Solid State Institute and Faculty of Electrical Engineering, Technion - Israel Institute of Technology, Haifa, Israel.
Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa, Israel.
Nature. 2020 Jun;582(7810):50-54. doi: 10.1038/s41586-020-2321-x. Epub 2020 Jun 3.
Advances in the research of interactions between ultrafast free electrons and light have introduced a previously unknown kind of quantum matter, quantum free-electron wavepackets. So far, studies of the interactions of cavity-confined light with quantum matter have focused on bound electron systems, such as atoms, quantum dots and quantum circuits, which are considerably limited by their fixed energy states, spectral range and selection rules. By contrast, quantum free-electron wavepackets have no such limits, but so far no experiment has shown the influence of a photonic cavity on quantum free-electron wavepackets. Here we develop a platform for multidimensional nanoscale imaging and spectroscopy of free-electron interactions with photonic cavities. We directly measure the cavity-photon lifetime via a coherent free-electron probe and observe an enhancement of more than an order of magnitude in the interaction strength relative to previous experiments of electron-photon interactions. Our free-electron probe resolves the spatiotemporal and energy-momentum information of the interaction. The quantum nature of the electrons is verified by spatially mapping Rabi oscillations of the electron spectrum. The interactions between free electrons and cavity photons could enable low-dose, ultrafast electron microscopy of soft matter or other beam-sensitive materials. Such interactions may also open paths towards using free electrons for quantum information processing and quantum sensing. Future studies could achieve free-electron strong coupling, photon quantum state synthesis and quantum nonlinear phenomena such as cavity electro-optomechanics.
超快自由电子与光相互作用的研究进展引入了一种以前未知的量子物质，即量子自由电子波包。到目前为止，对腔约束光与量子物质相互作用的研究主要集中在束缚电子系统上，如原子、量子点和量子电路，这些系统受到其固定能态、光谱范围和选择定则的极大限制。相比之下，量子自由电子波包没有这些限制，但到目前为止，还没有实验表明光子腔对量子自由电子波包的影响。在这里，我们开发了一个用于自由电子与光子腔相互作用的多维纳米尺度成像和光谱学的平台。我们通过相干自由电子探针直接测量腔光子寿命，并观察到与以前的电子光子相互作用实验相比，相互作用强度增强了一个数量级以上。我们的自由电子探针解析了相互作用的时空和能量动量信息。通过对电子能谱的拉比振荡进行空间映射，验证了电子的量子性质。自由电子与腔光子的相互作用可以实现软物质或其他对束流敏感材料的低剂量、超快电子显微镜检查。这种相互作用也可能为自由电子用于量子信息处理和量子传感开辟道路。未来的研究可能会实现自由电子强耦合、光子量子态合成以及腔电光机械等量子非线性现象。
