Topological phase rectification via Aharonov-Bohm interference in a Majorana--quantum-dot interferometer
We propose and theoretically investigate a topological superconducting rectifier based on a quantum-dot--Majorana interferometer. The Aharonov-Bohm phase, controlled by a magnetic flux threading the interferometer loop, tunes the quantum interference between a trivial $2\pi$-periodic quantum-dot channel and a topological $4\pi$-periodic Majorana channel. At non-integer flux, this interference generates a persistent current background $I_{\rm off}$ that shifts the current-phase relation into a unipolar regime, in which the supercurrent flows strictly in one direction. We introduce a signed unipolarity factor $\eta_u$, with $|\eta_u|>0.5$ defining the unipolar regime, and establish its quantitative relationship to the conventional diode efficiency $\eta$. The unipolarity proves robust against variations of the quantum-dot level, spin polarization, and Majorana hybridization, is enhanced by stronger Majorana coupling and Rashba spin-orbit interaction, and persists at realistic temperatures and under quasiparticle poisoning. We further propose a topological diode figure of merit $\mathcal{Z}_{\rm TD}$, defined from the Fourier spectrum of $\eta_u$, whose nonzero value provides a model-independent signature of the $4\pi$-periodic Majorana channel and distinguishes topological from trivial rectification mechanisms. Our findings establish the quantum-dot--Majorana interferometer as a promising route toward high-performance topological superconducting diodes with clear experimental signatures accessible via standard dc transport measurements.