Speaker
Description
Beyond the concept of Cooper pairs, Cooper quartets are exotic fermionic aggregates forming the basis of charge-$4e$ superconductivity. They provide a platform to explore genuine four-body interactions, with potential relevance for topological matter and strongly correlated quantum systems. However, their realization, engineering, and unambiguous detection remain outstanding challenges.
Here, we propose a scheme to realize Cooper quartets in a triple-quantum-dot system coupled to three conventional superconducting leads via a nonlocal Josephson junction. By engineering both interdot and intradot interactions, we demonstrate that the ground state can be driven into a coherent superposition of the vacuum |0> and a four-electron state |4e>, characteristic of a quartet condensate. We show that crossed Andreev reflection processes play a central role, enabling the splitting of Cooper quartets in superconductors across different quantum dots. The system is shown to support a pi-periodic Josephson current, which can be nonlocally controlled by the superconducting phase of a separate terminal.
This mechanism establishes a route to generating coherent four-body correlations in hybrid superconducting nanostructures. More generally, the nonlocal nature of the quartet ground state suggests the emergence of correlated behavior in multiterminal geometries, defining a broader class of interacting Andreev matter, potentially exhibiting nontrivial topological properties.
References
L. Chirolli, A. Braggio, and F. Giazotto, Cooper quartets in interacting hybrid superconducting systems, Phys. Rev. Res. 6, 033171 (2024).