Modern astronomers make their discoveries primarily using sensitive cameras attached to telescopes. These cameras are similar to commercial digital cameras but are designed to be as efficient as possible at detecting the very low light levels coming from the night sky. Also, many discoveries in astronomy are made using cameras and telescopes that detect light that is invisible to the human eye such as infrared and X-ray radiation. Technological innovation in physics and engineering leads to the development of new cameras that either have the ability to see fainter sources or to see different wavelengths of light previously undetected. One example of this is the development of sensitive detectors called bolometers that have been used detect light with wavelengths on the order of 1 mm - i.e. longer wavelength than optical and infrared radiation but not quite radio waves. To detect mm-wave and far-infrared radiation, bolometers are cooled to very low temperatures. Advances in the design of bolometers and in very cold refrigerators led to new cameras for astronomy such as the SCUBA camera on the JCMT telescope in Hawaii that discovered new types of galaxies that only give off light at these long wavelengths. These detectors also were used on telescopes attached to giant balloons such as the BOOMERANG experiment to measure the ripples in the cosmic microwave background for the first time. Because of this, the next two space telescopes to be launched by the European Space Agency in 2008, the PLANCK and HERSCHEL telescopes will use these ultra-cold bolometers. Technological advances that benefit astronomy also can have applications in other areas. Obviously, X-ray cameras are useful for both space-astronomy and medical physics. Bolometer cameras designed to detect light with wavelength of 0.01 mm are commercially available and used to for 'thermal imaging' or infrared night vision. In this research, we will be looking to develop new detectors that bridge the gap between the infrared bolometer cameras and the astronomical bolometer cameras. This gap corresponds to light with frequencies from 0.1-10 THz and is known as the 'THz gap'. There are many research groups in the world now working to develop technologies for these wavelengths as it is one of the few regions of the electromagnetic spectrum yet to be fully exploited either by astronomers or by industry.

Detector arrays are used in many familiar technologies for forming images of the world we live in. The most common detector array known as the charged coupled device (CCD) array forms the basis of many digital and phone cameras. Such detector arrays are sensitive to light in the optical region of the electromagnetic spectrum (the colours of the rainbow - red through to blue). However there is a wealth of information contained in the regions of the electromagnetic spectrum outside of the range of the human eye. For example you may have seen infrared images taken from police or rescue helicopters using special cameras searching at night. Infrared light is no different to optical light and in most cases is generated by the same mechanism - heat. If one were to heat a piece of metal to a few hundred degrees centigrade we would notice it glowing red. Heat it further and it would glow yellow then white. If we let it cool again we would see the white glow fade to yellow which would fade to red and then to no glowing at all. In fact this is not the case. The metal is now glowing in a region of the electromagnetic spectrum known as the infrared. The only reason we do not observe this is because our eyes are insensitive to this light. We can however sense infrared light and it is what we more commonly refer to as heat. If one moved their hand near a warm piece of metal (such as a household radiator) without touching it we would feel that it was hot from the infrared radiation warming our skin. If the metal were to cool back down to room temperature it would still be glowing in the infrared but now much less intensely. The infrared region of the spectrum lies just beyond the red region of the visible spectrum but as we move further past the infrared from the visible spectrum we enter what is known as the THz region of the electromagnetic spectrum. The THz region of the spectrum is of great interest to research and industry alike. For example many materials that are opaque to visible light are transparent to THz light. In this example if one had an array of THz detectors one could image objects beneath a surface that would otherwise be invisible. You may have experienced such systems in some airports where they are used for security purposes to detect concealed objects on passengers. Beyond security, the imaging of THz light has many applications ranging from quality control (imaging the invisible circuitry of an encased computer chip for example) to looking at the THz light emitted from biological samples used to deduce their chemical composition. However to date developing detectors that can sense THz light has proven complex and expensive hence THz imaging arrays are not commonplace in the world of research or industry. The proposed research will develop a new type of detector called the Lumped Element Kinetic Inductance Detector (LEKID). The LEKID is sensitive not only to optical, THz and infrared light but also ultra-violet light and X-rays. The LEKID is also very simple to fabricate into large imaging arrays making it a viable option for the commercial and industrial applications. The one drawback of the LEKID is that it must be cooled to very low temperatures. Known as cryogenic temperatures the temperature the LEKID operates at is of order -273 degrees centigrade and is close to the lowest temperature physically possible referred to as absolute zero. However, recent development in cryogenic technology has made achieving these low temperatures relatively simple. Detectors operating at these low temperatures have significant advantage over their room temperature rivals, being of order 10,000 times more sensitive and generally much faster. This property allows for the first time THz imaging at video frame rates. The idea of a THz video has excited many research scientists as they would now have the ability to watch how a system emitting THz light evolves in real time which has never before been possible.

Quantum mechanics promises to be the driving force underneath the next technological revolution, and quantum cryptography, providing a commercial solution for the ultimate security, may well be considered the harbinger of this change. With this proposal, we aim at showing how quantum mechanics can allow to overcome the limits faced in the detection of long wavelength radiation, specifically at terahertz frequencies. Terahertz is a portion of the electromagnetic spectrum that is both extremely hard to access to, and incredibly important from a technological standpoint. It is indeed a key player in security (explosives, drugs, and hazard-free concealed weapons detection), telecommunications (increased data-rate of short distance wireless communication), monitoring and quality control (spectroscopy). Despite its high potential, the lack of efficient sources and detectors prevents a widespread commercial application of terahertz time-domain spectroscopy and imaging. Yet, a number of high-tech companies are investing into terahertz technology and recent market studies hint for a 40%/year increase in the turnover associated to this technology. It is therefore vital to identify now strategies for overcoming the limitations of the current terahertz detectors. This proposal aims at developing such a strategy exploiting the unique properties of quantum, entangled states of light. Entangled photons, separated in space but sharing a common wavefunction, can be generated by commercial nonlinear crystals and boost unusual properties not accessible by classical means. Two of these properties, namely the ability to acquire twice the phase of a classical state upon propagation and the reduced amplitude noise below the classical shot-noise limit, offer a mean for increasing the sensitivity of terahertz time-domain detectors, that operate indeed as a differential phase sensor. Combining such an improvement with recent concepts of super-resolved imaging will also result in an increased resolution of long wavelength mapping. Combining for the first time concepts of quantum optics, recognised as a main pillar for our future technology, and of terahertz photonics, boosting a number of underdeveloped application potential, this proposal is in line with the research strategy set by the UK research councils, and promise to deliver impact on a number of different disciplines, such as biology and material science, as well as on the quality control and security inspection activities.