References of "Nunnenkamp, Andreas"
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See detailCharge pumping through a polaron quantum dot
Haughian, Patrick UL; Yap, Han Hoe; Walter, Stefan et al

Poster (2017, July)

Nanoelectromechanical systems exhibit a rich phenomenology due to the interaction of electronic and mechanical degrees of freedom. If this interaction is sufficiently strong, it leads to drastic ... [more ▼]

Nanoelectromechanical systems exhibit a rich phenomenology due to the interaction of electronic and mechanical degrees of freedom. If this interaction is sufficiently strong, it leads to drastic suppression of conductance ("Franck-Condon blockade''). We show that this blockade can be exponentially lifted by application of an AC voltage. Multi-parameter drive protocols generate a pump current which enjoys the same enhancement. [less ▲]

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See detailLifting the Franck-Condon blockade in driven quantum dots
Haughian, Patrick UL; Walter, Stefan; Nunnenkamp, Andreas et al

in Physical Review. B : Condensed Matter (2016), 94

Electron-vibron coupling in quantum dots can lead to a strong suppression of the average current in the sequential tunneling regime. This effect is known as Franck-Condon blockade and can be traced back ... [more ▼]

Electron-vibron coupling in quantum dots can lead to a strong suppression of the average current in the sequential tunneling regime. This effect is known as Franck-Condon blockade and can be traced back to an overlap integral between vibron states with different electron numbers which becomes exponentially small for large electron-vibron coupling strength. Here, we investigate the effect of a time-dependent drive on this phenomenon, in particular the effect of an oscillatory gate voltage acting on the electronic dot level. We employ two different approaches: perturbation theory based on nonequilibrium Keldysh Green's functions and a master equation in Born-Markov approximation. In both cases, we find that the drive can lift the blockade by exciting vibrons. As a consequence, the relative change in average current grows exponentially with the drive strength. [less ▲]

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See detailMicrowave-controlled coupling of Majorana bound states
Schmidt, Thomas UL; Nunnenkamp, Andreas; Bruder, Christoph

in New J. Phys. (2013), 15

We propose microwave-controlled rotations for qubits realized as Majorana bound states. To this end, we study an inhomogeneous Kitaev chain in a microwave cavity. The chain consists of two topologically ... [more ▼]

We propose microwave-controlled rotations for qubits realized as Majorana bound states. To this end, we study an inhomogeneous Kitaev chain in a microwave cavity. The chain consists of two topologically nontrivial regions separated by a topologically trivial, gapped region. The Majorana bound states at the interfaces between the left (right) regions and the central region are coupled, and their energies are split by virtual cotunneling processes. The amplitude for these cotunneling processes decreases exponentially with the number of sites of the gapped region, and the decay length diverges as the gap of the topologically trivial region closes. We demonstrate that microwave radiation can exponentially enhance the coupling between the Majorana bound states, both for classical and quantized electric fields. By solving the appropriate Liouville equation numerically, we show that microwaves can drive Rabi oscillations in the Majorana sector. Our model emerges as an effective description of a topological semiconductor nanowire in a microwave cavity. Thus, our proposal provides an experimentally feasible way to obtain full single-qubit control necessary for universal quantum computation with Majorana qubits. [less ▲]

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See detailMajorana Qubit Rotations in Microwave Cavities
Schmidt, Thomas UL; Nunnenkamp, Andreas; Bruder, Christoph

in Phys. Rev. Lett. (2013), 110

Majorana bound states have been proposed as building blocks for qubits on which certain operations can be performed in a topologically protected way using braiding. However, the set of these protected ... [more ▼]

Majorana bound states have been proposed as building blocks for qubits on which certain operations can be performed in a topologically protected way using braiding. However, the set of these protected operations is not sufficient to realize universal quantum computing. We show that the electric field in a microwave cavity can induce Rabi oscillations between adjacent Majorana bound states. These oscillations can be used to implement an additional single-qubit gate. Supplemented with one braiding operation, this gate allows us to perform arbitrary single-qubit operations. [less ▲]

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