This work demonstrates that repeated weak measurements together with postselection can produce sharp dynamical discontinuities in meter observables, even in minimal quantum systems. The discontinuous behavior is governed by the polar angle of the postselected state, which serves as a continuous control parameter. As this angle is varied, the expectation value of the meter observables changes abruptly at the point where the imaginary part of the associated weak value, a complex quantity that arises in weak measurements with postselection, becomes zero. Such nonanalytic behavior emerges only when the weak value is genuinely complex for a range of postselection angles. If the weak value remains purely real for all angles, the dynamics remain smooth. The discontinuity originates from an exchange of stability between fixed points of the nonunitary Kraus operator governing the meter's evolution. Remarkably, despite the absence of a thermodynamic limit, the relaxation time in the vicinity of the discontinuity exhibits universal critical behavior characterized by a critical exponent equal to 1, independent of system parameters. These results establish the weak value as a tunable control parameter capable of inducing nonanalytic dynamical responses and reshaping the stability structure of measurement-induced quantum dynamics.

Quantum sensing leverages nonclassical resources to enhance precision. In particular, Greenberger-Horne-Zeilinger (GHZ) states can, in principle, attain the Heisenberg limit that surpasses the standard quantum limit. While many studies have examined how open-system noise—typically modeled with Lindblad master equations—degrades GHZ-based metrology, coherent control imperfections during state preparation and readout have received less attention. Here, we analyze the effect of detuning between actual and nominal spin frequencies in a GHZ-state preparation scheme employing a frequency-selective pulse. We show that detuning induces coherent, systematic error that prevents GHZ sensing from reaching the Heisenberg limit. To mitigate this effect, we design a composite-pulse protocol that compensates for detuning-induced errors and improves the sensitivity under the effect of coherent error.

The zero-error capacity of a noisy classical channel quantifies its ability to transmit information with absolute certainty, i.e., without any probability of error. In contrast to Shannon's standard channel capacity, which remains unaffected by preshared no-signaling correlations, zero-error capacity can be enhanced through nonlocal correlations. In this work, we investigate zero-error communication utility of nonlocal correlations arising in the 2-2-$m$ Bell scenario, where two parties have two inputs and $m$ possible outcomes per input. For all $m\ge 2$, we construct examples of noisy classical channels with zero unassisted zero-error capacity that, when assisted by extremal 2-2-$m$ nonlocal correlations, can transmit one bit of information. Extending this analysis to the 2-$m$-2 Bell scenario, we identify channels with zero unassisted zero-error capacity that can nonetheless perfectly transmit $logm$ bits of information. While nonlocal correlations arising from quantum entangled states cannot achieve a positive zero-error capacity for these channels, we show that they can, however, enhance the success probability of one-shot transmission of classical messages. We also derive a nontrivial upper bound on the extent to which a given no-signaling correlation can activate the zero-error capacity of noisy classical channels. Finally, we show that the maximal zero-error communication advantage achievable with a no-signaling correlation lower bounds its classical simulation cost, thus linking its usefulness for communication to the classical cost of simulating it.

We investigate the energy spectra of electron-positron pairs produced in bound-bound transitions of muonic atoms. These nonradiative transitions provide a distinctive mechanism of matter creation. Our spectral analysis demonstrates that the electron and positron spectra exhibit a strong dependence on the orbital angular momentum of the initial state. For transitions from excited $s$ states to the ground state, the spectra are governed primarily by the Coulomb interaction. In contrast, for transitions originating from $p$ and $d$ states, the Breit interaction is the dominant factor. Since pair production is strongest for $2p$ states, the Breit interaction ultimately determines the overall spectral shape.

