Coherent Non-Local Subspace Dynamics Induced by Zeno Measurements

We describe how an entangling operation related to a CPHASE gate may be implemented by drawing on unique features of quantum measurement. The dynamics of a quantum system can be frozen by sufficiently strong monitoring, i.e., by the quantum Zeno effect. We show here that it is possible to combine local unitary operations and Zeno blocking of a single transition within a larger quantum system, in such a way that an effective non-local quantum operation is performed in an unmonitored subspace. We illustrate ideal realizations of such a process in detail, and then further describe the conditions under which it may be implemented using the dispersive continuous monitoring techniques commonly used in superconducting qubit systems. The scheme is experimentally feasible, and an implementation of it will be described in the talk by E. Blumenthal et al.