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Tuning a radio to your favorite station is a search for the right frequency amid the noise. The new device does the same, but for waves about three millimeters long. Such waves come from distant galaxies and possibly from dark matter particles. The device is a pattern of superconducting niobium traces on a silicon wafer. Each trace resonates at its own frequency, like a guitar string at its own note.

Previously, similar devices lost half the signal due to an extra resistor. Here the resistor is removed, and the signal travels with almost no loss. In a simulation of ten traces, the frequency resolution was as sharp as a good musical tuner: notes differing by less than one percent can be told apart. The first trace captured 82% of the incoming energy, like eight out of ten guests showing up for a dinner party.

But there is a fly in the ointment. As the signal travels along the chain of traces, each successive one siphons off a little energy — about 0.85%. For ten traces, that is trivial, but for three hundred, it becomes a noticeable leak. The scientists calculated that with a cleaner dielectric, the losses would drop tenfold, and a chain of three hundred traces would work. That is exactly how many are needed to cover the atmospheric transparency window at 90 gigahertz — where the sky is especially clear for such observations.

The device is largely immune to typical manufacturing imperfections: small variations in trace width or metal thickness do not break the tuning. It is sensitive only to the thickness of the dielectric substrate, like a guitar whose scale length is off by half a millimeter. This means such spectrometers could be stamped out by the hundreds for future sky surveys. Then the map of matter distribution in the universe would become more detailed, and the search for dark matter more sensitive.