similar to the Eratosthenian basalts beneath the
The Channel 1 data reveal that the Eratosthenian basalts at the landing site extend to a depth
of ~35 m (layer d in Fig. 2, A and B), which is
consistent with the depth estimated from nearby impact craters that have excavated deeper
Imbrian materials (14). Two clear interfaces that
feature higher radar reflection strengths are
shown at depths ~35 m and ~50 m (layer e in
Fig. 2B), respectively. This fifth layer (layer e), is
interpreted to be the paleoregolith formed on
top of the Imbrian lava flows (>~3.3 Ga) (11),
over which the Eratosthenian basalts were emplaced subsequently. A deeper layer between
~50 and 140 m has similar radar reflections to
the Eratosthenian basalts resolved in layer d,
suggesting that this layer probably represents
the latest Imbrian basalts that filled in the
Imbrium basin around 3.3 Ga (layer f in Fig.
2B). Other subhorizontal interfaces are visible
at depths larger than ~140 m, such as those at
depths of ~240 and ~360 m (layers g, h, and i
in Fig. 2B). Interestingly, layer g shows different
reflection texture compared with layers f and h.
The reflection wave is comparable to those of
bedded rocks—e.g., sedimentary or pyroclastic
rocks on Earth. Considering the geological history of the lunar mare area (15), we propose that
this layer is probably bedded or interlayered lava
flow and/or pyroclastic rocks or thin and multilayered basaltic lavas.
Current regional geologic studies suggest that
at least five episodes of lava eruptions filled the
northeast region of the Imbrium basin, forming
about 1-km-thick basaltic layers (16). Yutu’s LPR
has revealed five distinct episodes of pyroclastic/
lava filling events within the upper ~400 m depth,
although it is very likely that more episodes of
volcanic eruptions have filled the Imbrium basin
at greater depths (8).
Integrated geologic and geophysical explorations using the scientific payloads onboard the
Yutu rover have revealed the detailed subsurface
geological structures and the geological history
of this area. Compared with previous Apollo and
Luna landing sites, this area has the youngest
mare basalts that appear to have unusual petro-fabric characteristics. The LPR data have revealed
complex subsurface structures of shallow crust
within the mare, providing valuable information
to reveal the lava eruption extents, style, and filling history within the Imbrium basin and the
production history of regolith since ~3.3 Ga (Fig.
3). The available data suggest that the diversity of
geological characteristics and thermal history
of different lunar mare areas indicates there is
more complex geological history than we had
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All the authors acknowledge support from the Key Research
Program of the Chinese Academy of Sciences (grant
KGZD-EW-603). L.X., Z. Y.X., J.N.Z., L.Q., and J.H. acknowledge
support of the Natural Science Foundation of China (grant
41373066). X.P.Z. acknowledges support from the Science and
Technology Development Fund (FDCT) of Macau (grants
068/2011/A, 048/2012/A2, and 091/2013/A3). We thank C. L. Li
and the Ground Application System of Lunar Exploration, National
Astronomical Observatories, Chinese Academy of Sciences, for
their valuable and efficient help on data calibration and supplying.
Author contributions: L.X., Z. Y.X., J.N.Z., L.Q., Y.L.Z., J.H., H.Z.,
X.P.Z., J. W., Q. Huang, and Q. He processed the imagery data
and conducted image and radar data interpretation and geological
analysis. P.M.Z., G. Y.F., N.Z., and Y.F. Y processed LPR data and
did interpretation. B.Z, Y.C.J., Q. Y.Z., S.X.S., Y.X.L., and Y.Z.G.
are team members of the LPR instrument. All authors contributed
to the writing of the paper. The imagery data obtained by
the Panoramic Camera onboard Yutu are the level 2C data.
The imagery data obtained by the Descent Camera onboard
the Chang’E-3 lander are the level 2A data. The IDs for the images
used in the figures are listed in table S2 in the supplementary
materials. Data presented in this paper are hosted at
Materials and Methods
Figs. S1 to S14
Tables S1 and S2
11 August 2014; accepted 5 February 2015
Strongly correlated quantum
walks in optical lattices
Philipp M. Preiss,1 Ruichao Ma,1 M. Eric Tai,1 Alexander Lukin,1 Matthew Rispoli,1
Philip Zupancic,1 Yoav Lahini,2 Rajibul Islam,1 Markus Greiner1†
Full control over the dynamics of interacting, indistinguishable quantum particles is an
important prerequisite for the experimental study of strongly correlated quantum
matter and the implementation of high-fidelity quantum information processing. We
demonstrate such control over the quantum walk—the quantum mechanical analog of
the classical random walk—in the regime where dynamics are dominated by interparticle
interactions. Using interacting bosonic atoms in an optical lattice, we directly observed
fundamental effects such as the emergence of correlations in two-particle quantum walks,
as well as strongly correlated Bloch oscillations in tilted optical lattices. Our approach can
be scaled to larger systems, greatly extending the class of problems accessible via
Quantum walks are the quantum me- chanical analogs of the classical random walk process, describing the propagation of quantum particles on periodic poten- tials (1, 2). Unlike classical objects, par-
ticles performing a quantum walk can be in a
superposition state and take all possible paths
through their environment simultaneously, lead-
ing to faster propagation and enhanced sensi-
tivity to initial conditions. These properties have
generated considerable interest in using quan-
tum walks for the study of position-space quan-
tum dynamics and for quantum information
processing (3). Two distinct models of quantum
walk with similar physical behavior were devised:
(i) the discrete-time quantum walk (1), in which
the particle propagates in discrete steps deter-
mined by a dynamic internal degree of freedom,
and (ii) the continuous-time quantum walk (2),
in which the dynamics is described by a time-
independent lattice Hamiltonian.
Experimentally, quantum walks have been im-
plemented for photons (4), trapped ions (5, 6),
and neutral atoms (7–9), among other platforms
(4). Until recently, most experiments were aimed
at observing the quantum walks of a single quan-
tum particle, which are described by classical
SCIENCE sciencemag.org 13 MARCH 2015 • VOL 347 ISSUE 6227 1229
1Department of Physics, Harvard University, Cambridge, MA
02138, USA. 2Department of Physics, Massachusetts
Institute of Technology, Cambridge, MA 02139, USA.
*Present address: Institute for Quantum Electronics, ETH Zürich,
8093 Zürich, Switzerland. †Corresponding author. E-mail:
RESEARCH | REPORTS