Probing Majorana bound states via a pn junction containing a quantum dot

We propose an alternative route to transport experiments for detecting\nMajorana bound states (MBSs) by combining topological superconductivity with\nquantum optics in a superconducting $pn$ junction containing a quantum dot\n(QD). We consider a topological superconductor (TSC) hosting two Majorana bound\nstates at its boundary ($n$ side). Within an effective low-energy model, the\nMBSs are coherently tunnel-coupled to a spin-split electron level on the QD\nwhich is placed close to one of the MBSs. Holes on the QD are tunnel-coupled to\na normal conducting reservoir ($p$ side). Via electron-hole recombination,\nphotons in the optical range are emitted, which have direct information on the\nMBS-properties through the recombined electrons. Using a master equation\napproach, we calculate the polarization-resolved photon emission intensities\n(PEIs). In the weak coupling regime between MBSs and QD, we find an analytical\nexpression for the PEI which allows to clearly distinguish the cases of well\nseparated MBSs at zero energy from overlapping MBSs. For separated MBSs, the\nMajorana spinor-polarization is given by the relative widths of the two PEI\npeaks associated with the two spin states on the QD. For overlapping MBSs, a\ncoupling to the distant (nonlocal) MBS causes a shift of the emission peaks.\nAdditionally, we show that quasiparticle poisoning (QP) influences the PEI\ndrastically and changes its shot noise from super-Poissonian to sub-Poissonian.\nIn the strong coupling regime, more resonances emerge in the PEI due to\nspin-mixing effects. Finally, we comment on how our proposal could be\nimplemented using a Majorana nanowire.\n