A combinatorial optimization problem becomes very difficult in situations where the energy landscape is rugged, and the global minimum locates in a narrow region of the configuration space. When using the quantum approximate optimization algorithm (QAOA) to tackle these harder cases, we find that difficulty mainly originates from the QAOA quantum circuit instead of the cost function. To alleviate the issue, we selectively drop the clauses defining the quantum circuit while keeping the cost function intact. Due to the combinatorial nature of the optimization problems, the dropout of clauses in the circuit does not affect the solution. Our numerical results confirm improvements in QAOA's performance with various types of quantum-dropout implementations.

Quantum sensing exploits quantum phenomena to enhance the detection and estimation of classical parameters of physical systems and biological entities, particularly so as to overcome the inefficiencies of its classical counterparts. A particularly promising approach within quantum sensing is quantum optical coherence tomography which relies on nonclassical light sources to reconstruct the internal structure of multilayered materials. Compared to traditional classical probing, quantum optical coherence tomography provides enhanced-resolution images and is unaffected by even-order dispersion. One of the main limitations of this technique lies in the appearance of artifacts and echoes, i.e., fake structures that appear in the coincidence interferogram, which hinder the retrieval of information required for tomography scans. Here, by utilizing a full theoretical model, in combination with a fast genetic algorithm to postprocess the data, we successfully extract the morphology of complex multilayered samples and thoroughly distinguish real interfaces, artifacts, and echoes. We test the effectiveness of the model and algorithm by comparing its predictions to experimentally generated interferograms through the controlled variation of the pump wavelength. Our results could potentially lead to the development of practical high-resolution probing of complex structures and noninvasive scanning of photodegradable materials for biomedical imaging/sensing, clinical applications, and materials science.

Extreme states of matter that exist for a short time need probing with compact proton sources. Here, the generation of a compact MeV-energy proton source from few-cycle laser pulse interaction with narrow gas-jet target is demonstrated numerically. We realize such proton source by incorporating a gas mixture which is optimal for generation of quasimonoenergetic proton bunches. In the presented laser-plasma interaction we identify the ion acceleration from magnetic vortex, charge separation, and collisionless shock wave. The proposed particle source is excellent for applications where moderate-energy proton bunches are used at high repetition rate. We prove the applicability of this scheme for generating a pulsed spherical neutron burst with $\sim 100\mathrm{ps}$ duration.

We propose a way to discover, in tabletop experiments, spacetime-emergent materials, that is, materials holographically dual to higher-dimensional quantum gravity systems under the AdS/CFT. The emergence of the holographic spacetime is verified by a mathematical imaging transform of the response function on the material. We consider theories on a one-dimensional ring-shaped material and compute the response to a scalar source locally put at a point on the ring. When the theory on the material has a gravity dual, the imaging in the low-temperature phase exhibits a distinct difference from the ordinary materials: The spacetime-emergent material can look into the holographically emergent higher-dimensional curved spacetime and provides an image as if a wave had propagated there. Therefore the image is an experimental signature of the spacetime emergence. We also estimate the temperature, ring size, and source frequency usable in experiments, with an example of a quantum critical material, ${\mathrm{TlCuCl}}_3$.

It is commonly believed that nonuniform Berry curvature destroys the Girvin-MacDonald-Platzman algebra and as a consequence destabilizes fractional Chern insulators. In this work, we disprove this common lore by presenting a theory for all topological ideal flatbands with nonzero Chern number $\mathcal{C}$. The smooth single-particle Bloch wave function is proven to admit an exact color-entangled form as a superposition of $\mathcal{C}$ lowest Landau level type wave functions distinguished by boundary conditions. Including repulsive interactions, Abelian and non-Abelian model fractional Chern insulators of Halperin type are stabilized as exact zero-energy ground states no matter how nonuniform the Berry curvature is, as long as the quantum geometry is ideal and the repulsion is short-ranged. The key reason is the existence of an emergent Hilbert space in which Berry curvature can be exactly flattened by adjusting the wave function's normalization. In such space, the flatband-projected density operator obeys a closed Girvin-MacDonald-Platzman type algebra, making exact mapping to $\mathcal{C}$-layered Landau levels possible. In the end, we discuss applications of the theory to moiré flatband systems, with a particular focus on the fractionalized phase and the spontaneous symmetry-breaking phase recently observed in graphene-based twisted materials.

Motivated by the higher Chern bands of twisted graphene multilayers, we consider flat bands with arbitrary Chern number $C$ with ideal quantum geometry. While $C>1$ bands differ from Landau levels, we show that these bands host exact fractional Chern insulator (FCI) ground states for short-range interactions. We show how to decompose ideal higher Chern bands into separate ideal bands with Chern number 1 that are intertwined through translation and rotation symmetry. The decomposed bands admit an $\mathrm{SU}\left(C\right)$ action that combines real space and momentum space translations. Remarkably, they also allow for analytic construction of exact many-body ground states, such as generalized quantum Hall ferromagnets and FCIs, including flavor-singlet Halperin states and Laughlin ferromagnets in the limit of short-range interactions. In this limit, the $\mathrm{SU}\left(C\right)$ action is promoted to a symmetry on the ground-state subspace. While flavor singlet states are translation symmetric, the flavor ferromagnets correspond to translation broken states and admit charged skyrmion excitations corresponding to a spatially varying density wave pattern. We confirm our analytic predictions with numerical simulations of ideal bands of twisted chiral multilayers of graphene, and discuss consequences for experimentally accessible systems such as monolayer graphene twisted relative to a Bernal bilayer.