We present a theoretical investigation of ion-induced Coulomb explosion imaging (CEI) of pyridazine molecules driven by energetic ${\mathrm{C}}^{5+}$ projectiles, using time-dependent density-functional theory (TDDFT) with Ehrenfest nuclear dynamics. By systematically varying the projectile's impact point and orientation relative to the molecular plane, we compare orthogonal and in-plane trajectories and quantify their effects on fragment momenta, electron-density response, and atom-resolved ionization. Newton plots and time-resolved density snapshots show that trajectories avoiding direct atomic collisions yield the most faithful structural reconstructions, whereas direct impacts impart large, highly localized momenta that distort the recovered geometry. Planar trajectories generate substantially greater ionization and broader momentum distributions than orthogonal ones due to deeper traversal through the molecular electron cloud. Quantitative analysis of electron removal at 10 fs confirms that projectile proximity and orientation strongly modulate both local and global ionization. These findings clarify how impact geometry governs the fidelity of ion-induced CEI structural recovery and help explain the variability and noise observed in experimental CEI measurements. More broadly, the results highlight both the strengths and the intrinsic limitations of ion-induced CEI and identify key considerations for interpreting experiments.

Cold hybrid ion-atom systems represent an expanding frontier in quantum science, yet the role of the radio-frequency (rf) drive field in their collision dynamics remains inadequately understood. In this work, we investigate how the rf drive frequency in a Paul trap affects collisions in a hybrid system of neutral ${}^{87}\mathrm{Rb}$ atoms with multiple ionic species (e.g., ${}^{87}\mathrm{Rb}^{+},{}^{87}\mathrm{Rb},{}^{87}\mathrm{Rb}$, etc.). By monitoring the temporal evolution of atomic ions, molecular ions, and neutral atoms across a range of rf drive frequencies, we observe that distinct inelastic processes are selectively enhanced at different rf drive frequencies: Exothermic atomic ion-atom collisions dominate at lower rf drive frequencies, whereas molecular ion-atom quenching becomes prominent at higher rf drive frequencies. Moreover, the total-collision-rate coefficient exhibits a marked, nonmonotonic dependence on the rf drive frequency. These findings support a physical picture in which the time-dependent trap potential promotes the formation of trap-assisted ion-atom transient complexes, which actively participate in and reshape the collision dynamics. Our work thus provides insights into the role of the rf drive field in hybrid ion-atom systems featuring multiple ionic species.

The generation of high harmonics is a strongly nonlinear effect that allows to probe properties of the target and to study electron dynamics in matter. It has been investigated in many different kinds of targets, including molecular gases, liquids, and solids. Recently, high-harmonic generation was studied in organic molecular crystals by Wiechmann et al. [Nat. Commun. 16, 9890 (2025)]. There it was found that the laser-polarization-dependent harmonic yield was sensitive to the weak couplings between nearest- and next-nearest-neighbor molecules. In this paper, the impact of the laser polarization angle and the intermolecular interaction on the harmonic yield is examined in detail using a simple but insightful two-dimensional tight-binding system that models a molecular dimer, i.e., two weakly coupled molecules. We find that the intensities of lower harmonic orders tend to maximize for a laser polarization direction aligning with the molecular axes, whereas higher harmonic orders rather show the strongest yield for a polarization direction along the intermolecular axis. We further demonstrate that the harmonic order at which the maximum flips from the molecular to the intermolecular direction strongly depends on the intermolecular coupling strength. To gain a deeper insight into the origins of the findings, we include a detailed adiabatic analysis, showing that the flipping of the maximum yield towards the intermolecular direction is already contained qualitatively in the adiabatically following states.

We present a theoretical study on the strong-field ionization dynamics of nitrogen molecules driven by two-color circularly polarized (TCP) laser fields. The photoelectron momentum distributions (PMDs) exhibit a significant dependence on the molecular alignment angle and field ellipticity. Notably, these PMDs exhibit temporal triple-slit interference, with the photoelectron tunneling time governing the interference pattern, which displays an asymmetric shift. Employing the molecular quantum trajectory Monte Carlo model, we trace photoelectron trajectories to reveal that the Coulomb potential induces pronounced asymmetry in the PMDs as well as accounts for the localized enhancement and suppression of photoelectron yields. Furthermore, we demonstrate that the temporal intracycle interference patterns can be effectively modulated by tuning the laser ellipticity. This work provides insights into the characteristic structures of diatomic molecular PMDs in TCP fields and suggests a possible framework for the coherent control of electron dynamics via molecular alignment and laser ellipticity.

