arXiv Physics @arxiv_physics@qoto.org

GaN defect-based quantum emitters are promising candidates for quantum information technologies, although their underlying nature remains elusive. In this work, we present results on the temperature-dependent emission polarization of GaN defect single-photon emitters integrated with solid immersion lenses. The photoluminescence (PL) remains linearly polarized over the temperature range of 10K to 300K, with a slight rotation in the polarization direction observed at intermediate temperatures. Possible mechanisms responsible for this behavior are analyzed, and a roadmap for future research is outlined.

Humanity must solve the problems that threaten human health during long-term space flight. An unexpected solution is suggested by an experiment on people staying in a closed life support system model, conducted more than 50 years ago in Krasnoyarsk. The high level of carbon dioxide established after the start of the experiment changed the metabolism of the inhabitants. We present the interpretation of the results of the Krasnoyarsk experiment through understanding the effect of hypercapnia on metabolism for the first time in this work. Hypercapnia suppressed the possibility of developing metabolic acidosis and activated fat oxidation. The change in the respiratory quotient caused by hypercapnia stabilized the composition of the gas mixture in the closed life support system and ensured the stability of the system.

While solid-state protein junctions have shown efficient electron transport over lengths that surpass those of conventional organic semiconducting systems, interfacial or contact effects may obscure the intrinsic protein charge transport properties. Therefore, contact resistance (RC) effects need to be quantified and then minimized, which poses a problem if 4-probe geometries cannot be used. Here we show how RC can be extracted quantitatively from the measured junction resistance (RP) by using the extrapolated zero-length resistance (RZLR) and short-circuit resistance (RS). We used AC (impedance spectroscopy) and DC measurements to examine charge transport in junctions of human serum albumin (HSA) and bacteriorhodopsin (bR) films with varying thicknesses. Three contact configurations, Si-Au, Au-EGaIn, and, in a micropore device (MpD), Au-Pd, were compared. While Si-Au and Au-EGaIn junctions exhibit substantial RC that we ascribe to interfacial oxides and electrostatic protein-electrode interactions, MpD effectively eliminates RC, enabling measuring the intrinsic electron transport across HSA and bR films. The exponential length dependence of RP shows a transport decay constant (beta) that varies with interfacial conditions, underscoring the role of contact engineering. By minimizing RC, exceptionally low beta values (0.7 to 1.1 per nm) are found, proving that, indeed, proteins can have outstanding charge transport efficiencies.

This paper introduces results for the characteristically near Stein-Weiss groups inherent in vector fields in the complex plane $\mathbb{C}$. Near groups are discerned in the context of characteristic nearness approximation spaces (cNASs). A characteristic of a Stein-Weiss group is a holomorphic mapping $φ:\mathbb{R}\to\mathbb{C}$ defined by $φ(t)=e^{jt}$, which defines a vector field in the complex plane. All characteristic vectors emanate from the same fixed point in $\mathbb{C}$, namely, 0.

To overcome antimalarial drug resistance, carbohydrate derivatives as selective PfHT1 inhibitor have been suggested in recent experimental work with orthosteric and allosteric dual binding pockets. Inspired by this promising therapeutic strategy, herein, molecular dynamics simulations are performed to investigate the molecular determinants of co-administration on orthosteric and allosteric inhibitors targeting PfHT1. Our binding free energy analysis capture the essential trend of inhibitor binding affinity to protein from published experimental IC50 data in three sets of distinct characteristics. In particular, we rank the contribution of key residues as binding sites which categorized into three groups based on linker length, size of tail group, and sugar moiety of inhibitors. The pivotal roles of these key residues are further validated by mutant analysis where mutated to nonpolar alanine leading to reduced affinities to different degrees. The exception was fructose derivative, which exhibited a significant enhanced affinity to mutation on orthosteric sites due to strong changed binding poses. This study may provide useful information for optimized design of precision medicine to circumvent drug-resistant Plasmodium parasites with high efficacy.

