Nuclear spins in nanostructures

Abstract

We review recent theoretical and experimental advances toward understanding the effects of nuclear spins in confined nanostructures. These systems, which include quantum dots, defect centers, and molecular magnets, are particularly interesting for their importance in quantum information processing devices, which aim to coherently manipulate single electron spins with high precision. On one hand, interactions between confined electron spins and a nuclear-spin environment provide a decoherence source for the electron, and on the other, a strong effective magnetic field that can be used to execute local coherent rotations. A great deal of effort has been directed toward understanding the details of the relevant decoherence processes and to find new methods to manipulate the coupled electron-nuclear system. A sequence of spectacular new results have provided understanding of spin-bath decoherence, nuclear spin diffusion, and preparation of the nuclear state through dynamic polarization and more general manipulation of the nuclear-spin density matrix through ''state narrowing.'' These results demonstrate the richness of this physical system and promise many new mysteries for the future. 1 Introduction The last several years have seen a series of breakthroughs in single-spin measurement and manipulation, motivated in large part by the potential for future quantum information processing devices [1,2]. The spin coherence times for confined electrons in semiconductor quantum dots [3][4][5][6][7][8][9][10], phosphorus donor impurities in silicon [11,12], nitrogen vacancy (NV) centers in diamond [13][14][15], and in molecular magnets [16,17] is typically limited by the interaction between the electron and nuclear spins in the host material. The coherent manipulation of electron spins therefore requires a complete understanding of the nuclear spins in these materials, typically in the presence of localized electrons.A great deal of work has been done many years ago on ensembles of electron spins at donor impurities, including experimental [18][19][20] and theoretical [21,22] studies of

Hyperfine interactions in two-dimensional HgTe topological insulators

“…29 Hyperfine (HF) interactions between the electron and nuclear spins can play an important role in nanostructureseven though it is often weak. [30][31][32][33] For instance, in quantum dots, HF interactions can limit the coherence of single electronic spins [34][35][36][37] and, moreover, it can even lead to current hysteresis due to bistability of the dynamical nuclear spin polarization. [38][39][40][41] A HF-induced nuclear spin ordering in interacting 1D [42][43][44] and 2D 45,46 systems has also been discussed.…”

“…[38][39][40][41] A HF-induced nuclear spin ordering in interacting 1D [42][43][44] and 2D 45,46 systems has also been discussed. Most studies consider the so-called contact HF interaction, [30][31][32][33] which is relevant for electrons in orbital states with S-like symmetry, e.g., the conduction band in GaAs. …”

“…Moreover, we have included the atomic volume 81 v a explicitly here as it is often done for HF related calculations. [47][48][49][50] It depends on the choice of the individual normalization of the envelope functions and the lattice periodic functions, respectively, if v a should be included explicitly, 30 as discussed in Appendix B.…”

Maximizing the purity of a qubit evolving in an anisotropic environment

“…67. For heavy holes, the ratio |A/A (e) | of hole to electron hyperfine coupling strengths has been estimated theoretically 33 in GaAs and confirmed experimentally 68,69 in InGaAs and InP/GaInP to be of order |A/A (e) | ∼ 0.1.…”

Hyperfine induced electron spin and entanglement dynamics in double quantum dots: The case of separate baths

“…10 we illustrate the rule by plotting the dynamics for randomly correlated initial states with coefficients in [−1,1] by considering parameters satisfying and violating Eq. (14). We choose a rather small system of I = 40 and concentrate on the case of broken inversion symmetry = 0.019A.…”