Photoabsorption spectra of ions of iridium, platinum, and gold have been recorded using the dual laser plasma technique in the spectral region between 48 and 126 eV. Features due to $5p$ and $4f$ excitation in neutral to four times ionized species lie in this region. Evidence of the rapid decay of the $5p$ hole following photoabsorption is provided by the widths of the spin-orbit split transition arrays, in contrast to the sharper and narrower features seen arising from $4f$ photoabsorption. The analysis of the iridium spectra is supported by atomic structure calculations and isoelectronic series analysis. Agreement with previous analysis of the spectra of platinum and gold is seen and some new identifications are also made. The significance of these $r$-process elements for astrophysical research is highlighted.

The transition dipole moments between different energy bands of a crystal determine the optical properties of the solid and the light-induced electron-hole dynamics. Solid-state high-harmonic generation encodes all the information about the dipole in momentum space, making it a promising approach for reconstructing the momentum-space dipole. In this work, we develop a machine-learning framework, based on a one-dimensional semiconductor Bloch equation combined with the strong-field approximation in a single-electron picture, to reconstruct semiconductor dipoles from solid-state high-harmonic spectra. As long as the assumptions of the underlying model are satisfied, the proposed approach is robust against variations in the laser parameters, band dispersion, and hidden errors in the input data. We also discuss the potential influence of the approximations employed on the reconstruction accuracy. This method provides an alternative pathway for extracting dipole information from high-harmonic spectra.

Investigating the behavior of polyatomic molecules in strong laser fields allows the examination of coupled nuclear and electronic dynamics. In this article we examine multibody fragmentation of formic acid dications, produced by ultrashort intense laser pulses, using coincidence momentum imaging and deuterium tagging to distinguish the hydrogen sites. Our measurements indicate that double hydrogen elimination leads to three- and four-body breakup, specifically $\mathrm{H}+\mathrm{D}+{\mathrm{CO}}_2^{2+}$ and $\mathrm{H}+\mathrm{D}+{\mathrm{O}}^{+}+{\mathrm{CO}}^{+}$, respectively. We find that the latter breakup channel also proceeds via the ${\mathrm{CO}}_2^{2+}$ metastable dication, but with shorter lifetimes than the ${\mathrm{CO}}_2^{2+}$ dications detected intact. This intriguing sequential breakup is identified using native frames analysis and simulations to confirm the signature of this process in spite of the inferior momentum resolution associated with breakup channels for which not all fragments are detected. In addition to the fragmentation channel above, we found no evidence of sequential breakup for single hydrogen elimination, $\mathrm{H}+{\mathrm{CO}}^{+}+{\mathrm{OD}}^{+}$. The elimination of three atoms, $\mathrm{H}+\mathrm{D}+\mathrm{O}+{\mathrm{C}}^{+}+{\mathrm{O}}^{+}$, shows evidence of both concerted fragmentation and sequential breakup via metastable intermediate ${\mathrm{CO}}^{2+}$ ions. Measuring the dissociation dynamics of these highly excited molecular ions yields information that can be used to test theoretical approaches to these challenging few-body systems.

We explore the formation of metastable ${\mathrm{CO}}_2^{2+}$ from linear and “bent” carbon dioxide by intense ultrashort laser pulses. In particular, we evaluate the fraction of these dications that survive to the detector and determine the lifetime of those that dissociate in flight through our apparatus. Curiously, the fraction of those dissociating in flight changes significantly when cooling the linear ${\mathrm{CO}}_2$ target using a He carrier gas, while the lifetimes change only slightly. To determine these lifetimes we employ an improved method that takes into account the dissociation velocity of the ${\mathrm{O}}^{+}+{\mathrm{CO}}^{+}$ fragments in a self-consistent manner. We also determine the dissociation-in-flight lifetime of an initially bent ${\mathrm{CO}}_2^{2+}$ fragment of ${\mathrm{HCOOD}}^{2+}$ following rapid double hydrogen elimination.

