» Research » Department of Quantum Science & Technology » Solid state spectroscopy group » High data storage capacity quantum memories
Figure 1: One concept for a highly multiplexed memory. (a) A high optical depth crystal is divided into voxels that can be addressed by translating the crystal. (b) Inside each voxel, information is stored using an off-resonant Raman protocol using holographic multiplexing (a changing angle between pump and signal beams encodes multiple modes into the same volume).
One of the major applications for rare earth quantum memories is in quantum networks, where the memory serves to synchronise operations in the network. To enable high transmission rates through the network, the memory must have a high data storage capacity. For example, for a memory storage time of one second, even a MHz transmission rate requires the storage of 106 modes.
Multimode storage has proven very difficult, and quantum memories have only demonstrated the storage of a handful of modes to date. The problem is that storage of many modes at high efficiency requires a material with very high optical density. Current memory materials, which have low dopant concentrations of rare earth ions, typically have low optical densities, of the order of 1cm-1.
We are investigating the use of stoichiometric rare earth crystals for high data storage capacity quantum memories. With a rare earth concentration of 100%, these crystals can have optical densities three orders of magnitude greater than common doped crystals. With such high optical densities, the data storage capacity of these crystals is likely to hit a more fundamental limit – the interactions between the rare earth ions. We are studying these interactions to understand how they will affect storage densities, to inform the choice of material and memory protocol that will provide the best performance.
Memory protocols achieve multimode storage using a variety of multiplexing methods, including spatial, spectral, and time multiplexing. The highest storage density is likely to be obtained with a combination of these multiplexing methods, and we are studying a number of multiplexed implementations of common memory protocols to understand how best to meet the needs of quantum network applications.
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