Status of the Daya Bay Reactor Neutrino Oscillation Experiment

The last unknown neutrino mixing angle $\theta_{13}$ 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 $sin^2(2\theta_{13})$ 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

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 $\sim10^{-13}$ eV$\cdot$m, the \emph{out-of-plane} component of the spin of the electron can be generated up to 0.42 $\hbar$. 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

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 $E = 0$ states) and open boundary conditions (two $E = 0$ states and one each $E = \pm \sqrt{2}$). 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 $E = 0$ 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

Out-of-time-ordered correlators in quantum Ising chain

Out-of-time-ordered correlators (OTOC) have been proposed to characterize quantum chaos in generic systems. However, they can also show interesting behavior in integrable models, resembling the OTOC in chaotic systems in some aspects. Here we study the OTOC for different operators in the exactly-solvable one-dimensional quantum Ising spin chain. The OTOC for spin operators that are local in terms of the Jordan-Wigner fermions has a "shell-like" structure: after the wavefront passes, the OTOC approaches its original value in the long-time limit, showing no signature of scrambling; the approach is described by a $t^{-1}$ power law at long time $t$. On the other hand, the OTOC for spin operators that are nonlocal in the Jordan-Wigner fermions has a "ball-like" structure, with its value reaching zero in the long-time limit, looking like a signature of scrambling; the approach to zero, however, is described by a slow power law $t^{-1/4}$ for the Ising model at the critical coupling. These long-time power-law behaviors in the lattice model are not captured by conformal field theory calculations. The mixed OTOC with both local and nonlocal operators in the Jordan-Wigner fermions also has a "ball-like" structure, but the limiting values and the decay behavior appear to be nonuniversal. In all cases, we are not able to define a parametrically large window around the wavefront to extract the Lyapunov exponent.Comment: Published version; Note added in the Discussion section; 11 pages of main text+6 pages of appendices, 12 figure

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

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

Spin Distribution in Diffraction Pattern of Two-dimensional Electron Gas with Spin-orbit Coupling

Spin distribution in the diffraction pattern of two-dimensional electron gas by a split gate and a quantum point contact is computed in the presence of the spin-orbit coupling. After diffracted, the component of spin perpendicular to the two-dimensional plane can be generated up to 0.42 $\hbar$. The non-trivial spin distribution is the consequence of a pure spin current in the transverse direction generated by the diffraction. The direction of the spin current can be controlled by tuning the chemical potential.Comment: 9 page