The study of $gammagammatogammapsi(2S)$ at Belle

Using $980~rm fb^{-1}$ of data on and around the $Upsilon(nS)(n=1,2,3,4,5)$ resonances collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider, the two-photon process $gammagammato gammapsi(2S)$ is studied from $sqrt{s} = 3.7$ to $4.2~{rm GeV}$ for the first time. Evidence is found for a structure in the invariant mass distribution of $gammapsi(2S)$ at $M_1 = 3921.3pm 2.4 pm 1.6~{rm MeV}/c^2$ with a width of $Gamma_1 = 0.0pm 5.3 pm 2.0~{rm MeV}$ and a significance of $4.0sigma$ including systematic uncertainties, and another structure is seen at $M_2 = 4014.4pm 4.1 pm 0.5~{rm MeV}/c^2$ with a width of $Gamma_2 = 6pm 16 pm 6~{rm MeV}$ and a global significance of $2.8sigma$ including the look-elsewhere effect, if the mass spectrum is parametrized with the incoherent sum of two Breit-Wigner functions. The upper limits of the widths are determined to be $Gamma_1^{rm UL} = 11.5~{rm MeV}$ and $Gamma_2^{rm UL} = 39.3~{rm MeV}$ at 90% confidence level. The production rates are determined to be $Gamma_{gammagamma}{cal B}(R_1togammapsi(2S)) = 8.2pm 2.3pm 0.9~{rm eV}$ assuming $(J^{PC}, |lambda|) =(0^{++}, 0)$ and $1.6pm 0.5pm 0.2~{rm eV}$ with $(2^{++}, 2)$ for the first structure and $Gamma_{gammagamma}{cal B}(R_2togammapsi(2S)) = 5.3pm 2.7pm 2.5~{rm eV}$ with $(0^{++}, 0)$ and $1.1pm 0.5pm 0.5~{rm eV}$ with $(2^{++}, 2)$ for the second one. Here, the first errors are statistical and the second systematic.

Preparing Narrow Velocity Distributions for Quantum Memories in Room-Temperature Alkali Vapours

Quantum memories are a crucial technology for enabling large-scale quantum networks through synchronisation of probabilistic operations. Such networks impose strict requirements on quantum memory, such as storage time, retrieval efficiency, bandwidth, and scalability. On- and off-resonant ladder protocols on warm atomic vapour platforms are promising candidates, combining efficient high-bandwidth operation with low-noise on-demand retrieval. However, their storage time is severely limited by motion-induced dephasing caused by the broad velocity distribution of atoms comprising the vapour. In this paper, we demonstrate velocity selective optical pumping to overcome this decoherence mechanism. This will increase the achievable memory storage time of vapour memories. This technique can also be used for preparing arbitrarily shaped absorption profiles, for instance, preparing an atomic frequency comb absorption feature.

Room Temperature Atomic Frequency Comb Memory for Light

We demonstrate coherent storage and retrieval of pulsed light using the atomic frequency comb quantum memory protocol in a room temperature alkali vapour. We utilise velocity-selective optical pumping to prepare multiple velocity classes in the $F=4$ hyperfine ground state of caesium. The frequency spacing of the classes is chosen to coincide with the $F=4 - F=5$ hyperfine splitting of the $6^2$P$_{3/2}$ excited state resulting in a broadband periodic absorbing structure consisting of two usually Doppler-broadened optical transitions. Weak coherent states of duration $2,mathrm{ns}$ are mapped into this atomic frequency comb with pre-programmed recall times of $8,mathrm{ns}$ and $12,mathrm{ns}$, with multi-temporal mode storage and recall demonstrated. Utilising two transitions in the comb leads to an additional interference effect upon rephasing that enhances the recall efficiency.

Optimal Coherent Filtering for Single Noisy Photons

We introduce a filter using a noise-free quantum buffer with large optical bandwidth that can both filter temporal-spectral modes, as well as inter-convert them and change their frequency. We show that such quantum buffers optimally filter out temporal-spectral noise; producing identical single-photons from many distinguishable noisy single-photon sources with the minimum required reduction in brightness. We then experimentally demonstrate a noise-free quantum buffer in a warm atomic system that is well matched to quantum dots and can outperform all intensity (incoherent) filtering schemes for increasing indistinguishability.

Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr2O4

In spinels ACr2O4 (A=Mg, Zn) realisation of the classical pyrochlore Heisenberg antiferromagnet model is complicated by a strong spin-lattice coupling: the extensive degeneracy of the ground state is lifted by a magneto-structural transition at TN=12.5 K. We study the resulting low-temperature low-symmetry crystal structure by synchrotron x-ray diffraction. The consistent features of x-ray low-temperature patterns are explained by the tetragonal model of Ehrenberg et. al (Pow. Diff. 17, 230( 2002)), while other features depend on sample or cooling protocol. Complex partially ordered magnetic state is studied by neutron diffraction and spherical neutron polarimetry. Multiple magnetic domains of configuration arms of the propagation vectors k1=(1/2 1/2 0), k2=(1 0 1/2) appear. The ordered moment reaches 1.94(3) muB/Cr3+ for k1 and 2.08(3) muB/Cr3+ for k2, if equal amount of the k1 and k2 phases is assumed. The magnetic arrangements have the dominant components along the [110] and [1-10] diagonals and a smaller c-component. By inelastic neutron scattering we investigate the spin excitations, which comprise a mixture of dispersive spin waves propagating from the magnetic Bragg peaks and resonance modes centered at equal energy steps of 4.5 meV. We interpret these as acoustic and optical spin wave branches, but show that the neutron scattering cross sections of transitions within a unit of two corner-sharing tetrahedra match the observed intensity distribution of the resonances. The distinctive fingerprint of cluster-like excitations in the optical spin wave branches suggests that propagating excitations are localized by the complex crystal structure and magnetic orders.

The Distance and the near-IR extinction of the Monoceros Supernova Remnant

Supernova remnants (SNRs) embody the information of the influence on dust properties by the supernova explosion. Based on the color indexes from the 2MASS photometric survey and the stellar parameters from the SDSS$-$DR12$/$APOGEE and LAMOST$-$DR2$/$LEGUE spectroscopic surveys, the near-infrared extinction law and the distance of the Monoceros SNR are derived together with its nearby two nebulas -- the Rosette Nebula and NGC 2264. The distance is found at the position of the sharp increase of interstellar extinction with distance and the nebular extinction is calculated by subtracting the foreground interstellar extinction. The distance of the Monoceros SNR is determined to be $1.98,$kpc, larger than previous values. Meanwhile, the distance of the Rosette Nebula is $1.55,$kpc, generally consistent with previous work. The distance between these two nebulas suggests no interaction between them. The distance of NGC 2264, $1.20,$kpc, exceeds previous values. The color excess ratio, $E_{rm JH}/E_{rm JK_S}$, is 0.657 for the Monoceros SNR, consistent with the average value 0.652 for the Milky Way (Xue et al. 2016). The consistency is resulted from that the SNR material is dominated by interstellar dust rather than the supernova ejecta. $E_{rm JH}/E_{rm JK_S}$ equals to 0.658 for the Rosette Nebula, further proving the universality of the near-infrared extinction law.

Uncovering High Thermoelectric Figure of Merit in (Hf,Zr)NiSn Half-Heusler Alloys

Half-Heusler alloys (MgAgSb structure) are promising thermoelectric materials. RNiSn half-Heusler phases (R=Hf, Zr, Ti) are the most studied in view of their thermal stability. The highest dimensionless figure of merit (ZT) obtained is ~1 in the temperature range ~450-900oC, primarily achieved in nanostructured alloys. Through proper annealing, ZT~1.2 has been obtained in a previous ZT~1 n-type (Hf,Zr)NiSn phase without the nanostructure. There is an appreciable increase in the power factor, decrease in charge carrier density, and increase in carrier mobility. The findings are attributed to the improvement of structural order. Present approach may be applied to optimize the functional properties of Heusler-type alloys.