The photos show a gold chandelier. Almost none of what you see is the computer. The actual qubits sit on a chip the size of a coin at the bottom. Everything above the chip is thermal plumbing built to keep it colder than deep space.
The dilution refrigerator
A superconducting qubit only behaves like a quantum object near absolute zero. The machine that reaches that temperature is a dilution refrigerator, and it cools in stages.
The outer chamber holds vacuum. A pulse-tube cooler brings the stack down to about 4 kelvin. A dilution unit then mixes two helium isotopes, helium-3 and helium-4. Helium-3 crossing into the dilute phase absorbs heat, which pulls the coldest stage, the mixing chamber, down to about 10 millikelvin. The chip mounts on that coldest plate.
This is why the machine is tall. Each cooling stage is a gold-plated copper plate, and the whole stack, shields, plates, plumbing, looks like a chandelier.
The chip
The chip is a printed superconducting circuit, often niobium or aluminum on sapphire or silicon. Each qubit is a small oscillator running near 5 GHz, with a nonlinear element called a Josephson junction that turns the oscillator into an effective two-level system. One chip holds tens to hundreds of qubits plus the couplers and readout resonators that connect them. See Superconducting Qubits Explained for the physics.
The wiring
Microwave signals reach the chip through coaxial cables that descend every stage. Each cable anchors thermally at each plate so it does not carry heat from room temperature down to the qubits. Attenuators on the way down keep noise out. Amplifiers near the bottom raise the weak readout signal before it travels back up. A single qubit needs several lines for control and readout, which is why the wiring bundle dwarfs the chip.
The control electronics
At room temperature, racks of arbitrary waveform generators and digitizers sit next to the fridge. They produce the precise microwave pulses that act as gates and capture the readout signals. The control stack is classical hardware, and it is a large fraction of the total cost and footprint.
Why so cold
The cooling has a concrete reason. A qubit at 5 GHz must start in its ground state. At room temperature, thermal noise leaves about 1,250 photons in that mode. At 15 millikelvin, the count drops below one in ten million. The fridge buys a near-zero probability that the qubit starts in the wrong state. Noise, not the chip, is the enemy the whole machine fights.
Not all quantum computers look like this
Only superconducting machines and some spin qubits need the full dilution refrigerator. Neutral atom and photonic machines run at room temperature in a vacuum chamber. SAXON Q sells a diamond-based machine with no cryostat. The chandelier is the signature of one modality, not all of them. See Types of Quantum Computers Compared.
Next steps
- How much does a quantum computer cost: the cryostat is a large part of the bill
- IBM's modular cryogenic cells: how fridges get linked together for scale
- T1 vs T2: what noise does to the qubits once they are cold