RQC Seminar
82nd RQC Seminar
Speaker
Prof. Valentin Freilikher
( Dept. of Physics Bar-Ilan University )Date
16：00-17：00, September 7, 2023 (Thursday)
Venue
Hybrid(ZOOM・ Wako Main Research 3F 345-347 Seminar Room C01）
Title
How quantum particles and classical waves propagate in fluctuating environments:
general results and applicationsInquiries
rqc_info[at]ml.riken.jp
Abstract
Certain degree of disorder is unavoidable in any natural media or tailor-made structures. Scattering on fluctuations has a pronounced, sometimes determining impact on the quantum mesoscopic transport, where the phase coherence of electrons, the finite number of eigenstates through which they can scatter, as well as the correlations between these states play a significant role. The common perspective of the physics of wave processes in fluctuating environment, presented in this lecture, provides a unifying, general framework for a diverse variety of specific physical settings, ranging from electronic conductance to communication lines, radar, etc. A good starting point for setting up the general formalism for mesoscopic scattering is the observation that electrons in a potential behave similarly to electromagnetic waves in a dielectric medium. Since this analogy provides the bridge across which many of the results from optics can be carried over to the domain of mesoscopic quantum transport theory, and vice versa, I'll start by elucidating this connection. Then, after a succinct historical overview, the modern experimental and theoretical methods and the state of art in exploring different aspects of transport through random media will be presented. The most common in nature ballistic, diffusive, and localized transport mechanisms will be discussed. In particular, I'll show that although the effects of disorder are usually destructive, causing undesirable losses of energy and coherence, the random scattering, being treated properly, can be put to use to suppress reflection in favour of transmission, and vice versa. In more detail, I will focus on the latest researches and discoveries. Contrary to the common long-held believe that electron or light beams disperse homogeneously in a diffusive medium, quite recently, it was understood that it is significantly structured, concentrating in relatively narrow non-interacting transmission eigenchannels (TEs). Each TE is uniquely characterised by the input wave front, which maintains its shape through the sample; and by the transmission coefficient, τ, whose probability distribution is bimodal – it is picked at τ = 1 and τ = 0, corresponding to highly transparent and reflecting channels respectively. This property opens up outstanding possibilities to control quantum systems in disordered environment, in particular, to tailor the flux distribution and to focus it through scattering media by wave-front shaping. Remarkably, it suggests that a diffusive medium can enhance spatial resolution, potentially surpassing the diffraction limit. In conclusion, I'll highlight pressing challenges in the field that warrant immediate attention and resolution.