Long-lived photon echo induced by nuclear spin fluctuations in charged InGaAs quantum dots

We study the role of the hyperfine interaction between nuclei and resident electrons in the formation of a three-pulse spin-dependent photon echo from self-assembled (In,Ga)As semiconductor quantum dots. In zero magnetic field we observe an oscillatory coherent optical response, which is detected in a time window of 10 ns, which is significantly longer than the radiative lifetime of trions of 0.26 ns. The oscillations occur due to spin precession of the resident electron spins in the effective fluctuating nuclear field, whose direction and magnitude are different in each quantum dot. We evaluate the mean field of nuclear spin fluctuations root < B-N(2)>=6.4 mT. Owing to the specific mechanism of spin initialization, which depends on the direction and magnitude of the effective nuclear field, the spin-dependent photon echo extends the possibilities for exploring the hyperfine interaction in semiconductor quantum dots.