Quantum Force Research Articles

Fermionic Casimir energy in Horava–Lifshitz scenario

In this work, we investigate the violation of Lorentz symmetry through the Casimir effect, one of the most intriguing phenomena in modern physics. The Casimir effect, which represents a macroscopic quantum force between two neutral conducting surfaces, is widely regarded as a triumph of Quantum Field Theory. In this study, we present new results for the Casimir effect, focusing on the contribution of mass associated with fermionic quantum fields confined between two large parallel plates, in the context of Lorentz symmetry violation within the Horava–Lifshitz formalism. To calculate the Casimir energy and pressure, we impose a MIT bag boundary condition on the two plates, compatible with the higher-order derivative term in the modified Dirac equation. Our results reveal a strong influence of Lorentz violation on the Casimir effect. We observe that the Casimir energy is significantly affected, both in intensity and sign, potentially resulting in a repulsive or attractive force between the plates, depending on the critical exponent associated with the Horava–Lifshitz formalism.

Effect of spin quantum force on lower and upper hybrid waves’ instability under the influence of an electron beam in a magnetized semiconductor plasma

Effect of spin quantum force on lower and upper hybrid waves’ instability under the influence of an electron beam in a magnetized semiconductor plasma

Adjusting the Energy Profile for CH-O Interactions Leads to Improved Stability of RNA Stem-Loop Structures in MD Simulations.

The role of ribonucleic acid (RNA) in biology continues to grow, but insight into important aspects of RNA behavior is lacking, such as dynamic structural ensembles in different environments, how flexibility is coupled to function, and how function might be modulated by small molecule binding. In the case of proteins, much progress in these areas has been made by complementing experiments with atomistic simulations, but RNA simulation methods and force fields are less mature. It remains challenging to generate stable RNA simulations, even for small systems where well-defined, thermostable structures have been established by experiments. Many different aspects of RNA energetics have been adjusted in force fields, seeking improvements that are transferable across a variety of RNA structural motifs. In this work, the role of weak CH···O interactions is explored, which are ubiquitous in RNA structure but have received less attention in RNA force field development. By comparing data extracted from high-resolution RNA crystal structures to energy profiles from quantum mechanics and force field calculations, it is shown that CH···O interactions are overly repulsive in the widely used Amber RNA force fields. A simple, targeted adjustment of CH···O repulsion that leaves the remainder of the force field unchanged was developed. Then, the standard and modified force fields were tested using molecular dynamics (MD) simulations with explicit water and salt, amassing over 300 μs of data for multiple RNA systems containing important features such as the presence of loops, base stacking interactions as well as canonical and noncanonical base pairing. In this work and others, standard force fields lead to reproducible unfolding of the NMR-based structures. Including a targeted CH···O adjustment in an otherwise identical protocol dramatically improves the outcome, leading to stable simulations for all RNA systems tested.

The quantum transition of the two-dimensional Ising spin glass

Quantum annealers are commercial devices that aim to solve very hard computational problems1, typically those involving spin glasses2,3. Just as in metallurgic annealing, in which a ferrous metal is slowly cooled4, quantum annealers seek good solutions by slowly removing the transverse magnetic field at the lowest possible temperature. Removing the field diminishes the quantum fluctuations but forces the system to traverse the critical point that separates the disordered phase (at large fields) from the spin-glass phase (at small fields). A full understanding of this phase transition is still missing. A debated, crucial question regards the closing of the energy gap separating the ground state from the first excited state. All hopes of achieving an exponential speed-up, compared to classical computers, rest on the assumption that the gap will close algebraically with the number of spins5–9. However, renormalization group calculations predict instead that there is an infinite-randomness fixed point10. Here we solve this debate through extreme-scale numerical simulations, finding that both parties have grasped parts of the truth. Although the closing of the gap at the critical point is indeed super-algebraic, it remains algebraic if one restricts the symmetry of possible excitations. As this symmetry restriction is experimentally achievable (at least nominally), there is still hope for the quantum annealing paradigm11–13.

