Optical precursors in waveguide quantum electrodynamics

TL;DR

This paper explores the microscopic origins of optical precursors in waveguide quantum electrodynamics, demonstrating that even a few qubits can produce observable precursors, advancing the potential for dispersion engineering with minimal quantum systems.

Contribution

It reveals that precursors can be generated with very few qubits, and clarifies their microscopic origin in waveguide QED, enabling dispersion control with minimal quantum resources.

Findings

Precursors appear even with just two qubits due to dispersion.

Electromagnetically-induced transparency enhances precursor observation.

A single qutrit can generate precursors under certain conditions.

Abstract

When a broadband signal propagates through a dispersive medium, some frequency components move faster than the center of the pulse. This leads to the appearance of precursors, transient signals that emerge from the medium earlier than the main part of the pulse and seem to propagate superluminally. Here, we investigate the microscopic origin of precursors in a minimal setup: an array of qubits coupled to a waveguide. The linear transmission function only converges to that of a continuous medium for large qubit numbers. Nevertheless, the dispersion produced by only two qubits is enough to produce oscillatory transients. Precursors are best observed under conditions of electromagnetically-induced transparency, as the center of the pulse is significantly delayed. Under these conditions, just a single qutrit is enough to generate a precursor. Our results pave the way towards dispersion engineering of light with just a few qubits, and can be realized with superconducting qubits coupled to transmission lines or atoms coupled to optical waveguides.