  Time and energy of quantum processes are a tradeoff against each other. We
propose to ascribe to any given quantum process a time-energy cost to quantify
how much computation it performs. Here, we analyze the time-energy costs for
general quantum measurements, along a similar line as our previous work for
quantum channels, and prove exact and lower bound formulae for the costs. We
use these formulae to evaluate the efficiencies of actual measurement
implementations. We find that one implementation for a Bell measurement is
optimal in time-energy. We also analyze the time-energy cost for unambiguous
state discrimination and find evidence that only a finite time-energy cost is
needed to distinguish any number of states.
