${\text{La}}_2{\mathrm{NiO}}_4$ is an antiferromagnetic insulator with a structural resemblance to its cuprate counterpart, ${\mathrm{La}}_2{\mathrm{CuO}}_4$. However, ${\mathrm{La}}_2{\mathrm{CuO}}_4$ has a ${\mathrm{Cu}}^{2+}$ or $3d^9$ electronic configuration that needs to be hole or electron doped for superconductivity, whereas ${\mathrm{La}}_2{\mathrm{NiO}}_4$ is $3d^8$ with divalent ${\mathrm{Ni}}^{2+}$. Making a cuprate analog through conventional electron doping is impractical due to the rarity of tetravalent substituents for trivalent La. Here, we propose an alternative route: intercalating topotactical hydrogen, which is possible through electric-field-controlled protonation and transforms ${\mathrm{La}}_2{\mathrm{NiO}}_4$ into a $3d_{x^2-y^2}$ single-band two-dimensional antiferromagnetic Mott insulator analogous to ${\mathrm{La}}_2{\mathrm{CuO}}_4$. This we find through density-functional theory and dynamical mean-field theory calculations. The furthergoing dynamical vertex approximation predicts that $\mathrm{H}\text{−}{\mathrm{La}}_2{\mathrm{NiO}}_4$ can host $d$-wave superconductivity under 15% hole doping with a critical temperature above 20 K. Our findings not only suggest a new method for tuning the electronic structure of layered nickelates but also provide theoretical evidence for a new nickelate superconductor, awaiting experimental synthesis.

We propose a theory for the microscopic origin of the multiple superconducting and magnetic phases observed in ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ based on the existence of Van Hove singularities near the Fermi energy. The nonsymmorphic symmetry of this material implies that these singularities are located away from high-symmetry momenta; i.e., they have so-called type-II character. This allows us to include the significant Rashba spin-orbit coupling in ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ in a parquet renormalization group approach. When Fermi-surface nesting is strong, our analysis reveals two closely competing superconducting states with opposite parities, as well as an instability toward spin-density wave states that support both of them, consistent with the phase diagram of ${\mathrm{CeRh}}_2{\mathrm{As}}_2$. Type-II Van Hove singularities are generic to nonsymmorphic space groups, and so our theory implies that many other compounds may support closely competing even- and odd-parity superconductivity.

Su-Schrieffer-Heeger-like (SSH-like) electron-phonon interactions can drive the formation of light (bi)polarons and several novel states of matter. It is, therefore, prudent to develop experimental protocols for identifying such couplings in real materials and quantifying their strength. Here, we investigate how resonant inelastic x-ray scattering (RIXS) probes electron-phonon interactions in the one-dimensional half-filled Hubbard-SSH model with on-site phonons. Using the density matrix renormalization group method, we compute the full RIXS response and find that the lattice excitations generated during the scattering process inevitably couple to the system’s charge and magnetic sectors, resulting in combined multiparticle excitations that cannot be easily disentangled from one another. While this aspect complicates the interpretation of RIXS experiments, we outline how it can be leveraged to identify and quantify SSH-like interactions in quantum materials.

We study the interplay of electron-electron and electron-disorder scattering in correlated Fermi liquids by the disordered Hubbard model using dynamical mean-field theory with an IPT-CPA solver. We find significant violations of Matthiessen’s rule (additivity of scattering mechanisms) that we explain in terms of the screening of the disorder potential by interactions, leading to a protection of the electron-electron inelastic scattering rate against disorder. We also show that large disorder can lead to a surprising enhancement of the electron-electron scattering that contrasts with the competition seen in the elastic channel. Our results compare positively with available resistivity data in the disordered Fermi liquid phase of the correlated organic metals $\kappa \text{−}{(\mathrm{ET})}_2\mathrm{X}$, and rationalize the strong sample dependence of the $T^2$ coefficients observed in the resistivity of correlated perovskite oxides such as ${\mathrm{SrVO}}_3$.

In correlated transition-metal oxides, orbital-ordering appears to always precede magnetic ordering ($T_N<T_{\mathrm{OO}}$). The $R{\mathrm{VO}}_3$ series is the exception: it exhibits an inversion of $T_N$ and $T_{\mathrm{OO}}$ with increasing rare-earth radius $R_I$. Why vanadates are different is not understood. Here we show that the reason is fundamental: when lattice effects dominate orbital physics, magnetic order follows orbital order, and thus $T_N<T_{\mathrm{OO}}$. This is what happens in most transition-metal oxides, and it is what quenches exotic quantum orbital phases. In the $R{\mathrm{VO}}_3$ series, however, lattice effects become ineffective with increasing $R_I$, while, at the same time, for antiferromagnetic spin order, the orbital-independent dipolar spin-spin interaction dominates. This has consequences well beyond the $R{\mathrm{VO}}_3$ series itself. In fact, the subtle balance of interactions leading to the $T_N\text{−}{T}_{\mathrm{OO}}$ inversion not only explains why it is so rare, but also gives the criteria for finding it in other materials. The mechanism behind transitions inversion makes such systems an ideal playground for studying unconventional orbital phases. The results presented here rely on the decomposition of the order parameter into irreducible tensors, which allows us to identify the mechanism driving the transition.

