Zero Temperature Case Research Articles

Dynamical Coulomb blockade: An all electrical probe of the ultrastrong light-matter coupling regime

The regime of ultrastrong light-matter coupling (USC) has attracted considerable interest recently, as it predicts fascinating quantum phenomena such as the presence of virtual photons in the ground state. Here we propose theoretically an approach to probe the quantum correlations in USC systems based on an electrical transport experiment. Namely, we consider the case in which the light-matter coupled system constitutes the electromagnetic environment of an ultrasmall tunnel junction operating in the regime of a dynamical Coulomb blockade (DCB). Unlike optical spectroscopy, such a probe can be seen as a nondemolition measurement of the USC system ground state. We have developed two approaches in order to evaluate the effect of the light-matter coupled states on the tunneling process. The first is a generalized, multimode Peierls substitution for the tunneling Hamiltonian. The second is based on the P(E) theory describing a DCB, where the USC system is treated as an equivalent circuit. The two approaches are consistent, whereas the second one enables us explicitly to take into account the presence of dissipation. This study has been performed for the zero-temperature case, which is pertinent for the terahertz spectral range where excitation energies are typically much higher compared to the microwave domain, where DCB was first studied. Published by the American Physical Society 2024

Unveiling SU(3) flux tubes at nonzero temperature: electric fields and magnetic currents

We report on the results of measuring the chromoelectric fields in a flux tube created by a static quark-antiquark pair in finite-temperature SU(3) gauge theory. Below the deconfinement temperature the field behavior is similar to the zero-temperature case. Above the deconfinement temperature the field shape remains the same, but the field values drop when the distance between the quark and antiquark increases, thus showing the disappearance of the confining potential.

Grid entropy in last passage percolation — A superadditive critical exponent approach

Working in the setting of i.i.d. last-passage percolation on RD with no assumptions on the underlying edge-weight distribution, we arrive at the notion of grid entropy — a Subadditive Ergodic Theorem limit of the entropies of paths with empirical measures weakly converging to a given target, or equivalently a deterministic critical exponent of canonical order statistics associated with the Levy-Prokhorov metric. This provides a fresh approach to an entropy first developed by Rassoul-Agha and Seppäläinen as a large deviation rate function of empirical measures along paths. In their 2014 paper, variational formulas are developed for the point-to-point/point-to-level Gibbs Free Energies as the convex conjugates of this entropy. We rework these formulas in our new framework and explicitly link our descriptions of grid entropy to theirs. We also improve on a known bound for this entropy by introducing a relative entropy term in the inequality. Furthermore, we show that the set of measures with finite grid entropy coincides with the deterministic set of limit points of empirical measures studied in a 2020 paper by Bates. We partially answer a directed polymer version of a question of Hoffman which was previously tackled in the zero temperature case by Bates.

Phase separation in binary Bose mixtures at finite temperature

We investigate the magnetic behavior of finite-temperature repulsive two-component Bose mixtures by means of exact path-integral Monte-Carlo simulations. Novel algorithms are implemented for the free energy and the chemical potential of the two components. Results on the magnetic susceptibility suggest that the conditions for phase separation are not modified from the zero temperature case. This contradicts previous predictions based on approximate theories. We also determine the temperature dependence of the chemical potential and the contact parameters for experimentally relevant balanced mixtures.

Axial-vector form factor of nucleons at finite temperature from the AdS/QCD soft-wall model

The axial-vector form factor of the nucleons is studied at a finite temperature using the holographic soft-wall model with the thermal dilaton field. We use the bulk interaction action known from the zero temperature case and apply the profile functions of fields thermalized by the interaction with the thermal dilaton field. The dependence of the axial form factor on the square of the transferred momentum and the temperature is plotted for the ground and excited states of the nucleons.

The pion-kaon scattering amplitude and the {K}_0^{ast }(700) and K∗(892) resonances at finite temperature

We perform a complete calculation of the pion-kaon scattering amplitude in Chiral Perturbation Theory at finite temperature, paying particular attention to the analytic structure of the amplitude and the main differences with respect to the zero temperature case. We also extend the Inverse Amplitude Method at finite temperature for unequal-mass scattering processes, which allows us to unitarize the amplitude and obtain the thermal evolution of the {K}_0^{ast }(700) and K∗(892) pole parameters. As a direct application of our analysis, we show that the thermal evolution of the {K}_0^{ast }(700) resonance is crucial to explain the behavior of the scalar susceptibility for isospin I = 1/2, which in turn, is directly connected with chiral and U(1)A restoration properties of the QCD phase diagram.

