Ultrafast conditional carrier dynamics in semiconductor quantum dots

We provide direct evidence that the macroscopic response of the gain dynamics in electrically-pumped InGaAs/GaAs quantum dots is a superposition of intradot relaxation dynamics from microstates with multiple discrete carrier numbers. The gain recovery in the presence of an optical pre-pump fully depleting the ground-state gain is measured to be faster than without pre-pump. This effect, opposite to expectations from rate equations with mean-field carrier distributions, is due to a conditional gain recovery in which microstates with slow internal dynamics are suppressed by the pre-pump. The effect is evident at 15K and still observable at 300 K, beneficial for high-speed optical signal processing.