Inside the receiver of a telescope aimed at the oldest glow in the universe sits a tiny thermometer chip. It's so sensitive that the heat from a single photon can warm it noticeably. But to hear that whisper of heat, you need a middleman — an amplifier that doesn't add its own noise.

That middleman is a two-stage cascade of superconducting loops — SQUIDs. The first stage, made of four loops, catches the weak magnetic signal from the thermometer; the second, a chain of a hundred loops, boosts it to a level that ordinary electronics can handle. All of this works inside a refrigerator at 0.3 kelvin — colder than deep space.

Such an amplifier is needed for polarization maps of the cosmic microwave background. From these, scientists hope to see the imprint of primordial gravitational waves — ripples in space born in the first instants after the Big Bang.

The two-stage design is like an interpreter who first listens to a quiet voice and then repeats it loudly for the audience. The key is that the interpreter doesn't make up words: the system noise stays low, and the signal doesn't drown in interference.