Holographic Schwinger Effect with a Rotating Probe D3-Brane

This paper, among other things, talks about possible research on the holographic Schwinger effect with a rotating probe D3-brane. We discover that for the zero temperature case in the Schwinger effect, the faster the angular velocity and the farther the distance of the test particle pair at D3-brane, the potential barrier of total potential energy also grows higher and wider. This paper shows that at a finite temperature, when S5 without rotation is close to the horizon, the Schwinger effect fails because the particles remain in an annihilate state, which is an absolute vacuum state. However, the angular velocity in S5 will avoid the existence of an absolute vacuum near the horizon. For both zero and finite temperature states, the achieved results completely agree with the results of the Dirac-Born-Infeld (DBI) action. So the theories in this paper are consistent. All of these show that these theories will play important roles in future pair production research.

Finite-temperature dynamical quantum phase transition in a non-Hermitian system

We investigate the interplay between the non-Hermiticity and finite temperature in the context of mixed state dynamical quantum phase transition (MSDQPT). We consider a $p$-wave superconductor model, encompassing complex hopping and non-Hermiticity that can lead to gapless phases in addition to gapped phases, to examine the MSDQPT and winding number via the intra-phase quench. We find that the MSDQPT is always present irrespective of the gap structure of the underlying phase, however, the profile of Fisher zeros changes between the above phases. Such occurrences of MSDQPT are in contrast to the zero-temperature case where DQPT does not take place for the gapped phase. Surprisingly, the half-integer jumps in winding number at zero-temperature are washed away for finite temperature in the gapless phase. We study the evolution of the minimum time required by the system to experience MSDQPT with the inverse temperature such that gapped and gapless phases can be differentiated. Our study indicates that the minimum time shows monotonic (non-monotonic) behavior for the gapped (gapless) phase.

High-frequency magnetic response of superparamagnetic composites of spherical Fe65Co35 nanoparticles

The response of composites of magnetic nanoparticles (MNPs) with randomly-oriented magnetocrystalline anisotropy axes to a linearly-polarized ac field or a rotating field is studied with regard to the concept of using superparamagnetic nanocomposites as core materials for high (sub-GHz and GHz) frequency power conversion devices. We perform micromagnetic simulations of systems of spherical 5nm-diameter nanoparticles of Fe65Co35 with two different concentrations arranged periodically within a dielectric matrix, including thermal fluctuations of the magnetization within the stochastic thermal field. Because the particles are closely packed, the effect of surface anisotropy is neglected. The dependence of the amplitude of the magnetic response function on temperature is determined. We show the inapplicability of Brown’s classic theory of thermal excitations in single-domain magnetic particles for given material parameters even in the absence of the magnetostatic field. Magnetostatic interactions of MNPs are found to be necessary for stabilizing the dynamical magnetic response in the high temperature (low-energy-barrier) range. They allow for driving magnetization oscillations at room temperature with amplitude comparable to the zero-temperature case. Dynamical (hysteretic and residual) losses are discussed.

Embedding short-range correlations in relativistic density functionals through quasi-deuterons

The formation of clusters at sub-saturation densities, as a result of many-body correlations, constitutes an essential feature for a reliable modelization of the nuclear matter equation of state (EoS). Phenomenological models that make use of energy density functionals (EDFs) offer a convenient approach to account for the presence of these bound states of nucleons when introduced as additional degrees of freedom. However, in these models clusters dissolve, by construction, when the nuclear saturation density is approached from below, revealing inconsistencies with recent findings that evidence the existence of short-range correlations (SRCs) even at larger densities. The idea of this work is to incorporate SRCs in established models for the EoS, in light of the importance of these features for the description of heavy-ion collisions, nuclear structure and in the astrophysical context. Our aim is to describe SRCs at supra-saturation densities by using effective quasi-clusters immersed in dense matter as a surrogate for correlations, in a regime where cluster dissolution is usually predicted in phenomenological models. Within the EDF framework, we explore a novel approach to embed SRCs within a relativistic mean-field model with density dependent couplings through the introduction of suitable in-medium modifications of the cluster properties, in particular their binding energy shifts, which are responsible for describing the cluster dissolution. As a first exploratory step, the example of a quasi-deuteron within the generalized relativistic density functional approach is investigated. The zero temperature case is examined, where the deuteron fraction is given by the density of a boson condensate. For the first time, suitable parameterizations of the cluster mass shift at zero temperature are derived for all baryon densities. They are constrained by experimental results for the effective deuteron fraction in nuclear matter near saturation and by microscopic many-body calculations in the low-density limit. A proper description of well-constrained nuclear matter quantities at saturation is kept through a refit of the nucleon meson coupling strengths. The proposed parameterizations allow to also determine the density dependence of the quasi-deuteron mass fraction at arbitrary isospin asymmetries. The strength of the deuteron-meson couplings is assessed to be of crucial importance. Novel effects on some thermodynamic quantities, such as the matter incompressibility, the symmetry energy and its slope, are finally discerned and discussed. The findings of the present study represent a first step to improve the description of nuclear matter and its EoS at supra-saturation densities in EDFs by considering correlations in an effective way. In a next step, the single-particle momentum distributions in nuclear matter can be explored using proper wave functions of the quasi-deuteron in the medium. The momentum distributions are expected to exhibit a high-momentum tail, as observed in the experimental study of SRCs by nucleon knockout with high-energy electrons. This will be studied in a forthcoming publication with an extensive presentation of the theoretical method and the results.

