An accurate atomic mass of ${}^4\mathrm{He}$ (or the alpha particle) is required for deriving the atomic mass of the electron from proposed measurements of the ground-state $g$ factor of ${}^4\mathrm{He}^{+}$. However, there is a six-standard deviation discrepancy between a recent measurement [S. Sasidharan, O. Bezrodnova, S. Rau, W. Quint, S. Sturm, and K. Blaum, Phys. Rev. Lett. 131, 093201 (2023)] and the measurement by Van Dyck et al. [R. S. Van Dyck, Jr., D. B. Pinegar, S. Van Liew, and S. L. Zafonte, Int. J. Mass Spectrom. 251, 231 (2006)], on which the current values in the Atomic Mass Evaluation and CODATA tabulation of fundamental constants are based. By measuring the cyclotron frequency ratios of ${}^4\mathrm{He}^{+}$ to ${\mathrm{D}}_2^{+}$, and of ${}^4\mathrm{He}^{+}$ to ${\mathrm{H}}_2{\mathrm{D}}^{+}$, we find the mass of ${}^4\mathrm{He}$ to be $4.00260325467\left(8\right)\mathrm{u}$, favoring the more recent value.

We demonstrate a direct one-to-one correspondence between nonlinear optical fields in defocusing Kerr media and wave functions in weakly interacting Bose-Einstein condensates or quantum fluids. Based on this correspondence, we propose the existence of excitations in an optical vortex beam characterized by a helical deformation of its phase singularity core. These excitations are direct analogs of Kelvin waves known in quantum and classical fluid dynamics. We further show that the excitations exhibit two distinct branches, one of which includes a stationary solution. A feasible experimental scheme for generating these excitations is also discussed.

One core of quantum metrology is the utilization of entanglement to enhance measurement precision beyond the standard quantum limit. Here, we utilize the Floquet-engineered two-axis twisting (TAT) and turning dynamics to generate Greenberger-Horne-Zeilinger (GHZ)-like states for quantum metrology. Using both analytical semiclassical and quantum approaches, we find that the desired $N$-particle GHZ-like state can be produced in a remarkably short time, $t_{\mathrm{opt}}\propto lnN/N$, and its quantum Fisher information $F_{\mathrm{Q}}^{\mathrm{opt}}\propto N^2$ approaches the Heisenberg limit. Owing to the rapid state preparation, it shows outstanding robustness against decoherence. Moreover, using the Floquet-engineered anti-TAT-and-turn, one may implement an efficient interaction-based readout protocol to extract the signal encoded in this GHZ-like state. This Floquet-engineered anti-TAT-and-turn approach offers a viable method to achieve effective time-reversal dynamics to improve measurement precision and resilience against detection noise, all without the need to invert the sign of the nonlinear interaction. This study paves a way for achieving entanglement-enhanced quantum metrology via rapid generation of GHZ-like states at high particle numbers through continuous Floquet engineering.

We construct an optical tweezer array for Rb atoms that provides the same trapping potentials for ground and Rydberg levels. By comparing the value of the trapping field detuning from the $40s\text{−}6p$ transition frequency required to create such an array with that previously measured in an optical lattice [J. Lampen et al., Phys. Rev. A 98, 033411 (2018)], we determine the modification of the polarizability of a Rydberg state atom confined in a spatially varying optical potential, as predicted by Topcu and Derevianko [Phys. Rev. A 88, 043407 (2013)]. A state-insensitive atom array should enable more complex quantum computation by allowing the tweezer potentials to remain on during Rydberg gate operations.

Photonics provides a viable path to a scalable fault-tolerant quantum computer. The natural framework for this platform is measurement-based quantum computation, where fault-tolerant graph states supersede traditional quantum error-correcting codes. However, the existing formalism for foliation—the construction of fault-tolerant graph states—does not reveal how certain properties, such as single-shot error correction, manifest in the measurement-based setting. We introduce the fault complex, a representation of dynamic quantum error-correction protocols particularly well suited to describe foliation. Our approach enables precise computation of fault tolerance properties of foliated codes and provides insights into circuit-based quantum computation. Analyzing the fault complex yields improved thresholds for three- and four-dimensional toric codes, a generalization of stability experiments, and the existence of single-shot lattice surgery with higher-dimensional topological codes.

