Electron-spin quantum computation: Three- and four-body interactions and other implementation challenges

Ryan Woodworth, Ari Mizel, Daniel A. Lidar

Electron spins in semiconductor quantum dots are promising candidates for the experimental realization of solid-state qubits. We analyse the dynamics of a system of three qubits arranged in a linear geometry and a system of four qubits arranged in a square geometry. Calculations are performed for several quantum dot confining potentials. In the three-qubit case, three-body effects are identified that have an important quantitative influence upon quantum computation. In the four-qubit case, the full Hamiltonian is found to include both three-body and four-body interactions that significantly influence the dynamics in physically relevant parameter regimes. We consider the implications of these results for the encoded universality paradigm applied to the four-electron qubit code; in particular, we consider what is required to circumvent the four-body effects in an encoded system (four spins per encoded qubit) by the appropriate tuning of experimental parameters.

Klaus Mølmer, Arzhang Ardavan, Andrew D. Briggs +4 more

Ari Mizel, Daniel A. Lidar

In the effort to design and to construct a quantum computer, several leading proposals make use of spin-based qubits. These designs generally assume that spins undergo pairwise interactions. We point out that, when several spins are engaged mutually in pairwise interactions, the quantitative strengths of the interactions can change and qualitatively new terms can arise in the Hamiltonian, including four-body interactions. In parameter regimes of experimental interest, these coherent effects are large enough to interfere with computation and may require new error correction or avoidance techniques.

M. E. Hawley, Geoff W. Brown, G. P. Berman

Thomas Schäpers

Wen-Zhang Liu, Jinfu Zhang, Long, Gui Lu

Four-body interaction plays an important role in many-body systems, and it can exhibit interesting phase transition behaviors. Historically it was the need to efficiently simulate quantum systems that lead the idea of a quantum computer. In this Letter, we report the experimental demonstration of a four-body interaction in a four- qubit nuclear magnetic resonance quantum information processor. The strongly modulating pulse is used to implement spin selective excitation. The results show a good agreement between theory and experiment.