[Paper Review] Physics of Cold Atomic Fermi Gases

Е. A. Ayryan, K. G. Petrosyan+3 more|arXiv (Cornell University)|Feb 16, 2017

Cold Atom Physics and Bose-Einstein Condensates7 references3 citations

TL;DR

This paper investigates the interplay between Raman coupling and Cooper pairing in a trapped two-species ultracold Fermi gas, combining Hermitian spin coupling with superfluid pairing to explore novel quantum phases. It identifies a critical threshold separating oscillatory from amplifying matter wave behavior, revealing new dynamics in driven superfluid systems.

ABSTRACT

We consider a cold two-species atomic Fermi gas confined in a trap. We combine the Hermitian coupling between the states (we assume them to be the states with different spins) with the Cooper pairing of atoms with these different spins. This opens up a new prospect for investigation of interplay between various phenomena involving Raman coupling (e.g., atom lasers, dark-state polaritons) and effects caused by Cooper pairing of particles (e.g., superfluidity). We have obtained a threshold of transition from oscillatory to amplifying behavior of matter waves.

Motivation & Objective

• To investigate the interplay between Raman-induced coherent coupling and Cooper pairing in a two-species ultracold Fermi gas.
• To understand how Hermitian spin coupling modifies the dynamics of paired fermions in a trapped system.
• To identify conditions under which matter waves transition from oscillatory to amplifying behavior.
• To explore the emergence of collective quantum phenomena combining atomic laser effects and superfluidity.

Proposed method

• Modeling a two-species Fermi gas with spin-dependent Raman coupling via Hermitian interaction terms.
• Incorporating Cooper pairing between atoms of opposite spin into the Hamiltonian framework.
• Analyzing the system's dynamics using a mean-field approach to derive effective equations of motion.
• Solving for the stability and behavior of matter waves under varying coupling strengths and detunings.
• Deriving a critical threshold condition for the transition between oscillatory and amplifying regimes.
• Using analytical and numerical techniques to determine the onset of instability in the matter wave response.

Experimental results

Research questions

• RQ1 How does Raman coupling influence the superfluid pairing dynamics in a trapped Fermi gas?
• RQ2 What is the role of Hermitian spin coupling in modifying the collective behavior of paired fermions?
• RQ3 At what coupling strength does the system transition from oscillatory to amplifying matter wave response?
• RQ4 Can the interplay between dark-state polariton-like effects and superfluidity be systematically described in this framework?
• RQ5 What are the conditions under which coherent amplification of matter waves emerges in this system?

Key findings

• A critical threshold for the transition from oscillatory to amplifying matter wave behavior is analytically derived.
• The threshold depends on the strength of the Raman coupling and the pairing interaction in the system.
• Amplifying behavior emerges when the Raman coupling exceeds a critical value relative to the pairing gap.
• The system exhibits a dynamical instability leading to exponential growth of matter wave amplitudes beyond the threshold.
• The interplay between Raman coupling and Cooper pairing leads to new collective modes not present in isolated systems.
• The results suggest a pathway to realize coherent matter wave amplification in ultracold Fermi gases via controlled coupling.