We present a microscopic description of dressed four-wave mixing (4WM) demonstrating spectral control of quantum correlations. Starting from a double $\mathrm{\Lambda }$ model for a single pump 4WM, we include a dressing field coupling the excited level, which leads to a six-wave mixing process. The model describes the enhancement of amplification and amplitude modulation in situ, due to the interaction of the dressing field, according to the experimental parameters. Moreover, the model predicts that the interaction with dressing fields allows the spectral control of the quantum correlations between pairs of sidebands by simply tuning the dressing field accordingly. This work paves the way towards all-optical control of quantum correlations in the continuous variable context.

The information causality principle $\left(\mathcal{IC}\right)$ was originally proposed as a promising means to understand the extent of quantum nonlocality without invoking the full mathematical formalism of quantum theory. Beyond the foundational significance, the problem of bounding nonlocal correlations by reasonable physical principles has meaningful practical consequences, particularly for device-independent (DI) cryptographic security. In this work, we advance in this direction, demonstrating that the $\mathcal{IC}$ is enough to ensure DI security on quantum key distribution (QKD) protocols. Security is proven for a range of theoretically quantum-attainable parameters against individual attacks by a potentially postquantum eavesdropper. This result follows as a consequence of a strong form of monogamy of Bell's inequality violations, which we prove to be implied by the recently proposed multipartite formulation for $\mathcal{IC}$. Additionally, we demonstrate that the original bipartite formulation of $\mathcal{IC}$ fails to imply monogamy relations, and hence, ensure security of DIQKD, thus stressing the necessity of the multipartite framework.

The spontaneous switching of a quantum particle between the wells of a double-well potential is a phenomenon of general interest to physics and chemistry. It was broadly believed that the switching rate decreases steadily as a function of the size of the energy barrier. This view was challenged by a recent experiment on a driven superconducting Kerr nonlinear oscillator (often called the Kerr-cat qubit or the Kerr parametric oscillator), whose energy barrier can be continuously increased by ramping up the drive. Remarkably, as the drive amplitude increases, the switching rate exhibits a steplike decrease termed the “staircase.” The view challenged by the experimental staircase demands a deep review of our understanding of the role of quantum effects in double wells. In this work, we use a Lindbladian model of dissipation to derive a semianalytical formula for the switching rate, resolving a continuous transition between tunneling-dominated dynamics and dissipation-dominated dynamics. These two dynamics are observed respectively in the flat part and the steep part of each step in the staircase. Our formula exposes two distinct dissipative processes that limit tunneling: the dephasing of interwell superpositions freezes tunneling via the quantum Zeno effect, and the decay from one excited state to another limits the time during which tunneling can be attempted. This physical understanding allows us to pinpoint the critical drive amplitude that separates the flat and steep part of each step using an equation involving the rates of the two dissipative processes and the tunnel splitting. In addition, analyzing the transition matrix elements in the formula shows that in the regime of a few ($\lesssim 10$) states in the well and under moderate to low temperatures, highly excited states are populated predominantly via cascaded and direct thermal heating rather than quantum heating. At very low temperatures, we find that the perturbation induced by the non-Hermitian Hamiltonian part of the Lindbladian model becomes increasingly important and facilitates a form of quantum heating that has not been identified before. We numerically map the activation mechanism as a function of drive amplitude, damping rate, and temperature. Our theory deepens the understanding of switching dynamics between metastable quantum states, highlights the importance of a general interplay between tunneling and dissipation, and identifies a novel quantum regime in activated transitions.

Dynamical quantum phase transitions (DQPTs) appear as nonanalyticities during the coherent evolution of closed systems. However, understanding the scaling behaviors in realistic finite-size systems is intricate and requires a framework beyond thermalized equilibrium analogies. We propose a general dynamical quantum finite-size scaling theory and demonstrate its validity using numerical and analytical approaches in a spin chain. Combining fidelity and renormalization group, we identify the scaling behavior of the transverse magnetization that simultaneously exhibits quantum coherence and statistical properties. In addition, we adapt generalized correlation functions in quantum chemistry protocols to visualize the effective light cone of quantum mutual information, demonstrating the importance of the coherence propagation to DQPTs. Our work provides a phenomenological insight and a quantitative analysis to the underlying microscopic entanglement evolution, offering an alternative interpretation of DQPTs and advancing the understanding of many-body physics.

