Nature Commun. 4, 3527 (2013)

Credit: © 2013 NPG

In quantum information science, the ability to transfer a quantum state between a single photon and matter is essential for realizing a quantum memory. Dong-Sheng Ding and co-workers at the University of Science and Technology in Hefei, China, have now demonstrated a quantum memory that operates by using single photons to carry spatial information in the form of orbital angular momentum. The scheme relies on electromagnetically induced transparency in a cold 85Rb atomic ensemble. A proof-of-principle experiment was conducted using non-classical photon pairs generated by spontaneous four-wave mixing in a cold 85Rb atomic ensemble. One photon (wavelength, 780 nm) is used as a trigger, whereas the other (wavelength, 795 nm) is stored in a second cold 85Rb atomic ensemble. The researchers found that noise mainly originated from a photon generated by a specific atomic transition, and they developed an optical excitation technique to suppress the noise. Photons with an orbital angular momentum state that gave rise to a doughnut-shaped spatial intensity distribution were stored inside the atomic ensemble for 100 ns, and were then retrieved using a single-mode optical fibre. The obtained spatial intensity images of the photons had a similarity of 0.996, indicating successful operation of the quantum image memory.