18 January 2019 Hugues Vincelette
Sébastien Jezouin, postdoctoral fellow at IQ


Sébastien Jezouin, postdoctoral fellow

Photo : IQ

Born in Paris, a city where the student population represents twice the population of the entire city of Sherbrooke, Sébastien Jezouin has made his way to the Institut quantique for a postdoctoral internship.

Guided by the quality of the equipment and the reputation of some of its researchers, including Prs Alexandre Blais and Bertrand Reulet, Sébastien comes to refine his knowledge on quantum circuits in a broader sense.

As he points out, “For some time now, researchers have been able to make electrical circuits that behave in a quantum way. That macroscopic objects obey the same quantum laws as microscopic objects, atoms or photons, was a bit of a surprise at the time. What was surprising was that it proved to be a source of discoveries and generated a number of applications.”


Sébastien contextualizes and describes his research project in a few paragraphs: “In their quest to build a quantum computer, physicists are led to work with signals that can be as weak as a single photon. Given the very low energy it has (a microwave photon has about 50,000 times less energy than an optical photon), such a signal is not directly detectable by conventional measuring devices.

This is particularly a question of temperature. Compared to the calm and frozen world of the cryostat from which the quantum signal originates (the temperature is only 0.01 degrees above absolute zero), our world is like a volcano in eruption.

To survive, the signal must therefore be strengthened, more precisely amplified, inside the cryostat itself and the amplifier itself must be a quantum device.

The realization of these quantum amplifiers is a very active field of research. Different models exist, but most are limited by narrow bandwidths (a few tens of MHz compared to an operating frequency of several GHz). Recently, an amplifier with a bandwidth of several GHz has been manufactured, but its manufacture is extremely complex.

I am currently working in collaboration with Udson C. Mendes, postdoctoral fellow in Alexandre Blais’ group, towards the realization of a quantitatively limited amplifier with a bandwidth of several GHz while having a relatively simple architecture. The first year of my project essentially consisted in developing and providing solutions to the experimental challenges generated by the theoretical constraints. I am confident that I will be able to build a functional amplifier in the near future.”


Dedicating yourself to fundamental research requires method and preparation, and Sébastien Jezouin is well aware of this. “In fundamental research, we pursue avenues that seem promising to us, then we make the samples, it is difficult to predict in advance and with precision the final result. We have to go towards things that have not been done, test new possibilities, which require work upstream to know what we can do and how we want to do it.”

Sébastien will continue his research at the IQ this year, he would like to join the CNRS when he returns to France.



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