Search

Energy is no doubt an intuitive concept. Following a previous analysis on the nature of elementary particles and associated elementary quantum fields, the peculiar status and role of energy is scrutinised further at elementary and larger scales. Energy physical characterisation shows that it is a primordial component of reality highlighting the quantum fields natural tendencies to interact, the elementary particles natural tendency to constitute complex bodies and every material thing natural tendency to actualise and be active. Energy therefore is a primordial notion in need of a proper assessment., Comment: 30 pages, 5 figures

Electro-optical modulation is widely employed for optical signal processing and in laser technology. To date, it is efficiently realized in integrated photonic systems as well as in bulk optics devices. Yet, the achievement of modulators exploiting Pockels effect in flat optics, essential to scale down the electric radiation-optical control in free space, currently lag behind bulk and on-chip integrated platforms in terms efficiency and speed. We bridge this gap realizing a metasurface based on lithium niobate (LiNbO3) on insulator that leverages on resonances with quality-factor as high as 8e3 to achieve fast electrical modulation of both linear and nonlinear optical properties. LiNbO3, well known for its high nonlinear susceptibility and wide transparency window across the infrared and visible spectrum, is employed to realize an asymmetric, one-dimensional array of nanowires, exhibiting resonances with linewidth < 0.2 nm. By applying a CMOS-compatible electrical bias, the metasurface imparts a relative reflectivity modulation around 0.1, with a modulation efficiency, defined as relative modulation per applied Volt, larger than 0.01 V^-1 on a bandwidth of about 1 GHz. We also demonstrated more than one order of magnitude intensity modulation of the second harmonic seeded by a continuous-wave laser, with a modulation efficiency of about 0.12 V^-1. This dual modulation capability, rooted in the interplay between optical resonances and electric field manipulation, holds significant potential for cutting-edge applications in high-speed photonics, nonlinear optics, and reconfigurable communication systems. Our findings highlight the transformative potential of LiNbO3-based metasurfaces for integration into next-generation optical technologies that demand rapid, efficient electrical control of light.

We consider a run-and-tumble particle on a half-line with an absorbing target at the origin. The particle has an internal velocity state that switches between two opposite values at Poisson-distributed times. The position of the particle evolves according to an overdamped Langevin dynamics with a spatially-periodic force field such that every point in a given period interval is accessible to the particle. The survival probability of the particle satisfies a backward Fokker--Planck equation, whose Laplace transform yields systems of equations for the moments of the first-passage time of the particle at the origin. The mean first-passage time has already been calculated assuming that the particle exits the system almost surely. We calculate the probability that the particle reaches the origin in a finite time, given its initial position and velocity. We obtain an integral condition on the force, under which the particle has a non-zero survival probability. The conditioned average of the first-passage time at the origin (over the trajectories that reach the origin) is obtained in closed form, both in the latter case and in the case of almost-sure exit. As an application, we consider a piecewise-constant force field that alternates periodically between two opposite values. In the limit where the period is short compared to the mean free path of the particle, the exit probability and the mean first-return time at the origin coincide with the values obtained in the case of an effective constant drift, which we calculate explicitly., Comment: 35 pages, 2 figures; V2: 36 pages, 3 figures, numerical simulations added, typos corrected; V3: 35 pages, corrections and clarifications; V4: 43 pages, corrections to Section 4, Section 5 added, Appendix C added

Quantum Approximate Optimization Algorithm (QAOA) is one of the most short-term promising quantum-classical algorithm to solve unconstrained combinatorial optimization problems. It alternates between the execution of a parametrized quantum circuit and a classical optimization. There are numerous levers for enhancing QAOA performances, such as the choice of quantum circuit meta-parameters or the choice of the classical optimizer. In this paper, we stress on the importance of the input problem formulation by illustrating it with the resolution of an industrial railway timetabling problem. Specifically, we present a generic method to reformulate any polynomial problem into a Polynomial Unconstrained Binary Optimization (PUBO) problem, with a specific formulation imposing penalty terms to take binary values when the constraints are linear. We also provide a generic reformulation into a Quadratic Unconstrained Binary Optimization (QUBO) problem. We then conduct a numerical comparison between the PUBO with binary penalty terms and the QUBO formulations proposed on a railway timetabling problem solved with QAOA. Our results illustrate that the PUBO reformulation outperforms the QUBO one for the problem at hand.

