A2 Term Research Articles

First lattice QCD calculation of J/ψ semileptonic decay containing D and Ds particles

We perform the first lattice calculation on the semileptonic decay of J/ψ using the (2+1)-flavor Wilson-clover gauge ensembles generated by CLQCD collaboration. Three gauge ensembles with different lattice spacings, from 0.0519 to 0.1053 fm, and pion masses, mπ∼300 MeV, are utilized. After a naive continuum extrapolation using three lattice spacings, we obtain Br(J/ψ→Dseνe)=1.90(6)(5)Vcs×10−10 and Br(J/ψ→Deνe)=1.21(6)(9)Vcd×10−11, where the first errors are statistical, and the second come from the uncertainties of Cabibbo-Kobayashi-Maskawa matrix element Vcs(d). The ratios of the branching fractions between lepton μ and e are also calculated as RJ/ψ(Ds)=0.97002(8) and RJ/ψ(D)=0.97423(15) after performing a continuum limit including only a2 term. The ratios provide necessary theoretical support for the future experimental test of lepton flavor universality. Published by the American Physical Society 2024

Computation of the complex energy shift of decaying states in intense laser fields

We present a specific calculation concerning laser-assisted decaying systems with non-Hermitian spectral calculations merged with the (t,t’)-formalism to estimate the possible intense laser-field-induced corrections to the lifetime of quasi-stationary states. The perturbed complex energy shift caused by the external vector potential which represents the linearly and circularly polarized laser field is calculated in details. This wavefunction-centered method implies the unsuitability of the radiation gauge and length gauge when quasi-stationary states are considered and described within the framework of non-hermitian quantum mechanics since in this case the A2 term cannot be transformed out.

Optical-cavity mode squeezing by free electrons.

The generation of nonclassical light states bears a paramount importance in quantum optics and is largely relying on the interaction between intense laser pulses and nonlinear media. Recently, electron beams, such as those used in ultrafast electron microscopy to retrieve information from a specimen, have been proposed as a tool to manipulate both bright and dark confined optical excitations, inducing semiclassical states of light that range from coherent to thermal mixtures. Here, we show that the ponderomotive contribution to the electron-cavity interaction, which we argue to be significant for low-energy electrons subject to strongly confined near-fields, can actually create a more general set of optical states, including coherent and squeezed states. The postinteraction electron spectrum further reveals signatures of the nontrivial role played by A 2 terms in the light-matter coupling Hamiltonian, particularly when the cavity is previously excited by either chaotic or coherent illumination. Our work introduces a disruptive approach to the creation of nontrivial quantum cavity states for quantum information and optics applications, while it suggests unexplored possibilities for electron beam shaping.

Experimental quantum simulation of superradiant phase transition beyond no-go theorem via antisqueezing

The superradiant phase transition in thermal equilibrium is a fundamental concept bridging statistical physics and electrodynamics, which has never been observed in real physical systems since the first proposal in the 1970s. The existence of this phase transition in cavity quantum electrodynamics systems is still subject of ongoing debates due to the no-go theorem induced by the so-called A2 term. Moreover, experimental conditions to study this phase transition are hard to achieve with current accessible technology. Based on the platform of nuclear magnetic resonance, here we experimentally simulate the occurrence of an equilibrium superradiant phase transition beyond no-go theorem by introducing the antisqueezing effect. The mechanism relies on that the antisqueezing effect recovers the singularity of the ground state via exponentially enhancing the zero point fluctuation of system. The strongly entangled and squeezed Schrödinger cat states of spins are achieved experimentally in the superradiant phase, which may play an important role in fundamental tests of quantum theory and implementations of quantum metrology.

Fundamental Models in the Light–Matter Interaction: Quantum Phase Transitions and the Polaron Picture

AbstractThe light–matter interaction not only is ubiquitous in nature but also can be simulated in various artificial systems. Besides the tunability of artificial quantum systems, the experimental access to the ultra‐strong and even deep‐strong couplings has brought a regime with novel phenomenology. Theoretically the finding of the integrability for the quantum Rabi model (QRM) has attracted tremendous attention to the study of the QRM and its extensions which are fundamental models of the light–matter interaction. With the continuing enhancements of coupling strengths, a most fascinating phenomenon of these light–matter models is that they can exhibit few‐body quantum phase transitions (QPTs), while a full understanding of these QPTs is a challenge. The polaron picture is a method capable of analyzing these fundamental models in the entire coupling regime and extracting the essential physics behind the QPTs. A review of its extensive applications on the fundamental light–matter models is presented, with discussions on the phase diagrams and QPT‐related features. The universality of critical exponent of the anisotropic QRM as well as the possibility of QPTs in A2 terms are also addressed.