Disordered potentials fundamentally affect transport and coherence in quantum systems, giving rise to a Bose-glass phase in interacting bosonic systems—an insulating yet compressible phase lacking long-range coherence. Directly measuring a reduced coherence length of the Bose glass has been a outstanding challenge. We address this by employing Talbot interferometry combined with single-atom-resolved detection in a quantum-gas microscope. Using ultracold bosonic atoms in a two-dimensional lattice with site-resolved, reproducible disorder, we identify the Bose-glass phase through in situ density distributions and particle-number fluctuations, quantified via the Edwards-Anderson parameter, and through the visibility of interference patterns after time of flight. By driving the system across the Bose-glass phase, we further observe signatures of nonergodic dynamics. Our studies provide a starting point to further explore disordered systems in and out of equilibrium, and are relevant for understanding the dynamics and stability of disordered and glasslike quantum states in solid-state systems.

Modern optomechanical systems employ increasingly sophisticated quantum-mechanical states of light to probe and manipulate mechanical motion. Squeezed states are now used routinely to enhance the sensitivity of gravitational-wave interferometers to small external forces, and they are also used in feedback-based trapping and damping experiments on the same interferometers to enhance the achievable cooling of fluctuations in the differential test mass mode [Whittle, et al., Science 372, 1333 (2021)]. In this latter context, an accurate accounting of the true test mass motion, incorporating all sources of loss, the effect of feedback control, and the influence of classical force and sensing noises, is paramount. We work within the two-photon formalism to provide such an accounting, which extends a previously described decomposition of the quantum-mechanical noise of the light field [McCuller, et al., Phys. Rev. D 104, 062006 (2021)]. This decomposition provides insight, rooted in physically motivated parameters, into the optimal squeezed state and feedback control configuration that should be employed to achieve the lowest fluctuations. We apply this formalism to feedback damping experiments in current and possible future gravitational-wave interferometers—LIGO $\mathrm{A}+$, LIGO Voyager, Cosmic Explorer (CE), and CE Voyager—and discuss how these multi-degree-of-freedom systems might be compared to a single degree-of-freedom oscillator. We find that, for the oscillator definition used most commonly in the literature so far, occupation numbers below 1 are possible in these interferometers over a frequency range comparable to the bandwidth of the trapped and cooled oscillator. We also discuss several technical issues in cooling experiments with gravitational-wave detectors.

The ranges of existence and stability of dark cavity-soliton stationary states in a Fabry-Pérot resonator with a Kerr nonlinear medium, vectorial polarization components, and normal dispersion are determined. The Fabry-Pérot configuration introduces nonlocal coupling that shifts the cavity detuning by the round-trip average power of the intracavity field. When compared with ring resonators, nonlocal coupling leads to strongly detuned dark cavity solitons that exist over a wide range of detunings. We study symmetry breaking between fields of opposite circular polarization characterized by a codimension-2 bifurcation point unique to the regime of normal group velocity dispersion. We show the spontaneous formation of regular dark soliton crystals separated by Turing patterns of alternating polarization via ‘‘self-crystallization’’ due to long-range interactions. Frequency combs of dark soliton crystals of two orthogonal polarizations in Fabry-Pérot resonators display three separate components corresponding to the cavity repetition rate, the wavelength of the periodic pattern, and the soliton lattice spacing. The system also displays the formation of stationary and dynamical vectorial dark-bright solitons. These solutions are different from previous realizations with bichromatic driving in ring resonators, are composed of locked switching fronts, and can undergo Hopf bifurcations when scanning the detuning. Interacting oscillating dark-bright solitons display antiphase dynamics that changes first into quasiperiodic oscillations and then into in-phase dynamics when increasing the cavity length.

