Recent advances in ultrafast measurement in cold atoms, as well as pump-probe spectroscopy of ${\mathrm{K}}_3{\mathrm{C}}_{60}$ films, have opened the possibility of rapidly quenching systems of interacting fermions to, and across, a finite temperature superfluid transition. However, determining that a transient state has approached a second-order critical point is difficult, as standard equilibrium techniques are inapplicable. We show that the approach to the superfluid critical point in a transient state may be detected via time-resolved transport measurements, such as the optical conductivity. We leverage the fact that quenching to the vicinity of the critical point produces a highly time dependent density of superfluid fluctuations, which affect the conductivity in two ways. First, by inelastic scattering between the fermions and the fluctuations, and second by direct conduction through the fluctuations, with the latter providing a lower resistance current carrying channel. The competition between these two effects leads to nonmonotonic behavior in the time-resolved optical conductivity, providing a signature of the critical transient state.

Understanding magnetic interactions in the parent compounds of high-temperature superconductors forms the basis for determining their role for the mechanism of superconductivity. For parent compounds of iron pnictide superconductors such as $A{\mathrm{Fe}}_2{\mathrm{As}}_2$ ($A=\mathrm{Ba}$, Ca, Sr), although spin excitations have been mapped out throughout the entire Brillouin zone, the respective measurements were carried out on twinned samples and did not allow for a conclusive determination of the spin dynamics. Here we use inelastic neutron scattering to completely map out spin excitations of $\sim 100\%$ detwinned ${\mathrm{BaFe}}_2{\mathrm{As}}_2$. By comparing observed spectra with theoretical calculations, we conclude that the spin excitations can be well described by an itinerant model when taking into account moderate electronic correlation effects.

This Letter uses density functional, dynamical mean field, and Landau-theory methods to elucidate the interplay of electronic and structural energetics in the Mott metal-insulator transition. A Landau-theory free energy is presented that incorporates the electronic energetics, the coupling of the electronic state to local distortions and the coupling of local distortions to long-wavelength strains. The theory is applied to ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$. The change in lattice energy across the metal-insulator transition is comparable to the change in electronic energy. Important consequences are a strongly first order transition, a sensitive dependence of the phase boundary on pressure and that the geometrical constraints on in-plane lattice parameter associated with epitaxial growth on a substrate typically change the lattice energetics enough to eliminate the metal-insulator transition entirely.

In this Letter, we report a resonant x-ray scattering measurement of stripelike charge order in the 1/8th doped component of electronically phase-separated, orthorhombic ${\mathrm{La}}_2{\mathrm{CuO}}_{4+y}$. This observation is coupled to the absence of any resonant (001) peak, which at different resonant energies has been identified with the presence of low-temperature-tetragonal-like structural tilt patterns or nematicity in the CuO planes. Thus, we provide evidence that structural pinning is not necessary for the formation of static charge stripes and that the relationship between charge nematicity and stripes may not be simple.

The ground state of two-dimensional (2D) electron systems with equal low densities of electrons and holes in nearby layers is an exciton fluid. We show that a reservoir for excitons can be established by contacting the two layers separately and maintaining the chemical potential difference at a value less than the spatially indirect band gap, thereby avoiding the presence of free carriers in either layer. Equilibration between the exciton fluid and the contacts proceeds via a process involving virtual intermediate states in which an unpaired electron or hole virtually occupies a free carrier state in one of the 2D layers. We derive an approximate relationship between the exciton-contact equilibration rate and the electrical conductances between the contacts and individual 2D layers when the contact chemical potentials align with the free-carrier bands, and explain how electrical measurements can be used to measure thermodynamic properties of the exciton fluids.

The interfacial mechanics of soft elastic networks plays a central role in biological and technological contexts. Yet, effects of solid capillarity have remained controversial, primarily due to the strain-dependent surface energy. Here we derive the equations that govern the selection of contact angles of liquid drops on elastic surfaces from variational principles. It is found that the substrate’s elasticity imposes a nontrivial condition that relates pinning, hysteresis, and contact line mobility to the so-called Shuttleworth effect. We experimentally validate our theory for droplets on a silicone gel, revealing an enhanced contact line mobility when stretching the substrate.

Active qubit reset is a key operation in many quantum algorithms, and particularly in quantum error correction. Here, we experimentally demonstrate a reset scheme for a three-level transmon artificial atom coupled to a large bandwidth resonator. The reset protocol uses a microwave-induced interaction between the $|f,0⟩$ and $|g,1⟩$ states of the coupled transmon-resonator system, with $|g⟩$ and $|f⟩$ denoting the ground and second excited states of the transmon, and $|0⟩$ and $|1⟩$ the photon Fock states of the resonator. We characterize the reset process and demonstrate reinitialization of the transmon-resonator system to its ground state in less than 500 ns and with 0.2% residual excitation. Our protocol is of practical interest as it has no additional architectural requirements beyond those needed for fast and efficient single-shot readout of transmons, and does not require feedback.

