Free Radiation Field Research Articles

Zeta-regularized vacuum expectation values

It has recently been shown that vacuum expectation values and Feynman path integrals can be regularized using the Fourier integral operator ζ-function, yet the physical meaning of these ζ-regularized objects was unknown. Here, we show that ζ-regularized vacuum expectations appear as continuum limits using a certain discretization scheme. Furthermore, we study the rate of convergence for the discretization scheme using the example of a one-dimensional hydrogen atom in (−π, π) which we evaluate classically, using the Rigetti quantum virtual machine and on the Rigetti 8Q quantum chip “Agave” device. We also provide the free radiation field as an example for the computation of ζ-regularized vacuum expectation values in a gauge theory.

Subradiance-protected excitation transport

We explore excitation transport within a one-dimensional chain of atoms where the atomic transition dipoles are coupled to the free radiation field. When the atoms are separated by distances smaller or comparable to the wavelength of the transition, the exchange of virtual photons leads to the transport of the excitation through the lattice. Even though this is a strongly dissipative system, we find that the transport is subradiant, that is, the excitation lifetime is orders of magnitude longer than the one of an individual atom. In particular, we show that a subspace of the spectrum is formed by subradiant states with a linear dispersion relation, which allows for the dispersionless transport of wave packets over long distances with virtually zero decay rate. Moreover, the group velocity and direction of the transport can be controlled via an external uniform magnetic field while preserving its subradiant character. The simplicity and versatility of this system, together with the robustness of subradiance against disorder, makes it relevant for a range of applications such as lossless energy transport and long-time light storage.

Subradiance via Entanglement in Atoms with Several Independent Decay Channels.

Spontaneous emission of atoms in free space is modified by the presence of other atoms in close vicinity inducing collective super- and subradiance. For two nearby atoms with a single decay channel the entangled antisymmetric superposition state of the two single excited states will not decay spontaneously. No such excited two-atom dark state exists, if the excited state has two independent optical decay channels of different frequencies or polarizations. However, we show that for an excited atomic state with N-1 independent spontaneous decay channels one can find a highly entangled N-particle dark state, which completely decouples from the vacuum radiation field. It does not decay spontaneously, nor will it absorb resonant laser light. Mathematically, we see that this state is the only such state orthogonal to the subspace spanned by the atomic ground states. Moreover, by means of generic numerical examples we demonstrate that the subradiant behavior largely survives at finite atomic distances including dipole-dipole interactions.

SU-G-TeP1-03: Beam Quality Correction Factors for Linear Accelerator with and Without Flattening Filter

Purpose: The impact of removing the flattening filter on absolute dosimetry based on IAEA's TPR-398 and AAPM's TG-51 was investigated in this study using Monte Carlo simulations. Methods: The EGSnrc software package was used for all Monte Carlo simulations performed in this work. Five different ionization chambers and nine linear accelerator heads have been modeled according to technical drawings. To generate a flattening filter free radiation field the flattening filter was replaced by a 2 mm thick aluminum layer. Dose calculation in a water phantom were performed to calculate the beam quality correction factor kQ as a function of the beam quality specifiers %dd(10)x, TPR20,10 and mean photon and electron energies at the point of measurement in photon fields with (WFF) and without flattening filter (FFF). Results: The beam quality correction factor as a function of %dd(10)x differs systematically between FFF and WFF beams for all investigated ionization chambers. The largest difference of 1.8% was observed for the largest investigated Farmer-type ionization chamber with a sensitive volume of 0.69 cm3. For ionization chambers with a smaller nominal sensitive volume (0.015 – 0.3 cm3) the deviation was less than 0.4% between WFF and FFF beams for %dd(10)x > 62%. The specifier TPR20,10 revealed only a good correlation between WFF and FFF beams (< 0.3%) for low energies. Conclusion: The results confirm that %dd(10)x is a suitable beam quality specifier for FFF beams with an acceptable bias. The deviation depends on the volume of the ionization chamber. Using %dd(10)x to predictkQ for a large volume chamber in a FFF photon field may lead to not acceptable errors according to the results of this study. This bias may be caused by the volume effect due to the inhomogeneous photon fields of FFF linear accelerators.

Lifetime and emission characteristics of collective electronic excitations in two-dimensional optical lattices

Collective electronic excitations in planar optical lattices exhibit strong modifications of the radiative damping rate and directional emission pattern as compared to a single excited atom. Collective excitations for long wave numbers and polarizations orthogonal to the lattice plane exhibit superradiance with a very short lifetime and a tightly confined emission direction. For shorter wavelength and in-plane polarization, they can possess a long lifetime, which, beyond a critical wave number, tends to infinity. Those excitations thus become metastable and decoupled from the free radiation field. They can store a single energy quantum for a long time and transfer the excitation over long distances. In general the spatial, polarization, and frequency dependence of the emission pattern can provide us with optical and electronic properties of optical lattices.

