Thursday, November 23, 2023
15:30 - 17:00
15:30: Randolf Pohl - "Laser spectroscopy of muonic ions and other simple atoms"
Laser spectroscopy of simple atoms is sensitive to properties of the atomic nucleus, such as its charge and magnetization distribution, or its polarizability. This allows determining the nuclear parameters from atomic spectroscopy, but also limits the attainable precision for the determination of fundamental constants or the test of QED and the Standard Model.
In light muonic atoms and ions, one negative muon replaces all atomic electrons, resulting in a calculable hydrogen-like system. Due to the muon’s large mass (200 times the electron mass), the muon orbits the nucleus on a 200 times smaller Bohr radius, increasing the sensitivity of muonic atoms to nuclear properties by 200^3 = 10 million.
Our laser spectroscopy of muonic hydrogen through helium has resulted in a 10fold increase in the precision of the charge radius of the proton, deuteron, and the stable helium nuclei. Next we're measuring the hyperfine splitting in muonic hydrogen to obtain information about the magnetization of the proton. In Mainz, we’re setting up an experiment to determine the triton charge radius by laser spectroscopy of atomic tritium.
 Antognini et al. [CREMA Collaboration], Science 339, 417 (2013)
 Pohl et al. [CREMA Collaboration], Science 353, 669 (2016)
 Krauth et al. [CREMA Collaboration], Nature 589, 527 (2021)
 Schuhmann et al. [CREMA Collaboration], arXiv 2305.11679 (2023)
16:15: David Clement - "Large quantum fluctuations and suppression of Bogoliubov pairing in strongly-interacting Bose gases"
Strongly-correlated materials are characterized by the strong, non-Gaussian, correlations between their constituent particles. Their theoretical description requires non-perturbative approaches and, in turn, a departure from the correlation patterns predicted by perturbative (Gaussian) theories is a hallmark of the strongly-correlated regime. Exploiting the capability to detect individual metastable Helium atoms in momentum space , we explore this scenario in a gas of interacting Bosons.
At weak interactions, a cornerstone in the description of quantum fluids is the well-known Bogoliubov theory. At the microscopic level, this theory predicts that interactions deplete the condensate through the formation of pairs with opposite momenta, known as quantum depletion. We have recently confirmed this microscopic prediction, revealing the effect of linearised quantum fluctuations .
To enter the strongly-interacting regime, we vary the amplitude of a 3D optical lattice . We find that the Bogoliubov momentum pairing becomes suppressed as interactions grow stronger . Numerical simulations confirm that our observations arises from non-linear quantum fluctuations, which are distinctive features of the strongly-correlated regime. Finally, we offer a physical picture of how non-Gaussian correlations emerge between the momentum modes of strongly-interacting bosons.
 H. Cayla et al. Physical Review A 97, 061609(R) (2018); A. Tenart et al. Physical Review Research 2, 013017 (2020).
 A. Tenart et al. Nature Physics 17, 1364 (2021).
 C. Carcy et al. Physical Review Letters 126, 045301(2021).
 In preparation (2023).
VU University Amsterdam - Faculty of Science - Physics and Astronomy
3Bo5 NU bldg
hard condensed matter, particle phenomenology, quantum matter
prof. dr. Randolf Pohl, dr. David Clement