Quantization Of Electromagnetic Field Research Articles

Control of light-induced torque in quantum well waveguides through electron spin coherence

We explore the mechanical effects of light interacting with a quantum well waveguide, specifically focusing on the emergence of quantized torque. We investigate the response of the waveguide to the influence of two intense coupling fields in conjunction with two weaker fields. We find that the electron spin coherence plays a crucial role in amplifying the torque applied to the waveguide emitters. This heightened torque, in turn, triggers a distinctive circular current flow pattern within the waveguide. Furthermore, we explore different scenarios for modulating the torque by adjusting system parameters, thereby establishing a means to control current flow. The emergence of a light-induced quantized torque not only illuminates the interplay between quantum emitters and electromagnetic fields but also opens up exciting possibilities for innovative approaches to govern induced-torque behavior within quantum well waveguides.

Relativistic single-electron wavepacket in quantum electromagnetic fields: quantum coherence, correlations, and the Unruh effect

Conventional formulation of QED since the 50s works very well for stationary states and for scattering problems, but with newly arisen challenges from the 80s on, where real time evolution of particles in a nonequilibrium setting are required, and quantum features such as coherence, dissipation, correlation and entanglement in a system interacting with its quantum field environment are sought after, new ways to formulate QED suitable for these purposes beckon. In this paper we present a linearized effective theory using a Gaussian wavepacket description of a charged relativistic particle coupled to quantum electromagnetic fields to study the interplay between single electrons and quantum fields in free space, at a scale well below the Schwinger limit. The proper values of the regulators in our effective theory are determined from the data of individual experiments, and will be time-dependent in the laboratory frame if the single electrons are accelerated. Using this new theoretical tool, we address the issues of decoherence of flying electrons in free space and the impact of Unruh effect on the electrons. Our result suggests that vacuum fluctuations may be a major source of blurring the interference pattern in electron microscopes. For a single electron accelerated in a uniform electric field, we identify the Unruh effect in the two-point correlators of the deviations from the electron’s classical trajectory. From our calculations we also bring out some subtleties, involving the bosonic versus fermionic spectral functions.

Electromagnetic field quantization in the presence of a moving nanoparticle

An appropriate Lagrangian is considered for a system comprising a moving nanoparticle in a semi-infinite space, and the electromagnetic and matter fields are quantized. Through an analysis of the absorbed power radiation, it is demonstrated that the quantum friction experienced by high-velocity nanoparticles can be identified as a dissipative term in the radiation power of the nanoparticle. The absorbed power radiation for a moving nanoparticle is derived and compared with that of a static one. By considering two different temperature scenarios, it is explicitly shown that the absorbed power radiation for a moving nanoparticle always contains a negative term in its power spectrum, which can be attributed to the power lost due to non-contact quantum friction.

Quantum dots interacting with a non-classical field under Kerr-phase modulation as a resource for repeatable quantum algorithms

An analytical solution describing the dynamics of a hybrid system comprising an interacting quantum dot and a quantum electromagnetic field in the presence of Kerr nonlinearity is obtained. A completely new regime of interaction is found. It provides stable periodically repeating dynamics for the total bipartite system and for the quantum dot excitation, accompanied by full and pure revivals. This is even observed when the initial field state is in a squeezed vacuum. Periodical strong entanglement and full disentanglement between the interacting subsystems are demonstrated. The obtained regime forms the basis for the development of quantum information algorithms and photon–matter interfaces involving these hybrid systems. The formation of non-Gaussian field states is revealed. Methods to control and manage the specific features of the found pure and mixed states of the considered subsystems are developed.

Numerical framework for modeling quantum electromagnetic systems involving finite-sized lossy dielectric objects in free space

The modified Langevin noise formalism [A. Drezet, Phys. Rev. A 95, 023831 (2017); O. D. Stefano, S. Savasta, and R. Girlanda, J. Mod. Opt. 48, 67 (2001)] has been proposed for the correct characterization of quantum electromagnetic fields in the presence of finite-size lossy dielectric objects in free space. The main modification to the original one [T. Gruner and D.-G. Welsch, Phys. Rev. A 53, 1818 (1996); H. T. Dung, L. Kn\"oll, and D.-G. Welsch, Phys. Rev. A 57, 3931 (1998)] (also known as the Green's function approach for a bulk inhomogeneous lossy dielectric medium) was to introduce another fluctuating source in reaction to the radiation loss. Consequently, the resulting electric field operator is now determined by (i) boundary-assisted and (ii) medium-assisted fields on an equal footing, which originate from radiation and medium losses, respectively. However, due to the lengthy mathematical manipulation and complicated concepts, the validity of the modified Langevin noise formalism has not been clearly confirmed yet. In this work, we propose and develop a numerical framework for the modified Langevin noise formalism by exploiting computational electromagnetic methods. Specifically, we present utilization of the finite-element method to numerically solve plane-wave-scattering and point-source-radiation problems whose solutions are boundary-assisted and medium-assisted fields, respectively. We numerically validated the modified Langevin noise model calculating the Purcell factor of a two-level atom inside or outside a lossy dielectric slab. The proposed numerical framework is particularly useful for analyzing the dynamics of multilevel atoms near plasmonic structures or metasurfaces in the open space.