The concept of parity describes the inversion symmetry of a system and is of fundamental relevance in the standard model, quantum information processing, and field theory. In quantum electrodynamics, parity is conserved and large field gradients are required to engineer the parity of the light-matter interaction operator. In this work, we engineer a potassiumlike artificial atom represented by a specifically designed superconducting flux qubit. We control the wave function parity of the artificial atom with an effective orbital momentum provided by a resonator. By irradiating the artificial atom with spatially shaped microwave fields, we select the interaction parity in situ. In this way, we observe dipole and quadrupole selection rules for single state transitions and induce transparency via longitudinal coupling. Our work advances the design of tunable artificial multilevel atoms to a new level, which is particularly promising with respect to quantum chemistry simulations with near-term superconducting circuits.

We show a relation between entanglement and correlations of any form. The internal entanglement of a bipartite system, and its correlations with another system, limit each other. A measure of correlations, of any nature, cannot increase under local operations. Examples are the entanglement monotones, the mutual information that quantifies total correlations, and the Henderson-Vedral measure of classical correlations. External correlations, evaluated by such a measure, set a tight upper bound on the internal entanglement that decreases as they increase, and so does quantum discord.

We study spectral statistics in spatially extended chaotic quantum many-body systems, using simple lattice Floquet models without time-reversal symmetry. Computing the spectral form factor $K(t)$ analytically and numerically, we show that it follows random matrix theory (RMT) at times longer than a many-body Thouless time, $t_{\text{Th}}$. We obtain a striking dependence of $t_{\text{Th}}$ on the spatial dimension $d$ and size of the system. For $d>1$, $t_{\text{Th}}$ is finite in the thermodynamic limit and set by the intersite coupling strength. By contrast, in one dimension $t_{\text{Th}}$ diverges with system size, and for large systems there is a wide window in which spectral correlations are not of RMT form. Lastly, our Floquet model exhibits a many-body localization transition, and we discuss the behavior of the spectral form factor in the localized phase.

While winding a particlelike excitation around a looplike excitation yields the celebrated Aharonov-Bohm phase, we find a distinctive braiding phase in the absence of such mutual winding. In this Letter, we propose an exotic particle-loop-loop braiding process, dubbed the Borromean rings braiding. In the process, a particle moves around two unlinked loops, such that its trajectory and the two loops form the Borromean rings or more general Brunnian links. As the particle trajectory does not wind with any of the loops, the resulting braiding phase is fundamentally different from the Aharonov-Bohm phase. We derive an explicit expression for the braiding phase in terms of the underlying Milnor’s triple linking number. We also propose topological quantum field theories consisting of an $AAB$-type topological term which realize the braiding statistics.

The pseudorapidity distributions of dijets as functions of their average transverse momentum ($p_{\mathrm{T}}^{\text{ave}}$) are measured in proton-lead ($p\mathrm{Pb}$) and proton-proton ($pp$) collisions. The data samples were collected by the CMS experiment at the CERN LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. A significant modification of the $p\mathrm{Pb}$ spectra with respect to the $pp$ spectra is observed in all $p_{\mathrm{T}}^{\text{ave}}$ intervals investigated. The ratios of the $p\mathrm{Pb}$ and $pp$ distributions are compared to next-to-leading order perturbative quantum chromodynamics calculations with unbound nucleon and nuclear parton distribution functions (PDFs). These results give the first evidence that the gluon PDF at large Bjorken $x$ in lead ions is strongly suppressed with respect to the PDF in unbound nucleons.

Based on an $e^{+}{e}^{-}$ collision data sample corresponding to an integrated luminosity of $567{\mathrm{pb}}^{-1}$ taken at the center-of-mass energy of $\sqrt{s}=4.6\mathrm{GeV}$ with the BESIII detector, we measure the absolute branching fraction of the inclusive decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }+X$ to be $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }+X)=(38.2_{-2.2}^{+2.8}\pm 0.9)\%$ using the double-tag method, where $X$ refers to any possible final state particles. In addition, we search for direct $CP$ violation in the charge asymmetry of this inclusive decay for the first time, and obtain ${\mathcal{A}}_{CP}\equiv [\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }+X)-\mathcal{B}({\overline{\mathrm{\Lambda }}}_c^{-}\to \overline{\mathrm{\Lambda }}+X)]/[\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }+X)+\mathcal{B}({\overline{\mathrm{\Lambda }}}_c^{-}\to \overline{\mathrm{\Lambda }}+X)]=(2.1_{-6.6}^{+7.0}\pm 1.6)\%$, a statistically limited result with no evidence of $CP$ violation.

