2 November 2018 Hugues Vincelette
The experimental possibilities of qudits

Clément Godfrin’s Article in Nature

Photo : IQ

Clément Godfrin is a postdoctoral fellow at the IQ under the direction of Professors Eva Dupont-Ferrier and Michel Pioro-Ladrière. His academic career began in Brest, France, where he was born. He moved on to Paris for a master’s degree, and then Grenoble for a doctorate at the Institut Néel.

 At the IQ, he focuses on spins in silicon-based structures, specifically on the interaction between these spins and photons, to implement quantum information protocols. More generally, he is passionate about conducting experiments based on theories of forerunners, such as Einstein, Schrödinger or Planck: Thanks to the development of experimental techniques (cryogenics, nanofabrication, electronics, etc.), we can now make systems that closely resemble the thought experiments imagined by the founding fathers of quantum mechanics over a hundred years ago. “I like to carry out what are called ‘toy model’ experiments that involve a very small number of components (atom, photon, etc.) and gaining an in-depth understanding of the fundamental mechanisms of quantum mechanics.”

Publication in Nature

The Institut quantique annually hosts about ten postdoctoral fellows like Clément from around the world. This has led them to collaborate with other graduate-level research teams.

As a member of a research team at the Institut Néel, Clément contributedas the first authorto research that Naturehas just published, which is entitledGeneralized Ramsey interferometry explored with a single nuclear spin qudit.He gives the following overview: “The publication is related to my dissertation work. I had the chance to work on a topic that was developed by the team of Franck Balestro and Wolfgang Wernsdorfer for more than ten years at the Institut Néel in Grenoble: the molecular magnet transistor. Thanks to quantum transport measurements through a single TbPc2 molecule under fields and at a very low temperature, we can read and manipulate the nuclear spin of a Terbium atom. This unique nuclear spin, strongly isolated from its environment, retains its quantum properties for durations of about one second. It forms a four-level system, a veritable test bed to probe the properties of quantum mechanics. Among these fascinating properties, the superposition of states and phase interference are two fundamental mechanisms that come from the promising power of quantum computing. In this latest publication, we probed these properties by applying interference protocols involving the phases of the four nuclear spin states. This allowed us, among other things, to directly measure the phase of a quantum gate and the coherence time of a three-state superposition. This is the first time that such a degree of control of a single multi-level nuclear spin has been demonstrated. Now the community is looking to put several of these systems next to each other and have them interact in a way that would implement ever more complex quantum protocols. The next step will therefore be to pair this spin with other spins by using, for example, molecules carrying several magnetic centres or photons by using systems based on superconductors.”

Why Choose Sherbrooke?

Clément explains that a combination of several factors led him to choose the Institut quantique. The first contact with Sherbrooke was made seven years ago through a fellowship in Michel Pioro-Ladrière’s group. From this very first visit, Clément discovered a working atmosphere that he enjoyed, which is an important aspect of research. Later, during a visit to the Institut quantique, he became better acquainted with the team, whose expertise and skills in quantum physics impressed him. “After a doctorate, it is crucial to find a dynamic place where you can enjoy great freedom. That’s what I found here,” he says. Quebec’s wide-open natural spaces were the last argument that convinced the outdoors enthusiast to settle in the Estrie region.

What’s Next ?

Clément unhesitatingly answers questions about his professional projects after his stay at the IQ: “I would like to continue in research. I’m thinking of doing another postdoctoral fellowship to continue learning experimental techniques to probe and play more efficiently with quantum systems. Many teams around the world are currently working on systems linking spin and superconducting circuits. I would like to continue in this direction.”

Until then, Clément will undoubtedly have the opportunity to contribute to other publications.

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