Interaction-free Measurements via Quantum Zeno Stabilization
In quantum mechanics, a repeated measurement of a systems state freezes its evolution - a peculiar behavior known as the quantum Zeno effect. In our experiments, only atoms in the Zeemna level mF = -1 can scatter photons from a laser field, which implements a continuous measurement of the spin state of the atoms in the spinor condensate.Thereby, the transfer of atoms to the Zeeman level mF = +1 by spin-changing collisions is suppressed by the quantum Zeno effect as depicted in (b).
In a famous Gedanken experiment depicted in (a), an ultra sensitive bomb which explodes as a result of the slightest interaction - even if only a single photon is absorbed - can be detected without explosion with a success rate of 50%. With our setup, we can measure the presence of the laser field without scattering a single photon. Ideally, this interaction-free detection of the laser can reach a 100% success rate if a perfect Zeno suppression is reached. We demonstrate an efficiency beyond 50% - the best result that can be achieved without exploiting the Zeno effect.