Searching for new materials hosting flat bands is pivotal for exploring strongly correlated effects and designing sensitive quantum devices, but remains challenging. We present a general method for realizing flat bands based on mathematical optimization and symmetry analysis. The method enables the discovery of $\sim 1000$ types of two-dimensional lattices that can host flat bands, in sharp contrast with $\sim 10$ flat-band lattices predicted previously besides the well-known ones. We further verify the method using first-principles calculations. Our approach provides new insights for the design of flat-band lattices, particularly when aiming to create experimentally feasible configurations.

The low-energy physics of Tomonaga-Luttinger liquids (TLLs) is controlled by the Luttinger parameter. We demonstrate that this parameter can be extracted from a single wave function for one-component TLLs with periodic boundary condition. This method relies on the fact that TLLs are described by conformal field theory in which crosscap states can be constructed. The overlaps between the crosscap states and the ground state as well as some excited states are proved to be universal numbers that directly reveal the Luttinger parameter. In microscopic lattice models, crosscap states are formed by putting each pair of antipodal sites into a maximally entangled state. Analytical and numerical calculations are performed in a few representative models to substantiate the conformal field theory prediction. The extracted Luttinger parameters are generally quite accurate in finite-size systems with moderate lengths, so there is no need to perform data fitting and/or finite-size scaling.

In ferroelectric (FE) semiconductors with strong spin-orbit coupling, the electron’s spin direction is locked to its momentum by an intrinsic spin-orbit field (SOF) switchable by ferroelectric polarization. This provides a promising platform for novel nonvolatile spintronic devices. Here, we propose exploiting the switchable SOF to realize a FE spin-orbit valve (FE-SOV), where two FE semiconductors are separated by a thin barrier layer. Because of the locking between the SOF and polarization direction, the conductance of the FE-SOV strongly depends on the relative orientation of polarization of the two FE semiconductors. Using a tight-binding model and density functional theory calculations for FE-SOVs based on two-dimensional FE SnTe and Bi, we demonstrate a giant FE-SOV effect that is characterized by the conductance change of several orders in magnitude. Our work enriches spin-orbit physics of ferroelectrics and proposes a new type of all-electric control of a nonvolatile spin-orbitronic device, which holds promise for future electronic and memory applications.

Ferromagnetic semiconductors offer an efficient way to achieve high spin polarization via spin filtering effect. Large tunneling magnetoresistance (TMR) can then be realized when multiple spin filters are put in series, as recently demonstrated in van der Waals 2D A-type antiferromagnets such as ${\mathrm{CrI}}_3$ and CrSBr. However, the interlayer antiferromagnetic ground state of these magnets inherently results in a high resistance state at zero field, and this volatile behavior limits potential applications. Here we fabricate hybrid spin filters using 2D ferromagnetic metal ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ and semiconductor ${\mathrm{CrBr}}_3$, which are nonvolatile as two magnets are magnetically decoupled. We achieve large TMR of around 100%, with its temperature dependence well fitted by the extended Jullière model. Additionally, the devices allow spin injection tuned through bias voltage, and TMR polarity reversals are observed. Our work opens a new route to develop 2D magnetic semiconductor based spintronics.

Landauer’s limit on heat dissipation during information erasure is critical as devices shrink, requiring optimal pure-state preparation to minimize errors. However, Nernst’s third law states this demands infinite resources in energy, time, or control complexity. We address the challenge of cooling quantum systems with finite resources. Using Markovian collision models, we explore resource trade-offs and present efficient cooling protocols (that are optimal for qubits) for coherent and incoherent control. Leveraging thermodynamic length, we derive bounds on heat dissipation for swap-based strategies and discuss the limitations of preparing pure states efficiently.

