# Bosonic superfluid transport in a quantum point contact

## TL;DR

This paper develops a microscopic theory for heat and particle transport in a Bose-Einstein condensate through a quantum point contact, revealing unique tunneling processes and harmonic behaviors distinct from fermionic superconductors.

## Contribution

It introduces the concept of condensate tunneling processes and anomalous tunneling in bosonic superfluids, highlighting their effects on AC Josephson currents and transport properties.

## Key findings

- Presence of odd and even harmonics in AC Josephson current.
- Dissipative and nondissipative components obeying different laws.
- Breakdown of the bosonic Wiedemann-Franz law at zero temperature.

## Abstract

We present a microscopic theory of heat and particle transport of an interacting, low temperature Bose-Einstein condensate in a quantum point contact. We show that, in contrast to charged, fermionic superconductors, bosonic systems feature tunneling processes of condensate elements, leading to the presence of odd-order harmonics in the AC Josephson current. A crucial role is played by an anomalous tunneling process where condensate elements are coherently converted into phonon excitations, leading to even-order harmonics in the AC currents as well as a DC contribution. At low bias, we find dissipative components obeying Ohm's law, and bias-independent nondissipative components, in sharp contrast to fermionic superconductors. Analyzing the DC contribution, we find zero thermopower and Lorenz number at zero temperature, a breakdown of the bosonic Wiedemann-Franz law. These results highlight importance of the anomalous tunneling process inherent to charge neutral superfluids. The consequences could readily be observed in existing cold-atom transport setups.