Speaker
Description
Repeated Interaction Schemes (RIs) or Quantum Collision Models (CMs) are a class of discrete time system-environment models where, in their simplest formulation, the environment is considered as a large collection of identical and independent subunits, called ancillas, and the system-environment dynamics is viewed as a sequence of two-body unitary collisions. Each ancilla can interact only one time with the system before to be replaced, or equivalently it is possible to consider a single environmental ancilla whose state is refreshed after each collision [1]. Initially introduced in early 60s, RIs come back to fore in the 2000s for their power to decompose complex system-environment dynamics into simple elementary contributions. This approach has been revealed useful in many research areas, such as quantum optics, quantum metrology, quantum thermodynamics, and quantum computing [1].
The project on which this talk is based is available on the arXiv [2]. Inspired by a numerical study [3], we adopted an RIs approach to investigate a two-level system coupled to an environmental two-level ancilla through a well-defined interaction Hamiltonian. Taking the system in a random initial state and the ancilla in a Gibbs thermal state at some inverse temperature β, we proved that the steady-state reached by the system is diagonal, and we found an analytical exact expression for the steady-state population. Furthermore, we investigated the thermodynamics of the process and the nonequilibrium nature of its steady state, computing the required number of iterations and the associated energy cost to reach and maintain the nonequilibrium steady-state, adopting both numerical and analytical tools. Ongoing research project extends this work to more generally discussed approaches for Gibbs state preparation on a quantum computer, along with a deeper study of thermodynamical resource requirements. We also aim to extend our results to more general systems relevant for quantum technology.
References:
[1] Ciccarello, F.; Lorenzo, S.; Giovannetti, V.; Palma, G. M. Quantum Collision Models: Open System Dynamics from Repeated Interactions. Physics Reports 2022, 954, 1–70. https://doi.org/10.1016/j.physrep.2022.01.001.
[2] Prositto, A.; Forbes, M.; Segal, D. Equilibrium and Nonequilibrium Steady States with the Repeated Interaction Protocol: Relaxation Dynamics and Energetic Cost. arXiv 2025.
https://doi.org/10.48550/ARXIV.2501.05392.
[3] Guarnieri, G.; Morrone, D.; Çakmak, B.; Plastina, F.; Campbell, S. Non-Equilibrium Steady-States of Memoryless Quantum Collision Models. Physics Letters A 2020, 384 (24), 126576.
https://doi.org/10.1016/j.physleta.2020.126576.
| Theme | Theme 1. Energy advantage and cost of quantum technology |
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