← Back to Path
1 / 6
THE CHANDELIER
Inside a dilution refrigerator
Plates
50 K, 4 K, 0.8 K, 0.1 K and 10 mK.
Wiring
Coax lines with attenuators on each plate.
At the bottom
The chip, inside a magnetic shield.
Each plate is colder than the one above it.
COOLDOWN
From room temperature to 10 mK
Pulse tube
Pre-cools the plates to about 50 K and 3 K.
Dilution
Takes the bottom plate to about 10 mK.
Time
Typically one to two days.
Modern 'dry' fridges need no bath of liquid helium.
THE TRICK
How dilution cooling works
Two layers
Below 0.87 K the helium mixture separates.
Crossing
Helium-3 crossing the boundary absorbs heat.
A cycle
The still pumps it out and it's recycled.
A continuous cycle that can run for months.
COOLING POWER
Every wire costs cooling power
Q̇ ∝ T²
Cooling power falls steeply as it gets colder.
Microwatts
That's all there is to spend at 10 mK.
Scaling
Thousands of wires means a heat problem.
Wiring is one of the hardest problems in scaling up.
ATTENUATION
Keep room-temperature noise out
Thermal noise
About 1,000 photons per mode at 300 K and 6 GHz.
Attenuators
Absorb noise on each plate.
Target
Below 0.001 photons at the chip.
The fridge's wiring is designed as carefully as the chip.
UNIT 20 STUDY COMPLETE
🧊
Ready for the Fab Challenge?
You've explored a dilution fridge in 3D, cooled it down, learned the helium-3 trick and designed a quiet drive line.