Real-time observation of interfering crystal electrons in high-harmonic generation

TL;DR

This paper observes real-time quantum interference of electrons in a bulk solid during high-harmonic generation, revealing new mechanisms for ultrafast light sources and electronics at optical frequencies.

Contribution

It provides the first direct time-domain observation of interfering crystal electrons in high-harmonic generation, uncovering a novel non-perturbative quantum interference mechanism.

Findings

HH emission occurs as subcycle bursts aligned with field crests

Identifies a new quantum interference involving multiple valence bands

Results suggest pathways for solid-state attosecond sources and optical quantum logic

Abstract

Accelerating and colliding particles has been a key strategy to explore the texture of matter. Strong lightwaves can control and recollide electronic wavepackets, generating high-harmonic (HH) radiation which encodes the structure and dynamics of atoms and molecules and lays the foundations of attosecond science. The recent discovery of HH generation in bulk solids combines the idea of ultrafast acceleration with complex condensed matter systems and sparks hope for compact solid-state attosecond sources and electronics at optical frequencies. Yet the underlying quantum motion has not been observable in real time. Here, we study HH generation in a bulk solid directly in the time-domain, revealing a new quality of strong-field excitations in the crystal. Unlike established atomic sources, our solid emits HH radiation as a sequence of subcycle bursts which coincide temporally with the field crests of one polarity of the driving terahertz waveform. We show that these features hallmark a novel non-perturbative quantum interference involving electrons from multiple valence bands. The results identify key mechanisms for future solid-state attosecond sources and next-generation lightwave electronics. The new quantum interference justifies the hope for all-optical bandstructure reconstruction and lays the foundation for possible quantum logic operations at optical clock rates.