Nonequilibrium QED

red ballRadiation Pressure arises in a non-equilibrium steady state with different temperatures

     

yellow ballAt 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)

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

yellow ball "Nonequilibrium Electromagnetic Fluctuations: Heat Transfer and Interactions,"

M. Krüger, T. Emig, and M. Kardar, Phys. Rev. Lett. 106, 210404 (2011)

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.

red ball  As example, consider forces between two micro-spheres at different temperatures:

yellow ball "Non-equilibrium Casimir forces: Spheres and sphere-plate,"

M. Krüger, T. Emig,G. Bimonte and M. Kardar, Europhys. Lett. 95, 21002 (2011) (1 micron Si O2 spheres, force on #2)

yellow ball Whereas the equilibrium force (attractive) falls off as 1/d6, the non-equilibrium force decays as 1/d2. ( * )

yellow ball The non-equilibrium force can be attractive and repulsive.  ( * )

yellow ball Unlike in thermal equilibrium, there are points of stable levitation.  ( * )

yellow ball Forces are not equal and opposite, with points of equal force in the same direction!  ( * )