A weird electronic state accompanied with an anomalous superconducting precursor and/or exotic orders, called the pseudogap state, arises prior to a superconducting condensate in underdoped cuprates that are situated near Mott transition. Another way to make the system approach the Mott transition is the variation of bandwidth or correlation strength, which gives a new dimension to exploring this exotic state. Here we report nuclear magnetic resonance (NMR) studies on layered organic superconductors with half-filled bands whose widths are pressure tuned near the Mott transition. The system situated on the verge of the Mott transition shows a pseudogap-like anomalous suppression of spin excitations on cooling from well above the superconducting critical temperature $T_c$. The pressure variation of the NMR relaxation rate shows that the pseudogap-like behavior is rapidly suppressed by applying pressure. The NMR experiments under various magnetic fields varied up to 18 T proves the absence of symmetry breaking orders that compete with superconductivity, such as charge orders, in the metallic phase. Remarkably, the pseudogap-like behavior above $T_c$ and the superconducting condensate fade out in parallel under ascending magnetic fields with similar field-orientation dependence, indicating a superconducting precursor is the predominant origin of the pseudogap. Our further investigation of different materials, which take different “distances” from the Mott transition by chemical pressure, confirms that the superconducting precursor is not the conventional amplitude fluctuations arising from low dimensionality but unconventional preformation of Cooper pairs enhanced near the Mott transition. These findings conclude that preformed Cooper pairs persist up to twice as high as $T_c$ on the verge of the bandwidth-controlled Mott transition.

Simultaneous manipulation of charge and spin density distributions in materials is the key element required in spintronics applications. Here we study the formation of coupled spin and charge densities arising in scattering of electrons by domains of local magnetization producing a position-dependent Zeeman field in the presence of the spin-momentum locking typical for topological insulators. Analytically and numerically calculated scattering pattern is determined by the electron energy, domain magnetization, and size. The spin-momentum locking produces strong differences with respect to the spin-diagonal scattering and leads to the scattering asymmetry with a nonzero mean scattering angle as determined by only two parameters characterizing the system. To extend the variety of possible patterns, we study scattering by diffraction gratings and propose to design them in modern nanostructures based on topological insulators to produce desired distributions of the charge and spin densities. These results can be useful for engineering of magnetic patterns for electron optics to control coupled charge and spin evolution.

We investigate the influence of the temporal variations of various medium parameters on the propagation of Dirac-type waves in materials where the quasiparticles are described by a generalized version of the pseudospin-1/2 Dirac equation. Our considerations also include the propagation of electromagnetic waves in metamaterials with the Dirac-type dispersion. We focus on the variations of the scalar and vector potentials, mass, Fermi velocity, and tilt velocity describing the Dirac cone tilt. We derive the scattering coefficients associated with the temporal interfaces and slabs analytically and find that the temporal scattering is caused by the changes of the mass, Fermi velocity, and vector potential, but does not arise from the changes of the scalar potential and tilt velocity. We also explore the conditions under which the temporal Brewster effect and total interband transition occur and calculate the change in total wave energy. We examine bilayer Dirac temporal crystals where parameters switch between two different sets of values periodically and prove that these systems do not have momentum gaps. Finally, we assess the potential for observing these temporal scattering effects in experiments.

The proteins involved in cells' mechanobiological processes have evolved specialized and surprising responses to applied forces. Biochemical transformations that show catch-to-slip switching and force-induced pathway switching serve important functions in cell adhesion, mechanosensing and signaling, and protein folding. We show that these switching behaviors are generated by singularities in the flow field that describes force-induced deformation of bound and transition states. These singularities allow for a complete characterization of switching mechanisms in two-dimensional (2D) free energy landscapes, and provide a path toward elucidating novel forms of switching in higher dimensional models. Remarkably, the singularity that generates a catch-slip switch occurs in almost every 2D free energy landscape, implying that almost any bond admitting a 2D model will exhibit catch-slip behavior under appropriate force. We apply our analysis to models of selectin-ligand catch bonds and antigen extraction to illustrate how these singularities provide an intuitive framework for explaining known behaviors and predicting new behaviors.

We propose a spin-orbit-coupled Floquet spinor Bose-Einstein condensate (BEC) which can be implemented by Floquet engineering of a quadratic Zeeman field. The Floquet spinor BEC has a Bessel-function-modulated Rabi frequency and a Floquet-induced spin-exchange interaction. The quantum phase diagram of the spin-orbit-coupled Floquet spinor BEC is investigated by considering antiferromagnetic or ferromagnetic spin-spin interactions. In comparison with the usual spin-orbit-coupled spin-1 BEC, we find that a stripe phase for antiferromagnetic interactions can exist in a large quadratic Zeeman field regime, and a different stripe phase with an experimentally favorable contrast for ferromagnetic interactions is uncovered.

