Hybridization and Spin Decoherence in Heavy-Hole Quantum Dots

We theoretically investigate the spin dynamics of a heavy hole confined to an unstrained III-V semiconductor quantum dot and interacting with a narrowed nuclear-spin bath. We show that band hybridization leads to an exponential decay of hole-spin superpositions due to hyperfine-mediated nuclear pair flips, and that the accordant single-hole-spin decoherence time $T_2$ can be tuned over many orders of magnitude by changing external parameters. In particular, we show that, under experimentally accessible conditions, it is possible to suppress hyperfine-mediated nuclear-pair-flip processes so strongly that hole-spin quantum dots may be operated beyond the “ultimate limitation” set by the hyperfine interaction which is present in other spin-qubit candidate systems.

Figure 1

Decoherence rate $1/T_2$ from Eq. (12) as a function of the HH Zeeman energy ${\omega }_n=g_h{\mu }_{B}B+pI{A}_{\mathrm{HH}}$. For $L=10\mathrm{nm}$ and $a_z=4\mathrm{nm}$, we estimate $N\simeq 7.3\times {10}^4$. Inset: $1/T_2$ for fields up to 1 T (axes in the same units as in the main figure).

Figure 2

Maximum of the decoherence rate $1/T_2$ as a function of the QD height $a_z$. For increasing $a_z$, the maximal value of $1/T_2$ decreases (see main plot) and the position of the maximum is shifted (see inset).