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Abstract Nonlinear mean field dynamics enables quantum information processing operations that are impossible in linear one‐particle quantum mechanics. In this approach, a register of bosonic qubits (such as neutral atoms or polaritons) is initialized into a symmetric product state through condensation, then subsequently controlled by varying the qubit‐qubit interaction. An experimental implementation of quantum state discrimination, an important subroutine in quantum computation, with a toroidal Bose–Einstein condensate is proposed. The condensed bosons here are atoms, each in the same superposition of angular momenta 0 and , encoding a qubit. A nice feature of the protocol is that only a readout of individual quantized circulation states (not superpositions) is required. 

Abstract Since the first isolation of graphene, the importance of van der Waals (vdW) interactions has become increasingly recognized in the burgeoning field of layered materials. In this work, infrared nanoimaging techniques and theoretical modeling are used to unravel the critical role played by interfacial vdW interactions in governing the stability of violet phosphorus (VP)—a recently rediscovered wide bandgap p‐type semiconductor—when exfoliated on different substrates. It is demonstrated that vdW interactions with the underlying substrate can have a profound influence on the stability of exfoliated VP flakes and investigate how these interactions are affected by flake thickness, substrate properties (e.g., substrate hydrophilicity, surface roughness), and the exfoliation process. These findings highlight the key role played by interfacial vdW interactions in governing the stability and physical properties of layered materials, and can be used to guide substrate selection in the preparation and study of this important class of materials. 

Abstract Nonlinear qubit master equations have recently been shown to exhibit rich dynamical phenomena such as period doubling, Hopf bifurcation, and strange attractors usually associated with classical nonlinear systems. Here we investigate nonlinear qubit models that support tunable Lorenz attractors. A Lorenz qubit could be realized experimentally by combining qubit torsion, generated by real or simulated mean field dynamics, with linear amplification and dissipation. This would extend engineered Lorenz systems to the quantum regime, allowing for their direct experimental study and possible application to quantum information processing. 

Abstract Violet phosphorus (VP) is garnering attention for its appealing physical properties and potential applications in optoelectronics. A comprehensive investigation of the photodegradation and thermal effects of exfoliated VP on SiO₂/Si substrates is presented. The degradation rate of VP is strongly influenced by the wavelength and exposure duration of light. Light illumination of VP above the bandgap leads to faster degradation, attributed to interactions with reactive oxygen species. Power‐dependent photoluminescence (PL) measurements at low temperature (T = 4 K) show neutral exciton (X⁰) and trion (T) intensities linearly increase with excitation power, while the energy difference between peak energies decreases. The T/X⁰spectral weight ratio increases from 0.28 at 300 K to 0.69 at 4 K, suggesting enhanced T formation due to reduced phonon scattering. Temperature‐dependent Raman is used to investigate the phonon properties of VP. Tracking peak positions of 9 Raman modes with temperature, the linear first‐order temperature coefficient is obtained and found to be linear for all modes. The results provide a deeper understanding of VP's degradation behavior and implications for optoelectronic applications. 

Abstract Engineering electronic bandgaps is crucial for applications in information technology, sensing, and renewable energy. Transition metal dichalcogenides (TMDCs) offer a versatile platform for bandgap modulation through alloying, doping, and heterostructure formation. Here, the synthesis of a 2D Mo_xW_1‐xS₂graded alloy is reported, featuring a Mo‐rich center that transitions to W‐rich edges, achieving a tunable bandgap of 1.85 to 1.95 eV when moving from the center to the edge of the flake. Aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy showed the presence of sulfur monovacancy, V_S, whose concentration varied across the graded Mo_xW_1‐xS₂layer as a function of Mo content with the highest value in the Mo‐rich center region. Optical spectroscopy measurements supported by ab initio calculations reveal a doublet electronic state of V_S, which is split due to the spin‐orbit interaction, with energy levels close to the conduction band or deep in the bandgap depending on whether the vacancy is surrounded by W atoms or Mo atoms. This unique electronic configuration of V_Sin the alloy gave rise to four spin‐allowed optical transitions between the V_Slevels and the valence bands. The study demonstrates the potential of defect and optical engineering in 2D monolayers for advanced device applications. 

Abstract Any stater= (x,y,z) of a qubit, written in the Pauli basis and initialized in the pure stater= (0, 0, 1), can be prepared by composing three quantum operations: two unitary rotation gates to reach a pure state $\mathit{r}={\left(x^2+y^2+z^2\right)}^{-\frac{1}{2}}\times (x,y,z)$on the Bloch sphere, followed by a depolarization gate to decrease ∣r∣. Here we discuss the complementary state-preparation protocol for qubits initialized at the center of the Bloch ball,r=0, based on increasing or amplifying ∣r∣ to its desired value, then rotating. Bloch vector amplification increases purity and decreases entropy. Amplification can be achieved with a linear Markovian completely positive trace-preserving (CPTP) channel by placing the channel’s fixed point away fromr=0, making it nonunital, but the resulting gate suffers from a critical slowing down as that fixed point is approached. Here we consider alternative designs based on linear and nonlinear Markovian PTP channels, which offer benefits relative to linear CPTP channels, namely fast Bloch vector amplification without deceleration. These gates simulate a reversal of the thermodynamic arrow of time for the qubit and would provide striking experimental demonstrations of non-CP dynamics. 

Abstract Models of nonlinear quantum computation based on deterministic positive trace‐preserving (PTP) channels and evolution equations are investigated. The models are defined in any finite Hilbert space, but the main results are for dimension . For every normalizable linear or nonlinear positive map ϕ on bounded linear operatorsX, there is an associated normalized PTP channel . Normalized PTP channels include unitary mean field theories, such as the Gross–Pitaevskii equation for interacting bosons, as well as models of linear and nonlinear dissipation. They classify into four types, yielding three distinct forms of nonlinearity whose computational power are explored. In the qubit case, these channels support Bloch ball torsion and other distortions studied previously, where it has been shown that such nonlinearity can be used to increase the separation between a pair of close qubit states, suggesting an exponential speedup for state discrimination. Building on this idea, the authors argue that this operation can be made robust to noise by using dissipation to induce a bifurcation to a novel phase where a pair of attracting fixed points create an intrinsically fault‐tolerant nonlinear state discriminator. 

Interatomic potentials for single-layer MoS₂and MoSe₂were developed by training an artificial neural network with a reference data set generated using density functional theory.