For concentrations between dilute and the highly concentrated limit of almost 5 M, we compare our explicit-water molecular dynamics simulations of ${\mathrm{LiH}}_2{\mathrm{PO}}_4$ (which dissociates into ${\mathrm{H}}_2{\mathrm{PO}}_4^{-}$ anions relevant to biochemical processes and ${\mathrm{Li}}^{+}$ cations relevant to battery technology) to our pulsed-field gradient NMR measurements of ion diffusion, and find compensation between electrostatic and osmotic forces. The significance is that, noticing that the Kirkwood equation holds when using its exact solution but seemingly is violated when making the traditional approximation of using total force relaxation time in place of the memory relaxation time, we explain slower translational diffusion with increasing ion concentration as a dynamical effect arising from growing memory relaxation time. Physically, 2 orders of magnitude separate the timescales of electrostatic and osmotic forces from the total force such that dynamical correlations between force components lead to concentration-independent total force variance and force relaxation time.

Owing to the sustained energy input, active nematics can spontaneously generate topological defects, which generally undergo chaotic motions ruled by active hydrodynamics. Here, we combine theory and simulations to investigate the structure and dynamics of topological defects in three-dimensional (3D) active nematics under boundary twisting, similar to twisted bilayer graphene. We show that increasing twist angle will lead to the transition of defect patterns from wedge-twist defect loops to pure-twist defect lines. These defect lines can organize into ordered networks, which oscillate persistently and propagate as a wave. Intriguingly, the wave speed of defect networks is significantly faster than that of local active flows, in contrast to the traditional active defects. We identify that the fast propagation of 3D topological defects results from the activity-driven defect pattern transition and the vertical oscillations mediated by the nematic elasticity. These findings reveal the marked influence of boundary perturbations on active nematics and could also provide a simple strategy to program 3D defect dynamics.

Heisenberg’s uncertainty principle, coherence, and Bell nonlocality have been individually examined through many experiments. In this Letter, we systematically characterize all of this quantumness in a unified manner. We first construct universal uncertainty relations to reveal intrinsic features of incompatible measurements, which include all the state-independent uncertainties as special cases. We further extend to witness both quantum coherence and Bell nonlocality. We finally perform experiments with unified two-photon states and validate the uncertainty principle, coherence, and Bell nonlocality within experimental error. Our methods for witnessing quantumness are valuable in characterizing quantum correlations in quantum information processing.

The performance of quantum key distribution (QKD) heavily depends on statistical inference. For a broad class of protocols, the central statistical task is a random sampling problem, customarily addressed using a hypergeometric tail bound due to Serfling. Here, we provide an alternative solution for this task of unprecedented tightness among QKD security analyses. As a by-product, confidence intervals for the average of nonidentical Bernoulli parameters follow too. These naturally fit in statistical analyses of decoy-state QKD and also outperform standard tools. Last, we show that, in a vast parameter regime, the use of tail bounds is not enforced because the cumulative mass function of the hypergeometric distribution is accurately computable. This sharply decreases the minimum block sizes necessary for QKD, and reveals the tightness of our analytical bounds when moderate-to-large blocks are considered.

In this Letter, we propose a stringy model for $n$-point tree-level form factor with the off-shell operator in the scalar and gluon theories from the bosonic string disk amplitude: $n$ open string states and one closed string state scatter on the disk. In the field-theory limit (${\alpha }^{\prime }\to 0$), the “stringy form factor” reduces to the form factor, which helps us to investigate the hidden properties of the field-theory form factors, manifest the factorization and soft behaviors, and uncover more nontrivial relations between form factors and scattering amplitudes.

We explore the effects of including the energy dependence determined from evolution equations within the color glass condensate framework on observables in ultrarelativistic heavy-ion collisions. This amounts to integrating the JIMWLK evolution equations into the impact parameter-dependent glasma model, which is then coupled to viscous relativistic hydrodynamics. This methodology allows for a systematic representation of nuclei at specific Bjorken-$x$ values, which are probed at different center-of-mass energies of the collision and rapidities of final state particles. Comparing the methodology to the conventional impact parameter-dependent glasma model, we find significant effects on multiplicity distributions and particle spectra, especially in smaller collision systems at the highest center-of-mass energies. Our results highlight the importance of incorporating nonlinear QCD evolution in the description of heavy-ion collisions at varying center-of-mass energies, as the precise extraction of transport coefficients will be affected. This Letter establishes a robust framework for understanding the quark gluon plasma and nuclear structure at high energy, integrating small-$x$ physics into the initial conditions of heavy-ion collisions.

