Suppressed Kondo effect and Kosterlitz-Thouless-type phase transition induced by level difference in a triple dot...

Area of Science:

• Quantum Information Science
• Condensed Matter Physics
• Quantum Computing

Background:

• Quantum dot systems are crucial for quantum information processing, quantum simulation, and quantum computation.
• Demonstrating and controlling quantum states is a fundamental challenge in these fields.
• Understanding electron interactions and spin coupling in multi-dot systems is key to advancing quantum technologies.

Purpose of the Study:

• To report a peculiar electron state in a parallel triple quantum dot device.
• To investigate the breakdown of Ruderman-Kittel-Kasuya-Yosida interaction under specific conditions.
• To explore the resulting spin coupling and its impact on quantum dot conductance.

Main Methods:

• Fabrication and characterization of a parallel triple quantum dot device.
• Systematic variation of energy level differences between quantum dots.
• Analysis of electron transport measurements and theoretical modeling (many-body effects, effective Kondo model).

Main Results:

• Observed a peculiar electron state where Ruderman-Kittel-Kasuya-Yosida interaction becomes invalid.
• Demonstrated antiferromagnetic spin coupling between two dots, leading to zero or full conductance.
• Showcased suppression of the Kondo effect with equal level differences due to inter-dot transport loops.
• Observed a near-unitary Kondo peak with symmetric level differences due to suppressed inter-dot transport.

Conclusions:

• The discovered electron state offers novel control over quantum dot conductance.
• Voltage-controllable quantum phase transitions (Kosterlitz-Thouless and first-order) are achievable.
• The findings provide insights into many-body effects and effective Kondo models for quantum information processing.