Knight-field-enabled nuclear spin polarization in single quantum dots

We demonstrate dynamical nuclear-spin polarization in the absence of an external magnetic field by resonant circularly polarized optical excitation of a single electron or hole charged quantum dot. Optical pumping of the electron spin induces an effective inhomogeneous magnetic (Knight) field that determines the direction along which nuclear spins could polarize and enables nuclear-spin cooling by suppressing depolarization induced by nuclear dipole-dipole interactions. Our experiments constitute a first step towards a quantum measurement of the Overhauser field.     

Optical pumping of quantum-dot nuclear spins

Hyperfine interactions with randomly oriented nuclear spins present a fundamental decoherence mechanism for electron spin in a quantum dot, that can be suppressed by polarizing the nuclear spins. Here, we analyze an all-optical scheme that uses hyperfine interactions to implement laser cooling of quantum-dot nuclear spins. The limitation imposed on spin cooling by the dark states for collective spin relaxation can be overcome by modulating the electron wave function.     

Higher NORs-expression in lymphocyte of trisomy 21 babies/children: in vivo evaluation

Extra chromosome 21 of Down syndrome (DS) or trisomy 21 patients contains an average of 40 extra copies of rRNA genes and the in vivo regulation of these genes is not known. The objective of this work is to compare the NORs expression in interphase nuclei in non-stimulated lymphocytes of DS patients and healthy controls. Because the AgNOR staining is the indicator of the active rRNA genes, comparison of the image analysis values of AgNORs area between DS's and healthy controls' interphase lymphocytes is considered to be sufficient to evaluate the level of rDNA activities in the two groups. The Nucleolus Organizer Regions area/Total Nuclear area (NORa/TNa) was calculated using a computer program designed by us. 100 consecutive NORa/TNa per individual were evaluated. We report that 24 DS children's peripheral lymphocytes show significantly higher NORa/TNa mean value (6.32 +/- 1.77%) than that of the 20 healthy controls' cells (5.31 +/- 1.34%) (2-tailed Mann-Whitney U test, z = 19.4, P = 0.000). The same is true for the nucleolus (AgNOR spot) number per nucleus. The mean value of nucleoli number per nucleus in DS lymphocytes was significantly higher than that of the controls: z = 14.6, P = 0.000. In conclusion, extra rRNA genes on the chromosome 21 are not down-regulated in DS patients' lymphocytes. Rather, extra NORs expressions in 'in vivo' condition contribute to the increase of AgNORs area and AgNOR spots number per nucleus. This is the first work on the comparison of NORs activities in resting (non-stimulated) interphase lymphocytes between DS and healthy controls.     

High efficiency photon counting using stored light

We propose a method that can, in principle, achieve nearly ideal photon counting, by combining the techniques of photonic quantum memory and ion-trap quantum-state measurements. After mapping the quantum state of a propagating light pulse onto metastable collective excitations of a trapped cold atomic gas, it is possible to monitor the resonance fluorescence induced by an additional laser field that couples only to the metastable excited state. Even with a photon collection/detection efficiency as low as 10%, it is possible to achieve photon counting with efficiency exceeding 99%.