Q u a n t u m    R e p e a t e r s

Pictured is an ultra-cold cloud of rubidium-85 atoms suspended in ultra-high vacuum via cooling lasers and magnetic fields.

Our long term goal is to achieve quantum networking based on telecommunications quantum repeater. We have proposed a new strategy for a quantum repeater at telecommunications wavelengths with long-lived atomic memory, and we have experimentally demonstrated its critical elements in a cold atomic ensemble. Using atomic cascade emission in rubidium-85, we generated an entangled pair of 1.53 µm and 780 nm photons. The former is ideal for long-distance quantum communication, while the latter is naturally suited for mapping to a long-lived atomic memory.

The above image displays the fluorescence of laser-cooled neutral rubidium-85 atoms collected by a back lit CCD array. These ultra cold atoms are collectively used to store quantum information.

We have made significant advances in the generation, distribution, and storage of qubit entanglement using narrow-band 780/795 nm photons, including atom-photon entanglement and matter-light qubit conversion, Bell inequality violation between a collective atomic qubit and a photon, storage and retrieval of single photons transmitted between remote quantum memories, and light-matter qubit conversion and entanglement of remote atomic qubits. Together, these works have realized the essential elements of a telecommunications quantum repeater.