiment demonstrates a new method for creating supersonic flows in atomic superfluids, which may find applications in quantum simulations of curved spacetime, supersonic turbulence, and self-oscillating dynamics in dissipative many-body systems.

We analyze the Markovian dynamics of a quantum system composed of two interacting quantized fields, each coupled to a thermal reservoir with the same average number of thermal excitations ${\overline{n}}_{\text{th}}$, but with different decay rates ${\gamma }_j$ (with $j=1,2$). By employing superoperator techniques and applying two nonunitary transformations, the Lindblad master equation is reformulated into a von Neumann-like form governed by an effective non-Hermitian Hamiltonian. Under these conditions, the structure of the effective Hamiltonian remains equivalent to that of the zero-temperature case, indicating that the essential features of the system dynamics are preserved even in the presence of thermal excitations. As an illustrative example of the method, photon coincidence rates are presented for an initial state composed of two indistinguishable photons.

We report the enhanced optical transmission in the coherent, off-resonant excitation of Rydberg atom gases at room temperature via a two-photon process. Here thermal resonance-enhanced transparency (TRET) is induced when the detuning of the two lasers is adjusted to compensate the atomic thermal-motion-induced energy shifts, i.e., single- and two-photon Doppler shifts. We show that the atomic velocity is mapped into the transmission of the probe fields, which can be altered by independently and selectively exciting different velocity groups through sweeping the detuning. The maximal transmission in TRET is about 8 times higher than that under electromagnetically induced transparency (EIT). Utilizing the TRET effect, we enhance the sensitivity of a Rydberg microwave receiver to be $28.7{\mathrm{nV}\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1/2}$, ultimately reaching a factor of 2.1 of the EIT case. When atoms of separate velocity groups are excited simultaneously by multiple laser sets of different detuning, the receiver sensitivity increases with the number of laser sets. Our study paves the way to exploit light-matter interaction via the TRET, and contributes to current efforts in developing quantum sensing, primary gas thermometry, and wireless communication with room-temperature atomic gases.

The Chern-Simons (CS) invariant is a fundamental topological invariant describing the topological invariance of three-dimensional (3D) space based on the Chern-Simons field theory. To date, direct measurement of the CS invariant in a physical system remains elusive. Here, the CS invariant is experimentally measured by quenching a 2D optical Raman lattice with 1/2 spin in ultracold atoms. With a recently developed Bloch state tomography, we measure the expectation values of three Pauli matrices in 2D quasimomentum space plus 1D time $\left[\right(2+1\left)\mathrm{D}\right]$, and then respectively extract the Berry curvature and the corresponding Berry connection. By integrating the product of these two quantities, we obtain the CS invariants near $\pm 1$ and 0, which are consistent with theoretical predictions. We also observe transitions among these values, which indicates the change of the topology of the quantum state in $(2+1)\mathrm{D}$ quantum dynamics.

Singular optics studies light's topological defects, pioneered by the discovery that phase vortex lines, strands of destructive interference, naturally occur in scalar wave fields. General electromagnetic waves, however, are described by three-dimensional vectors making scalar phase vortices, which depend on the choice of coordinate basis, less meaningful. Polarization singularities instead capture the vector texture of nonparaxial light with separate descriptions for the electric and magnetic fields. But these polarization textures cannot be fundamental because electromagnetic laws can be expressed not only by separate electric and magnetic fields, but by linear combinations of the two. We propose fundamental, basis-independent topological features generic in electromagnetic fields: one- and two-dimensional structures that relate to time-averaged symmetries held locally by the combined electric- and magnetic-field polarization geometry.

Quantum criticality of open many-body systems has attracted lots of interest for emergent phenomena and universality. Here we present the exact steady state of the quantum van der Pol oscillator using the complex $P$-representation. We show the threshold corresponds to a dissipative phase transition with abrupt changes of steady-state properties and enhanced metrology. The critical behaviors and finite-size effects are investigated through the analytical steady state. We obtain divergent quantum Fisher information (QFI) in the thermodynamic limit both at the critical point and in the time crystal phase, but only the QFI at the critical point approaches the Heisenberg limit. We further prove that the steady-state photon number is the optimized estimated observable with the largest signal-to-noise ratio. We show that the Heisenberg-limited metrology originates from the enhancement of the photon number's susceptibility with a scaling larger than the enhancement of the standard deviation of the photon number. Our work reveals the underlying relation between the time crystal, dissipative phase transition, and enhanced metrology.

