>Next, a short but powerful laser pulse is fired into the water jet. This bumps electrons out of the dissolved salts, essentially boosting the conductivity of the water. A second laser can read back what state the water is in, providing the “on” and “off” options of an existing transistor.
Sounds like an optical computer much more than a water computer (compared to e.g. microfluidics), and it's much less surprising that an optical switch would switch fast.
So I've been out of Chemistry for the best part of a decade but I think the novel part of this is exploiting the fact that water based solvents are insanely efficient at propagating charge.
Here is some reading I think nay be relevant[0][1][2] but tldr thanks to the miracle of hydrogen bonding, protons/electrons can "transfer" through water by an extremely fast chain reaction of proton association/dissociation - thereby circumventing diffusion as a transfer mechanism.
Laser is a useful interface because lasers can be controlled digitally and provide a convenient way of ionising the solution, but this seems like quite a cool hack exploiting the properties of water to me.
The question is: how are the laser an photodiodes driven? Also water? I bet no. Just transistors... so, why not use the transistors switching the laser directly, without the whole laser/water/photodiode path?
Foundational research into principles that leads nowhere is not the problem. The pool of cool ideas like this is unknowably large, and it would be sad to not see papers like this from time time. [Edit: as long as it is a high-quality study of course.]
The true problem of the publish-or-perish world is the moral hazard that it causes. In booming fields, it is very seductive to abuse statistics or to outright fake data. These are not always caught by peer review!
> Because the laser pulse is so fast, the water can switch states in a matter of picoseconds, which are trillionths of a second. This translates to potential computer speeds in the terahertz (THz) range – that’s 1,000 GHz, which is far faster than any existing semiconductor can switch.
Picoseconds means under 1000GHz. 1ps would be 1000GHz.
Transistors can switch in picoseconds. The fastest basic bulk silicon ones hundreds of GHz as far as I know. More exotic ones I'm sure could be made a lot faster.
So exactly how much faster is this water based switching device than a transistor? Hopefully the author was not under the impression that transistor switching speed was on the order of CPU clock frequency.
According to the article, they have demonstrated the generation of a signal with the frequency of 3 THz, and the switching time is under 200 fs (exponential edge with a time constant of 70 fs).
The shortest laser pulses are much shorter than any pulses that can be generated with electronic devices, and they are generated by various optical means.
There are no transistor circuits that go into THz, but only into hundreds of GHz, and at those high frequencies they are not pulse circuits, but amplifiers or oscillators.
A review of potential future transistors that will go into low THz:
Iodine in water ionized on the picosecond scale, by laser pulse.
Would be mildly surprised if that didn't happen that fast. I guess the interesting twist is that the medium is flowing liquid.
How long does this state last? If one were to, say, write a series of bits into the upstream side of the flow, how many such bits could you recover downstream? The potential I see here is possibly a delay line for THz band signals, not so much the basis for logic for a 1000GHz CPU. But delay lines are darned useful things.
You can describe any transistor with the same words as "shine a laser at a material to change it, and then use another laser to detect the difference":
"apply a voltage at a device to change it, and then use another voltage to detect the difference (i.e. to detect if a current passes)".
This is an optical switch, like a transistor is an electrical switch. An optical switch that is not very efficient, because the transmission is varied only between 100% and 80%, but one that is very fast.
It can be used in THz range mixers and oscillators.
In the definition of any controlled switch, e.g. transistor, optical switch or any other kind, it is essential that there are two distinct quantities, e.g. voltages or light beams, one that controls the output state and one that provides power to the output circuit.
A resistor corresponds to a tinted window, not to an optical switch.
Ok, with that addition, here is another analogy: I have one battery that I use to charge a capacitor. Then I have another battery in my voltmeter, which I use to measure the voltage over the capacitor. How does this make it possible to build logic gates with capacitors?
Instead of trying to generalize the principle, why don't you explain how you can make logic gates using the technology of the article? And how can you tie these logic gates together without the signal becoming weaker between input and output?
The comment above yours said "and then ... detect the difference", implying sequential action and a real change of state - not simultaneous action+measure.
"""Because the laser pulse is so fast, the water can switch states in a matter of picoseconds, which are trillionths of a second."""
Although after reading, I must agree that the time-scale feels quite ridiculous!!
(EDIT: RE: "Capacitors can't be logic gates" below - Maybe. But if 1+0=1, and 1+1=2, then surely differentiating 0/1 vs 2 on the output creates an AND gate?)
(I am "posting too fast" with 3 posts in the last hour. Sorry :)
Note that in a transistor, "another voltage to detect the difference" can be used to trigger another transistor, and so on. Until the laser reading the state of water can itself trigger a write in another water "switch", this is just a cute dead-end phenomenon.
> To replace electronic components with optical ones, an equivalent optical transistor is required. This is achieved using materials with a non-linear refractive index.
There is no impediment for making a complex logic gate by an arbitrary series-parallel connection of the output light beams.
The output of such a logic gate cannot be connected to the input of an identical logic gate, because the input and the output light beams have different frequencies.
This is a problem common for many kinds of optical switches. It is likely that any conversion circuit that could be inserted between two such logic gates would be much slower than them, negating any speed advantage.
This does not really matter, because such optical switches are not intended for making logic circuits.
That doesn't involve a laser like in the article, and is probably much slower. I don't think you can get Terahertz speeds by just using Newtonian physics on water.
While the paper's keywords list includes both microfluidics and photonics, nothing about the device is anything like an opto-fluidic logic gate. The laser is used to measure properties of cells suspended in the fluid, with the output light signal being processed by conventional photonics.
>> Because the laser pulse is so fast, the water can switch states in a matter of picoseconds, which are trillionths of a second. This translates to potential computer speeds in the terahertz (THz) range – that’s 1,000 GHz,
This in not comparable to transistors in a computer. Transistors use charge (electrons) to switch current (electrons) in order to build boolean gates and logic circuits. Those lasers are probably not optically controlled, and even if they were and could be made into optical logic circuits, their speed will be limited by their size and the speed of light.
Yes, I'd say it's switching losses driving power dissipation, mostly, but also the amplification factor (often written as 60mV/decade). Bipolar transistors are still better at that.
I haven't read the article yet, but I can imagine a chip with watercooling microfluidic channels, possibly also used to transmit informations (kind of like hormones in the bloodstream). If it is useful as a computing medium why not?
Compactness and timing. I don’t know why picosecond switching is a big deal, here? A 3Ghz part with a transistor depth of 40 would require a top end switching rate of 8 picoseconds — and that’s really going to make PD unhappy, as it’d leave no timing margin. At best, this tech is 2–4x faster than the device in your pocket; it’s probably slower, knowing the timing rates of some of the analog-on-digital parts being shipped, right now.
Sounds like an optical computer much more than a water computer (compared to e.g. microfluidics), and it's much less surprising that an optical switch would switch fast.