Superconducting Islands Amplify Photon Pressure

The ripple in space that we call a photon, or wave/particle of light, does have some mass, but it is so small that is almost zero. It normally takes millions of photons just to measure any impact at all. Joint research based in Finland shows that an island of superconductivity can amplify the ability to detect the radiation pressure of light by a factor of a million.

The significance of this might be applied to making advanced solar sail materials that are more efficient, or even some form of photon engine propulsion. Since superconductivity is easier to achieve in the low temperatures of space, space based applications are a natural pairing for this technology. On a micro scale, the research opens up vistas of new tools for research and the manipulation of matter and energy.

When mediated by superconductivity, light pushes matter million times more

When a mirror reflects light, it experiences a slight push. This radiation pressure can be increased considerably with the help of a small superconducting island. This was revealed by the joint research done in the Aalto University and the Universities of Jyväskylä and Oulu. The finding paves a way for the studies of mechanical oscillations at the level of a single photon, the quantum of light. The results of the research were published in Nature Communications in April.

In our everyday lives, the effects of the radiation pressure of light can be neglected. Your furniture is not moved over even though the light, or more generally the electromagnetic radiation, emitted by your lamps bounces off from its surfaces thus creating a radiation pressure force. An ordinary 100 Watt light-bulb causes a radiation pressure that is only a trillionth (one part to 1000000000000) of the normal atmospheric pressure. Nevertheless, in space the relevance of the phenomenon becomes apparent: because of the radiation pressure the tails of comets typically point away from the Sun. Radiation pressure has also been proposed as the propulsion for the solar sails.

In the recent years, the radiation pressure has been harnessed also in the field of laser physics. It can be used to couple the electromagnetic laser field to, for example, the movement of the small mechanical oscillators that can be found inside ordinary watches. Due to the weakness of the interaction, one typically needs substantially strong laser fields.

– Radiation pressure physics in these systems have become measurable only when the oscillator is hit by millions of photons, explains theorist Jani Tuorila from the University of Oulu.

In the work reported here, the researchers combine their knowledge on experimental and theoretical physics, and show how the strength of the radiation pressure coupling can be considerably increased. They placed a superconducting island in between the electromagnetic field and the oscillator to mediate the interaction.

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