0.141" semi-rigid coax, diameter of champions.

> 0.141" semi-rigid coax, diameter of champions.

I wonder if we measure it more precisely we'll get to something closer to 1.4142135623730950488...

It would be a bit of a surprise since the unit of measure is inches and I'm not sure what inches would have to do with quantum computing. I feel like the inch is essentially a random factor here.

I’d make this cable as a form of art.

Close, as the ratio of the inner and outer conductor diameters, to exactly get 50 Ohms, is an irrational number.

Thanks! Is my assumption of liquid helium running somewhere correct? I figure that's the only way to reach the temperatures required (single digit kelvins, no?)

It is even worse than single digit Kelvin.

Liquid Nitrogen with pumping: 40 K for a few thousand dollars.

Run of the mill Liquid Helium: 4 K for tens to hundreds of thousands of dollars.

But for these devices you need 15mK which is reachable only if you mix two different isotopes of Helium and pump the mixture into vacuum. Such a device is up to 1M$ and more.

And the insides of that device are in vacuum (actually, air freezing into ice on top of the chip can be a problem). The brass is basically the heat conductor between the chip and the cold side of your pumped He mixture (which is *not* just sloshing inside the whole body of the cryostat where the chips are).

Another reason you do not want the He sloshing around is because you will be opening this to make changes to the device and do not want all the extremely expensive He3 (the special isotope you need for the mixture) to be lost.

FWIW... small DR's are under 400k USD. The big ones are ~1M USD or more.

What’s a DR? Something refrigerator?

Dilution refrigerator. They are the type of refrigerator used to chill quantum computing devices. The wikipedia article has a pretty good description of how they work. It took me a few reads to understand it!

It's much colder than that, single-digit millikelvin. They use He-3/4 dilution refrigerators [1]. Getting things cold and electromagnetically-quiet enough that the quantum state doesn't collapse is a big challenge in the field.

1 - https://en.wikipedia.org/wiki/Dilution_refrigerator

And if you need colder than 2mk, nuclear demagnetization:

https://en.wikipedia.org/wiki/Magnetic_refrigeration#Nuclear...

And some people think the brain can be deterministic at 300K.

Why not? Computers are deterministic at higher temperatures.

Even assuming a computer model, think of an analog computer with long integration times, potentially high gain for thermal noise terms, simulating a chaotic system.

Or, look at literature on error rates for people performing simple repetitive tasks.