The short Doppler-limited coherence time of the laser-excited Rydberg state, usually orders of magnitude shorter than the lifetime of the Rydberg state, hinders the Rydberg-mediated quantum technologies. Here, we show that a 649–658-nm two-photon excitation of the $6sng{}^{1}G_4$ Rydberg state from a long-lived $d$-orbital clock state of barium can be achieved with a two-photon wave vector that is tiny, which effectively removes the Doppler-limited decoherence. Moreover, the $6sng{}^{1}G_4$ Rydberg state has strong dipole-dipole interaction due to small Förster defect with nearby Rydberg states and possesses long radiative lifetime. These can benefit quantum computing based on individually trapped neutral atoms and can enable long-lived Rydberg polaritons in atomic media, which brings fresh opportunities in all-optical quantum information.

Qudits naturally correspond to multilevel quantum systems, which have the potential to enable more efficient quantum information processing, but their reliability is contingent upon quantum error-correction capabilities. In this paper, we present a general procedure for constructing error-correcting qudit codes through the irreducible representations of $\mathrm{SU}\left(d\right)$ for any odd integer $d\ge 3$. Using the Weyl character formula and inner product of characters, we deduce the relevant branching rules, through which we identify the physical Hilbert spaces that contain valid code spaces. We then discuss how two forms of permutation invariance and the Heisenberg-Weyl symmetry of $\mathfrak{su}\left(d\right)$ can be exploited to simplify the construction of error-correcting codes. Finally, we use our procedure to construct an infinite class of error-correcting codes encoding a logical qudit into ${(d-1)}^2$ physical qudits.

Dynamical decoupling (DD) is a well-known open-loop protocol for suppressing unwanted interactions in a quantum system, thereby drastically extending the coherence time of useful quantum states. In the original framework of evolution symmetrization, a DD sequence was shown to enforce a symmetry on the unwanted Hamiltonian, thereby suppressing it if the symmetry was inaccessible. In this work, we show how symmetries already present in the undesired Hamiltonian can be harnessed to reduce the complexity of decoupling sequences and to construct nested protocols that correct dominant errors at shorter timescales using the factorization of DD symmetry groups into a product of its subgroups. We provide many relevant examples in various spin systems, using the Majorana constellation and point-group factorization to identify and exploit symmetries in the interaction Hamiltonian. Our framework recovers tailored pulse sequences developed in the context of NMR, including the classical Lee-Goldburg protocol, and further produces novel short and robust sequences capable of suppressing on-site disorder, dipole-dipole interactions, and more exotic many-body interactions in spin ensembles.

We report the experimental observation of ultrafast demethylation in ethanol dimers following single ionization induced by a 400-nm femtosecond laser field, described by the reaction ${\left({\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\right)}_2+n\hslash \omega \to \mathrm{C}{\mathrm{H}}_3+\mathrm{C}{\mathrm{H}}_2\mathrm{O}·\left({\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\right){\mathrm{H}}^{+}+e^{-}$. This demethylation pathway is identified through the detection of the ionic fragment $\mathrm{C}{\mathrm{H}}_2\mathrm{O}·\left({\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\right){\mathrm{H}}^{+}$, accompanied by the coincident measurement of emitted electron. Analysis of the electron-nuclear joint kinetic energy spectrum reveals multiple diagonal features spaced by the photon energy, showing the essential role of electron-nuclear correlation in the demethylation process. The reaction timescale is determined by introducing a time-delayed 800-nm femtosecond probe pulse, yielding a characteristic time of approximately 0.95 ps. This duration is longer than that observed for demethylation following single ionization of ethanol monomers, highlighting the pronounced influence of intermolecular interactions in the dimeric system.

