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 but
Nature 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
heats up when a photon is absorbed The subsequent rise and fall of the temperature is recorded to determine the photon energy. These detectors are employed by astronomers for rocket-based observations of photons at x-ray avelengths with an energy 100 to 1, 000 times that of visible photons. but thei sensitiv ity is not suf ficient to record visible photons, with an energy of 1.5 to 3 Over the past decade, new devices have been develo ped that are more sensitive and can record visible photons 3-9. These detectors fall into two classes. The first is the bolometer which uses the heating effect as mentioned above to determine photon energy. The thermometer inside such a device, recording the temperature change is a strip of partly superconducting metal3 5; the readout amplif ier is also superconducting. As superconductivity the flow of current without resistance -is a low-temperature property, the entire structure of the device is a cryogenic environment (which is easier to engineer than a device with only some superconducting components) The second class of detector makes use of the electron excitations created in solids by the energy of an incoming photon Numerous observations have been made with such detectors developed at the european Space agency z-9, including observations of the Crab nebula and short-period binary systems, known as polars. The readout e lectron ics of these detectors, however, operates at room temperature, with the consequence that the number of channels that can be read out is limite So far, the number of pixels in an image has been limited to 36. Clever device design mig ht mean that this number of pixels can be expanded by a factor of maybe 10 to 20, but the engineering is proving dif ficult Day et a/ i now present a new approach to the problem of photon detection. Their device contains a superconducting film held at low temperature. Inside the film resistanceless current flows in the form of electron pairs. If a photon hits the device, it can break up some of these pairs, with the result that the supercurrent becomes more 'sluggish'l0. That increase in slugg ishness can be detected in the surrounding microwave circuitry. The nature of the measurement is akin to watching an object on a spring vibrating at the natural oscillation rate: the rate of the spring s vibration reveals the mass(sluggishness) of the object The authors also show that cryogenic electronics systems already available are adequate for the readout of the signal from their device Device and readout together make the desired single-photon detector. Moreover, the method of readout used can be rather easily generalized to accommodate hundreds, and perhaps thousands of pixels. Other fields of science such as fluorescence microscopy studies of single molecules, should also benef it from this new detector technology
heats up when a photon is absorbed. The subsequent rise and fall of the temperature is recorded, to determine the photon energy. These detectors are employed by astronomers for rocket-based observations of photons at X-ray wavelengths, with an energy 100 to 1,000 times that of visible photons. But their sensitivity is not suf ficient to record visible photons, with an energy of 1.5 to 3 electronvolts. Over the past decade, new devices have been developed that are more sensitive and can record visible photons3-9. These detectors fall into two classes. The first is the bolometer, which uses the same heating ef fect as mentioned above to determine photon energy. The thermometer inside such a device, recording the temperature change, is a strip of partly superconducting metal3, 6; the readout amplifier is also superconducting. As superconductivity — the flow of current without resistance — is a low-temperature property, the entire structure of the device is a cryogenic environment (which is easier to engineer than a device with only some superconducting components). The second class of detector makes use of the electron excitations created in solids by the energy of an incoming photon5. Numerous observations have been made with such detectors developed at the European Space Agency7-9, including observations of the Crab nebula and short-period binary systems, known as polars9. The readout electronics of these detectors, however, operates at room temperature, with the consequence that the number of channels that can be read out is limited. So far, the number of pixels in an image has been limited to 36. Clever device design might mean that this number of pixels can be expanded by a factor of maybe 10 to 20, but the engineering is proving dif ficult. Day et al. 1 now present a new approach to the problem of photon