Laboratoire de Physique de la Matière Condensée

– Assistant Professor at Ecole Polytechnique
– Researcher at PMC in the Electrons Photons Surfaces Group
– PI of the QCMX Lab : QCMX website
– Faculty member of the Physics Department of Ecole Polytechnique & IP Paris

Contact :
– Address : PMC, Ecole Polytechnique, 91128 Palaiseau, France
– E-mail : joel.griesmar-AT-polytechnique.edu
– Phone : +33169334743
– Office : Building 83, 1st floor, Office 83-20-27
– Linkedin

Research :
– ORCID 0000-0002-0586-6757
– Google Scholar
– arXiv publications

Biography :
After joining Ecole Polytechnique in 2011, where I specialized in condensed matter physics, I obtained a Master’s degree in physics from the Freie Universität in Berlin, where I studied the growth of EuS films on InAs and InP substrates.

I then did my thesis from 2015 to 2018 at the Collège de France in Paris, where I developed a spectrometer based on the Josephson effect in tunnel junctions between two superconductors separated by an insulator. When a DC voltage is applied, a Cooper pair can tunnel only if it emits a photon of energy proportional to the applied voltage. The absorption of these photons is directly measured on the junction’s current-voltage characteristic as a current peak.

After that, I did a two-year post-doc at the University of Sherbrooke, Quebec. There, I continued my interest in voltage-biased Josephson junctions. By exploiting the non-linearity of a junction, I developed a photo-multiplier that converts a microwave photon at one frequency into several photons at another frequency. In this way, I measured a threefold increase in the number of photons injected.

I joined the QCMX team as a post-doc in October 2021 to study Andreev bound states in carbon nanotubes. To observe these states, we’ll be using a new two-tone spectroscopy technique improving on the one I developed during my thesis.

In September 2022, I was finally hired as an assistant professor in the same laboratory to develop protected superconducting qubits.