Accurate phase measurement lies at the heart of precision experimental physics. I propose a scheme for precise measurement of optical phase beyond the classical limit, using novel sources of non-classical light. The phase resolution of standard interferometers with coherent laser light is limited by shot noise to one over the square root of the total number of photons detected. Ultimately, the limit is the Heisenberg limit of one over the total photons number, which holds promise for a dramatic improvement in resolution and detection speed for large photon numbers. Achieving Heisenberg limited phase detection is therefore ‘a holy grail’ of quantum measurement, yet to date it was realized only with very small photon numbers. The main approach so far requires use of non-classical (phase squeezed) states of light with inherent quantum correlations, which are sensitive to loss and require ideal (100% efficient) photo detectors to detect the correlation. Use of realistic detectors severely limits the degree to which the squeezing, even if originally high, can be exploited in reality. I propose to approach this problem from a fresh angle using a source of broadband squeezed light produced by broadband parametric down conversion pumped by a narrowband laser. Although the quantum squeezing of this light is directly applicable to sub-shot noise measurement, it was not used for this purpose so far because standard photo detectors are too slow to detect the ultrafast correlation. Here I suggest to use broadband sum-frequency generation (SFG) as a physical ultrafast two-photon detector to relieve this problem. Due to the broad input bandwidth of the SFG on one hand, and narrow output bandwidth on the other hand, SFG acts as an ultrafast quantum correlation detector with superb noise rejection. Classically, SFG correlation detection is useful for many applications, such as optical spread spectrum communication, optical tomography and lithography, which will be explored also.
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