The quantum Fisher information (QFI) is a fundamental quantity of interest in many areas from quantum metrology to quantum information theory. It can in particular be used as a witness to establish the degree of multiparticle entanglement in quantum many-body systems. In this work, we use polynomials of the density matrix to construct monotonically increasing lower bounds that converge to the QFI. Using randomized measurements we propose a protocol to accurately estimate these lower bounds in state-of-the-art quantum technological platforms. We estimate the number of measurements needed to achieve a given accuracy and confidence level in the bounds, and present two examples of applications of the method in quantum systems made of coupled qubits and collective spins.

We propose a new scalable architecture for trapped ion quantum computing that combines optical tweezers delivering qubit state-dependent local potentials with oscillating electric fields. Since the electric field allows for long-range qubit-qubit interactions mediated by the center-of-mass motion of the ion crystal alone, it is inherently scalable to large ion crystals. Furthermore, our proposed scheme does not rely on either ground-state cooling or the Lamb-Dicke approximation. We study the effects of imperfect cooling of the ion crystal, as well as the role of unwanted qubit-motion entanglement, and discuss the prospects of implementing the state-dependent tweezers in the laboratory.

The first measurements of differential branching fractions of inclusive semileptonic $B\to X_u{\ell }^{+}{\nu }_{\ell }$ decays are performed using the full Belle data set of $711{\mathrm{fb}}^{-1}$ of integrated luminosity at the $\mathrm{\Upsilon }(4S)$ resonance and for $\ell =e$, $\mu$. With the availability of these measurements, new avenues for future shape-function model-independent determinations of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$ can be pursued to gain new insights in the existing tension with respect to exclusive determinations. The differential branching fractions are reported as a function of the lepton energy, the four-momentum-transfer squared, light-cone momenta, the hadronic mass, and the hadronic mass squared. They are obtained by subtracting the backgrounds from semileptonic $B\to X_c{\ell }^{+}{\nu }_{\ell }$ decays and other processes, and corrected for resolution and acceptance effects.

We present the first measurement of the timelike Compton scattering process, $\gamma p\to p^{\prime }{\gamma }^{*}({\gamma }^{*}\to e^{+}{e}^{-})$, obtained with the CLAS12 detector at Jefferson Lab. The photon beam polarization and the decay lepton angular asymmetries are reported in the range of timelike photon virtualities $2.25<Q^{\prime 2}<9{\mathrm{GeV}}^2$, squared momentum transferred $0.1<-t<0.8{\mathrm{GeV}}^2$, and average total center-of-mass energy squared $s=14.5{\mathrm{GeV}}^2$. The photon beam polarization asymmetry, similar to the beam-spin asymmetry in deep virtual Compton scattering, is sensitive to the imaginary part of the Compton form factors and provides a way to test the universality of the generalized parton distributions. The angular asymmetry of the decay leptons accesses the real part of the Compton form factors and thus the $D$-term in the parametrization of the generalized parton distributions.

Description of periodically and resonantly driven quantum systems can lead to solid state models where condensed matter phenomena can be investigated in time lattices formed by periodically evolving Wannier-like states. Here, we show that inseparable two-dimensional time lattices with the Möbius strip geometry can be realized for ultracold atoms bouncing between two periodically oscillating mirrors. Effective interactions between atoms loaded to a lattice can be long-ranged and can be controlled experimentally. As a specific example, we show how to realize a Lieb lattice model with a flat band and how to control long-range hopping of pairs of atoms in the model.

Physical properties of two-dimensional van der Waals (vdWs) structures depend sensitively on both stacking orders and interlayer interactions. Yet, in most cases studied to date, the interlayer interaction is considered to be a “static” property of the vdWs structures. Here we demonstrate that applying a scanning tunneling microscopy (STM) tip pulse on twisted bilayer graphene (TBG) can induce sub-Ångstrom fluctuations of the interlayer separation in the TBG, which are equivalent to dynamic vertical external pressure of about 10 GPa on the TBG. The sub-Ångstrom fluctuations of the interlayer separation result in large oscillations of the energy separations between two van Hove singularities (VHSs) in the TBG. The period of the oscillations of the VHSs spacing is extremely long, about 500–1000 sec, attributing to tip-induced local stress in the atomic-thick TBG. Our result provides an efficient method to tune and measure the physical properties of the vdWs structures dynamically.

