PCSV · Point contacts for quantum spin valleytronics (PCSV)

Point contacts for quantum spin valleytronics (PCSV)

Since the discovery of the transistor in 1948, semiconductor electronics have changed our lives in unprecedented ways. The enormous miniaturization of transistors, which has triggered an exponential increase of the world’s computational power, is reaching a fundamental limit. In this context, the achievement of complex operations by alternative approaches is crucial for the future of computation. A recently developed alternative relies on the quantum entanglement between the ultimately small quantum dots (QD) and has already proved to be faster than conventional computations for certain operations. However, the realization of complex operations relies on the transfer of quantum information, which is a bottleneck due to the destructive effects of interactions with the environment. In this context, van der Waals heterostructures made of bilayer graphene (BLG) and hexagonal boron nitride (hBN), where information can be stored in the spin and valley degrees of freedom, arise as new platforms for quantum coherent transport. Their long spin and valley coherence times make these systems promising for quantum computing but electronic transport in quantum coherent BLG devices needs further experimental studies. For this purpose, PCSV studies electrostatically defined quantum point contacts (QPCs) in BLG-based novel device platforms where charge transport between the QPCs occurs in a ballistic manner. The results show that electron beams can keep their valley coherence even after being reflected by electrostatically-defined edges. In addition, PCSV shows that, under the application of moderate out-of-plane magnetic fields, these QPCs become quarter metals capable of emitting completely spin and valley-polarized currents. These results open the way for new devices where the spin and valley degrees of freedom are used as information carriers and may serve as new interconnects between QDs in future BLG-based quantum computing devices.

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