We study classical and quantum echoes in a Kerr oscillator driven by a frequency-controlling pulsed perturbation. We consider the dynamical response to the perturbation for a single coherent state and for Schrödinger cat states constructed as both balanced and imbalanced superpositions of two coherent states. For individual coherent states, we demonstrate that a weak parametric drive yields a long-lived sequence of classical echoes. Cat states are found to exhibit distinct quantum echoes that are sensitive to the initial relative phase and weights of the coherent states in superposition. We examine the effect of dissipation on quantum echoes and quantum revivals of cat states. We demonstrate that, even when dissipation suppresses quantum revivals, quantum echoes can be recovered by properly tuning the timing and strength of the perturbation. These results may be useful for characterizing and mitigating errors of cat qubits.

The two-body contact is a fundamental quantity of a dilute Bose gas that relates the thermodynamics to the short-distance two-body correlations. For a Bose gas in an optical lattice, near the superfluid–Mott-insulator transition, we show that a “universal” contact $C_{\mathrm{univ}}$ can be defined from the singular part $P-P_{\mathrm{MI}}$ of the pressure ($P_{\mathrm{MI}}$ is the pressure of the Mott insulator). Its expression $C_{\mathrm{univ}}=C_{\mathrm{DBG}}\left(\right|n-n_{\mathrm{MI}}|,a^{*})$ coincides with that of a dilute Bose gas provided we consider the effective “scattering length” $a^{*}$ of the quasiparticles at the quantum critical point (QCP) rather than the scattering length in vacuum, and the excess density $|n-n_{\mathrm{MI}}|$ of particles (or holes) with respect to the Mott insulator. Close to the transition, we find that the singular part $n_{\mathbf{k}}^{\mathrm{sing}}=n_{\mathbf{k}}-n_{\mathbf{k}}^{\mathrm{MI}}$ of the momentum distribution exhibits a high-momentum tail of the form $Z_{\mathrm{QP}}{C}_{\mathrm{univ}}/{\left|\mathbf{k}\right|}^4$ over a broad region of the Brillouin zone, where $Z_{\mathrm{QP}}$ is the quasiparticle weight of the elementary excitations at the QCP. Our results demonstrate that the notion of contact extends to strongly correlated lattice bosons, and we argue that the contact $C_{\mathrm{univ}}$ can be measured in state-of-the-art experiments on Bose gases in optical lattices and magnetic insulators.

We analyze the scaling of quantum Fisher information with the number of system particles in the limit of large number of particles, as a function of the number of parties interacting with each other, for encoding Hamiltonians having $k$-body interactions, where $k$ is arbitrary. We find that estimation of coupling strength of such arbitrary-body encoding Hamiltonians provides a super-Heisenberg scaling that increases monotonically with an increase in the number of interacting particles, in the limit of large number of system particles. Moreover, we ask if genuine multiparty entanglement is indispensable in attaining the best metrological precision if we employ nonlocal terms in the Hamiltonian. We identify a dichotomy in the answer. Specifically, we find that Hamiltonians having odd-body interactions necessarily require genuine multipartite entanglement in probes to attain the best metrological precision, but the situation is opposite in the case of Hamiltonians with even-body interactions. The optimal probes corresponding to Hamiltonians that contain even-body interaction terms may be entangled, but certainly not so in all bipartitions, and particularly it is possible to attain optimal precision using asymmetric probes. Asymmetry, which therefore is a resource in this scenario rather than genuine multiparty entanglement, refers to the disparity between states of local parts of the global system. Thereby we find a complementarity in the requirement of asymmetry and genuine entanglement in optimal probes for estimating strength of odd- and even-body interactions respectively. Additionally, we provide an upper bound on the number of parties up to which one can always obtain an asymmetric product state that gives the best metrological precision for even-body interactions. En route, we find the quantum Fisher information in closed form for two- and three-body interactions for arbitrary number of parties. Additionally, we analyze the finite-size scaling of the QFI and examine the impact of local dephasing noise during the encoding process. We also provide an analysis of the case when the Hamiltonian contains local fields and up to $k$-body interaction terms, where the strength of interaction gradually decreases with an increase in the number of parties interacting with each other. Interestingly, we find a similar dichotomy in the nature of the optimal probe in this case as well, i.e., for encoding Hamiltonians with up to even- and odd-body interactions. Further, we identify conditions on the local component of the Hamiltonian for which this dichotomy is still shown to exist for two- and three-body encoding Hamiltonians with arbitrary local dimensions.

