Theory of Andreev Blockade in a Double Quantum Dot with a Superconducting Lead

TL;DR

This paper introduces Andreev blockade, a novel quantum transport phenomenon in double quantum dots with superconducting leads, characterized by electron blockade due to suppressed Andreev reflections, with implications for quantum device design.

Contribution

It presents the theoretical framework for Andreev blockade, highlighting its unique transport signatures and conditions under which it occurs, supported by recent experimental evidence.

Findings

Andreev blockade occurs for any occupation adjacent to the superconductor.

It is lifted when quasiparticles enter the superconducting lead.

Supports potential observation in superconductor-semiconductor devices.

Abstract

A normal metal source reservoir can load two electrons onto a double quantum dot in the spin-triplet configuration. We show that if the drain lead of the dot is a spin-singlet superconductor, these electrons cannot form a Cooper pair and are blockaded on the double dot. We call this phenomenon Andreev blockade because it arises due to suppressed Andreev reflections. We identify transport characteristics unique to Andreev blockade. Most significantly, it occurs for any occupation of the dot adjacent to the superconductor, in contrast with the well-studied Pauli blockade which requires odd occupations. Andreev blockade is lifted if quasiparticles are allowed to enter the superconducting lead, but it should be observable in the hard gap superconductor-semiconductor devices. A recent experiment tests this model and finds support for several predictions made here~[P. Zhang, H. Wu, J. Chen, S. A. Khan, P. Krogstrup, D. Pekker, and S. M. Frolov, arXiv:2102.03283 (2021)]. Andreev blockade should be considered in the design of topological quantum circuits, hybrid quantum bits and quantum emulators.