Controlled manipulation, storage, and retrieval of quantum information are essential for quantum communication and computing. Quantum memories for light, realized with cold atomic samples as the storage medium, are prominent for their high storage efficiencies and lifetime. A team of experimental physicists from the Johannes Gutenberg-Universität Mainz and Beihang University has successfully demonstrated the controlled transport of stored light over 1.2 mm in a cloud of ultracold atoms.
In the experiment by Li et al., atoms of rubidium-87 are first pre-cooled and then transported to the main test area, which is a custom-made vacuum chamber; there they are cooled to temperatures of just a few microkelvins. Image credit: Li et al., doi: 10.1103/PhysRevLett.125.150501.
“The controlled manipulation and storage of quantum information as well as the ability to retrieve it are essential prerequisites for achieving advances in quantum communication and for performing corresponding computer operations in the quantum world,” said senior author Professor Patrick Windpassinger, a physicist in the Institut für Physik at the Johannes Gutenberg-Universität Mainz.
“Optical quantum memories, which allow for the storage and on-demand retrieval of quantum information carried by light, are essential for scalable quantum communication networks.”
“For instance, they can represent important building blocks of quantum repeaters or tools in linear quantum computing.”
“In recent years, clouds of atoms have proven to be media well suited for storing and retrieving optical quantum information.”
“Using a technique called electromagnetically induced transparency, incident light pulses can be trapped and coherently mapped to create a collective excitation of the storage atoms.”
“Since the process is largely reversible, the light can then be retrieved again with high efficiency.”
Professor Windpassinger and colleagues used ultracold atoms of rubidium-87 as a storage medium for the light.
“We stored the light by putting it in a suitcase so to speak, only that in our case the suitcase was made of a cloud of cold atoms,” Professor Windpassinger said.
“We moved this suitcase over a short distance and then took the light out again.”
“This is very interesting not only for physics in general, but also for quantum communication, because light is not very easy to ‘capture,’ and if you want to transport it elsewhere in a controlled manner, it usually ends up being lost.”
The team recently developed a technique that allows clouds of cold atoms to be transported on an ‘optical conveyor belt,’ which is produced by two laser beams.
“The advantage of this method is that a relatively large number of atoms can be transported and positioned with a high degree of accuracy without significant loss of atoms and without the atoms being unintentionally heated,” the authors said.
“We now succeeded in using this method to transport atomic clouds that serve as a light memory. The stored information can then be retrieved elsewhere.”
“Refining this concept, the development of novel quantum devices, such as a racetrack memory for light with separate reading and writing sections, could be possible in the future.”
The team’s work was published in the journal Physical Review Letters.
Wei Li et al. 2020. Controlled Transport of Stored Light. Phys. Rev. Lett 125 (15): 150501; doi: 10.1103/PhysRevLett.125.150501