Entanglement and excited-state quantum phase transition in an extended Dicke model

We investigate the properties of entanglement and excited-state quantum phase transition (ESQPT) in a hybrid atom-optomechanical system in which an optomechanical quadratic interaction is introduced into a normal Dicke model. Interestingly, by preparing the ancillary mode in a coherent state, both the quantum entanglement and ESQPT can be realized in a relative weak-coupling condition. Moreover, the entanglement is immune to the A2 term, and a reversed trend of the entropy is obtained when the A2 term is included. Density of states (DoS) and Peres lattice are used to investigate ESQPTs. Compared to a normal Dicke model, the DoS enlarges exp(2rα) times if the ancillary mode is prepared in a coherent state. This work is an extension of the ground-state quantum phase transition, which may inspire further exploration of the quantum criticality in many-body systems.

Modified climate influence on rates development of spring barley in Ukraine

Materials of World statistics show that today climate change on the planet coincides with the period of the rise of food shortages in the world community. To assess the possible impact of climate change in Ukraine agro-climatic indicators used two scenarios: a "moderate" - A1B which provides a balance between all energy sources, and "hard" - A2, which provides for ne-uncertainty regarding the determining factors and is based on the use of cut - modeling concepts that are used are similar, assumptions regarding determinant factors. One of the simplest methods reflect possible changes in the climate regime any meteorological values are compared with past data, including se-sized perennial in the reference period. In this study, the baseline is set between 1986 and 2005 according to agro-climatic directory Ukraine. According to calculations by climate change scenarios A2 and A1B terms and sowing spring barley next phase of development before. But the pace of the offensive phase, resulting in phase between the time for all periods will increase, which will increase the growing season. The most significant change scenarios will be observed in the amounts of precipitation. These changes will increase slight moisture crops in all areas except the steppe.

Relativistic effects in double ionization of helium via Compton scattering

In this article we present the relativistic calculations, based on the QED theory, for double ionization of helium by the Compton scattering. In particular, we calculate the contribution of the spin–flip amplitude to the total cross section. Due to this amplitude the final triplet spin state of the ejected electrons is possible. In the calculations based on the non–relativistic A2 term of the electron–photon interaction only the singlet spin state for the final electrons is allowed. We further assume the shake-off mechanism for process of double ionization. For the ground state of helium we use both the non–correlated and highly correlated wave function. We also discuss a degree of the scattered photon polarization in correlation with the formation of spin triplet state. Our calculations cover the photon impact energy range from 150 to 1000keV.

Light-matter decoupling and A(2) term detection in superconducting circuits.

The spontaneous and stimulated emission of a superconducting qubit in the presence of propagating microwaves originates from an effective light-matter interaction that, similarly to the case of the atomic case, can contain a diamagnetic term proportional to the square vector potential A2. In the present work we prove that an increase in the strength of the diamagnetic term leads to an effective decoupling of the qubit from the electromagnetic field, and that this effect is observable at any range of qubit-photon coupling. To measure this effect we propose to use a transmon suspended over a transmission line, where the relative strength of the A2 term is controlled by the qubit-line separation. We show that the spontaneous emission rate of the suspended transmon onto the line can, at short distances, increase with such a separation, instead of decreasing.

Structural and Enzymatic Insights into the ATP Binding and Autophosphorylation Mechanism of a Sensor Histidine Kinase