Phase separation is a ubiquitous and emerging mechanism underlying intracellular organization. Yet how distinct molecular compositions in phase-separated condensates are established and what prohibits these condensates from randomly fusing together remain largely unanswered. Here, through proposing a Cahn-Hilliard phase-field model paired with Ginzburg-Landau free-energy scheme, we explored how compositions are assembled in messenger RNAs (mRNAs)-driven protein droplets with respect to distinct physical properties. By analyzing the intradroplet heteropatterning of two specific droplets ($CLN3$ mRNA- and $BNI1$ mRNA-driven Whi3 droplets), we demonstrated that the growth rate of droplet size and higher-order complexes assembly in droplet are severally determined by the diffusion rate of droplet and the binding rate of mRNA with protein. While considering the three-species mixed system of two mRNAs that share a common binding protein, the two specific droplets preferentially assemble separately rather than colocalize. We found the two droplets compete with each other by snatching the protein that has been recruited into the other droplet when the free protein is insufficient. Further analysis dissects that the gradient–interfacial energy coefficients, initial mRNAs levels, and mRNAs-protein binding rates can efficiently shift the spatial patterns of the two specific droplets from segregation to the shared interface or enclosed patterns. All three patterns obtained by tuning the initial mRNAs levels or mRNA-protein binding rates have been experimentally observed. Another unreported core-shell pattern is predicted by synergistically reducing the gradient and interfacial energy coefficients. Our findings shed light on the establishment of intradroplet compositions in condensates with distinct physical properties and the general control mechanisms of phase-separated pattern formation.

We present a theoretical formulation for the multiphoton diffraction phenomenology in the nonrelativistic limit, suitable for interpreting high-energy x-ray diffraction measurements using synchrotron radiation sources. A hierarchy of approximations and the systematic analysis of limiting cases are presented. A convolutional representation of the diffraction signal allows classification of the physical resources contributing to the correlation signatures. The formulation is intended for developing a theoretical description capable of describing the plausible absence or presence of correlation signatures in elastic and inelastic diffractive scattering. Interpreting these correlation signatures in terms of the incoming field modulated many-body electronic density correlations provides a unique perspective for structural imaging studies. More essentially, it offers a framework necessary for theoretical developments of associated reconstruction algorithms.

We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of ${\mathrm{CePdAl}}_3$. In comparison to the properties of polycrystalline ${\mathrm{CePdAl}}_3$ reported in the literature, which displays a tetragonal crystal structure and no long-range magnetic order, our single crystals exhibit an orthorhombic structure ($Cmcm$) and antiferromagnetic order below a Néel temperature $T_1=5.6$ K. The specific heat at zero field shows two anomalies, namely, a broad transition at $T_1=5.6$ K followed by a $\lambda$-anomaly at $T_2=5.4$ K. A conservative estimate of the Sommerfeld coefficient of the electronic specific heat, $\gamma =121\mathrm{mJ}{\mathrm{K}}^{-2}{\mathrm{mol}}^{-1}$, indicates a moderately enhanced heavy-fermion ground state. A twin microstructure evolves in the family of planes spanned by the basal plane lattice vectors ${\mathbf{a}}_{\mathrm{o}}$ and ${\mathbf{c}}_{\mathrm{o}}$ , with the magnetic hard axis ${\mathbf{b}}_{\mathrm{o}}$ common to all twins. The antiferromagnetic state is characterized by a strong a${}_{\mathrm{o}}$, c${}_{\mathrm{o}}$ easy-plane magnetic anisotropy where the a${}_{\mathrm{o}}$ direction is the easy axis in the easy plane. A spin-flop transition induced under magnetic field along the easy directions, results in complex magnetic phase diagrams. Taken together, our results reveal a high sensitivity of the magnetic and electronic properties of ${\mathrm{CePdAl}}_3$ to its structural modifications.

Finite-size effects arise when a sample of particles is not sufficient to provide a statistically satisfactory description of the bulk environment of a physical system. As a consequence, a reliable estimate of finite-size effects in many-particle systems is key to judge the validity of a theoretical model or the accuracy of a numerical simulation. In this context, we propose the use of a theorem on the free-energy cost for separating a system into smaller independent subsystems [J. Stat. Mech.: Theory Exp. (2017) 083201; Lett. Math. Phys. 112, 97 (2022)] to estimate the relevance of finite-size effects in thermodynamic quantities from computer simulations. The key aspect of this study is that for two-body potentials, as mostly occurring in physics, the method requires only two-body distribution functions and the particle number density. The calculation of the involved physical quantities can be done numerically on a three-dimensional grid. In some cases even analytical estimates are possible and as an example the uniform interacting electron gas in the ground state is considered; we derive an approximating scaling law for the finite-size effects.