Waeber A M, Gillard G, Ragunathan G, Hopkinson M, Spencer P, Ritchie D A, Skolnick M S, Chekhovich E A
Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK.
Walter Schottky Institut and Physik-Department, Technische Universität München, Am Coulombwall 4, 85748, Garching, Germany.
Nat Commun. 2019 Jul 17;10(1):3157. doi: 10.1038/s41467-019-11160-6.
Coherence of solid state spin qubits is limited by decoherence and random fluctuations in the spin bath environment. Here we develop spin bath control sequences which simultaneously suppress the fluctuations arising from intrabath interactions and inhomogeneity. Experiments on neutral self-assembled quantum dots yield up to a five-fold increase in coherence of a bare nuclear spin bath. Numerical simulations agree with experiments and reveal emergent thermodynamic behaviour where fluctuations are ultimately caused by irreversible conversion of coherence into many-body quantum entanglement. Simulations show that for homogeneous spin baths our sequences are efficient with non-ideal control pulses, while inhomogeneous bath coherence is inherently limited even under ideal-pulse control, especially for strongly correlated spin-9/2 baths. These results highlight the limitations of self-assembled quantum dots and advantages of strain-free dots, where our sequences can be used to control the fluctuations of a homogeneous nuclear spin bath and potentially improve electron spin qubit coherence.
固态自旋量子比特的相干性受到自旋浴场环境中的退相干和随机涨落的限制。在此，我们开发了自旋浴场控制序列，该序列能同时抑制浴场内部相互作用和不均匀性所产生的涨落。对中性自组装量子点的实验表明，裸核自旋浴场的相干性提高了多达五倍。数值模拟与实验结果相符，并揭示了一种涌现的热力学行为，即涨落最终是由相干性不可逆地转化为多体量子纠缠所导致的。模拟表明，对于均匀自旋浴场，我们的序列在使用非理想控制脉冲时也很有效，而即使在理想脉冲控制下，不均匀浴场的相干性本质上也是有限的，尤其是对于强相关的自旋 - 9/2 浴场。这些结果突出了自组装量子点的局限性以及无应变量子点的优势，在无应变量子点中，我们的序列可用于控制均匀核自旋浴场的涨落，并有可能提高电子自旋量子比特的相干性。
