Our group is concerned with research in quantum theory, information theory and the interplay between these fields. We explore applied and fundamental questions related to the certification, the quantification and development of resources for quantum technologies. More on the research section.
We are based in the Institut de Physique Théorique (CEA/CNRS/Univeristé Paris-Saclay).
We are currently open to PhD students and Post-Doctoral applications. We welcome people from all background and particulary encourage people from minorities in science to apply. Anyone interested can contact Nicolas Sangouard or Jean-Daniel Bancal for more information.
Master students interested in a master thesis or an internship in quantum information theory can contact Nicolas Sangouard or Jean-Daniel Bancal. In particular, we currently offer a funded Master thesis on Automated design of quantum circuits by reinforcement learning. More information and contact can be found here.
1 Oct 2021
The standard approach for building a quantum computer consists in realising an enormous processor with millions of qubits. This raises significant engineering challenges in qubit integration and packaging, refrigerated space and cooling power. We have considered an alternative architecture where a small processor is combined with a memory. As in a classical computer, the basic idea is to store all the information in a quantum memory, release a few qubit states to process them in the processor, store them back to the memory and repeat the process until the computation is done. We have shown that this reduces the number of qubits in the processor by two orders of magnitudes for factoring 2048 bit RSA integers using Shor’s algorithm. One additional order of magnitude is even achievable by choosing an appropriate error correction code. Details have been published in Physical Review Letters. They received an editor’s suggestion, a synopsis from Physics and have been highlighted by CEA.
30 Jul 2021
Symmetries play an important role in many areas of physics and often lead to drastic simplifications. Together with collaborators at the University of Geneva, the University of Cologne and the Perimeter Institute, we developed RepLAB, a toolbox to study finite representations of compact groups and decompose them efficiently. The toolbox’s built-in interface with convex optimization solvers makes it particularly suitable to solve concrete problems with symmetries.
19 Feb 2021
Together with teams from EPFL and MIT, we succeeded to leverage universal properties of spontaneous Raman scattering to demonstrate Bell correlations between light and a collective molecular vibration. By measuring the decay of these hybrid photon-phonon Bell correlations with sub-picosecond time resolution, we found that they survive over several hundred oscillations at ambient conditions. Our results pave the way for ultra-fast quantum technologies and promote a new technique to probe the role of phonon-mediated entanglement in chemistry or even biology. These results have been published in Science Advances, and highlighted by the CEA (french).
02 Oct 2020
Quantum entanglement is a crucial resource for quantum communication devices. Together with the universities of Geneva and Basel, we have successfully entangled the outputs of two optical fibers sharing a single photon at a distance of 2 km. This shows how a form of quantum entanglement that is simple to produce can be distributed and detected over long distances — one more step towards the construction of a secure internet. Our results have been published in Physical Review Letters and highlighted by the CEA.
11 Jun 2020
Hackers in possession of quantum computers represent a serious threat to today’s cryptosystems. Researchers are therefore working on new encryption methods based on the principles of quantum mechanics. However, current encryption protocols assume that the communicating devices are known, trustworthy entities. But what if this is not the case and the devices leave a back door open for eavesdropping attacks? In collaboration with the group of Professor Renato Renner of ETH Zurich, we made a step towards fully secure encryption with untrusted devices. Our results have been published in Physical Review Letters and highlighted by the university of Basel.
13 May 2020
The no-signalling principle imposes constraints that are expected to be satisfied by any “reasonable” theory: a choice of measurement setting made in one place should not affect the statistics observed at a distance. This principle has proven particularly fruitful in studying generalized probabilistic models in Bell scenarios. With the recent generalization of Bell nonlocality to networks, we set out to examine with colleagues from Geneva, Bristol, Brussels and Zurich how the principle of no-signalling could be complemented by the independence assumption of distinct source inherent to networks. In a paper published in Nature Communications we show that the resulting condition of non-signaling and independence (NSI) gives rise to highly nontrivial constraints even in absence of measurement settings. This suggest that generalized probabilistic theories on networks have a rich structure.