Linear optics and photodetection achieve near-optimal unambiguous coherent state discrimination

Coherent states of the quantum electromagnetic field, the quantum description of ideal laser light, are prime candidates as information carriers for optical communications. A large body of literature exists on their quantum-limited estimation and discrimination. However, very little is known about the practical realizations of receivers for unambiguous state discrimination (USD) of coherent states. Here we fill this gap and outline a theory of USD with receivers that are allowed to employ: passive multimode linear optics, phase-space displacements, auxiliary vacuum modes, and on-off photon detection. Our results indicate that, in some regimes, these currently-available optical components are typically sufficient to achieve near-optimal unambiguous discrimination of multiple, multimode coherent states.

Peculiarities of exciton formation in 2D semiconductor nanostructures induced by quantum electromagnetic field under nonlinear self-phase modulation

Specific features of the excitation of a 2D semiconductor nanosystem by non-classical light in a solid state micro-resonator are found under the impact of the Kerr phase nonlinearity in the cavity. Different regimes of excitation are revealed in dependence on the efficiency of the nonlinearity. A negative impact of the nonlinear self-phase modulation on the excitation is found to be compensated by proper choice of the field frequency detuning. The possibility to controllably enhance a certain excitation channel by varying field frequency detuning is demonstrated and the value of the optimal detuning is found analytically. The effect of transfer of non-classical features from the field to the electronic subsystem is revealed. The formation of the photon-like non-classical excitonic states is demonstrated. The obtained results seem to be a basis for the creation of the light–matter interface and development of quantum information algorithms in solid state nanosystems.

Quantum coherence of relativistic wavepackets in electromagnetic vacuum

We have developed a linearized effective theory with quantum mechanical Gaussian wavepacket of a charged relativistic particle coupled to quantum electromagnetic fields at a scale well below the Schwinger limit. Using this effective theory, we study the quantum decoherence of single electrons at rest due to their interactions with electromagnetic vacuum. According to the existing data of electron interference experiments in electron microscopes, the values of the parameters in our effective theory are chosen. With these values, we find that weak decoherence by vacuum fluctuations may have blurred the interference pattern in Ref. [1].

Off-Resonant Dicke Quantum Battery: Charging by Virtual Photons

We investigate a Dicke quantum battery in the dispersive regime, where the photons trapped in a resonant cavity are much more energetic with respect to the two-level systems embedded into it. Under such off-resonant conditions, even an empty cavity can lead to the charging of the quantum battery through a proper modulation of the matter–radiation coupling. This counterintuitive behaviour has its roots in the effective interaction between two-level systems mediated by virtual photons emerging from the fluctuations of the quantum electromagnetic field. In order to properly characterize it, we address relevant figures of merit such as the stored energy, the time required to reach the maximum charging, and the averaged charging power. Moreover, the possibility of efficiently extracting energy in various ranges of parameters is discussed. The scaling of stored energy and power as a function of the number N of two-level systems and for different values of the matter–radiation coupling is also discussed, showing, in the strong coupling regime, performances in line with what is reported for the Dicke quantum battery in the resonant regime.

Multipolar quantum electrodynamics of localized charge-current distributions: Spectral theory and renormalization

We formulate a nonrelativistic quantum field theory to model interactions between quantized electromagnetic fields and localized charge-current distributions. The electronic degrees of freedom are encoded in microscopic polarization and magnetization field operators whose moments are identified with the multipole moments of the charge-current distribution. The multipolar Hamiltonian is obtained from the minimal coupling Hamiltonian through a unitary transformation, often referred to as the Power-Zienau-Woolley transformation; we renormalize this Hamiltonian using perturbation theory, the result of which is used to compute the leading-order radiative corrections to the electronic energy levels due to interactions between the electrons and quantum vacuum fluctuations in the electromagnetic field. Our renormalized energy shift constitutes a generalization of the Lamb shift in atomic hydrogen, valid for general localized assemblies of atoms and molecules, possibly with net charge but absent a free current. By expanding the fields in a series of multipole moments, our results can be used to study contributions to this energy shift coming from specific multipole moments of arbitrary order.