SQL adventure builder (SQLab) is an open-source framework for creating SQL games that are embedded within the very database they query. Students' answers are evaluated using query fingerprinting, a novel technique that allows for better feedback than traditional SQL online judge systems. Fingerprints act as tokens that are used to unlock messages encrypted in an isolated auxiliary table. These messages may include hints, answer keys, examples, explanations, or narrative elements. They can also contain the problem statement of the next task, which turns them into nodes in a virtual DAG with queries as edges. This makes it possible to design a coherent adventure with a storyline of arbitrary complexity. This paper describes the theoretical underpinnings of SQLab's query fingerprinting model, its implementation challenges, and its potential to improve SQL education through game-based learning. The underlying concepts are fully cross-vendor, and support for SQLite, PostgreSQL and MySQL is already available. As a proof of concept, two games, 30 exercises and one mock exam were tested over a three-year period with about 300 students., Comment: 36 pages

Miniaturizing nonlinear optical components is essential for integrating advanced light manipulation into compact photonic devices, enabling scalable and cost-effective applications. While monocrystalline lithium niobate thin films advance nonlinear nanophotonics, their high inertness limits the design of top-down fabricated nanostructures. Here we present a versatile bottom-up fabrication method based on nanoimprint lithography for achieving polycrystalline lithium niobate nanostructures, and demonstrate its significant potential for nonlinear metasurfaces. The fabrication enables nearly vertical features and aspect ratios of up to 6, which we combine with a novel solution-derived material with high effective second-order nonlinearity of d_{eff}=5 pm/V. On this platform, we demonstrate second-harmonic focusing over a broad spectral range from near-UV to near-IR, increasing the nonlinear signal intensity by up to 34 times. Our method enables the first lithium niobate metalens and expands the field of nonlinear metasurfaces by providing a low-cost, highly scalable fabrication method for engineered nonlinear nanostructures

Nonlinear disordered media uniquely combine multiple scattering and second-harmonic generation. Here, we investigate the statistical properties of the nonlinear light generated within such media. We report super-Rayleigh statistics of the second-harmonic speckle intensity, and demonstrate that it is caused by the mesoscopic correlations arising in extreme scattering conditions. The measured conductance is the lowest ever observed in an isotropically scattering 3D medium, with applications in broadband second-harmonic generation, wavefront shaping in nonlinear disordered media, and photonic computing., Comment: 13 pages, 10 figures

Grover Search is currently one of the main quantum algorithms leading to hybrid quantum-classical methods that reduce the worst-case time complexity for some combinatorial optimization problems. Specifically, the combination of Quantum Minimum Finding (obtained from Grover Search) with dynamic programming has proved particularly efficient in improving the complexity of NP-hard problems currently solved by classical dynamic programming. For these problems, the classical dynamic programming complexity in $\mathcal{O}^*(c^n)$, where $\mathcal{O}^*$ denotes that polynomial factors are ignored, can be reduced by a hybrid algorithm to $\mathcal{O}^*(c_{quant}^n)$, with $c_{quant} < c$. In this paper, we provide a bounded-error hybrid algorithm that achieves such an improvement for a broad class of NP-hard single-machine scheduling problems for which we give a generic description. Moreover, we extend this algorithm to tackle the 3-machine flowshop problem. Our algorithm reduces the exponential-part complexity compared to the best-known classical algorithm, sometimes at the cost of an additional pseudo-polynomial factor.

Organizations across various industries are still exploring the potential of Generative Artificial Intelligence (GenAI) to enhance knowledge work. While innovation is often viewed as a product of individual creativity, it more commonly unfolds through a highly structured, collaborative process where creativity intertwines with knowledge work. However, the extent and effectiveness of GenAI in supporting this process remain open questions. Our study investigates this issue using a collaborative practice research approach focused on three GenAI-enabled innovation projects conducted over a year within three different organizations. We explored how, why, and when GenAI could be integrated into design sprints, a highly structured, collaborative, and human-centered innovation method. Our research identified challenges and opportunities in synchronizing AI capabilities with human intelligence and creativity. To translate these insights into practical strategies, we propose four recommendations for organizations eager to leverage GenAI to both streamline and bring more value to their innovation processes: (1) establish a collaborative intelligence value loop with GenAI; (2) build trust in GenAI, (3) develop robust data collection and curation workflows, and (4) cultivate a craftsmanship mindset., Comment: 46 pages, 4 figures

Optical quantum communication technologies are making the prospect of unconditionally secure and efficient information transfer a reality. The possibility of generating and reliably detecting quantum states of light, with the further need of increasing the private data-rate is where most research efforts are focusing. The physical concept of entanglement is a solution guaranteeing the highest degree of security in device-independent schemes, yet its implementation and preservation over long communication links is hard to achieve. Lithium niobate-on-insulator has emerged as a revolutionising platform for high-speed classical telecommunication and is equally suited for quantum information applications owing to the large second-order nonlinearities that can efficiently produce entangled photon pairs. In this work, we generate maximally entangled quantum states in the time-bin basis using lithium niobate-on-insulator photonics at the fibre optics telecommunication wavelength, and reconstruct the density matrix by quantum tomography on a single photonic integrated circuit. We use on-chip periodically-poled lithium niobate as source of entangled qubits with a brightness of 242 MHz/mW and perform quantum tomography with a fidelity of 91.9+-1.0 %. Our results, combined with the established large electro-optic bandwidth of lithium niobate, showcase the platform as perfect candidate to realise fibre-coupled, high-speed time-bin quantum communication modules that exploit entanglement to achieve information security.

