QUROPE Quantum Information Processing and Communication in Europe

Der diesjährige Max-Rössler-Preisträger, der Physiker Andreas Wallraff, forscht mit dem Ziel quantenmechanische Maschinen zu bauen. Der Max-Rössler-Preis ist der höchst dotierte Forscherpreis der ETH Zürich und wurde 2007 durch eine Donation an den «Strategischen Fonds» der ETH Zürich Foundation ins Leben gerufen. 

Der ETH-Physiker Andreas Wallraff entwickelt Mikrochips, die tausendmal energieeffizienter sind als herkömmliche Computer.

Photons in the microwave frequency range are important in quantum research - for quantum information processors, for example. Now, for the first time, researchers have achieved the controlled production of single photons in the microwave region and successfully detected them with highly sensitive measuring instruments - although they are 100,000 times weaker than the photons emitted by an electric light bulb. 

Thirty-three Swiss research groups have joined the National Centre of Competence in Research "Quantum Science and Technology" (QSIT) with the aim of exploring the boundaries between classical and quantum mechanics, and combining different research approaches. The researchers are not just hoping for success with regard to a quantum computer. The leading house is ETH Zurich with Director Klaus Ensslin, a professor of experimental physics. 

We demonstrate the realization of a hybrid solid-state quantum device, in which a semiconductor double quantum dot is dipole coupled to the microwave field of a superconducting coplanar waveguide resonator. The double dot charge stability diagram extracted from measurements of the amplitude and phase of a microwave tone transmitted through the resonator is in good agreement with that obtained from transport measurements.

Teleportation of a quantum state may be used for distributing entanglement between distant qubits in quantum communication and for quantum computation. Here we demonstrate the implementation of a teleportation protocol, up to the single-shot measurement step, with superconducting qubits coupled to a microwave resonator. Using full quantum state tomography and evaluating an entanglement witness, we show that the protocol generates a genuine tripartite entangled state of all three qubits.

The Toffoli gate is a three-quantum-bit (three-qubit) operation that inverts the state of a target qubit conditioned on the state of two control qubits. It makes universal reversible classical computation possible and, together with a Hadamard gate, forms a universal set of gates in quantum computation. It is also a key element in quantum error correction schemes. The Toffoli gate has been implemented in nuclear magnetic resonance, linear optics8 and ion trap systems.

We present measurements of a hybrid system consisting of a microwave transmission-line resonator and a lateral quantum dot defined on a GaAs heterostructure. The two subsystems are separately characterized and their interaction is studied by monitoring the electrical conductance through the quantum dot. The presence of a strong microwave field in the resonator is found to reduce the resonant conductance through the quantum dot and is attributed to electron heating and modulation of the dot potential.

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. In addition to providing a new readout mechanism, this architecture has the potential to isolate the dots from the environment and to provide long distance coupling between spatially separated dots.

The Toffoli gate is a three-qubit operation that inverts the state of a target qubit conditioned on the state of two control qubits. It enables universal reversible classical computation, forms a universal set of gates in quantum computation together with a Hadamard gate and is also a key element in quantum error correction schemes. Here, Andreas Wallraff and colleagues at ETH-Zurich demonstrated the implementation of a Toffoli gate with three superconducting transmon qubits coupled to a microwave resonator.