Amir Rahmani

Instytut Fizyki PAN, Warsaw, Poland

 

Quantum Many-Body Interactions and Light-Matter Coupling: Expanding the Frontier of Reservoir Computing and Machine Learning

When: 12:00-13:00 CET, December 2nd (Tuesday), 2024

Where: Sala de Juntas, ICMM-CSIC, Campus de Cantoblanco, Madrid

Quantum reservoir computing (QRC) has emerged as a powerful paradigm for tackling machine-learning tasks by using the rich dynamics of quantum systems. At its core, QRC relies on effective control drives to encode input data and nonlinear mappings to transform these inputs into output features. Photonic platforms are likely candidates for QRC. However, they often lack sufficient nonlinearity for optimal performance. To overcome this limitation, a hybrid optoelectronic approach can be used, combining the speed of optical processing with the inherent nonlinearity of electronics. In this seminar, we present a method to enhance nonlinearity by employing wavefunction engineering within the regime of light-matter coupling. We explore various structures, including GaAs and TMD materials in cavities and waveguides. Through some examples, we demonstrate improvements in the accuracy of some quantum tasks, highlighting the potential of QRC in advancing machine learning.

 

 

Levente Rózsa

HUN-REN Wigner Research Centre for Physics.

 

Inertial spin dynamics

When: 12:00-13:00 CET, January 23th (Thursday), 2024

Where: Sala de Seminarios (182), ICMM-CSIC, Campus de Cantoblanco, Madrid

 

Inertial spin dynamics emerges in magnetic materials at very short time scales where the directions of the atomic magnetic moment and angular momentum become separated, and nutation can be observed. The inertia gives rise to additional high-frequency or nutational excitations recently detected in ferromagnetic resonance experiments [1]. Here, the signatures of inertial spin dynamics are discussed theoretically in various types of magnetic ordering. Nutational resonances hybridize more strongly with precessional resonances in antiferromagnets than in ferromagnets [2]. These high-frequency excitations form nutational spin-wave bands, which are simply shifted by a constant frequency compared to the low-frequency bands in ferromagnets, while in antiferromagnets the nutational bands have a maximum in the center of the Brillouin zone [3]. In conical spin spirals, nutational spin waves may display non-reciprocal propagation or form flat bands [4]. It is demonstrated that a resonant excitation of the nutation may be utilised for switching the order parameter [5]. The switching is found to proceed faster in antiferromagnets than in ferromagnets, and in antiferromagnets tuning the excitation frequency can be used to control the direction of the switching.

 

[1] K. Neeraj et al., Nat. Phys. 17, 245 (2021).

[2] R. Mondal, S. Großenbach, L. Rózsa, and U. Nowak, Phys. Rev. B 103, 104404 (2021).

[3] R. Mondal and L. Rózsa, Phys. Rev. B 106, 134422 (2022).

[4] M. Cherkasskii, R. Mondal, and L. Rózsa, Phys. Rev. B 109, 184424 (2024).

[5] L. Winter, S. Großenbach, U. Nowak, and L. Rózsa, Phys. Rev. B 106, 214403 (2022)