Connecting two surface-code patches may require significantly higher noise at the interface. We show, via circuit-level simulations under a depolarizing noise model with idle errors, that surface codes remain fault tolerant despite substantially elevated interface error rates. Specifically, we compare three strategies—direct noisy links, gate teleportation, and a CAT-state gadget—for both rotated and unrotated surface codes, and demonstrate that careful design can mitigate hook errors in each case so that the full code distance is preserved for both $X$ and $Z$. Although these methods differ in space and time overhead and performance, each offers a viable route to modular surface-code architectures. Our results, obtained with stim and pymatching, confirm that high-noise interfaces can be integrated fault-tolerantly without compromising the code's essential properties, indicating that fault-tolerant scaling of error-corrected modular devices is within reach with current technology.

Dipolar supersolids—quantum states that are simultaneously superfluid and solid—have had their superfluid nature rigorously tested, while their solid nature remain uncharted. Arguably, the defining characteristic of a solid is the existence of elastic shear waves. In this work we investigate transverse wave packet propagation in dipolar supersolids with triangular and honeycomb structure. Remarkably, the honeycomb supersolid displays anomalous dispersion, supporting waves traveling faster than the transverse speed of sound. While the distinction between anomalous and normal dispersion appears subtle, it has a profound influence on both the transport and scattering properties. For both supersolid phases, we calculate the shear modulus, a key parameter that quantifies the material's rigidity. Our findings are pertinent to current experimental efforts scrutinizing the fundamental properties of supersolids.

Contextuality is a fundamental property of quantum mechanics. Contrary to entanglement, which can only exist in composite systems, contextuality is also present for single entities. The case of a three-level system is of particular interest because—in agreement with the Bell-Kochen-Specker theorem—it is the simplest in which quantum contextuality is necessarily present. We verify that the polarizations of spin-1 massive particles produced at collider experiments indeed exhibit contextuality. To this purpose we consider $W$ gauge bosons produced in top-quark decays, $J/\psi$ and $K^{*}{\left(892\right)}^0$ mesons created in $B$-meson decays, and $\varphi$ mesons resulting from ${\chi }_c^0$ charmonium decays, making use of the data collected and analyzed by the ATLAS, LHCb, and BESIII collaborations, respectively. The polarizations of all these four particles show contextuality with a significance of more than $5\sigma$.

We present a cooling method for a strongly interacting trapped quantum gas. By applying a magnetic-field modulation with frequencies close to the binding energy of a molecular bound state we selectively remove dimers with high kinetic energy from the sample. We demonstrate cooling of the sample over a wide range of interaction strengths and measure a high cooling efficiency of $\gamma =4$ that exceeds all previous cooling near Feshbach resonances.

Manipulating intracluster ion-molecule reactions via the control of vibrational excitation states of the parent cluster ion holds significant promise. Herein, we studied the effect of vibrational excitation on intracluster ion-molecule reactions within the ethylene dimer ion ${\left({\mathrm{C}}_2{\mathrm{H}}_4\right)}_2{}^{+}$ focusing on the formation of ${\mathrm{C}}_4{\mathrm{H}}_8{}^{+}, {\mathrm{C}}_3{\mathrm{H}}_5{}^{+}$, and ${\mathrm{C}}_4{\mathrm{H}}_7{}^{+}$ ions, utilizing femtosecond laser pulses and ab initio calculations. Via coincident photoelectron and ion detection, we reconstructed the initial vibrational excitation state population (IVP) of the parent ion and found a correlation between the IVP and product formation. Our study shows that the branching ratios for ${\mathrm{C}}_4{\mathrm{H}}_8{}^{+}, {\mathrm{C}}_4{\mathrm{H}}_7^{+}$, and ${\mathrm{C}}_3{\mathrm{H}}_5^{+}$ ions are dominated by low, medium, and high vibrational states, respectively, and there is a clear competition among them. Further analysis confirmed that laser intensity affects the IVP, which determines the yield of each decay channel. Our study establishes a direct link between IVP and product distribution in intracluster ion-molecule reactions and demonstrates the potential to steer reaction outcomes by varying laser field intensity, which opens avenues to the tailored control of reactions in various intracluster systems.

Multiphoton resonances to high-lying energy levels represent an unavoidable source of Floquet heating in strongly driven quantum systems. In this work, we extend the recently developed two-tone approach of “canceling” multiphoton resonances to shaken lattices in the Hubbard regime. Our experiments show that even for strong lattice shaking, the inclusion of a weak second drive leads to cancellation of multiphoton heating resonances. Surprisingly, the optimal canceling amplitude depends on the Hubbard interaction strength $U$, in qualitative agreement with exact diagonalization calculations. Our results call for novel analytical approaches to capture the physics of strongly driven, strongly interacting many-body systems.

