Universal control using the quantum Zeno effect
The Zeno effect occurs in quantum systems when a very strong measurement is applied, which can alter the dynamics in non-trivial ways. Despite being dissipative, the measurement divides the Hilbert space into subspaces with distinct eigenvalues of the measured observable, and give rise to `Zeno dynamics’ within each subspace. The dynamics stay coherent within any degenerate subspaces of the measurement, and surprisingly can transform a trivial (e.g., non-interacting with local control only) quantum system into one with universal control within the Zeno subspace. We will show how the application of such a measurement can turn a single-qubit operation into a two- or multi-qubit entangling gate in a non-interacting system. We demonstrate this gate between two effectively non-interacting transmon qubits.
Our Zeno gate works by imparting a geometric phase on the system, conditioned on it lying within a particular non-local subspace. These results demonstrate how universality can be generated not only by non-local coherent interactions as is typically employed in quantum information platforms, but also by dissipative measurements.