Physics

Transistor

CMOS

Phase noise

Noise (video)

Noise figure

Image (mathematics)

Optics

Low-noise amplifier

Voltage

Y-factor

Atomic physics

Artificial intelligence

Amplifier

Cryogenics

Liquid helium

Chemistry

Materials science

Cascade

Microwave

Computer science

Noise temperature

Superconductivity

Helium

Quantum mechanics

Noise generator

Chromatography

Optoelectronics

Cryostat

Review of Scientific Instruments

We present a cryogenic microwave noise source with a characteristic impedance of 50 Ω, which can be installed in a coaxial line of a cryostat. The bath temperature of the noise source is continuously variable between 0.1 K and 5 K without causing significant back-action heating on the sample space. As a proof-of-concept experiment, we perform Y-factor measurements of an amplifier cascade that includes a traveling wave parametric amplifier and a commercial high electron mobility transistor amplifier. We observe system noise temperatures as low as 680−200+20 mK at 5.7 GHz corresponding to 1.5−0.7+0.1 excess photons. The system we present has immediate applications in the validation of solid-state qubit readout lines.

Characterizing cryogenic amplifiers with a matched temperature-variable noise source