Open-Circuit Ultrafast Generation of Nanoscopic Toroidal Moments: The Swift Phase Generator

Efficient and flexible schemes for a swift, field-free control of the phase in quantum devices have far-reaching impact on energy-saving operation of quantum computing, data storage, and sensoring nanodevices. A novel approach for an ultrafast generation of a field-free vector potential that is tunable in duration, sign, and magnitude, allowing to impart non-invasive, spatiotemporally controlled changes to the quantum nature of nanosystems is reported. The method relies on triggering a steady-state toroidal moment in a donut-shaped nanostructure that serves as a vector-potential generator and quantum phase modulator. Irradiated by moderately intense, few cycle THz pulses with appropriately shaped polarization states, the nano donut is brought to a steady-state where a nearby object does not experience electric or magnetic fields but feels the photo-generated vector potential. Designing the time structure of the driving THz pulses allows for launching picosecond trains of vector potentials which is the key for a contact-free optimal control of quantum coherent states. This research can trigger a new class of ultrafast quantum devices operated and switched in an energy-efficient, contact and field-free manner, enabling new techniques for use in quantum information, magnetic nanostructures, and superconducting tunnel junctions as well as in toroidally ordered systems and multiferroics.