Lattice spin models featuring kinetic constraints constitute a paradigmatic setting for the investigation of glassiness and localization phenomena. The intricate dynamical behavior of these systems is a result of the dramatically reduced connectivity between many-body configurations. This truncation of transition pathways often leads to a fragmentation of the Hilbert space, yielding highly collective and therefore often slow dynamics. Moreover, this mechanism supports the formation of characteristic elementary excitations, which we investigate here theoretically in a two-dimensional Rydberg lattice gas. We explore their properties as a function of interaction strength and range, and illustrate how they can be experimentally probed with a spectroscopic scheme. Here, we show that the transition rate to certain delocalized superposition states of elementary excitations displays collective many-body enhancement.

In conventional quantum mechanics, all unitary evolution takes place within the spacetime Hilbert space ${\mathcal{H}}_{xt}=L^2\left({\mathcal{M}}_{xt}\right)$, with time as the sole evolution parameter. The momentum-energy representation $\varphi (k,E)$ is treated merely as a Fourier reexpression of the same state: kinematically equivalent but dynamically inert. Here we activate a previously frozen dual description between the conjugate pairs $(x,t)$ and $(k,E)$, by extending quantum theory to an enlarged Hilbert-space setting ${\mathcal{H}}_{\mathrm{total}}$ containing two dynamical sectors, ${\mathcal{H}}_{xt}$ and ${\mathcal{H}}_{kE}$, within which the momentum-energy sector ${\mathcal{H}}_{kE}=L^2\left({\mathcal{M}}_{kE}\right)$ carries its own autonomous unitary evolution generated by a self-adjoint operator $\widehat{\mathcal{T}}$. The resulting framework establishes a fundamental duality between two complementary but dynamically incompatible descriptions of a single global quantum state. Physical influence between the two descriptions is mediated through a projection that enforces a consistent choice of evolution parameter. As illustrative examples of this projection mechanism, we show that the dual-manifold framework generically yields a uniform background energy contribution, as well as a characteristic exponential boundary relation that emerges near a singularity. These structures resemble features encountered in certain gravitational contexts, but arise here independently of any gravitational dynamics. They are presented solely as structural consequences of the dual quantum framework, illustrating how nontrivial large-scale features can emerge from the underlying quantum description.

A quantum thermodynamic system is described by a Hamiltonian and a list of conserved, noncommuting charges, and a fundamental goal is to determine the minimum energy of the system subject to constraints on the charges. Recently, Liu et al. [arXiv:2505.04514] proposed first- and second-order classical and hybrid quantum-classical algorithms for solving a dual chemical potential maximization problem, and they proved that these algorithms converge to global optima by means of gradient-ascent approaches. In this paper, we benchmark these algorithms on several problems of interest in thermodynamics, including one- and two-dimensional quantum Heisenberg models with nearest- and next-nearest-neighbor interactions and with the charges set to the total $x, y$, and $z$ magnetizations. We also offer an alternative compelling interpretation of these algorithms as methods for designing ground and thermal states of controllable Hamiltonians, with potential applications in molecular and material design. Furthermore, we introduce stabilizer thermodynamic systems as thermodynamic systems based on stabilizer codes, with the Hamiltonian constructed from a given code's stabilizer operators and the charges constructed from the code's logical operators. We benchmark the aforementioned algorithms on several examples of stabilizer thermodynamic systems, including those constructed from the one-to-three-qubit repetition code, the perfect one-to-five-qubit code, and the two-to-four-qubit error-detecting code. Finally, we observe that the aforementioned hybrid quantum-classical algorithms, when applied to stabilizer thermodynamic systems, can serve as alternative methods for encoding quantum information into stabilizer codes at a fixed temperature, and we provide an effective method for warm-starting these encoding algorithms whenever a single qubit is encoded into multiple physical qubits.

