The engineering of artificial systems hosting topological excitations is at the heart of current condensed matter research. Most of these efforts focus on single-particle properties, neglecting possible engineering routes via the modifications of the fundamental many-body interactions. Interestingly, recent experimental breakthroughs have shown that Coulomb interactions can be efficiently controlled by substrate screening engineering. Inspired by this success, we propose a simple platform in which topologically nontrivial many-body excitations emerge solely from dielectrically engineered Coulomb interactions in an otherwise topologically trivial single-particle band structure. Furthermore, by performing a realistic microscopic modeling of screening engineering, we demonstrate how our proposal can be realized in one-dimensional systems such as quantum-dot chains. Our results put forward Coulomb engineering as a powerful tool to create topological excitations, with potential applications in a variety of solid-state platforms.

Entanglement plays a crucial role in the security of quantum key distribution. A secret key can only be obtained by two parties if there exists a corresponding entanglement-based description of the protocol in which entanglement is witnessed, as shown by Curty et al. [M. Curty, M. Lewenstein, and N. Lütkenhaus, Phys. Rev. Lett. 92, 217903 (2004)]. Here we investigate the role of entanglement for the generalization of quantum key distribution to the multipartite scenario, namely, conference key agreement. In particular, we ask whether the strongest form of multipartite entanglement, namely, genuine multipartite entanglement, is necessary to establish a conference key. We show that, surprisingly, a nonzero conference key can be obtained even if the parties share biseparable states in each round of the protocol. Moreover, we relate conference key agreement with entanglement witnesses and show that a nonzero conference key can be interpreted as a nonlinear entanglement witness that detects a class of states which cannot be detected by usual linear entanglement witnesses.

We explore the photon-number distribution of bimodal quantum-dot micropillar lasers with a two-channel transition-edge sensor (TES) detection system. The two channels of the photon-number-resolving TES system simultaneously detect light emission of two orthogonal components of the micropillar's fundamental emission mode. The applied experimental scheme provides unprecedented access to the joint photon-number distribution and enables a profound insight into the dynamics and photon statistics of the gain-coupled mode components. In particular, the two-channel TES measurements reveal an optical bistability of the correlated laser modes leading to temporal hopping between emission associated with Poissonian and thermal-like emission statistics. The experimental data and theoretical modeling based on Monte Carlo simulations are in good agreement and reveal the anticorrelated behavior of the mode hopping, which results in intensity fluctuations and superthermal values of the autocorrelation function. Our investigations clearly demonstrate the great benefit of using photon-number-resolving detectors in nanophotonics to explore the rich physics of multimode micro- and nanolasers.

Quasiperiodicity has long been known to be a potential platform to explore exotic phenomena, realizing an intricate middle point between ordered solids and disordered matter. In particular, quasiperiodic structures are promising playgrounds to engineer critical wave functions, a powerful starting point to engineer exotic correlated states. Here we show that systems hosting a quasiperiodic modulation of antiferromagnetism and spin-singlet superconductivity, as realized by atomic chains in twisted van der Waals materials, host a localization-delocalization transition as a function of the coupling strength. Associated with this transition, we demonstrate the emergence of a robust quasiperiodic critical point for arbitrary incommensurate potentials, which appears for generic relative weights of the spin-singlet superconductivity and antiferromagnetism. We show that inclusion of residual electronic interactions leads to an emergent spin-triplet superconducting state, which gets dramatically enhanced at the vicinity of the quasiperiodic critical point. Our results put forward quasiperiodicity as a powerful knob to engineer robust superconducting states, providing an alternative pathway towards artificially designed unconventional superconductors.

Based on first-principles calculations including a Coulomb repulsion term, we identify trends in the electronic reconstruction of $A{\mathrm{NiO}}_2/{\mathrm{SrTiO}}_3\left(001\right)$ ($A=\mathrm{Pr}$, La) and $A{\mathrm{CuO}}_2/{\mathrm{SrTiO}}_3\left(001\right)$ ($A=\mathrm{Ca}$, Sr). Common to all cases is the emergence of a quasi-two-dimensional electron gas (q2DEG) in ${\mathrm{SrTiO}}_3$(001), albeit the higher polarity mismatch at the interface of nickelates versus cuprates to the nonpolar ${\mathrm{SrTiO}}_3\left(001\right)$ substrate ($3+/0$ versus $2+/0$) results in an enhanced q2DEG carrier density. The simulations reveal a significant dependence of the interfacial Ti $3d_{xy}$ band bending on the rare-earth-metal ion in the nickelate films, being $20–30\%$ larger for ${\mathrm{PrNiO}}_2$ and ${\mathrm{NdNiO}}_2$ than for ${\mathrm{LaNiO}}_2$. Contrary to expectations from the formal polarity mismatch, the electrostatic doping in the films is twice as strong in cuprates as in nickelates. We demonstrate that the depletion of the self-doping rare-earth-metal $5d$ states enhances the similarity of nickelate and cuprate Fermi surfaces in film geometry, reflecting a single hole in the Ni and Cu $3d_{x^2-y^2}$ orbitals. Finally, we show that ${\mathrm{NdNiO}}_2$ films grown on a polar ${\mathrm{NdGaO}}_3\left(001\right)$ substrate feature a simultaneous suppression of q2DEG formation as well as Nd $5d$ self-doping.