A plasmon, a collective mode of electronic excitation in solid-state detectors, provides a novel way to detect light dark matter (DM). In this work, we present the conditions of DM to produce a plasmon resonance, requiring relativistic velocities for light DM, and generalize the collective excitation framework to account for relativistic DM. As a demonstration, we consider the cosmic ray boosted DM and find that the plasmon resonance can be significantly enhanced in the scenario with a light mediator. Utilizing the first data from the SENSEI experiment with the skipper CCDs at SNOLAB, we obtain a new strong limit on the sub-MeV DM-electron scattering cross section.

LISA Pathfinder was a mission designed to test key technologies required for gravitational wave detection in space. Magnetically driven forces play a key role in the instrument sensitivity in the low-frequency regime, which corresponds to the measurement band of interest for future space-borne gravitational wave observatories. Magnetically induced forces couple to the test mass motion, introducing a contribution to the relative acceleration noise between the free-falling test masses. In this Letter we present the first complete estimate of this term of the instrument performance model. Our results set the magnetic-induced acceleration noise during the February 2017 noise run of ${0.25}_{-0.08}^{+0.15}\mathrm{fm}{\mathrm{s}}^{-2}/\sqrt{\mathrm{Hz}}$ at 1 mHz and ${1.01}_{-0.24}^{+0.73}\mathrm{fm}{\mathrm{s}}^{-2}/\sqrt{\mathrm{Hz}}$ at 0.1 mHz. We also discuss how the nonstationarities of the interplanetary magnetic field can affect these values during extreme space weather conditions.

We examine the relation between supersymmetric localization on ${\mathbb{S}}^4$ and standard QFT results for nonconformal theories in flat space. Specifically, we consider $1/2$ BPS circular Wilson loops in four-dimensional $\mathrm{SU}(N)$ $\mathcal{N}=2$ supersonic Yang-Mills theories with massless hypermultiplets in an arbitrary representation $\mathcal{R}$ such that the $\beta$ function is nonvanishing. On ${\mathbb{S}}^4$, localization maps this observable into an interacting matrix model. Despite broken conformal symmetry at the quantum level, we show that within a specific regime of validity the matrix model predictions are consistent with perturbation theory in flat space up to order $g^6$. At this order, the reorganization of Feynman diagrams based on the matrix model potential, which has been widely tested in conformal models, also applies in nonconformal setups and is realized, in perturbative field theory, through highly nontrivial interference mechanisms.

We calculate the general planar dual-conformally invariant double-pentagon and pentabox integrals in four dimensions. Concretely, we derive onefold integral representations for these elliptic integrals over polylogarithms of weight three. These integral representations allow us to determine the respective symbols using consistency conditions alone. Together with the previously calculated double-box integral, these integrals suffice to express all two-loop planar scattering amplitudes in maximally supersymmetric Yang-Mills theory in four dimensions—which we thus calculate for any number of particles and any helicity configuration.

The duality between color and kinematics brings many simplifications to the construction of scattering amplitudes. Here, we show that satisfaction of the tree-level Bern-Carrasco-Johansson relations can dramatically simplify loop computations even when the loop-level relations are not explicitly satisfied. We introduce an agglomerative algorithm, color-dual cut tiling, that builds the entire integrand from the simplest on-shell conditions applied to a seed of off-shell integrand information. Specifically, we demonstrate that for two-to-two scattering at three loops in the maximally supersymmetric gauge theory there is sufficient information contained in planar cuts—completely determined by positivity constraints—to generate all of the nonplanar sector. We further make use of the generalized double copy to generate a representation of maximally supersymmetric gravity as a functional of the planar SYM input. We close with comments on generalizations and possible applications of the approach.

