Quadrupolar induced suppression of nuclear spin bath fluctuations in self-assembled quantum dots

Abstract: Decoherence in quantum logic gates (qubits) due to interaction with the surrounding environment is a major obstacle to the practical realization of quantum information technologies. For solid state electron-spin qubits the interaction with nuclear spins is the main problem. One particular, neradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear-nuclear dipolar interactions. Due to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here we report direct measurement of nuclear spin bath coherence in individual strained InGaAs/GaAs quantum dots: nuclear spin-echo coherence times in the range T2~1.2 - 4.5 ms are found. Based on these T2 values we demonstrate that quadrupolar interactions make nuclear fluctuations in strained quantum dots much slower compared to lattice matched GaAs/AlGaAs structures. Such fluctuation suppression is particularly strong for arsenic nuclei due to the effect of atomic disorder of gallium and indium alloying. Our findings demonstrate that quadrupolar effects can help to solve the long-standing challenge of designing a scalable hardware for quantum computation: III-V semiconductor spin-qubits can be engineered to have a noise-free nuclear spin bath (previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling is challenging).