Dilution refrigerator

Superconducting qubits lose their state even from a tiny amount of heat. So they are cooled to only about 0.01 to 0.02 degrees above absolute zero (minus 273.15 degrees Celsius), the floor below which temperature cannot go. The device that does this is the dilution refrigerator.

It uses the way heat is carried away when two kinds of helium (helium-3 and helium-4) mix. It is made of several layers of golden disks that get colder toward the bottom, so it looks like a chandelier. It is the most eye-catching part of a quantum computer in photos, and the qubit chip hangs at the very bottom, in the coldest spot.

Just as you need a very quiet room to hear a small whisper in a library, to handle a qubit's faint signal you have to remove almost all the "noise" of heat.

This cooling equipment is a big part of why superconducting quantum computers are large and expensive. To add more qubits, the refrigerator has to grow too, so cooling technology sets how big a quantum computer can be.