One favorable situation for spins to enter the long-sought quantum spin liquid (QSL) state is when they sit on a kagome lattice. No consensus has been reached in theory regarding the true ground state of this promising platform. The experimental efforts, relying mostly on one archetypal material ${\mathrm{ZnCu}}_3{(\mathrm{OH})}_6{\mathrm{Cl}}_2$, have also led to diverse possibilities. Apart from subtle interactions in the Hamiltonian, there is the additional degree of complexity associated with disorder in the real material ${\mathrm{ZnCu}}_3{(\mathrm{OH})}_6{\mathrm{Cl}}_2$ that haunts most experimental probes. Here we resort to heat transport measurement, a cleaner probe in which instead of contributing directly, the disorder only impacts the signal from the kagome spins. For ${\mathrm{ZnCu}}_3{(\mathrm{OH})}_6{\mathrm{Cl}}_2$, we observed no contribution by any spin excitation nor obvious field-induced change to the thermal conductivity. These results impose strong constraints on various scenarios about the ground state of this kagome compound: while certain quantum paramagnetic states other than a QSL may serve as natural candidates, a QSL state, gapless or gapped, must be dramatically modified by the disorder so that the kagome spin excitations are localized.

Optical phenomena associated with an extremely localized field should be understood with considerations of nonlocal and quantum effects, which pose a hurdle to conceptualize the physics with a picture of eigenmodes. Here we first propose a generalized Lorentz model to describe general nonlocal media under linear mean-field approximation and formulate source-free Maxwell’s equations as a linear eigenvalue problem to define the quasinormal modes. Then we introduce an orthonormalization scheme for the modes and establish a canonical quasinormal mode framework for general nonlocal media. Explicit formalisms for metals described by a quantum hydrodynamic model and polar dielectrics with nonlocal response are exemplified. The framework enables for the first time a direct modal analysis of mode transition in the quantum tunneling regime and provides physical insights beyond usual far-field spectroscopic analysis. Applied to nonlocal polar dielectrics, the framework also unveils the important roles of longitudinal phonon polaritons in optical response.

Despite there being an infinite variety of types of flow, most rheological studies focus on a single type such as simple shear. Using discrete element simulations, we explore bulk granular systems in a wide range of flow types at large strains and characterize invariants of the stress tensor for different inertial numbers and interparticle friction coefficients. We identify a strong dependence on the type of flow, which grows with increasing inertial number or friction. Standard models of yielding, repurposed to describe the dependence of the stress on flow type in steady-state flow and at finite rates, are compared with data.

We report angle resolved photoemission experiments on a newly discovered family of kagome metals $R{\mathrm{V}}_6{\mathrm{Sn}}_6$ ($R=\mathrm{Gd}$, Ho). Intrinsic bulk states and surface states of the vanadium kagome layer are differentiated from those of other atomic sublattices by the real-space resolution of the measurements with a small beam spot. Characteristic Dirac cone, saddle point, and flat bands of the kagome lattice are observed. Our results establish the two-dimensional (2D) kagome surface states as a new platform to investigate the intrinsic kagome physics.

