# Open-circuit ultrafast generation of nanoscopic toroidal moments: The swift phase generator

## TL;DR

This paper introduces a novel ultrafast, field-free method to generate and control vector potentials in nanosystems using a nanostructure driven by shaped THz pulses, enabling contactless quantum phase manipulation.

## Contribution

The authors propose a new approach for ultrafast, tunable generation of vector potentials via a nanostructure's steady-state toroidal moment, advancing quantum device control without external fields.

## Key findings

- Successful quantum dynamic simulations demonstrating the scheme's feasibility.
- Broadband tunable radiation emitted during the toroidal moment rise.
- Potential applications in quantum information and energy-efficient nanodevices.

## Abstract

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. We report 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, spatio-temporally controlled changes to the quantum nature of nanosystems. 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 nor 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. During the toroidal moment rise up time radiation is emitted which can be tuned in a very broad frequency band. We carry out full-fledged quantum dynamic simulations, and theoretical analysis to illuminate the underlying principles and to endorse the feasibility, robustness, and versatility of the scheme. This research could 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.