"Near-field" & Fluctuational QED

Radiation Pressure is a feature of non-equilibrium steady states with different temperatures

           

yellow ball At short scales "near-field effects" due to evanescent waves modify classical "Stefan-Boltzmann" law:

yellow ball  "Surface Phonon Polaritons Mediated Energy Transfer between Nanoscale Gaps," S.Shen, A. Narayanaswamy, G. Chen

Nano Lett. 9, 2909 (2009) Breaking the law, at the nanoscale (MIT news, July 29, 2009)

A generalized approach for computation of Casimir forces, as well as radiation and heat transfer.

yellow ball  "Non-equilibrium Fluctuational QED: Heat Radiation, Heat Transfer and Force,"

G. Bimonte, T. Emig, M. Kardar, and M. Krüger, Annual Review of Condensed Matter Physics 8, 119 (2017)

S.M. Rytov (1959):      "Fluctuational QED"

yellow ball  Fluctuating currents in each object are related to its temperature by a fluctuation-dissipation condition:

yellow ball  The EM field due to thermal fluctuations of one object is related to overall Green's function by:

yellow ball  The overall fluctuations with many objects at different temperatures is then given by:

yellow ball From EM correlations follow the stress tensor and the Poynting vector, hence forces and radiation.

  Heat transfer at short distances is dominated by evanescent modes at material dependent resonances.

For a single dominant frequency , the heat flux diverges at small separations as

Ratchet force due to magnetic field; [far-field (photons) versus near-field (polaritons)]

          

The propulsive force increases in the near-field regime, even more rapidly than the increase in heat transfer!

Scaled motive force F (red diamonds), and heat transfer H (gray circles) for a SiC plate and one of n-InSb subject to a magnetic field along the x-axis. The dots correspond to numeric calculations and the continuous lines to the small d asymptotes. Note that the force changes sign from +y to -y (dark red to light red diamond) at large separation. Inset: [f(ω)/h(ω)](ωd) for d= 1nm.

(Figure parameters: B= 10T, T1= 300K, T2= 270K.)