Machine-learning semilocal density functional theory for many-body lattice models at zero and finite temperature

We introduce a machine-learning density-functional-theory formalism for the spinless Hubbard model in one dimension at both zero and finite temperature. In the zero-temperature case this establishes a one-to-one relation between the site occupation and the total energy, which is then minimised at the ground-state occupation. In contrast, at finite temperature the same relation is defined between the Helmholtz free energy and the equilibrium site occupation. Most importantly, both functionals are semi-local, so that they are independent from the size of the system under investigation and can be constructed over exact data for small systems. These 'exact' functionals are numerically defined by neural networks. We also define additional neural networks for finite-temperature thermodynamical quantities, such as the entropy and heat capacity. These can be either a functional of the ground-state site occupation or of the finite-temperature equilibrium site occupation. In the first case their equilibrium value does not correspond to an extremal point of the functional, while it does in the second case. Our work gives us access to finite-temperature properties of many-body systems in the thermodynamic limit.

Holographic complexity of LST and single trace Toverline{T}

In this work, we continue our study of string theory in the background that interpolates between AdS3 in the IR to flat spacetime with a linear dilaton in the UV. The boundary dual theory interpolates between a CFT2 in the IR to a certain two-dimensional Little String Theory (LST) in the UV. In particular, we study computational complexity of such a theory through the lens of holography and investigate the signature of non-locality in the short distance behavior of complexity. When the cutoff UV scale is much smaller than the non-locality (Hagedorn) scale, we find exotic quadratic and logarithmic divergences (for both volume and action complexity) which are not expected in a local quantum field theory. We also generalize our computation to include the effects of finite temperature. Up to second order in finite temperature correction, we do not any find newer exotic UV-divergences compared to the zero temperature case.

Energy of a free Brownian particle coupled to thermal vacuum

Experimentalists have come to temperatures very close to absolute zero at which physics that was once ordinary becomes extraordinary. In such a regime quantum effects and fluctuations start to play a dominant role. In this context we study the simplest open quantum system, namely, a free quantum Brownian particle coupled to thermal vacuum, i.e. thermostat in the limiting case of absolute zero temperature. We analyze the average energy E=E(c) of the particle from a weak to strong interaction strength c between the particle and thermal vacuum. The impact of various dissipation mechanisms is considered. In the weak coupling regime the energy tends to zero as E(c) sim c, ln {(1/c)} while in the strong coupling regime it diverges to infinity as E(c) sim sqrt{c}. We demonstrate it for selected examples of the dissipation mechanisms defined by the memory kernel gamma (t) of the Generalized Langevin Equation. We reveal how at a fixed value of c the energy E(c) depends on the dissipation model: one has to compare values of the derivative gamma '(t) of the dissipation function gamma (t) at time t=0 or at the memory time t=tau _c which characterizes the degree of non-Markovianity of the Brownian particle dynamics. The impact of low temperature is also presented.

Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets

The Nd permanent magnet (${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$) is an indispensable material used in modern energy conversion devices. The realization of high coercivity at finite temperatures is an important issue. One of the important ingredients for controlling the coercive force is the surface property of magnetic grains. It has been found by first-principles studies that the Nd atoms in the first (001) surface layer facing the vacuum have in-plane anisotropy perpendicular to the $c$ axis, which may decrease the coercivity. Focusing on the surface anisotropy effect on the coercivity, we examine the coercivity at zero and finite temperatures using an atomistic model reflecting the lattice structure of the Nd magnet with a stochastic Landau-Lifshitz-Gilbert equation method. We study three general cases, in which the Nd atoms in surface layers have (1) no anisotropy, (2) in-plane anisotropy, and (3) reinforced anisotropy for two types of surface, (001) and (100) surfaces. We find that in contrast to the zero-temperature case, owing to the thermal fluctuation effect, the modification of only the first surface layer has little effect on the coercivity at finite temperatures. However, the modification of a few layers results in significant effects. We discuss the details of the dependences of the coercivity on temperature, the type of surface, and modified layer depth, and also the features of domain growth in magnetization reversal.

Parallel propagating electromagnetic waves in magnetized quantum electron plasmas with finite temperature.

