2018. November 21.

Sir Michael Berry, known for the quantum mechanical Berry phase, visits Budapest as a guest of the MTA-BME Morphodynamics Research Group, and gives two talks at BME on December 12 and 13.

The first talk is a public lecture, aimed at a broad audience. Please sign up HERE if you'd like to participate. Details of the first talk:

**Time and location:** December 12, 2018, 16:00, BME building K, room 134.**Website of the event** (in Hungarian): Alkalmazott Matematikai Nap**Registration: **https://regisztracio.bme.hu/michael-berry-eloadas-20181212**Title:*** Nature's optics and our understanding of light***Speaker**: Michael Berry (Bristol)

**Abstract:** "Optical phenomena visible to everyone abundantly illustrate important ideas in science and mathematics. The phenomena considered include rainbows, sparkling reflections on water, green flashes, earthlight on the moon, glories, daylight, crystals, and the squint moon. The concepts include refraction, wave interference, numerical experiments, asymptotic, Regge poles, polarization singularities, conical intersections, and visual illusions."

Details of the second talk:

**Time and location: **December 13, 2018, 15:00, BME K épület, Oktatói Klub**Title:** *Variations on a theme of Aharonov and Bohm***Speaker:** MIchael Berry (Bristol)

**Abstract:** "The Aharonov-Bohm effect (AB) concerns the role in quantum physics of the vector potential of an impenetrable line of magnetic flux. Its partial anticipation by Ehrenberg and Siday, in terms of interference, was an approximation whose wavefunction was not singlevalued, and whose connection with the singlevalued AB wave involves topology: waves winding round the flux (‘many-whirls representation’). AB is a fine illustration of idealization in physics. There are four AB effects, depending on whether the waves and the flux are classical or quantum. In the classical-classical case, many details of the AB wavefunction have been explored experimentally in ripples scattered by a water vortex, where the flow velocity of the water corresponds to the vector potential. The AB wave possesses a phase singularity, and there is a similar phenomenon in general interferometers. Gauge-invariant AB streamlines exhibit extraordinary sub-wavelength structure. Connections between the AB wave and edge diffraction (Cornu spiral) enable calculation of the quantum force (recently observed), and lead to extremely accurate approximations."