Exact Dynamics of Finite-Bath Open Quantum Systems Enables Foundational Understanding of Non-Markovian Channels

Open quantum systems, those interacting with their environment, present a fundamental challenge to physicists seeking to understand and control quantum behaviour, and Devvrat Tiwari and Subhashish Banerjee, both from the Indian Institute of Technology Jodhpur, now offer a comprehensive approach to modelling these systems. The researchers achieve exact dynamics for a central spin model representing a finite-bath open system, investigating both constant and time-dependent interactions between the system and its environment. This work characterises a new communication channel and provides microscopic insight into established non-Markovian behaviour, crucially delivering exact master equations for both interaction scenarios. By developing a novel technique based on the concept of a minimal dissipator, the team establishes a foundational understanding of finite-bath open systems and opens doors to a range of potential applications across physics.

Scientists have derived exact equations to describe how a quantum system evolves when connected to a finite-sized ‘bath’, representing its environment. The team investigated two distinct interaction types: one involving energy exchange and another causing a loss of quantum coherence, revealing new quantum channels that govern information transfer between the system and its environment.

Bosonic Baths Cannot Mimic Random Telegraph Noise

This study rigorously demonstrates that a quantum system interacting with a standard bosonic bath cannot exhibit the dynamics of a two-level system undergoing Random Telegraph Signal (RTS) noise. RTS noise is characterised by random switching between two states, and this research proves that the standard bosonic bath, a common model for environmental interactions, cannot produce this specific type of noise. The team described the evolution of a quantum system coupled to a bosonic bath, deriving an expression for how the system’s quantum properties change over time. Focusing on the dephasing factor, which governs the loss of quantum coherence, the researchers showed that for the bosonic bath to produce RTS-like behaviour, this factor must satisfy a specific mathematical equation. However, detailed calculations proved this equation cannot be satisfied, demonstrating that the dynamics of the bosonic bath are fundamentally incompatible with RTS noise, even for a commonly used model of the bath’s frequency distribution. This work provides a definitive answer to a long-standing question in quantum physics, clarifying the limitations of bosonic bath models.

Exact Dynamical Maps for Open Quantum Systems

This work presents a significant advancement in understanding the dynamics of open quantum systems interacting with a finite-sized environment. Researchers have developed a novel technique to derive master equations, which describe the evolution of a quantum system, from its underlying dynamics using the concept of a minimal dissipator. Applying this technique to the central spin model, a widely studied system in quantum physics, they have obtained exact dynamical maps for two distinct types of system-bath interactions: dissipative interactions and pure dephasing interactions. These analyses reveal new quantum channels and corresponding Kraus operators, fundamental tools for describing quantum information transfer.

Notably, the dissipative interaction leads to a new, exact phase covariant master equation, even in strong coupling regimes, offering a more accurate description of system evolution. Furthermore, the investigation of pure dephasing interactions with stochastic coupling produces a random telegraph noise (RTN) evolution, providing insights into microscopic stochastic processes. The team also demonstrated the applicability of these master equations in quantum thermodynamics, establishing a relationship between charging power and quantum heat current. The wide experimental accessibility of the central spin model, using platforms like Rydberg atoms, Nitrogen-Vacancy centers, and NMR spin systems, suggests that these theoretical results can be readily tested and applied in experimental settings, potentially leading to advancements in quantum technologies and our understanding of fundamental quantum phenomena.