Rare Earth Atoms See the Light

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“The first light pulse creates a set of atoms we ‘talk’ to in a specific state and we call that state ‘in phase’ because all the atoms are created at the same time by this optical pulse,” Bouwmeester explained. “However, the individual atoms have slightly different frequencies because of residual coupling to neighboring atoms, which affects their time evolution and causes decoherence in the system.” Decoherence is the inability to keep track of how the system evolves in all its details.

“The trick is that the second light pulse changes the state of the system so that it evolves backwards, causing the atoms to return to the initial phase,” he continued. “This makes everything coherent and causes the atoms to collectively emit the light they absorbed from the first pulse.”

The strength of the photon echo contains important information about the fundamental properties of the ytterbium in the host material. “By analyzing the strength of these photon echoes, we are learning about the fundamental interactions of ytterbium with its surroundings,” Bouwmeester said. “Now we’re working on strengthening the Purcell effect by making the storage rings we use smaller and smaller.”

According to Bouwmeester, quantum computation needs to be compatible with optical communication for information to be shared and transmitted. “Our ultimate goal is to be able to communicate to a single ytterbium atom; then we can start transferring the quantum state of a single photon to a single ytterbium atom,” he added. “Coupling the quantum state of a photon to a quantum solid state is essential for the existence of a quantum Internet.”