Dilution Fridge

A cQED experiment runs inside a dilution refrigerator — the coldest man-made environment, reaching 10–20 mK. Explore each temperature stage, the microwave wiring, and the physics at each level.

Selected stage

Mixing chamber

10–20 mK

Drive (input)

Readout (output)

Drag to orbit · Scroll to zoomClick a stage below to inspect

Temperature stages

Temperature scale (log)

300 K

4.2 K

700 mK

100 mK

10–20 mK

~15 mK

15 mK300 K

Mixing chamber

10–20 mK

The coldest point in the fridge. ³He crosses from the concentrated phase to the dilute phase here, absorbing heat. The qubit chip mounts directly to this plate.

Components at this stage

Qubit sample package
Circulator (signal isolation)
Quantum-limited TWPA (sometimes)
−20 dB cold attenuators

Physics

kT ≈ 1.3 µeV ≪ ℏω_q ~ 20–50 µeV. Thermal photon population n̄ = 1/(e^(ℏω/kT)−1) ≈ 10⁻⁸ — the qubit sees essentially no thermal excitations.

Microwave signal chain

Drive line (input)

Room-temp AWG → coax → 300K flange → 4K (−3 dB) → Still (−3 dB) → Cold plate (−20 dB) → MXC (−20 dB) → qubit. Total attenuation ~−60 dB to suppress Johnson noise.

AWG signal source

−3 dB @ 4K

−3 dB @ Still

−20 dB @ Cold plate

−20 dB @ MXC

Qubit drive port

Readout line (output)

Qubit → readout resonator → circulator (MXC) → isolator → TWPA (optional, MXC) → HEMT (4K) → room-temp amplifiers → digitiser.

Readout resonator

Circulator @ MXC

TWPA (quantum-limited)

HEMT amp @ 4K

RT amplifiers

Digitiser / ADC