Quantum memories are devices that can store quantum information for a long time with very high fidelity and efficiency. They are key components for quantum repeaters which are essential for future long distance quantum communication and more generally, quantum network. Quantum memories are generally a light-matter interface since the quantum information to be stored is usually encoded on a beam of light.
Figure 1: Mapping quantum information onto a quantum memory device.
Here in Lund we are working with developing rare earth ion doped solid state quantum memories for example Presidium doped yttrium silicate (Pr:YSO). Rare earth ions doped crystals are very promising candidate for quantum memory because of their excellent coherence properties as well as strong light-matter interaction.
There are various ways to obtain quantum memory, such as:
- Electromagnetically Induced Transparency (EIT)
- Controlled Reversible Inhomogeneous Broadening (CRIB)
- Atomic Frequency Comb (AFC)
- Gradient Echo Memory (GEM)
- Far off-resonant Raman memory
- Revival Of Silenced Echo
Among all of which AFC is especially attractive for its multimode capacity.
To obtain high efficiency quantum memory, it is necessary to have high absorption depth. We are now investigating cavity enhanced quantum memory, which in principle can achieve about unity efficiency. The best we have achieved now is 56%, and we believe this number can be futher improved.
Figure 2: Comparing the area of first echo at 1.1µs and the area of input pulse gives us a memory efficiency of 56%.
Experimental detail and the results can be found in our Publications .