Bottleneck Effects and Harmonic-Type Velocity Bounds for Periodic Quantum Walks
Speaker(s): Darren C. Ong (Xiamen University Malaysia)
Time: 10:00-11:00 September 8, 2026
Venue: Room 77201, Jingchunyuan 78, BICMR
We prove explicit upper bounds on the propagation velocity of one-dimensional quantum walks with periodic coins of arbitrary period. We treat two complementary settings. First, in a perturbative regime where one transmission parameter is small, we show that the corresponding almost reflecting coin acts as a bottleneck for transport: the velocity is bounded linearly in this parameter, with an explicit leading order estimate. Second, for arbitrary nonzero transmission parameters, we prove a general a priori bound in terms of their harmonic mean, together with a refined version that detects the spatial variation of neighboring coins.
