400,000 pixel SNSPD unveiled

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When imaging faint objects such as distant stars or exoplanets, capturing every last bit of light is crucial to get the most out of a scientific mission. These cameras must be extremely low-noise, and be able to detect the smallest quantities of light—single photons.  Superconducting cameras excel in both of these criteria, but have historically not been widely applicable because their camera sizes have been small, rarely exceeding a few thousand pixels, which limits their ability to capture high-resolution images.  However, a team of researchers has recently shattered that barrier, developing a superconducting camera with 400,000 pixels, which could be used to detect faint astronomical signals in a wide range of wavelengths—from the ultraviolet to the infrared.

While plenty of other camera technologies exist, cameras using superconducting detectors are very appealing for use in astronomical missions due to their extremely low-noise operation.  When imaging faint sources, it is crucial that a camera report the quantity of received light faithfully, and not skew the amount of light received or inject its own false signals.   Superconducting detectors are more than capable of this task, owing to their low-temperature operation and unique composition.

But while superconducting detectors hold great promise for astronomical applications, their usage in that field has been stymied by small camera sizes that permit relatively few pixels.  Because these detectors are so sensitive, it is difficult to pack a lot of them into a small area without them interfering with each other.  In addition, since these detectors need to be kept cold in a cryogenic refrigerator, only a handful of wires can be used to carry the signals from the camera to the warmer readout electronics.

To overcome these limitations, researchers at the National Institute of Standards and Technology (NIST), the NASA Jet Propulsion Laboratory (JPL), and the University of Colorado Boulder applied time-domain multiplexing technology to the interrogation of two-dimensional superconducting-nanowire single photon detector (SNSPD) arrays. The individual SNSPD nanowires are arranged as intersecting rows and columns. When a photon arrives, the times it takes to trigger a row detector and a column detector are measured to ascertain which pixel sent the signal. This method allows the camera to efficiently encode its many rows and columns onto just a few readout wires instead of thousands of wires. 

SNSPDs are one type of detector in a collection of many such superconducting detector technologies, including microwave kinetic inductance detectors (MKID), transition-edge sensors (TES), and quantum capacitance detectors (QCD).  SNSPDs are unique in that they are able to operate much warmer than the millikelvin temperatures required by those other technologies, and can have extremely good timing resolution, although they are not able to resolve the color of individual photons.  SNSPDs have been collaboratively researched by NIST, JPL, and others in the community for almost two decades, and this most recent work was only possible thanks to the advances generated by the wider superconducting detector community.

NASA

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