Smoothing is a technique for estimating the state of an imperfectly monitored open system by combining both prior and posterior measurement information. In the quantum regime, current approaches to smoothing either give unphysical outcomes, due to the noncommutativity of the measurements at different times, or require assumptions about how the environment is measuring the system, which with current technology is unverifiable. We propose a novel definition of the smoothed quantum state based on quantum Bayesian retrodiction, which mirrors the classical retrodictive approach to smoothing. This approach always yields physical results and does not require any assumption on the environment. We show that this smoothed state has, on average, greater purity than the state reconstructed using just the prior information. Finally, we make a connection with the smoothing theory of Guevara and Wiseman in a well-studied regime, and describe from a purely quantum perspective how it conditions on the posterior information.

Nonlocal correlations created in networks with multiple independent sources enable surprising phenomena in quantum information and quantum foundations. The presence of independent sources, however, makes the analysis of network nonlocality challenging, and even in the simplest nontrivial scenarios a complete characterization is lacking. In this Letter we study one of the simplest of these scenarios, namely that of distributions invariant under permutations of parties in the minimal triangle network, which features no inputs and binary outcomes. We perform an exhaustive search for triangle-local models, and from it we infer analytic expressions for the boundaries of the set of distributions that admit such models, which we conjecture to be all the tight Bell inequalities for the scenario. Armed with them and with improved outer approximations of the set, we provide insights on the existence of a classical-quantum gap in the triangle network with binary outcomes.

The ${\mathrm{RaOCH}}_3$ molecule is one of the most sensitive systems for electron electric dipole moment ($e\mathrm{EDM}$) searches. Its hyperfine and $K\text{−}\mathrm{doubling}$ structure in the external electric field is of key importance for preparing and interpreting the experiment. We proposed the method for calculation of the symmetric top molecules and applied it for ${\mathrm{RaOCH}}_3$. Hyperfine structure, $K$ doubling, and sensitivity of the molecule to $e\mathrm{EDM}$ in the external electric field were calculated.

We present a method for target finding in LIDAR applications using high-dimensional Bell states. Combined with a sequential decision rule, this scheme asymptotically achieves zero error probability with finite average energy expenditure. This result stems from the synergy of high-dimensional entanglement suppressing false positives and the sequential decision rule optimizing energy usage. This analysis provides a theoretical foundation to further explore quantum sensing protocols that may significantly outperform classical methods in noisy environments.

Tomographic locality is a principle commonly used in the program of finding axioms that pick out quantum theory within the landscape of possible theories. The principle asserts the sufficiency of local measurements for achieving a tomographic characterization of any bipartite state. In this work, we explore the meaning of the principle of tomographic locality by developing a simple scheme for generating a wide variety of theories that violate the principle. In this scheme, one starts with a tomographically local theory—which can be classical, quantum, or postquantum—and a physical symmetry, and one restricts the processes in the theory to all and only those that are covariant with respect to the collective action of that symmetry. We refer to the resulting theories as twirled worlds. We show that failures of tomographic locality are ubiquitous in twirled worlds. From the possibility of such failures in classical twirled worlds, we argue that the failure of tomographic locality (i.e., tomographic nonlocality) does not imply ontological holism. Our results also demonstrate the need for researchers seeking to axiomatize quantum theory to take a stand on the question of whether there are superselection rules that have a fundamental status.

While the special properties of exceptional points (EPs) may improve application relevant features such as hypersensing, often their realization requires a precise fine-tuning of parameters. Here we report the robust formation of EP chains in coupled optical microcavities over intercavity distances $D$ on the order of the cavity size. We find that coupling, or more generally, the availability of an outer (coupling) channel, is sufficient to induce EPs in the parameter space spanned by the refractive index $n$ along with $D$. This occurs even at $D$ of several wavelengths, yielding a network of EPs in parameter space with a periodicity of the order of the wavelength in the $D$ direction. Upon the increase of $n$, we observe a sharp transition in the sign of the chirality measured in one of the cavities that further structures the system properties. While the details of the Riemannian surfaces associated with the formation of exceptional points are mode dependent and allow for a variety of single-cavity chiralities, we find the underlying mechanism to be universal, robust, applicable to other and more general coupled systems, and promising for potential applications such as optical measurements of pressure, voltages, or distances.

