||This article provides insufficient context for those unfamiliar with the subject. (October 2009)|
A quantum sensor can measure the effect of the quantum state of another system on itself. The mere act of measurement influences the quantum state and alters the probability and uncertainty associated with its state during measurement.
The Defense Advanced Research Projects Agency has recently[when?] launched a research program in optical quantum sensors that seeks to exploit ideas from quantum metrology and quantum imaging, such as quantum lithography and the NOON state, in order to achieve these goals with optical sensor systems such as lidar. 
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