Quantum information

Resilient AND SCALABLE Quantum Information Processing

Audrey Bienfait, Pascal Degiovanni, Sylvain Hermelin, Benjamin Huard, F. Mezzacapo, T. Roscilde

In order to exploit and benefit from quantum properties of any physical quantum system, it is crucial to make them more resilient to decoherence and to enable scaling up these systems towards large number of entities.

We explore entanglement in out-of-equilibrium quantum systems, using fundamental quantum many-body phenomena to generate scalable multipartite entanglement.

In most platforms (such as atom arrays) the scalability of entanglement is limited by qubit losses and errors. We work to identify the most resilient forms of entangled states, and their associated time and interaction resources. We also work on extending the engineering of multipartite entanglement from qubits to qudits, implemented with large-spin magnetic atoms.

For electron flying qubits, we are developing interferometric protocols for electronic entanglement characterization.

We are also collaborating with the startup Alice & Bob to realize experiments on cat codes with superconducting circuits. Our team realizes experiments that test inventive strategies to realize in situ protection against error channels. We are developing new couplers for multi-photon dissipation that are at the basis of quantum error correction with cat codes.

Using superconducting circuits coupled to an ensemble of electronic spins, we are developping quantum memories for storing quantum states using long-coherence spins such as bismuth donors in silicon.

Quantum State Engineering

Pascal Degiovanni, Sylvain Hermelin, Benjamin Huard, F. Mezzacapo, T. Roscilde

Preparing or stabilizing non trivial quantum states in physical systems is an important task in quantum science. Our team addresses it in various platforms.

We study the potential of single electron currents for generating controlled entanglement as well as non-classical electromagnetic fields. Additionally, we study the quantum optics of plasmon modes within quantum Hall channels.

Quantum state engineering is also possible when atoms or qubits collectively strongly couple to the environment. We investigate how emitter interference effects can control entanglement in tunable emitter arrays.

Strong coupling between superconducting qubits and transmission lines allows probing of multimode light scattered by nonlinear elements. We use FPGA-based propagating state tomography and advanced amplification to explore this new quantum optics area. We also use measurement backaction and machine learning to prepare quantum states of superconducting resonators.

Classical–Quantum Boundary

Pascal Degiovanni, Tommaso Roscilde, Jean-Marie Stephan

Understanding how classical behaviors emerge from quantum dynamics is a central puzzle of quantum theory since its birth. Our team works on this topic from several perspectives.

We also investigate the emergence of an objective classical picture (through the so-called quantum Darwinism approach), by exploring how the reconstructed classical picture depends on available observer resources.

We investigate the fundamental question of what mechanisms limit the spreading of quantum correlations and multipartite entanglement in bulk quantum materials at equilibrium. Relevant examples are the concentration of correlations in systems dominated by quantum disorder, and symmetry breaking in ordered systems. An appealing perspective is to use quantum criticality between such regimes to enhance quantum correlations.

RANDOMIZED MEASUREMENTS

Luca Lionni

In the recent years, randomized measurements, distributions of randomly rotated local observables, have been shown to be a great tool to characterize the state and correlations of quantum systems. We are expanding this tool from small systems to multipartite quantum states. In particular, we simplify calculations under the approximation of large local dimension using recent developments in random matrix theory.