A qubit coupled with confined phonons: the interplay between true and fake decoherence

Area of Science:

• Quantum physics
• Condensed matter physics
• Quantum information science

Background:

• Investigates quantum decoherence in finite-size lattices, where phonons are not a simple reservoir.
• Highlights the dual nature of decoherence origins: qubit-phonon entanglement and qubit-induced frequency renormalization.
• Addresses the initial thermalization of the lattice as a key factor.

Purpose of the Study:

• To analyze the decoherence of a qubit coupled with phonons in a finite lattice.
• To differentiate and understand the contributions of true and fake decoherence mechanisms.
• To explore the influence of phonon lifetime on decoherence dynamics.

Main Methods:

• Application of quantum Langevin theory to model phonons as an open system coupled to a thermal bath.
• Analysis of qubit-phonon entanglement and its effect on decoherence.
• Investigation of qubit-induced phonon frequency renormalization and its impact on thermal decoherence.

Main Results:

• Confined phonons remain sensitive to the qubit, leading to a twofold decoherence origin.
• Qubit-phonon entanglement results in incomplete true decoherence.
• Qubit renormalization of phonon frequency causes fake decoherence upon thermal averaging.
• Phonon finite lifetime significantly impacts true decoherence but not fake decoherence.

Conclusions:

• The interplay between true and fake decoherence exhibits rich dynamics with various regimes depending on model parameters.
• Finite lattice effects introduce complexities beyond standard reservoir-based decoherence models.
• Understanding these decoherence mechanisms is crucial for quantum information processing in solid-state systems.