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.
Research Themes
Quantum Memories
Quantum Photonics
Optical and Spin Spectroscopy
News (archive)
Broadband and long-duration optical memory in 171Yb3+:Y2SiO5
November, 2025
We developed a new frequence-agile optical pumping laser setup for the Yb:YSO quantum memory. This allows for broadband and long-lived optical storage over 250 MHz for up to 125 µs and paves the way towards a 288 MHz-wide spin-wave storage. More details can be found in the article.
Quantum Networks using Rare-Earth Ions
June, 2025
This review, written in collaboration with Wolfgang Tittel at UniGe and Adam Kinos, Lars Rippe, and Andreas Walther at Lund University, highlights the potential of rare-earth ion-doped crystals for application as a platform for quantum networks. As a part of quantum repeaters, quantum memories based on ensembles of rare-earth ions are likely to become rapidly useful. The full article can be found here.
Efficient and reversible optical-to-spin conversion
April, 2025
The AFC spin-wave quantum memory protocol in a 151Eu3+:Y2SiO5 crystal offers the possibility of long storage times and on-demand readout. By applying a magnetic field and optimization using a developed simulation tool we were able to increase the conversion efficiency of the optical to spin conversion to up to 96% for a storage time of 500 µs! More details can be found in the article.
Swiss Quantum Call 2024 grant
December, 2024
The qram group (PI Mikael Afzelius) was awarded a 4-year 642 kCHF grant for the project "A quantum repeater node based on a broadband and highly multimode 171Yb:Y2SiO5 quantum memory", in the context of the Swiss Quantum Call 2024. In total 13 projects were supported, for a total of 16 MCHF. The funding source of this project will be SERI through the "Transitional measures".
Optical coherence and spin population in 171Yb3+:Y2SiO5
We continue our fruitful collaboration with the group of Dr. Philippe Goldner at Chimie ParisTech, PSL University, Paris. In this study, that has now appeared in Phys. Rev. B, we measure the optical coherence and spin dynamics from 40 mK to 18 K, for different 171Yb doping concentrations. At 3 K and below, we measure an optical linewidth of only 350 Hz (!), a key parameter for multimode quantum memory operation in this crystal. Read the complete study here.
Toward the Device-Independent Certification of a Quantum Memory
In collaboration with the Quantum Theory Group at the University of Geneva and the QIT Group at CEA/Université Paris-Saclay, we have developed and tested a robust self-testing method for certifying and characterizing a quantum memory. The results have been published in Physical Review Letters!
Quantum Transitional Measures Grant
The State Secretariat for Education, Research and Innovation (SERI) awarded 3.25 millions CHF for our 4-year project "Quantum communication networks: quantum encryption & repeaters" (see all approved projects), involving four Principal Investigators at the Department of Applied Physics: Mikael Afzelius, Rob Thew, Wolfgang Tittel and Nicolas Brunner. Our qram group led by Mikael Afzelius was awarded 683 kCHF in total.
The Quantum Transitional Measure was launched in an attempt to secure the European and international competitiveness and connectivity of the Swiss quantum research community, following exclusion of Swiss researches from the EU Quantum Technologies Flagship.
Coherent optical-microwave interface for manipulation of low-field electronic clock transitions in 171Yb3+:Y2SiO5
With our newly designed loop-gap microwave resonator we now have the chance to probe different microwave transitions and further investigate Yb:YSO. In this new publication we specifically looked at the low field dephasing process and managed to observe a spin coherence time of up to 10 ms.
Readout-Integrated Time-Bin Qutrit Analyzer for Echo-Based Quantum Memories
Fully analyzing the quantum state takes a lot of resorces and usually requires a dedicated measurement setup. In this publication we present a way of analyzing time-bin qutrit states using the readout protocol of our AFC spin-wave memory. You can read more about it in our new publication here.
Proposal for spin squeezing in rare-earth-ion-doped crystals with a four-color scheme
We recently worked on a project about generating spin squeezing in rare-earth ion doped crystals, in collaboration with the Quantum Theory Group at the university of Geneva and the Université de Cote d'Azur. The result of this work just got published in Physical Review A, the full article can be viewed here.
