Spin squeezing and light entanglement in coherent population trapping

Area of Science:

• Atomic physics
• Quantum optics
• Cavity quantum electrodynamics

Background:

• Coherent population trapping (CPT) is a quantum interference effect in multi-level atomic systems.
• Nonlinear optical effects, such as the Faraday effect, can be significant in atomic systems near resonance.
• Optical cavities enhance light-matter interactions and can provide feedback mechanisms.

Purpose of the Study:

• To investigate the generation of quantum squeezing and entanglement at the output of an optical cavity.
• To explore the role of a nonlinear Faraday effect in a coherent population trapping system.
• To demonstrate the use of cavity feedback for reducing quantum fluctuations and achieving spin squeezing.

Main Methods:

• Utilizing a cavity containing atoms interacting with two fields.
• Operating the system in a coherent population trapping configuration.
• Leveraging the nonlinear Faraday effect near a dark-state resonance.
• Employing cavity feedback to influence quantum fluctuations.

Main Results:

• Generation of strong squeezing and entanglement at the cavity output.
• Observation of a nonlinear Faraday effect influencing the interacting fields.
• Demonstration of cavity feedback reducing quantum fluctuations of ground state spin.
• Achieving strong steady-state spin squeezing.

Conclusions:

• Cavities containing atoms can generate significant quantum squeezing and entanglement.
• The nonlinear Faraday effect and cavity feedback are key mechanisms for achieving these quantum states.
• This work provides a pathway for generating and controlling spin-squeezed states in atomic systems.