Low-Field Optical Polarization in Type-II Quantum Dots via Nuclear-Driven Dark State Mixing.

Area of Science:

• Quantum Information Science
• Materials Science
• Condensed Matter Physics

Background:

• Semiconductor quantum dots (QDs) are crucial for quantum light emission and spin control.
• Type-I QDs are widely studied, but type-II systems offer underexplored potential for novel quantum phenomena.
• Controlling light polarization is essential for quantum technologies.

Purpose of the Study:

• To investigate low-field optical polarization in type-II In(Ga)As/GaAsSb quantum dots.
• To explore the mechanism of spin control via exciton mixing in type-II QDs.
• To establish type-II QDs as a viable platform for compact circularly polarized light sources.

Main Methods:

• Utilized low magnetic fields (as low as 0.17 T) to induce optical polarization.
• Investigated hyperfine-induced mixing between bright and dark excitons via level anticrossing.
• Developed a theoretical model based on spin Hamiltonian and spin-split state populations.
• Performed polarization recovery measurements to confirm nuclear spin interactions.

Main Results:

• Achieved low-field optical polarization in type-II In(Ga)As/GaAsSb QDs.
• Observed mirror-symmetric luminescence helicity, accurately reproduced by the theoretical model.
• Demonstrated that suppressed wave function overlap in type-II systems leads to reduced electron-hole exchange interaction.
• Confirmed the role of nuclear spin interactions in mediating electron spin precession.

Conclusions:

• Type-II QDs enable optical polarization control using weak magnetic fields and nonresonant linear excitation.
• The observed phenomena are driven by hyperfine-induced exciton mixing and nuclear spin interactions.
• Type-II QDs present a promising platform for developing compact sources of circularly polarized light for quantum applications.