High-Efficiency Quantum Interrogation Measurements via the Quantum Zeno Effect

The phenomenon of quantum interrogation allows one to optically detect the presence of an absorbing object, without the measuring light interacting with it. In an application of the quantum Zeno effect, the object inhibits the otherwise coherent evolution of the light, such that the probability that an interrogating photon is absorbed can in principle be arbitrarily small. We have implemented this technique, achieving efficiencies of up to $73\%$, and consequently exceeding the $50\%$ theoretical maximum of the original “interaction-free” measurement proposal. We have also predicted and experimentally verified a previously unsuspected dependence on loss.