In spite of the innumerable attempts to resolve the quantum measurement problem, almost since its beginning a century ago, a satisfactory solution still remains elusive. However, after the advent of quantum entanglement leading to environmental decoherence studies, a substantial leap forward has been achieved by Zurek and his associates. Their investigation has led to the existence of sturdy pointer states that survive decoherence leading to classicality although still remaining entangled with the environment and the apparatus states. But in order to avoid the inexplicable collapse postulate, Zurek invokes Everett's many world conjecture, which is not accepted by many experts. In this article, we present the observation of entanglement sudden death (ESD), demonstrating that disentanglement of the pointer states is caused by the quantum fluctuations of the electromagnetic field. We reveal that the decoherence between the pointer states and the environment is consistent with unitary evolution when the vacuum modes are included in the calculation, in analogy to the unitary evolution of the whole system in the spontaneous emission process. However, the ultimate state of the system is still subject to the totally unpredictable nature of individual quantum fluctuations, causing the stochastic appearance of an arbitrary classical state in von Neumann's collapse axiom even when the entire system evolves unitarily. Therefore, we suggest that an acceptable solution of the long standing measurement problem has finally been achieved.

We present a statistical simulation replicating the correlation observed in EPR coincidence experiments without needing non-local connectivity. We define spin coherence as a spin attribute that complements polarization by being anti-symmetric and generating helicity. Point particle spin becomes structured with two orthogonal magnetic moments, each with a spin of 1/2 these moments couple in free flight to create a spin-1 boson. Depending on its orientation in the field, when it encounters a filter, it either decouples into two independent fermion spins of 1/2 or it remains a boson and precedes without decoupling. The only variable in this study is the angle that orients a spin on the Bloch sphere, first identified in the 1920s. There are no hidden variables. The new features introduced in this work result from changing the spin symmetry from SU(2) to the quaternion group which complexifies the Dirac field. The transition from a free-flight boson to a measured fermion causes the observed violation of Bell's Inequalities and resolves the EPR paradox.

We propose a modular debiasing technique for discrete random sources, addressing the fundamental challenge of extracting high-quality randomness from imperfect physical processes. The method involves summing the outcomes of multiple independent trials from a biased source and reducing the sum modulo the number of possible outcomes, $m$. We provide a rigorous theoretical framework demonstrating that this simple operation guarantees the convergence of the output distribution to the ideal uniform distribution over $\{0, 1, \dots, m-1\}$. A key result is the method's remarkable robustness: convergence is proven for any initial bias (provided all outcomes have non-zero probability) and, critically, is maintained even under non-stationary conditions or time-dependent noise. Analytical bounds show an exponential rate of convergence, which is empirically validated by numerical simulations. This technique's simplicity, theoretical guarantees, robustness, and data efficiency make it particularly well-suited for practical implementation in quantum settings, such as spatial photon-detection-based Quantum Random Number Generators, enabling efficient extraction of high-quality randomness from experimentally imperfect sources.

Modern fundamental physics poses new questions for philosophy, which, as it seems to us, have not yet received appropriate attention from philosophers of science. This paper formulates a number of such questions in order to present them to the attention, first of all, of professional philosophers. A rough list of the main themes is as follows: 1) Cosmic variance problem and the meaning of theoretical cosmology; 2) Epistemological status of the concept of Multiverse in cosmology; 3) The operational status of quantum macrostates and the relation of this problem to cosmology; 4) The meaning of the physical reality in the ``final theory''; 5) Criticism of the string theory in the relation with the item 4 above.

In this paper, fundamental shear-horizontal SH0 mode Leaky Surface Acoustic Wave (LSAW) resonators on X-cut lithium niobate leveraging dense and robust electrodes such as gold and tungsten are demonstrated for extreme temperature operation in harsh environments. A novel post-processing approach based on in-band spurious mode tracking is introduced to enable reliable characterization under extreme parasitic loading during testing. Devices exhibit stable performance throughout multiple thermal cycles up to 1000 $^\circ$C, with an extrapolated electromechanical coupling coefficient kt2 = 25% and loaded quality factor Qp = 12 at 1000 $^\circ$C for tungsten devices, and kt2 = 17%, Qp = 100 at 900 $^\circ$C for gold devices.

