Extra Seminar - Würzburg ToCoTronics Colloquium

Real-world applications of quantum technology require the control of quantum states with close-to-perfect fidelity and precision. Theoretical simulations can be used to optimize device parameters and driving protocols, but this necessitates very accurate modeling including the effects of the surrounding environment. This is particularly challenging when the system-environment coupling is not weak and conventional master equations relying on the Born-Markov approximation are insufficient. This challenge can be addressed by Process Tensor Matrix Product Operators (PT-MPOs) [1], where real-time path integrals are combined with tensor networks to facilitate the efficient numerically exact prediction of quantum dynamics in open quantum systems. PT-MPOs account for all renormalization, correlation, and non-Markovian memory effects induced by the system-environment coupling. They allow for efficient sampling of system parameters and excitation protocols over millions of time steps [2]. Moreover, when combined with other PT-MPOs, they can describe systems coupled to multiple non-Markovian environment or multiple subsystems each coupled to a non-Markovian environment while accounting for non-additive cross-environment effects. Here, I present the concept of PT-MPOs
including links to quantum information theory and quantum process tomography [2]. I briefly report on available algorithms and codes. Furthermore, I summarize concrete applications and experiment-theory collaborations, where PT-MPOs enabled describing and predicting dynamics, spectra, and multitime correlation function in quantum-dot-based single [3] and entangled photon sources [4] as well as superradiance in multi-quantum-dot systems [5].

[1] M. Cygorek, M. Cosacchi, A. Vagov, V. M. Axt, B. W. Lovett, J. Keeling, E. M. Gauger, Nature Physics 18, 662 (2022)
[2] G. A. L. White, C. D. Hill, F. A. Pollock, L. C. L. Hollenberg, K. Modi, Nature Communications 11, 6301 (2020)
[3] K. Boos et al., Phys. Rev. Lett. 132, 053602 (2024)
[4] T. K. Bracht, M. Cygorek, T. Seidelmann, V. M. Axt, D. E. Reiter, Optica Quantum 1, 103 (2023)
[5] D. Hallett et al., arXiv:2410.17890 (2024)