Seminar DCMI and Axis 4 and 5, presented by Paul STEADMAN

Speaker: Paul STEADMAN (Responsable de la ligne I10 au Synchroton Diamond)

Abstract : A study of the electric current induced hysteresis in Pt/CoFeTaB thin films revealed an unexpected behaviour in the hysteresis curves measured using polarised soft X-ray reflectivity [1]. Following a detailed study of the polarisation dependence of the reflected intensity [2] both detailed calculations and experimental data revealed that the switching is Y type (magnetisation switching perpendicular to the current), is very sensitive to external magnetic fields and that, rather bizarrely, only part of the film is switching. In addition the importance of non-linear dependence on the magnetic scattering and its dependence on polarisation and energy have been uncovered experimentally and explained with a very simple model.

  • [1] D. M. Burn, R. Fan, O. Inyang, M. Tokac¸ L. Bouchenoire, A. T. Hindmarch and P. Steadman, P. (2022). Phys. Rev. B, 106, 094429.
  • [2] Raymond Fan, Kiranjot, Razan O. M. Aboljadayel, Kalel Alsaeed, Peter, J. Synchrotron Rad. (2024). 31, 493–507

Seminar Axis 1 and DON, presented by Saad Yalouz

Speaker : Saad Yalouz (Laboratoire de Chimie Quantique de Strasbourg)

Abstract : In the realm of quantum computing, the characterization of many-body systems stands out as one of the most promising applications for emerging quantum platforms. While significant effort has been dedicated to developing near-term quantum algorithms for describing purely fermionic systems (particularly for Quantum Chemistry), there exists a gap in extending beyond the “bare” electronic structure to encompass the influence of an external environment. This gap becomes apparent when considering hybrid “fermion+boson” systems, which naturally arise when the electronic structure of a system interacts with an external bosonic field, such as photons or phonons. The theoretical description of such systems poses a considerable challenge, necessitating the depiction of entanglement between the two types of particles. Addressing this challenge defines an interesting target for quantum computers. In this presentation, I will delve into recent endeavors initiated at the Laboratoire de Chimie Quantique Strasbourg to tackle these questions. Drawing from a polaritonic chemistry problem, I will elucidate how we are currently designing near-term quantum algorithms to describe both ground and excited states in such systems

Contact : Paul-Antoine Hervieux  

Seminar Axis 3 presented by Dr. Maurizio Mastropasqua Talamo

Dr. Maurizio Mastropasqua Talamo (Laboratoire Moltech-Anjou, Université d’Angers)

Abstract :

Starting from initial purposes of molecular recognition, the study of chiral pi-conjugated molecules and supramolecular assemblies have led over time to a deeper understanding of chirality-related properties which do not only rely upon geometric pairing but also involve polarization in light-matter interaction and spin selectivity in charge transport. These new properties have boosted the interest in the development of chiral organic semiconductors for advanced optoelectronics applications.

Many asymmetric synthetic techniques which are particularly important in the field of pharmaceutical synthesis, can enable the practical modification of pi-conjugated scaffolds with various stereogenic motifs, resulting in molecular semiconductors and chromophores showcasing diverse chirality-related properties.

Some examples of asymmetric modification of molecular semiconductors and chromophores will be given in this lecture along with a discussion about chirality-related properties observed within the newly synthesized materials.

Seminar DMONS – Axis 1 presented by Horacio Miguel PASTAWSKI

Horacio Miguel PASTAWSKI (Instituto de Física Enrique Gaviola, Universidad Nacional de Córdoba-CONICET, Academia Nacional de Ciencias-Argentina)

Abstract :

I will describe the qualitative features of our three-decade long experimental and theoretical quest to
identify emergent phenomena within the quantum dynamics of spin and charge excitations. A quantum
phase transition occurs as an analytical discontinuity of a physical observable, as illustrated by the
Anderson metal-insulator transition in disordered systems. We observed a clear phase transition in the
case of two interacting nuclear spins undergoing Rabi oscillations in presence of a spin environment [1],
that, according to the Fermi Golden Rule, results in an imaginary energy in a 2×2 non-Hermitian effective
Hamiltonian [2]. The oscillations became a purely exponential decay when their coupling strength fell
below a critical value. Our first experimental hint that many-body interactions could lead to irreversible
dynamics, appeared when confronting the insurmountable limitations in performing a perfect time-
reversal procedure, even in a fairly well-controlled setting of nuclear spins [3]. After a decade of work,
we experimentally observed [4] a phase transition to an intrinsically irreversible regime in the
thermodynamic limit. However, its analytical proof has initially eluded us [5]. Recently, we observed a
striking universal stability of coherently diffusive one-dimensional systems with respect to decoherence
[6]. This approach gives a new insight to the “poised realm” hypothesis, promoted for biological systems,
stating that the edge of chaos is a favorable condition to charge and excitonic transport. As pointed out
by R. Laughlin, classical chaos can lead to diffusion, and hence, to a form of quantum dynamics extremely
robust against environmental noise.

[1] Environmentally induced quantum dynamical phase transition in a spin swapping operation, G.A. Álvarez, E.P.Danieli,
P.R.Levstein, and H.M. Pastawski,J. Chem. Phys. 124, 1 (2006);
[2] Revisiting the Fermi Golden Rule: Quantum dynamical phase transition as a paradigm shift H. M. Pastawski Physica B 398,
278 (2007);
[3] Attenuation of polarization echoes in NMR: A test for the emergence of Dynamical Irreversibility in Many-Body Quantum
Systems. P.R. Levstein, G. Usaj, H.M. Pastawski, J. Chem. Phys. 108, 2718 (1998);
[4] Perturbation-independent decay of the Loschmidt echo in a many-spin system studied through scaled dipolar dynamics. C.M.
Sánchez, A.K. Chattah, K.X. Wei, L. Buljubasich, P. Cappellaro, and H.M. Pastawski, Phys. Rev. Lett. 124, 030601 (2020);
[5] Loschmidt echo in many-spin systems: a quest for intrinsic decoherence and emergent irreversibility P. R. Zangara and H. M.
Pastawski, Phys. Scr. 92, 033001(2017);
[6] Universal stability of coherently diffusive 1D systems with respect to decoherence. F.S. Lozano-Negro, E. Alvarez Navarro,
N.C. Chávez, F. Mattiotti, F. Borgonovi, H.M. Pastawski, G.L.Celardo, arXiv.2307.05656.

Contact : Rodolfo JALABERT :