Power/Performance Bits: Aug. 26

Oxford researchers have discovered a quantum effect in which excited atoms can be turned on their head to create superabsorbing systems to make the ultimate camera pixel; University of Tokyo researchers have demonstrated a colossal optical isolator effect driven by spin helix that holds promise in future high capacity communications.

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Making light work of snaps
‘Superradiance’, a phenomenon where a group of atoms charged up with energy act collectively to release a far more intense pulse of light than they would individually, is well-known to physicists. In theory the effect can be reversed to create a device that draws in light ultra-efficiently. This could be revolutionary for devices ranging from digital cameras to solar cells. But there’s a problem: the advantage of this quantum effect is strongest when the atoms are already 50% charged – and then the system would rather release its energy back as light than absorb more.

Now a team led by Oxford University theorists believes it has found the solution to this seemingly fundamental problem. Part of the answer came from biology. The lead researcher said he was inspired to study ring molecules, because they are what plants use in photosynthesis to extract energy from the Sun. What they discovered is that they should be able to go beyond nature’s achievement and create a quantum superabsorber.

At the core of the new design is a molecular ring, which is charged to 50% by a laser pulse in order to reach the ideal superabsorbing state – that needs to be kept in that condition. For this the team proposes exploiting a key property of the ring structure: each time it absorbs a photon, it becomes receptive to photons of a slightly higher energy. Charging the device is like climbing a ladder whose rungs are increasingly widely spaced.

Superabsorbing ring could make light work of snaps. (Source: University of Oxford)

Superabsorbing ring could make light work of snaps.
(Source: University of Oxford)

Eventually, harvesting sunlight in a highly-efficient way might one day be possible using superabsorbing systems based on this design, but a more immediate application would be building an extremely sensitive light sensor that could form the basis of new camera technology.

High capacity communications devices
With promise in future high capacity communications, a research group at the University of Tokyo Graduate School of Engineering have discovered a new optical functionality of helical electron spin structures that emerge in matter and by which the optical absorption of counter-propagating light beams is greatly differentiated.

When a helical spin structure shows up in matter, the light coming from the left side transmits, but the light coming from the right side is absorbed on the resonance of the electromagnon. (Source: University of Tokyo)

When a helical spin structure shows up in matter, the light coming from the left side transmits, but the light coming from the right side is absorbed on the resonance of the electromagnon.
(Source: University of Tokyo)

The research group found that the electromagnon, a kind of collective spin motion, emerges in the gigahertz to terahertz frequency range when the helical electron spin structure is present. Due to the helical electron spin structure possessing both “magnetism” and “chirality,” it was further discovered that the electromagnon exhibits a colossal magnetochiral effect. Using this magnetochiral effect, the research group succeeded in altering the extinction coefficient by up to 400% depending on the propagation direction of light beams.

According to the researchers, R&D of optical devices for control of light (electromagnetic waves) in the frequency region including the higher gigahertz and terahertz, which is expected to be used for applications including future high capacity communications. They said the current result may be used for the development of optical devices such as isolators that only permit light to pass in one direction and optical devices for the control of light via external electrical and magnetic signals.