Occam's Razor Description of Sudden Energy Transitions in a Rabi-Driven Quantum Bit Under Frequent Observation

Overview & Synopsis

The fundamental law of parsimony in science, which is colloquially referred to as Occam's razor, gives precedence to simplicity in the development of a theory. We wish to illustrate this principle by revisiting the issue related to the long-lasting continuous experimental measurement of a Rabidriven qubit (Z. Minev et al. Nature 2019, 570, 200). We propose a simple and basic explanation of the results that proceeds from the variance property of the Hamiltonian in the case of a weak Rabi drive. This variance provides a large statistical time-dependent range of available values for the qubit energy (namely, its standard deviation) that spreads out about Rabi's well-known harmonic state-flipping mean value. In the presence of a long-lasting continuous measurement process like in Minev et al experiment, the resulting "quantum Zeno freezing" of the observed system keeps its energy frozen in its initial state as long as this remains possible within the standard deviation of the energy. Otherwise the system suddenly experiences a quantum jump between the two energy levels-dubbed a quantum Zeno jump-in order to resume its state-freezing dynamics. Some link is made with the dynamics of swapping gates in quantum information processing.