The quantum no-broadcasting theorem states that it is fundamentally impossible to perfectly replicate an arbitrary quantum state, even if correlations between the copies are allowed. While quantum broadcasting cannot occur through any physical process, it can be achieved via postprocessing of experimental data using a process called virtual quantum broadcasting (VQB). In this work, we report an experimental implementation of a quantum circuit based on the linear combination of unitaries, integrated with a postprocessing protocol, to realize VQB in a nuclear magnetic resonance system. VQB can be expressed as a linear combination of two channels: the universal cloner, which broadcasts the target quantum state, and the universal antisymmetrizer, which reduces broadcasting error. We implement both channels within the same circuit and demonstrate that the universal cloner is the closest physical map to VQB. In addition, we show how the universal antisymmetrizer can be utilized to mitigate imperfections in the cloner, enabling near-ideal fidelity. Our method is applicable to broadcasting quantum systems of any dimension.

Polarons have emerged as a powerful concept across many fields in physics to study an impurity coupled to a quantum bath. The interplay between impurity physics and the formation of composite objects remains a relevant problem to understand how few- and many-body states are robust towards complex environments and polaron physics. In most cases, impurities are modeled as pointlike objects. The question we address here is how quasiparticle properties are affected when impurities possess an internal structure. The simplest yet fundamental structure for the impurity is a dimer state. Here, we investigate the polaronic properties of a dimer dressed by the elementary excitations of a bosonic bath. We solve the two-body impurity-impurity problem to determine the position and broadening of the bound state and consider the polaron dressing using a field-theory approach. We demonstrate the emergence of different dressed dimer regimes, where polaron dressing drives a dimer from a well-defined to an ill-defined bound state.

Recent interest in the studies of structured states obtained in relativistic electron beams has highlighted the use of two alternative descriptions, each based on a different wave function and the related space-time density. Although both wave functions obey the Dirac equation (one directly and the other through a Foldy-Wouthuysen transformation), they lead to different dynamics and properties, such as the presence or absence of spin-orbit interactions. In this work we investigate wave-packet dynamics for the Klein-Gordon equation, which displays the same ambiguity regarding the choice of different densities, in a setting involving Klein tunneling across a series of supercritical potential barriers. Relying on the superradiant character of this setting, we obtain solutions to the wave-packet dynamics indicating that the density based on a Foldy-Wouthuysen transformation of the wave function can be locally amplified outside the light cone. In principle, the exponential increase of the charge due to the field inhomogeneities can lead to an arbitrarily large amplification over macroscopic distances. These results question the interpretation of the Foldy-Wouthuysen density as a fundamentally correct probability or charge density.

Light-induced molecular dynamics often involve the excitation of several electronic, vibrational, and rotational states. Since the ensuing electronic and nuclear motion determines the pathways and outcomes of photoinduced reactions, our ability to monitor and understand these dynamics is crucial for molecular physics, physical chemistry, and photobiology. However, characterizing this complex motion represents a significant challenge when different degrees of freedom are strongly coupled. In this Letter, we demonstrate how the interplay between vibrational, rotational, and electronic degrees of freedom governs the evolution of molecular wave packets in the low-lying states of strong-field-ionized sulfur dioxide. Using time-resolved Coulomb explosion imaging (CEI) and quantum mechanical wave packet simulations, we directly map the bending vibrations of the molecule, show how the vibrational wave packet is influenced by molecular alignment, and elucidate the consequences of nuclear motion for the coupling between the two lowest electronic states of the cation. Our results demonstrate that multicoincident CEI can be an efficient experimental tool for characterizing coupled electronic and nuclear motion in polyatomic molecules.

The interplay of quantum emitters and non-Hermitian structured baths has received increasing attention in recent years. Here we predict unconventional quantum optical behaviors of quantum emitters coupled to a non-Hermitian topological bath, which is realized in a 1D Su-Schrieffer-Heeger photonic chain subjected to nonlocal dissipation. In addition to the Hermitian-like chiral bound states in the middle line gap and skin-mode-like hidden bound states inside the point gap, we identify peculiar in-gap chiral and extended photon-emitter dressed states. This is due to the competition of topological-edge localization and non-Hermitian skin-mode localization in combination with the non-Bloch bulk-boundary correspondence. Strikingly, dissipation can shape the wave-function profile of the dressed state. Furthermore, when two emitters are coupled to the same bath, such in-gap dressed states can mediate the nonreciprocal long-range emitter-emitter interactions, with the interaction range limited only by the dissipation of the bath. Our work opens the door to further study rich quantum optical phenomena and exotic many-body physics utilizing quantum emitters coupled to non-Hermitian baths.

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.

