A Quantum Logic Gate Representation of Quantum Measurement: Reversing and Unifying the Two Steps of von Neumann's Model

Abstract

In former work, quantum computation has been shown to be a problem solving process essentially affected by both the reversible dynamics leading to the state before measurement, and the logical-mathematical constraints introduced by quantum measurement (in particular, the constraint that there is only one measurement outcome). This dual influence, originated by independent initial and final conditions, justifies the quantum computation speed-up and is not representable inside dynamics, namely as a one-way propagation. In this work, we reformulate von Neumann's model of quantum measurement at the light of above findings. We embed it in a broader representation based on the quantum logic gate formalism and capable of describing the interplay between dynamical and non-dynamical constraints. The two steps of the original model, namely (1) dynamically reaching a complete entanglement between pointer and quantum object and (2) enforcing the one-outcome-constraint, are unified and reversed. By representing step (2) right from the start, the same dynamics of step (1) yields a probability distribution of mutually exclusive measurement outcomes. This appears to be a more accurate and complete representation of quantum measurement. PACS: 03.67.-a, 03.67.Lx, 03.65.Bz