We present a method that uses radio-frequency pulses to cancel the quadrupole shift in optical clock transitions. Quadrupole shifts are an inherent inhomogeneous broadening mechanism in trapped ion crystals and impose one of the limitations forcing current optical ion clocks to work with a single probe ion. Canceling this shift, at each interrogation cycle of the ion frequency, reduces the complexity in using $N>1$ ions in clocks, thus allowing for a reduction of the instability in the clock frequency by $\sqrt{N}$ according to the standard quantum limit. Our sequence relies on the tensorial nature of the quadrupole shift, and thus also cancels other tensorial shifts, such as the tensor ac stark shift. We experimentally demonstrate our sequence on three and seven ${{}^{88}\mathrm{Sr}}^{+}$ ions trapped in a linear Paul trap, using correlation spectroscopy. We show a reduction of the quadrupole shift difference between ions to the $\approx 10\mathrm{mHz}$ level where other shifts, such as the relativistic second-order Doppler shift, are expected to limit our spectral resolution. In addition, we show that using radio-frequency dynamic decoupling we can also cancel the effect of first-order Zeeman shifts.

In this Letter, we study the splashing behavior of droplets upon impact onto a variety of substrates with different wetting properties, ranging from hydrophilic to superhydrophobic surfaces. In particular, we study the effects of the dynamic contact angle on splashing. The experimental approach uses high-speed imaging and image analysis to recover the apparent contact angle as a function of the spreading speed. Our results show that neither the Capillary number nor the so-called splashing parameter are appropriate to characterize the splashing behavior under these circumstances. However, we show that the maximum dynamic advancing contact angle and the splashing ratio $\beta$ adequately characterize the splashing behavior.

The physical particles in supersymmetric Yang-Mills (SYM) theory are bound states of gluons and gluinos. We have determined the masses of the lightest bound states in SU(3) $\mathcal{N}=1$ SYM theory. Our simulations cover a range of different lattice spacings, which for the first time allows an extrapolation to the continuum limit. Our results show the formation of a supermultiplet of bound states, which provides a clear evidence for unbroken supersymmetry.

We introduce a new “quantile” analysis strategy to study the modification of jets as they traverse through a droplet of quark-gluon plasma. To date, most jet modification studies have been based on comparing the jet properties measured in heavy-ion collisions to a proton-proton baseline at the same reconstructed jet transverse momentum ($p_T$). It is well known, however, that the quenching of jets from their interaction with the medium leads to a migration of jets from higher to lower $p_T$, making it challenging to directly infer the degree and mechanism of jet energy loss. Our proposed quantile matching procedure is inspired by (but not reliant on) the approximate monotonicity of energy loss in the jet $p_T$. In this strategy, jets in heavy-ion collisions ordered by $p_T$ are viewed as modified versions of the same number of highest-energy jets in proton-proton collisions, and the fractional energy loss as a function of jet $p_T$ is a natural observable ($Q_{AA}$). Furthermore, despite nonmonotonic fluctuations in the energy loss, we use an event generator to validate the strong correlation between the $p_T$ of the parton that initiates a heavy-ion jet and the $p_T$ of the vacuum jet which corresponds to it via the quantile procedure ($p_T^{\text{quant}}$). We demonstrate that this strategy both provides a complementary way to study jet modification and mitigates the effect of $p_T$ migration in heavy-ion collisions.

A more detailed test of the implementation of nuclear forces that drive shell evolution in the pivotal nucleus ${}^{42}\mathrm{Si}$—going beyond earlier comparisons of excited-state energies—is important. The two leading shell-model effective interactions, SDPF-MU and SDPF-U-Si, both of which reproduce the low-lying ${}^{42}\mathrm{Si}(2_1^{+})$ energy, but whose predictions for other observables differ significantly, are interrogated by the population of states in neutron-rich ${}^{42}\mathrm{Si}$ with a one-proton removal reaction from ${}^{43}\mathrm{P}$ projectiles at $81\mathrm{MeV}/\mathrm{nucleon}$. The measured cross sections to the individual ${}^{42}\mathrm{Si}$ final states are compared to calculations that combine eikonal reaction dynamics with these shell-model nuclear structure overlaps. The differences in the two shell-model descriptions are examined and linked to predicted low-lying excited $0^{+}$ states and shape coexistence. Based on the present data, which are in better agreement with the SDPF-MU calculations, the state observed at 2150(13) keV in ${}^{42}\mathrm{Si}$ is proposed to be the ($0_2^{+}$) level.

