Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin

Quantum state transfer from flying photons to stationary matter qubits is an important element in the realization of quantum networks. Self-assembled semiconductor quantum dots provide a promising solid-state platform hosting both single photon and spin, with an inherent light-matter interface. Here, we develop a method to coherently and actively control the single-photon frequency bins in superposition using electro-optic modulators, and measure the spin-photon entanglement with a fidelity of $0.796\pm0.020$. Further, by Greenberger-Horne-Zeilinger-type state projection on the frequency, path and polarization degrees of freedom of a single photon, we demonstrate quantum state transfer from a single photon to a single electron spin confined in an InGaAs quantum dot, separated by 5 meters. The quantum state mapping from the photon's polarization to the electron's spin is demonstrated along three different axis on the Bloch sphere, with an average fidelity of $78.5\%$.Comment: Experiment finished in 2013, presented in QD2014 Pisa, under review in Phys. Rev. Let

Temperature-dependent Mollow triplet spectra from a single quantum dot: Rabi frequency renormalisation and sideband linewidth insensitivity

We investigate temperature-dependent resonance fluorescence spectra obtained from a single self-assembled quantum dot. A decrease of the Mollow triplet sideband splitting is observed with increasing temperature, an effect we attribute to a phonon-induced renormalisation of the driven dot Rabi frequency. We also present first evidence for a non-perturbative regime of phonon coupling, in which the expected linear increase in sideband linewidth as a function of temperature is cancelled by the corresponding reduction in Rabi frequency. These results indicate that dephasing in semiconductor quantum dots may be less sensitive to changes in temperature than expected from a standard weak-coupling analysis of phonon effects.Comment: Close to published version, new figure and minor changes to the text. 5 pages, 3 figure

Phonon induced line broadening and population of the dark exciton in a deeply trapped localized emitter in monolayer WSe2

We acknowledge financial support by the State of Bavaria. Y.-M.H. acknowledges support from the Sino-German (CSC-DAAD) Postdoc Scholarship Program. This publication was funded by the German Research Foundation (DFG) and the University of Wuerzburg in the funding programme Open Access Publishing.We study trapped single excitons in a monolayer semiconductorwith respect to their temperature stability, spectral diffusion and decaydynamics. In a mechanically exfoliated WSe2 sheet, we could identifydiscrete emission features with emission energies down to 1.516 eV whichare spectrally isolated in a free spectral range up to 80 meV. The strongspectral isolation of our localized emitter allow us to identify strongsignatures of phonon induced spectral broadening for elevated temperaturesaccompanied by temperature induced luminescence quenching. A directcorrelation between the droop in intensity at higher temperatures with thephonon induced population of dark states in WSe2 is established. While ourexperiment suggests that the applicability of monolayered quantum emittersas coherent single photon sources at elevated temperatures may be limited,the capability to operate them below the GaAs band-edge makes themhighly interesting for GaAs-monolayer hybrid quantum photonic structures.PostprintPeer reviewe

The Simulation of Non-Abelian Statistics of Majorana Fermions in Ising Chain with Z2 Symmetry

In this paper, we numerically study the non-Abelian statistics of the zero-energy Majorana fermions on the end of Majorana chain and show its application to quantum computing by mapping it to a spin model with special symmetry. In particular, by using transverse-field Ising model with Z2 symmetry, we verify the nontrivial non-Abelian statistics of Majorana fermions. Numerical evidence and comparison in both Majorana-representation and spin-representation are presented. The degenerate ground states of a symmetry protected spin chain therefore previde a promising platform for topological quantum computation.Comment: 5 pages,4 figure

Optimization-Based Peptide Mass Fingerprinting for Protein Mixture Identification

*Motivation:* In current proteome research, peptide sequencing is probably the most widely used method for protein mixture identification. However, this peptide-centric method has its own disadvantages such as the immense volume of tandem Mass Spectrometry (MS) data for sequencing peptides. With the fast development of technology, it is possible to investigate other alternative techniques. Peptide Mass Fingerprinting (PMF) has been widely used to identify single purified proteins for more than 15 years. Unfortunately, this technique is less accurate than peptide sequencing method and cannot handle protein mixtures, which hampers the widespread use of PMF technique. If we can remove these limitations, PMF will become a useful tool in protein mixture identification. 
*Results:* We first formulate the problem of PMF protein mixture identification as an optimization problem. Then, we show that the use of some simple heuristics enables us to find good solutions. As a result, we obtain much better identification results than previous methods. Moreover, the result on real MS data can be comparable with that of the peptide sequencing method. Through a comprehensive simulation study, we identify a set of limiting factors that hinder the performance of PMF method in protein mixtures. We argue that it is feasible to remove these limitations and PMF can be a powerful tool in the analysis of protein mixtures