Quantum memories for the 1550 nm telecommunication band

A global quantum communication network offers the promise of provably secure transmission of information. Any future globally deployed quantum communication network will require information to be transmitted over large distances, most likely using optical fibre. Therefore, to minimise the transmission losses, all elements of such a network should operate in the low-loss C-band for optical fibre at 1550 nm, which is currently used in the telecommunications industry.

One crucial component for a quantum network is a quantum memory, capable of synchronising operations in different parts of the network. Quantum memories operate at a specific wavelength determined by the material used. Developing suitable materials for a quantum memory operating at 1550 nm has proven challenging, with the memory storage times currently limited to 50 ns, orders of magnitude smaller than what is required for a long-range quantum network.

The rare-earth ion erbium has an optical transition in the telecommunications C-band, making it an ideal candidate for building quantum memories at 1550 nm. However, previous investigations have shown that the ground states that would be utilised for storing the quantum information have a short lifetime, much shorter than in other rare earth ions commonly used for quantum memories. This would limit the obtainable storage time of an erbium quantum memory.

We recently showed that we could turn off the mechanism causing the short lifetime by applying a large magnetic field to the erbium crystal. This allowed us to achieve a quantum coherence time of 1.3 s, 8 orders of magnitude larger than the current quantum memory storage times. This is the first material identified that is suitable for the development of a long-term quantum memory operating at the 1550 nm telecommunication wavelength and we are currently working to demonstrate such a memory. Further, by implementing our entanglement generation and distribution protocol in erbium, we will be in a position to demonstrate the building-blocks of a quantum communication network that can take advantage of the existing optical fibre network.

Selected publications

Matthew Sellars

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