Research Results

The following links contain short summaries of recently published papers.

L. Steffen et al., Physical Review Letters 108, 260506, published 28 June 2012

Tomography is the main method used for measuring the fidelity of an experimentally implemented quantum process. However, it is a very inefficient method since the number of measurements as well as the time needed for the data post-processing scale exponentially with the number of qubits.

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S. Berger et al., Physical Review B 85, 220502(R), published 07 June 2012 M. Pechal et al., Phys. Rev. Lett. 108, 170401, published 23 April 2012

When a quantum mechanical system evolves under a time-dependent Hamiltonian, it acquires not only the wellknown dynamic phase, which is the time-integral of the energy of the system, but also a geometric phase. As indicated by its name, it is of a purely geometric nature in that it solely depends on the trajectory of the quantum system in state space.

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T. Frey et al., Phys. Rev. Lett 108, 046807, published 25 January 2012

We have realized a novel device in which a semiconductor double quantum dot is dipole coupled to a GHz-frequency high-quality transmission line resonator. This approach allows us to characterize the properties of the double dot by measuring both its dispersive and dissipative interaction with the resonator.

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M. Baur et al., Phys. Rev. Lett. 108, 040502, 24 January 2012

Teleportation of a quantum state may be used for distributing entanglement between distant qubits in quantum communication and for quantum computation.

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A. Fedorov et al., Nature 481, 170–172, published 14 December 2011

The Toffoli gate is a three-qubit operation that inverts the state of a target qubit conditioned on the state of two control qubits.

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