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arXiv:2404.15216 · Physical Review A

Geometric phase of a two-level atom near a dielectric nanosphere out of thermal equilibrium

Ehsan Amooghorban, S. Shahidani, Somaye Mohamadi Abdhvand

Published Sep 10, 2024• 1 citation
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Abstract

We study the geometric phase (GP) of a two-level atom coupled to an environment composed of free space and a dielectric nanosphere in thermal and out of thermal equilibrium. We analytically and numerically analyze the optical properties and loss of the dielectric medium, along with the nonequilibrium effects of the environment on the GP. In the weak coupling limit, we find that the correction to the GP depends on the partial local density of photonic states at the atom position, and an effective parameter that emerges out of the nonequilibrium configuration of the system. The GP exhibits a significant enhancement due to the excitation of evanescent surface waves at its resonance frequency. It is shown that the GP acquired by the atomic system out of thermal equilibrium is always bounded between the thermal-equilibrium counterparts. Furthermore, the temperature difference between the nanosphere and free space can play an important role in the GP only at moderate atomic distances from the nanosphere. Our results elegantly demonstrate properties of the GP near material media that can support phononic modes and pave the way for further research of GP as a resource for quantum computation.

DOI
10.1103/physreva.110.033710

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We study the geometric phase (GP) of a two-level atom coupled to an environment composed of free space and a dielectric nanosphere in thermal and out of thermal equilibrium. We analytically and numerically analyze the optical properties and loss of the dielectric medium, along with the nonequilibrium effects of the environment on the GP. In the weak coupling limit, we find that the correction to the GP depends on the partial local density of photonic states at the atom position, and an effective parameter that emerges out of the nonequilibrium configuration of the system. The GP exhibits a significant enhancement due to the excitation of evanescent surface waves at its resonance frequency. It is shown that the GP acquired by the atomic system out of thermal equilibrium is always bounded between the thermal-equilibrium counterparts. Furthermore, the temperature difference between the nanosphere and free space can play an important role in the GP only at moderate atomic distances from the nanosphere. Our results elegantly demonstrate properties of the GP near material media that can support phononic modes and pave the way for further research of GP as a resource for quantum computation.
We discuss how the thermalization of an elementary quantum system is modified when the system is placed in an environment out of thermal equilibrium. To this aim we provide a detailed investigation of the dynamics of an atomic system placed close to a body of arbitrary geometry and dielectric permittivity, whose temperature TMT_MTM​ is different from that of the surrounding walls TWT_WTW​. A suitable master equation for the general case of an NNN-level atom is first derived and then specialized to the cases of a two- and three-level atom. Transition rates and steady states are explicitly expressed as a function of the scattering matrices of the body and become both qualitatively and quantitatively different from the case of radiation at thermal equilibrium. Out of equilibrium, the system steady state depends on the system-body distance, on the geometry of the body and on the interplay of all such parameters with the body optical resonances. While a two-level atom tends toward a thermal state, this is not the case already in the presence of three atomic levels. This peculiar behavior can be exploited, for example, to invert the populations ordering and to provide an efficient cooling mechanism for the internal state of the quantum system. We finally provide numerical studies and asymptotic expressions when the body is a slab of finite thickness. Our predictions can be relevant for a wide class of experimental configurations out of thermal equilibrium involving different physical realizations of two or three-level systems.
We discuss how the thermalization of an elementary quantum system is modified when the system is placed in an environment out of thermal equilibrium. To this aim we provide a detailed investigation of the dynamics of an atomic system placed close to a body of arbitrary geometry and dielectric permittivity, whose temperature TM{T}_{\mathrm{M}}TM​ is different from that of the surrounding walls TW{T}_{\mathrm{W}}TW​. A suitable master equation for the general case of an NNN-level atom is first derived and then specialized to the cases of a two- and three-level atom. Transition rates and steady states are explicitly expressed as a function of the scattering matrices of the body and become both qualitatively and quantitatively different from the case of radiation at thermal equilibrium. Out of equilibrium, the system steady state depends on the system-body distance, on the geometry of the body, and on the interplay of all such parameters with the body optical resonances. While a two-level atom tends toward a thermal state, this is not the case already in the presence of three atomic levels. This peculiar behavior can be exploited, for example, to invert the populations ordering and to provide an efficient cooling mechanism for the internal state of the quantum system. We finally provide numerical studies and asymptotic expressions when the body is a slab of finite thickness. Our predictions can be relevant for a wide class of experimental configurations out of thermal equilibrium involving different physical realizations of two- or three-level systems.
