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.
Geneva Quantum Centre – a faculty center on quantum science and technology
A new faculty centre has been launched at the University of Geneva, focusing on Quantum Science and Technology which we are a big part of. You can read more about this in the official statement here.
Non-classical correlations over 1250 modes between telecom photons and 979-nm photons stored in 171Yb3+:Y2SiO5
Our newest publication appears in Nature Communications where we show a record breaking number of simultaneous stored modes in our Yb quantum memory using a 100 MHz broad AFC. We also showcase remote distribution over 5 km using a repeater-like setup where we store non-classical correlations for 25 microseconds.
Multimode capacity of atomic-freqeuncy comb quantum memories
Our new paper detailing the multimode capacity of atomic-frequency comb memories has just been published in Quantum science and Technology. This paper was a written in collaboration with Margherita Mazzera at Heriot-Watt University in Edinburgh, UK and the group of Hugues de Riedmatten at ICFO in Barcelona, Spain.
Storage of photonic time-bin qubits for up to 20 ms in a rare-earth doped crystal
In our latest paper, we show a revamped europium-based quantum memory. By using the AFC spin-wave protocol in a ~mT magnetic field with a dynamical decoupling sequence, we first demonstrate how our memory is capable of storing 6 temporal modes of weak coherent states of light with average photon number of 1 up to 100 ms, while keeping the noise at readout low enough for a signal-to-noise ratio always above 2. We then generate a time-bin qubit by exploiting our multimode capacity and store it for 20 ms with the same memory protocol. Thanks to a modified readout pulse, we can perform a full quantum tomography of the retrieved state and obtain a quantum storage fidelity of 85% without an external interferometer. Since we found that the limitations in noise and storage time are technical, these benchmarks can be improved further in the near future and lead us closer to a working quantum repeater.
Congratulations Dr. Ortu!
We congratulate Antonio to his fantastic PhD. He successfully defended his thesis on "Rare earth quantum memories: spectroscopy of a new platform and quantum storage implementations".
Return to Ancienne Ecole de Médicine
As of October we have moved our labs out of the villa in Pinchat to the newly renovated Ancienne Ecole de Médicine in the city center. We have three new labs where we are building up our quantum memories and installing new exciting spectroscopy experiments.
Optical and spin manipulation of non-Kramers rare-earth ions in a weak magnetic field for quantum memory applications
In order to make full use of the excellent spin coherence properties of non-Kramers-doped crystals, a static magnetic bias field needs to be applied. In this work we are investigating how a moderate magnetic field of a few milli-Tesla affects each step of the AFC-spin-wave storage protocol and conclude that this regime allows for long and efficient storage in a scenario that is technically easy to implement.
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.