Decoherence dynamics in molecular qubits: Exponential, Gaussian and beyond.

Area of Science:

• Quantum Information Science
• Chemical Physics
• Condensed Matter Physics

Background:

• Quantum systems coupled to an environment (bath) experience decoherence, losing their quantum properties over time.
• Commonly observed decoherence patterns include Gaussian and exponential decay, but their origins are not fully understood.
• Understanding decoherence is crucial for developing robust quantum technologies and interpreting experimental results.

Purpose of the Study:

• To investigate how the structure of system-bath interactions determines temporal decoherence patterns in molecular and other qubits.
• To analyze the conditions under which Gaussian and exponential decay, or other forms, emerge.
• To connect decoherence dynamics with spectroscopic line shape theory.

Main Methods:

• Analysis based on a pure dephasing model allowing for analytical treatment.
• Examination of qubit-bath states, including initially unentangled and entangled states.
• Investigation of the influence of temperature, interaction strength, and bath correlation time.

Main Results:

• Decoherence is generally an exponential of oscillatory functions, with periods linked to bath frequencies.
• Gaussian decay is prevalent at early times for unentangled states and is favored by higher temperatures and interaction strengths.
• Strict exponential decay is rare, occurring only in specific models or under particular entanglement conditions (momentum displacement).

Conclusions:

• Gaussian decay is often a more appropriate model for molecular electronic decoherence than exponential decay, despite its imperfections.
• The study reveals a direct link between decoherence dynamics and spectroscopic line shapes (Gaussian peaks for Gaussian decay, Lorentzian for exponential).
• Entangling system-bath dynamics can generate Gaussian spectral peaks even without initial environmental inhomogeneity.