Solid-state coherent interface between microwaves and Telecom-C band light

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Quantum communication networks promises to distribute information in absolute secure way and it is based on dissemination of quantum entangled states over a large scale computing architecture. The core elements of future quantum networks, i.e. quantum repeaters as well as network nodes, can be realized by using qubits and quantum memories of diverse physical nature. Today, elementary quantum networks linking two remote single atoms have been demonstrated. Solid-state systems such as superconducting quantum circuits, nano-mechanical devices, and spin doped solids potentially offer larger scalability and faster operation time compared to systems based on the single atom approach. However, such solid-state devices operate at microwave and RFs, which are less suitable for long-range quantum communication than fiber-optical channels due to losses in cables and the high noise temperature of antennas (about 100 K) for radio-relay communication. To establish a fiber-optical link between them, one has to use a quantum media converter, i.e. a device which coherently interfaces matter and photonic qubits.In this project we will focus on frequency converted based on isotopically enriched Yttrium-Lithium tetrafluoride (YLiF4) doped with isotopes of erbium ions. The advantage of using rare-earth-ion doped crystal is the ability to implement multi-mode conversion protocol. Isotopically enriched crystals are known for their ultra-narrow inhomogeneous broadening, which is believed to be crucial for the implementation of quantum interfaces between Telecom-C around 1.54 um photons and superconducting quantum circuits. In our project we will focus on implementation of bi-directional conversion of coherent microwave to optical fields by using such a crystal. In order to reach the aim of the project few intermediate steps shall be fulfilled. Since there were only few experiments with such crystals, we will initially explore its coherent properties at millikelvin temperatures and small magnetic field, i.e. at operating conditions of superconducting qubits. Then we are going to implement conversion of microwave and optical fields to a spin excitation of doped rare-earth ions by using electromagnetically-induced-transparency and measure storage time. Finally, by using optical pumping or spin echo technique the spin wave excitation will be converted into coherent optical fields or microwave field and the conversion efficiency will be measured.