Towards relativistic atomic physics. Part 1. The rest-frame instant form of dynamics and a canonical transformation for a system of charged particles plus the electro-magnetic field

A complete exposition of the rest-frame instant form of dynamics for arbitrary isolated systems (particles, fields, strings, fluids) admitting a Lagrangian description is given. The starting point is the parametrized Minkowski theory describing the system in arbitrary admissible noninertial frames in Minkowski space-time, which allows one to define the energy-momentum tensor of the system and to show the independence of the description from the clock synchronization convention and from the choice of the 3-coordinates. The restriction to the inertial rest frame, centered on the inertial observer having the Fokker–Pryce center-of-inertia world line, and the study of relativistic collective variables replacing the nonrelativistic center of mass lead to the description of the isolated system as a decoupled globally defined noncovariant canonical external center of mass carrying a pole–dipole structure (the invariant mass M and the rest spin [Formula: see text] of the system) and an external realization of the Poincaré group. Mc and [Formula: see text] are the energy and angular momentum of a unfaithful internal realization of the Poincaré group built with the energy-momentum tensor of the system and acting inside the instantaneous Wigner 3-spaces where all the 3-vectors are Wigner covariant. The vanishing of the internal 3-momentum and of the internal Lorentz boosts eliminate the internal 3-center of mass inside the Wigner 3-spaces, so that at the end the isolated system is described only by Wigner-covariant canonical internal relative variables. Then an isolated system of positive-energy-charged scalar articles with mutual Coulomb interaction plus a transverse electromagnetic field in the radiation gauge is investigated as a classical background for defining relativistic atomic physics. The electric charges of the particles are Grassmann-valued to regularize the self-energies. The external and internal realizations of the Poincaré algebra in the rest-frame instant form of dynamics are found. This allows one to define explicitly the rest-frame conditions and their gauge-fixings (needed for the elimination of the internal 3-center of mass) for this isolated system. It is shown that there is a canonical transformation that allows one to describe the isolated system as a set of Coulomb-dressed charged particles interacting through a Coulomb plus Darwin potential plus a free transverse radiation field: these two subsystems are not mutually interacting (the internal Poincaré generators are a direct sum of the two components) and are interconnected only by the rest-frame conditions and the elimination of the internal 3-center of mass. Therefore in this framework with a fixed number of particles there is a way out from the Haag theorem, at least at the classical level.

Simultaneous ionization and excitation by photon absorption in He

Second order terms of the time dependent perturbation theory expansion were used to calculate the simultaneous ionization and excitation of helium as result of a photon absorption. In this calculation, the perturbing Hamiltonian was assumed to be the sum of the interaction between the electrons and their interactions with the free radiation field. According to this model, the correlated transition resulting from the photon absorption can be calculated using the independent particle model to describe the atom states. In the present, the cross section for the correlated photon ionization in He was calculated using screened hydrogenic wave functions. The sum over the intermediate states required by the present approach was taken up to the tenth shell. No significant differences were observed in the results considering higher shells intermediate states. Correlated photon ionization cross section values are presented for energies of the absorbed photon varying from 70 up to 1500 eV and for transitions where the ionization of the helium atom is followed by simultaneous excitation of the second electron to a higher shell, that is He(1s 2)+ hν→He + (n s 1 or n p 1)+ e − , with n varying from 2 up to 6. Comparison of the present calculations with the results of measurements from several authors shows a very good agreement while the results of other theoretical calculations exhibit considerable discrepancies.

Analysis of a two-atom double-slit experiment based on environment-induced measurements

To investigate the effect of the environment on a quantum-mechanical system we consider two two-level atoms in a free radiation field in the presence of a screen. By assuming that the screen causes continuous ideal measurements on the free radiation field we derive a quantum jump description for the state of the atoms. Our results are consistent with the master equation for dipole interacting atoms, but give more insight in the time evolution of a single system. To illustrate this we derive a necessary and sufficient criterion for interference in a two-atom double-slit experiment and analyze bunching in the statistics of photons emitted in a certain direction.