Neutron-induced reaction cross sections of short-lived nuclei are imperative to understand the origin of heavy elements in stellar nucleosynthesis and for societal applications, but their measurement is extremely complicated due to the radioactivity of the targets involved. One way of overcoming this issue is to combine surrogate reactions with the unique possibilities offered by heavy-ion storage rings. In this work, we describe the first surrogate-reaction experiment in inverse kinematics, which we successfully conducted at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, using the ${}^{208}\mathrm{Pb}(p,p^{\prime })$ reaction as a surrogate for neutron capture on ${}^{207}\mathrm{Pb}$. Thanks to the outstanding detection efficiencies possible at the ESR, we were able to measure for the first time the neutron-emission probability as a function of the excitation energy of ${}^{208}\mathrm{Pb}$. We have used this probability to select different descriptions of the $\gamma$-ray strength function and nuclear level density, and provide reliable results for the neutron-induced radiative capture cross section of ${}^{207}\mathrm{Pb}$ at energies for which no experimental data exist.

Throughout quantum science and technology, measurement is used as a powerful resource for nonlinear operations and quantum state engineering. In particular, single-photon detection is commonly employed for quantum-information applications and tests of fundamental physics. By contrast, and perhaps counterintuitively, measurement of the absence of photons also provides useful information, and offers significant potential for a wide range of new experimental directions. Here, we propose and experimentally demonstrate cooling of a mechanical resonator below its laser-cooled mechanical occupation via zero-photon detection on the anti-Stokes scattered optical field and verify this cooling through heterodyne measurements. Our measurements are well captured by a stochastic master equation and the techniques introduced here open new avenues for cooling, quantum thermodynamics, quantum state engineering, and quantum measurement and control.

We report on the topological pumping of quadratic optical solitons, observed through their quantized transport in a dynamic optical potential. A distinctive feature of this system is that the two fields with different frequencies, which together form the quadratic soliton, evolve in separate yet topologically equivalent dynamic optical potentials. Pumping in this system exhibits several notable differences from pumping in cubic media. While Chern indices characterizing quantized transport for uncoupled fundamental and second harmonic waves are nonzero, small-amplitude solitons with narrow spectra do not move, thus revealing a nontopological phase. As the nonlinearity increases, the system undergoes a sharp transition, depending on the velocity of one of the sublattices forming dynamical potential, into the phase where the quantized transport of quadratic solitons governed by nonzero Chern numbers is observed. The power level at which this transition occurs increases with increase of pumping velocity, and the transition is observed even in the regime when the adiabatic approximation no longer applies. Unlike in cubic media, in a quadratic medium neither breakup of topological pumping nor fractional pumping at high power levels are observed.

Super-resolution imaging methods that combine interferometric axial (z) analysis with single-molecule localization microscopy (iSMLM) have achieved ultrahigh 3D precision and contributed to the elucidation of important biological ultrastructures. However, their dependence on imaging multiple phase-shifted output channels necessitates complex instrumentation and operation. To solve this problem, we develop an interferometric superresolution microscope capable of optimal direct axial nanoscopy, termed VILM (Vortex Interference Localization Microscopy). Using a pair of vortex phase plates with opposite orientation for each dual-opposed objective lens, the detection point-spread functions (PSFs) adopt a bilobed profile whose rotation encodes the axial position. Thus, direct 3D single-molecule coordinate determination can be achieved with a single output image. By reducing the number of output channels to as few as one and utilizing a simple $50:50$ beam splitter, the imaging system is significantly streamlined, while the optimal iSMLM imaging performance is retained, with axial precision 2 times better than the lateral. The capability of VILM is demonstrated by resolving the architecture of microtubules and probing the organization of tyrosine-phosphorylated signaling proteins in integrin-based cell adhesions.

