6,444 research outputs found
Status of the Daya Bay Reactor Neutrino Oscillation Experiment
The last unknown neutrino mixing angle is one of the
fundamental parameters of nature; it is also a crucial parameter for
determining the sensitivity of future long-baseline experiments aimed to study
CP violation in the neutrino sector. Daya Bay is a reactor neutrino oscillation
experiment designed to achieve a sensitivity on the value of
to better than 0.01 at 90% CL. The experiment consists of
multiple identical detectors placed underground at different baselines to
minimize systematic errors and suppress cosmogenic backgrounds. With the
baseline design, the expected anti-neutrino signal at the far site is about 360
events per day and at each of the near sites is about 1500 events per day. An
overview and current status of the experiment will be presented.Comment: 4 pages, 4 figures. Proceedings of the 35th International Conference
of High Energy Physics, July 22-28, 2010, Paris, Franc
Signatures of strong correlation effects in RIXS on Cuprates
Recently, spin excitations in doped cuprates are measured using the resonant
inelastic X-ray scattering (RIXS). The paramagnon dispersions show the large
hardening effect in the electron-doped systems and seemingly
doping-independence in the hole-doped systems, with the energy scales
comparable to that of the antiferromagnetic magnons. This anomalous hardening
effect was partially explained by using the strong coupling t-J model but with
a three-site term(Nature communications 5, 3314 (2014)). However we show that
hardening effect is a signature of strong coupling physics even without
including this extra term. By considering the t-t'-t"-J model and using the
Slave-Boson (SB) mean field theory, we obtain, via the spin-spin
susceptibility, the spin excitations in qualitative agreement with the
experiments. These anomalies is mainly due to the doping-dependent bandwidth.
We further discuss the interplay between particle-hole-like and paramagnon-like
excitations in the RIXS measurements.Comment: 7 pages, 6 figure
Exact Quantum Many-Body Scar States in the Rydberg-Blockaded Atom Chain
A recent experiment in the Rydberg atom chain observed unusual oscillatory
quench dynamics with a charge density wave initial state, and theoretical works
identified a set of many-body "scar states" showing nonthermal behavior in the
Hamiltonian as potentially responsible for the atypical dynamics. In the same
nonintegrable Hamiltonian, we discover several eigenstates at \emph{infinite
temperature} that can be represented exactly as matrix product states with
finite bond dimension, for both periodic boundary conditions (two exact
states) and open boundary conditions (two states and one each ). This discovery explicitly demonstrates violation of strong
eigenstate thermalization hypothesis in this model and uncovers exact quantum
many-body scar states. These states show signatures of translational symmetry
breaking with period-2 bond-centered pattern, despite being in one dimension at
infinite temperature. We show that the nearby many-body scar states can be well
approximated as "quasiparticle excitations" on top of our exact scar
states, and propose a quasiparticle explanation of the strong oscillations
observed in experiments.Comment: Published version. In addition to (v2): (1) Add additional proofs to
the exact scar states and intuitions behind SMA and MMA to the appendices.
(2) Add entanglement scaling of SMA and MMA to the appendice
Non-magnetic Stern-Gerlach Experiment from Electron Diffraction
Using the wave nature of the electrons, we demonstrate that a transverse spin
current can be generated simply by the diffraction through a single slit in the
spin-orbital coupling system of the two-dimensional electron gas. The
diffracted electron picks up the transverse momentum. The up spin electron goes
one way and the down spin electron goes the other, producing the coherent spin
current. In the system of spin-orbital coupling eVm, the
\emph{out-of-plane} component of the spin of the electron can be generated up
to 0.42 . Based on this effect, a novel device of grating to distill
spin is designed. Two first diffraction peaks of electron carry different
spins, duplicating the non-magnetic version of Stern-Gerlach experiment. The
direction of the spin current can be controlled by the gate voltage with low
energy cost.Comment: 4 pages, 4 figure
Explicit construction of quasi-conserved local operator of translationally invariant non-integrable quantum spin chain in prethermalization
We numerically construct translationally invariant quasi-conserved operators
with maximum range M which best-commute with a non-integrable quantum spin
chain Hamiltonian, up to M = 12. In the large coupling limit, we find that the
residual norm of the commutator of the quasi-conserved operator decays
exponentially with its maximum range M at small M, and turns into a slower
decay at larger M. This quasi-conserved operator can be understood as a dressed
total "spin-z" operator, by comparing with the perturbative Schrieffer-Wolff
construction developed to high order reaching essentially the same maximum
range. We also examine the operator inverse participation ratio of the
operator, which suggests its localization in the operator Hilbert space. The
operator also shows almost exponentially decaying profile at short distance,
while the long-distance behavior is not clear due to limitations of our
numerical calculation. Further dynamical simulation confirms that the
prethermalization-equilibrated values are described by a generalized Gibbs
ensemble that includes such quasi-conserved operator.Comment: 22 pages with 13 pages of main text, 9 figures and 5 appendices
(published version
Unified structure for exact towers of scar states in the AKLT and other models
Quantum many-body scar states are many-body states with finite energy density in non-integrable models that do not obey the eigenstate thermalization hypothesis. Recent works have revealed "towers" of scar states that are exactly known and are equally spaced in energy, specifically in the AKLT model, the spin-1 XY model, and a spin-1/2 model that conserves number of domain walls. We provide a common framework to understand and prove known exact towers of scars in these systems, by evaluating the commutator of the Hamiltonian and a ladder operator. In particular we provide a simple proof of the scar towers in the integer-spin 1d AKLT models by studying two-site spin projectors. Through this picture we deduce a family of Hamiltonians that share the scar tower with the AKLT model, and also find common parent Hamiltonians for the AKLT and XY model scars. We also introduce new towers of exact states, organized in a "pyramid" structure, in the spin-1/2 model through successive application of a non-local ladder operator
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