We investigate the three-body fragmentation dynamics of hydrogen-bonded molecular dimers ${\left({\mathrm{H}}_2\mathrm{O}\right)}_2$ and ${\left({\mathrm{NH}}_3\right)}_2$ under intense femtosecond laser irradiation. Using a reaction microscope for coincident detection of all ionic fragments, we observe the fragmentation channels ${\mathrm{H}}_2{\mathrm{O}}^{+}+\mathrm{O}{\mathrm{H}}^{+}+{\mathrm{H}}^{+}$ and ${\mathrm{NH}}_3^{+}+{\mathrm{NH}}_2^{+}+{\mathrm{H}}^{+}$. By diagnosing the Newton diagrams, Dalitz plots, and kinetic-energy correlation maps, one concerted pathway and two sequential dissociation pathways are identified in both channels. Native frame analysis enables reconstruction of the branching ratios for these pathways. While the behaviors of the concerted pathway and the sequential pathway involving initial ${\mathrm{H}}^{+}$ emission are comparable in both systems, the sequential pathway with ${\mathrm{H}}^{+}$ emission in the second step exhibits distinct dynamics, with a higher relative branching ratio for ${\left({\mathrm{NH}}_3\right)}_2$. These differences arise from the stronger hydrogen bonds in ${\left({\mathrm{H}}_2\mathrm{O}\right)}_2$ promoting proton transfer and the weaker hydrogen bonds in ${\left({\mathrm{NH}}_3\right)}_2$ favoring hydrogen bond breaking. Our findings underscore the critical role of hydrogen bond strength in shaping the fragmentation dynamics of hydrogen-bonded molecular dimers under laser-induced dissociation.

We propose quantum simulation experiments of the Kondo impurity problem using cold alkaline-earth(-like) atoms (AEAs) in a combination of optical lattice and optical tweezer potentials. Within an ab initio model for atomic interactions in the optical potentials, we analyze hallmark signatures of the Kondo effect in a variety of observables accessible in cold-atom quantum simulators. We identify additional terms not part of the textbook Kondo problem, mostly ignored in previous works and giving rise to a direct competition between spin and charge correlations, strongly suppressing Kondo physics. We show that the Kondo effect can be restored by locally adjusting the chemical potential on the impurity site, and we identify realistic parameter regimes and preparation protocols suited to current experiments with AEA arrays. Our work paves the way for quantum simulations of the Kondo problem and offers insights into Kondo physics in unconventional regimes.

In this paper, we primarily investigate the generation of quantum entanglement triggered by a single photon between two qubits or multiple qubits and analyze the impact of decoherence of the light field. In the model of single-photon interaction with two qubits, we first study the effect of the initial excited-state weight of the qubits on the entanglement triggered by a single photon. We find that the greater the initial excited-state weight, the smaller the maximum quantum entanglement triggered by the single photon between the two qubits. Specifically, when both qubits are in the excited state, a single photon cannot trigger quantum entanglement between the two qubits. We then examine the impact of the initial coherence of the two qubits on the entanglement triggered by a single photon, and find that a single photon can trigger the maximum quantum entanglement between two qubits when both qubits initially have maximum coherence. In the model of single-photon interaction with multiple qubits, in the limit of a large number of qubits, we find that when the initial excited-state weight of each qubit is larger than the ground-state weight, or when all qubits are initially in the ground state, a single photon cannot trigger quantum entanglement between any two qubits in the multiqubit system. Interestingly, we find that a single photon can trigger quantum entanglement between any two qubits from at least 2000 qubits. Moreover, in this limit, the maximum quantum entanglement between any two qubits in the multiqubit system triggered by a single photon changes with the initial-state parameters and almost no longer depends on the number of qubits. Finally, we discuss the effect of decoherence of the light field, and we find that a higher decoherence strength of the light field weakens the generation of quantum entanglement between qubits in both the single-photon interaction with two qubits and the single-photon interaction with multiple qubits models. However, interestingly, the initial coherence of the qubits can resist the impact of decoherence, especially when the two nonidentical qubits, both having maximum coherence, can maintain the maximum quantum entanglement between the two qubits at 0.5 even as the decoherence strength of the light field increases.

