Laser Control of Dissipative Two-Exciton Dynamics in Molecular Aggregates

There are two types of two-photon transitions in molecular aggregates, that is, non-local excitations of two monomers and local double excitations to some higher excited intra-monomer electronic state. As a consequence of the inter-monomer Coulomb interaction these different excitation states are coupled to each other. Higher excited intra-monomer states are rather short-lived due to efficient internal conversion of electronic into vibrational energy. Combining both processes leads to the annihilation of an electronic excitation state, which is a major loss channel for establishing high excitation densities in molecular aggregates. Applying theoretical pulse optimization techniques to a Frenkel exciton model it is shown that the dynamics of two-exciton states in linear aggregates (dimer to tetramer) can be influenced by ultrafast shaped laser pulses. In particular, it is studied to what extent the decay of the two-exciton population by inter-band transitions can be transiently suppressed. Intra-band dynamics is described by a dissipative hierarchy equation approach, which takes into account strong exciton-vibrational coupling in the non-Markovian regime.Comment: revised version, fig. 8 ne

IR Spectrum of the O-H......O Hydrogen Bond of Phthalic Acid Monomethylester in Gas Phase and in CCl4_4 Solution

The absorption spectrum of the title compound in the spectral range of the Hydrogen-bonded OH-stretching vibration has been investigated using a five-dimensional gas phase model as well as a QM/MM classical molecular dynamics simulation in solution. The gas phase model predicts a Fermi-resonance between the OH-stretching fundamental and the first OH-bending overtone transition with considerable oscillator strength redistribution. The anharmonic coupling to a low-frequency vibration of the Hydrogen bond leading to a vibrational progression is studied within a diabatic potential energy curve model. The condensed phase simulation of the dipole-dipole correlation function results in a broad band in the 3000 \cm region in good agreement with experimental data. Further, weaker absorption features around 2600 \cm have been identified as being due to motion of the Hydrogen within the Hydrogen bond.Comment: Contribution to Horizons in Hydrogen Bond Research Conference, Paris 200

Machine-learning-inspired quantum optimal control of nonadiabatic geometric quantum computation via reverse engineering

Quantum control plays an irreplaceable role in practical use of quantum computers. However, some challenges have to be overcome to find more suitable and diverse control parameters. We propose a promising and generalizable average-fidelity-based machine-learning-inspired method to optimize the control parameters, in which a neural network with periodic feature enhancement is used as an ansatz. In the implementation of a single-qubit gate by cat-state nonadiabatic geometric quantum computation via reverse engineering, compared with the control parameters in the simple form of a trigonometric function, our approach can yield significantly higher-fidelity ($>99.99\%$) phase gates, such as the $\pi / 8$ gate (T gate). Single-qubit gates are robust against systematic noise, additive white Gaussian noise and decoherence. We numerically demonstrate that the neural network possesses the ability to expand the model space. With the help of our optimization, we provide a feasible way to implement cascaded multi-qubit gates with high quality in a bosonic system. Therefore, the machine-learning-inspired method may be feasible in quantum optimal control of nonadiabatic geometric quantum computation.Comment: 12 pages, 8 figure

Overlapping and Distinct Roles of HAM Family Genes in Arabidopsis Shoot Meristems

In Arabidopsis shoot apical meristems (SAMs), a well-characterized regulatory loop between WUSCHEL (WUS) and CLAVATA3 (CLV3) maintains stem cell homeostasis by regulating the balance between cell proliferation and cell differentiation. WUS proteins, translated in deep cell layers, move into the overlaying stem cells to activate CLV3. The secreted peptide CLV3 then regulates WUS levels through a ligand-receptor mediated signaling cascade. CLV3 is specifically expressed in the stem cells and repressed in the deep cell layers despite presence of the WUS activator, forming an apical-basal polarity along the axis of the SAM. Previously, we proposed and validated a hypothesis that the HAIRY MERISTEM (HAM) family genes regulate this polarity, keeping the expression of CLV3 off in interior cells of the SAM. However, the specific role of each individual member of the HAM family in this process remains to be elucidated. Combining live imaging and molecular genetics, we have dissected the conserved and distinct functions of different HAM family members in control of CLV3 patterning in the SAMs and in the de novo shoot stem cell niches as well

Quantum computation in silicon-vacancy centers based on nonadiabatic geometric gates protected by dynamical decoupling

Due to strong zero-phonon line emission, narrow inhomogeneous broadening, and stable optical transition frequencies, the quantum system consisting of negatively charged silicon-vacancy (SiV) centers in diamond is highly expected to develop universal quantum computation. We propose to implement quantum computation for the first time using SiV centers placed in a one-dimensional phononic waveguide, for which quantum gates are realized in a nonadiabatic geometric way and protected by dynamical decoupling (DD). The scheme has the feature of geometric quantum computation that is robust to control errors and the advantage of DD that is insensitive to environmental impact. Furthermore, the encoding of qubits in long-lifetime ground states of silicon-vacancy centers can reduce the effect of spontaneous emission. Numerical simulations demonstrate the practicability of the SiV center system for quantum computation and the robustness improvement of quantum gates by DD pulses. This scheme may provide a promising path toward high-fidelity geometric quantum computation in solid-state systems

Simple scheme for expanding a polarization-entangled W state by adding one photon

We propose a simple scheme for expanding a polarization-entangled W state. By mixing a single photon and one of the photons in an n-photon W state at a polarization-dependent beam splitter (PDBS), we can obtain an (n+1)-photon W state after post-selection. Our scheme also opens the door for generating n-photon W states using single photons and linear optics.Comment: 3 pages, 2 figure

Control of plant stem cell function by conserved interacting transcriptional regulators

Plant stem cells in the shoot apical meristem (SAM) and root apical meristem are necessary for postembryonic development of aboveground tissues and roots, respectively, while secondary vascular stem cells sustain vascular development. WUSCHEL (WUS), a homeodomain transcription factor expressed in the rib meristem of the Arabidopsis SAM, is a key regulatory factor controlling SAM stem cell populations, and is thought to establish the shoot stem cell niche through a feedback circuit involving the CLAVATA3 (CLV3) peptide signalling pathway. WUSCHEL-RELATED HOMEOBOX 5 (WOX5), which is specifically expressed in the root quiescent centre, defines quiescent centre identity and functions interchangeably with WUS in the control of shoot and root stem cell niches. WOX4, expressed in Arabidopsis procambial cells, defines the vascular stem cell niche. WUS/WOX family proteins are evolutionarily and functionally conserved throughout the plant kingdom and emerge as key actors in the specification and maintenance of stem cells within all meristems. However, the nature of the genetic regime in stem cell niches that centre on WOX gene function has been elusive, and molecular links underlying conserved WUS/WOX function in stem cell niches remain unknown. Here we demonstrate that the Arabidopsis HAIRY MERISTEM (HAM) family of transcription regulators act as conserved interacting cofactors with WUS/WOX proteins. HAM and WUS share common targets in vivo and their physical interaction is important in driving downstream transcriptional programs and in promoting shoot stem cell proliferation. Differences in the overlapping expression patterns of WOX and HAM family members underlie the formation of diverse stem cell niche locations, and the HAM family is essential for all of these stem cell niches. These findings establish a new framework for the control of stem cell production during plant development