Manipulating photons in atomic ensembles

  Ofer Firstenberg   
Weizmann Institute of Science

Manipulating photons at the quantum level requires a coherent and efficient interface between light and matter. Gaseous ensembles of hot or ultracold atoms provide such an interface. They offer various collective quantum states – spins and electronic orbitals –  that strongly couple to propagating photons.

One use of such an interface is the reversible exchange of quantum information between (flying) photonic qubits and (stationary) matter qubits. To this end, we employ collective excitations of the electronic or nuclear spins, which can store quantum information for seconds and even hours. The reversible exchange is essential for quantum network components, from quantum memories and repeaters for long-distance communication to distributed quantum computing.

Alternatively, the light-matter interface can be used to endow propagating photons with matter-like attributes, such as mass and mutual interactions. Here we employ collective excitations of high electronic orbitals with a large electric dipole moment (Rydberg levels), leading to effective long-range photon-photon interactions. These interactions realize the regime of quantum nonlinear optics. They produce nonclassical photonic states and deterministically entangle photons. We study the photon dynamics, governed by photonic bound states, and observe two-photon (conditional) phase flips, genuine three-photon interactions, and optical quantum vortices.