Precision spectroscopy and matter-wave interferometry with simple Rydberg atoms
Prof. Dr. Stephen D. Hogan (Department of Physics and Astronomy, University College London, UK)

Rydberg states, the bound quantum states of an attractive 1/r potential, play a central role in many precision spectroscopic tests of fundamental physics with atoms and molecules, e.g., [1,2]. As perhaps the simplest Rydberg system, the positronium atom - composed of an electron bound to its antiparticle the positron, and therefore a purely leptonic system described almost entirely by bound state QED theory - offers unique opportunities for studies of this kind. However, because of its short ground-state annihilation lifetime (142 ns) many precision experiments with positronium must be performed with longer-lived excited states - Rydberg states. The efficient preparation of Rydberg states in positronium is now possible following developments in positron beam and trap technologies [3], and the motion of the atoms excited to these states can be controlled and manipulated using inhomogeneous electric fields through the methods of Rydberg-Stark deceleration [4]. In this talk I will describe new precision microwave spectroscopic measurements of the triplet n=2 fine structure in positronium that takes advantage of these developments. I will also present a new technique for performing matter-wave interferometry with atoms in Rydberg states that has been developed using helium atoms [5], but in the future could be exploited for accurate gravity measurements with Rydberg positronium.

[1] A. Beyer, L. Maisenbacher, A. Matveev, R. Pohl, K. Khabarova, A. Grinin, T. Lamour, D. C. Yost, Th. W. Hänsch, N. Kolachevsky, and Th. Udem, The Rydberg constant and proton size from atomic hydrogen, Science 358, 79 (2017) [2] N. Hölsch, M. Beyer, E. J. Salumbides, K. S. E. Eikema, W. Ubachs, Ch. Jungen, and F. Merkt, Benchmarking Theory with an Improved Measurement of the Ionization and Dissociation Energies of H2, Phys. Rev. Lett. 122, 103002 (2019) [3] T. E. Wall, A. M. Alonso, B. S. Cooper, A. Deller, S. D. Hogan, and D. B. Cassidy, Selective Production of Rydberg-Stark States of Positronium, Phys. Rev. Lett. 114, 173001 (2015) [4] S. D. Hogan, Rydberg-Stark deceleration of atoms and molecules, EPJ Techniques and Instrumentation 3, 1 (2016) [5] J. E. Palmer and S. D. Hogan, Electric Rydberg-atom interferometry, Phys. Rev. Lett. 122, 250404 (2019)