Low-frequency spectroscopy for quantum multi-level systems

TL;DR

This paper explores how low-frequency spectroscopy reveals complex interference patterns in multi-level quantum systems, especially in silicon quantum dots, offering new insights into their spectral properties.

Contribution

It introduces a novel approach to analyze resonance line shapes in multi-level quantum systems using low-frequency spectroscopy, extending understanding beyond two-level systems.

Findings

Resonance shapes can vary from convex arcs to concave heart-shaped and harp-shaped lines.

The resonance line shapes are influenced by the entire energy spectrum of the system.

Application demonstrated on valley-orbit silicon quantum dots.

Abstract

A periodically driven quantum system with avoided-level crossing experiences both non-adiabatic transitions and wave-function phase changes. These result in coherent interference fringes in the system's occupation probabilities. For qubits, with repelling energy levels, such interference, named after Landau-Zener-Stuckelberg-Majorana, displays arc-shaped resonance lines. We demonstrate that in the case of a multi-level system with an avoided-level crossing of the two lower levels, the shape of the resonances can change from convex arcs to concave heart-shaped and harp-shaped resonance lines. In this way, the shape of such resonance fringes is defined by the whole spectrum, providing insight on the slow-frequency system spectroscopy. As a particular example, we consider this for valley-orbit silicon quantum dots.