The complete control of wave transport and localization has been a longstanding pursuit in wave physics research, spanning various fields from solid-state to matter-wave physics and photonics. One of the most significant coherent transport effects is Bloch oscillation (BO). BO refers to the periodic oscillatory motion of electrons in solids under a direct current (DC)-driving electric field.
Super-Bloch oscillations (SBOs) are enormous oscillatory motions achieved by applying detuned DC- and AC-driving electrical fields simultaneously. Regarded as amplified versions of BOs, SBOs receive less attention than regular BOs mainly because their experimental observations are more challenging and demand a much longer particle coherence time.
A uniue feature of SBOs involves coherent oscillation inhibition driven by an AC-renormalization effect, resulting in the localization of an oscillation pattern with minimal amplitude. Referred to as the “collapse” of SBO, this intriguing phenomenon occurs primarily in the strong AC-driving regime, not previously explored in electronic and other SBO-based experiments.
Existing theoretical and experimental studies on SBOs have primarily focused on simple sinusoidal AC-driving cases, leaving the collapse of SBOs under more general AC-driving formats unexplored. This leaves the potential for manipulating coherent waves using SBOs unexplored.
Researchers from Wuhan National Laboratory for Optoelectronics and School of Physics, Huazhong University of Science and Technology (HUST), and Polytechnic University of Milan collaborated on a recent study to address these issues.
Advanced Photonics reported that the researchers combined a DC-driving and a nearly detuned AC-driving electric field in the synthetic temporal lattice, successfully achieving SBOs up to the strong-driving regime. They observed the SBO collapse effect for the first time and expanded SBOs into arbitrary-wave driving situations.
By adjusting the synthetic DC and AC electric fields, researchers were able to demonstrate the disappearance of oscillation amplitude and reversal of initial oscillation direction at specific driving amplitudes, indicating the clear presence of SBO collapse.
When subjected to sinusoidal AC-driving, they found that as the amplitude-to-frequency ratio of the AC-driving field matches the root of the first-order Bessel function, SBO collapse occurs, resulting in a complete inhibition of oscillation with a disappearing oscillation amplitude and a reversal of the initial oscillation direction upon crossing the collapse point.
The distinct rapid swing characteristics of SBOs and the collapse of SBOs were also examined through the Fourier spectrum of oscillation patterns. Researchers expanded their observations from sinusoidal driving to arbitrary-wave driving, thus discovering generalized SBOs with adjustable collapse conditions.
Lastly, the study utilizes the feature of oscillation direction reversal to develop adaptable temporal beam routers and splitters.
“This work realizes periodic oscillations and transportation for optical pulses, which may also find wide applications in versatile temporal-beam control in light routing, splitting, and localization for next-generation optical communications and signal processing,” said corresponding author Stefano Longhi, professor at the Polytechnic Institute of Milan.
Journal reference:
- Xinyuan Hu, Shulin Wang, Chengzhi Qin, Chenyu Liu, Lange Zhao, Yinglan Li, Han Ye, Weiwei Liu, Stefano Longhi, Peixiang Lu, Bing Wang. Observing the collapse of super-Bloch oscillations in strong-driving photonic temporal lattices. Advanced Photonics, 2024; DOI: 10.1117/1.AP.6.4.046001