Abstract
Various promising qubit concepts have been put forward recently based on engineered superconductor subgap states like Andreev bound states, Majorana zero modes or the Yu-Shiba-Rusinov (Shiba) states. The coupling of these subgap states via a superconductor strongly depends on their spatial extension and is an essential next step for future quantum technologies. Here we investigate the spatial extension of a Shiba state in a semiconductor quantum dot coupled to a superconductor. With detailed transport measurements and numerical renormalization group calculations we find a remarkable more than 50 nm extension of the zero energy Shiba state, much larger than the one observed in very recent scanning tunneling microscopy measurements. Moreover, we demonstrate that its spatial extension increases substantially in a magnetic field.
Highlights
Various promising qubit concepts have been put forward recently based on engineered superconductor subgap states like Andreev bound states, Majorana zero modes or the YuShiba-Rusinov (Shiba) states
Shiba states were widely studied in two different types of systems: (a) in STM measurements, when magnetic particles are deposited on the surface of a superconductor[37,38,39,40,41,42,43,44,45,46,47,48], and (b) in nanocircuits, when a quantum dot is attached to the superconductor[49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69]
We implement a combined approach of systems (a) and (b), where a tunnel probe is attached to a superconductor–quantum dot hybrid
Summary
Various promising qubit concepts have been put forward recently based on engineered superconductor subgap states like Andreev bound states, Majorana zero modes or the YuShiba-Rusinov (Shiba) states. The coupling of these subgap states via a superconductor strongly depends on their spatial extension and is an essential step for future quantum technologies. The quantum dot realization enables the tuning of the energy of the Shiba state via the level position or the tunnel couplings by using external gate voltages[61,62] Another advantage of the latter setup is the potential to apply an external magnetic field without stability issues
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