Open Quantum System Response from the Hierarchy of Pure States

Area of Science:

• Quantum Mechanics
• Spectroscopy
• Statistical Physics

Background:

• Calculating spectral properties of open quantum systems interacting with their environment is complex.
• Experimental validation of theoretical predictions relies on accurate spectral feature calculations.

Purpose of the Study:

• To demonstrate the efficacy of the stochastic Hierarchy of Pure States (HOPS) approach for calculating open quantum system responses.
• To present the HOPS method in a novel, self-contained manner using probe driving and response as a framework.

Main Methods:

• Utilizing the stochastic Hierarchy of Pure States (HOPS) for open quantum system dynamics.
• Applying importance sampling for nonlinear HOPS and stochastic treatment of thermal environments.
• Employing exponential representation of Ohmic bath correlation functions and hierarchy truncation.

Main Results:

• HOPS efficiently calculates system response to coherent probe driving, even for strong interactions.
• For weak driving, HOPS simplifies susceptibility calculation by canceling inherent fluctuations, matching linear response theory.
• Results agree with experimental data for damped spin systems, reflecting transitions in motion via the transmission spectrum.
• Susceptibility as a function of temperature shows a maximum, indicating stochastic resonance.

Conclusions:

• The HOPS method is a powerful and efficient tool for analyzing spectral properties of open quantum systems.
• HOPS accurately describes both linear and nonlinear response regimes, including phenomena like stochastic resonance.
• The study provides a comprehensive presentation of the HOPS approach, suitable for understanding complex quantum dynamics.