NIST researchers enhance photon detection accuracy

National Institute of Standards and Technology (NIST) researchers announced on January 5 advances made in the fabrication of superconducting nanowires to improve the precision of detecting individual particles of light by 74 picoseconds.

The new design improves on NIST’s 2011 tungsten-silicon alloy material, allowing it to operate at higher (though still cryogenic) temperatures and at a higher electrical current. The higher temperature simplifies refrigeration while the higher current cuts jitter in half, from about 150 picoseconds to 76 picoseconds.

Although 74 picoseconds may not sound like much—a picosecond is a trillionth of a second—it is a big deal in the quantum world where light particles, or photons, can carry valuable information. In this case it means that much less “jitter,” or uncertainty in the arrival time of a photon. Less jitter means that photons can be spaced more closely together but still be correctly detected. This enables communications at a higher bit rate with more information transmitted in the same period.

Every little bit helps when trying to receive faint signals reliably, according to NIST, as researchers want to decode as much information as possible from the quantum properties of billions of photons, or determine if “entangled” photons have properties that are linked before—or only after—being measured.

NIST researchers enhanced the detector’s light absorption and efficiency by embedding the chip in a cavity made of gold mirrors and layers of other unreactive materials. Nanowire detectors are superfast, counting tens of millions of photons per second, and generating few “dark” (or false) counts. Originally they were inefficient—meaning they missed photons they should have counted—but NIST has been fine-tuning their properties, first by boosting efficiency and now reducing jitter.

Researchers demonstrated detector efficiencies of 87 percent at wavelengths that are useful in telecommunications. This was almost as efficient as tungsten-silicon devices (93 percent) but with significantly lower jitter.

The detectors were made in NIST Boulder’s microfabrication facility. Researchers from the University of Geneva in Switzerland and the Jet Propulsion Laboratory at the California Institute of Technology also contributed to the work.