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Superconducting Qubits: Quantum computing with Josephson Junctions


The project aims at fabrication of systems of quantum logic gates by developing Josephson Junction (JJ) and SQUID technologies to achieve initialisation, processing and read-out of super conducting qubit information. The first objective is to improve single-qubit technologies for hybrid charge and flux qubits, and to control the coherence properties and the dynamics of single qubit operations. The major objective is to fabricate and control several coupled JJ qubits, to operate universal logic gates and to test circuits for multi-qubit entanglement and simple quantum algorithms. The final objective is to gain sufficient knowledge for a realistic assessment of the scalability of Josephson junction technologies for information processing, contributing to a "Roadmap for Quantum Computing".

The proposal concerns development of an elementary scalable quantum processor using Josephson junction (charge and flux state) qubits, single-electron and SQUID technologies to achieve initiation, processing and read-out of information. The first objective is to improve and maintain coherence of several types of single qubits long enough for relevant operations to be performed. The major objective is to operate universal quantum gates using Josephson junction circuits, and to test circuits for entanglement of multi-qubit systems. In parallel, a theoretical analysis of the dynamics of qubit systems and quantum gates will be continued. Major objectives involve design optimisation, non-destructive control of qubit systems, effects of quantum leakage on multi-qubit operations, and fidelity of simple quantum algorithms.

The conceptual focus of research lies in "Quantum computing and communications" while the technologies employed fall within the area of "Nano-technology information devices". Low -capacitance super conducting tunnel junctions have a unique potential for buildings sufficiently large scale, still controllable coherent systems of qubits of information with long decoherence time. They represent one of the most promising and realistic approaches for creating a technology of quantum computers. At low temperatures the circuit variables (flux and charge) at the circuit nodes behave quantum mechanically. One can use external potentials on gate electrodes and external magnetic fields in SQUID loops to vary the quantum mechanical coupling in the systems; and tune the coherent superposition with external control "knobs" is an important step towards implementation of quantum computing schemes. Furthermore, the fact that one can design the circuit using standard electron lithography techniques makes them most appropriate for physical implementation. The role of dissipation and its influence on decoherence requires careful investigation and optimisation. A very important step was recently demonstrated by Vion et al.(submitted to science), who succeeded to manipulate Josephson junction quibits in a quantum coherent way over nearly one microsecond. The SQUIBIT-2 team successfully works with this technology and is therefore in an excellent position to accomplish real progress toward controllable few-qubit gates and eventually an elementary quantum processor using scalable solid-state nano-technology.

Call for proposal

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