We study the thermalization of an elementary quantum system modeled by a two-level atom interacting with stationary electromagnetic fields out of thermal equilibrium near a dielectric slab. The slab is held at a temperature different from that of the region where the atom is located. We find that when the slab is nonabsorbing and nondispersive, out-of-thermal-equilibrium effects exist only when its thickness is infinite. In other words, no out-of-thermal-equilibrium effects appear for a real dielectric slab of a finite thickness ddd. Furthermore, a finite thick dielectric slab with a tiny imaginary part in the relative permittivity $\mathrm{Im}\ensuremath{\epsilon}$ behaves like a half-space dielectric substrate if $\frac{\mathrm{Im}\ensuremath{\epsilon}}{\sqrt{\mathrm{Re}\ensuremath{\epsilon}\ensuremath{-}1}}\frac{d}{{\ensuremath{\lambda}}_{0}}>1$ is satisfied, where ${\ensuremath{\lambda}}_{0}$ is the transition wavelength of the atom. This condition can serve as a guide for an experimental verification, using a dielectric substrate of a finite thickness, of the effects that arise from out-of-thermal-equilibrium fluctuations with a half-space (infinite thickness) dielectric.
The photon-number statistics from resonance fluorescence of a two-level atom near a metal nanosphere driven by a laser field with finite bandwidth is studied theoretically. Our analysis shows that all interesting physics here takes place in a small area around the nanosphere where the near field and the atom-nanosphere coupling essentially affect the radiative properties of the atom. Computer modeling estimates this area roughly as $r\ensuremath{\le}2a$ (r(r(r is the distance from the center of the nanosphere to the atom), with aaa being the radius of the nanosphere. At the larger distances, the influence of the nanoparticle vanishes and the atom tends to behave similarly to that in free space. It is shown that the distribution function p(n,T)p(n,T)p(n,T) of the emission probability of nnn photons in a given time interval TTT in steady-state resonance fluorescence drastically depends on the atom location around the nanosphere for $r\ensuremath{\le}2a$, featuring a characteristic twist in the ridgelike dependence and a convergence time of up to $9\ensuremath{\mu}\text{s}$, two orders of magnitude slower than for the atom in free space. At large distances, the distribution converges to a Gaussian one, as for the atom in free space. The typical convergence time scale at large distances r>2ar>2ar>2a tends to the convergence time of the atom in free space. There are also two areas symmetrical around the nanosphere in which $\ensuremath{\Omega}\ensuremath{\sim}\ensuremath{\gamma}$ and the convergence time goes to zero. This behavior is determined by the interplay of the radiative and nonradiative decay rates of the atom due to the coupling with the metal nanosphere and by the near-field intensity. Additional parameters are the normalized laser frequency detuning from the atomic resonance and the bandwidth of the incoming laser field.
The energy–level shifts of an atom located at a distance Z outside a dielectric half–space are calculated at finite temperatures. The refractive index of the medium is real and frequency independent; the limiting case of perfect reflectors is also considered. The analytic expressions for the energy–level shifts are analysed in various regimes of temperature and of the distance of the atom from the surface. The significance of thermal corrections in comparison with zero–temperature effects is analysed in each regime and discussed for recent experiments.
We study the internal dynamics of an elementary quantum system placed close to a body held at a temperature different from that of the surrounding radiation. We derive general expressions for lifetime and density matrix valid for bodies of arbitrary geometry and dielectric permittivity. Out of equilibrium, the thermalization process and steady states become both qualitatively and quantitatively significantly different from the case of radiation at thermal equilibrium. For the case of a three-level atom close to a slab of finite thickness, we predict the occurrence of population inversion and an efficient cooling mechanism for the quantum system, whose effective internal temperature can be driven to values much lower than both involved temperatures. Our results show that non-equilibrium configurations provide new promising ways to control the state of an atomic system.