Enhanced coherence of a quantum doublet coupled to Tomonaga–Luttinger liquid leads

Abstract

We use boundary field theory to describe the phases accessible to a tetrahedral qubit coupled to Josephson junction chains acting as Tomonaga-Luttinger liquid leads. We prove that, in a pertinent range of the fabrication and control parameters, an attractive finite coupling fixed point emerges due to the geometry of the composite Josephson junction network. We show that this new stable phase is characterized by the emergence of a quantum doublet which is robust not only against the noise in the external control parameters (magnetic flux, gate voltage) but also against the decoherence induced by the coupling of the tetrahedral qubit with the superconducting leads. We provide protocols allowing to read and to manipulate the state of the emerging quantum doublet and argue that a tetrahedral Josephson junction network operating near the new finite coupling fixed point may be fabricated with today' s technologies.

Quantum impurity in a Luttinger liquid: Universal conductance with entanglement renormalization

“…Even in the simplest case, the Y junction with three LL wires, not all the fixed points are fully understood by the CFT [19]. We expect that boundary MERA can provide a new approach to gain insights into the properties of possible RG fixed points and their classification for more complicated multiwire junctions [49][50][51][52][53][54][55][56][57][58], spinful LL wires [59], junctions of LL wires with different interaction strength in each wire [60][61][62][63][64], and junctions of Josephsonjunction networks [65,66]. Potentially, the boundary MERA also provides an unbiased numerical RG method to resolve the issue about whether the conductance of Y junction can break the single-particle unitarity in the strong attractive interaction regime [19,58].…”

Kondo length in bosonic lattices

“…Within the continuous bosonic field framework, the open boundary conditions of the chain are accounted for by imposing Neumann-like boundary conditions on the field Φ(x, τ ) at both boundaries 76,[89][90][91] , that is…”

Transfer matrix approach to the persistent current in quantum rings: Application to hybrid normal-superconducting rings

“…The corresponding model Hamiltonian can be recovered from Eq. (14) in the p-wave case and from Eq. (33) in the s-wave case, by setting to zero the length of one of the two regions.…”

“…A large amount of literature about persistent current in a normal mesoscopic ring has addressed a number of issues such as the effect of disorder in the ring with consequent possible halving in the period of the current 7,8 , the role of the spin degree of freedom 9 , the consequences of the electron-electron interaction, with and without impurity scattering 10 , and the presence of spin-orbit interaction 11 (for a recent comprehensive review on electron transport in mesoscopic rings see, for instance, [12]). Moreover, the issue of how the current is affected by collective fluctuations in quasi one-dimensional superconducting rings with a weak link has been considered 13 , together with the possibility of using small superconducting rings, realized with pertinent Josephson junction networks, as high-coherence quantum devices [14][15][16] . Recent progresses in the fabrication of nanostructures made it possible to engineer hybrid devices where superconductivity is induced by proximity effect only in a section of the ring 17 (Hybrid Rings (HRs)).…”