Controlling quantum matter with light offers a promising route to dynamically tune its many-body properties, ranging from band topology1,2 to superconductivity3. However, achieving such optical control for strongly correlated electron systems in the steady state has remained elusive. Here we demonstrate optical switching of the spin-valley degree of freedom of itinerant ferromagnets in twisted MoTe2 (t-MoTe2) homobilayers. This system uniquely features flat valley-contrasting Chern bands and exhibits a range of strongly correlated phases at various moiré lattice fillings, including Chern insulators and ferromagnetic metals4-7. We show that the spin-valley orientation of all of these phases can be dynamically reversed by resonantly exciting the exciton-polaron8 transitions with circularly polarized light. These findings not only provide direct evidence for non-thermal optical switching of a ferromagnetic spin state at zero magnetic field but also demonstrate the possibility of dynamical control over a topological order parameter, paving the way for optical generation of chiral edge modes and topological quantum circuits.
Controlling precursor reactivity through ligand design remains a central challenge in the colloidal synthesis of III-V quantum dots (QDs). In particular, InSb QDs have been difficult to access due to hazardous metal-hydride reductants and limited precursor availability. Here, we report a metal-reductant-free route employing tris(dimethylamino)phosphine [P(NMe2)(3)], whose function as a reductant or a P(-III) source is determined by the coordination environment of SbCl3. When Sb-oleylamine (OlNH(2)) complexes are used, P(NMe2)(3) reduces both Sb and In precursors, producing phase-pure InSb QDs. In contrast, Sb-trioctylphosphine (TOP) complexes undergo partial Sb(+III) reduction via electrons released from TOP oxidation, while P(NMe2)(3) simultaneously reduces In and generates P(-III) species, enabling controlled formation of alloyed InP1-xSbx QDs (0.6 <= x < 1). P-31 NMR and EXAFS analyses reveal that the Sb-TOP complex exists in a dynamic chloride-phosphine equilibrium, which governs P(-III) availability and reaction selectivity. This mechanistic insight demonstrates that ligand coordination can be leveraged to modulate precursor reactivity, selectively direct reduction pathways, and achieve controlled alloying in colloidal III-V QDs. The resulting QDs exhibit sharp excitonic absorption and band-edge emission in the short-wavelength infrared (SWIR) region, bridging the previously inaccessible spectral gap between InP and InSb. Beyond InSb and InP1-xSbx, these findings establish a general design principle: dynamic ligand environments can be exploited to tune reactivity, composition, and alloy formation in colloidal semiconductors. This work thus provides a safe, high-yielding, mechanistically rational strategy for Sb-based III-V QDs and lays the foundation for extending optoelectronic functionality through precise precursor engineering.
Optically active defects in hexagonal boron nitride (hBN) have become amongst the most attractive single-photon emitters in the solid state, owing to their high-quality photophysical properties, combined with the unlimited possibilities of integration offered by the host two-dimensional material. In particular, the B centres, with their narrow linewidth, low wavelength spread and controllable positioning, have raised a particular interest for integrated quantum photonics. However, to date, either their excitation or their detection has been performed non-resonantly due to the difficulty of rejecting the backreflected laser light at the same wavelength, thereby preventing to take full benefit from their high coherence in quantum protocols. Here, we make use of a narrow-linewidth emitter integrated in a hybrid metal-dielectric structure to implement crossed-polarisation laser rejection. This allows us to observe resonantly scattered photons, with associated experimental signatures of optical coherence in both continuous-wave (cw) and pulsed regimes, respectively the Mollow triplet and Hong-Ou-Mandel interference from zero-phonon-line emission. The measured two-photon interference visibility of 0.92 demonstrates the potential of B centres in hBN for applications to integrated quantum information.
Electrons in solids owe their properties to the periodic potential landscapes they experience. The advent of moiré lattices has revolutionized our ability to engineer such landscapes on nanometer scales, leading to numerous groundbreaking discoveries. Despite this progress, direct imaging of these electrostatic potential landscapes remains elusive. In this work, we introduce the Atomic Single Electron Transistor (SET), a novel scanning probe utilizing a single atomic defect in a van der Waals (vdW) material, which serves as an ultrasensitive, high-resolution potential imaging sensor. Built upon the quantum twisting microscope (QTM) platform, this probe leverages the QTM's distinctive capability to form a pristine, scannable 2D interface between vdW heterostructures. Using the Atomic SET, we present the first direct images of the electrostatic potential in one of the most canonical moiré interfaces: graphene aligned to hexagonal boron nitride. Our results reveal that this potential exhibits an approximate C6 symmetry, has minimal dependence on the carrier density, and has a substantial magnitude of 60 mV even in the absence of carriers. Theoretically, the observed symmetry can only be explained by a delicate interplay of physical mechanisms with competing symmetries. Intriguingly, the magnitude of the measured potential significantly exceeds theoretical predictions, suggesting that current understanding may be incomplete. With a spatial resolution of 1 nm and a sensitivity to detect the potential of even a few millionths of an electron charge, the Atomic SET opens the door for ultrasensitive imaging of charge order and thermodynamic properties for a range of quantum phenomena, including various symmetry-broken phases, quantum crystals, vortex charges, and fractionalized quasiparticles.
Black-box optimization (BBO) is used in materials design, drug discovery, and hyperparameter tuning in machine learning. The world is experiencing several of these problems. In this review, a factorization machine with quantum annealing or with quadratic-optimization annealing (FMQA) algorithm to realize fast computations of BBO using Ising machines (IMs) is discussed. The FMQA algorithm uses a factorization machine (FM) as a surrogate model for BBO. The FM model can be directly transformed into a quadratic unconstrained binary optimization model that can be solved using IMs. This makes it possible to optimize the acquisition function in BBO, which is a difficult task using conventional methods without IMs. Consequently, it has the advantage of handling large BBO problems. To be able to perform BBO with the FMQA algorithm immediately, we introduce the FMQA algorithm along with Python packages to run it. In addition, we review examples of applications of the FMQA algorithm in various fields, including physics, chemistry, materials science, and social sciences. These successful examples include binary and integer optimization problems, as well as more general optimization problems involving graphs, networks, and strings, using a binary variational autoencoder. We believe that BBO using the FMQA algorithm will become a key technology in IMs including quantum annealers.
