Increased coherence thanks to cooling


A team of researchers from the SNI network has increased the coherence of an electron spin in a quantum dot to over half a microsecond for the first time. The scientists achieved the more than 150-fold increase in coherence time by using the electron spin-nuclear spin interaction, which causes the spin system to cool down to 100 microkelvin.

Researchers led by Prof. Richard Warburton (Department of Physics and the Swiss Nanoscience Institute at the University of Basel, Switzerland) and Dr. Arne Ludwig (University of Bochum, Germany) use quantum dots of the semiconductor gallium arsenide for their research. They trap individual electrons in the quantum dot and are thus able to create an interface between the emitted single photons and a stationary spin memory.

Due to the interaction with hundreds of thousands of nuclear spins in the gallium arsenide quantum dot, the coherence time of the spin of these trapped electrons was previously only a few nanoseconds. In a publication in the scientific journal Physical Review Letters, the researchers have now shown how they were able to extend the coherence time of the electron spin to 0.6 microseconds.

They achieved this over 150-fold improvement in the coherence time by using the interactions of electron spins and nuclear spins to cool the spin system from 4 Kelvin to 100 microkelvins, thereby increasing the coherence time.

"With this technique, which has not yet been demonstrated on this quantum dot system, we were able to solve a major weakness of quantum dots. Now the coherence time is much longer than the time to control the spin and also much longer than the emission time of single photons." comments Giang N. Nguyen, first author of the study from the Warburton team.

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Research group Prof. Richard Warburton