DesK is a sensor histidine kinase (HK) that allows Bacillus subtilis to respond to cold shock, triggering the adaptation of membrane fluidity via transcriptional control of a fatty acid desaturase. It belongs to the HK family HPK7, which includes the nitrogen metabolism regulators NarX/Q and the antibiotic sensor LiaS among other important sensor kinases. Structural information on different HK families is still scarce and several questions remain, particularly concerning the molecular features that determine HK specificity during its catalytic autophosphorylation and subsequent response-regulator phosphotransfer reactions. To analyze the ATP-binding features of HPK7 HKs and dissect their mechanism of autophosphorylation at the molecular level, we have studied DesK in complex with ATP using high resolution structural approaches in combination with biochemical studies. We report the first crystal structure of an HK in complex with its natural nucleotidic substrate. The general fold of the ATP-binding domain of DesK is conserved, compared with well studied members of other families. Yet, DesK displays a far more compact structure at the ATP-binding pocket: the ATP lid loop is much shorter with no secondary structural organization and becomes ordered upon ATP loading. Sequence conservation mapping onto the molecular surface, semi-flexible protein-protein docking simulations, and structure-based point mutagenesis allow us to propose a specific domain-domain geometry during autophosphorylation catalysis. Supporting our hypotheses, we have been able to trap an autophosphorylating intermediate state, by protein engineering at the predicted domain-domain interaction surface.

Optimizing Nano-silver Formation by Fusarium oxysporum PTCC 5115 Employing Response Surface Methodology

Fusarium oxysporum was grown in medium containing malt, yeast extracts and glucose on shaker at 25±1ÂoC and180 rpm for 96 h. The mycelia were used to convert silver nitrate solution into nano-silver. The bioconversion was optimized through response surface methodology-central composite design .The factors which affected the process were pH, temperature, agitation rate, concentration of silver nitrate, time of reaction and weight of Fusarium oxysporum mass. The R2 was calculated to be 98% indicating the accuracy and ability of the polynomial model to be suitable and reasonable. Positive coefficient of the factors like concentration of silver nitrate solution (E) and weight of Fusarium oxysporum biomass (F), quadratic terms A2, B2, F2 and interaction term BC affected linearly formation of nano-silver whereas negative coefficient of pH(A), temperature (B), rate of agitation(C), time(D) along with quadratic terms C2, D2, E2, and interaction terms such as BF decreased the nano-silver formation.

Spontaneous emission of light from atoms: the model

AbstractWe investigate (non‐relativistic) atomic systems interacting with quantum electromagnetic field (QEF). The resulting model describes spontaneous emission of light from a two‐level atom surrounded by various initial states of the QEF. We assume that the quantum field interacts with the atom via the standard, minimal‐coupling Hamiltonian, with the A2 term neglected. We also assume that there will appear at most single excitations (photons). By conducting the analysis on a general level we allow for an arbitrary initial state of the QEF (which can be for instance: the vacuum, the ground state in a cavity, or the squeezed state). We derive a Volterra‐type equation which governs the time evolution of the amplitude of the excited state. The two‐point function of the initial state of the QEF, integrated with a combination of atomic wavefunctions, forms the kernel of this equation.

Spin filtering in an electromagnetic structure

We investigate possible spin-dependent resonant tunneling through double-barrier electromagnetic structure. We point out that previous related studies contain serious errors in the calculation and the correct ones show much reduced spin polarization in the tunneling. In this study, we show that the significant amount of spin polarization with nice resonant structures can be achieved by applying a proper electric field subject to the given magnetic barriers. The electric potential U, which is crucial in our model, is chosen to exactly cancel the A2 term originated from the applied magnetic field. In this way, we can remove unwanted obstacles and expedite the tunneling of electrons.

Influence of Quadrupolar Ordering Factor on Supermolecular Structure in Ferroelectric Sm C*

We have synthesized the compound: 2-methylbutyl-4-n-nonanoyloxybiphenyl-4′-carboxylate (MBOBC). MBOBC shows the inversions in the sign of the spontaneous polarization, what was first reported by Goodby et al.[1] and Eidenschink et al.[2]. This ferroelectric liquid crystals has been studied by dielectric, densytometric, refractometric an X-ray measurements. After comparing the PS taken from experiment and obtained from theoretical approximation[3,4,5], the contribution of the dipolar a1 and quadrupolar a2 terms in the rotational potential have been estimated.