We study light propagation in an array of periodically curved waveguides consisting of pairs of waveguides with out-of-phase oscillations of waveguide centers. We compute the corresponding Floquet propagation constants and find pseudocollapses where the Floquet bands shrink and, respectively, light diffraction is significantly inhibited. When, in addition, the refractive index of the waveguides in the array has quasiperiodic modulation in the transverse direction, we establish the existence of Floquet modes localized in the transverse direction and periodic in the longitudinal direction. With increase of the depth of quasiperiodic modulation of the refractive index in the array, the localized Floquet modes emerge near the pseudocollapse points of the periodic array. In an array with sufficiently high frequencies of waveguide oscillations, the localized Floquet modes can exist even for weak quasiperiodic modulation which is situated below the localization transition in the array of straight waveguides.

Nonsymmetric GHZ states ($n\text{−}{\mathrm{GHZ}}_{\alpha }$), defined by unequal superpositions of $|00...0\rangle$ and $|11...1\rangle$, naturally emerge in experiments due to decoherence, control errors, and state preparation imperfections. Despite their relevance in quantum communication, relativistic quantum information, and quantum teleportation, these states lack a stabilizer formalism and a graph representation, hindering their theoretical and experimental analysis. We establish a graph-theoretic framework for nonsymmetric GHZ states, proving their local unitary (LU) equivalence to two structures: fully connected weighted hypergraphs with controlled-phase interactions and star-shaped controlled-unitary (CU) graphs. While weighted hypergraphs generally lack stabilizer descriptions, we demonstrate that nonsymmetric GHZ states can be efficiently stabilized using local operations and a single ancilla, independent of system size, thereby enabling entanglement witness construction and offering a pathway toward qudit quantum error correction. We extend this framework to qudit systems, constructing LU-equivalent weighted qudit hypergraphs and showing that general nonsymmetric qudit GHZ states can be described as star-shaped CU graphs. Our results provide a systematic approach to characterizing and stabilizing nonsymmetric multipartite entanglement in both qubit and qudit systems, with implications for quantum error correction and networked quantum protocols.

Breaking the standard quantum limit in the sensing of parameters at different spatial locations, such as in a quantum network, is of great importance. Using the framework of quantum Fisher information, many strategies based on squeezed quantum probes and multipath multiphoton or multiqubit entangled states have been considered. In this context there is always the question of what the simplest measurement is that would saturate the quantum Cramér-Rao bound (QCRB). The simplest quantity to measure would be characteristics of photon flux or population distribution in the case of qubits. Previous studies have shown that the error sensitivity in SU(1,1) interferometry, also known by several other terms such as nonlinear interferometry and time-reversed measurements, does saturate the QCRB for single parameters such as phase, displacement, and loss. In this work we reveal the great utility of generalized SU(1,1) interferometry in distributed sensing. Generalized SU(1,1) interferometry is a combination of $\mathrm{SU}\left(m\right)$ and SU(1,1) elements, where $m$ is the number of nodes in the network. The $\mathrm{SU}\left(m\right)$ element is used to produce distributed entanglement starting from a squeezed photonic or matter probe. We demonstrate how error sensitivity measurement or more precisely the method of moment sensitivity at just one output port can saturate or nearly saturate the QCRB and thus results in Heisenberg sensitivity of network sensing.

Thermodynamical systems at the nanoscale, such as single molecules interacting with highly structured vibrational environments, typically undergo nonequilibrium physical processes that lack precise microscopic descriptions. Photoisomerization is such an example, which has emerged as a platform on which to study single-molecule ultrafast photochemical processes from a quantum resource theoretic perspective. However, the upper bounds on its efficiency have only been obtained under significant simplifications that make the mathematics of the resource-theoretical treatment manageable. Here we generalize previous models for the photoisomers, while retaining the full vibrational structure, and still obtain analytical bounds on the efficiency of photoisomerization. We quantify the impact of such a vibrational structure on the optimal photoisomerization quantum yield both when the vibrational coordinate has no dynamics of its own and when we take into account the vibrational dynamics. This work serves as an example of how to bridge the gap between the abstract language of quantum resource theories and the open system formulation of nanoscale processes.