given the observed cell fate frequencies and the
number of observed lineage trees, we estimated
the chance for such an outcome to be only 2.4%
(methods). Thus, we conclude that a model in
which the sporadic entry of R cells into the cell
cycle activates a developmental-like program of
fate, leading to a burst of neurogenic activity,
provides the most plausible explanation of the
In this study, we used chronic imaging of individual R cells and their progeny to characterize
the cellular dynamics underlying adult hippocampal
neurogenesis. Our data show that, after activation,
Ascl1-targeted R cells enter a developmental-like
program, eliciting a burst of neurogenic activity.
However, self-renewal is temporally limited: We
did not observe repeated shuttling between quies-cenceandproliferation, leadingto aloss ofactivated
R cells. These findings do not rule out the previously
reported presence of stem cells in the mammalian
DG that shuttle back and forth between quiescence and activity, dividing for extended periods
(7, 31, 32). Stem cell heterogeneity has been postulated, and the Ascl1-targeted population analyzed
here may not include all subtypes that are capable
of generating neuronal progeny in the adult DG
(33–35). Previous data suggested that about 10
to 15% of all granule cells are adult-generated
in the mouse hippocampus. This indicates that
adult neural stem cells generate 30,000 to 45,000
granule cells during the entire life span (5, 36, 37),
which, as a fraction of the total neuronal population, appears to be lower in the rodent than in the
human DG (38). We found that, once activated,
individual Ascl1-targeted R cells generated 4.8
neurons on average. On the basis of previous
estimates that the DG contains ~10,000 R cells in
2-month-old mice (8), the total number of cells
that can be generated by Ascl1-targeted cells with
the principles of clonal expansion described here
(~45,000) appears to be sufficient to explain a
substantial part of hippocampal neurogenesis.
Our in vivo imaging results elucidate the cellular
dynamics of physiological adult neurogenesis
and form the basis to understand the molecular
mechanisms governing the steps from dividing
stem cells to newborn neurons.
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We thank S. April for help with analyzing R cell morphology and
D. L. Moore and D. C. Lie for comments on the manuscript.
Funding: This work was supported by the European Research
Council (to S.J. and F.H.), the Swiss National Science Foundation
(BSCGI0_157859 to S.J.), the Zurich Neuroscience Center, and
the Wellcome Trust (098357/Z/12/Z to B.D.S.). G.A.P. was
supported by a European Molecular Biology Organization Long-Term Fellowship. M.B. was supported by a SystemsX transition
postdoctoral fellowship. Author contributions: G.A.P. developed
the imaging approach, performed imaging, analyzed data, and
cowrote the manuscript. S.B. performed imaging, analyzed data,
and revised the manuscript. S.C. codeveloped the imaging
approach and performed imaging. M.B. analyzed data and revised
the manuscript. D.J.J. and B.D.S. contributed to the concept,
performed theoretical modeling, and cowrote the manuscript.
F.H. contributed to the concept and revised the manuscript.
S.J. developed the concept and wrote the manuscript. Competing
interests: None declared. Data and materials availability: The
data reported are presented in the main paper and the
Materials and Methods
Figs. S1 to S7
Tables S1 and S2
Movies S1 to S3
27 July 2017; accepted 13 December 2017
Coherent single-atom superradiance
Junki Kim, Daeho Yang, Seung-hoon Oh, Kyungwon An*
Superradiance is a quantum phenomenon emerging in macroscopic systems whereby
correlated single atoms cooperatively emit photons. Demonstration of controlled collective
atom-field interactions has resulted from the ability to directly imprint correlations with an
atomic ensemble. Here we report cavity-mediated coherent single-atom superradiance:
Single atoms with predefined correlation traverse a high–quality factor cavity one by one,
emitting photons cooperatively with the N atoms that have already gone through the cavity
(N represents the number of atoms). Enhanced collective photoemission of N-squared
dependence was observed even when the intracavity atom number was less than unity.
The correlation among single atoms was achieved by nanometer-precision position control
and phase-aligned state manipulation of atoms by using a nanohole-array aperture. Our
results demonstrate a platform for phase-controlled atom-field interactions.
Superradiance is a collective radiation phe- nomenon by a number of quantum emit- ters (1). In the original prediction, exchange symmetry is present in closely packed emit- ters whose interparticle distance is much
smaller than the transition wavelength, and there-
fore dipole-dipole correlation emerges during their
spontaneous decay process. The correlation makes
the ensemble behave collectively and induces en-
hanced interaction with the vacuum fields, leading
to stronger and faster radiation emission compared
with the ordinary spontaneous emission. Early
experiments performed with a large number of
emitters (as in a dense atomic vapor or in a beam)
reported observations consistent with the predic-
tion (2, 3). Recent technical advances have enabled
the realization of superradiance in various systems,
such as a Bose-Einstein condensate (4), quantum
dots (5), and trapped atoms coupled to a cavity (6).
The mutual phase correlation among atoms is
the key to superradiance: It can make the ensem-
ble behave as a single macrodipole. Moreover,
direct control of atomic phases enables control-
lable collective atom-field interactions. In recent
experiments, the phase of atoms in an ensemble
662 9 FEBRUARY 2018 • VOL 359 ISSUE 6376 sciencemag.org SCIENCE
Department of Physics and Astronomy and Institute of
Applied Physics, Seoul National University, Seoul 08826,
Republic of Korea.
*Corresponding author. Email: email@example.com