Energy Transfer in Restricted Geometry: Polyisoprene−Poly(methyl methacrylate) Block Copolymer Interfaces

The kinetics of direct nonradiative energy transfer between dyes confined to the 2.6 nm wide interface region of polyisoprene−poly(methyl methacrylate) block copolymer films are reported. This system differs from restricted geometry systems examined previously because of the diffuse nature of the edges of the confining space. The interface thickness is similar in magnitude to the characteristic distance for energy transfer (R0 = 2.3 nm) for the donor−acceptor dye pair (phenanthrene−anthracene) employed here. Samples were prepared from matched pairs of block copolymers, one containing a donor dye and the other an acceptor dye, at the PI−PMMA junction. Donor fluorescence decay profiles were fitted to the Klafter−Blumen expression [ID(t) = A1 exp{−(t/τD) − P(t/τD)β} + A2 exp(−t/τD)] containing the additional A2 term to account for donors (ca. 3%) outside the interface. The parameters obtained followed the predicted behavior, namely, that the preexponential term P was proportional to the acceptor concentration, whereas the stretched-exponential parameter β was independent of the global acceptor concentration CA for acceptor-to-donor ratios CA/CD > 1. One of the most unusual features of the data is a crossover in β observed as a function of a global acceptor concentration CA for a certain range of donor−acceptor composition, CA/CD < 1.

Quantum theory of quantum-well polaritons in semiconductor microcavities.

The polariton Hamiltonian for a quantum well embedded in a cavity of finite width is derived. The exciton-light interaction is formulated in second quantization and the photon self-interaction term A2 is included. The importance of the A2 term turns out to be relevant in the case of large values of the cavity width. By solving the equation of motion the dispersion relations for upper and lower polaritons are found. A comparison is made with existing measurements of polariton absorption peaks. The limit of infinite cavity width is carried out and the known results for a quantum well in an infinite medium are recovered.

On polariton instability and thermodynamic phase transition in a photon-matter system

It is shown that the rotating wave approximation in the minimal coupling Hamiltonian with the A2 term leads to an incorrect energy spectrum of the polariton mode: in particular, to a spurious polariton instability which should not occur for a photon-matter system consisting of radiation and atoms without the Coulomb interaction. Thus the counter-rotating term in the presence of the A2 term plays a crucial role in the instability property of the system. The super-radiant phase transition in the Dicke model is shown to be accompanied by polariton instability, and therefore by instability of the ground state of the photon-matter system. The rotating wave approximation, as well as the neglect of the A2 term, should therefore not be made for the study of the thermodynamic phase transition and instability properties of the ground state of the system.

Effect of spin-spin interaction on the super-radiant phase transition for the Dicke Hamiltonian

The thermodynamic equilibrium properties of the Dicke Hamiltonian for a collection of spin-1/2 particles interacting via magnetic dipole interaction with a single mode of the radiation field and with each other by spin-spin interaction are analysed and the conditions for the existence of a super-radiant phase transition are derived. It is shown, using the approximate long-range spin-spin interaction (MI), in the Dicke Hamiltonian, that the conditions for the existence of the super-radiant phase transition are invariant with respect to isotropic MI whether or not the A2 term is included.

Phase transition of a system of two-level atoms

A very simple treatment is presented to describe a phase transition present in Dicke's model for super-radiance, in the off-resonance case and for a single radiation mode. The results agree with previous authors, although the use of mod n( states provides a transparent physical interpretation. The results show that if the A2 term is kept in the Hamiltonian, the phase transition persists, thus clarifying some recent controversy on the subject. The thermodynamic variables are calculated above and below Tc. The phase transition is shown to be a consequence of an instability of the ground state. The behaviour of (aDagger a) and (SZ) is explored as a function of temperature. (aDagger a) goes to zero as (Tc-T) near the critical temperature.

A2 Term, Renormalization of Matter-Photon Interaction and Coherent States in Matter-Photon Systems

A non-relativistic quantum theory of matter-photon interaction is formulated, within the framework of the dipole approximation, by employing a canonical transformation to diago­ nalize the A' term plus the free photon Hamiltonian. The matter-photon interaction is there­ by expressed rigorously in a renormalized A·p form. Using this form for the Dicke model of two-level atoms interacting with a single-mode radiation field, we examine a possibility of the occurrence of stationary coherent states which could arise for a photon and atomic polarization as the ground state of the system, deducing a condition for such coherent states. The condition, expressed as an inequality which imposes a stable nontrivial Bloch angle of the uniform atomic polarization, is identical with that for the occurrence of a second order phase transition, and indicates that the non-existence of a second order phase transition pointed out by Rza2ewski et al. io; in fact a consequence of the present treatment of the A'­ term renormalization. However, a fulfillment of the condition is recovered, if exchange­ type atom-atom interaction is taken into account in the matter system. We also present a method to construct an effective Hamiltonian of atom-atom interaction which is equivalent to the above Dicke model in the thermodynamic limit.