# Noise of a chargeless Fermi liquid

## TL;DR

This paper develops a Fermi liquid theory for a superconductor-quantum dot-normal metal junction near a parity transition, revealing a hidden symmetry and an effective charge of 2e in the noise characteristics.

## Contribution

It introduces a novel Fermi liquid framework for chargeless quasiparticles in a superconducting quantum dot system, uncovering hidden symmetries and effective charge behavior.

## Key findings

- Back scattering noise shows an effective charge of 2e.
- Strong noise suppression occurs at unitary conductance.
- Mapping to the Anderson model reveals hidden U(1) symmetry.

## Abstract

We construct a Fermi liquid theory to describe transport in a superconductor-quantum dot- normal metal junction close to the singlet-doublet (parity changing) transition of the dot. Though quasiparticles do not have a definite charge in this chargeless Fermi liquid, in case of particle-hole symmetry, a mapping to the Anderson model unveils a hidden U(1) symmetry and a corresponding pseudo-charge. In contrast to other correlated Fermi-liquids, the back scattering noise reveals an effective charge equal to the charge of Cooper pairs, $e^* = 2e$. In addition,we find a strong suppression of noise when the linear conductance is unitary, even for its non-linear part.