![]() ![]() Exploiting the strong electron-nuclear feedback we drive the inhomogeneous ensemble of electron spins into single frequency Larmor precession about a transverse magnetic field. We expose this inhomogeneous ensemble of singly-charged (In,Ga)As/GaAs QDs to a high repetition laser operated at 1 GHz rate. To prove its universality, we apply our method to an ensemble of QDs and detect their joint response. Using a single pulsed laser source it becomes possible to control the state of all QDs whose optical transitions fall into the spectrum of the laser at the same time. In this paper, we explore an alternative and universal tool that has relaxed requirements on spectral and other material contents-related differences of single QDs. All these experiments were realized on single QDs and required a high spectral precision. Further advancement in the reduction of nuclear spin fluctuations led to the possibility to implement all-optical access to the individual quantized transitions of the strongly coupled electron-nuclear spin systems 14. A way to reduce these fluctuations was first elaborated theoretically 8 and later demonstrated in a series of experiments 9, 10, 11, 12, 13. The idea to transfer the electron spin state to the surrounding nuclear spins is aggravated by the intrinsic nuclear spin fluctuations 4. The advantage of this approach is that the electron spin coherence is limited to several microseconds at low temperatures 5, but the nuclear spin coherence can last milliseconds 6, allowing in particular the implementation of quantum repeater schemes 7. ![]() The electron spin is coupled to the nuclear spins of the QD crystal lattice by the hyperfine interaction 4, which could allow one to design schemes where the angular momentum of the photon is transferred to the nuclear spins using the electron spin as auxiliary state. ![]() The prominent advantage of QDs is their strong optical dipole moment, which allows efficient coupling of photons to the confined electron spins, according to optical selection rules. One of the possible hybrid qubit realizations is the spin of an electron confined in a semiconductor quantum dot (QD), which is interacting with the surrounding nuclear spins 3. As the race for the best qubit candidate is still ongoing, it becomes clear that there will be no monolithic solution, but rather a hybrid solution combining different excitations, each exploiting its own best property while contributing to the common goal of the targeted quantum technology. At the heart of these technologies are solid state quantum bits (qubits) and their entanglement 3. This is confirmed by the development and first implementation of quantum communication 1 and quantum computing 2. The last decade has been marked by unprecedented progress in the development of quantum technologies. Finally, we show that the highly periodic optical excitation can be used as universal tool for strongly reducing the nuclear spin fluctuations and preparation of a robust nuclear environment for subsequent manipulation of the electron spins, also at varying operation frequencies. Furthermore, we demonstrate that an optical detuning of the pump pulses from the probed optical transitions induces a directed dynamic nuclear polarization and leads to a discretization of the total magnetic field acting on the electron ensemble. Despite the strong inhomogeneity of the electron g factor, the spectral spread of optical transitions, and the broad distribution of nuclear spin fluctuations, we are able to push the whole ensemble of excited spins into a single Larmor precession mode that is commensurate with the laser repetition frequency. The coherent electron spin dynamics of an ensemble of singly charged (In,Ga)As/GaAs quantum dots in a transverse magnetic field is driven by periodic optical excitation at 1 GHz repetition frequency.
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