We investigate the out-of-equilibrium dynamics of quantum information in one-dimensional systems undergoing a quantum quench using a local perspective based on the information lattice. This framework provides a scale- and space-resolved decomposition of quantum correlations, enabling a hydrodynamic description of the information flow through well-defined local densities—termed local information—and currents. We apply this framework to three local quenches in noninteracting fermionic chains: (i) the release of a single particle into an empty tight-binding chain, (ii) the connection of two critical chains via the removal of a central barrier, and (iii) the coupling of a topological Kitaev chain to a critical chain. In each case, the information lattice reveals the local structure of correlation buildup and information interface effects, going beyond global measures such as the von Neumann entropy. In particular, through the information lattice, we uncover the signatures in the local information flow associated with topological edge modes and analytically explain the fractional von Neumann entropy values observed in Majorana quench protocols. Our approach is general and applicable to interacting, disordered, and open systems, providing a powerful tool for characterizing quantum information dynamics.

We investigated two deprotonated paracoumaric acid model chromophores of the photoactive yellow protein, ${\mathrm{pCE}}^{-}$ and ${\mathrm{pCK}}^{-}$, using action-absorption spectroscopy. Employing cryogenic cooling, we determined the ${\mathrm{S}}_0\text{−}{\mathrm{S}}_1$ band origins and associated vibrational resonances, which were found to reside within the electronic continuum, rendering them susceptible to autodetachment. Resonances observed below the electron-detachment threshold were attributed to dipole-bound states of the neutral radical core, probed via resonant two-photon excitation and detachment. Above the electron-detachment limit, we identified dipole-resonance states susceptible to autodetachment. The experimental approach, combining 6 K helium-buffer gas cooling with an ion-storage ring, proved effective in resolving vibrational modes of both the neutral radical core and the valence-excited ${\mathrm{S}}_1$ state, revealing soft-mode resonances down to 50–100 ${\mathrm{cm}}^{-1}$. Time-resolved action detection indicates that internal conversion competes with autodetachment.

We consider the problem of reproducing one quantum measurement given the ability to perform another. We give a general framework and specific protocols for this problem. For example, we show how to use available “imperfect” devices a small number of times to implement a target measurement with average error that drops off exponentially with the number of imperfect measurements used. We hope that could be useful in near-term applications as a type of lightweight error mitigation of the measuring devices. As well as the view to practical applications, we consider the question from a general theoretical perspective in the most general setting where both the available and target measurements are arbitrary generalized quantum measurements. We show that this general problem in fact reduces to the ability to reproduce the statistics of (complete) von Neumann measurements, and that in the asymptotic limit of infinitely many uses of the available measurement, a simple protocol based upon “classical cloning” can perfectly achieve this task. We show that asymptotically any nontrivial quantum measurement can reproduce any other. We also study optimal protocols for a fixed number of uses of the available measurement. This includes, but is not limited to, improving both noisy and lossy quantum measurements. Furthermore, we show that, in a setting where we perform multiple measurements in parallel, we can achieve finite-rate measurement reproduction, by using block-coding techniques from classical information theory. Finally, we show that advantages can also be gained by making use of probabilistic protocols.

We propose that a nuclear clock based on the Th v ion can surpass the accuracy of clocks built with other thorium ions. The ${\mathrm{Th}}^{4+}$ ion has a rigid closed-shell core with zero total electron angular momentum, suppressing frequency shifts from black-body radiation and stray external fields that act mainly on electrons. We calculate the energy shift of the nuclear clock transition frequency in ${}^{229}\mathrm{Th}$ due to the Coulomb field of atomic electrons and find a relative frequency difference of $2.8\times {10}^{-7}$ between Th iv and Th v, 12 orders of magnitude larger than the projected ${10}^{-19}$ fractional uncertainty of a nuclear clock. We also perform calculations for Th v energy levels, ionization potential, static polarizability, quadratic Zeeman shift, and the black-body radiation shift of the nuclear line. Additionally, we determine the nuclear transition frequencies in two thorium ions and a neutral atom: ${\nu }_N=2,020,406.964\left(70\right)\mathrm{GHz}$ in Th iii, ${\nu }_N=2,020,408.264\left(100\right)\mathrm{GHz}$ in Th ii, and ${\nu }_N=2,020,408.364\left(100\right)\mathrm{GHz}$ in Th i.