Quantum force sensing by digital twinning of atomic Bose-Einstein condensates

High sensitivity detection plays a vital role in science discoveries and technological applications. While intriguing methods utilizing collective many-body correlations and quantum entanglements have been developed in physics to enhance sensitivity, their practical implementation remains challenging due to rigorous technological requirements. Here, we propose an entirely data-driven approach that harnesses the capabilities of machine learning, to significantly augment weak-signal detection sensitivity. In an atomic force sensor, our method combines a digital replica of force-free data with anomaly detection technique, devoid of any prior knowledge about the physical system or assumptions regarding the sensing process. Our findings demonstrate a significant advancement in sensitivity, achieving an order of magnitude improvement over conventional protocols in detecting a weak force of approximately 10−25N. The resulting sensitivity reaches 1.7(4)×10−25N/Hz\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.7(4)\ imes 1{0}^{-25}\\,{{{{{{{\\rm{N}}}}}}}}/\\sqrt{{{{{{{{\\rm{Hz}}}}}}}}}$$\\end{document}. Our machine learning-based signal processing approach does not rely on system-specific details or processed signals, rendering it highly applicable to sensing technologies across various domains.

Quantum–classical correspondence in spin–boson equilibrium states at arbitrary coupling

The equilibrium properties of nanoscale systems can deviate significantly from standard thermodynamics due to their coupling to an environment. We investigate this here for the θ-angled spin–boson model, where we first derive a compact and general form of the classical equilibrium state including environmental corrections to all orders. Secondly, for the quantum spin–boson model we prove, by carefully taking a large spin limit, that Bohr’s quantum–classical correspondence persists at all coupling strengths. This shows, for the first time, the validity of the quantum–classical correspondence for an open system and gives insight into the regimes where the quantum system is well-approximated by a classical one. Finally, we provide the first classification of the coupling parameter regimes for the spin–boson model, from weak to ultrastrong, both for the quantum case and the classical setting. Our results shed light on the interplay of quantum and mean force corrections in equilibrium states of the spin–boson model, and will help draw the quantum to classical boundary in a range of fields, such as magnetism and exciton dynamics.

Casimir Forces in CFT with Defects and Boundaries

We investigate the quantum forces occurring between the defects and/or boundaries of a conformal field theory (CFT). We propose to model imperfect defects and boundaries as localized relevant double-trace operators that deform the CFT. Our focus is on pointlike and codimension-one planar defects. In the case of two parallel membranes, we point out that the CFT 2-point function tends to get confined and develops a tower of resonances with a constant decay rate when the operator dimension approaches the free field dimension. Using a functional formalism, we compute the quantum forces induced by the CFT between a variety of configurations of pointlike defects, infinite plates and membranes. Consistency arguments imply that these quantum forces are attractive at any distance. Forces of the Casimir–Polder type appear in the UV (ultraviolet), while forces of the Casimir type appear in the IR (infrared), in which case the CFT gets repelled from the defects. Most of the forces behave as a non-integer power of the separation, controlled by the dimension of the double-trace deformation. In the Casimir regime of the membrane–membrane configuration, the quantum pressure behaves universally as 1/ℓd; however, information about the double-trace nature of the defects still remains encoded in the strength of the pressure.

Synthesis, NMR, FT-IR, FT-Raman spectra and thermal studies of Choline bis(trifluoromethylsulfonyl)imide ionic liquid combined with DFT calculations

In an environmentally friendly manner, the reaction of choline chloride ([CHOL+][(Cl−]) with lithium bis(trifluoromethanesulfonyl)imide ([Li+][(CF3SO2)2N−]) in water leads to the formation of the ionic liquid(IL)choline bis(trifluoromethanesulfonyl)imide ([CHOL+][(CF3SO2)2N−]).The ionic liquid IL have been characterized by using1H, 13C and, 19F-NMR, FT-IR and FT-Raman spectroscopies. The experimental spectra have been combined with B3LYP/6–311++G** calculations to obtain complete assignments of vibrational spectra of IL and its cation by using the scaled mechanical quantum force field (SQMFF) methodology and the Molvib program. Here, we reported the 102 vibration modes of IL and the 36 of cation together with the scaled force constants for both species. The predicted structure shows the formation of the S-O···H interaction in agreement with experiments. Very good correlations evidence the comparisons among the experimental and theoretical NMR, FT-IR and FT-Raman spectra. The existence of the strong S-O···H interaction and other weak H bonds interactions are supported by NBO and AIM calculations. The analyses of gap values suggest a higher reactivity of IL in gas phase and a higher stability in aqueous solution. The comparison of this IL with [C8DABCO+][(CF3SO2)2N−] reveal that the [C8DABCO+] cation increases the reactivity of latter IL in solution. Besides a detailed characterization of its thermal (TGA/DSC) is presented. Investigation of the thermal properties demonstrated that the investigated IL can be classified as an ionic liquid, as the melting temperature is near room temperature. A glass transition and a cold crystallization were revealed at -75 and -26 °C.