Behavior of the bacterial flagellar motor depends sensitively on the external loads it drives. Motor switching, which provides the basis for the run-and-tumble behavior of flagellated bacteria, has been studied for motors under zero to high loads, revealing a nonequilibrium effect that is proportional to the motor torque. However, behavior of the motor switching at stall (with maximum torque) remains unclear. An extrapolation from previous studies would suggest the maximum nonequilibrium effect for motor switching at stall. Here, we stalled the motor using optical tweezers and studied the motor switching with a high time resolution of about 2 ms. Surprisingly, our results showed exponentially distributed counterclockwise (CCW) and clockwise (CW) intervals, indicating that motor switching at stall is probably an equilibrium process. Combined with previous experiments at other loads, our result suggested that the nonequilibrium effect in motor switching arises from the asymmetry of the torque generation in the CCW and CW directions. By including this nonequilibrium effect in the general Ising-type conformation spread model of the flagellar switch, we consistently explained the motor switching over the whole range of load conditions. We expect to see a similar mechanism of nonequilibrium regulation in other molecular machines.

Emerging dynamical constraints resulting from intersite interactions severely limit particle mobility in polar lattice gases. Whereas in absence of disorder hard-core Hubbard models with only strong nearest-neighbor interactions present Hilbert space fragmentation but no many-body localization for typical states, the $1/r^3$ tail of the dipolar interaction results in Hilbert space shattering, as well as in a dramatically slowed down dynamics and eventual disorder-free localization. Our results show that the study of the intriguing interplay between disorder- and interaction-induced many-body localization is within reach of future experiments with magnetic atoms and polar molecules.

According to first-principle lattice QCD calculations, the transition from quark-gluon plasma to hadronic matter is a smooth crossover in the region ${\mu }_B\le T_c$. In this range the ratio, $C_6/C_2$, of net-baryon distributions are predicted to be negative. In this Letter, we report the first measurement of the midrapidity net-proton $C_6/C_2$ from 27, 54.4, and 200 GeV $\mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy Ion Collider (RHIC). The dependence on collision centrality and kinematic acceptance in ($p_T$, $y$) are analyzed. While for 27 and 54.4 GeV collisions the $C_6/C_2$ values are close to zero within uncertainties, it is observed that for 200 GeV collisions, the $C_6/C_2$ ratio becomes progressively negative from peripheral to central collisions. Transport model calculations without critical dynamics predict mostly positive values except for the most central collisions within uncertainties. These observations seem to favor a smooth crossover in the high-energy nuclear collisions at top RHIC energy.

The leading quantum electrodynamic corrections to the nuclear magnetic shielding in one- and two-electron atomic systems are obtained in a complete form, and the shielding constants of ${}^1\mathrm{H}$, ${}^3{\mathrm{He}}^{+}$, and ${}^3\mathrm{He}$ are calculated to be $17.735436(3)\times {10}^{-6}$, $35.507434(9)\times {10}^{-6}$, and $59.967029(23)\times {10}^{-6}$, respectively. These results are orders of magnitude more accurate than previous ones, and, with the ongoing measurement of the nuclear magnetic moment of ${}^3{\mathrm{He}}^{+}$ and planned ${{}^3\mathrm{He}}^{2+}$, they open the window for high-precision absolute magnetometry using ${}^3\mathrm{He}$ NMR probes. The presented theoretical approach is applicable to all other light atomic and molecular systems, which facilitates the improved determination of magnetic moments of any light nuclei.

Singular behaviors are increasingly being found in structures supporting bound states in the continuum (BICs), while the nonreciprocity with spectral phase singularity has not been reported. Here, we demonstrate the origin, evolution, and application of topological phase singularity pairs (TPSPs) resulting from BICs in nonreciprocal and non-Hermitian systems. The nonreciprocity contributes to creating accidental BICs asymmetrically, each of which can split into TPSP with topological charges $\pm 1$ in reflection phases by inserting loss. The formation, annihilation, and revival processes of these TPSPs can be selectively controlled via either material or radiative loss. The criteria to predict both number and angular positions of asymmetric BICs are established. Near-complete violation of Kirchhoff’s law of thermal radiation has been correspondingly manifested over a wide angular range. The unveiled physics synergizing nonreciprocity and topology will bring new opportunities in multidisciplinary areas like thermal science, magneto-optics, or topological metasurfaces.