This paper offers educational insight into the Dirac equation, examining its historical context and contrasting it with the earlier Schrödinger and Klein-Gordon (KG) equations. The comparison highlights their Lorentz transformation symmetry and potential probabilistic interpretations. We explicitly solve the free-particle dynamics in Dirac's model, revealing the emergence of negative-energy solutions. This discussion examines the Dirac Sea Hypothesis and explores the solutions' inherent helicity. Additionally, we demonstrate how the Dirac equation accounts for spin and derive the Pauli equation in the non-relativistic limit. The Foldy-Wouthuysen transformation reveals how the equation incorporates spin-orbit interaction and other relativistic effects, ultimately leading to the fine structure of hydrogen. A section on relativistic covariant notation is included to emphasize the invariance of the Dirac equation, along with more refined formulations of both the KG and Dirac equations. Designed for undergraduate students interested in the Dirac equation, this resource provides a historical perspective without being purely theoretical. Our approach underscores the significance of a pedagogical method that combines historical and comparative elements to profoundly understand the role of the Dirac equation in modern physics.

In this paper, we explore power law solution of FLRW universe model that is associated with a variable cosmological term $Λ(t)$ as a linear function of $\frac{\ddot{a}}{a}, (\frac{\dot{a}}{a})^2$ and $ρ$. The model parameters were estimated on the basis of the four data sets: The Hubble 46 data, the Union 2.1 compilation data sets comprising of distance modulus of 580 SNIa supernovae at different redshifts, the Pantheon data set which contains Apparent magnitudes of 1048 SNIa supernovae at various redshifts and finally BAO data set of volume averaged distances at 5 redshifts. We employ the conventional Bayesian methodology to analyze the observational data and also the Markov Chain Monte Carlo (MCMC) technique to derive the posterior distributions of the parameters. The best fit values of Hubble parameter $H_0$ as per the four data sets are found as $61.53^{+0.453}_{-0.456}$, $ 69.270^{+0.229}_{-0.228}$, $78.116^ {+0.480}_{-0.479}$, and $ 71.318 ^{+2.473}_{-2.283}$ respectively. Off late the present value of Hubble parameters $H_0$ were empirically given as 73 and 67.7 (km/s)/Mpc using distance ladder techniques and measurements of the cosmic microwave background. The OHD+BAO+Union and ~OHD+Pan+BAO+Union combined data sets provide the best fit Hubble parameter value $H_0$ as $67.427^{+0.197}_{-0.199}$ and $74.997^{+0.143}_{-0.145}$ respectively. The various geometrical and physical properties of the model were also investigated and were found in good agreements with observations.

According to the Krizek-Somer hypothesis [New Astron. 17, 1 (2012); Grav. Cosmol. 21, 59 (2015)], a biological evolution of the Earth is possible only at certain values of the Hubble parameter, because the increasing luminosity of the Sun should be compensated by the increasing orbital radius of the Earth due to the local Hubble expansion, thereby keeping the Earth's surface temperature sufficiently stable. Here, we examine this hypothesis in light of the recent data on the surface temperature on the early Earth, thereby imposing a few constraints on the admissible values of the local Hubble parameter. As follows from our analysis, the Krizek-Somer mechanism might be a valuable tool to resolve the important geophysical and paleontological puzzles, but the particular value of the local Hubble parameter is substantially affected by the current uncertainties in our knowledge about the temperature and other properties of the early Earth.

The Amaterasu\footnote{named for a sun goddess in Japanese mythology.} cosmic ray particle announced in November 2023 is extraordinary. Its direction points back to the Local Void which contains no galaxies or known source. It is possible to show that the direction could not have been bent significantly by magnetic fields within the Milky Way. This collection of facts constitutes a paradox. In the present paper, we offer a resolution within the Electromagnetic Accelerating Universe (EAU) model in which a central rôle is played by charged Primordial Extremely Massive Black Holes (PEMBHs) whose Coulomb interactions underly accelerating expansion. Because structure formation of PEMBHs is electromagnetic while that for galaxies is gravitational, it is reasonable to expect PEMBHs inside the Local Void. We provide an example where the cosmic ray primary is an antiproton and present it as supportiing evidence for the EAU model.

