Quantum Information in Electron Microscopes

Since its inception, research of quantum optics has extended our understanding of light–matter interactions and enabled novel applications of such interactions. Until recently, all the work in this field has been focused on light interacting with bound-electron systems – such as atoms, molecules, quantum dots, and quantum circuits. In contrast, markedly different physical phenomena could be found in free-electron systems, the energy distribution of which is continuous and not discrete, implying tunable transitions and selection rules. Bound electrons typically have their transitions limited to the optical spectrum (visible, IR) or lower frequencies, while free electrons can have transitions in extreme UV and X-rays. Free electrons are also particularly useful as a probe of matter for spectroscopy and imaging of condensed matter effects.

We explore these ideas with a new experimental platform: a laser-driven electron microscope. With it, we observe the quantized interaction between relativistic free electrons and femtosecond laser pulses, which open intriguing prospects in quantum optics and quantum electrodynamics.

I will present my group's theoretical and experimental work in the field:We observed quantum phase-matching between an electron wave and a light wave, creating for the first time a free-electron comb. In such a coherent comb of quantized electron energies, a single electron is both accelerated and decelerated by simultaneously absorbing and emitting hundreds of photons. 

We developed the platform for studying cavity quantum electrodynamics at the nanoscale with free electrons and observed their coherent interaction with cavity photons. We directly measure the cavity photon lifetime and show more than an order of magnitude enhancement in the fundamental electron–photon interaction strength. These capabilities open new paths toward using free electrons as carriers of quantum information, as we explore with theory and experiments.