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Publication - Professor Sandu Popescu

    How Energy Conservation Limits Our Measurements


    Navascues, M & Popescu, S, 2014, ‘How Energy Conservation Limits Our Measurements’. Physical Review Letters, vol 112.


    Observations in quantum mechanics are subject to complex restrictions arising from the principle of energy conservation. Determining such restrictions, however, has been so far an elusive task, and only partial results are known. In this Letter, we discuss how constraints on the energy spectrum of a measurement device translate into limitations on the measurements which we can effect on a target system with a nonconstant energy operator. We provide efficient algorithms to characterize such limitations and, in case the target is a two-level quantum system, we quantify them exactly. Our Letter, thus, identifies the boundaries between what is possible or impossible to measure, i.e., between what we can see or not, when energy conservation is at stake.

    Full details in the University publications repository