A new computational technique accurately models decoherence’s impact on light–matter interactions within waveguide quantum electrodynamics. Matias Bundgaard-Nielsen and colleagues at the Technical University of Denmark present a matrix product state (MPS) method capable of modelling decoherence processes via density matrices, representing a key advancement over previous approaches. The method utilises collision quantum optics and efficiently incorporates various loss mechanisms, including emitter pure dephasing and off-chip radiative decay, to simulate complex waveguide QED systems such as two-level systems and multi-emitter setups. By modelling these realistic dissipation dynamics, the research offers vital insights into the behaviour of quantum systems and enables improved designs for quantum technologies.
A six-fold increase in simulated timescales for waveguide quantum electrodynamics has been achieved, surpassing limitations that previously restricted simulations to Markovian dynamics. This advancement results from employing a density matrix-based matrix product state (MPS) method, enabling accurate modelling of non-Markovian effects arising from time delays and memory effects within the system.
Traditionally, waveguide QED simulations have relied on the Markov approximation, which assumes that the system’s memory of past events is negligible. However, in many realistic scenarios—particularly those involving long propagation delays within the waveguide or slow emitter dynamics—this approximation breaks down. The method explicitly accounts for the system’s history, allowing the simulation of phenomena that depend on non-Markovian effects. In particular, it incorporates realistic decoherence mechanisms such as pure dephasing, which perturbs the phase coherence of quantum states, and off-chip radiative decay, where excitation energy is lost to the environment outside the waveguide.
