Strong hyperfine-induced modulation of an optically driven hole spin in an InAs quantum dot

Abstract

Compared to electrons, holes in InAs quantum dots have a significantly weaker hyperfine interaction that leads to less dephasing from nuclear spins. Thus many recent studies have suggested that nuclear spins are unimportant for hole spin dynamics compared to electric field fluctuations. We show that the hole hyperfine interaction can have a strong effect on hole spin coherence measurements through a nuclear feedback effect. The nuclear polarization is generated through a unique process that is dependent on the anisotropy of the hole hyperfine interaction and the coherent precession of nuclear spins, giving rise to strong modulation at the nuclear precession frequency.The hyperfine interaction between electron spins and nuclear spins in solid state materials has been of particular interest over the past decade, largely driven by a desire to take advantage of electron spins as quantum bits [1]. For electron spins in quantum dots (QDs), the hyperfine interaction with a bath of nuclear spins is the dominant source of dephasing as fluctuations in the nuclear polarization induce fluctuations in the electron spin precession frequency through the Overhauser shift [2,3]. For holes, however, the contact hyperfine interaction, which dominates for electron spins, is suppressed due to the p orbital symmetry of the top of the valence band. The dipole-dipole hyperfine interaction is still present, but it is an order of magnitude weaker and is very anisotropic [4][5][6][7][8][9], leading to hopes of a highly coherent hole spin qubit.

Maximizing the purity of a qubit evolving in an anisotropic environment

“…These out-of-phase modulations generally lead to a sequence of maxima at twice the nuclear Larmor frequency, similar to the result seen for modulations in the experiment of Ref. 42. We note that the same modulations with the same frequency are predicted within this model for free-induction decay [the limit n = 0 of an n-pulse dynamical decoupling sequence, see Eq.…”

“…42 Those experiments showed similar modulations as seen here, although the authors of Ref. 42 have interpreted the modulations in their data in terms of a dynamic nuclear polarization effect. Two of the correlators above are shown for typical experimental parameters in Fig.…”

“…37 Measurements of a coherent-population-trapping dip 39,40 have suggested long hole-spin coherence times, 100 ns. These measurements have been supported by timedomain studies for single-hole spin echoes 41,42 and modelocking or spin-echo measurements for ensembles. 43,44 Alternative measurements of hole-spin dynamics have been performed through spin-noise spectroscopy, revealing a probable anisotropic decay of hole-spin coherence.…”

“…(77) [40][41][42] we expect some contribution from the second term to survive this dephasing mechanism. Such a pure-dephasing process is investigated in detail in Sec.…”

Consequences of Spin-Orbit Coupling at the Single Hole Level: Spin-Flip Tunneling and the Anisotropic g Factor

“…The hole properties are traced to the amount of HH-LH subband mixing [12,13], which is related to the details of quantum confinement, strain, and the spin-orbit interaction. The early prediction of greatly reduced hyperfine interaction between hole and nuclear spins, and concomitant increased coherence times [14,15], were confirmed experimentally in systems with small HH-LH mixing realized as selfassembled dots (SADs) [16][17][18] or nanowires [19]. In this regime the strong anisotropy of the hole g-factor is expected [12].…”