We demonstrate transport rectification in a Hermitian Hamiltonian quantum ratchet by a dissipative, dynamic impurity. While the bulk of the ratchet supports transport in both directions, the properly designed loss function of the local impurity acts as a direction-dependent filter for the moving states. We analyze this scheme theoretically by making use of Floquet $S$-matrix theory. In addition, we provide direct experimental observation of one-way transmittance in periodically modulated plasmonic waveguide arrays containing a local impurity with engineered losses.

The situation of self-compression and concomitant supercontinuum generation in a multipass cell is analyzed in numerical simulations. This study focuses on multipass cells that contain a dielectric slab as nonlinear medium and overcompensate the dispersion of the slab with intracavity dispersive coatings. A $2\mathrm{D}+1$ unidirectional pulse propagation equation is utilized to simulate the pulse evolution through successive passes. We observe a previously unreported effect of space-time focusing, leading to a pronounced blue shift, similar to what had been observed in filament compression experiments before. This effect competes with detrimental pulse breakup, which can nevertheless be mitigated under suitable choice of cavity parameters. We further analyze resulting coherence properties, in both the time and frequency domains. Our analysis shows highly favorable properties of multipass cell compression schemes when nonlinearity and dispersion are distributed over as many cavity passes as possible. This quasicontinuous approach is particularly promising for spectral broadening schemes that allow for stabilization of the carrier-envelope phase.

Spatial organization of proteins in cells is important for many biological functions. In general, the nonlinear, spatially coupled models for protein-pattern formation are only accessible to numerical simulations, which has limited insight into the general underlying principles. To overcome this limitation, we adopt the setting of two diffusively coupled, well-mixed compartments that represents the elementary feature of any pattern—an interface. For intracellular systems, the total numbers of proteins are conserved on the relevant timescale of pattern formation. Thus the essential dynamics is the redistribution of the globally conserved mass densities between the two compartments. We present a phase-portrait analysis in the phase-space of the redistributed masses that provides insights on the physical mechanisms underlying pattern formation. We demonstrate this approach for several paradigmatic model systems. In particular, we show that the pole-to-pole Min oscillations in Escherichia coli are relaxation oscillations of the MinD polarity orientation. This reveals a close relation between cell polarity oscillatory patterns in cells. Critically, our findings suggest that the design principles of intracellular pattern formation are found in characteristic features in these phase portraits (nullclines and fixed points). These features are not uniquely determined by the topology of the protein-interaction network but depend on parameters (kinetic rates, diffusion constants) and distinct networks can give rise to equivalent phase portrait features.

The ubiquitous presence of shot noise sets a fundamental limit to the measurement precision in classical metrology. Recent advances in quantum devices and novel quantum algorithms utilizing interference effects are opening new routes for overcoming the detrimental noise tyranny. However, further progress is limited by the restricted capability of existing algorithms to account for the decoherence pervading experimental implementations. Here, adopting a systematic approach to the evaluation of effectiveness of metrological procedures, we devise the Linear Ascending Metrological Algorithm (LAMA), which offers a remarkable increase in precision in the demanding situation where a decohering quantum system is used to measure a continuously distributed variable. We introduce our protocol in the context of magnetic field measurements, assuming superconducting transmon devices as sensors operated in a qudit mode. Our findings demonstrate a quantum-metrological procedure capable of mitigating detrimental dephasing and relaxation effects.

