Abstract:
Here we build the bridge between spin measurements and spin dynamics in driven systems. First, we analyze the physical meaning of a possible experiment aimed at the simultaneous measurement of two non-commuting spin components. We demonstrate that switching of a strong spin-orbit interaction in a solid or in a cold-atom system for a short time simulates a simultaneous von Neumann measurement of non-commuting spin components. By mapping spin dynamics onto coordinate-space motion such a measurement determines time averages of spin operators which, unlike their instantaneous values, may be evaluated simultaneously to an arbitrary accuracy. As a result, some spin processes in the presence of spin-orbit coupling should demonstrate the Zeno effect: a frequent observation of the system prohibits the evolution.
Next, we consider joint effects of tunneling and spin-orbit coupling on driven spin dynamics in a multi-level system. Tunneling plays the crucial role in the formation of the Rabi-like spin-flip transitions. In contrast to the weak electric field behavior, the spin flip rate becomes much smaller than expected for the two-level system and shows oscillating dependence on the driving field amplitude. In addition, the full spin flip becomes very difficult to achieve. These two effects can be seen as the Zeno effect of slowing down the dynamics of an observable by its measurement.