Dissipative phase transitions (DPTs) are defined by sudden changes in the physical properties of nonequilibrium open quantum systems and they present characteristics that have no analog in closed and thermal systems. Several methods to detect and characterize DPTs have been suggested in the literature, the most famous of which, the Liouvillian gap, can be derived from a spectral analysis of the Liouvillian superoperator that governs the complex interplay between coherent and dissipative dynamics. Here we consider the output current, defined as the average total quantum jumps per unit time between the open quantum system and the environment. We propose that output current fluctuations and in particular their dynamical correlations, their power spectrum, and their characteristic timescale can provide valuable information about DPTs, confirming a dramatic change of behavior at the critical point. We validate our proposal using the dissipative $XYZ$ model and the nonlinear driven-dissipative Kerr model, showing good agreement with previous estimates of the location of the critical point. Compared to previous approaches, our proposal could already be experimentally tested in optical systems, providing a practical method to detect criticality in quantum open systems.

Nondemolition readout and high-fidelity unconditional reset of qubits are key requirements for practical quantum computation. For superconducting qubits, readout and reset are typically realized using resonators based on dispersive approximation. However, violations of the approximation often lead to detrimental effects on the qubit. In this work, we demonstrate nondemolition fluorescence readout and high-fidelity unconditional reset of a fluxonium qubit via dissipation engineering without employing a resonator. We design and implement a planar filter to protect the qubit from energy relaxation while enhancing the relaxation of the readout transition. By appropriately selecting the readout transition, we achieve fluorescence readout with enhanced quantum nondemolitionness. We also realize fast, high-fidelity, and all-microwave unconditional reset of the fluxonium qubit. These results highlight the potential of superconducting quantum computing architectures without relying on dispersive interaction between qubits and resonators.

We present a general theory of gain-modified emission dynamics between two quantum emitters (two level systems) in a linear gain medium, demonstrating how gain modifies the usual radiative decay rates and interemitter coupling and decay rates, from purely lossy systems. We derive a Born-Markov master equation that shows explicitly how gain modifies the usual rates appearing for two emitters in a loss-only medium and introduces new gain terms. We then present Bloch equations in the bare state basis as well as a dressed-state basis (using superradiant and subradiant states). As an application of the theory, we show calculations for a fully three-dimensional metal dimer in a gain-compensated medium containing two quantum emitters and show explicit solutions in terms of the quasinormal modes, which easily allows one to obtain all the relevant decay rates. We study the modified decay dynamics, gain excited pumping, as well as the entanglement entropy and spectral emission. We also demonstrate how a breakdown of the weak excitation approximation in the presence of gain requires a careful treatment beyond a linear response, which yields nontrivial incoherent coupling terms that typically are not included in dipole-dipole coupling models and heuristic gain pumping models.

We perform narrowline cooling of single dysprosium atoms trapped in a one-dimensional optical tweezer array, employing the narrow single-photon transition at 741 nm. At the trapping wavelength of 532 nm, the excited state is less trapped than the ground state. To obtain efficient cooling performances, we chirp the frequency of the cooling beam to subsequently address the red sidebands of different motional states. We demonstrate the effectiveness of the cooling protocol through Raman thermometry, which we characterize for our experimental conditions. We obtain an array of 75 atoms close to the motional ground state in the radial direction of the tweezers. Our results demonstrate the possibility to manipulate the motional degree of freedom of dysprosium in optical tweezer arrays, a key ingredient to exploit the potential of lanthanide-based tweezer platforms for quantum science.

Through left- or right-handed twisting, we investigate the impact of mirror-asymmetry (chirality) of the conducting boundary conditions of an equilaterial triangular cross section electromagnetic resonator. We observe the generation of eigenmodes with nonzero electromagnetic helicity as a result of the coupling of near degenerate ${\mathrm{TE}}_{11(p+1)}$ and ${\mathrm{TM}}_{11p}$ modes. This can be interpreted as an emergence of magnetoelectric coupling, which in turn produces a measurable shift in resonant mode frequency as a function of twist angle. We show that this coupling mechanism is equivalent to introducing a nonzero chirality material parameter ${\kappa }_{\text{eff}}$ or axion field ${\theta }_{\text{eff}}$ to the medium. Our findings demonstrate the potential for real-time, macroscopic manipulation of electromagnetic helicity.

We have performed microwave spectroscopy of sodium least-bound molecular states, improving the precision of the knowledge of their energies at zero magnetic field by almost three orders of magnitude. Our experimental observations give us access also to states submitted to predissociation, a phenomenon where a bound molecular state can naturally decay into the continuum. Our findings are compared to numerical calculations based on the latest interpolation of sodium interaction potentials and show good agreement, with slight discrepancies in the zero-field energy of the molecular states, suggesting a need for small adjustment of the interaction potentials.

