Researchers from the UNIGE team at the University of Geneva, Switzerland, successfully stored a quantum bit in a crystal for 20 milliseconds, setting a new world record, laying an important foundation for the development of long-distance quantum communication network.
Today, within the framework of the European Quantum Flagship program, Mikael Afzelius’ team has succeeded in taking human scientific research one step further by storing a qubit for 20 milliseconds. To do this, they used crystals doped with europium, which are capable of absorbing light before emitting light.
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As you may have heard, one of the main obstacles to building a long-range quantum communication system is that photons will be lost after traveling hundreds of kilometers, and the signal will naturally disappear. To this end, the “repeater” based on quantum memory was born. In order for the repeater to function better, the quantum information needs to be stored for a longer time.
“This is a new world record for a quantum memory based on a solid-state system, in this case, a crystal. We even managed to reach the 100-millisecond mark with very little loss of fidelity,” the researchers enthused.”
Moreover, the UNIGE researchers used metal crystals doped with certain rare earths (in this case, europium), which can absorb light and then emit light. The crystals were kept at -273.15°C (absolute zero) because the thermal agitation of the crystals would disrupt atomic entanglement once this temperature was exceeded by 10°C.
“We apply a small magnetic field of one-thousandth of a Tesla to the crystal and use a dynamic decoupling method, which involves sending strong radio frequencies to the crystal,” explains Antonio Ortu, a postdoctoral fellow at UNIGE’s Department of Applied Physics.
The effect of these techniques is to decouple rare-earth ions from perturbations in the environment and improve the memory performance we know so far by a factor of nearly 40.”
The results of this study constitute a major advance in the development of long-distance quantum communication networks. In addition, they brought the storage of quantum states carried by photons to a timescale that humans can estimate.