Bose-Einstein condensates (BECs) of neutral atoms constitute an important quantum system for fundamental research and precision metrology. Many applications require short preparation times of BECs, for example, for optimized data acquisition rates in scientific applications, and reduced dead times and improved bandwidths for atomic quantum sensors. Here, we report on the generation of rubidium BECs with a repetition rate of more than $2\mathrm{Hz}$. The system relies on forced evaporation in a dynamically adjusted optical potential, which is created by the spatial modulation of laser beams. Our system provides a versatile source of the ubiquitous rubidium BECs, and promotes their exploitation for high-precision atom interferometers.

In an effort to obtain the signature of a new vector boson unambiguously from the measured nonlinear isotope shift (IS) effects in three recent experiments [Phys. Rev. X 12, 021033 (2022); Phys. Rev. Lett. 128, 163201 (2022); and Phys. Rev. Lett. 134, 063002 (2025)], very precise values of quadrupole moments and IS constants for the $6s{}^2{S}_{1/2}\to 5d{}^2{D}_{3/2}$ and $6s{}^2{S}_{1/2}\to 5d{}^2{D}_{5/2}$ clock transitions of ${}^{171}{\mathrm{Yb}}^{+}$ are presented. This is accomplished by incorporating contributions from the computationally challenging triply excited configurations through the relativistic coupled-cluster (RCC) theory. Testament of quality atomic wave functions of states of the above transitions, obtained using the RCC theory, are gauged by comparing the calculated energies and magnetic dipole hyperfine structure constants with their measurements. The improved quadrupole moments from this work will be immensely useful to estimate quadrupole shifts of the clock transitions of ${\mathrm{Yb}}^{+}$. Complementary approaches are employed to ascertain accuracy and comprehend roles of orbital relaxation and correlation effects in evaluating the IS constants. Combining these constants with the IS measurements from Phys. Rev. Lett. 128, 163201 (2022), differential nuclear charge radii of the Yb isotopes are inferred that deviate by 6–7% from the literature data.

We explore the self-sustained Josephson-junction dynamics in dipolar supersolids, predicting the possibility of self-trapping alongside the experimentally observed Josephson oscillations [G. Biagioni et al., Nature (London) 629, 773 (2024)]. Using an asymmetric two-mode (ATM) model to describe a triangular dipolar supersolid, validated through Gross-Pitaevskii simulations, we demonstrate that the system's symmetry enables a consistent two-mode mapping despite the presence of seven droplets. Hence the associated Hamiltonian allows us to straightforwardly determine the self-trapping regime. Additionally, we show that bringing the system into rotation preserves its ability to sustain the Josephson-junction dynamics across its full range and we assess the robustness of the ATM model under these conditions. We further find that the off-axis droplets move in the radial direction during the evolution in accordance with the size of the central droplet. Such movements do not interfere with the model predictions.

The hyperfine structure of ${}^{229}\mathrm{Th}^{3+}$ ions in the nuclear ground state is investigated via laser spectroscopy of trapped ${\text{Th}}^{3+}$ ions that are sympathetically cooled by laser-cooled ${}^{88}\mathrm{Sr}^{+}$ ions in a linear Paul trap. The isotope shift to ${}^{230}\mathrm{Th}^{3+}$ and the hyperfine constants for the magnetic dipole ($A$) and electric quadrupole ($B$) interactions for the $5F_{5/2}$ and $6D_{5/2}$ electronic states of ${}^{229}\mathrm{Th}^{3+}$ are determined. These measurements provide nuclear moments of ${}^{229}\mathrm{Th}$ with reduced uncertainty and serve as a preparation for improved hyperfine spectroscopy of the 8.4 eV nuclear isomeric state in ${}^{229}\mathrm{Th}^{3+}$ ions.

We introduce a new member to the class of semisuper Efimov effects, where an infinite number of bound states emerge with their binding energies obeying the universal scaling law $E_n\sim e^{-2{(\pi n/\gamma )}^2}$ for sufficiently high excitation $n\in \mathbb{N}$. Our system consists of a pair of two-component fermions in three dimensions at infinite scattering length, which furthermore interact with a boson confined in two dimensions so as to form a three-body bound state at zero energy. When another boson is added, the exchange of the resonant pair of fermions between two bosons leads to the semisuper Efimov effect of four such particles with the scaling exponent $\gamma$ determined by the mass ratio of bosons to fermions. If bosons exist in three dimensions, an infinite number of bound states do not emerge, but some of them may survive for a large mass ratio, making our findings potentially relevant to two-neutron halo nuclei as well as ultracold atoms.

The study of the long-time dynamics of quantum systems can be a real challenge, especially in systems such as ultracold gases, where the required timescales may be longer than the lifetime of the system itself. In this Letter, we show that it is possible to access the long-time spin dynamics of a strongly repulsive atomic gas mixture in shorter times. The shortcut-to-dynamics protocol that we propose does not modify the fate of the observables, but effectively jumps ahead in time without changing the system's inherent evolution. Just as the next-chapter button in a movie player that allows to quickly reach the part of the movie one wants to watch, it is a leap into the future.

