The effect of measurements in quantum systems has always been a cryptic concept and a source of many debates and interpretations of quantum mechanics. At its core is the deterministic evolution of unobserved systems versus the stochastic evolution of systems undergoing measurements.
A case in point is the coherent oscillations of quantum two-level systems, which have been studied extensively in both experiments and theoretical studies. Many such systems were observed under free evolution as well as destructive projective measurements. Frequent measurements of the latter kind lead to the Zeno effect, in which the coherent oscillations are blocked, and the evolution of the system is frozen to one of its eigenstates.
In the intermediate regime of partial measurements, however, the dynamics is much richer, showing a cascade of transitions in the system dynamics depending on the measurement strength. In our lab, we measure these transitions using a state-of-the-art experimental setup of superconducting circuits, unveiling the different stages of the Quantum Zeno Effect.
Z. K. Minev et al., To catch and reverse a quantum jump mid-flight. Nature 570, 200-204 (2019).
K. Snizhko, P. Kumar et al., Quantum Zeno effect appears in stages. Physical Review Research 2, 033512 (2020).