The long reach of ratchet forces
Asymmetry: Can asymmetry and ratchet forces be used to extract energy from fluctuations?
This is clearly not possible in thermal equilibrium (time reversal symmetry).
Non-equilibrium fluctuations can indeed generate force and motion
- Random motions of bacteria:
Disordered boundaries destroy bulk phase separation in active scalar matter
Yidan Ben Dor, Sunghan Ro, Yariv Kafri, M. Kardar, Julien Tailleur, Phys. Rev. E 105, 044603 (2022) (offline)
Disorder at boundary acts as randomly placed ratchets that stir up the interior of the active fluid over long distances.
The effect of the disordered boundary currents is strong enough to destroy phase separation in the bulk!
Thermal non-equilibrium forces from a gas can be combined with ratchet forces to extract work
Radiative heat transfer as source of non-equilibrium fluctuations?
Radiation and force from a heated ratchet:
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"Near Field Propulsion Forces from Nonreciprocal Media," D. Gelbwaser, N. Graham, M. Kardar, M. Krüger, Phys. Rev. Lett. 126, 170401 (2021).
Reciprocity of electromagnetic field equations: 
"Nonreciprocal radiative heat transfer between two planar bodies," L. Fan, ..., C. Fan, PRB 101, 085407 (2020).
The reciprocity condition can be broken in a number of ways, e.g. by magneto-optical coupling
Asymmetry is quantified by the ratio of cyclotron frequency to a material (e.g. plasma) frequency 
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Due to dispersion relation of photons (relevant at far fields): 
Can near field effects increase the magnitude of the ratchet force?