We analytically investigate the Liouvillian exceptional point manifolds (LEPMs) of a two-qubits open system, where one qubit is coupled to a dissipative polarization bath. Exploiting a $Z_2$ symmetry, we block diagonalize the Liouvillian and show that one symmetry block yields two planar LEPMs while the other one exhibits a more intricate, multisheet topology. The intersection curves of these manifolds provide a phase diagram for effective Zeno transitions at small dissipation. These results are consistent with a perturbative extrapolation from the strong Zeno regime. Interestingly, we find that the fastest relaxation to the nonequilibrium steady state occurs on LEPMs associated with the transition to the effective Zeno regime.

We report measurements of the Bose-Einstein condensate critical temperature shift due to dipolar interactions, employing samples of ultracold erbium atoms which feature significant (magnetic) dipole-dipole interactions in addition to tunable contact interactions. Using a highly prolate harmonic trapping potential, we observe a clear dependence of the critical temperature on the orientation of the dipoles relative to the trap axis. Our results are in good agreement with mean-field theory for a range of contact interaction strengths. This work creates an opportunity for further investigations into beyond-mean-field effects and the finite-temperature phase diagram in the more strongly dipolar regime where supersolid and droplet states emerge.

We solve the problem of a dimer moving on a spherical surface and find that its binding energy and wave function are sensitive to the total angular momentum. The dimer gets squeezed in the direction orthogonal to the center-of-mass motion and can qualitatively change its geometry from two dimensional to one dimensional. These results suggest that combining the curved geometry with finite angular momentum may give rise to qualitatively new many-body phenomena in ultracold shell-shaped gases.

One of the most striking quantum phenomena is superposition, where one particle simultaneously inhabits different states. Most methods to verify coherent superposition are indirect, in that they require the distinct states to be recombined. Here, we adapt an xor game, in which a “test” photon is placed in a superposition of two orthogonal spatial modes, and each mode is sent to separated parties who perform local measurements on their modes without reinterfering the original modes. We show that by using a second identical “measurement” photon the parties are nonetheless able to verify if the test photon was placed in coherent superposition of the two spatial modes. We then turn this game into a resource-efficient verification scheme, obtaining a confidence that the particle is superposed which approaches unity exponentially fast. We demonstrate our scheme using a single photon, obtaining a 99% confidence that the particle is superposed with only 37 copies. Our work shows the utility of xor games to verify quantum resources, allowing us to efficiently detect quantum superposition without reinterfering the superposed modes.

We theoretically study the intrinsic spin Hall effect in parity-time ($\mathcal{PT}$)-symmetric spin-orbit-coupled quantum gases confined in an optical lattice. The interplay of the $\mathcal{PT}$ symmetry and the spin-orbit coupling leads to a doubly degenerate noninteracting band structure in which the spin polarization and the Berry curvature of any Bloch state are opposite to those of its degenerate partner. Using experimentally available systems as examples, we show that such a system with a two-component Fermi gas exhibits an intrinsic spin Hall effect akin to that found in the context of electronic materials. For a two-component Bose gas, however, an unconventional spin Hall effect emerges in which the spin polarization and the currents are coplanar and the spin Hall conductivity displays a characteristic anisotropy. We propose to detect such an unconventional spin Hall effect in harmonically trapped systems using dipole oscillations and perform extensive numerical simulations to validate the proposal. Our work paves the way for quantum simulation of the solid-state intrinsic spin Hall effect and experimental explorations of unconventional spin Hall effects in quantum gases.

In this study, we theoretically analyzed a control protocol based on “time-dependent resonance” in nearly adiabatic two-level quantum systems, demonstrating that it exhibits properties equivalent to adiabatic control. This protocol is based on “time-dependent resonance,” where the frequency corresponds to the time-dependent energy gap. Through numerical calculations, we showed that this protocol serves as an optimal control protocol. This approach enables efficient and high-precision transitions to the target state. Our findings provide an alternative perspective on quantum optimal control theory and suggest potential applications in qubit controls and quantum information processing.

Recently, the resource theory of imaginarity has attracted much attention. As with other resources such as quantum correlations, coherence, and asymmetry, an important task in the resource theory of imaginarity is deimaginarity, which is to transform a state into a free state in the resource theory of imaginarity by the random covariant-free unitary operations. Here, we consider an asymptotic limit of infinitely many copies and vanishingly small error, and analyze the deimaginarity cost. We prove that the deimaginarity cost of a state is equal to its regularized relative entropy of imaginarity, which can be seen as an operational interpretation of the relative entropy of imaginarity.