Quantum Information Processing with Spin Systems: from modelling to realistic implementations

Íñigo Arrazola, Y. Minoguchi, Marc-Antoine Lemonde +2 more

We analyze the implementation of high-fidelity, phonon-mediated gate operations and quantum simulation schemes for spin qubits associated with silicon vacancy centers in diamond. Specifically, we show how the application of continuous dynamical decoupling techniques can substantially boost the coherence of the qubit states while increasing at the same time the variety of effective spin models that can be implemented in this way. Based on realistic models and detailed numerical simulations, we demonstrate that this decoupling technique can suppress gate errors by more than two orders of magnitude and enable gate infidelities below $\ensuremath{\sim}{10}^{\ensuremath{-}4}$ for experimentally relevant noise parameters. Therefore, when generalized to phononic lattices with arrays of implanted defect centers, this approach offers a realistic path toward moderate- and large-scale quantum devices with spins and phonons at a level of control that is competitive with other leading quantum-technology platforms.

Davide Rossini

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

Witold Aleksander Jacak

The recent huge increase of the interest in the implementation of quantum information processing (QIP) focused an attention on the semiconductor quantum dots (QDs) as nano-systems with controllable quantum states both in charge and spin degrees of freedom.This creates an opportunity for discussing and modeling of QD-based qubits and quantum-logic gates for prospective quantum computer.Despite of many efforts in this respect the progress is, however, disappointing and the barrier of so-called diVincenzo criteria required to be fulfilled for the QIP technology is not broken and even not approached in any realistic proposal of using QDs for qubits and quantum gates.The reason of this situation is linked with unavoidable restrictions imposed on the coherence and the coherent control of quantum states in QDs, which precludes scalable implementation of qubits and quantum gates based on QDs.The decoherence of charge and of spin degrees of freedom in QDs and QD-systems locates inconveniently straight in the middle of the required six-orders of magnitude diVincenzo window for time scale of the control in comparison to the decoherence rate.This leads to the so-called 'three-orders time-limit' for QIP implementations in QDs.Some advantages of spin degrees of freedom in QDs can be noticed, however.Even though the time scale of the decoherence of spin in of particular practical importance magnetic QDs still is located in the center of six-orders diVincenzo window, the amplitude of the phase decoherence of spin might be frozen on a small level in proximity of the zero temperature.Short critical overview of the dephasing restrictions imposed on the QD technology is the aim of this chapter.

János A. Bergou, Mark S. Hillery, Mark E. Saffman

Yang Dong, Shao-Chun Zhang, Y. H. Zheng +7 more

Experimental realization of a universal set of quantum logic gates with high fidelity is critical to quantum-information processing, which is always challenging due to the inevitable interaction between the quantum system and environment. Geometric quantum computation is noise immune, and thus, offers a robust way to enhance control fidelity. Here, we experimentally implement the recently proposed extensible nonadiabatic holonomic quantum computation with solid spins in diamond at room temperature, which maintains both flexibility and resilience against decoherence and system-control errors. Compared with the previous geometric method, the fidelities of a universal set of holonomic single-qubit and two-qubit quantum logic gates are improved in experiments. Therefore, this work makes a step towards high-fidelity quantum-information processing based on extensible nonadiabatic holonomic quantum computation in realistic systems.