Investigation of thermal stress effects on subthreshold conduction in nanoscale p-FinFET from Multiphysics perspective

The rising temperature due to a self-heating or thermal environment not only degrades the subthreshold performance but also intensifies thermal stress, posing a severe challenge to device performance and reliability design. The thermal stress effects on the ON-state performance of the p-type fin field-effect transistor were previously studied. However, as far as we know, how thermal stress affects its subthreshold conduction remains unclear, which is studied in this manuscript. The impact of thermal stress due to the self-heating of adjacent devices on subthreshold conduction is investigated by solving the quantum transport, thermal conduction, and force balance equations for ballistic transport and dissipative transport with phonon scattering. Then, the thermal stress effects at different ambient temperatures are further discussed and analyzed. The simulation results show that the OFF-state leakage current can be reduced by thermal stress, even up to 9.28% for the (110)/[001] device operating at an ambient temperature of 550 K, and its reduction is the comprehensive result of the thermal stress effects on the band structure, potential profile, carrier distribution, and source-to-drain tunneling. In addition, the thermal stress has no significant effects on subthreshold swing although it can change the magnitude of the subthreshold current. Moreover, the effect of thermal stress on subthreshold conduction is highly dependent on the thermal environment of the device and the crystal orientation of the channel semiconductor material.

The electromagnetic field’s quantum nature and spin

The interaction of the electron (charge) with the electromagnetic field is investigated using the minimum coupling prescription, in which the electron’s spin appears in the Dirac and Pauli–Schrödinger equations. However, we analyze the use of this approach in Maxwell’s equations and the repercussions here. The application of this prescription resulted in novel electrodynamics associated with spin. The complex Maxwell’s equations are discovered to describe a massless electromagnetic field governed by the Dirac equation interacting with a particle with a double charge whose wavefunction is the electromagnetic field’s energy density. The conservation equation for electromagnetic field helicity (spin) is obtained directly from the new electrodynamics. We demonstrated that the quantization of the electromagnetic field (Maxwell’s equations) interacting with a photon field results in the electromagnetic field’s quantization. The energy density of the electromagnetic field is shown to fulfill a massless Dirac equation. This indicates the material nature of the electromagnetic field (photon). As a result, the electromagnetic spin charge and current densities are determined. We obtained the Josephson energy–current relationship from the spin current produced by an electromagnetic field. A quantum nonlinear Ohm’s law is developed. Quantum power and force associated with the quantum nature of the electromagnetic field are proposed.

A first principles derivation of energy-conserving momentum jumps in surface hopping simulations.

The fewest switches surface hopping (FSSH) method proposed by Tully in 1990 [Tully, J. Chem. Phys. 93, 1061 (1990)]-along with its many later variations-forms the basis for most practical simulations of molecular dynamics with electronic transitions in realistic systems. Despite its popularity, a rigorous formal derivation of the algorithm has yet to be achieved. In this paper, we derive the energy-conserving momentum jumps employed by FSSH from the perspective of quantum trajectory surface hopping (QTSH) [Martens, J. Phys. Chem. A 123, 1110 (2019)]. In the limit of localized nonadiabatic transitions, simple mathematical and physical arguments allow the FSSH algorithm to be derived from first principles. For general processes, the quantum forces characterizing the QTSH method provide accurate results for nonadiabatic dynamics with rigorous energy conservation, at the ensemble level, within the consistency of the underlying stochastic surface hopping without resorting to the artificial momentum rescaling of FSSH.