We studied parallel propagating electromagnetic waves in a magnetized quantum electron plasma of finite temperature, as an extension of our previous study on a zero temperature plasma. We obtained simple analytic dispersion relations in the long wavelength limit that included the thermal effect as correction terms to the zero temperature results. As in the zero temperature case, the lower branch of the R wave showed significant damping and became ill-defined at short wavelengths. Quantum effects seemed to give qualitative changes, such as the appearance of anomalous dispersion regions, to the classical dispersion relations when v_{F}/v_{th}≤0.2 for a set of exemplary parameters of v_{F}=0.1c and ω_{ce}/ω_{pe}=0.05 was used. We also noted that introduction of the Planck constant in the quantum Vlasov equation changed the shape of the anomalous dispersion region qualitatively, by forming a normal dispersion region in the middle of the original single broad anomalous dispersion region.

Nucleons and higher spin baryon resonances: An AdS/QCD configurational entropic incursion

Families of $J^P=1/2+$ nucleons (N(939), N(1440), N(1710), N(1880), N(2100), N(2300)) and $J^P=3/2-$ nucleons (N(1520), N(1700), N(1875) and N(2120)) are scrutinized from the point of view of the configurational entropy (CE). The mass spectra of higher $J^P$ resonances in each one of these families are then obtained when configurational-entropic Regge trajectories, that relate the CE of nucleon families to both their $J^P$ spin and also to their experimental mass spectra, are interpolated. The mass spectra of the next generation of nucleon resonances are then compared to already established baryonic states in PDG. Besides the zero temperature case, the finite temperature analysis is also implemented.

Properties of Binary Components and Remnant in GW170817 Using Equations of State in Finite Temperature Field Theory Models

Abstract We investigate gross properties of binary components and remnant in GW170817 using equations of state (EoSs) within the finite temperature field theoretical models. We also adopt finite temperature EoSs in the density-dependent hadron field theory for this study. Properties of binary components are studied using zero temperature EoSs. Particularly, we investigate tidal deformabilities and radii of binary components in light of GW170817. An analytical expression relating the radii and the combined tidal deformability is obtained for binary neutron star masses in the range 1.1 M ⊙ ≲ M ≲ 1.6 M ⊙. The upper bound on the tidal deformability gives the upper bound on the neutron star radius as 13 km. Next, the role of finite temperature on the remnant in GW170817 is explored. In this case, we investigate the gravitational and baryon mass, radius, Kepler frequency, and moment of inertia of the rigidly rotating remnant for different EoSs at fixed entropy per baryon. The remnant radius is enlarged due to thermal effects compared with the zero temperature case. Consequently, it is found that the Kepler frequency is much lower at higher entropy per baryon than that of the case at zero temperature. These findings are consistent with the results found in the literature.

Holographic excited states in AdS black holes

We have recently presented a geometry dual to a Schwinger-Keldysh closed time contour, with two equal β/2 length Euclidean sections, which can be thought of as dual to the Thermo Field Dynamics formulation of the boundary CFT. In this work we study non-perturbative holographic excitations of the thermal vacuum by turning on asymptotic Euclidean sources. In the large-N approximation the states are found to be thermal coherent states and we manage to compute its eigenvalues. We pay special attention to the high temperature regime where the manifold is built from pieces of Euclidean and Lorentzian black hole geometries. In this case, the real time segments of the Schwinger-Keldysh contour get connected by an Einstein-Rosen wormhole through the bulk, which we identify as the exterior of a single maximally extended black hole. The Thermal-AdS case is also considered but, the Lorentzian regions become disconnected, its results mostly follows from the zero temperature case.

Decay of Phase-Imprinted Dark Soliton in Bose–Einstein Condensate at Nonzero Temperature

We study relaxation dynamics of dark soliton, created by a phase-imprinted method, in a two-dimensional trapped Bose-Einstein condensate at non-zero temperatures by using the projected Gross-Pitaevskii equation. At absolute zero temperature, a dark soliton is known to decay with a snake instability. At non-zero temperature, as we expected, we find that this snake instability cannot be clearly seen as in the absolute zero temperature case because of the presence of thermal fluctuations. However, we find that the decay rate, the half width of the overlap integral with respect to the phase-imprinted initial state, shows a power low decay as a function of the energy and finally remains a non-zero value.

Plasmon modes in MLG-2DEG heterostructures: Temperature effects

We calculate the plasmon frequency and damping rate in a double-layer system made of monolayer graphene and GaAs quantum well at finite temperature using the random-phase-approximation dielectric function and taking into account the inhomogeneity of the dielectric background of the system. We show that the temperature, interlayer correlation parameters and dielectric background inhomogeneity affect significantly the plasmon frequencies and damping rates of the system. At low temperatures, acoustic (optical) plasmon frequency increases (decreases) with the increase of temperature. We also find that damping rates of both plasmon modes increase remarkably compared to the zero-temperature case.