We revisit gravitational wave (GW) memory as the key to measuring spacetime symmetries, extending beyond its traditional role in GW searches. In particular, we show how these symmetries may be probed via displacement and spin memory observations, respectively. We further find that the Einstein Telescope’s (ET) sensitivity enables constraining the strain amplitude of a displacement memory to 2% and that of spin memory to 22%. Finally, we point out that neglecting memory could lead to an overestimation of measurement uncertainties for parameters of binary black hole (BBH) mergers by about 10% in ET.

We compute the fifth post-Minkowskian (5PM) order contributions to the scattering angle and impulse of classical black hole scattering in the conservative sector at first self-force order using the worldline quantum field theory formalism. This challenging four-loop computation required the use of advanced integration-by-parts and differential equation technology implemented on high-performance computing systems. Use of partial fraction identities allowed us to render the complete integrand in a fully planar form. The resulting function space is simpler than expected: In the scattering angle, we see only multiple polylogarithms up to weight three and a total absence of the elliptic integrals that appeared at 4PM order. All checks on our result, both internal—cancellation of dimensional regularization poles and preservation of the on-shell condition—and external—matching the slow-velocity limit with the post-Newtonian (PN) literature up to 5PN order and matching the tail terms to the 4PM loss of energy—are passed.

The LHCb Collaboration measures production of the exotic hadron ${\chi }_{c1}(3872)$ in proton-nucleus collisions for the first time. Comparison with the charmonium state $\psi (2S)$ suggests that the exotic ${\chi }_{c1}(3872)$ experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may modify ${\chi }_{c1}(3872)$ production rates. This is the first measurement of the nuclear modification factor of an exotic hadron.

Recent experimental confirmation of spin inertia in ferromagnets positions this well-developed material class as a prime candidate for THz frequency applications. Spin-torque driven critical spin dynamics, such as auto-oscillations, play the central role in many spin-based technologies. Yet, the pressing question on spin inertia’s effect on spin-torque driven dynamics in ferromagnets has remained unexplored. Here, we develop the theoretical framework of precessional auto-oscillations for ferromagnets with spin inertia. We discover and introduce the concept of nutational auto-oscillations and demonstrate that they can become pivotal for future ultrahigh frequency technologies. We conclude by revealing parallels between spin dynamics in ferrimagnets and inertial ferromagnets and derive an isomorphism that establishes a foundation for synergistic knowledge transfer between these research fields.

A unitary Fermi gas in an isotropic harmonic trap is predicted to show scale and conformal symmetry that have important consequences in its thermodynamic and dynamical properties. By experimentally realizing a unitary Fermi gas in an isotropic harmonic trap, we demonstrate its universal expansion dynamics along each direction and at different temperatures. We show that as a consequence of SO(2,1) symmetry, the measured release energy is equal to that of the trapping energy. We further observe the breathing mode with an oscillation frequency twice the trapping frequency and a small damping rate, providing the evidence of SO(2,1) symmetry. In addition, away from resonance when scale invariance is broken, we determine the effective exponent $\gamma$ that relates the chemical potential and average density along the BEC-BCS crossover, which qualitatively agrees with the mean field predictions. This Letter opens the possibility of studying nonequilibrium dynamics in a conformal invariant system in the future.

Disorder at etched edges of graphene quantum dots (GQD) enables random all-to-all interactions between localized charges in partially filled Landau levels, providing a potential platform to realize the Sachdev-Ye-Kitaev (SYK) model. We use quantum Hall edge states in the graphene electrodes to measure electrical conductance and thermoelectric power across the GQD. In specific temperature ranges, we observe a suppression of electric conductance fluctuations and slowly decreasing thermoelectric power across the GQD with increasing temperature, consistent with recent theory for the SYK regime.

The Kibble-Zurek mechanism (KZM) describes the nonequilibrium dynamics and topological defect formation in systems undergoing second-order phase transitions. KZM has found applications in fields such as cosmology and condensed matter physics. However, it is generally not suitable for describing first-order phase transitions. It has been demonstrated that transitions in systems like superconductors or charged superfluids, typically classified as second order, can exhibit weakly first-order characteristics when the influence of fluctuations is taken into account. Moreover, the order of the phase transition (i.e., the extent to which it becomes first rather than second order) can be tuned. We explore quench-induced formation of topological defects in such tunable phase transitions and propose that their density can be predicted by combining KZM with nucleation theory.

Er doped Si light-emitting diodes may find important applications in silicon photonics and optical quantum computing. These diodes exhibit an emission efficiency 2 orders of magnitude higher at reverse bias than forward bias due to impact excitation. However, physics of impact excitation in these devices remains largely unexplored. In this work, we fabricated an Er/O/B codoped Si light-emitting diode which exhibits a strong electroluminescence by the impact excitation of electrons inelastically colliding the Er ions. An analytical impact-excitation theory was established to predict the electroluminescence intensity and internal quantum efficiency which fit well with the experimental data. From the fittings, we find that the excitable Er ions reach a record concentration of $1.8\times {10}^{19}{\mathrm{cm}}^{-3}$ and up to 45% of them is in an excitation state by impact excitation. This work has important implications for developing efficient classical and quantum light sources based on rare earth elements in semiconductors.

