Multi-Qubit Gates in Arrays Coupled by 'Always On' Interactions

Abstract

Recently there has been interest in the idea of quantum computing without control of the physical interactions between component qubits. This is highly appealing since the 'switching' of such interactions is a principal difficulty in creating real devices. It has been established that one can employ 'always on' interactions in a one-dimensional Heisenberg chain, provided that one can tune the Zeeman energies of the individual (pseudo-)spins. It is important to generalize this scheme to higher dimensional networks, since a real device would probably be of that kind. Such generalisations have been proposed, but only at the severe cost that the efficiency of qubit storage must *fall*. Here we propose the use of multi-qubit gates within such higher-dimensional arrays, finding a novel three-qubit gate that can in fact increase the efficiency beyond the linear model. Thus we are able to propose higher dimensional networks that can constitute a better embodiment of the 'always on' concept - a substantial step toward bringing this novel concept to full fruition.

20 pages in preprint format, inc. 3 figures. This version has fixed typos and printer-friendly figures, and is to appear in NJP

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• Quantum Computing in Arrays Coupled by 'Always On' Interactions
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• What is a quantum computer, and how do we build one?
• Optical Quantum Computation with Perpetually Coupled Spins
• Entanglement generation and protection by detuning modulation
• Efficient quantum computation within a disordered Heisenberg spin-chain
• Universal quantum computation by the unitary control of ancilla qubits and using a fixed ancilla-register interaction
• Molecular architectures based on pi-conjugated block copolymers for global quantum computation
• Overcoming disorder in superconducting globally driven quantum computing