Kyrylo Snizhko
Geometric phases can be induced in a quantum system not only by Hamiltonian evolution but also via a sequence of projective measurements (in which case they are known as the Pancharatnam phase). We have explored what happens upon replacing the projective (“strong”) measurements with so-called weak measurements. The induced phase exhibits an abrupt change of behaviour as the measurement is tuned from infinitely strong to infinitely weak [1–3]. This transition happens at a certain critical measurement strength and is related to a change in the topology of the surface spanned by measurement-induced quantum trajectories. Recently this transition has been observed in a system based on a superconducting qubit [4].
[1] V. Gebhart, K. Snizhko, T. Wellens, A. Buchleitner, A. Romito, and Y. Gefen, Topological transition in measurement-induced geometric phases, Proc. Natl. Acad. Sci. 117, 5706 (2020).[2] K. Snizhko, P. Kumar, N. Rao, and Y. Gefen, Weak-measurement-induced asymmetric dephasing: a topological transition, arXiv:2006.13244.
[3] K. Snizhko, N. Rao, P. Kumar, and Y. Gefen, Weak-measurement-induced phases and dephasing: broken symmetry of the geometric phase, arXiv:2006.14641.
[4] Y. Wang, K. Snizhko, A. Romito, Y. Gefen, and K. Murch, Observing a topological transition in weak-measurement-induced geometric phases, arXiv:2102.05660.