21 Oct 2019
Optical frequency photons play an important role in quantum communication, thanks to the ability of carrying quantum information over large distances. To create such photon and to process the information they carry, cavity QED has a great potential to exploit. In this scope, the Warburton group in Basel developed a gated semi-conductor quantum-dot strongly coupled to an optical micro-cavity. We developed a detailed theoretical model of such a hybrid system which allowed us to gain insight into the physics of this coherent exciton-photon interface and demonstrate its great potential for future quantum communications. These results have been published in the prestigious journal Nature and highlighted by the University of Basel. Optical frequency photons play an important role in quantum communication, thanks to the ability of carrying quantum information over large distances. To create such photon and to process the information they carry, cavity QED has a great potential to exploit. In this scope, the Warburton group in Basel developed a gated semi-conductor quantum-dot strongly coupled to an optical micro-cavity. We developed a detailed theoretical model of such a hybrid system which allowed us to gain insight into the physics of this coherent exciton-photon interface and demonstrate its great potential for future quantum communications. These results have been published in the prestigious journal Nature and highlighted by the University of Basel.
06 May 2019
Please join us in congratulating Alexey Melnikov for winning the Cozzarelli Prize in the physical and mathematical sciences category. This award acknowledges Melnikov et al. “Active learning machine learns to create new quantum experiments”, a paper published in PNAS, in which reinforcement learning is used to explore a space of possible quantum experiments in order to find one (or more) design fulfilling a specific aim. This price was delivered personally to Alexey and his coauthors during a ceremony in Washington D.C.. Alexey Melnikov appeared recently on national russian television news, in which he talks (Russian) about his prize.
12 Feb 2019
Quantum entanglement and Bell nonlocality are two fundamental properties of quantum systems whose relation still remains poorly understood today. A remarkable link between them has been known for a long time, however, namely that every pure bipartite states violates some Bell inequality. In other words, the entanglement of a pure bipartite state can be demonstrated device-independently, a result sometimes referred to as Gisin’s theorem. Almost three decades later, we show with colleagues from the university of Innsbruck in Austria that this statement can be generalized to multipartite systems in the following way: the genuine entanglement of every pure multipartite state can be demonstrated device-independently. The algorithmic construction of Svetlichny-type inequalities that we propose to reach this conclusion is economical in resources and provides a natural level of resistance to noise. Our results has been published in PRL.
21 Dec 2018
Bell tests provide certification techniques that are device-independent, that is, they do not rely on a detailed description of the hardware. In a recent article published in Physical Review Letter, we showed how to certify the quality of specific type of joint measurements, namely Bell-state measurements, device independently. Our certificate is noise-tolerant, hence opening a way for an experimental realisation. These results might play an important role for certifying the building blocks of future quantum networks.
05 Nov 2018
Please join us in congratulating Roman Schmied, Jean-Daniel Bancal, Baptiste Allard, Matteo Fadel, Valerio Scarani, Philipp Treutlein and Nicolas Sangouard for winning the Paul Ehrenfest Best Paper Award for Quantum Foundations 2017. The committee awarded the prize to Schmied et al. “for the certification of Bell nonlocality in a many-body quantum system composed of hundreds of atoms, thereby confirming the presence of quantum effects at the mesoscopic scale”. Some of the authors were present to receive the award in Vienna, as shown in the photograph. The prize-winning work can be found here.
02 Nov 2018
The field of quantum computing has made great strides in the past decade or so. As the field continues to proceed towards performing quantum-enabled computation at increasing scale and precision, certification of the constituent ingredients of a quantum computer becomes increasingly crucial. In this work we provide a method based on Bell’s theorem to certify coherent operations for the storage, processing and transfer of quantum information. This completes the set of tools needed to certify all the building blocks of a quantum computer. These results have been published in Physical Review Letters, and have been highlighted by the SNSF and also in the Department website.