Scientists in the US have demonstrated a new technique for generating photons for use in optical quantum information processing: using a laser to excite a single photon from a cloud of rubidium gas.
The technique, developed at the Georgia Institute of Technology Research, exploits the properties of an atom in which one or more electrons has been excited near ionisation energy levels, the so-called Rydberg state. In this state, an atom will interact very strongly with its neighbours, preventing the excitation of electrons on other atoms within an area of 10 to 20 microns. This is known as the Rydberg Blockade.
The researchers discovered that if they confined their rubidium gas to an area covered by the Rydberg Blockade, they could ensure that just one Rydberg atom could form when the cloud was illuminated by lasers. This meant that they could reliably create a single photon, with many known properties, from their starting cloud of gas.
Alex Kuzmich, a professor in the School of Physics at the Georgia Institute of Technology explains in the announcement: "We are able to convert Rydberg excitations to single photons with very substantial efficiency, which allows us to prepare the exact state we want every time. This new system offers a fertile area for investigating entangled states of atoms, spin waves and photons."
Co-author Yaroslav Dudin says that the new source generates photons about a thousand times faster than existing systems. "The numbers are very good for our first experimental implementation."
Next, the group plans to work on developing a quantum gate, but they acknowledge that other attempts within the research community to do this have not been successful. But if it could be done, it would allow the researchers to "deterministically create complex entangled states of atoms and light, which would add valuable capabilities to the fields of quantum networks and computing," Kuzmich said. "Our works points in this direction."
The new technique, announced under embargo, was scheduled to be reported April 19 in Science Express, the rapid online publication of the journal Science. The research was supported by the National Science Foundation (NSF), and by the Air Force Office of Scientific Research (AFOSR).