The $\mathcal{PT}$-symmetric non-Hermitian systems have been widely studied and explored both in theory and in experiment due to their various interesting features. In this work we focus on the dynamical features of a triple-qubit system, one of which evolves under a local $\mathcal{PT}$-symmetric Hamiltonian. An abnormal dynamic pattern in the entropy evolution process is identified that presents a parameter-dependent stable state, determined by the non-Hermiticity of Hamiltonian in the broken phase of $\mathcal{PT}$ symmetry. The entanglement and mutual information of a two-body subsystem can increase beyond the initial values, which do not exist in the Hermitian and two-qubit $\mathcal{PT}$-symmetric systems. Moreover, an experimental demonstration of the stable states in non-Hermitian systems with nonzero entropy and entanglement is realized on a four-qubit quantum simulator with nuclear spins. Our work reveals the distinctive dynamic features in the triple-qubit $\mathcal{PT}$-symmetric system and paves the way for practical quantum simulation of multiparty non-Hermitian system on quantum computers.

Recently a few 2D AKLT models have been shown to be gapped, including the one on the hexagonal lattice, whose local spin magnitude is spin-3/2. Here we report the existence of a nonzero spectral gap on several nontrivial AKLT models having either solely spin-2 or mixed spin-2 and spin-1 degrees of freedom. The hybrid models we consider are defined on the 3D diamond and 2D kagome lattices, where lattice sites are spin-2 and one single spin-1 degree of freedom is added on some or all of the edges. Although the spectral gap problem for the uniformly spin-2 AKLT models on the diamond, kagome, and square lattices is still open, we are able to establish the existence of the gap for spin-2 AKLT models on two planar lattices, which we call the inscribed square lattice and the triangle-octagon lattice, respectively. So far these latter two are the only two uniformly spin-2 AKLT models that have a provable nonzero gap above the ground state. We also discuss some attempts to prove the gap existence on both the square and kagome lattices. In addition, we show that if one can show that the gap of a finite-size, weighted AKLT Hamiltonian is larger than a certain threshold, then the original AKLT model on the square lattice is gapped in the thermodynamic limit. The threshold of the gap we obtain scales inversely with the linear size of the problem.

We explain how gapped quantum spin liquids, both conventional and “fractonic,” may be unambiguously diagnosed experimentally using the technique of multidimensional coherent spectroscopy. “Conventional” nonchiral gapped quantum spin liquids (e.g., $Z_2$ spin liquid) do not have sharp signatures in linear response, but they $\mathit{do}$ have clear fingerprints in nonlinear response, accessible through the already existing experimental technique of two-dimensional coherent spectroscopy. Type I fracton phases (e.g., X-cube) are (surprisingly) even easier to distinguish, with strongly suggestive features even in linear response, and unambiguous signatures in nonlinear response. Type II fracton systems, like Haah's code, are most subtle, and they may require consideration of high-order nonlinear response for unambiguous diagnosis.

Optical control of chirality in chiral superconductors bears potential for future topological quantum computing applications. When a chiral domain is written and erased by a laser spot, the Majorana modes around the domain can be manipulated on ultrafast timescales. Here we study topological superconductors with two chiral order parameters coupled via light fields by a time-dependent real-space Ginzburg-Landau approach. Continuous optical driving, or the application of supercurrent, hybridizes the two chiral order parameters, allowing one to induce and control the superconducting state beyond what is possible in equilibrium. We show that superconductivity can even be enhanced if the mutual coupling between two order parameters is sufficiently strong. Furthermore, we demonstrate that short optical pulses with spot size larger than a critical one can overcome a counteracting diffusion effect and write, erase, or move chiral domains. Surprisingly, these domains are found to be stable, which might enable optically programmable quantum computers in the future.

Precise control and study of molecules is challenging due to the variety of internal degrees of freedom and local coordinates that are typically not controlled in an experiment. Employing quantum gas microscopy to position and resolve the atoms in Rydberg macrodimer states solves most of these challenges and enables unique access to the molecular frame. Here, we demonstrate this approach and present photoassociation studies in which the molecular orientation relative to an applied magnetic field, the polarization of the excitation light, and the initial atomic state are fully controlled. The observed dependencies allow for an electronic structure tomography of the molecular state. We additionally observe an orientation-dependent Zeeman shift, and we reveal a significant influence on it caused by the hyperfine interaction of the macrodimer state. Finally, we demonstrate control over the electrostatic binding potential by engineering a gap between two crossing pair potentials. Our results establish macrodimers as the most sensitive tool to benchmark Rydberg interaction potentials, and they open new perspectives for improving Rydberg dressing schemes.