We investigate the photovoltaic effect of atomtronics induced by an artificial gauge field in four optical potentials. Under an effective magnetic flux, the atom occupation probability would be polarized in a double-dot system, which gives rise to an atomic current. The relation between the atomic current and magnetic flux behaves like the current-phase property in a Josephson junction. A neutral particle photovoltaic cell is well defined by the atomic opened system that has an effective voltage and two different poles corresponding to two internal states of atomtronics. The atom flow is controllable by tuning the direction of incident light and other parameters. The detection of the atomic current intensity is available through an optical emission spectrum in experiments.

We show experimentally that a pair of disks settling at negligible Reynolds number ($\sim {10}^{-4}$) displays two classes of bound periodic orbits, each with transitions to scattering states. We account for these dynamics, at leading far-field order, through an effective Hamiltonian in which gravitational driving endows orientation with the properties of momentum. This treatment is successfully compared against the measured properties of orbits and critical parameters of transitions between types of orbits. We demonstrate a precise correspondence with the Kepler problem of planetary motion for a wide range of initial conditions, find and account for a family of orbits with no Keplerian analog, and highlight the role of orientation as momentum in the many-disk problem.

The creation and disruption of inertially collimated plasma flows are investigated through experiment, simulation, and analytical modeling. Supersonic plasma jets are generated by laser-irradiated plastic cones and characterized by optical interferometry measurements. Targets are magnetized with a tunable $B$ field with strengths of up to 5 T directed along the axis of jet propagation. These experiments demonstrate a hitherto unobserved phenomenon in the laboratory, the magnetic disruption of inertially confined plasma jets. This occurs due to flux compression on axis during jet formation and can be described using a Lagrangian-cylinder model of plasma evolution implementing finite resistivity. The basic physical mechanisms driving the dynamics of these systems are described by this model and then compared with two-dimensional radiation-magnetohydrodynamic simulations. Experimental, computational, and analytical results discussed herein suggest that contemporary models underestimate the electrical conductivity necessary to drive the amount of flux compression needed to explain observations of jet disruption.

Obtaining an accurate ground state wave function is one of the great challenges in the quantum many-body problem. In this Letter, we propose a new class of wave functions, neural network backflow (NNB). The backflow approach, pioneered originally by Feynman and Cohen [Phys. Rev. 102, 1189 (1956)], adds correlation to a mean-field ground state by transforming the single-particle orbitals in a configuration-dependent way. NNB uses a feed-forward neural network to learn the optimal transformation via variational Monte Carlo calculations. NNB directly dresses a mean-field state, can be systematically improved, and directly alters the sign structure of the wave function. It generalizes the standard backflow [L. F. Tocchio et al., Phys. Rev. B 78, 041101(R) (2008)], which we show how to explicitly represent as a NNB. We benchmark the NNB on Hubbard models at intermediate doping, finding that it significantly decreases the relative error, restores the symmetry of both observables and single-particle orbitals, and decreases the double-occupancy density. Finally, we illustrate interesting patterns in the weights and bias of the optimized neural network.

Bulk ${\mathrm{LiOsO}}_3$ was experimentally identified as a “ferroelectric” metal where polar distortions coexist with metallicity [Shi et al., Nat. Mater. 12, 1024 (2013)]. It is generally believed that polar displacements in a ferroelectric metal cannot be switched by an external electric field. Here, via comprehensive density functional theory calculations, we demonstrate that a two-unit cell-thick ${\mathrm{LiOsO}}_3$ thin film exhibits a ferroelectric ground state having an out-of-plane electric dipole moment that can be switched by an external electric field. Moreover, its dipole moment-versus-electric field hysteresis loop is asymmetric because only surface Li ions’ displacements are reversed by the external electric field whereas the field-induced force on inner Li atoms is nearly fully screened by itinerant electrons. As a relevant by-product of our study, we also extend the concept of “Born effective charge” to finite metallic systems, and show its usefulness to rationalize the observed effects.

We implement a cold-damping scheme to cool one mode of the center-of-mass motion of an optically levitated nanoparticle in ultrahigh vacuum (${10}^{-8}\mathrm{mbar}$) from room temperature to a record-low temperature of $100\mu \mathrm{K}$. The measured temperature dependence on the feedback gain and thermal decoherence rate is in excellent agreement with a parameter-free model. For the first time, we determine the imprecision-backaction product for a levitated optomechanical system and discuss the resulting implications for ground-state cooling of an optically levitated nanoparticle.

