The reversibility of the transfer of energy from the magnetic field to the surrounding plasma during magnetic reconnection is examined. Trajectories of test particles in an analytic model of the fields demonstrate that irreversibility is associated w
ith separatrix crossings and regions of weaker magnetic field. Inclusion of a guide field increases the degree of reversibility. Full kinetic simulations with a particle-in-cell code support these results and demonstrate that while time-reversed simulations at first un-reconnect, they eventually evolve into a reconnecting state.
The interactions between electrons and antiferromagnetic magnons (AFMMs) are important for a large class of correlated materials. For example, they are the most plausible pairing glues in high-temperature superconductors, such as cuprates and iron pn
ictides. However, unlike electron-phonon interactions (EPIs), clear-cut observations regarding how electron-AFMM interactions (EAIs) affect the band structure are still lacking. Consequently, critical information on the EAIs, such as its strength and doping dependence, remains elusive. Here we directly observe that EAIs induces a kink structure in the band dispersion in Ba$_{1-x}$K$_x$Mn$_2$As$_2$, and subsequently unveil several key characteristics of EAIs. We found that the coupling constant of EAIs can be as large as 6, and it shows huge doping dependence and temperature dependence, all in stark contrast to the behaviors of EPI and beyond our current understanding of EAIs. Such a colossal renormalization of electronic bands by EAIs drives the system to the Stoner criteria, giving the intriguing ferromagnetic state in Ba$_{1-x}$K$_x$Mn$_2$As$_2$. Our results expand the current knowledge of EAIs, which may facilitate the further understanding of many correlated materials where EAIs play a critical role, such as high-temperature superconductors.
We report our nuclear magnetic resonance (NMR) study on the structurally spin chain compound Ni$_2$NbBO$_6$ with complex magnetic coupling. The antiferromagnetic transition is monitored by the line splitting resulting from the staggered internal hype
rfine field. The magnetic coupling configuration proposed by the first-principle density functional theory (DFT) is supported by our NMR spectral analysis. For the spin dynamics, a prominent peak at $Tsim35$ K well above the N{e}el temperature ($T_Nsim20$ K at $mu_0H=10$ T) is observed from the spin-lattice relaxation data. As compared with the dc-susceptibility, this behavior indicates a antiferromagnetic coupling with the typical energy scale of $sim3$ meV. Thus, the Ni$_2$NbBO$_6$ compound can be viewed as strongly ferromagnetically coupled armchair spin chains along the crystalline $b$-axis. These facts place strong constraints to the theoretical model for this compound.
A large cylindrical cadmium molybdate crystal with natural isotopic abundance has been used to fabricate a scintillating bolometer. The measurement was performed above ground at milli-Kelvin temperature, with simultaneous readout of the heat and the
scintillation light. The energy resolution as FWHM has achieved from 5 keV (at 238 keV) to 13 keV (at 2615 keV). We present the results of the $alpha$ versus $beta$/$gamma$ events discrimination. The low internal trace contamination of the $mathrm{CdMoO_4}$ crystal was evaluated as well. The detector performance with preliminary positive indications proves that cadmium molybdate crystal is a promising absorber for neutrinoless double beta decay scintillating bolometric experiments with $mathrm{{}^{116}Cd}$ and $mathrm{{}^{100}Mo}$ nuclides in the next-generation technique.
Quantum communication protocols based on nonclassical correlations can be more efficient than known classical methods and offer intrinsic security over direct state transfer. In particular, remote state preparation aims at the creation of a desired a
nd known quantum state at a remote location using classical communication and quantum entanglement. We present an experimental realization of deterministic continuous-variable remote state preparation in the microwave regime over a distance of 35 cm. By employing propagating two-mode squeezed microwave states and feedforward, we achieve the remote preparation of squeezed states with up to 1.6 dB of squeezing below the vacuum level. We quantify security in our implementation using the concept of the one-time pad. Our results represent a significant step towards microwave quantum networks between superconducting circuits.
Hyperbolic Meta-Materials~(HMMs) are anisotropic materials with permittivity tensor that has both positive and negative eigenvalues. Here we report that by using a type II HMM as cladding material, a waveguide which only supports higher order modes c
an be achieved, while the lower order modes become leaky and are absorbed in the HMM cladding. This counter intuitive property can lead to novel application in optical communication and photonic integrated circuit. The loss in our HMM-Insulator-HMM~(HIH) waveguide is smaller than that of similar guided mode in a Metal-Insulator-Metal~(MIM) waveguide.
Stimulated Raman adiabatic passage (STIRAP) offers significant advantages for coherent population transfer between un- or weakly-coupled states and has the potential of realizing efficient quantum gate, qubit entanglement, and quantum information tra
nsfer. Here we report on the realization of STIRAP in a superconducting phase qutrit - a ladder-type system in which the ground state population is coherently transferred to the second-excited state via the dark state subspace. The result agrees well with the numerical simulation of the master equation, which further demonstrates that with the state-of-the-art superconducting qutrits the transfer efficiency readily exceeds $99%$ while keeping the population in the first-excited state below $1%$. We show that population transfer via STIRAP is significantly more robust against variations of the experimental parameters compared to that via the conventional resonant $pi$ pulse method. Our work opens up a new venue for exploring STIRAP for quantum information processing using the superconducting artificial atoms.
We report a systematic study on the crystal growth of the rare-earth titanates $R_2$Ti$_2$O$_7$ ($R$ = Gd, Tb, Dy, Ho, Y, Er, Yb and Lu) and Y-doped Tb$_{2-x}$Y$_x$Ti$_2$O$_7$ ($x$ = 0.2 and 1) using an optical floating-zone method. High-quality sing
le crystals were successfully obtained and the growth conditions were carefully optimized. The oxygen pressure was found to be the most important parameter and the appropriate ones are 0.1--0.4 MPa, depending on the radius of rare-earth ions. The growth rate is another parameter and was found to be 2.5--4 mm/h for different rare-earth ions. X-ray diffraction data demonstrated the good crystallinity of these crystals. The basic physical properties of these crystals were characterized by the magnetic susceptibility and specific heat measurements.
With angle-resolved photoemission spectroscopy, we studied the electronic structure of TaFe$_{1.23}$Te$_3$, which is a two-leg spin ladder compound with a novel antiferromagnetic ground state. Quasi-two-dimensional Fermi surface is observed, indicati
ng sizable inter-ladder hopping, which would facilitate the in-plane ferromagnetic ordering through double exchange interactions. Moreover, an energy gap is not observed at the Fermi surface in the antiferromagnetic state. Instead, the shifts of various bands have been observed. Combining these observations with density-functional-theory calculations, we propose that the large scale reconstruction of the electronic structure, caused by the interactions between the coexisting itinerant electrons and local moments, is most likely the driving force behind the magnetic transition. TaFe$_{1.23}$Te$_3$ thus provides a simpler system that contains similar ingredients as the parent compounds of iron-based superconductors, which yet could be readily modeled and understood.
A Cooper pair insulator (CPI) phase emerges near the superconductor-insulator transitions of a number of strongly-disordered thin film systems. Much recent study has focused on a mechanism driving the underlying Cooper pair localization. We present d
ata showing that a CPI phase develops in amorphous Pb$_{0.9}$Bi$_{0.1}$ films deposited onto nano-porous anodized aluminum oxide surfaces just as it has been shown to develop for a-Bi films. This result confirms the assertion that the CPI phase emerges due to the structure of the substrate. It supports the picture that nanoscale film thickness variations induced by the substrate drive the localization. Moreover, it implies that the CPI phase can be induced in any superconducting material that can be deposited onto this surface.
