Correlation Functions and Photon-Photon Interactions Controlled by a Giant Atom

TL;DR

This paper explores how a giant atom coupled to a waveguide can control photon-photon interactions and correlations, enabling switching between bunching and antibunching regimes through phase tuning.

Contribution

It introduces an extended input-output formalism to analyze photon scattering in giant atoms, revealing phase-dependent control of photon statistics and dynamics.

Findings

Photon correlations depend on pulse width and atomic lifetime ratio.

Tuning the phase allows switching among three photon statistical regimes.

Experimental feasibility is discussed for superconducting circuit implementations.

Abstract

Waveguide quantum electrodynamics (WQED) provides a powerful platform for exploring quantum optical phenomena by enhancing atom-photon interactions through photon confinement in a waveguide. Here we investigate the photon-scattering dynamics of a weak coherent pulse incident from the left on a giant atom coupled to a bidirectional waveguide, focusing on effects absent in the small-atom approximation. Using an extended input-output formalism, we calculate the relevant correlation functions and show that the competition between two scattering processes is governed by the ratio of the pulse width to the atomic lifetime, leading to time-dependent switching between bunching and antibunching. In addition, tuning the phase accumulated between the two coupling points of the giant atom allows the photon statistics to be switched among three distinct regimes, each with a finite phase bandwidth. We also discuss the experimental feasibility in superconducting circuits. Our results provide a route toward giant-atom-based control of photon pulses and potential applications in quantum control.