# Quantum storage of photons carrying orbital angular momentum

### Thursday, 25 Sep. 2014, 14:00 - 15:00

**Presenter:** Elisabeth Giacobino

**Host:** Anton Zeilinger

**Where:** Lise-Meitner Lecture Hall, 1nd Floor, Boltzmanngasse 5, 1090 Vienna

For quantum information, critical resources are quantum memories, which enable the storage of quantum data. They will also allow the distribution of entanglement at large distances, in order to overcome transmission losses, since the no-cloning theorem prevents the amplification of a quantum signal.

A quantum memory relies on an efficient coupling between light and matter, in order to achieve reversible mapping of quantum photonic information in and out of the material system. Our system involves the transfer of quantum information from light to atoms (writing) and back from atoms to light (retrieval), using electromagnetically induced transparency (EIT) in three-level transitions in a cold cesium atomic ensemble.

With this set-up we have shown efficient storage of pulses carrying orbital angular momentum (OAM) at the single photon level. Laguerre-Gauss LG+1 and LG-1 modes were imprinted on the signal pulse, using a spatial light modulator. Then superpositions of LG modes, i.e. Hermite Gaussian modes were stored and retrieved. A full memory characterization (process tomography) over the Bloch sphere was performed and allowed us to demonstrate quantum fidelity. We thus demonstrated a quantum memory for orbital angular momentum photonic qubits.

Single photons carrying OAM are promising for the implementation of qubits and qudits since OAM constitutes a quantized and infinite space. Interfacing them with quantum memories opens the way to their use in quantum networks.