Hybrid quantum computing

A quantum computer uses superposition states to accomplish tasks (e.g., database search and factoring of integers) more efficiently than any known classical computing strategy. In conventional registers for quantum information processing, quantum bits are associated with individual two-level quantum systems. Separate addressing and interaction with these systems permit one-bit gates, while an interaction between systems is needed
to accomplish two-bit gates.

The seminar will review recent theoretical proposals to implement quantum computing in collective excitation degrees of freedom in ensembles of
identical quantum systems. In these proposals one does not address individual particles, but one needs a suitable global interaction to perform
quantum logic operations in the system.

Such a global interaction exists in hybrid systems where large ensembles of electron or nuclear spins in a solid are collectively coupled to
superconducting qubit elements via a quantized cavity field. These physical components are optimal for the very different tasks of stable memory and
rapid processing functions, needed in a quantum computer  The main ideas of the spin-ensemble encoding and impressive preliminary proof-of-principle
experiments will be discussed.