Vortex beams with a twisted wavefront possess both intrinsic and extrinsic orbital angular momenta. Their coupling (viz. orbital-orbital coupling) leads to an orbital angular momentum Hall effect previously found in light, providing applications in light manipulation. Here an analogous orbital Hall effect in acoustics is reported via modeling vortex beam propagation in an inhomogeneous medium. A shift of the beam center perpendicular to the inhomogeneous direction is numerically observed to follow a path predicted by ray theory in the weak inhomogeneity approximation where the coupling and conservation of total angular momenta are identified. Experimental observation of the acoustic phenomenon with the aid of a gradient metasurface or a stratified fluid is proposed.

Non-Fermi liquids (NFLs) are a class of strongly interacting gapless fermionic systems without long-lived quasiparticle excitations. An important group of NFL models feature itinerant fermions coupled to soft bosonic fluctuations near a quantum-critical point and are widely believed to capture the essential physics of many unconventional superconductors. However, numerically, the direct observation of a canonical NFL behavior in such systems, characterized by a power-law form in the Green's function, has been elusive. Here, we consider a Sachdev-Ye-Kitaev (SYK)-like model with random Yukawa interaction between critical bosons and fermions (dubbed the Yukawa-SYK model). We show that it is immune from the minus-sign problem and hence can be solved exactly via large-scale quantum Monte Carlo simulation beyond the large-$N$ limit accessible to analytical approaches. Our simulation demonstrates that the Yukawa-SYK model features “self-tuned quantum criticality”; namely, the system is critical independent of the bosonic bare mass. We put these results to the test at finite $N$, and our unbiased numerics reveal clear evidence of these exotic quantum-critical NFL properties—the power-law behavior in the Green's function of fermions and bosons—which propels the theoretical understanding of critical Planckian metals and unconventional superconductors.

Chirality and chiral molecules are key elements in modern chemical and biochemical industries. Individual addressing and the eventual separation of chiral enantiomers have been and still are important elusive tasks in molecular physics and chemistry, and a variety of methods have been introduced over the years to achieve these goals. Here, we theoretically demonstrate that a pair of cross-polarized THz pulses interacting with chiral molecules through their permanent dipole moments induces in these molecules an enantioselective orientation. This orientation persists for a long time, exceeding the duration of the THz pulses by several orders of magnitude, and its dependency on temperature and pulses' parameters is investigated. This persistent orientation may enhance the deflection of the molecules in inhomogeneous electromagnetic fields, potentially leading to viable separation techniques.

Finding pure states in an enlarged Hilbert space that encode the mixed state of a quantum field theory as a partial trace is necessarily a challenging task. Nevertheless, such purifications play the key role in characterizing quantum information-theoretic properties of mixed states via entanglement and complexity of purifications. In this article, we analyze these quantities for two intervals in the vacuum of free bosonic and Ising conformal field theories using the most general Gaussian purifications. We provide a comprehensive comparison with existing results and identify universal properties. We further discuss important subtleties in our setup: the massless limit of the free bosonic theory and the corresponding behavior of the mutual information, as well as the Hilbert space structure under the Jordan-Wigner mapping in the spin chain model of the Ising conformal field theory.

Conservation principles are essential to describe and quantify dynamical processes in all areas of physics. Classically, a conservation law holds because the description of reality can be considered independent of an observation (measurement). In quantum mechanics, however, invasive observations change quantities drastically, irrespective of any classical conservation law. One may hope to overcome this nonconservation by performing a weak, almost noninvasive measurement. Interestingly, we find that the nonconservation is manifest even in weakly measured correlations if some of the other observables do not commute with the conserved quantity. Our observations show that conservation laws in quantum mechanics should be considered in their specific measurement context. We provide experimentally feasible examples to observe the apparent nonconservation of energy and angular momentum.

Magnetic skyrmions are topological spin textures that can be used as information carriers for the next-generation information storage and processing. The electric-field controlling of skyrmions in such devices is essential but remains technologically challenging. Here, using the first-principle calculation and the Ginzburg-Landau theory, we propose a reliable process for writing and deleting skyrmions by electric fields, on the platform of a multiferroic heterostructure, particularly the ${\text{Cr}}_2{\text{Ge}}_2{\text{Te}}_6/{\text{In}}_2{\text{Se}}_3$ heterostructure. We show that the electric field controls the electric polarization and indirectly influences the antisymmetric Dzyaloshinskii-Moriya interaction (DMI) between the magnetic moments. The latter is responsible for the generation and removal of the skyrmion spin textures, and we study this mechanism by the Ginzburg-Landau analysis. We discuss the real-space Berry curvature, topological Hall effects, possible quantum anomalous Hall effect, and other competing magnetic structures. These results represent examples of quantum technology and may have potential applications in future skyrmionics and the device fabrication.