量子力学物質は、正負の振動ではなく、正パルスだけのように発光する。 Quantum materials emit light as though it were only a positive pulse, rather than a positive-negative oscillation.
2022-05-23 ミシガン大学
レーザーパルスは量子ビットのエネルギー状態を操作するのに使用できるが、量子情報を符号化するための電荷キャリアを移動させることができれば、室温でのアプローチも含め、異なる方法でコンピューティングを行うことができる。赤外線とマイクロ波の中間に位置するテラヘルツ光は、発振速度が速いため高速に動作するが、波の形が問題である。すなわち、電磁波は、正と負、両方の和がゼロになるような振動を発生させなければならない。
- https://news.umich.edu/emulating-impossible-unipolar-laser-pulses-paves-the-way-for-processing-quantum-information/
- https://www.nature.com/articles/s41377-022-00824-6
空間的に間接的なバンド間遷移によるスケーラブルな高繰り返しサブ半周期テラヘルツパルス Scalable high-repetition-rate sub-half-cycle terahertz pulses from spatially indirect interband transitions
Christian Meineke,Michael Prager,Johannes Hayes,Qiannan Wen,Lukas Zheyi Kastner,Dieter Schuh,Kilian Fritsch,Oleg Pronin,Markus Stein,Felix Schäfer,Sangam Chatterjee,Mackillo Kira,Rupert Huber & Dominique Bougeard
Light: Science & Applications Published:23 May 2022
DOI:https://doi.org/10.1038/s41377-022-00824-6
Abstract
Intense phase-locked terahertz (THz) pulses are the bedrock of THz lightwave electronics, where the carrier field creates a transient bias to control electrons on sub-cycle time scales. Key applications such as THz scanning tunnelling microscopy or electronic devices operating at optical clock rates call for ultimately short, almost unipolar waveforms, at megahertz (MHz) repetition rates. Here, we present a flexible and scalable scheme for the generation of strong phase-locked THz pulses based on shift currents in type-II-aligned epitaxial semiconductor heterostructures. The measured THz waveforms exhibit only 0.45 optical cycles at their centre frequency within the full width at half maximum of the intensity envelope, peak fields above 1.1 kV cm−1 and spectral components up to the mid-infrared, at a repetition rate of 4 MHz. The only positive half-cycle of this waveform exceeds all negative half-cycles by almost four times, which is unexpected from shift currents alone. Our detailed analysis reveals that local charging dynamics induces the pronounced positive THz-emission peak as electrons and holes approach charge neutrality after separation by the optical pump pulse, also enabling ultrabroadband operation. Our unipolar emitters mark a milestone for flexibly scalable, next-generation high-repetition-rate sources of intense and strongly asymmetric electric field transients.