We explore the paired superfluid phases of a Fermi gas in the presence of a continuous Rabi drive. We focus on the case where two components are Rabi coupled strongly enough that they form hybrid superpositions, which in turn interact with an uncoupled third component. Using a generalized Bardeen-Cooper-Schrieffer (BCS) ansatz, we show that there are two coupled superfluid order parameters, and we obtain the associated free energy and quasiparticle excitation spectrum. We find that we can drive BCS-BCS, BCS-Bose-Einstein condensate (BEC), and BEC-BEC crossovers purely by varying the detuning of the Rabi drive from the bare transition, with the precise crossover depending on the sign of the underlying interactions between the coupled and uncoupled components. We furthermore identify an exotic excited branch which features both normal to BCS superfluid transitions, as well as a BCS-BEC-BCS crossover. Introducing a generalized Thouless criterion, we show that this behavior is reflected in the critical temperature for superfluidity. Our Rabi-coupled scenario also possesses additional thermodynamic properties related to the pseudospin of the coupled components, which provide novel signatures of the state of the many-body system. The Rabi-driven Fermi gas thus emerges as a unique platform for engineering and probing a rich array of multiband superfluid phases.

We derive an extended version of the hierarchical equations of motion (HEOM) to compute output physical properties of a bosonic environment, which is allowed to be initially prepared at an earlier time in a non-Gaussian input state and then nonperturbatively interact with a quantum system with a linear environmental operator. While spectral assumptions analogous to those used in the regular HEOM are imposed to compute dynamical output bath observables, they are not required to model input states or output observables at a fixed time, in this case leading to time-dependent contributions to the equations. In the Markovian limit, we use this formalism to derive an input-output Lindblad equation which can be used to extend the applicability of the regular version. For a given desired input state and output observable, the range of the indexes extending the regular HEOM is, by construction, bounded. Overall, the aim of this formalism is to take advantage of the efficiency and generality of the HEOM framework to model non-Gaussian input states and the dynamics of environmental observables in bosonic, non-Markovian open quantum systems.

Understanding how to control phase transitions in quantum systems is at the forefront of research for the development of new quantum materials and technologies. Here, we study how the coupling of a quantum system to a non-Markovian environment, i.e., an environment with a frequency-dependent spectral density inducing memory effects, can be used to generate and reshape phase transitions and squeezing in matter phases. Focusing on a Lipkin-Meshkov-Glick model, we demonstrate that non-Markovian dissipation can be leveraged to engineer tricriticality via the fusion of second-order and first-order critical points. We identify phases that arise from different ways of breaking the single weak symmetry of our model, which led us to examine an alternative concept of directional spontaneous symmetry breaking (DSSB) as a general framework to understand this phenomenon. We show that signatures of DSSB can be seen in the emergence of spin squeezing along different directions, and that the latter is controllable via non-Markovian effects, opening up possibilities for applications in quantum metrology. Finally, we propose an experimental implementation of our non-Markovian model in cavity QED. Our work features non-Markovianity as a resource for controlling phase transitions in general systems, and highlights shortcomings of the Markovian limit in this context.

We derive a generalized quantum Langevin equation and its fluctuation-dissipation relation describing the quantum dynamics of a tagged particle interacting with a medium (environment), where both the particle and the environment are driven by an external time-dependent (e.g. oscillating) field. We specialize on the case of a charged tagged particle interacting with a bath of charged oscillators, under an external ac electric field, although the results are much more general and can be applied to any type of external time-dependent fields. We derive the corresponding quantum Langevin equation, which obeys a modified fluctuation-dissipation relation (FDR) where the ac field plays an explicit role. The modified FDR is non-Markovian even if the undriven particle-bath system is Markovian without the external field. We provide an illustration of the usefulness of these results and derive a new form of the quantum Nyquist noise for the voltage fluctuations in electrical circuits under ac conditions (finite frequency), which is the most general since it also accounts for the response of the heat bath (e.g. lattice ions) to the applied ac electric field in the GHz–THz region, of relevance for 5G/6G wireless technologies. This generalized quantum fluctuation-dissipation relation for driven systems can also find other applications ranging from quantum noise in quantum optics to quantum computing with trapped ions.

