All-optical implementation of a dynamic decoupling protocol for hole spins in (In,Ga)As quantum dots

We demonstrate the potential of a periodic laser-pulse protocol for dynamic decoupling of hole spins in (In,Ga)As quantum dots from surrounding baths. When doubling the repetition rate of inversion laser pulses between two reference pulses for orienting the spins, we find that the spin coherence time is increased by a factor of 2.

Figure 1

(a) Time-resolved ellipticity measurements at $B=1$ T with pump-probe repetition period $T_R=132$ ns at $T=6$ K. The black, top trace shows the spin polarization around the pump incidence at zero delay without applying RPs. The middle, blue trace shows a measurement with an additional RP train shifted by 1.1 ns to earlier times (see the green arrow) relative to the pump train with a RP period $T_{\text{RP}}=13.2$ ns, resulting in a hole spin echo 2.2 ns before pump incidence. In the lower, red trace the RP period is reduced to $T_{\text{RP}}=6.6$ ns so that the number of rotations between two pump pulses is doubled compared to the 13.2-ns RP period. (b) Scheme of RP application (green) and echo appearance (blue upper trace) for $T_{\text{RP}}=13.2$ ns between two pump pulses (black) with $T_R=79.2$ ns. (c) Echo appearance (red upper trace) for $T_{\text{RP}}=6.6$ ns. The additional RP incidences are indicated by the open green pulses.

Figure 2

Spin-echo emergence at time $2\Delta t$ for different arrival times $\Delta t$ of the RP, $-1.5$ and $-1$ ns, as indicated by the green arrows before pump pulse arrival at zero delay. $B$ = 1 T at $T$ = 6 K.

Figure 3

(a) Normalized ellipticity amplitude of mode-locked hole spins right before a pump pulse in dependence of the time after previous pump incidence $t=T_R$ without RP application. (b) Normalized echo amplitudes in dependence of the time after previous pump incidence $t=T_R+2\Delta t$ with $\Delta t=-1.1$ ns for a RP separation of $T_{\text{RP}}=13.2$ ns. (c) Normalized echo amplitudes for $T_{\text{RP}}=6.6$ ns.