Quantum computing and the orthogonality catastrophe

Quantum physics is evolving from a purely academic field towards building actual technologies with potential applications. Among those, the quantum computer is one of the most fascinating possibilities. Operating a quantum computer is however a race against time, as one needs to build up entanglement before decoherence sets in. In this project, we will be interested in evaluating how the many-quantum-bits wave-function is affected by decoherence. We will design innovative numerical tools (based on tensor networks and matrix product states technology) as well as make use of the theory of orthogonality catastrophe developed in the context of solid state physics. From the understanding of how one or two quantum bits behave, we will extrapolate to the behavior of several tens of quantum bits, thereby shedding new light on the feasibility of different practical routes for quantum processing (superconducting, semi-conducting…). We will also endeavor to run some quantum circuits on actual quantum chips (such as IBM or Rigetti) in order to tabulate the simulations with actual experimental data and evaluate the current state-of-the-art of the field.

The work will involve theoretical / formalism aspects as well as numerics. The Internship/PhD will take place within the theory group of CEA Grenoble, IRIG, PHELIQS (Photonics NanoElectronics and Quantum engineering). Our group contains 15-20 researchers working on nanoelectronics, superconductivity, magnetism and electronic correlations in close collaboration with experimental groups. The project itself will be done under the direction of Christoph Groth and Xavier Waintal.

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