
‘A Swiss cheese-like material’ that can solve equations - ausbah
https://penntoday.upenn.edu/news/penn-engineers-demonstrate-metamaterials-can-solve-equations
======
wwarner
This is pretty cool. I don't know the nature of the calculation performed, but
if it's an integral that took say 1000 clock cycles on a single core 1Ghz
digital computer, and if it's true that the meta-material will scale down 1
picosecond for the same calculation, then this is around a 1,000,000x speedup.
Further, if you can create a set of say 100 integrators and differentiators
into which you can decompose all your complicated math operations, then you
have yourself a very very fast general purpose higher order math module.

~~~
opwieurposiu
Those 1000 clock cycles get you a perfect digital answer that is the same
every time. This analog version gets you a faster answer with less accuracy
and repeatability. This may be useful in some situations, but I would not call
it general purpose.

~~~
wwarner
I'm just speculating, but I don't see why you can't quantize the output
electrically. I guess I'm suggesting a mixed mode system, where an electronic
cpu sends an array of values to an optical system that performs a calculation
and returns a result electronically.

~~~
opwieurposiu
Sure you can quantize the output but that is not going to help your accuracy.
Today's Ghz CPU is 64bit, today's Ghz ADCs are 8 to 16bits. This gets you ~3
to ~5 decimal sig figs for analog and ~15.9 decimal sig figs for 64bit
floating point. That's assuming your analog side is perfect, which is unlikely
to say the least.

[http://www.ti.com/data-converters/adc-circuit/high-
speed/rf-...](http://www.ti.com/data-converters/adc-circuit/high-speed/rf-
sampling.html)

Also note the fast ones require 1+ watts per channel and cost $700+ each. Not
cheap in power or in money.

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monocasa
Really reminds me of a special type of analog computer that wasn't mentioned,
but was definitely used in old school engineering: using conductive paper to
model all sorts of fields.

[https://en.m.wikipedia.org/wiki/Teledeltos](https://en.m.wikipedia.org/wiki/Teledeltos)

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jcims
Similar research using optical diffraction to build neural networks:

[https://arxiv.org/pdf/1804.08711.pdf](https://arxiv.org/pdf/1804.08711.pdf)

TWiML podcast of same: [https://twimlai.com/twiml-talk-237-deep-learning-in-
optics-w...](https://twimlai.com/twiml-talk-237-deep-learning-in-optics-with-
aydogan-ozcan/)

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LolWolf
Hey! I currently work on inverse design at the Nanoscale and Quantum Photonics
lab [0], which is the approach the authors used in this paper.

If you have any questions (about the specifics of the paper, or, more
generally, about the process), feel free to send them over :)

\---

[0] nqp.stanford.edu

~~~
opwieurposiu
How many sig figs can you get out of this microwave implementation?

In my experience trying to get RF measurements repeatable starts to become
tricky at around 1% error. The dielectric constant of plastic parts changes
constantly, capacitors age, etc. How sensitive is this device to temperature,
humidity, barometric pressure, etc?

~~~
LolWolf
It's unclear. Depending on the fabrication constraints/robustness constraints
they added to the inverse design procedure (which they don't really mention in
the paper), it could be either extremely robust or extremely sensitive.
Generally, in terms of measurements, if the conditions are controlled, it's
pretty easy to get small noise (especially in the case where these devices are
so large, as is their wavelength) relative to most perturbations that happen
in the lab. Overall, this is not really mentioned in the paper (unless I
missed it), so I'm afraid I can't give you a direct answer on what they do,
just that it is possible (via this method) to design a device which is
relatively robust to these changes.

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based2
[https://www.reddit.com/r/programming/comments/b4ceu9/new_pho...](https://www.reddit.com/r/programming/comments/b4ceu9/new_photonic_calculus_metamaterial_solves/)

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kirykl
Amusingly, the overhead view of their structure looks vaguely like an overhead
view of the brain

~~~
kylek
Funny, it reminded me of the Plinko board from The Price is Right [0].
Strangely, this is almost exactly how I explain to myself in dumbed-down terms
(armchair-quantum-physicising over here) of how quantum computation might
actually work. I never imagined it could actually be mapped to a physical
structure.

