Scientists develop ‘quick and efficient’ way to create single photons

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Scientists from Georgia Tech have developed what they say is a quick and efficient way to create single photons for potential use in optical quantum information processing systems.
The technique takes advantage of the properties of atoms with one or more electrons excited to a condition of near ionisation known as the Rydberg state. These atoms – with a principal quantum number greater than 70 – have exaggerated electromagnetic properties and interact strongly with one another.

The researchers say this allows one Rydberg atom to block the formation of additional excited atoms within an area of 10 to 20µm. That Rydberg atom can then be converted to a photon, ensuring that – on average – only one photon is produced from a rubidium cloud containing hundreds of densely packed atoms. "We are able to convert Rydberg excitations to single photons with substantial efficiency, which allows us to prepare the state we want every time," explained Professor Alex Kuzmich from Georgia Tech's School of Physics. "This new system offers a fertile area for investigating entangled states of atoms, spin waves and photons. We hope this will be a first step toward doing a lot more with this system." The researchers used lasers to illuminate a dense ensemble of several hundred rubidium 87 atoms that had been laser cooled and confined in an optical lattice. The illumination boosted one atom from the entire cloud into the Rydberg state. "The excited Rydberg atom needs space around it and doesn't allow any other Rydberg atoms to come nearby," said research assistant Yaroslav Dudin. "Our ensemble has a limited volume, so we couldn't fit more than one of these atoms into the space available." The researchers' next goal may be the development of a quantum gate between light fields. The quantum gating of photons has been proposed and pursued by many research groups, so far unsuccessfully. "If this can be realised, such quantum gates would allow us to deterministically create complex entangled states of atoms and light, which would add valuable capabilities to the fields of quantum networks and computing," Prof Kuzmich said. "Our works points in this direction."