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Following a flurry of activity in the 1990s, there is now a resurgence of interest in optical solitons: three papers in this issue present diverse insights into their manipulation, behaviour and potential practical use. First, Marco Peccianti and colleagues show how to control the path of spatial solitons travelling through anematic liquid crystal by electrically altering the refractive index of different regions of the material. Carmel Rotschild and colleagues report an extremely long-range interaction between spatial solitons — which usually only interact when they're less than a few beam widths apart — travelling within a heat-sensitive nonlinear medium. And finally, Joe Mok and colleagues demonstrate the ability to tune the speed of gap solitons, slowing them to a sixth of the speed of light in vacuum by launching them near the band edge of a fibre Bragg grating.
Two recent developments suggest how familiar properties of gravity and matter may emerge from the quantum geometry that underlies loop quantum gravity.
Classically, the second law of thermodynamics implies that our knowledge about a system always decreases. A more flattering interpretation connects entropy with the uncertainty inherent to quantum mechanics.
The ability to control the path of optical spatial solitons — non-spreading filaments of light that travel through a bulk nonlinear medium — could aid their use in signal processing and other photonics applications.
The process of adsorption and subsequent desorption of gases in porous materials often shows hysteretic behaviour. A combination of diffusion measurements and numerical modelling could now explain why.
The discovery that microfluidic 'crystals' exhibit long-range collective behaviour demonstrates their potential use as a testbed for studying dissipative self-organization and other non-equilibrium phenomena.
Most techniques for slowing light are limited in the delay time that can be achieved relative to the temporal pulse width. The use of gap solitons could help overcome this limitation.