[0]
[https://en.wikipedia.org/wiki/Plinko](https://en.wikipedia.org/wiki/Plinko)

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hesdeadjim
Given that the future of computing seems to push more and more towards DSP,
this seems like it could be an exceedingly powerful technique. Especially if
the tech could reach the goal of on-the-fly reprogramming.

I’ve wondered when we will see FPGAs integrated on die with a regular CPU for
a similar purpose.

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damip
This work focuses on steady-state computing, but it could also be interesting
to use transient physical behaviors to process time-varying signals

Maybe by modelling dynamical systems as "neural nets" as in:
[https://arxiv.org/abs/1806.07366](https://arxiv.org/abs/1806.07366) and
[https://arxiv.org/abs/1808.08412](https://arxiv.org/abs/1808.08412)

Or by using complicated physical systems we don't even understand to build
Echo State Networks:
[http://www.scholarpedia.org/article/Echo_state_network](http://www.scholarpedia.org/article/Echo_state_network)

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TripleH
For a novice like me, it sounds a bit like quantum computing, where rather
than "digitalizing" a physical problem like we do with classic computing, we
use physical properties of elements (like the spin of an electron) to solve
it. How far does this analogy go ?

~~~
yetihehe
About halfway between digital and quantum computers.

    
    
      Wholly quantum - uses both wave and particle behaviours and entanglement
      Wave computation like in article - just waves
      Digital computation - just impulses or currents in conductors.

------
8bitsrule
Very interesting, look forward to seeing this develop.

Reminds me of the analog delay-line memories from the 1940s to the late 1960s
([https://en.wikipedia.org/wiki/Delay_line_memory#Mercury_dela...](https://en.wikipedia.org/wiki/Delay_line_memory#Mercury_delay_lines))
and bucket-brigade devices of the 1970s.
([https://en.wikipedia.org/wiki/Bucket-
brigade_device](https://en.wikipedia.org/wiki/Bucket-brigade_device)) But in a
whole-new dimension.

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Tomminn
Does anybody know how difficult these problems are to solve once you've
already calculated the relevant kernel?

Let's say I had that kernel stored in a database, is it just a matrix
multiplication or two to calculate the solution? If so, doesn't that kind of
invalidate the idea that this is a bottleneck problem that requires a speed-
up? Especially once you take into account read/write speeds on the physical
structure?

I guess my point here is the correct benchmark is pre-memoized code. I'd be
interested how it performs against _that_ benchmark.

------
amelius
> but if you want to change the shape of the room, for example, you will have
> to make a new kernel.

So you can't iteratively improve your room, unless you don't mind fabricating
all the kernels.

~~~
jarfil
> Scaling down the concept to the scale where it could operate on light waves
> and be placed on a microchip

> “We could use the technology behind rewritable CDs to make new Swiss cheese
> patterns as they’re needed,”

Could be not much different from compiling and running stuff on an FPGA.

~~~
sbzodnsbd
Assuming these structures can be changed like an FPGA.

It’s not obvious how you can change the microstructure of a material to
something you like in minutes.

~~~
lostmsu
Well, there are CD-RWs

~~~
sbzodnsbd
For a 2D structure, maybe. What is the depth of the feature though? I saw
those pictures as light shining along the plane, not across it (am I wrong?).
If it’s across it’s not obvious that CDRW’s features are deep enough and the
“empty” space transparent enough.

How about 3D micro-structures? It’s hard enough to make a one off 3D structure
reproducible, never mind a changeable one.

