Dynamics of a qubit as a classical stochastic process with time-correlated noise: minimal measurement invasiveness

Abstract

So far it has been shown that the quantum dynamics cannot be described as a classical Markov process unless the number of classical states is uncountably infinite. In this paper, we present a stochastic model with time-correlated noise that exactly reproduces any unitary evolution of a qubit and requires just four classical states. The invasive updating of just one bit during a measurement accounts for the quantum violation of the Leggett-Garg inequalities. Unlike in a pilot wave theory, the stochastic forces governing the jumps among the four states do not depend on the quantum state, but only on the unitary evolution. This model is used to derive a local hidden variable model, augmented by one bit of classical communication, for simulating entangled Bell states.