Quantum Metrology in the Noisy Intermediate‐Scale Quantum Era

AbstractQuantum metrology pursues the physical realization of higher‐precision measurements to physical quantities than the classically achievable limit by exploiting quantum features, such as entanglement and squeezing, as resources. It has potential applications in developing next‐generation frequency standards, magnetometers, radar, and navigation. However, the ubiquitous decoherence in the quantum world degrades the quantum resources and forces the precision back to or even worse than the classical limit, which is called the no‐go theorem of noisy quantum metrology and greatly hinders its applications. Therefore, how to realize the promised performance of quantum metrology in realistic noisy situations attracts much attention in recent years. The principle, categories, and applications of quantum metrology are reviewed. Special attention is paid to different quantum resources that can bring quantum superiority in enhancing sensitivity. Then, the no‐go theorem of noisy quantum metrology and its active control under different kinds of noise‐induced decoherence situations are introduced.

On tests of the quantum nature of gravitational interactions in presence of non-linear corrections to quantum mechanics

When two particles interact primarily through gravity and follow the laws of quantum mechanics, the generation of entanglement is considered a hallmark of the quantum nature of the gravitational interaction. However, we demonstrate that entanglement dynamics can also occur in the presence of a weak quantum interaction and non-linear corrections to local quantum mechanics, even if the gravitational interaction is classical or absent at short distances. This highlights the importance of going beyond entanglement detection to conclusively test the quantum character of gravity, and it requires a thorough examination of the strength of other quantum forces and potential non-linear corrections to quantum mechanics in the realm of large masses.

Properties of Hermite–Gaussian beams via the quantum potential

In this work we compute, via the quantum potential approach, the Hamiltonian system determined by Hermite–Gaussian beams. Then we show that the integral curves of the Poynting vector, exact optics energy trajectories, conform to a subset of solutions to the corresponding Hamilton equations lying on hyperboloidal surfaces. The geometrical light rays associated with these beams are given by the tangent lines to the integral curves of the Poynting vector at the zeroes of the quantum potential, and the caustic region coincides with the zeroes of quantum potential and quantum force. One of the main contributions of this work is to present the relationship between the physical phase kΦ, the geometrical-optics phase kΦ G , and the quantum potential QHG in the Hermite–Gaussian beams. Furthermore, note that for any solution to the paraxial wave equation in free space, the tangent lines to the integral curves of the Poynting vector that correspond to the geometric light rays are those that pass through the points where the region determined by zeroes of the quantum potential is tangent to the geometrical caustic determined by the geometric light rays.

Classicality of single quantum particles in curved spacetime through the hydrodynamical reformulation of quantum mechanics

Single-particle physics focuses on the behavior and properties of individual particles, providing insight into the building blocks of quantum mechanics. The theory of quantum particles in curved spacetime has been getting attention in recent years for gaining a deeper understanding of the relationship between quantum mechanics and general relativity, the two pillars of modern physics. In this note, we show how single quantum particles can obtain classical behavior. In particular, for a quantum particle that follows the Klein–Gordon equation in curved spacetime in the presence of external potential, we show that when the amplitude of its wavefunction follows the Klein–Gordon equation with an arbitrary effective mass, empty curved spacetime, but with the same curved geometry appearing in the original Klein–Gordon equation of the wavefunction, the quantum force of the particle vanishes, providing a classical description of the quantum particle using a system of coupled classical equations. The result relies on the Madelung hydrodynamical reformulation of quantum mechanics. Understanding how quantum systems transition to a classical behavior is a long-standing challenge in mesoscopic physics, with important implications for a wide range of applications, from quantum computing to condensed matter physics. The result provides a fresh perspective on the relations between quantum and classical effects in curved spacetime.

Stability analysis of linear ion waves leading to nonlinear shock and soliton structures in a dense quantum plasma with strongly coupled ions and degenerate electrons

In a quantum plasma with strongly coupled ions and Fermi degenerate electron fluids, features of low frequency wave dispersion and nonlinear electrostatic structure formation are explored. Dynamics of strongly coupled ions is considered through a generalized momentum balance equation over the visco-elastic relaxation time for ion correlations and viscosity of ion fluid through shear. Quantum forces associated with degenerate electron fluid include many-particle effect of exchange-correlations, quantum statistical-pressure and quantum recoil effect. The system supports dispersive shock and soliton structures regulated by the Korteweg-de Vries Burger equation and modified-Korteweg-de Varies equation, respectively which are derived and solved analytically. Only monotonic shock structures are observed for a given value of the Burger factorμ. For solitary structures, the amplitude and width depend upon quantum dispersive effects of electrons.

