Coupled Quantum Dots may allow to store quantum information

Image of a novel system of coupled quantum dots taken with a scanning tunneling microscope shows electrons orbiting within two concentric sets of closely spaced rings, separated by a gap. The inner set of rings represents one quantum dot; the outer, brighter set represents a larger, outer quantum dot. Credit: NIST

Researchers at the National Institute of Standards and Technology (NIST) and their colleagues have for the first time created and imaged a novel pair of quantum dots. Quantum dots are tiny islands of confined electric charge that act like interacting artificial atoms.

To fabricate the quantum dots, the team used the ultra-sharp tip of a Scanning Tunneling Microscope (STM) as if it were a stylus of an Etch A Sketch. Hovering the tip above an ultracold sheet of graphene (a single layer of carbon atoms arranged in a honeycomb pattern), the researchers briefly increased the voltage of the tip. 

The electric field generated by the voltage pulse penetrated through the graphene into an underlying layer of boron nitride, where it stripped electrons from atomic impurities in the layer and created a pileup of electric charge. The pileup corralled freely floating electrons in the graphene, confining them to a tiny energy well.

But when the team applied a magnetic field of 4 to 8 tesla (about 400 to 800 times the strength of a small bar magnet), it dramatically altered the shape and distribution of the orbits that the electrons could occupy. Rather than a single well, the electrons now resided within two sets of concentric, closely spaced rings within the original well separated by a small empty shell. The two sets of rings for the electrons now behaved as if they were weakly coupled quantum dots. 

Such “coupled” quantum dots could serve as a robust quantum bit, or qubit, the fundamental unit of information for a quantum computer.

Moreover, the patterns of electric charge in the island can’t be fully explained by current models of quantum physics, offering an opportunity to investigate rich new physical phenomena in materials. (SciTechDaily)

These findings have been published in Physical Review B.

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