For a general model of mesoscopic multilevel quantum dot, we determine the necessary conditions for existence an anomalous Josephson current with spontaneously broken time-reversal symmetry. They correspond to finite spin-orbit coupling, suitably oriented Zeeman field, and dot being chiral conductor. We provide analytical expressions supercurrent covering wide parameter regime.

We formulate and apply a low-energy transport theory for hybrid quantum devices containing junctions of topological superconductor (TS) wires conventional normal (N) or superconducting (S) leads. model TS as spinless $p$-wave superconductors derive their boundary Keldysh Green's function, capturing both the Majorana end state continuum quasiparticle excitations in unified manner. also specify this function finite-length wire. Junctions connecting different parts device are described by...

We study charge transport in voltage-biased single-channel junctions involving helical superconductors with finite Cooper pair momentum. For a Josephson junction, the equilibrium current-phase relation shows superconducting diode effect: critical current depends on propagation direction. formulate scattering theory for diodes and show that multiple Andreev reflection processes cause rich subharmonic structure dc current-voltage curve at low temperatures small voltages due to Doppler shifts...

We investigate the dynamics of a two-level Andreev bound state system in transmissive quantum point contact embedded an rf SQUID. Coherent coupling levels to circulating supercurrent allows manipulation and readout level states. The Hamiltonian for is derived, effect interaction with fluctuations induced flux studied. also consider inductive qubits discuss relevant SQUID parameters qubit operation readout.

We study the combined effects of spin-orbit interaction, magnetic field, and Coulomb charging on Josephson current-phase relation, $I(\ensuremath{\varphi})$, for a multilevel quantum dot tunnel contacted by two conventional $s$-wave superconductors with phase difference $\ensuremath{\varphi}$. A general model is formulated analyzed in cotunneling regime (weak coupling) deep subgap limit, fully taking into account interaction effects. determine conditions observing finite anomalous...

We study transport through a Coulomb blockaded topologically nontrivial superconducting wire (with Majorana end states) contacted by metallic leads. An exact formula for the current this interacting single-charge transistor is derived in terms of spectral functions. A comprehensive picture follows from three different approaches. find oscillations with universal halving finite-temperature peak conductance under strong blockade conditions, where valley mainly comes elastic cotunneling. The...

We derive and analyze the effective low-energy theory for interacting electrons in a cylindrical nanowire made of strong topological insulator. Three different approaches provide consistent picture band structure, where surface states forming inside bulk gap correspond to one-dimensional bands indexed by total angular momentum. When half-integer magnetic flux pierces nanowire, we find strongly correlated helical Luttinger liquid topologically protected against weak disorder. describe how...

We study Coulomb charging effects for transport through a topologically nontrivial superconducting wire, where Majorana bound states are present at the interface to normal-conducting leads. construct general Keldysh functional integral representation, and provide detailed results nonlinear current-voltage relation under weak blockade conditions.

We propose active steering protocols for quantum state preparation in circuits where each system qubit is connected to a single detector qubit, employing simple coupling selected from small set of operators. The decision made such that the expected cost-function gain one time step maximized. apply these several many-qubit models. Our results are underlined by three remarkable insights. First, we show standard fidelity does not give useful cost function; instead, successful achieved including...

Transport through a single-molecular conductor is considered, showing negative differential conductance behavior associated with phonon-mediated electron tunneling processes. This theoretical work motivated by recent experiment Leroy et al. using carbon nanotube contacted scanning microscope tip [Nature 432, 371 (2004)], where of the breathing-mode phonon side peaks could be observed. A peculiarity this system that couplings which inject electrons and those collect them on substrate are...

Excess quasiparticles play a crucial role in superconducting quantum devices ranging from qubits to sensors. In this work we analyze their dynamics for phase-biased finite-length weak links with several Andreev subgap states, where the coupling microwave resonator allows parity state (even/odd) readout. Our theory shows that almost perfect dynamical polarization given sector is achievable by applying pulse matching transition opposite sector. results qualitatively explain key features of...

We develop a Green's function approach for the nonequilibrium dynamics of multi-level quantum dots coupled to multiple fermionic reservoirs in presence bosonic environment. Our theory is simpler than Keldysh and goes beyond scattering state constructions. In concrete terms, we study Josephson junctions containing dot an electromagnetic region, spin-orbit interactions, Zeeman field, principle also Coulomb interactions can be included. then Mpemba effects, assuming that average phase...

We develop a Green's function approach for the nonequilibrium dynamics of multilevel quantum dots coupled to multiple fermionic reservoirs in presence bosonic environment. Our theory is simpler than Keldysh and goes beyond scattering state constructions. In concrete terms, we study Josephson junctions containing dot an electromagnetic region, spin-orbit interactions, Zeeman field, principle Coulomb interactions can also be included. then Mpemba effects, assuming that average phase difference...