A recent experiment showed the superconducting transition temperature in the Ruddlesden-Popper bilayer ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ decreases monotonically with increasing pressure above 14 GPa. In order to unravel the underlying mechanism for this unusual dependence, we performed theoretical investigations by combining the density functional theory (DFT) and the unbiased functional renormalization group (FRG). Our DFT calculations show that the Fermi pockets are essentially unchanged with increasing pressure (above 14 GPa), but the bandwidth is enlarged, and particularly the interlayer hopping integral between the nickel $3d_{3z^2-r^2}$ orbitals is enhanced. From the DFT band structure, we construct the bilayer tight-binding model in terms of the nickel $3d_{3z^2-r^2}$ and $3d_{x^2-y^2}$ orbitals. On this basis, we investigate the superconductivity induced by correlation effects by FRG calculations. We find consistently $s_{\pm }$-wave pairing triggered by spin fluctuations, but the latter are weakened by pressure and lead to a decreasing transition temperature versus pressure, in qualitative agreement with the experiment. We emphasize that the itinerancy of the $d$ orbitals is important and captured naturally in our FRG calculations, and we argue that the unusual pressure dependence would be unnatural, if not impossible, in the otherwise local-moment picture of the nickel $d$ orbitals. This sheds light on the pertinent microscopic description, and more importantly the mechanism, of superconductivity in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$.

The interplay between disorder and quantum interference leads to a wide variety of physical phenomena including celebrated Anderson localization—the complete absence of diffusive transport due to quantum interference between different particle trajectories. In two dimensions, any amount of disorder is thought to induce localization of all states at long enough length scales. In this Letter, we present an argument providing a mechanism for disrupting localization: by tuning the underlying curvature of the manifold on which diffusion takes place. We show that negative curvature manifolds contain a natural infrared cutoff for the probability of self-returning paths. We calculate the Cooperon—directly related to the weak-localization corrections to the conductivity—in hyperbolic space. It is shown that negative curvature leads to a rapid growth in the number of available trajectories a particle can coherently traverse in a given time, reducing the importance of interference effects and restoring diffusive behavior even in the absence of inelastic collisions. We further argue that on certain manifolds with variable curvature the hyperbolic regions dominate due to intermittency and arrest weak localization, which may be of relevance to two-dimensional materials due to surface roughness. This result may be amenable to experimental verification through the use of quantum simulators. Finally, we use results on mixed-curvature gravity by Zel’dovich to argue that our generic result on the absence of weak localization in two dimensions also applies to surfaces of mixed curvature, which may be of relevance to realistic experiments on weakly disordered metallic films on rough substrates.

The properties of fractional Chern insulator (FCI) phases and the phase transitions between FCIs and Mott insulators in bosonic systems are well studied. The continuous transitions between FCI and superfluids (SFs), however, despite the inspiring field theoretical predictions [M. Barkeshli and J. McGreevy, Phys. Rev. B 89, 235116 (2014); M. Barkeshli and J. McGreevy, Phys. Rev. B 86, 075136 (2012); M. Barkeshli et al., Phys. Rev. Lett. 115, 026802 (2015); X.-Y. Song et al., Phys. Rev. B 109, 085143 (2024); and X.-Y. Song and Y.-H. Zhang, SciPost Phys. 15, 215 (2023)], have not been directly verified. The existing numerical results of the FCI-SF transition are either indirect or clearly first order. Here, by simply tuning the bandwidth of the Haldane honeycomb lattice model, we find direct transitions from a bosonic FCI at $\nu =1/2$ filling of a flat Chern band to two SF states with bosons condensed at momenta $M$ or $\mathrm{\Gamma }$, respectively. While the $\mathrm{FCI}\text{−}\mathrm{SF}(M)$ transition is first order, the $\mathrm{FCI}\text{−}\mathrm{SF}(\mathrm{\Gamma })$ transition is found to be continuous, and the bipartite entanglement entropy at the critical point with the area-law scaling is consistent with the critical theories. Through finite-size criticality analysis, the obtained critical exponents $\beta \approx 0.35(5)$ and $\nu \approx 0.62(12)$ are both compatible with those of the 3D $XY$ universality class within numerical uncertainty and possibly more exotic beyond-Landau ones. This Letter thence presents a direct numerical demonstration of a continuous FCI-SF transition between a topologically ordered phase and a spontaneous continuous symmetry-breaking phase, and further indicates the zero-field bosonic FCI might be realized from a SF state by gradually flattening the dispersion of the Chern band, through the (quasi)adiabatic preparation in ultracold atom systems.