Metastability is ubiquitous in diverse complex systems. In open quantum systems, metastability offers protection against dissipation and decoherence, yet its application in quantum batteries remains unexplored. We propose a solid-state open quantum battery where metastable states enable stable superextensive charging without complicated protocols and energy storage with extended lifetime. Using a realistic organic maser platform, we show the controllable manner of the work extraction from the quantum battery, which can be exploited for on-demand coherent microwave emission at room temperature. These results not only demonstrate the usefulness of metastability for developing the quantum batteries robust against energy losses, but also provide a paradigm of the practical quantum device powered up by quantum batteries.

A central requirement in asymmetric quantum nonlocality protocols, such as quantum steering, is the precise reconstruction of state assemblages—statistical ensembles of quantum states correlated with remote classical signals. Existing steering works often rely on simplifying assumptions about detection efficiency and photon loss. Here we introduce a generalized loss model for assemblage tomography that uses conical optimization techniques combined with maximum-likelihood estimation. This approach allows us to accurately estimate assemblages without assuming uniform detection efficiency on the untrusted party's side. Using an evidence-based framework grounded in the Akaike information criterion, we demonstrate faithful reconstructions while balancing model complexity. We validate our results through numerical simulations and an experimental setup, showing robust performance in assemblage estimation when applied to experimentally relevant data.

Incoherent stochastic processes added to unitary dynamics are typically deemed detrimental since they are expected to diminish quantum features such as superposition and entanglement. Instead of exhibiting energy-conserving persistent coherent motion, the dynamics of such open systems feature, in most cases, a steady state, which is approached in the long-time limit from all initial conditions. This can, in fact, be advantageous as it offers a mechanism for the creation of robust quantum correlations on demand without the need for fine-tuning. Here, we show this for a system consisting of two coherently coupled bosonic modes, which is a paradigmatic scenario for the realization of quantum resources such as squeezed entangled states. Rather counterintuitively, the mere addition of incoherent hopping, which results in a statistical coupling between the bosonic modes, leads to steady states with robust quantum entanglement and enables the emergence of persistent coherent nonstationary behavior.

Searches for time-reversal symmetry ($T$) violations using spin sensors are susceptible to spurious frequency shifts and noise from magnetic fields, which can mask signals originating from beyond-standard-model new physics. Therefore, a comagnetometer—an auxiliary sensor that allows mundane magnetic-field effects to be differentiated from new physics—is an essential feature of many precision measurements. We characterize an intrinsic comagnetometer that is available in crystals, which can be used to suppress spurious magnetic-field effects through comparing sets of ions related by spatial reflection symmetry. We find that the new-physics measurement channel can be effectively shielded to better than $10\mu \mathrm{G}$, without the need for active or passive magnetic shields. Our measurements demonstrate precise and accurate control over magnetic systematic errors, laying the groundwork for improved searches of $T$ violation using solid-state systems.

Quantum control plays a crucial role in enhancing precision scaling for quantum sensing. However, most existing protocols require perfect control, even though real-world devices inevitably have control imperfections. Here, we consider a fundamental setting of quantum sensing with time domain imperfections, where the duration of control pulses and the interrogation time are all subject to uncertainty. Under this scenario, we investigate the task of frequency estimation in the presence of a non-Markovian environment. We design a control strategy and prove that it outperforms any control-free strategies, recovering the optimal Heisenberg limit up to a small error term that is intrinsic to this model. We further demonstrate the advantage of our control strategy via experiments on a nuclear magnetic resonance platform. Our findings confirm that the advantage of quantum control in quantum sensing persists even in the presence of imperfections.

We experimentally demonstrate cavity-free feedback cooling of the three lowest-lying collective modes of a Bose-Einstein condensate in a prolate harmonic trap. Using shadowgraph imaging as an in situ probe of the atomic density, we measure the time-dependent centers of mass and widths of the condensate in two dimensions and use these measurements to damp oscillations in the two visible dipole modes and the low-frequency quadrupole mode. By inducing oscillations in the condensate, we show that we can efficiently damp the dipole modes to a final mean phonon occupancy per atom of $<1$.