K-MM radiative-Auger transition probability calculationsfor Ca, Ti and Cr

The K-MM radiative-Auger transition probabilities for Ca, Tiand Cr were calculated using time-dependent perturbation theory.The atom plus the free radiation field are considered as beingone system and the transition of one state of the atom toanother results from the interaction between components of thissystem. The perturbing Hamiltonian is taken as the sum of theinteraction between the electrons participating directly in theprocess and their interaction with the radiation field. Underthis approach, the radiative-Auger process is describedconsidering second-order terms in time-dependent perturbationtheory series. The calculations were performed using screenedhydrogenic wavefunctions to describe the state of the atom.The results obtained are compared with recent experimental dataand other theoretical calculations.

Maximum entropy and poissonian characterization of the quantized radiation field

The least maximum entropy for the free radiation field occurs for the vacuum state of the radiation field and its unitary equivalents including the coherent state of an ideal laser. Comparisons are made with number measurement entropies obtained by projection or averaging of the number representation of the ideal laser.

Constructing a conserved flux from plane waves

The conserved vector flux is a useful construct for analyzing and designing optical concentrators. We derive an expression for the flux, starting from the free radiation field. With our method, conservation of the flux is automatic, and limits to conservation in certain optical systems follow.

The four states of the Massless neutrino with pauli coupling by Spin-Gauge invariance

The Pauli coupling \(a\bar \psi \sigma ^{uv} \psi F_{uv} \) is introduced for four-component neutrino states and related to local T4⊂SU(2,2) spin-gauge (not internal symmetry) transformations applied to the massless Dirac equation. The well-known left-right asymmetry for free neutrino helicity states is generalised and discussed for Pauli-coupled neutrinos. An explicit exact solution is obtained for Pauli-coupled neutrino equations in an external free radiation field by the use of the above local spin-gauge transformations. It is also suggested that local SL(2, C)⊂SU(2,2) spin-gauge transformations can be used to obtain models of neutral currents for neutrinos.

A rigged Hilbert space for the free radiation field

We here construct a rigged Hilbert space suitable for the description of the free radiation field in a box and in the Coulomb gauge. We prove the continuity of the main observables on this structure.

Gravitational radiation resistance, radiation damping and field fluctuations

Application is made of two different generalised fluctuation-dissipation theorems and their derivations to the calculation of the gravitational quadrupole radiation resistance using the radiation-reaction force given by Misner, Thorne and Wheeler (1973) and the usual tidal force on one hand and the tidal force and the free gravitational radiation field on the other hand. The quantum-mechanical version (including thermal generalisations) of the well known classical quadrupole radiation damping formula is obtained as a function of the radiation resistance.

Consequences of gauge-fixing ambiguities in non-Abelian gauge theories in axial and Coulomb gauges

We consider a pure SU(2) non-Abelian gauge theory in a first-order canonical quantization scheme, and show how the proper treatment of zero modes in solving the constraint equations for the dependent variables leads to certain conditions on the physical states. In the axial gauge this leads to a result of Schwinger's. In the Coulomb gauge this leads to previously unknown conditions on the physical states, and to the conclusion that the theory does not describe a free radiation field under circumstances for which Gribov has shown that the vector potential becomes non-unique.

Foundations of stochastic electrodynamics.

Stochastic electrodynamics is classical electrodynamics with the hypothesis of a random background radiation in the whole space. The probability distributions of the Fourier components of this electromagnetic radiation are assumed Gaussian. Lorentz invariance fixes the spectrum of the radiation except for a constant, measuring its intensity, which is identified with Planck’s constant. A formalism is developed to deal with general stochastic problems, associating a Hilbert space with every set of random variables. Then, a mapping is defined of the algebra of continuous functions of the random variables onto the algebra of operators on the Hilbert space. A correspondence is found between probability distributions of the random variables and vectors in the Hilbert space. The case of Gaussian random variables is considered in detail. The formalism is applied to the study of the radiation field when some known amount of radiation is present besides the random background. This closely resembles the usual quantization of the free radiation field, although there are significant differences. In particular, not all vectors of the Hilbert space represent physical states in the present theory.

Investigation of thin linear antennas with displaced feed points in a plasma†

This paper is an extension of the recent work of Gupta (1968) in which the properties of a thin resonant antenna in a plasma are analysed using linearized hydrodynamic theory and assuming a general propagation constant for the current distribution, for an antenna having feed points displaced by λ0/2. In this paper the analysis is extended to include a non-resonant antenna and also the dependence of the properties of both types of antennas on the size of the displacement and value of the propagation constant. The field patterns in the plasma are calculated for two different values of the general propagation constant and for various lengths of the antennas. The results are compared with the free space radiation field strengths which are evaluated by setting the plasma frequency to zero. It is shown that the maximum field strength of both the resonant and the non-resonant types of antenna in free space increases considerably when the feed points are displaced to a, certain optimum value. The variation of the...