We confront observational data from gravitational wave event GW170817 with microscopic modeling of the cold neutron star equation of state. We develop and employ a Bayesian statistical framework that enables us to implement constraints on the equation of state from laboratory measurements of nuclei and state-of-the-art chiral effective field theory methods. The energy density functionals constructed from the posterior probability distributions are then used to compute consistently the neutron star equation of state from the outer crust to the inner core, assuming a composition consisting of protons, neutrons, electrons, and muons. In contrast to previous studies, we find that the 95% credibility range of predicted neutron star tidal deformabilities ($136<\mathrm{\Lambda }<519$) for a 1.4 solar-mass neutron star is already consistent with the upper bound deduced from observations of the GW170817 event. However, we find that lower bounds on the neutron star tidal deformability will very strongly constrain microscopic models of the dense matter equation of state. We also demonstrate a strong correlation between the neutron star tidal deformability and the pressure of beta-equilibrated matter at twice saturation density.

We study synchronization in a two-node network built out of the smallest possible self-sustained oscillator: a spin-1 oscillator. We first demonstrate that phase locking between the quantum oscillators can be achieved, even for limit cycles that cannot be synchronized to an external semiclassical signal. Building upon the analytical description of the system, we then clarify the relation between quantum synchronization and the generation of entanglement. These findings establish the spin-based architecture as a promising platform for understanding synchronization in complex quantum networks.

Miniaturized mechanical sensors rely on resonant operation schemes, unsuited to detect static forces. We demonstrate a nanomechanical sensor for static forces based on an optically trapped nanoparticle in vacuum. Our technique relies on an off-resonant interaction of the particle with a weak static force, and a resonant readout of the displacement caused by this interaction. We demonstrate a sensitivity of 10 aN to static gravitational and electric forces. Our work provides a tool for the closer investigation of short-range forces, and marks an important step towards the realization of matter-wave interferometry with macroscopic objects.

Particle-beam-driven plasma wakefield acceleration (PWFA) enables various novel high-gradient techniques for powering future compact light-source and high-energy physics applications. Here, a driving particle bunch excites a wakefield response in a plasma medium, which may rapidly accelerate a trailing witness beam. In this Letter, we present the measurement of ratios of acceleration of the witness bunch to deceleration of the driver bunch, the so-called transformer ratio, significantly exceeding the fundamental theoretical and thus far experimental limit of 2 in a PWFA. An electron bunch with ramped current profile was utilized to accelerate a witness bunch with a transformer ratio of $4.6_{-0.7}^{+2.2}$ in a plasma with length $\sim 10\mathrm{cm}$, also demonstrating stable transport of driver bunches with lengths on the order of the plasma wavelength.

The Landau bands of mirror symmetric 2D Dirac semimetals (e.g., odd layers of $ABA$ graphene) can be identified by their parity with respect to mirror symmetry. This symmetry facilitates a new class of counterpropagating Hall states. We predict the presence of a Laughlin-like correlated liquid state, at the charge neutrality point, with opposite but equal electron and hole filling factors $|{\nu }_{\pm }|=1/m$ ($m$ odd). This state exhibits fractionally charged quasiparticle-hole pair excitations and counterpropagating edge states with opposite parity. Using a bosonized one-dimensional edge state theory, we show that the fractionally quantized two-terminal longitudinal conductance, ${\sigma }_{xx}=2e^2/(mh)$, is robust to short-ranged intermode interactions.

In this work, we demonstrate a new route to realizing an experimentally controllable spin-Hall effect (SHE), on the surface of 3D topological insulators, which depends fundamentally on the spin-orbit-coupled (SOC) nature of the 2D Weyl fermions. Spin transport is solely due to the spin-torque current in this system, and the SHE arises from chiral spin-flip scattering off non-SOC scalar impurities, of potential strength $V$ and size $a$. The resultant spin-Hall angle has a fixed sign, with ${\theta }^{\mathrm{SH}}\sim O\{[V^2]/[v_F^2/a^2](k_{F}a{)}^4\}$ being a strongly dependent function of the Fermi wave vector ($k_F$) and Fermi velocity ($v_F$). Hence, the SHE can be tuned by adjusting the Fermi energy or impurity size.