Spontaneous decay of artificial atoms in a multi-qubit system

TL;DR

This paper investigates how the decay dynamics of a chain of noninteracting qubits in a waveguide depend on their spacing, revealing conditions for stationary states and oscillatory behavior related to dark and subradiant states.

Contribution

It provides a systematic analysis of qubit amplitude evolution in a multi-qubit waveguide system, highlighting the role of qubit spacing in decay behavior and state formation.

Findings

Stationary excitation levels occur when kd is a multiple of π.

Dark states prevent decay even without photon emission.

Vacuum Rabi oscillations appear for other kd values.

Abstract

We consider a one-dimensional chain of N equidistantly spaced noninteracting qubits embedded in an open waveguide. In the frame of single-excitation subspace, we systematically study the evolution of qubits amplitudes if the only qubit in the chain was initially excited. We show that the temporal dynamics of qubits amplitudes crucially depend on the value of kd, where k is the wave vector, d is a distance between neighbor qubits. If kd is equal to an integer multiple of $\pi$, then the qubits are excited to a stationary level which scales as SN^{-1}S. We show that in this case, it is the dark states which prevent qubits from decaying to zero even though they do not contribute to the output spectrum of photon emission. For other values of kd the excitations of qubits have the form of damping oscillations, which represent the vacuum Rabi oscillations in a multi-qubit system. In this case, the output spectrum of photon radiation is defined by a subradiant state with the smallest width.