Observation of interband Berry phase in laser-driven crystals

Area of Science:

• Quantum Physics
• Condensed Matter Physics
• Optics

Background:

• The Berry phase, a fundamental concept in quantum mechanics, typically arises from continuous cyclic evolution of quantum states.
• Previous experimental realizations of the Berry phase have relied on continuous paths, limiting its application in certain quantum phenomena.

Purpose of the Study:

• To introduce and experimentally demonstrate a novel manifestation of the Berry phase.
• To explore the accumulation of a geometric phase during discrete quantum evolution in light-driven crystals.
• To investigate the potential of this new Berry phase for studying light-driven topological phenomena and attosecond physics.

Main Methods:

• Utilizing a strong laser field to drive crystals, inducing discrete electronic wavefunction evolution between different bands.
• Engineering an internal interferometer within the crystal using less than one cycle of the driving laser field.
• Mapping the accumulated geometric phase onto the emission of higher-order harmonics for experimental detection.

Main Results:

• Successful demonstration of a Berry phase accumulation during a discrete quantum evolution process.
• Preservation of quantum coherence throughout the discrete phase evolution.
• Experimental evidence of the Berry phase through the analysis of higher-order harmonic generation.

Conclusions:

• This work presents a conceptually new way to realize and observe the Berry phase, distinct from continuous evolution methods.
• The findings offer new opportunities for exploring geometric phases in light-driven topological systems.
• The study contributes to the advancement of attosecond solid-state physics and the understanding of light-matter interactions in crystals.