78 research outputs found
Surface-atom force out of thermal equilibrium and its effect on ultra-cold atoms
The surface-atom Casimir-Polder-Lifshitz force out of thermal equilibrium is
investigated in the framework of macroscopic electrodynamics. Particular
attention is devoted to its large distance limit that shows a new, stronger
behaviour with respect to the equilibrium case. The frequency shift produced by
the surface-atom force on the the center-of-mass oscillations of a harmonically
trapped Bose-Einstein condensate and on the Bloch oscillations of an ultra-cold
fermionic gas in an optical lattice are discussed for configurations out of
thermal equilibrium.Comment: Submitted to JPA Special Issue QFEXT'0
Near-field heat transfer between graphene/hBN multilayers
We study the radiative heat transfer between multilayer structures made by a
periodic repetition of a graphene sheet and a hexagonal boron nitride (hBN)
slab. Surface plasmons in a monolayer graphene can couple with a hyperbolic
phonon polaritons in a single hBN film to form hybrid polaritons that can
assist photon tunneling. For periodic multilayer graphene/hBN structures, the
stacked metallic/dielectric array can give rise to a further effective
hyperbolic behavior, in addition to the intrinsic natural hyperbolic behavior
of hBN. The effective hyperbolicity can enable more hyperbolic polaritons that
enhance the photon tunneling and hence the near-field heat transfer. However,
the hybrid polaritons on the surface, i.e. surface plasmon-phonon polaritons,
dominate the near-field heat transfer between multilayer structures when the
topmost layer is graphene. The effective hyperbolic regions can be well
predicted by the effective medium theory (EMT), thought EMT fails to capture
the hybrid surface polaritons and results in a heat transfer rate much lower
compared to the exact calculation. The chemical potential of the graphene
sheets can be tuned through electrical gating and results in an additional
modulation of the heat transfer. We found that the near-field heat transfer
between multilayer structure does not increase monotonously with the number of
layer in the stack, which provides a way to control the heat transfer rate by
the number of graphene layers in the multilayer structure. The results may
benefit the applications of near-field energy harvesting and radiative cooling
based on hybrid polaritons in two-dimensional materials.Comment: 10 pages, 11 figure
Nonreciprocal heat flux via synthetic fields in linear quantum systems
We study the heat transfer between N coupled quantum resonators with applied
synthetic electric and magnetic fields realized by changing the resonators
parameters by external drivings. To this end we develop two general methods,
based on the quantum optical master equation and on the Langevin equation for
coupled oscillators where all quantum oscillators can have their own heat
baths. The synthetic electric and magnetic fields are generated by a dynamical
modulation of the oscillator resonance with a given phase. Using Floquet theory
we solve the dynamical equations with both methods which allow us to determine
the heat flux spectra and the transferred power. With apply these methods to
study the specific case of a linear tight-binding chain of four quantum coupled
resonators. We find that in that case, in addition to a non-reciprocal heat
flux spectrum already predicted in previous investigations, the synthetic
fields induce here non-reciprocity in the total heat flux hence realizing a net
heat flux rectification
New asymptotic behaviour of the surface-atom force out of thermal equilibrium
The Casimir-Polder-Lifshitz force felt by an atom near the surface of a
substrate is calculated out of thermal equilibrium in terms of the dielectric
function of the material and of the atomic polarizability. The new force decays
like at large distances (i.e. slower than at equilibrium), exhibits a
sizable temperature dependence and is attractive or repulsive depending on
whether the temperature of the substrate is higher or smaller than the one of
the environment. Our predictions can be relevant for experiments with ultracold
atomic gases. Both dielectric and metal substrates are considered.Comment: 4 pages, 3 figures. In press on Phys. Rev. Let
Measurement of the Temperature Dependence of the Casimir-Polder Force
We report on the first measurement of a temperature dependence of the
Casimir-Polder force. This measurement was obtained by positioning a nearly
pure 87-Rb Bose-Einstein condensate a few microns from a dielectric substrate
and exciting its dipole oscillation. Changes in the collective oscillation
frequency of the magnetically trapped atoms result from spatial variations in
the surface-atom force. In our experiment, the dielectric substrate is heated
up to 605 K, while the surrounding environment is kept near room temperature
(310 K). The effect of the Casimir-Polder force is measured to be nearly 3
times larger for a 605 K substrate than for a room-temperature substrate,
showing a clear temperature dependence in agreement with theory.Comment: 4 pages, 4 figures, published in Physical Review Letter
Radiation induced force between two planar waveguides
We study the electromagnetic force exerted on a pair of parallel slab
waveguides by the light propagating through them. We have calculated the
dependence of the force on the slab separation by means of the Maxwell--Stress
tensor formalism and we have discussed its main features for the different
propagation modes: spatially symmetric (antisymmetric) modes give rise to an
attractive (repulsive) interaction. We have derived the asymptotic behaviors of
the force at small and large separation and we have quantitatively estimated
the mechanical deflection induced on a realistic air-bridge structure.Comment: 10 pages, 6 figure
Hybrid thermal Yagi-Uda nanoantennas for directional and narrow band long-wavelength IR radiation sources
We investigate the possibility of spatially and spectrally controlling the thermal infrared emission by exploitation of the Yagi-Uda antenna design. Hybrid antennas composed of both SiC and Au rods are considered and the contributions of emission from all the elements, at a given equilibrium temperature, are taken into account. We show that the detrimental effect due to thermal emission from the not ideal parasitic elements drastically affect the performances of conventional thermal Au antennas in the 12 ÎĽm wavelength range. Nevertheless, our results show that the hybrid approach allows the development of efficient narrow-band and high directivity sources. The possibility of exploiting the Yagi-Uda design both in transmission and in reception modes, may open the way to the realization of miniaturized, efficient, robust and cheap sensor devices for mass-market applications. 2020 Optical Society of America
Optimization of highly circularly polarized thermal radiation in -MoO/-GaO twisted layers
We investigate a bi-layer scheme for circularly polarized infrared thermal
radiation. Our approach takes advantage of the strong anisotropy of
low-symmetry materials such as -GaO and -MoO. We
numerically report narrow-band, high degree of circular polarization (over
0.85), thermal radiation at two typical emission frequencies related to the
excitation of -GaO optical phonons. Optimization of the degree
of circular polarization is achieved by a proper relative tilt of the crystal
axes between the two layers. Our simple but effective scheme could set the
basis for a new class of lithography-free thermal sources for IR bio-sensing.Comment: 11 pages, 6 figure
Scattering-matrix approach to Casimir-Lifshitz force and heat transfer out of thermal equilibrium between arbitrary bodies
We study the radiative heat transfer and the Casimir-Lifshitz force occurring
between two bodies in a system out of thermal equilibrium. We consider bodies
of arbitrary shape and dielectric properties, held at two different
temperatures, and immersed in a environmental radiation at a third different
temperature. We derive explicit closed-form analytic expressions for the
correlations of the electromagnetic field, and for the heat transfer and
Casimir-Lifshitz force, in terms of the bodies scattering matrices. We then
consider some particular cases which we investigate in detail: the atom-surface
and the slab-slab configurations
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