Within the last several years, considerable progress has been made in developing a quantum computer, which holds the promise of solving problems a lot more efficiently¹ than a classical computer. Physicists² are now able to realize the basic building blocks, the quantum bits (qubits) in a laboratory, control them and use them for simple computations. For practical application, a particular class of quantum computers, the so-called adiabatic quantum computer, has recently generated a lot of interest among researchers and industry. It is designed to solve real-world optimization³ problems conventional computers are not able to tackle. All current approaches for adiabatic quantum computation face the same challenge: The problem is encoded in the interaction between qubits; to encode a generic⁴ problem, an all-to-all connectivity is necessary, but the locality of the physical quantum bits limits the available interactions. "The programming language of these systems is the individual interaction between each physical qubit. The possible input⁵ is determined⁶ by the hardware. This means that all these approaches face a fundamental challenge when trying to build a fully⁷ programmable quantum computer," explains Wolfgang Lechner from the Institute for Quantum Optics and Quantum Information (IQOQI) at the Austrian Academy of Sciences in Innsbruck.

 

Theoretical physicists Wolfang Lechner, Philipp Hauke and Peter Zoller have now proposed a completely new approach. The trio, working at the University of Innsbruck and the IQOQI, suggest overcoming the challenges by detaching the logical qubit from the physical implementation⁸. Each physical qubit corresponds to one pair of logical qubits and can be tuned⁹ by local fields. These could be electrical fields when dealing¹⁰ with atoms and ions or magnetic fields in superconducting qubits. "Any generic optimization problem can be fully programmed via the fields," explains co-author Philipp Hauke from the Institute for Theoretical Physics at the University of Innsbruck, Austria. "By using this approach we are not only avoiding the limitations posed by the hardware but we also make the technological¹¹ implementation scalable."

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