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arXiv · 1309.4430

High fidelity spin entanglement using optimal control

Florian Dolde·Ville Bergholm·Ya Wang·Ingmar Jakobi·Sebastien Pezzagna·Jan Meijer·Philipp Neumann·T. Schulte-Herbrueggen·Jacob Biamonte·Jörg Wrachtrup
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Abstract

Precise control of quantum systems is of fundamental importance for quantum device engineering, such as is needed in the fields of quantum information processing, high-resolution spectroscopy and quantum metrology. When scaling up the quantum registers in such devices, several challenges arise: individual addressing of qubits in a dense spectrum while suppressing crosstalk, creation of entanglement between distant nodes, and decoupling from unwanted interactions. The experimental implementation of optimal control is a prerequisite to meeting these challenges. Using engineered microwave pulses, we experimentally demonstrate optimal control of a prototype solid state spin qubit system comprising thirty six energy levels. The spin qubits are associated with proximal nitrogen-vacancy (NV) centers in diamond. We demonstrate precise single-electron spin qubit operations with an unprecedented fidelity F \approx 0.99 in combination with high-efficiency storage of electron spin states in a nuclear spin quantum memory. Matching single-electron spin operations with spin-echo techniques, we further realize high-quality entangled states (F > 0.82) between two electron spins on demand. After exploiting optimal control, the fidelity is mostly limited by the coherence time and imperfect initialization. Errors from crosstalk in a crowded spectrum of 8 lines as well as detrimental effects from active dipolar couplings have been simultaneously eliminated to unprecedented extent. Finally, by entanglement swapping to nuclear spins, nuclear spin entanglement over a length scale of 25 nm is demonstrated. This experiment underlines the importance of optimal control for scalable room temperature spin-based quantum information devices.

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Florian Dolde, Ville Bergholm, Ya Wang, Ingmar Jakobi, Sebastien Pezzagna, Jan Meijer, Philipp Neumann, T. Schulte-Herbrueggen, Jacob Biamonte, Jörg Wrachtrup. 2013-09-17. High fidelity spin entanglement using optimal control. https://doi.org/10.1038/ncomms4371

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