In quantum computing, cryogenics refers to the engineering of ultra-cold environments—typically colder than outer space—required to operate certain types of quantum processors.
While a laptop fan keeps a CPU at around 60°C ($333\text{ K}$), a quantum computer often needs to operate at $15\text{ millikelvin}$ ($0.015\text{ K}$). This is near absolute zero, the point where all atomic motion theoretically stops.
Here is an explanation of why this extreme cold is necessary, how it is achieved, and examples of the systems that use it.
1. Why do they need to be so cold?
Quantum information is incredibly fragile.
To Stop "The Shakes" (Thermal Noise):
5 At room temperature, atoms vibrate violently.6 If a qubit (quantum bit) is exposed to this heat, it cannot hold a quantum state (superposition).7 The thermal energy knocks the qubit out of its delicate state, causing decoherence (loss of information).8 Superconductivity: Many leading quantum computers (like those from IBM and Google) use "superconducting" materials (like aluminum or niobium).
9 These materials only conduct electricity with zero resistance when cooled below a specific critical temperature.10 If they warm up, they turn into normal resistors, and the quantum magic stops.Resetting to Zero: To start a calculation, qubits must be initialized to a "ground state" (energy level of 0).
11 If there is ambient heat, the qubits might randomly jump to a "1" state before the calculation even begins. The cold ensures they stay at "0" until told otherwise.12
Analogy: Trying to maintain a quantum state at room temperature is like trying to balance a house of cards on a table while an earthquake is happening. Cryogenics stops the earthquake (thermal vibrations) so the house of cards (qubits) can stand.
13
2. How is it achieved? The "Golden Chandelier"
The most iconic image of quantum computing—the gold, hanging structure often seen in press photos—is actually the cooling system, not the computer itself. This device is called a Dilution Refrigerator.
It does not cool the whole system at once; it uses a staged approach to lower the temperature layer by layer:
Stage 1 (4 Kelvin): The outer layers are cooled by a pulse tube (similar to a very fancy air conditioner) to about
16 $-269^\circ\text{C}$.17 This is already cold enough to liquefy helium.The Mixing Chamber (10-15 mK): At the very bottom of the "chandelier" is the processor. Here, a mix of two helium isotopes (Helium-3 and Helium-4) is circulated.
18 When these two isotopes are mixed and separated in a specific way, they absorb heat from their surroundings, driving the temperature down to millikelvin levels.19
3. Examples of Cryogenic Quantum Computers
Not all quantum computers need cryogenics (e.g., some photonic systems operate at room temperature), but the current market leaders rely heavily on it.
A. IBM Quantum System One & Eagle/Osprey Processors
Type: Superconducting Qubits (Transmons).
21 The Setup: IBM houses its chips inside massive dilution refrigerators.
22 The "chip" is located at the very bottom, shielded inside a vacuum can to prevent even a single air molecule from hitting it (which would transfer heat).Temperature:
23 $\sim 15\text{ mK}$.24
B. Google Sycamore
Type: Superconducting Qubits.
25 The Setup: Google's famous "quantum supremacy" experiment used the Sycamore processor, which requires cryogenic cooling to allow current to flow without resistance around its loops.
Wiring: One of the biggest challenges here is the cabling. They use hundreds of coaxial cables that run from room temperature down to the freezing chip. These cables must conduct electrical signals without conducting heat—a massive materials science challenge.
C. Silicon Spin Qubits (e.g., Intel, various university labs)26
Type: Spin Qubits (using electron spin in silicon).
27 The Setup: These look more like traditional computer chips but still require cooling to roughly $1\text{ Kelvin}$. While this is "hotter" than superconducting qubits (1 K is 1000 millikelvin), it is still deep cryogenics. The slightly higher temperature tolerance makes them potentially easier to scale in the future.
Summary Table: Temperature Scales
| Object | Temperature (Kelvin) | Temperature (Celsius) |
| Room Temperature | $300\text{ K}$ | $27^\circ\text{C}$ |
| Outer Space (Deep Space) | $2.7\text{ K}$ | $-270^\circ\text{C}$ |
| Silicon Spin Qubits | $\sim 1\text{ K}$ | $-272^\circ\text{C}$ |
| IBM/Google Qubits | $0.015\text{ K}$ (15 mK) | $-273.13^\circ\text{C}$ |
| Absolute Zero | $0\text{ K}$ | $-273.15^\circ\text{C}$ |
A Next Step for You
Would you like me to explain the difference between "Wet" and "Dry" dilution refrigerators (one consumes liquid helium, the other recycles it), or are you interested in how Cryo-CMOS is being developed to move the control electronics inside the fridge to reduce the messy cabling?
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