[sounds]

The writeup on phys.org is troublesome at best. Starting with the Ming Hsieh Department of Electrical and Computer Engineering, it buries the rest of that sentence in paragraph 5: USC (University of Southern California) and the Abbe Center of Photonics, Friedrich Schiller University Jena, Germany.

This team has made a nonlinear lattice that relies on something they call "Joule-Thomson-like expansion." The Joule-Thomsen effect is the ideal gas law in beginning science. PV=nRT. Compression heats a gas, expansion cools a gas.

Why they're studying the equivalent photonics principle [1] is that it focuses an array of inputs, "causing light to condense at a single spot, regardless of the initial excitation position." Usually the problem is that light is linearly independent: two beams blissfully ignore each other. To do useful switching or compute, one of the beams has to be able to act as a control signal.

A photon gas doesn't conserve the number of particles (n) like beginning physics would suggest. This lets the temperature of the gas control the output.

The temperature, driven by certain specific inputs, produces the nonlinear response. I didn't see a specific claim what gain they achieved.

This paper is more on the theoretical end of photonics research. Practical research such as at UBC Vancouver [2] where a device does "weight update speed of 60 GHz" and for clustering it can do "112 x 112-pixel images" - the tech doesn't compete well against electronics yet.

TSMC and NVidia are attempting photonics plays too. But they're only achieving raw I/O with photons. They can attach the fiber directly to the chip to save watts and boost speeds.

Basic physics gets in the way too. A photon's wavelength at near UV is 400 nanometers, but the transistors in a smartphone are measured at 7 nanometers ish. Electrical conduction is fundamentally smaller than a waveguide for light. Where light could maybe outshine electrons is in switching speed. But this research paper doesn't claim high switching speed.

[1] https://en.wikipedia.org/wiki/Photon_gas

[2] https://www.nature.com/articles/s41467-024-53261-x

[opticfluorine]

Minor nit, Joule-Thomson is not just the ideal gas law - it is a separate thermodynamic effect entirely. Case in point, for certain gases the change in temperature due to Joule-Thomson has the opposite sign that you would predict from the ideal gas law alone.

This has interesting applications. For example, you can exploit this with dilute metal vapor in an expanding helium gas to cool the metal vapor to very low temperature - the Joule-Thomson expansion of helium increases the helium's temperature by converting the energy of the intermolecular forces into heat. This draws out energy from the metal vapor. If done in a vacuum chamber, then in the region before the shockwave formed by the helium, the supercooled metal atoms will form small van der Waals clusters that can be spectroscopically probed in the jet. This was an interesting area of study back in the 80s that advanced our understanding of van der Waals forces.

[petermcneeley]

Light doesnt interact with itself directly without a third non-light partner. So yes the light of course needs to interact with lattice made of atoms to make any switching possible here. This is why we can see light from the stars though it had to travel through other light for millions of years.

[hinkley]

> TSMC and NVidia are attempting photonics plays too.

It's probably been six years since I looked at this space. The problem at the time for TSMC and several other people was that their solutions worked fairly well for firing photons vertically out of the chip and not well at all for firing them horizontally through the chip. I don't know if in the short term and mid term if an optical PCIe or memory bus is more overall horsepower than faster cross-chip communication in CPUs. But the solutions they were still chasing back then were good between chips, maybe between chiplets. Which could still be an interesting compromise.

> 400 nanometers, but the transistors in a smartphone are measured at 7 nanometers ish

The best em sensors need to be at least 1/10th the length of the frequency they are sending/receiving right? 40 nm isn't awful but it does suggest light for communication between functional units, rather than for assembling them.

[pezezin]

> A photon's wavelength at near UV is 400 nanometers, but the transistors in a smartphone are measured at 7 nanometers ish.

Not really, "7 nm" is just a marketing name, the actual transistors are around 50 nm:

https://en.wikipedia.org/wiki/7_nm_process

[mattashii]

It's true that the transistors are on the order of 50nm, but the conduits for getting the electrons to those transistors are presumably a bit smaller than that.

Probably not 7nm small, but not the full 50 nm either.