We report on the realization and characterization of a novel magic-wavelength nanofiber-based two-color optical dipole trap for cesium that allows us to generate two diametral periodic one-dimensional arrays of trapping sites with a spacing significantly smaller than half the resonant free-space wavelength of the cesium $D_2$ transition. This is achieved by launching a blue-detuned partial standing wave and two red-detuned light fields through the nanofiber. We trap and optically interface the atoms in the resulting periodic optical potential and characterize the trap by measuring the lifetime of the trapped atoms, the atom-light coupling strength, the filling factor, and the trap frequencies in the radial and axial directions. The implementation of this nanofiber-based optical interface with magic trapping wavelengths and sub-$\lambda /2$ spacing is an important step towards the exploration of novel collective radiative effects, such as selective radiance.

We present a class of generalized entropic quantum speed limits based on $\alpha \text{−}z$-Rényi relative entropy, a real-valued, contractive, two-parameter family of distinguishability measures. The quantum speed limit (QSL) falls into the class of Mandelstam-Tamm bounds, and it applies to finite-dimensional quantum systems that undergo a general physical process, i.e., their effective dynamics can be modeled by unitary or nonunitary evolutions. The results cover pure or mixed, separable, and entangled probe quantum states. The QSL time depends on the smallest and largest eigenvalues of the probe and instantaneous states of the system, and its evaluation requires low computational cost. In addition, it is inversely proportional to the time-average of the Schatten speed of the instantaneous state, which in turn is fully characterized by the considered dynamics. We specialize our results to the case of unitary and nonunitary evolutions. In the former case, the QSL scales with the inverse of the energy fluctuations, while the latter depends on the Schatten 1-norm of the rate of change of the quantum channel Kraus operators. We illustrate our findings for single-qubit and two-qubit states, and unitary and nonunitary evolutions. Our results may find applications in the study of entropic uncertainty relations, quantum metrology, and also entanglement entropies signaled by generalized entropies.

Ultracold dipolar hard-core bosons in optical ladders provide exciting possibilities for the quantum simulation of anisotropic spin ladders. We show that introducing a tilt along the rungs results in a rich phase diagram at unit rung filling. In particular, for a sufficiently strong dipolar strength, the interplay between the long-range tail of the dipolar interactions and the tilting leads to the emergence of a quantum floating phase, a critical phase with incommensurate density-density correlations. Interestingly, the floating phase is topological, constituting an intermediate gapless stage in the melting of a crystal into a gapped topological Haldane phase. This novel scenario for topological floating phases in dipolar spin ladders can be investigated in ongoing experiments.

Reconstruction of attosecond beatings by two-photon interferences (RABBIT) has amply been used to retrieve photoionization delays from photoelectron spectra measured in atoms and, more recently, in molecules. For the latter, the molecular orientation and multicenter nature of the potential felt by the escaping electron often makes the extraction of these delays problematic. One of the complications comes from the fact that the energy separation between the states of the resulting molecular cation is of the order of the photon energy of the driving infrared (IR) field, so that, during the ionization process, the IR field may induce resonant transitions between such states. This adds a third ionization path to the standard two-path ionization scheme of RABBIT. Here we present a detailed theoretical study of RABBIT in the acetylene molecule in which we have explicitly evaluated time-resolved photoelectron spectra as those recorded in actual experiments. We do so for both random and well-defined orientations of the molecule, and for photoelectron spectra integrated over and resolved in the photoelectron emission angle. We show that the presence of this additional third path can strongly affect the values and physical meaning of photoionization delays extracted from fits based on the commonly used two-path interference scheme. This is indeed the case for acetylene molecules parallel to the light polarization direction, where the extracted delays strongly depend on the IR frequency, while for molecules perpendicular to the polarization direction the standard two-path RABBIT conditions are fulfilled.

We study Heisenberg's uncertainty relation relative to a quantum reference frame (QRF). We introduce the QRF as a covariant phase space observable, show that when described relative to it, position and momentum appear compatible, and derive novel, frame-relative uncertainty relations. This is achieved by constructing a joint observable for position and momentum, and calculating the variances of its margins. We then verify that in the classical limit of the QRF, the standard uncertainty relations are recovered, fortifying claims that standard quantum theory must be understood relative to an external, classical frame. These results may open up new research directions at the interface between QRFs and incompatibility.

We investigate coherent multiple scattering effects in the random quantum kicked rotor model. By changing the starting time of the Floquet period, two classes of models can be introduced that exhibit similar interference structures. For one of the two classes, these structures appear on top of a nontrivial background, which we describe in detail. Its origin is identified and an approximate analytical formula is proposed. The asymptotic contrast profile, as well as the height of the coherent backscattering and the coherent forward scattering peaks, are also analyzed. Our findings are relevant to provide an interpretation of cold atom experiments aimed at observing such interference effects with matter waves.