detection. Their device contains a superconducting film held at low temperature. Inside the film, resistanceless current flows in the form of electron pairs. If a photon hits the device, it can break up some of these pairs, with the result that the supercurrent becomes more 'sluggish'10. That increase in sluggishness can be detected in the surrounding microwave circuitry. The nature of the measurement is akin to watching an object on a spring, vibrating at the natural oscillation rate: the rate of the spring's vibration reveals the mass ('sluggishness') of the object. The authors also show that cryogenic electronics systems already available are adequate for the readout of the signal f rom their device. Device and readout together make the desired single-photon detector. Moreover, the method of readout used can be rather easily generalized to accommodate hundreds, and perhaps thousands, of pixels. Other fields of science, such as fluorescence microscopy studies of single molecules, should also benefit f rom this new detector technology
The ultimate photon detector, however, is not yet at hand some challenges remain for Day and colleagues design 4: for example although there is very little noise in the readout system the detector itself has not yet achieved that low level of noise Whether the noise source is intrinsic or extrinsic is not clear, but i am optim istic that it can be remedied. Meanwhile, in the race to produce the ultimate photon detector, the other candidates (mentioned above) are advancing the winner winners -of this race will be determined in part by issues that go beyond performance, such as cost and ease of use. Practical eng ineering factors hold sway in astronomy just as in regular life. References 1 Day, P K, LeDuc, H G, Mazin, B A, Vayonakis, A&Zmuidzinas, J. Nature 425, 817-821 (2003).| Artic 2. Moseley, S. H, Mather, J. C.& McCammon, D. J. App. Phys. 56, 1257-1262 (1984).I Article I Is! I ChemPort I 3. Stahle, C. K, McCammon, D.& Irwin, K. D. Phys. Today 52, 32-37 (1999).II ChemPort I 4. Mather, J C. Nature 401, 654-655(1999).I Article I Sl I ChemPort 5. Twerenbold, D Rep. Prog. Phys. 59, 349-426(1996). I Article I IS! I ChemPort 6. Cabrera, B. et al. App/. Phys. Lett. 73, 735-737(1998). I Article I IS! I ChemPort 7. Peacock,A.etal.№aue381,135-137(1996).|△tice| IS I ChemPort丨 8. Nadis, S. Science 274, 36-38(1996). I Article isl I chemPort I P. AlP Proc. Conf. 605 (1), 559-564(2002).I Article I ch 10. VanDuzer, T.& Turner, C. W. Principles of Superconductive Devices and Circuits(Prentice Hall, Englewood Cliffs, New Jersey, 1999) 11. Cabrera, B et al. AlP Proc. Conf. 605(1), 565-570(2002).I Article I ChemPort I 12. Stevenson. tR pellerano fA. stahle. C. M la, K.& Schoelkopf, R. J. App/. Phy Lett. 80, 3012-3014(2002). I Article I IS! I ChemPort I R 1238-1242
The ultimate photon detector, however, is not yet at hand. Some challenges remain for Day and colleagues' design1: for example, although there is very little noise in the readout system, the detector itself has not yet achieved that low level of noise. Whether the noise source is intrinsic or extrinsic is not clear, but I am optimistic that it can be remedied. Meanwhile, in the race to produce the ultimate photon detector, the other candidates (mentioned above) are advancing11-13. The winner — or winners — of this race will be determined in part by issues that go beyond performance, such as cost and ease of use. Practical engineering factors hold sway in astronomy, just as in regular life. References 1. Day, P. K., LeDuc, H. G., Mazin, B. A., Vayonakis, A. & Zmuidzinas, J. Nature 425, 817-821 (2003). | Article | 2. Moseley, S. H., Mather, J. C. & McCammon, D. J. Appl. Phys. 56, 1257-1262 (1984). | Article | ISI | ChemPort | 3. Stahle, C. K., McCammon, D. & Irwin, K. D. Phys. Today 52, 32-37 (1999). | ISI | ChemPort | 4. Mather, J. C. Nature 401, 654-655 (1999). | Article | ISI | ChemPort | 5. Twerenbold, D. Rep. Prog. Phys. 59, 349-426 (1996). | Article | ISI | ChemPort | 6. Cabrera, B. et al. Appl. Phys. Lett. 73, 735-737 (1998). | Article | ISI | ChemPort | 7. Peacock, A. et al. Nature 381, 135-137 (1996). | Article | ISI | ChemPort | 8. Nadis, S. Science 274, 36-38 (1996). | Article | ISI | ChemPort | 9. Verhoeve, P. AIP Proc. Conf. 605 (1), 559-564 (2002). | Article | ChemPort | 10. VanDuzer, T. & Turner, C. W. Principles of Superconductive Devices and Circuits (Prentice Hall, Englewood Cliffs, New Jersey, 1999). 11. Cabrera, B. et al. AIP Proc. Conf. 605 (1), 565-570 (2002). | Article | ChemPort | 12. Stevenson, T. R., Pellerano, F. A., Stahle, C. M., Aidala, K. & Schoelkopf, R. J. Appl. Phys. Lett. 80, 3012-3014 (2002). | Article | ISI | ChemPort | 13. Schoelkopf, R. J. et al. Science 280, 1238-1242 (1998). | Article | PubMed | ISI | ChemPort |