Adiabatic quantum computation requires the system to be always maintained in its ground state. However, environmental noise readily disrupts this adiabatic process. Adiabatic speedup via leakage elimination operator (LEO) control, as one of the effective strategies, has been proposed to achieve adiabatic evolution in a shorter time frame, thus mitigating the detrimental effects of environmental noise. The LEO Hamiltonian can be realized by a sequence of pulses. While the pulse design via a traditional optimal algorithm is feasible for time-independent noise, it becomes more challenging for time-dependent cases. To ensure robust performance under time-dependent noise, we employ the neural network (NN)-based supervised learning algorithm for the pulse design. Our strategy is to incorporate the environmental parameters into the training process, then the resulting network can effectively accommodate a wide range of arbitrary parameters, including time-dependent cases. Specifically, the NN can learn the optimal total evolution time $T_{\text{tot}}$, without the need to set it as a known value a priori. Taking the adiabatic speedup of an open quantum qutrit system under time-dependent noise as an example, we identify a noise-insensitive path by adapting the ideal pulse shape originally designed for closed systems. Fidelity improvement has been obtained compared to the ideal pulses. Our approach offers an effective strategy to enhance the performance of various quantum information processing tasks under time-dependent noise, such as adiabatic quantum computation, quantum state transfer, or quantum state preparation.

Engineering effective Hamiltonians is essential for advancing quantum technologies, including quantum simulation, sensing, and computing. This paper presents a general framework for effective Hamiltonian engineering, enabling robust, precise, and efficient quantum control strategies. To achieve efficiency, we focus on creating target zeroth-order effective Hamiltonians while minimizing higher-order contributions and enhancing robustness against systematic errors. The control design identifies the minimal subspace of the toggling-frame Hamiltonian and the full set of achievable, zeroth-order, effective Hamiltonians. The framework also enables robust state transfer and characterization of achievable density matrices, and extends to stochastic fluctuations via a cumulant expansion. Examples are included to illustrate the process flow and resultant precision and robustness.

We elucidate the profound connection between physics and computation by proposing and examining the model of the non-Hermitian quantum computer (NQC). In addition to conventional quantum gates such as the Hadamard, phase, and cnot gates, this model incorporates a nonunitary quantum gate $G$. We show that the NQC is extraordinarily powerful, capable of solving not only all NP problems but also all problems within the complexity class ${\text{P}}^{♯\text{P}}$ in polynomial time. We investigate two physical schemes for implementing the nonunitary gate $G$ and find that the remarkable computational power of NQC originates from the exponentially large physical resources required.

In the absence of decoherence and disorder the current of noninteracting fermionic particles across a finite lattice connecting two reservoirs (leads) with different chemical potentials is known to be ballistic. It is also known that decoherence suppresses this ballistic current. However, if decoherence is weak, the change in the current can be undetectable. In this work we show that the effect of a weak decoherence can be amplified by orders of magnitude if the lattice has edge states. This allows us to use a lattice with edge states as a sensor for measuring the decoherence rate.

High-precision microwave spectroscopic measurements and analysis of rotational energy level transitions in the ground vibronic state of the open-shell barium monofluoride (BaF) molecule are reported with the purpose of contributing to studies of physics beyond the Standard Model. BaF is currently among the key candidate molecules being examined in the search for a measurable electron electric-dipole moment, $e\text{EDM}$, as well as the nuclear anapole moment. Employing Fourier-transform microwave spectroscopy, these pure rotational transition frequencies for the ${}^{138}\mathrm{Ba}{}^{19}\mathrm{F}, {}^{137}\mathrm{Ba}{}^{19}\mathrm{F}, {}^{136}\mathrm{Ba}{}^{19}\mathrm{F}, {}^{135}\mathrm{Ba}{}^{19}\mathrm{F}$, and ${}^{134}\mathrm{Ba}{}^{19}\mathrm{F}$ isotopologues are analyzed here in a combined global fit with previous microwave data sets for ${}^{138}\mathrm{Ba}{}^{19}\mathrm{F}$ ($v=0–4$), ${}^{137}\mathrm{Ba}{}^{19}\mathrm{F}$, and ${}^{136}\mathrm{Ba}{}^{19}\mathrm{F}$ using the program spfit. As a result, hyperfine parameters are significantly improved and we observe a distinctive structure in a Born-Oppenheimer breakdown (BOB) analysis of the primary rotational constant. This can be understood using the nuclear field shifts due to the known isotopic variation in the size of barium nuclei and in combination with the smaller linear mass-dependent BOB terms.