We determine $J^{PC}=0^{++}$ and $2^{++}$ hadron-hadron scattering amplitudes in the charmonium energy region up to 4100 MeV using lattice QCD, a first-principles approach to QCD. Working at $m_{\pi }\approx 391\mathrm{MeV}$, more than 200 finite-volume energy levels are computed and these are used in extensions of the Lüscher formalism to determine infinite-volume coupled-channel scattering amplitudes. We find that this energy region contains a single ${\chi }_{c0}$ and a single ${\chi }_{c2}$ resonance. Both are found as pole singularities on the closest unphysical Riemann sheet, just below 4000 MeV with widths around 70 MeV. The largest couplings are to kinematically closed $D^{*}{\overline{D}}^{*}$ channels in $S$-wave, and couplings to several decay channels consisting of pairs of open-charm mesons are found to be large and significant in both cases. Above the ground state ${\chi }_{c0}$, no other scalar bound states or near-$D\overline{D}$ threshold resonances are found, in contrast to several theoretical and experimental studies.

We present a merged-beams study of reactions between ${\mathrm{HD}}^{+}$ ions, stored in the Cryogenic Storage Ring (CSR), and laser-produced ground-term C atoms. The molecular ions are stored for up to 20 s in the extreme vacuum of the CSR, where they have time to relax radiatively until they reach their vibrational ground state (within 0.5 s of storage) and rotational states with $J\le 3$ (after 5 s). We combine our experimental studies with quasiclassical trajectory calculations based on two reactive potential energy surfaces. In contrast to previous studies with internally excited ${\mathrm{H}}_2^{+}$ and ${\mathrm{D}}_2^{+}$ ions, our results reveal a pronounced isotope effect, favoring the production of ${\mathrm{CH}}^{+}$ over ${\mathrm{CD}}^{+}$ across all collision energies, and a significant increase in the absolute rate coefficient of the reaction. Our experimental results agree well with our theoretical calculations for vibrationally relaxed ${\mathrm{HD}}^{+}$ ions in their lowest rotational states.

The Dyakonov-Perel (DP) mechanism of spin relaxation has long been considered irrelevant in centrosymmetric systems since it was developed originally for noncentrosymmetric ones. We investigate whether this conventional understanding extends to the realm of orbital relaxation, which has recently attracted significant attention. Surprisingly, we find that orbital relaxation in centrosymmetric systems exhibits the DP-like behavior in the weak scattering regime. Moreover, the DP-like orbital relaxation can make the spin relaxation in centrosymmetric systems DP-like through the spin-orbit coupling. We also find that the DP-like orbital and spin relaxations are anisotropic even in materials with high crystal symmetry (such as face-centered cubic structure) and may depend on the orbital and spin nature of electron wave functions.

Electrons residing in a flat-band system can play a vital role in triggering spectacular phenomenology due to relatively large interactions and spontaneous breaking of different degeneracies. In this work, we demonstrate chirally twisted triple bilayer graphene, a new moiré structure formed by three pieces of helically stacked Bernal bilayer graphene, as a highly tunable flat-band system. In addition to the correlated insulators showing at integer moiré fillings, commonly attributed to interaction induced symmetry broken isospin flavors in graphene, we observe abundant insulating states at half-integer moiré fillings, suggesting a longer-range interaction and the formation of charge density wave insulators which spontaneously break the moiré translation symmetry. With weak out-of-plane magnetic field applied, as observed half-integer filling states are enhanced and more quarter-integer filling states appear, pointing toward further quadrupling moiré unit cells. The insulating states at fractional fillings combined with Hartree-Fock calculations demonstrate the observation of a new type of correlated charge density wave insulators in graphene and points to a new accessible twist manner engineering correlated moiré electronics.

The momentum space Josephson effect describes the supercurrent flow between weakly coupled Bose-Einstein condensates (BECs) at two discrete momentum states. Here, we experimentally observe this exotic phenomenon using a BEC with Raman-induced spin-orbit coupling, where the tunneling between two local band minima is implemented by the momentum kick of an additional optical lattice. A sudden quench of the Raman detuning induces coherent spin-momentum oscillations of the BEC, which is analogous to the ac Josephson effect. We observe both plasma and regular Josephson oscillations in different parameter regimes. The experimental results agree well with the theoretical model and numerical simulation and showcase the important role of nonlinear interactions. We also show that the measurement of the Josephson plasma frequency gives the Bogoliubov zero quasimomentum gap, which determines the mass of the corresponding pseudo-Goldstone mode, a long-sought phenomenon in particle physics. The observation of momentum space Josephson physics offers an exciting platform for quantum simulation and sensing utilizing momentum states as a synthetic degree.

