In our recent work with LKB colleagues Claude Fabre and Nicolas Treps, we studied the fundamental limits of practical superresolution techniques. Ideally, intensity measurements in an optimal mode basis are able to resolve two arbitrarily close incoherent point sources. In the presence of crosstalk, no matter how small, we find that this is no longer true, and the resolution limit is determined by the crosstalk probability.

• M. Gessner, C. Fabre, N. Treps, Superresolution limits from measurement crosstalk, Phys. Rev. Lett. 125, 100501 (2020).

In our recent study we develop a framework to describe quantum-enhanced multiparameter measurements using the intuitive concept of squeezing. This allows us to optimize the sensitivity of multiparameter measurements and to design high-precision sensor networks with atomic and optical systems.

• M. Gessner, A. Smerzi, L. Pezzè, Multiparameter squeezing for optimal quantum enhancements in sensor networks, Nat. Commun. 11, 3817 (2020).

see also the LKB Announcement

We are happy to announce that Youcef Baamara from Sorbonne Université, after completing his Master's, is staying with us for his PhD thesis.

Contrôle du bruit de mesure de spin d'un ensemble d'atomes

Improving uncertainty relations with the quantum Fisher information

Superresolution limits from measurement crosstalk

Superresolution techniques based on intensity measurements after a spatial mode decomposition can overcome the precision of diffraction-limited direct imaging. However, realistic measurement devices always introduce finite crosstalk in any such mode decomposition. Here, we show that any nonzero crosstalk leads to a breakdown of superresolution when the number N of detected photons is large. Combining statistical and analytical tools, we obtain the scaling of the precision limits for weak, generic crosstalk from a device-independent model as a function of the crosstalk probability and N. The scaling of the smallest distance that can be distinguished from noise changes from N−1/2 for an ideal measurement to N−1/4 in the presence of crosstalk.

Spin squeezing and multipartite entanglement of particles and addressable modes

The spin squeezing coefficient reveals the multiparticle entanglement depth of an atomic system from collective measurements. The entanglement of addressable modes is typically detected with different methods that require local measurements on the modes. In this talk, we address the question, how much mode entanglement can we expect to generate by distributing a spin-squeezed ensemble into accessible modes. We show that under the assumption of indistinguishability, we can relate the spin-squeezing coefficient to well-known conditions for mode entanglement. Moreover, we point out the relation between different criteria for multiparticle entanglement based on the spin-squeezing coefficient.

Studying Electron Transfer Models with Cavity-QED-like Systems

We propose a trapped-ion quantum simulator as a platform for the study of electron transfer processes. In particular, we demonstrate how a driven trapped-ion system with controlled dissipation and electron-phonon interactions can be operated in parameter regimes of rich molecular charge transfer physics. Continuous controllability of the system parameters allows us to probe the transition between different transfer mechanisms, including classical and quantum regimes. This allows us not only to test widely-used transport models from chemistry, such as Marcus theory, but also to probe complex and largely unexplored regimes that are often unattainable in molecular experiments.