We investigate the possibility of implementing a given projection measurementusing linear optics and arbitrarily fast feedforward based on the continuousdetection of photons. In particular, we systematically derive the so-calledDolinar scheme that achieves the minimum error discrimination of binarycoherent states. Moreover, we show that the Dolinar-type approach can also beapplied to projection measurements in the regime of photonic-qubit signals. Ourresults demonstrate that for implementing a projection measurement with linearoptics, in principle, unit success probability may be approached even withoutthe use of expensive entangled auxiliary states, as they are needed in allknown (near-)deterministic linear-optics proposals.
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