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

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. 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.

The High‐Order Toroidal Moments and Anapole States in All‐Dielectric Photonics

“…Therefore, an experimental observation of standalone toroidal moments of any order could be complicated by the fact that their far‐field signature coincides with the one of their basic counterparts. However, nowadays there is a number of suggestions on how to directly observe dipole toroidal moments without mixing with other multipoles provided by particular designs and architectures (e.g., special configuration of resonator, or incident field configurations).…”

Vortex Ring and Helical Current Formation in Superconductors Driven by a THz‐Field‐Induced Toroidal Vector Potential

“…the torus limb and after the buildup, it can be well-modeled by B T ¼ A T0 e φ =ρ, [21] with A T0 ¼ μ 0 I=2π. [27] Thus, for convenience, we may write…”

“…Equation (1) follows from classical electrodynamics. For the details on how (or ) rises in time and stabilizes and on how to control its strength via the THz pulses and for information on the semiconductor torus parameters, we refer to work by Wätzel and Berakdar, [ 21 ] to avoid repetition and concentrate here on the SC part of the study. To simulate the dynamics of the order parameter Ψ, we solve for the time‐dependent Ginzburg–Landau (TDGL) equations.…”

“…The generated magnetic flux density (with a corresponding magnetic flux ) is fully confined to within the semiconductor torus and vanishes outside it. Outside the torus, the curl‐free (gauge invariant) vector potential (with ) signals the existence of a toroidal moment T hosted by the semiconductor torus and launched by the THz irradiation; [ 21 ] typical field lines of , which we use later in the numerical SC dynamics simulations are shown by Figure 1c. The torus geometry of the semiconductor is essential to support eigenstates that carry a poloidal current.…”

“…b) Two crossed time‐delayed THz pulses with radial polarization and linear polarization trigger within picoseconds resonant electronic transitions in the semiconductor ring generating a stationary poloidal charge current (green arrows). [ 21 ] The associated magnetic field is enclosed within the semiconductor. No electric or magnetic fields are generated outside the orange torus.…”