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Vanik E. Mkrtchian

Publications and source records attributed to Vanik E. Mkrtchian.

11 recordsLinked to original sources
arXiv2026

Resonances in light scattering from nonequilibrium dipole pairs

We identify a fundamentally new class of resonances in light scattering from a pair of point-like electric dipoles. These resonances arise from multiple scattering response and correspond to poles of the two-particle Green function. The realization of exact resonances requires violation of the optical theorem, which holds in equilibrium systems but can be violated under nonequilibrium conditions, without violating causality. As a concrete example, we show that a pumped two-level atom can realize the required polarizability and access the exact resonance regime. Our results for one electric and one magnetic dipole show how resonances can amplify a weak magnetic response of a single dipole to the incident field. In equilibrium systems, only approximate resonances with finite amplification are possible. Using the Drude model for metallic nanoparticles, we show that while equilibrium resonances enhance the scattering, they never exceed the optimal single-dipole response.

physics.optics↗
arXiv2025

Enhanced detection of time-dependent dielectric structure: Rayleigh's limit and quantum vacuum

Detection of scattered light can determine the susceptibility of dielectrics. Such imaging normally holds Rayleigh's limit: details finer than the wavelength of the incident light cannot be determined from the far-field zone. We show that time-modulation of an inhomogeneous dielectric can be used to determine its susceptibility. To this end, we focus on the inverse quantum optics problem for spatially and temporally modulated metamaterial, whose dielectric susceptibility is similar to moving dielectrics. We show that the vacuum contribution to the photodetection signal is non-zero due to the negative frequencies even in the far-field zone. Hence, certain dielectric features can be determined without radiating any incident field on the dielectric. When the incident light is scattered (or re-radiated), the determination of dielectric susceptibility is enhanced and overcomes Rayleigh's limit in the far-field zone. We study similar effects for an inhomogeneous dielectric moving with a constant speed, a problem we consider within relativistic optics. Now the vacuum contribution to the photodetection signal reflects dielectric features, can be long-range in space but is not a far-field effect.

quant-ph↗
arXiv2024

Angular distributions and polarization correlations of the two-photon spherical states

We have analyzed in detail the angular polarization properties in the center of mass reference frame of Landau's two-photon spherical states in momentum space. The angular distributions for fixed values of $J$ and $M$ do not depend on the parity but are defined by two different functions of the polar angle between the relative momentum and the quantization axes. The two-photon polarization density matrices are derived for each values of $J$, $M$, and $P$. The linear polarization correlations of individual photons are analyzed in detail. We find, besides the usual correlation laws for $J\geq 2$ in terms of $sin$ and $cos$ of the angle between the orientation of the analyzers, correlations in terms of the sum of the orientation angles of the analyzers.

quant-ph↗
arXiv2021

Bose-Einstein Condensation and quasicrystals

We consider interacting Bose particles in an external local potential. It is shown that large class of external quasicrystal potentials cannot sustain any type of Bose-Einstein condensates. Accordingly, at spatial dimensions $D\leq 2$ in such quasicrystal potentials a supersolid is not possible via Bose-Einstein condensates at finite temperatures. The latter also hold true for the two-dimensional Fibonacci tiling. However, supersolids do arise at $D\leq 2$ via Bose-Einstein condensates from infinitely long-range, nonlocal interparticle potentials.

cond-mat.quant-gas↗
arXiv2021

Bose-Einstein Condensation and Supersolids

We consider interacting Bose particles in an external potential. It is shown that a Bose-Einstein condensate is possible at finite temperatures that describes a supersolid in three dimensions (3D) for a wide range of potentials in the absence of an external potential. However, for 2D, a self-organized supersolid exists for finite temperatures provided the interaction between bosons is nonlocal and of infinitely long-range. It is interesting that in the absence of the latter type of potential and in the presence of a lattice potential, there is no Bose-Einstein condensate and so in such a case, a 2D supersolid is not possible at finite temperatures. We also propose the correct Bloch form of the condensate wave function valid for finite temperatures, which may be used as the correct trial wave function.

cond-mat.quant-gas↗
arXiv2020

Green function solution of generalised boundary value problems

We construct an expression for the Green function of a differential operator satisfying nonlocal, homogeneous boundary conditions starting from the fundamental solution of the differential operator. This also provides the solution to the boundary value problem of an inhomogeneous partial differential equation with inhomogeneous, nonlocal, and linear boundary conditions. The construction generally applies for all types of linear partial differential equations and linear boundary conditions.

math.AP↗
arXiv2018

Quantum entropy and polarization measurements of the two-photon system

We consider the bipartite state of a two-photon polarization system and obtain the exact analytical expression for the von Neumann entropy in the particular case of a 5-parameter polarization density matrix. We investigate and graphically illustrate the dependence of the entropy on these five parameters, in particular, the existence of exotic, transition from exotic to non-exotic, and non-exotic states, where the quantum conditional entropy is negative, both positive and negative, and positive, respectively. We study the "cooling" or "heating" effect that follows from the reduced density of photon 2 when a measurement is performed on photon 1.

quant-ph↗
arXiv2015

Friction forces on atoms after acceleration

The aim of this paper is to revisit the calculation of atom-surface quantum friction in the quantum field theory formulation put forward by Barton [New J. Phys. 12 (2010) 113045]. We show that the power dissipated into field excitations and the associated friction force depend on how the atom is boosted from being initially at rest to a configuration in which it is moving at constant velocity (v) parallel to the planar interface. In addition, we point out that there is a subtle cancellation between the one-photon and part of the two-photon dissipating power, resulting in a leading order contribution to the frictional power which goes as v^4. These results are also confirmed by an alternative calculation of the average radiation force, which scales as v^3.

quant-ph↗
arXiv2013

On non-equilibrium photon distributions in the Casimir effect

The electromagnetic field in a typical geometry of the Casimir effect is described in the Schwinger-Keldysh formalism. The main result is the photon distribution function (Keldysh Green function) in any stationary state of the field. A two-plate geometry with a sliding interface in local equilibrium is studied in detail, and full agreement with the results of Rytov fluctuation electrodynamics is found. As an illustration, plots are shown for a spectrum of the energy density between the plates.

quant-ph↗
arXiv2008

Artificial Rydberg Atom

We analyze bound states of an electron in the field of a positively charged nanoshell. We find that the binding and excitation energies of the system decrease when the radius of the nanoshell increases. We also show that the ground and the first excited states of this system have remarkably the same properties of the highly excited Rydberg states of a hydrogen-like atom i.e. a high sensitivity to the external perturbations and long radiative lifetimes.

quant-ph↗