23 January 2017 Correlated single photon stored in highly non-linear medium

An ICFO study in Nature Communications reports on the storage of a correlated single photon emitted by a quantum memory in a highly excited Rydberg medium. Being able to control the interaction between two single photons is a long standing goal in quantum photonics and quantum information science. Such possibility would enable a new regime of nonlinear optics as well as unlock several applications in quantum information science, including photonic quantum gates and deterministic Bell-state measurements. Within the field of quantum networks, achieving interactions between single photons from independent photon pairs, which are storable in quantum memories, are of uttermost importance.

In recent years, Rydberg atoms (atoms in highly excited states) have taken the stand as a powerful platform for performing non-linear optics at the single photon level, due to their long-range interaction. However, so far, most experiments showing nonlinearities at the single-photon level with Rydberg atoms have used weak classical input light.

Now ICFO researchers Emanuele Distante, Pau Farrera, Auxiliadora Padrón-Brito, Dr. David Paredes-Barato and Dr Georg Heinze, in the group led by ICREA Prof. Hugues de Riedmatten, report in Nature Communications the demonstration of the storage and retrieval of a paired single photon, emitted by an ensemble quantum memory in a strongly nonlinear medium based on highly excited Rydberg atoms. They show that nonclassical correlations between the two photons persist after retrieval from the Rydberg ensemble and demonstrate that the Rydberg ensemble displays optical non-linearity with input pulses containing a few tens of photons.

The results of this study mean an important step forward towards deterministic photon–photon interactions, and may enable deterministic Bell-state measurements with multimode quantum memories.