~~~
romwell
>How about 3D micro-structures? It’s hard enough to make a one off 3D
structure reproducible

Well, there are 3D printers :)

~~~
sbzodnsbd
Disclaimer: I find this _super_ cool. I love analog solutions to engineering
problems.

This is about optical wavelength length scales -> feature sizes << 1500nm for
infrared

3D printers’ feature sizes work for giga hertz waves (as a guestimate)
assuming:

\- The features can be printed - 3D have limitations after all.

\- the materials that can be 3D printed are optically suitable.

------
amelius
I think there is a problem with this technique.

Computing a kernel is an inverse problem, which is more difficult than solving
a system for a given right-hand-side.

Linear algebra tells us to never invert a matrix, and here we're actually
fabricating the inverse physically.

Or, of course, perhaps I'm misunderstanding something.

~~~
sbzodnsbd
You solve the inverse problem once. That’s takes a while.

Then you build it. More time.

Then you run it for thousands of different inputs. There’s the benefit.

For example:

You build a kernel describing the acoustics of a sound (ie a body of water)
once.

Then you can solve instantly what and where sounds (acoustics) are coming from

~~~
amelius
Well, if the inverse is dense and the excitation as well, then I can see an
advantage, because computing a solution by applying the inverse to the
excitation would be O(n^2). But I suppose that usually the excitation would be
sparse.

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dunefox
Is something like this composable? For example, if they build a kind of lambda
calculus for their 'hardware kernels' they can represent arbitrary
calculations (by composing them)? Because having to create a different kernel
for every calculation seems quite costly.

~~~
lenticular
It seems like it could be. This thing sounds like it focuses on Fredholm
integral equations, the solutions should be composable.

These are basically equations g(t) = Integral_t K(t,s) * f(s),

where K(t,s) (the kernel) and g(t) are known, but f(s) isn't. In physical
applications, t is usually time. A solution f(s) could be fed into the input
of the next device, at least mathematically.

------
mojuba
Just curious: how is this any better than an analog circuit (possibly an IC)
solving the same problem?

~~~
yetihehe
It's faster and can be miniaturised more than analog ic's, possibly using less
energy. Version used in article is proof of concept, selected for being easy
to manufacture with cheap equipment.

------
adamnemecek
Continuous variable quantum computing is going to be huge.

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zachruss92
This is the most clickbaity-y title I've seen in a long time! Not complaining,
it definitely piqued my interest. As a Philly native, I love that uPenn is
doing cool experiments like this.

~~~
dahdum
For me, clickbait has a negative connotation, the expectation that the article
won't deliver on the headline.

This article delivered. Such a cool experiment and field of study.

~~~
yaseer
I agree - this article was not clickbait. The content delivered on the title.

Piquing your interest with the title is just good headline-writing. It only
becomes clickbait when the title is a cynical perversion of the content.

~~~
pmoriarty
Just as fishing bait entice fish to bite the bait, clickbait titles entice
people to click the title.

If a title is interesting enough to get lots of people to click on it, it is
by definition clickbait.

Titles for interesting articles should themselves be interesting, as boring
titles for interesting articles would increase one's chance of missing them.

An interesting title is only objectionable is the article itself is not worth
reading.

~~~
IanCal
But the reason we call it bait and not just "fish food" is that it is there to
_trick_ the fish into doing something it does not want to do. Something is not
necessarily bait just because it's interesting or enticing.

~~~
pmoriarty
But there is no term like "clickfood" which would imply that the title is
interesting and the corresponding article is worth reading.

So people fixate on the title and call any interesting, well-written title
"clickbait" regardless of whether the article itself is worth reading or not.

I'm simply pointing out that such an enticing title is not necessarily bad if
the article itself is worth reading.

The alternative is a boring title, which is a disservice to any article worth
reading.

~~~
BubRoss
> But there is no term like "clickfood"

That's supposed to just be called journalism.

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beamatronic
Can we ask one of these new types of machines, quantum computers etc, whether
anti-gravity is possible ?