The prediction and realization of the quantum anomalous Hall effect are often intimately connected to honeycomb lattices in which the sublattice degree of freedom plays a central role in the nontrivial topology. Two-dimensional Wigner crystals, on the other hand, form triangular lattices without sublattice degrees of freedom, resulting in a topologically trivial state. Here, we discuss the possibility of spontaneously formed honeycomb-lattice crystals that exhibit the quantum anomalous Hall effect. Starting from a single-band system with nontrivial quantum geometry, we derive the mean-field energy functional of a class of crystal states and express it as a model of sublattice pseudospins in momentum space. We find that nontrivial quantum geometry leads to extra terms in the pseudospin model that break an effective “time-reversal symmetry” and favor a topologically nontrivial pseudospin texture. When the effects of these extra terms dominate over the ferromagnetic exchange coupling between pseudospins, the anomalous Hall crystal state becomes energetically favorable over the trivial Wigner crystal state.

Active solids such as cell collectives, colloidal clusters, and active metamaterials exhibit diverse collective phenomena, ranging from rigid body motion to shape-changing mechanisms. The nonlinear dynamics of such active materials remains, however, poorly understood when they host zero-energy deformation modes and when noise is present. Here, we show that stress propagation in a model of active solids induces the spontaneous actuation of multiple soft floppy modes, even without exciting vibrational modes. By introducing an adiabatic approximation, we map the dynamics onto an effective Landau free energy, predicting mode selection and the onset of collective dynamics. These results open new ways to study and design living and robotic materials with multiple modes of locomotion and shape change.

We describe a realistic mechanism whereby black holes with significant QCD color charge could have formed during the early Universe. Primordial black holes (PBHs) could make up a significant fraction of the dark matter if they formed well before the QCD confinement transition. Such PBHs would form by absorbing unconfined quarks and gluons and hence could acquire a net color charge. We estimate the number of PBHs per Hubble volume with near-extremal color charge for various scenarios and discuss possible phenomenological implications.

A key method to produce trapped and laser-cooled molecules is the magneto-optical trap (MOT), which is conventionally created using light red detuned from an optical transition. In this work, we report a MOT for CaF molecules created using blue-detuned light. The blue-detuned MOT (BDM) achieves temperatures well below the Doppler limit and provides the highest densities and phase-space densities reported to date in CaF MOTs. Our results suggest that BDMs are likely achievable in many relatively light molecules including polyatomic ones, but our measurements suggest that BDMs will be challenging to realize in substantially heavier molecules due to sub-mK trap depths. In addition to record temperatures and densities, we find that the BDM substantially simplifies and enhances the loading of molecules into optical tweezer arrays, which are a promising platform for quantum simulation and quantum information processing. Notably, the BDM reduces molecular number requirements ninefold compared to a conventional red-detuned MOT, while not requiring additional hardware. Our work therefore substantially simplifies preparing large-scale molecular tweezer arrays, which are a novel platform for simulation of quantum many-body dynamics and quantum information processing with molecular qubits.

Elucidating the physics of the single-orbital Hubbard model in its intermediate-coupling regime is a key missing ingredient to our understanding of metal-insulator transitions in real materials. Using recent nonperturbative many-body techniques that are able to interpolate between the spin-fluctuation-dominated Slater regime at weak coupling and the Mott insulator at strong coupling, we obtain the momentum-resolved spectral function in the intermediate regime and disentangle the effects of antiferromagnetic fluctuations and local electronic correlations in the formation of an insulating state. This allows us to identify the Slater and Heisenberg regimes in the phase diagram, which are separated by a crossover region of competing spatial and local electronic correlations. We identify the crossover regime by investigating the behavior of the local magnetic moment, shedding light on the formation of the insulating state at intermediate couplings.

The cross section of the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ has been measured in the center-of-mass energy range from 0.32 to 1.2 GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. The measurement is based on an integrated luminosity of about $88{\mathrm{pb}}^{-1}$, of which $62{\mathrm{pb}}^{-1}$ represent a complete dataset collected by CMD-3 at center-of-mass energies below 1 GeV. In the dominant region near the $\rho$ resonance a systematic uncertainty of 0.7% was achieved. The implications of the presented results for the evaluation of the hadronic contribution to the anomalous magnetic moment of the muon are discussed.

Interatomic Coulombic decay (ICD) plays a crucial role in weakly bound complexes exposed to intense or high-energy radiation. So far, neutral or ionic atoms or molecules have been prepared in singly excited electron or hole states that can transfer energy to neighboring centers and cause ionization and radiation damage. Here we demonstrate that a doubly excited atom, despite its extremely short lifetime, can decay by ICD; evidenced by high-resolution photoelectron spectra of He nanodroplets excited to the $2s2p+$ state. We find that ICD proceeds by relaxation into excited ${\mathrm{He}}^{*}{\mathrm{He}}^{+}$ atom-pair states, in agreement with calculations. The ability of inducing ICD by resonant excitation far above the single-ionization threshold opens opportunities for controlling radiation damage to a high degree of element specificity and spectral selectivity.