The series of meetings ``What comes beyond the Standard Models'' started in 1998 with the idea of organizing a workshop where participants would spend most of the time in discussions, confronting different approaches and ideas. The idea was successful and has developed into an annual workshop, which is taking place every year since 1998. Very open-minded and fruitful discussions have become the trademark of our workshops, producing several published works. We discussed a lot of concepts which could help to understand our universe from the level of the second quantized elementary fermion and boson fields up to the level of the born of our universe.

Many papers on modified gravity theories (MGTs), and metric-affine geometry have been published. New classes of black hole (BH), wormhole (WH), and cosmological solutions involving nonmetricity and torsion fields were constructed. Nevertheless, the fundamental problems of formulating nonmetric Einstein-Dirac-Maxwell (EDM), equations, and studying important nonmetric gravitational, electromagnetic and fermion effects have not been solved in MGTs. The main goal of this work is to elaborate on a model of nonmetric EDM theory as a generalisation of f(Q) gravity. We develop our anholonomic frame and connection deformation method, which allows us to decouple in a general form and integrate nonmetric gravitational and matter field equations. New classes of generated quasi-stationary solutions are defined by effective sources with Dirac and Maxwell fields, nonmetricity and torsion fields, and generating functions depending, in general, on all space-time coordinates. For respective nonholonomic parameterisations, such solutions describe nonmetric EDM deformations of BH and cosmological metrics. Variants of nonmetric BH, WH and toroid solutions with locally anisotropic polarisations of the gravitational vacuum, masses of fermions, and effective electromagnetic sources are constructed and analysed. Such nonmetric deformed physical objects can't be characterised in the framework of the Bekenstein-Hawking paradigm if certain effective horizon/ holographic configurations are not involved. We show how to define and compute other types of nonmetric geometric thermodynamic variables using generalisations of the concept of G. Perelman W-entropy.

In this paper I address the most common objections to the claim that Schrodinger was right in 1926: the wavefunction provides the correct, and complete, description of atomic phenomena. I suggest that the line of droplets in the Wilson cloud chamber, the click of the ``photon detector", and ``that dot on the screen" can all be explained within a context of wavefunction models and Schrodinger's-type equations, albeit nonlinear. No auxiliary hypotheses about point particles or probabilities are required. The random locations of the triggered ``particle detectors" can be explained by ``chaos" (meaning sensitive dependence on initial conditions). Even Born's ad hoc invocation of probabilities may be justifiable in certain circumstances. As an illustration, I present simulations from a (toy) wavefunction ``particle-detectors" model.

I show here that if we construct D-branes not in the form of infinite superpositions of string modes, in order to satisfy the technical condition of coherence by means of eigenstates of annihilation operators, but instead insist on an approximate but much more physical and practical definition based on phase coherence, we obtain finite (and hence realistic) superpositions of string modes that would form realistic D-branes that would encode (at least as a semiclassical approximation) various quantum properties. Re-deriving the AdS/CFT duality by starting in the pre-Maldacena limit from such realistic D-branes would lead to quantum properties on the AdS side of the duality. Causal structures can be modified in various many particle systems, including strings, D-branes, photons, or spins, however, there is a distinction between the emergence of an effective causal structure in the inner degrees of freedom of a material, in the form of a correlation generated effective metric for example in a spin liquid system, and the emergence of a causal structure in an open propagating system by using classical light. I will show how an Uhlmann gauge construction would add stability to a modified causal structure that would retain the shape of a closed causal loop. Various other ideas related to the quantum origin of the string length are also discussed and an analogy of the emergence of string length from quantum correlations with the emergence of wavelength of an electromagnetic wave from coherence conditions of photon modes is presented.

Achieving compact and efficient visible laser sources is crucial for a wide range of applications. However traditional semiconductor laser technology faces difficulties in producing high-brightness green light, leaving a green gap in wavelength coverage. Second-harmonic generation (SHG) offers a promising alternative by converting near-infrared sources to visible wavelengths with high efficiency and spectral purity. Here, we demonstrate efficient and tunable SHG within the green spectrum using a high-Q Si3N4 microresonator. A space-charge grating induced by the photogalvanic effect realizes reconfigurable grating numbers and flexible wavelength tuning. Additionally, grating formation dynamics and competition is observed. These findings underscore the potential of silicon nitride as a robust, integrative platform for on-chip, tunable green light sources.