We study the Josephson effect for a topologically nontrivial superconducting (TS) wire with Majorana fermion end states and tunnel-coupled to s-wave BCS (S) electrodes. In an S-TS junction, no supercurrent flow is possible under fairly general conditions. For S-TS-S bulk TS quasiparticles must be accessible have effect. noninteracting case, we derive exact current-phase relation (CPR) find \pi-periodic behavior negative critical current weak tunnel couplings. Charging effects then cause...

We provide a comprehensive theoretical description of low-energy quantum transport for Coulomb–Majorana junction, where several helical Luttinger liquid nanowires are coupled to joint mesoscopic superconductor with finite charging energy. Including the Majorana bound states formed near ends superconducting wire parts, we derive and analyze Keldysh phase action describing non-equilibrium charge properties junction. The physics corresponds two-channel Kondo model symmetry group SO(M), M is...

The equilibrium Josephson current through a nanoscale multilevel quantum dot with Rashba or Dresselhaus spin-orbit coupling $\ensuremath{\alpha}$ has been computed. critical can be drastically modified already by moderate $\ensuremath{\alpha}$. In the presence of Zeeman field, Datta-Das-like oscillatory dependencies on are predicted.

We study the Josephson effect in a trijunction formed by two topological superconductor (TS) wires and conventional $s$-wave superconductor. Using boundary Green's function formalism, analytical results for current-phase relation are obtained various limiting cases modeling TS via low-energy limit of Kitaev chain. show that transport critically depends on spin canting angle $\ensuremath{\theta}$ between polarizations wires, which turn suggests structure Majorana states can be accessed...

The clear-cut experimental identification of Majorana bound states in transport measurements still poses challenges. We here show that the zero-energy state formed at a junction three topological superconductor wires is directly responsible for giant shot noise amplitudes, particular low voltages and small contact transparency. only intrinsic limitation comes from current-induced dephasing rate due to multiple Andreev reflection processes.

We present a detailed theory for the Andreev level qubit, system consisting of highly transmissive quantum point contact embedded in superconducting loop. The two-level Hamiltonian levels interacting with phase fluctuations is derived by using path integral method. also derive kinetic equation describing qubit decoherence due to interaction acoustic phonons. collision terms are nonlinear fermionic nature states, leading slow nonexponential relaxation and dephasing at temperatures smaller...

We consider the energy spectrum and spin-parity structure of eigenstates for a quantum dot made strong topological insulator. Using effective low-energy theory in finite-length cylinder geometry, numerical calculations show that even at lowest scales, spin direction topologically protected surface mode is not locked to surface. find ``zero-momentum'' modes, subgap states localized near ``caps'' dot. Both texture are basically reproduced from an analytical Dirac fermion description. Our...

We propose and study a setup realizing stable manifold of non-Fermi liquid states. The device consists mesoscopic superconducting island hosting $N \ge 3$ Majorana bound states tunnel-coupled to normal leads, with Josephson contact bulk superconductor. find nontrivial interplay between multi-channel Kondo resonant Andreev reflection processes, which results in the fixed point manifold. scaling dimension leading irrelevant perturbation changes continuously within determines power-law...

Pure quantum states can be stabilized in open systems subject to external driving forces and dissipation by environmental modes. We show that driven dissipative (DD) Majorana devices offer key advantages for stabilizing degenerate state manifolds ("dark spaces") manipulating dark spaces, both with respect native (non-DD) DD platforms topologically trivial building blocks. For two tunnel-coupled boxes, using otherwise only standard hardware elements (e.g., a noisy electromagnetic environment...

The boundary Green's-function (bGF) approach has been established as a powerful theoretical technique for computing the transport properties of tunnel-coupled hybrid nanowire devices. Such nanowires may exhibit topologically nontrivial superconducting phases with Majorana bound states at their boundaries. We introduce general method bGF spinful multichannel lattice models such nanowires, where is expressed in terms roots secular polynomial evaluated complex momentum space. In many cases,...

We present a comprehensive theoretical framework for the Andreev bound-state population dynamics in superconducting weak links. Contrary to previous works, our approach takes into account generated nonequilibrium distribution of continuum quasiparticle states self-consistent way. As application theory, we show that coupling contact environmental phase fluctuations induces charge imbalance population. This is due breaking left-right symmetry rates connecting quasiparticles and system, causes...

We present a theoretical analysis of quasiparticle poisoning in Coulomb-blockaded Majorana fermion systems tunnel-coupled to normal-conducting leads. Taking into account finite-energy quasiparticles, we derive the effective low-energy theory and renormalization group analysis. find qualitatively new effects when state with very low energy is localized near tunnel contact. For $M=2$ attached leads, such ``dangerous'' processes cause spin $S=1/2$ single-channel Kondo effect, which can be...