Optical initialization, readout, and dynamics of a Mn spin in a quantum dot

We have investigated the spin preparation efficiency by optical pumping of individual Mn atoms embedded in CdTe/ZnTe quantum dots. Monitoring the time dependence of the intensity of the fluorescence during the resonant optical pumping process in individual quantum dots allows to directly probe the dynamics of the initialization of the Mn spin. This technique presents the convenience of including preparation and readout of the Mn spin in the same step. Our measurements demonstrate that Mn spin initialization, at zero magnetic field, can reach an efficiency of 75% and occurs in the tens of nanoseconds range when a laser resonantly drives at saturation one of the quantum-dot transition. We observe that the efficiency of optical pumping changes from dot-to-dot and is affected by a magnetic field of a few tens of millitesla applied in Voigt or Faraday configuration. This is attributed to the local strain distribution at the Mn location which predominantly determines the dynamics of the Mn spin under weak magnetic field. The spectral distribution of the spin-flip-scattered photons from quantum dots presenting a weak optical pumping efficiency reveals a significant spin relaxation for the exciton split in the exchange field of the Mn spin.

Optical control of the spin state of two Mn atoms in a quantum dot

We report on the optical spectroscopy of the spin of two magnetic atoms (Mn) embedded in an individual quantum dot interacting with a single electron, a single exciton, or a single trion. As a result of their interaction to a common entity, the Mn spins become correlated. The dynamics of this process is probed by time-resolved spectroscopy, which permits us to determine an optical orientation time in the range of a few tens of nanoseconds. In addition, we show that the energy of the collective spin states of the two Mn atoms can be tuned through the optical Stark effect induced by a resonant laser field.

Parti communiste et féminisme. De l’antifascisme à la transition démocratique en Espagne

Dans les années 1930, les femmes membres du Parti communiste espagnol (PCE) collaborent avec des représentantes du féminisme et réclament une égalité pour les femmes sans pour autant se déclarer féministes. Pendant la guerre civile, elles ne remettent pas en question l’attribution de tâches maternelles aux femmes, mais elles revendiquent une participation politique dans les mêmes conditions que les hommes. Au cours des années 1970 cependant, la culture politique communiste traditionnelle, qui repose sur une relation de genre inégale, est remplacée par une nouvelle culture, dans laquelle socialisme et égalité vont de pair. Pendant la transition démocratique, les militantes se considèrent comme féministes et demandent que les fondements théoriques du féminisme soient assumés par le Parti.