We discuss the nonlinear process of backward-wave parametric amplification and oscillation, phase matched using a nonlinear grating inside a chiral medium. Our theory shows a remarkable feature manifesting as photoinduced flipping of optical chirality between the signal and the idler waves, without any change in the structural chirality of the medium. We show that circular birefringence, induced by chirality, leads to two different nonlinear processes with different phase-matching conditions that are associated with opposite states of circular polarizations. When the incident pump and signal beams are linearly polarized initially, their state of polarization evolves in an elliptical fashion because of the two competing nonlinear processes taking place in parallel. We also discuss the properties of such cavityless optical parametric oscillators based on distributed feedback provided by the nonlinear grating used for quasi phase matching.

We report the demonstration of spatially translating a stored optical pulse at room temperature over distances exceeding one optical wavelength. By implementing an interferometric scheme, we further measure the average speed of this linear translation, thus harnessing a stopped-light experiment for a sensing application. This work extends the use of quantum memories beyond quantum communication and information contexts, opening a pathway to novel methods of velocity measurements with high sensitivity.

We demonstrate that a nonmagnetic silicon nanoparticle dimer can scatter visible light as a pure magnetic scatterer under plane-wave illumination, with magnetic resonance dominant and electric dipole responses suppressed. This is achieved by spectrally overlapping the magnetic dipole resonance with the electric toroidal and magnetic quadrupole modes. Then the destructive interference between the Cartesian electric dipole and the electric toroidal mode suppresses the spherical electric dipole response and thus generates a nonradiating anapole mode, enabling ideal magnetic resonance scattering with overlapping magnetic dipole and quadrupole responses in the far field. Moreover, the wavelengths of magnetic resonance responses are tunable in the visible light range.

We consider the quantum simulation of quadratic spin-phonon coupling in a crystal of trapped ions. The coupling is implemented using tightly focused optical tweezers on each ion that change the local trapping potential in a state-dependent way. By encoding spins in the internal states of the ions and adding a tunneling term via Mølmer-Sørensen-type interactions, we calculate the emergence of mobile bipolarons driven by the zero-point energy of the ion crystal phonons. We show that thermal occupation may pin the bipolarons for ion crystals at finite temperature. Our scheme can be used to study and illustrate the emergence of mobile bipolarons as a function of temperature.

The large majority of topological phases in one-dimensional many-body systems are known to be inherited from the corresponding single-particle Hamiltonian. In this work, we go beyond this assumption and find a new example of topological order induced through specific interaction couplings. Specifically, we consider a fermionic mixture where one component experiences a staggered on-site potential and it is coupled through density-dependent hopping interactions to the other fermionic component. Crucially, by varying the sign of the staggered potential, we show that this latter fermionic component can acquire topological properties. Due to matrix product state simulations, we prove this result both at equilibrium by extracting the behavior of correlation functions and in an out-of-equilibrium scheme by employing a Thouless charge pumping. Notably, we further discuss how our results can be probed in quantum simulators made up of ultracold atoms. Our results reveal an important and alternative mechanism that can give rise to topological order.

High-order harmonic generation (HHG) of an atom in a strong laser field provides a broad spectral bandwidth for attosecond pulse synthesis. However, due to complex electron dynamics in the atom, usually only a part of the HHG can be used for the synthesis of the attosecond pulse, which significantly limits the attosecond pulse width. In this work we theoretically study the synthesis of attosecond pulses from high-order harmonics generated by intense squeezed light. It is found that, unlike the coherent light, the whole HHG spectrum can be effectively used to synthesize attosecond pulses. By developing strong-field approximation theory in squeezed light, this is attributed to substantial suppression of long and multireturn electron trajectories at the single-atom level. Based on this novel scheme using intense squeezed light, we show that an isolated attosecond pulse can be synthesized from the entire HHG spectrum, and the pulse width is much shorter than that from the coherent light with the same laser parameters.

We investigate the possibility of using a Rabi drive to tune the interactions in an atomic Fermi gas. Specifically, we consider the scenario where two fermion species (spins) are Rabi coupled and interacting with a third uncoupled species. Using an exact calculation within a minimal low-energy model, we derive analytical expressions for the effective scattering length and effective range that characterize the collisions between a Rabi-dressed atom and an atom from the third species. In particular, we find that new scattering resonances emerge in the Rabi-coupled system, which we demonstrate are linked to the existence of hybrid two-body bound states. Furthermore, we show via a generalized Thouless criterion that the scattering properties have a direct impact on the superfluid transitions in the Rabi-coupled Fermi gas. The presence of Rabi-induced resonances thus has implications for the investigation of many-body physics with driven atomic gases.