Nature425,777-778(23 October2003),doi:10.1038/425777a pplied physics: To catch a photon DANIEL E PROBER Daniel e is in the Departments of Applied Physics and Physics, Yale Uhiversity, New Haven, Connecticut 06520-8284 e-mail: daniel prober@yale edu Astronomers crave a detector sensitive enough to detect a single photon and determine its energy. a new single-pixel dev ice can do this, and could also be built up into a large array suitable for a telescope. is the richest of the human senses, and detectors of light have long featured in science and tech nology In fields as diverse as telecommun ications medicine and astronomy there is demand for exquisitely sensitive detectors of the quantum of light, the photon But as yet there is no single commercial device that can simultaneously detect individual visible photons and record the colour (or energy) and arrival time of each photon. If such a detector existed it should also produce images with many picture elements(pixels )-and be af fordable day and colleagues now propose a dev ice, based on the pr incip le of kinetic inductance, that could function as an individual pixel in a photon detector(page 81z of this issue) Importantly, they show that the device has the necessary properties to allow the incorporation of many such pixels into the 'ultima te photon detector, one that could also be read out with practical, available electronics The search for the ultimate photon detector has been driven by astronomers, who are often faced with a limited number of photons to measure, emitted from some object in our Galaxy or beyond, and limited time in which to measure them. At present, astronomy is well served by the charge-coupled detector(CCD), familiar to many people as the CCd sensor in their digital camera or camcorder. Megapixe CCDs are now common. But this detector cannot resolve individual photons because the no ise occurring random ly in its readout electronics is too large to allot it. Moreover, the physics of the detector precludes the measurement of photon colour, unless colour filters are used. These reduce eff iciency, but without such filters a CCd would see only shades of grey To record single photons cleanly and to discern their energy and arrival time equires a detector that operates at low temperatures. Th is gets rid of the thermal agitation in the device that would disrupt a single-photon signal, and also means that materials and techniques can be used that are fundamentally different from those employed in the CCD. the first advance in cryogenic detector techno logy was the silicon 'microbolometer'2, in which a small piece of silicon is held at 0.05 K butNature 425, 777 - 778 (23 October 2003); doi:10.1038/425777a <> Applied physics: To catch a photon DANIEL E. PROBER Daniel E. Prober is in the Departments of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520-8284, USA. e-mail: daniel.prober@yale.edu Astronomers crave a detector sensitive enough to detect a single photon and determine its energy. A new single-pixel device can do this, and could also be built up into a large array suitable for a telescope. Vision is the richest of the human senses, and detectors of light have long featured in science and technology. In fields as diverse as telecommunications, medicine and astronomy, there is demand for exquisitely sensitive detectors of the quantum of light, the photon. But as yet there is no single commercial device that can simultaneously detect individual visible photons and record the colour (or energy) and arrival time of each photon. If such a detector existed, it should also produce images with many picture elements (pixels) — and be af fordable. Day and colleagues1 now propose a device, based on the principle of kinetic inductance, that could function as an individual pixel in a photon detector (page 817 of this issue). Importantly, they show that the device has the necessary properties to allow the incorporation of many such pixels into the 'ultimate' photon detector, one that could also be read out with practical, available electronics. The search for the ultimate photon detector has been driven by astronomers, who are of ten faced with a limited number of photons to measure, emitted f rom some object in our Galaxy or beyond, and limited time in which to measure them. At present, astronomy is well served by the charge-coupled detector (CCD), familiar to many people as the CCD sensor in their digital camera or camcorder. Megapixel CCDs are now common. But this detector cannot resolve individual photons, because the noise occurring randomly in its readout electronics is too large to allow it. Moreover, the physics of the detector precludes the measurement of photon colour, unless colour filters are used. These reduce ef ficiency, but without such filters a CCD would see only shades of grey. To record single photons cleanly and to discern their energy and arrival time requires a detector that operates at low temperatures. This gets rid of the thermal agitation in the device that would disrupt a single-photon signal, and also means that materials and techniques can be used that are fundamentally dif ferent f rom those employed in the CCD. The first advance in cryogenic detector technology was the silicon 'microbolometer'2, in which a small piece of silicon is held at 0.05 K but