Heisenberg uncertainty principle: an advanced undergraduate laboratory experiment based on quantum quadrature operators

The Heisenberg uncertainty principle (HUP) plays an important role in quantum mechanics. It is necessary to demonstrate this principle experimentally for undergraduates to understand HUP clearly. In this paper, we originally employ the quantum quadrature operators to demonstrate HUP in undergraduate laboratories. Starting from the quantization of electromagnetic field, we briefly review the definition of quadrature operators and demonstrate HUP via the variances of quadrature operators. And the scheme of HUP demonstration with homodyne detection is introduced. More importantly, we develop a tabletop experimental apparatus for the demonstration of HUP in undergraduate laboratories. Our proposal focuses on the basic quantum mechanics concepts, experimental principles, and instruction as well as experimental techniques. It provides a way to help undergraduates, especially the ones who will go on graduate study in quantum technology in the future, make connections between abstract quantum mechanics concepts and concrete experiments, which makes the concepts better understood.

Scattering of the quantized electromagnetic waves from a bi-anisotropic absorbing magneto-dielectric slab

A canonical quantization of electromagnetic field in the presence of a bi-anisotropic absorbing magneto-dielectric slab is provided. The quantized Maxwell’s equations in the presence of the slab are exactly solved and the time-space dependence of the quantized electric and magnetic fields are obtained. The Fock space of the total system is introduced. The scattering matrix of the bi-anisotropic magneto-dielectric slab is obtained in terms of the susceptibility tensors of the slab. The scattering matrix relates the annihilation operators of the outgoing quantized electromagnetic waves from the slab to the annihilation operators of the incoming quantized electromagnetic waves to the slab. The Fresnel’s coefficients of the bi-anisotropic magneto-dielectric slab are obtained in terms of the susceptibility tensors of the slab. The Fresnel’s coefficients relate the powers radiated by the outgoing quantized electromagnetic waves from the slab to the powers radiated by the incoming quantized electromagnetic waves to the slab. The radiated powers by the outgoing quantized electromagnetic waves are calculated in the special cases that the slab is in the thermal state and the incoming quantized electromagnetic waves to the slab are in the vacuum state and the coherent state.

Modeling of spontaneous emission in presence of cylindrical nanoobjects: the scattering matrix approach

We propose a method of analysis of spontaneous emission of a quantum emitter (an atom, a luminescence center, a quantum dot) inside or in vicinity of a cylinder. At the focus of our method are analytical expressions for the scattering matrix of the cylindrical nanoobject. We propose the approach to electromagnetic field quantization based of eigenvalues and eigenvectors of the scattering matrix. The method is applicable for calculation and analysis of spontaneous emission rates and angular dependences of radiation for a set of different systems: semiconductor nanowires with quantum dots, plasmonic nanowires, cylindrical hollows in dielectrics and metals. Relative simplicity of the method allows obtaining analytical and semi-analytical expressions for both cases of radiation into external medium and into guided modes.

Kazimirov efekat

Introduction/purpose: The quantization of the electromagnetic field gives rise to quantum fluctuations which in turn produce a force on macroscopic boundaries. This phenomenon is called the Casimir effect. Method: The second quantization of the electromagnetic field is employed. The Zeta function regularization technique has been applied. Results: Because of the electromagnetic field quantization, a force on macroscopic boundaries is observed. Conclusions: Vacuum fluctuations due to quantum effects give macroscopic results.

Electromagnetic viscosity in complex structured environments: From blackbody to quantum friction

We investigate the nonconservative open-system dynamics of an atom in a generic complex structured electromagnetic environment at temperature $T$. In such systems, when the atom moves along a translation-invariant axis of the environment, a frictional force acts on the particle. The effective viscosity due to friction results from the nonequilibrium interaction with the fluctuating (quantum) electromagnetic field, which effectively sets a privileged reference frame. We study the impact of both quantum or thermal fluctuations on the interaction and highlight how they induce qualitatively different types of viscosity, i.e. quantum and black-body friction. To this end, we develop a self-consistent non-Markovian description that contains the latter as special cases. In particular, we show how the interplay between the nonequilibrium dynamics, the quantum and the thermal properties of the radiation, as well as the confinement of light at the vacuum-material interface is responsible for several interesting and intriguing features. Our analyses is relevant for a future experimental test of noncontact friction and the resulting electromagnetic viscosity.

