Long-lived storage of a photonic qubit for worldwide teleportation

December 12, 2017 by Olivia Meyer-Streng, Max Planck Society
Artist’s view of global teleportation of quantum bits. Credit: Christoph Hohmann, Nanosystems Initiative Munich

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor Gerhard Rempe at the Max Planck Institute of Quantum Optics (MPQ) have now achieved a major breakthrough: they demonstrated the long-lived storage of a photonic qubit on a single atom trapped in an optical resonator. The coherence time of the stored quantum bit outlasts 100 milliseconds and therefore matches the requirement for the creation of a global quantum network in which qubits are directly teleported between end nodes. "The coherence times that we achieve represent an improvement by two orders of magnitude compared to the current state-of-the-art," says Professor Rempe. The study is published in Nature Photonics today.

Light is an ideal carrier for information encoded on single photons, but transfer over long distances is inefficient and unreliable due to losses. Direct teleportation between the end nodes of a network can be utilized to prevent the loss of precious . First, remote entanglement has to be created between the nodes; then, a suitable measurement on the sender side triggers the "spooky action at a distance," i.e. the instantaneous transport of the qubit to the receiver's node. However, the quantum bit may be rotated when it reaches the receiver and hence has to be reverted. To this end, the necessary information has to be classically communicated from sender to receiver. This takes a certain amount of time, during which the qubit has to be preserved at the receiver. Considering two network nodes at the most distant places on earth, this corresponds to a time span of 66 milliseconds.


"The major problem for storing quantum bits is the phenomenon of dephasing," explains Stefan Langenfeld, a doctoral candidate at the experiment. "Characteristic of a quantum bit is the relative phase of the wave functions of the atomic states that are coherently superimposed. Unfortunately, in real-world experiments, this phase relation is lost over time mostly due to interaction with fluctuating ambient magnetic fields."


Before the retrieval of the stored photonic quantum bit, the Raman transition is reversed. For a storage time of 10 milliseconds, the overlap of the stored photon with the retrieved photon is about 90%. This means, that the mere transfer of the atomic qubit to a less sensitive state configuration extends the coherence time by a factor of 10. Another factor of 10 was gained by adding a so-called "spin echo" to the experimental sequence. Here, the population of the two atomic states used for storage is swapped in the middle of the storage time. "The new technique allows us to preserve the quantum nature of the stored bit for more than 100 milliseconds," says Matthias Körber, a doctoral candidate at the experiment. "Although an envisioned global quantum network which allows for secure and reliable transport of quantum information still demands a lot of research, the long-lived storage of quantum bits is one of the key technologies and we believe that the current improvements will bring us a significant step closer to its realization."

Explore further: Quantum internet goes hybrid

More information: M. Körber et al. Decoherence-protected memory for a single-photon qubit, Nature Photonics (2017). DOI: 10.1038/s41566-017-0050-y

Related Stories

Quantum internet goes hybrid

November 22, 2017


A new kind of quantum computer

November 6, 2017

Quantum mechanics incorporates some very non-intuitive properties of matter. Quantum superposition, for example, allows an atom to be simultaneously in two different states with its spin axis pointed both up and down, or ...

Physicists mix waves on superconducting qubits

November 14, 2017


Quantum processor for single photons

July 7, 2016


Recommended for you

Hybrid device harvests both mechanical and magnetic energy

July 16, 2018


1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (1) Dec 13, 2017

So if I understand correctly, as each teleported qubit requires a classical bit, such a network would be safer, but not faster than current. That's a bummer...


Click here to reset your password.