Scalar-mediated quantum forces between macroscopic bodies and interferometry

We study the quantum force between classical objects mediated by massive scalar fields bilinearly coupled to matter. The existence of such fields is motivated by dark matter, dark energy, and by the possibility of a hidden sector beyond the Standard Model. We introduce the quantum work felt by an arbitrary (either rigid or deformable) classical body in the presence of the scalar and show that it is finite upon requiring conservation of matter. As an example, we explicitly show that the quantum pressure inside a Dirichlet sphere is finite — up to renormalizable divergences. With this method we compute the scalar-induced quantum force in simple planar geometries. In plane-point geometry we show how to compute the contribution of the quantum force to the phase shift observable in atom interferometers. We show that atom interferometry is likely to become a competitive search method for light particles bilinearly coupled to matter, provided that the interferometer arms have lengths below ∼10 cm.

Properties of the Airy beam by means of the quantum potential approach

By using the quantum potential approach, we show that: the Airy beam determines a Hamiltonian system with one degree of freedom for a particle of mass m = 1 evolving under the influence of a quantum potential, such that its associated quantum force is constant, the integral curves of the Poynting vector are parabolic ones and turn out to be a subset of solutions of the corresponding Hamilton equations, the geometrical light rays associated with the Airy beam, are given by the tangent lines to the zeroes of the quantum potential, and the caustic coincides with the zeros of the quantum potential. Furthermore, we present a derivation of the Airy beam from the quantum potential equations by assuming that the quantum force is constant.

On the origin of force sensitivity in tests of quantum gravity with delocalised mechanical systems

The detection of the quantum nature of gravity in the low-energy limit hinges on achieving an unprecedented degree of force sensitivity with mechanical systems. Against this background we explore the relationship between the sensitivity of mechanical systems to external forces and properties of the quantum states they are prepared in. We establish that the main determinant of the force sensitivity in pure quantum states is their spatial delocalisation and we link the force sensitivity to the rate at which two mechanical systems become entangled under a quantum force. We exemplify this at the hand of two commonly considered configurations. One that involves gravitationally interacting objects prepared in non-Gaussian states such as Schrödinger-cat states, where the generation of entanglement is typically ascribed to the accumulation of a dynamical phase between components in superposition experiencing varying gravitational potentials. The other prepares particles in Gaussian states that are strongly squeezed in momentum and delocalised in position where entanglement generation is attributed to accelerations. We offer a unified description of these two arrangements using the phase-space representation of the interacting particles, and link their entangling rate to their force sensitivity, showing that both configurations get entangled at the same rate provided that they are equally delocalised in space. Our description in phase space and the established relation between force sensitivity and entanglement sheds light on the intricacies of why the equivalence between these two configurations holds, something that is not always evident in the literature, due to the distinct physical and analytical methods employed to study each of them. Notably, our findings demonstrate that while the conventional computation of entanglement via the dynamical phase remains accurate for systems in Schrödinger-cat states, it may yield erroneous estimations for systems prepared in squeezed cat states.

Trajectory of a massive localized wave function in a curved spacetime geometry

Propagation of a localised wave function of a massive scalar field is investigated in its rest frame. The complete orthogonal Hermite-Gauss basis is presented, and the Gouy phase and Rayleigh scale notions are adapted. The leading and sub-leading gravitational corrections to a localised quantum wave function propagating in a general curved spacetime geometry are calculated within the Fermi coordinates around the time-like geodesic of its rest frame, and cross-talk coefficients among the modes are derived. It is observed that spherically symmetric modes propagate along the geodesic. However, non-spherical modes are found to experience a mode-dependent residual quantum force at the sub-leading order. It is shown that the residual force does not generate an escape velocity for in-falling wave functions but leads to a mode-dependent deflection angle for the scattered ones.