Ultrafast all-optical switching by single photons

An outstanding goal in quantum optics is the realization of fast optical non-linearities at the single-photon level. Such non-linearities would allow for the realization of optical devices with new functionalities such as a single-photon switch/transistor or a controlled-phase gate, which could form the basis of future quantum optical technologies. While non-linear optics effects at the single-emitter level have been demonstrated in different systems, including atoms coupled to Fabry-Perot or toroidal micro-cavities, super-conducting qubits in strip-line resonators or quantum dots (QDs) in nano-cavities, none of these experiments so far has demonstrated single-photon switching on ultrafast timescales. Here, we demonstrate that in a strongly coupled QD-cavity system the presence of a single photon on one of the fundamental polariton transitions can turn on light scattering on a transition from the first to the second Jaynes-Cummings manifold with a switching time of 20 ps. As an additional device application, we use this non-linearity to implement a single-photon pulse-correlator. Our QD-cavity system could form the building-block of future high-bandwidth photonic networks operating in the quantum regime

Bovine nuclear transfer embryo development using cells derived from a cloned fetus

Many different cell types have been used to generate nuclear transfer embryos and fetuses. However, little is known about the potential of fibroblasts derived from a nuclear transfer fetus as donor cells for nuclear transfer. The ability of cloned fetuses or animals to be cloned themselves is of great interest in determining whether successive generations of clones remain normal or accumulate genetic or phenotypic abnormalities. We generated a bovine fibroblast cell line from a cloned fetus, that continued to divide beyond 120 days (94 doublings,18 passages) in continuous culture. As long-term survival of cells in culture is a desirable characteristic for use in transgenic cell production, passage 2 and 18 cells were compared as donor cells for nuclear transfer (NT). When cells from passage 2 (2 weeks in culture) and passage 18 (4 months in culture) were used for nuclear transfer, there was no significant difference in development rate to blastocyst (35.3 versus 44.6%, P = 0.07). A greater proportion of late passage cells were in G0/G1 whether under serum-fed (64 versus 56%, P < 0.01) or serum-starved (95 versus 88%, P < 0.01) culture conditions. Following embryo transfer, equivalent day 30 pregnancy rates were observed for each group (P 2:2/19 versus P 18: 2/13). A slightly retarded fetus was surgically removed at day 56 and the remaining three fetuses died in utero by day 60 of gestation. Our results show that fibroblast cells derived from regenerated cloned fetuses are capable of both in vitro and in vivo development. The longevity of this regenerated cell line would allow more time for genetic manipulations and then to identify stable transfected cells prior to their use as NT donor cells. Although no live fetuses were produced in this study the results provide encouraging data to show that a cloned fetus can itself be recloned to produce another identical cloned fetus. Further studies on this and other recloned fetuses are necessary to determine whether the failure to produce live offspring was a result of inadequate sample size or due to the cell type selected. (C) 2001 Elsevier Science B.V. All rights reserved

Development rates of male bovine nuclear transfer embryos derived from adult and fetal cells

This study compared the nuclear transfer (NT) embryo development rates of adult and fetal cells within the same genotype. The adult fibroblast cells were obtained from a 21-yr-old Brahman bull. The fetal cells were derived from a Day 40 NT fetus previously cloned using cells from the Brahman bull. Overall, similar numbers of blastocysts developed from both adult (53 of 190; 28%) and fetal (39 of 140; 28%) donor cells. Improved blastocyst development rates were observed when fetal cells were serum-starved (serum-fed 12% vs. serum-starved 43%; P < 0.01) whereas there was no similar benefit when adult cells were serum-starved (both serum-fed and serum-starved 28%)

Evidence for placental abnormality as the major cause of mortality in first-trimester somatic cell cloned bovine fetuses

The production of cloned animals is, at present, an inefficient process. This study focused on the fetal losses that occur between Days 30-90 of gestation. Fetal and placental characteristics were studied from Days 30-90 of gestation using transrectal ultrasonography, maternal pregnancy specific protein b (PSPb) levels, and postslaughter collection of fetal tissue. Pregnancy rates at Day 30 were similar for recipient cows carrying nuclear transfer (NT) and control embryos (45% [54/120] vs. 58% [11/191), although multiple NT embryos were often transferred into recipients. From Days 30-90, 82% of NT fetuses died, whereas all control pregnancies remained viable. Crown-rump (CR) length was less in those fetuses that were destined to die before Day 90, but no significant difference was found between the CR lengths of NT and control fetuses that survived to Day 90. Maternal PSPb levels at Days 30 and 50 of gestation were not predictive of fetal survival to Day 90. The placentas of six cloned and four control tin vivo or in vitro fertilized) bovine pregnancies were compared between Days 35 and 60 of gestation. Two cloned placentas showed rudimentary development, as indicated by flat, cuboidal trophoblastic epithelium and reduced vascularization, whereas two others possessed a reduced number of barely discernable cotyledonary areas. The remaining two cloned placentas were similar to the controls, although one contained hemorrhagic cotyledons. Poor viability of cloned fetuses during Days 35-60 was associated with either rudimentary or marginal chorioallantoic development. Our findings suggest that future research should focus on factors that promote placental and vascular growth and on fetomaternal interactions that promote placental attachment and villous formation