Quantum theory of statistical radiation pressure in free space

Light is known to exert radiation pressure on any surface it is incident upon, via the transfer of momentum from the light to the surface. In general, this force is assumed to be pushing or repulsive in nature. In this paper, we present a quantum treatment of radiation pressure. We show that the interaction of an atom with light can lead to both repulsive and attractive forces due to absorption and emission of photons, respectively. An atom prepared in the excited state initially will experience a pulling force when interacting with light. On the other hand, if the atom is prepared in the ground state then the force will be repulsive, while having the same magnitude as in the earlier case. Therefore, for an ensemble of atoms, the direction of the net force will be decided by the excited and ground state populations. In the semi-classical treatment of light-matter interaction the absorption and emission processes have the same probability, therefore the magnitudes of the force in the two processes turn out to be the same. We obtain the effective emission profile for an excited atom interacting with quantum electromagnetic field, and show that in the quantum treatment, despite these probabilities being different, the magnitudes of the statistical force remain the same. This can be explained by noting that the extra contribution in the emission process is due to the interaction of the atom with the vacuum modes of electromagnetic field, results in symmetric emission profile, contributing to a net zero force on the atoms in an ensemble. We further identify the set of states of electromagnetic field which give rise to non-zero momentum transfer to the atom.

Motion induced excitation and electromagnetic radiation from an atom facing a thin mirror

We evaluate the probability of (de-)excitation and photon emission from a neutral, moving, non-relativistic atom, coupled to the quantum electromagnetic field and in the presence of a thin, perfectly conducting plane ("mirror"). These results extend, to a more realistic model, the ones we had presented for a scalar model, where the would-be electron was described by a scalar variable, coupled to an (also scalar) vacuum field. The latter was subjected to either Dirichlet or Neumann conditions on a plane. In our evaluation of the spontaneous emission rate produced when the accelerated atom is initially in an excited state, we pay attention to its comparison with the somewhat opposite situation, namely, an atom at rest facing a moving mirror.

Recent developments on the Casimir torque

The Casimir force acts on nearby surfaces due to zero-point fluctuations of the quantum electromagnetic field. In the nonretarded limit, the interaction is also known as the van der Waals force. When the electromagnetic response of the surfaces is anisotropic, a torque may act on the surfaces. Here, we review the literature and recent developments on the Casimir torque. The theory of the Casimir torque is discussed in an explicit example for uniaxial birefringent plates. Recent theoretical predictions for the Casimir torque in various configurations are presented. A particular emphasis is made on experimental setups for measuring the Casimir torque.

Coherent Stimulated Radiation, Coherent Spontaneous Radiation and Coupled Photon Pairs in Non-Uniform Thermally Excited Gaseous Media: Calculation Procedure

This work continues the author’s study of the processes of interaction between a quantum electromagnetic field and a spatially non-uniform gaseous medium [1, 5]. Previously unknown optical effects caused by consideration of high-order quantum correlators were discovered. This is caused by the problem of calculation of high-order photonic correlators starting from the fourth order, which appears when the interaction between the quantum electromagnetic field is described using the Feynman diagrams, According to T.A. Matsubara’s technique applied nowadays, these correlators are just neglected. The author’s articles [1, 5] describe the calculation method allowing us to avoid thiscomplication. The method is based on the following. High-order quantum correlators appear when multi-particle problems are studied. If the number of particles is small (hydrogen atom), the problem disappears. Therefore, if we replace a multi-particle problem with a single-particle problem (even if this particle is rather complex), the problem will be solved. Such solution (by using the Γ-operators technique) is described in the said author’s articles. While the standard secondary quantisation technique uses operators of creation and destruction of separate particles, the Γ-operators technique deals with operators of creation and destruction of photon conglomerates (systems). It turns out that high-order correlators just do not appear when the Γ-operators technique is used. This article demonstrates a specific example of application of the Γ-technique.

Dynamical Casimir effects with atoms: From the emission of photon pairs to geometric phases

The coupling between a moving ground-state atom and the quantum electromagnetic field is at the origin of several intriguing phenomena ranging from the dynamical Casimir emission of photons to Sagnac-like geometric phase shifts in atom interferometers. Recent progress in this emerging field reveals unprecedented connections between non-trivial aspects of modern physics such as electrodynamic retardation, non-unitary evolution in open quantum systems, geometric phases, non-locality and inertia.