Single Photon Sources:
An ideal single photon entangled pair source for a quantum repeater application should satisfy several conditions simultaneously. Since photons must interact efficiently with a quantum memory, the source must emit photons that are spectrally very pure (have a very narrow linewidth) and are aligned to the narrow energy transitions of the atomic ensemble used in the quantum memory.
A quantum repeater for long distance transmission requires pairs of ‘non-degenerate’ photons in which one photon at an atomic wavelength is suitable for quantum memory and the other photon at a telecom wavelength is suitable for long distance transmission in optical fibers. Alternatively, the photons may be degenerate (same wavelength) but compatible with a conversion quantum Interface that can alter their wavelength while preserving their quantum statistical properties.
In a quantum repeater scheme, photons arriving at a Bell state measurement device must interfere. This is a very technically challenging process for single photons since they must arrive at the exact same point on a beam-combiner at the exact same time. To achieve this, quantum memories can be used to store the quantum property of each photon until they are all available and ready, and then release the photons in a controlled way onto the beam-combiner for more efficient interference.
Our current research includes the implementation a quantum memory scheme called Electromagnetically Induced Transparency (EIT) in an ensemble of Cesium atoms, in which a laser control beam can turn ‘on’ or ‘off’ the storage of a single photon level signal.
A quantum interface is needed when different photon characteristics are optimal for certain tasks such as long-distance transmission, efficient detection or different quantum computing technology. For example, photons at wavelengths that are suitable for long distance transmission in optical fibers are not optimal for easy and efficient detection. A quantum interface in this case can convert the photons from the telecommunications band for transmission to the near visible band for detection while preserving the quantum statistical properties of the photons. On the other hand, photon pairs generated at atomic resonance wavelengths may need to be converted to a telecommunications band for long distance transmission. As another example, different quantum computing technologies rely on different wavelength photons. Transferring qubit states from photons at one wavelength to the other is necessary for connecting or scaling quantum computers.
We perform research and development on quantum repeaters and supporting measurement technologies. Our mission is to bridge the gap between fundamental quantum research and practical information technology applications. Our research aims to promote US innovation, industrial competitiveness and enhance the nation's security. For more information, contact project leader Dr. Xiao Tang. For more information concerning the ITL Quantum Information program, please select link 'ITL Quantum Information Program'.