Quantum Memories are devices that can store the quantum state of a photon, without destroying the volatile quantum information.
Quantum Memories will be key components in future quantum networks, such as Quantum Repeaters which can provide a solution for long-distance quantum communication beyond the limit of 200 km using today’s technology. In addition to future applications, Quantum Memories are fascinating because they provide a way to study how quantum effects such as entanglement can be transferred between physical systems of widely different nature, eg. between light and matter systems.
In our research we study light-matter interactions between photons, in the visible and telecommunications wavelength, with rare-earth-metal ions doped into optical crystals. These are highly interesting Quantum Memory materials since they have excellent coherence properties when cooled to below 4 Kelvin. This is crucial in order to avoid destroying the quantum interaction through local interactions such as with phonons. Using ideas developed in our research we have achieved several milestones, for example the first storage of a pseudo single photons, storage of multiple photonic qubits in a single neodymium-doped crystal, and more recently storage of a visible photon entangled with a telecom photon.