Welcome to the qram lab!
The long-term vision of the qram lab, led by Dr. Mikael Afzelius, is to develop a quantum repeater for long-distance quantum communication, based on spin-photon entanglement, quantum memories and teleportation of entanglement. To this end we explore rare-earth doped crystals, a leading solid-state candidate for quantum repeaters.
Our work is highly interdisciplinary as it covers fundamental material properties, coherent spectroscopy, quantum optics, and quantum memories. We strive to bring all this together in demonstrations of basic quantum repeater functionalities.
Spectral diffusion enhanced optical pumping
Together with our collaborators from Chimie ParisTech we published in this PRX paper a new method to polarize a large spin ensemble by only exciting a small subset of the spins using a laser. Altough very few spins are excited, the entire ensemble can be optically pumped into a single spin state, owing to spin-spin interactions and spectral diffusion of the excitation.
This novel polarisation technique reduces magnetic noise in a strongly interactive system, resulting in greatly enhanced optical coherence times, without the need to resort to strong magnetic fields or very low temperatures.
Enhancing coherence time in Eu:YSO using Dynamical Decoupling
One of the main limitations of storage time using atomic frequency combs (AFC) in rare earth ion doped crystals like Eu:YSO is the coupling of the dopant ions to their crystal environment. In this recent work we demonstrate a significant reduction of this coupling using so called dynamical decoupling techniques. Applying this method together with a carefully chosen magnetic bias field allows us to demonstrate optical storage with a coherence time of 0.5 s – a more than 300-fold increase of the previous state of the art for this system and protocol.
Optical light storage in 171Yb3+:YSO exceeding 1 ms
Our recent publication in PRL shows for the first time a storage of light in a nuclear-spin hybrid system using the AFC memory protocol.
This work further highlights the capabilities of Yb as a quantum memory and is a big steping stone towards the implementation of this new material into a global quantum network.
171Yb3+:YSO - The quantum memory of tomorrow
Our new Paper about the study of optical and spin coherence times in a new solid state material (171Yb3+:YSO crystal) containing electronic spins, was published in Nature Materials.
This material opens up a new field of possibilities for creating a global quantum network; it also underlines the importance of pursuing fundamental research in parallel with more applied research, such as devising a quantum memory.
Efficient optical pumping using hyperfine levels in 145Nd3+:YSO
Tradidionally in the rare-earth community is believed that Kramers ion-doped solids experience limited storage efficiency compared to non-Kramers. In our recent paper, published in NJP, we study the relaxation processes limiting optical pumping and achieve efficiencies comparable with state of the art non-Kramers quantum memories.