The previously unknown nucleus ${}^{20}\mathrm{Al}$ has been observed for the first time by detecting its in-flight decays. Tracking trajectories of all decay products with silicon microstrip detectors allowed for a conclusion that ${}^{20}\mathrm{Al}$ is unbound with respect to three-proton ($3p$) emission. The $3p$-decay energy of the ${}^{20}\mathrm{Al}$ ground state has been determined to be $1.93{(}_{-0.10}^{+0.12})\mathrm{MeV}$ through a detailed study of angular correlations of its decay products, ${}^{17}\mathrm{Ne}+p+p+p$. This value is significantly smaller than the predictions inferred from the isospin symmetry by using the known neutron separation energy of its mirror nucleus ${}^{20}\mathrm{N}$, which indicates a possible isospin symmetry breaking in the mirror nuclei ${}^{20}\mathrm{Al}$ and ${}^{20}\mathrm{N}$. This observed isospin symmetry breaking is supported by the calculations of the continuum embedded theoretical frameworks, describing the observed ${}^{20}\mathrm{Al}$ ground state as a $1p$ $s$-wave state with a spin-parity of $1^{-}$, which differs from the spin-parity ($2^{-}$) of the ${}^{20}\mathrm{N}$ ground state. The ${}^{20}\mathrm{Al}$ ground state decays by sequential $1p\text{−}2p$ emission via the intermediate ground state of ${}^{19}\mathrm{Mg}$, which is the first observed case of “daughter” $2p$ radioactivity following $1p$ decay of the parent state.

We present an optical technique for suppressing relaxation in alkali-metal spins using a single off-resonant laser beam. The method harnesses a physical mechanism that synchronizes Larmor precession in the two hyperfine manifolds, protecting magnetic coherence from relaxation caused by spin-exchange and other hyperfine-changing collisions. We experimentally demonstrate up to a ninefold reduction in decoherence of warm cesium vapor, achieving simultaneous protection from both spin-exchange relaxation and partial depolarization from coated cell walls. The technique substantially enhances the spin precession quality factor and maintains a stable gyromagnetic ratio independent of spin polarization, even under frequent collisions. These findings offer a pathway for mitigating dominant relaxation channels in alkali-metal-based applications and experiments, particularly in anti-relaxation-coated cells.

Quantum metrology employs entanglement to enhance measurement precision [V. Giovannetti et al., Quantum-enhanced measurements: Beating the standard quantum limit, Science 306, 1330 (2004), V. Giovannetti et al., Advances in quantum metrology, Nat. Photonics 5, 222 (2011), and L. Pezzè et al., Quantum metrology with nonclassical states of atomic ensembles, Rev. Mod. Phys. 90, 035005 (2018)]. The focus and progress so far have primarily centered on estimating a single parameter. In diverse application scenarios, estimation of more than one single parameter is often required. Joint estimation of multiple parameters can benefit from additional advantages for further enhanced precision. Here we report quantum-enhanced estimation of simultaneous spin rotations around two orthogonal axes, making use of spin-nematic squeezing in an atomic Bose-Einstein condensate. Aided by the $F=2$ atomic ground hyperfine manifold coupled to the nematic-squeezed $F=1$ states as an auxiliary field through a sequence of microwave (MW) pulses, multiple spin-1 observables are simultaneously measured, reaching an enhancement factor 3.3 to 6.3 decibels (dB) beyond the classical limit over a wide range of rotation angles. Our work realizes the first quantum enhanced multiparameter estimation using entangled massive particles. The techniques developed and the protocols implemented also highlight the application of two-mode squeezed vacuum states in quantum-enhanced sensing of noncommuting spin rotations simultaneously.

Controlling the dynamics of quantum many-body systems is crucial for developing quantum technologies. This work demonstrates that counterdiabatic (CD) driving provides a powerful tool for steering collective spin systems along entangled trajectories for a long time. In particular, CD driving leads to approximate stroboscopic freezing and eternal entanglement oscillations for a large class of initial states in the periodically driven Lipkin-Meshkov-Glick model. Intriguingly, CD driving generates spin squeezing and its associated metrologically useful multipartite entanglement at the mid-point of every drive cycle, when the system is initially prepared in a fully $x$-polarized state. The CD driving induced nonergodic dynamics is accompanied by a decrease in the average eigenstate entanglement and inverse participation ratio, thereby signaling greater eigenstate localization. Our work opens a new route to evade Floquet heating and control entanglement generation in collective spin systems.

Spin squeezing in a many-body system is a witness for entanglement and can enable measurement sensitivities beyond those achievable by only classical correlations. Here, working with ultracold ${}^7\mathrm{Li}$ atoms in an optical lattice, we demonstrate spin squeezing using short-range contact interactions in both one and three dimensions. In 1D, spin squeezing is shown to be insensitive to density fluctuations caused by holes. In 3D, however, we observe that holes strongly modify the squeezing dynamics, hindering the recently predicted emergence of scalable squeezing in 3D $XXZ$ spin systems. By developing a new theoretical model to account for spin-density coupling, we obtain strong quantitative agreement with the observed squeezing dynamics, resulting in $\approx 2\mathrm{dB}$ at 7% hole fraction. Our observations highlight the importance of understanding spin-density coupling in the dynamics of many interacting spins and lay the groundwork for improved spin squeezing in systems with only short-range interactions.