We are interested in the following validation problem for computational reductions: for algorithmic problems $P$ and $P^\star$, is a given candidate reduction indeed a reduction from $P$ to $P^\star$? Unsurprisingly, this problem is undecidable even for very restricted classes of reductions. This leads to the question: Is there a natural, expressive class of reductions for which the validation problem can be attacked algorithmically? We answer this question positively by introducing an easy-to-use graphical specification mechanism for computational reductions, called cookbook reductions. We show that cookbook reductions are sufficiently expressive to cover many classical graph reductions and expressive enough so that SAT remains NP-complete (in the presence of a linear order). Surprisingly, the validation problem is decidable for natural and expressive subclasses of cookbook reductions., Comment: Full version of an MFCS 2024 paper

Murunskite (K$_2$FeCu$_3$S$_4$) is a bridging compound between the only two known families of high-temperature superconductors. It is a semiconductor like the parent compounds of cuprates, yet isostructural to metallic iron-pnictides. Moreover, like both families, it has an antiferromagnetic (AF)-like response with an ordered phase occurring below $\approx$ 100 K. Through comprehensive neutron, M\"ossbauer, and XPS measurements on single crystals, we unveil AF with a nearly commensurate quarter-zone wave vector. Intriguingly, the only identifiable magnetic atoms, iron, are randomly distributed over one-quarter of available crystallographic sites in 2D planes, while the remaining sites are occupied by closed-shell copper. Notably, any interpretation in terms of a spin-density wave is challenging, in contrast to the metallic iron-pnictides where Fermi-surface nesting can occur. Our findings align with a disordered-alloy picture featuring magnetic interactions up to second neighbors. Moreover, in the paramagnetic state, iron ions are either in Fe$^{3+}$ or Fe$^{2+}$ oxidation states, associated with two distinct paramagnetic sites identified by M\"ossbauer spectroscopy. Upon decreasing the temperature below the appearance of magnetic interactions, these two signals merge completely into a third, implying an orbital transition. It completes the cascade of (local) transitions that transform iron atoms from fully orbitally and magnetically disordered to homogeneously ordered in inverse space, but still randomly distributed in real space., Comment: 17 pages, 8 figure, 2 tables (9 pages, 4 figures in the main text; 8 pages, 4 figures, 2 tables in the appendix)

Polarization-entangled photon pair sources are essential for diverse quantum technologies, such as quantum communication, computation, and imaging. However, the generation of complex polarization-entangled quantum states has long been constrained by the available nonlinear susceptibility tensor of natural nonlinear crystals, necessitating a cumbersome and intricate setup for additional coherent superposition or post-selection. In this study, we introduce and experimentally demonstrate a nanoscale polarization-entangled photon pair source utilizing an artificially-engineered metamaterial platform. This platform is based on a plasmonic metasurface that is strongly coupled to an epsilon-near-zero (ENZ) material. By precisely engineering resonances at both pump and signal/idler wavelengths, and leveraging the field enhancement provided by the ENZ effect, the photon pair generation efficiency of the 68-nm-thick metasurface is significantly boosted. More notably, the ENZ metasurface platform facilitates versatile manipulation of the system's anisotropic second-order nonlinear susceptibility tensor, enabling direct control over the polarization states of the photon pairs, which leads to the generation of a polarization-entangled Bell state without the need for additional components. Our approach opens a new avenue for the simultaneous photon pair generation and quantum state engineering in a compact platform.

We study the reactive synthesis problem for distributed systems with an unbounded number of participants interacting with an uncontrollable environment. Executions of those systems are modeled by data words, and specifications are given as first-order logic formulas from a fragment we call prefix first-order logic that implements a limited kind of order. We show that this logic has nice properties that enable us to prove decidability of the synthesis problem.

Intensity modulators are fundamental components for integrated photonics. From near infrared to visible spectral ranges, they find applications in optical communication and quantum technologies. In particular, they are required for the control and manipulation of atomic systems such as atomic clocks and quantum computers. Typical integrated electro-optic modulators operating at these wavelengths show high bandwidth and low voltage operation, but their extinction ratios are moderate. Here we present an integrated thin-film lithium niobate electro-optic modulator operating in the C-band, which uses a subsequent periodically poled waveguide to convert the modulated signal from 1536 nm to 768 nm using second harmonic generation. We demonstrate that the upconverted signal retains the characteristics of the modulated input signal, reaching a measured high bandwidth of 40 GHz. Due to the nature of the nonlinear process, it exhibits, with respect to the fundamental signal, a doubled extinction ratio of 46 dB, which is the highest recorded for near-infrared light on this platform., Comment: 4 pages, 3 figures

