Tunable Valley Splitting and Bipolar Operation in Graphene Quantum Dots.

Area of Science:

• Quantum physics
• Condensed matter physics
• Materials science

Background:

• Graphene quantum states exhibit 2-fold degeneracy in spin and 2-fold in valley degrees of freedom.
• Both spin and valley degrees of freedom are promising for qubit preparation in quantum computing.

Purpose of the Study:

• To demonstrate the tunability of the valley g-factor (g_v) in bilayer graphene quantum dots.
• To investigate the relationship between electronic dot size and valley g-factor.
• To explore bipolar operation and tunable double dot configurations in graphene quantum dots.

Main Methods:

• Fabrication and characterization of bilayer graphene quantum dots.
• Utilizing gate voltage adjustments to tune the valley g-factor.
• Measuring charging energy to determine electronic dot sizes.
• Performing experiments to achieve bipolar operation and observe electron-hole transitions.

Main Results:

• The valley g-factor (g_v) was successfully tuned by over a factor of 4, from 20 to 90, solely through gate voltage adjustments.
• Larger electronic dot sizes, determined by charging energy, correlated with increased valley g-factors.
• Bipolar operation was achieved, allowing the quantum dot to be charged with either electrons or holes.
• Tunable double dot systems were demonstrated through the addition of gates.

Conclusions:

• Gate voltage control offers a powerful method for tuning the valley g-factor in bilayer graphene quantum dots.
• The observed tunability and bipolar operation are significant steps towards realizing graphene-based quantum information processing.
• The versatile device architecture facilitates further exploration of multi-dot systems and advanced qubit functionalities.