Finding the right degrees of freedom is a key step in solving strongly interacting field theories. Considerable progress in this direction was made in the last decades for higher dimensional supersymmetric gauge theories, guided by dualities with string theory. Two complementary approaches have been particularly useful in the exploration of the quantum structure of these theories: one is supersymmetric localisation and the other is integrability. Very recently it was noticed that common structures appear in both approaches when they are applied to the N=2 super-conformal theory in four dimensions which is obtained as a Z_K orbifold of the N=4 super Yang-Mills (SYM) theory. This hints at a deeper structure underlying both localisation and integrability. A special class of three-point functions in the N=2 SYM theory were computed first by localisation, in terms of a Fredholm determinant of a Bessel operator generalising the Tracy-Widom distribution. The talk, based on a recently completed work in collaboration with Gwenaël Ferrando, Shota Komatsu and Gabriel Lefundes, will explain how this result can be derived from the integrability approach to correlation functions, which was developed initially for the N=4 SYM theory and where the Fredholm determinant appears naturally.

In Ikushima group, we are working on the ultimate control of electrons and light using advanced semiconductor technology. One of our targets is terahertz (THz) light, which lies in the band between radio waves and optical waves. We conduct research on fundamental physics utilizing semiconductor quantum structures, including single THz photon detection, THz amplification, and electron-phonon strong coupling (resonant polaron). Furthermore, we are exploring novel mechanisms that could bring transformative advancements not only in electronics and photonics but also in the field of information science, such as terahertz photonic circuits and optically programmable CMOS. In this seminar, I would like to focus on my work “detection of Landau emission in graphene” [1]. We provide experimental evidence for the occurrence of inter-LL radiative transitions in an electrically biased graphene Hall bar, where the wavelength of emission can be tuned by varying the applied magnetic field. A quantum-well based charge sensitive infrared phototransistor (CSIP) is used for detecting weak THz emission from graphene (Fig. 1(a)). THz emission is observed at around 5 T when the Hall voltage exceeds the corresponding LL energy spacing ΔELL01/e between the zero-energy (N = 0) and first excited (N = +1 or N = −1) LLs. We also investigated the emission spectra through measurements of the QW spectrum of the CSIP (Fig. 1(b)). The emission spectra are well explained by the N = +1 → 0 (or N = −1 → 0) inter-LL radiative transition in monolayer graphene. The linewidth of the emission spectra is estimated to be on the order of LF meV, even though no explicit LL splitting is observed in the magnetotransport at 5 T. I would like to discuss the possibilities and challenges of amplifying THz waves also. [1] F. Inamura et al., APL Photonics 9, 116LF1 (2024)

Flocks of birds, bacteria colonies, sheep herds, crowds of people ... are just some common examples of large groups of living entities behaving in a remarkable collective fashion. From a physicists viewpoint, these are systems composed of many interacting units, each somehow able to convert energy from their environment to stay 'alive' and perform some task. Such dynamics lifts the constraints imposed by equilibrium, opening many challenges and eventually the possibility for the rich phenomena displayed in the natural world. However, we lack a general theoretical framework to describe it. Much understanding has been gained from the investigation of model systems (both theoretical and experimental), usually dealing with 'active units' consisting in self-propelled particles with simple physical interactions, such as excluded volume. Interestingly, the mere competition between self-propulsion and crowding, is already enough to trigger a novel non-equilibrium phase transition. I will review our current understanding of this phenomenon, and I will then delve into a complementary perspective on active systems, as made of entities that interact in a non-reciprocal way. This will lead us to consider 'active' extensions of paradigmatic models in statistical mechanics, such as the Ising model, to decipher what such new ingredient brings into the classical picture of phase transitions.