Generating and interfering non-classical states of light is fundamental to optical quantum information science and technology. Quantum photonic integrated circuits provide one pathway towards scalability by combining nonlinear sources of non-classical light and programmable circuits in centimeter-scale devices. The key requirements for quantum applications include efficient generation of indistinguishable photon-pairs and high-visibility programmable quantum interference. Here, we demonstrate a lithium niobate-on-insulator (LNOI) integrated photonic circuit that generates a two-photon path-entangled state, and a programmable interferometer for quantum interference. We generate entangled photons with $\sim2.3\times10^8$ pairs/s/mW brightness and perform quantum interference experiments on the chip with $96.8\pm3.6\%$ visibility. LNOI is an emerging photonics technology that has revolutionized high-speed modulators and efficient frequency conversion. Our results provide a path towards large-scale integrated quantum photonics including efficient photon-pair generation and programmable circuits for applications such as boson sampling and quantum communications.

Second harmonic generation (SHG) is prohibited in centrosymmetric crystals such as silicon or germanium due to the presence of inversion symmetry. However, the structuring of such materials makes it possible to break the inversion symmetry, thus achieving generation of second-harmonic. Moreover, various symmetry properties of the resulting structure, such as chirality, also influence the SHG. In this work we investigate second harmonic generation from an array of nanohelices made of germanium. The intensity of the second harmonic displayed a remarkable enhancement of over 100 times compared to a non-structured Ge thin film, revealing the influence of interaction between nanohelices. In particular, nonlinear circular dichroism, characterized through the SHG anisotropy factor g, changed its sign not only with the helix handedness, but with its density as well. We believe that our discoveries will open up new paths for the development of nonlinear photonics based on metamaterials and metasurfaces made of centrosymmetric materials., Comment: 16 pages, 5 figures

We present details on a new measurement of the muon magnetic anomaly, $a_\mu = (g_\mu -2)/2$. The result is based on positive muon data taken at Fermilab's Muon Campus during the 2019 and 2020 accelerator runs. The measurement uses $3.1$ GeV$/c$ polarized muons stored in a $7.1$-m-radius storage ring with a $1.45$ T uniform magnetic field. The value of $ a_{\mu}$ is determined from the measured difference between the muon spin precession frequency and its cyclotron frequency. This difference is normalized to the strength of the magnetic field, measured using Nuclear Magnetic Resonance (NMR). The ratio is then corrected for small contributions from beam motion, beam dispersion, and transient magnetic fields. We measure $a_\mu = 116 592 057 (25) \times 10^{-11}$ (0.21 ppm). This is the world's most precise measurement of this quantity and represents a factor of $2.2$ improvement over our previous result based on the 2018 dataset. In combination, the two datasets yield $a_\mu(\text{FNAL}) = 116 592 055 (24) \times 10^{-11}$ (0.20 ppm). Combining this with the measurements from Brookhaven National Laboratory for both positive and negative muons, the new world average is $a_\mu$(exp) $ = 116 592 059 (22) \times 10^{-11}$ (0.19 ppm)., Comment: 48 pages, 29 figures; 4 pages of Supplement Material; version accepted for publication in Physical Review D

A non-conserving zero-range process with extensive creation, annihilation and hopping rates is subjected to local resetting. The model is formulated on a large, fully-connected network of states. The states are equipped with a (bounded) fitness level: particles are added to each state at a rate proportional to the fitness level of the state. Moreover, particles are annihilated at a constant rate, and hop at a fixed rate to a uniformly-drawn state in the network. This model has been interpreted in terms of population dynamics: the fitness is the reproductive fitness in a haploid population, and the hopping process models mutation. It has also been interpreted as a model of network growth with a fixed set of nodes (in which particles occupying a state are interpreted as links pointing to this state). In the absence of resetting, the model is known to reach a steady state, which in a certain limit may exhibit a condensate at maximum fitness. If the model is subjected to global resetting by annihilating all particles at Poisson-distributed times, there is no condensation in the steady state. If the system is subjected to local resetting, the occupation numbers of each state are reset to zero at independent random times. These times are distributed according to a Poisson process whose rate (the resetting rate) depends on the fitness. We derive the evolution equation satisfied by the probability law of the occupation numbers. We calculate the average occupation numbers in the steady state. The existence of a condensate is found to depend on the local behavior of the resetting rate at maximum fitness: if the resetting rate vanishes at least linearly at high fitness, a condensate appears at maximum fitness in the limit where the sum of the annihilation and hopping rates is equal to the maximum fitness., Comment: 26 pages, 1 figure; v2: 27 pages, some clarifications, typos corrected, references added; v3: 28 pages, some more clarifications and corrections, references added