We use an optimal control protocol to cool one mode of the center-of-mass motion of an optically levitated nanoparticle. The feedback technique relies on exerting a Coulomb force on a charged particle with a pair of electrodes and follows the control law of a linear quadratic regulator, whose gains are optimized by a machine learning algorithm in under 5 s. With a simpler and more robust setup than optical feedback schemes, we achieve a minimum center-of-mass temperature of 5 mK at $3\times {10}^{-7}\mathrm{mbar}$ and transients 10–600 times faster than cold damping. This cooling technique can be easily extended to 3D cooling and is particularly relevant for studies demanding high repetition rates and force sensing experiments with levitated objects.

Topological nonsymmorphic crystalline superconductivity (TNCS) is an intriguing phase of matter, offering a platform to study the interplay between topology, superconductivity, and nonsymmorphic crystalline symmetries. Interestingly, some of TNCSs are classified into ${\mathbb{Z}}_4$ topological phases, which have unique surface states referred to as a Möbius strip or an hourglass, and they have not been achieved in symmorphic superconductors. However, material realization of ${\mathbb{Z}}_4$ TNCS has never been known, to the best of our knowledge. Here, we propose that the paramagnetic superconducting phase of UCoGe under pressure is a promising candidate of ${\mathbb{Z}}_4$-nontrivial TNCS enriched by glide symmetry. We evaluate ${\mathbb{Z}}_4$ invariants of UCoGe by deriving the formulas relating ${\mathbb{Z}}_4$ invariants to the topology of Fermi surfaces. Applying the formulas and previous ab initio calculations, we clarify that three odd-parity representations out of four are ${\mathbb{Z}}_4$-nontrivial TNCS, whereas the other is also ${\mathbb{Z}}_2$-nontrivial TNCS. We also discuss possible ${\mathbb{Z}}_4$ TNCS in CrAs and related materials.

We report an experimental demonstration of a machine learning approach to identify exotic topological phases, with a focus on the three-dimensional chiral topological insulators. We show that the convolutional neural networks—a class of deep feed-forward artificial neural networks with widespread applications in machine learning—can be trained to successfully identify different topological phases protected by chiral symmetry from experimental raw data generated with a solid-state quantum simulator. Our results explicitly showcase the exceptional power of machine learning in the experimental detection of topological phases, which paves a way to study rich topological phenomena with the machine learning toolbox.

Equilibrium spatiotemporal correlation functions are central to understanding weak nonequilibrium physics. In certain local one-dimensional classical systems with three conservation laws they show universal features. Namely, fluctuations around ballistically propagating sound modes can be described by the celebrated Kardar-Parisi-Zhang (KPZ) universality class. Can such a universality class be found also in quantum systems? By unambiguously demonstrating that the KPZ scaling function describes magnetization dynamics in the $SU(2)$ symmetric Heisenberg spin chain we show, for the first time, that this is so. We achieve that by introducing new theoretical and numerical tools, and make a puzzling observation that the conservation of energy does not seem to matter for the KPZ physics.

Water channels are important to new purification systems, osmotic power harvesting in salinity gradients, hydroelectric voltage conversion, signal transmission, drug delivery, and many other applications. To be effective, water channels must have structures more complex than a single tube. One way of building such structures is through a water bridge between two disjoint channels that are not physically connected. We report on the results of extensive molecular dynamics simulation of water transport through such bridges between two carbon nanotubes separated by a nanogap. We show that not only can pressurized water be transported across a stable bridge, but also that (i) for a range of the gap’s width $l_g$ the bridge’s hydraulic conductance $G_b$ does not depend on $l_g$, (ii) the overall shape of the bridge is not cylindrical, and (iii) the dependence of $G_b$ on the angle between the axes of two nonaligned nanochannels may be used to tune the flow rate between the two.

We look for inherent structural characteristics hidden behind amorphous solid formation by using zero-temperature jammed packings of frictionless particles as models. Differently from previous geometrical approaches, we introduce a microscopic mechanical or vibrational order parameter $\mathrm{\Psi }$, which characterizes the susceptibility of particle motion to infinitesimal thermal excitation. We show that (i) the distribution of $\mathrm{\Psi }$ has a power-law tail toward high $\mathrm{\Psi }$ and (ii) the spatial organization of $\mathrm{\Psi }$ is characterized by a nontrivial scale-free correlation. Both findings (i) and (ii) are regarded as a real-space manifestation of marginal stability due to critical self-organization of jammed packings toward mechanical equilibrium. Furthermore, we find that the power-law exponent of the $\mathrm{\Psi }$ distribution tail shows a critical-like scaling behavior toward the unjamming transition, which unveils an intriguing interplay between jamming criticality and marginal stability. Our microscopic order parameter provides new structural insights into the marginal stability and instability of jammed packings and may shed light on the important common structural feature of amorphous solids.