this post was submitted on 06 Jul 2024
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No Stupid Questions

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[–] [email protected] 17 points 4 months ago* (last edited 4 months ago) (1 children)

No one has given a real answer yet, and I’ve worked with these before, so I’ll explain. The short answer is it has to do with the logistics of cooling something to near absolute zero.

The main component of a quantum computer is a tiny microchip, maybe a few centimeters across. The big chandelier is for cooling and interacting with the quantum computer. (Compare to a desktop computer which has a small CPU chip but most of the computer is for cooling, powering, or otherwise supporting that CPU).

Towards the center of the chandelier thing there is a mechanism called a “dilution refrigerator” which uses weird properties of liquid helium to cool the quantum chip to about 15mK above absolute zero. There are often other refrigeration techniques at work and the dilution fridge does the last step of cooling.

The twisting golden tubes are microwave waveguides. Essentially they are wires that carry signals to and from the quantum computing chip. The twists are there because there is a lot of thermal contraction that happens when cooling from room temperature to near absolute zero, and the loops give the tubes some slack to contract.

Not shown in pictures as often because it’s less exciting, but the whole chandelier thing is put in a big metal cylinder, and that cylinder is within another cylinder, like a Russian nesting doll. Sometimes there may even be a 3rd layer. The air gets pumped out of the cylinders so it’s a vacuum inside. The multiple layers of cylinders are needed because the black body radiation from the outermost layer (which will be at room temperature) would be too much incoming energy to keep the qubits cold enough.

Also not shown is this whole thing is connected to an elaborate system of vacuum pumps, other refrigeration machines, usually a box of electronics for signal generation, and a classical computer (a standard desktop computer) used to control everything.

Note that not all quantum computer types use this kind of chandelier thing, only ones that need the near-absolute-zero temperature, such as superconducting qubits (trapped ion, neutral atom, and photonic quantum computers use very different setups).

[–] [email protected] 3 points 4 months ago

This reads like SCP containment procedures.