Decay of bound states in the continuum of Majorana fermions induced by vacuum fluctuations: Proposal of qubit technology

Abstract

We report on a theoretical investigation of the interplay between vacuum fluctuations, Majorana quasiparticles (MQPs) and bound states in the continuum (BICs) by proposing a new venue for qubit storage. BICs emerge due to quantum interference processes as the Fano effect and, since such a mechanism is unbalanced, these states decay as regular into the continuum. Such fingerprints identify BICs in graphene as we have discussed in detail in Phys. Rev. B 92, 245107 and 045409 (2015). Here by considering two semi-infinite Kitaev chains within the topological phase, coupled to a quantum dot (QD) hybridized with leads, we show the emergence of a novel type of BICs, in which MQPs are trapped. As the MQPs of these chains far apart build a delocalized fermion and qubit, we identify that the decay of these BICs is not connected to Fano and it occurs when finite fluctuations are observed in the vacuum composed by electron pairs for this qubit. From the experimental point of view, we also show that vacuum fluctuations can be induced just by changing the chain-dot couplings from symmetric to asymmetric. Hence, we show how to perform the qubit storage within two delocalized BICs of MQPs and to access it when the vacuum fluctuates by means of a complete controllable way in quantum transport experiments.

Unveiling Majorana quasiparticles by a quantum phase transition: Proposal of a current switch

“…Furthermore, thermal broadening together with a coherence length much longer than the Kitaev chain size can also lead to the overlap of the MQPs at the chain edges, thus suppressing the ZBP signature 8 . Here our detection strategy adds a second QD to the system developed in our previous work 18 , where a novel technology for qubit storage was proposed based on bound states in the continuum (BICs) [19][20][21] formed by MQPs. Thus we show that by using a double-QD interferometer connected to a pair of topological Kitaev chains, as those sketched in Fig.1(a), that an emerging QPT then unveils a MQP when the setup operates under the "Switch" regime for the current, namely: if the upper QD is coupled simultaneously to the Kitaev chains, the interferometer "feels" the two MQPs at the edges of the chains just as an ordinary fermion and the current travels exclusively through the lower dot (blue panel of Fig.1(b)) once the other dot presents a superconducting gap that prevents the current.…”

Spin-dependent coupling between quantum dots and topological quantum wires

“…In this paper we study MBSs formed in a quantum wire with proximity-induced superconductivity near a quantum dot [28][29][30][31][32][33][34][35][36][37], which is also formed inside a quantum wire, all of which are subject to an applied magnetic field perpendicular to the SOI. First calculating the wave functions of the quantum dot and MBSs, which can be done analytically in the strong spin-orbit regime, we are able to find the spin dependence of the quantum dot-MBS coupling which has been largely neglected [21,22,28,29].…”

Majorana bound state in the continuum: Coupling between a Majorana bound state and a quantum dot mediated by a continuum energy spectrum

“…Motivated by the interference phenomena taking place in electronic systems in analogy with the photonic counterpart, the presence of BICs promoted by MBS has been investigated [31,32]. Related to this problem, interplay between MBSs and BICs have been proposed as a useful tool to perform applications in quantum computing, allowing, for instance, to read/write information through veil/unveil these states [33][34][35]. Indeed, MBS provides a quite attractive way to produce BICs as they are topologically protected against local perturbation [36,37].…”