A dilution refrigerator is the cooling machine that brings superconducting quantum processors down to roughly 10 millikelvin, a fraction of a degree above absolute zero. It works in two stages: a pulse-tube cooler first brings the stack to about 4 kelvin, then a dilution unit circulates a mixture of helium-3 and helium-4, and helium-3 crossing into the dilute phase absorbs heat, which pulls the coldest stage, the mixing chamber, down to millikelvin temperatures. The quantum chip mounts on that coldest plate, with microwave wiring thermally anchored at every stage so the cables do not leak heat back down to the qubits. The purpose is concrete: at 5 GHz a qubit must start in its ground state, and cooling from room temperature to 15 millikelvin drops the thermal photon count in that mode from about 1,250 to below one in ten million. The refrigerator, not the chip, is most of what you see in photos of a superconducting quantum computer.
Related Terms
Superconducting Qubit
HardwareA qubit built from a superconducting circuit containing one or more Josephson junctions, cooled to near absolute zero and controlled with microwave pulses.
QPU
HardwareA quantum processing unit (QPU) is physical hardware that stores qubits and runs quantum gates using superconducting circuits, trapped ions, photons, or neutral atoms.
Transmon
HardwareThe most common superconducting qubit design, which trades a small amount of nonlinearity for a large capacitor that makes the qubit far less sensitive to charge noise.