Search

The introduction of non-Hermiticity has greatly enriched the research field of traditional condensed matter physics, and eventually led to a series of discoveries of exotic phenomena. We investigate the effect of non-Hermitian imaginary hoppings on the attractive Hubbard model. The exact bound-pair solution shows that the electron-electron correlation suppresses the non-Hermiticity, resulting in off-diagonal long-range order (ODLRO) ground state. In a large negative $U $ limit, the ODLRO ground state corresponds to $\eta $-spin ferromagnetic states. We also study the system with mixed hopping configuration. The numerical result indicates the existence of the transition from normal to $\eta $-pairing ground states by increasing the imaginary hopping strength. Our results provide a promising approach for the non-Hermitian strongly correlated system., Comment: 10 pages, 4 figures

We study the response of a thermal state of the Hubbard-like system to either global or local non-Hermitian perturbation, which coalesces the degenerate ground state within the $U(1)$ symmetry breaking phase. We show that the dynamical response of the system is strongly sensitive to the underlying quantum phase transition (QPT) from a Mott insulator to a superfluid state. The Uhlmann fidelity in the superfluid phase decays to a steady value determined by the order of the exceptional point (EP) within the subspace spanned by the degenerate ground states but remains almost unchanged in the Mott insulating phase. It demonstrates that the phase diagram at zero temperature is preserved even though a local probing field is applied. Specifically, two celebrated models including the Bose-Hubbard model and the Jaynes-Cummings-Hubbard model are employed to demonstrate this property in the finite-size system, wherein fluctuations of the boson and polariton number are observed based on EP dynamics. This work presents an alternative approach to probe the superfluid-insulator QPT at non-zero temperature., Comment: 8 pages, 5 figures

We study an anisotropic two-dimensional non-Hermitian Lieb lattice, where the staggered gain and loss present in the horizontal and vertical directions, respectively. The intra-cell nonreciprocal coupling generates magnetic flux enclosed in the unit cell of the Lieb lattice and creates nontrivial topology. The active and dissipative topological edge states are along the horizontal and vertical directions, respectively. The two-dimensional non-Hermitian Lieb lattice also supports passive topological corner state. At appropriate magnetic flux, the non-Hermiticity can alter the corner state from one corner to the opposite corner as the non-Hermiticity increases. The gapless phase of the Lieb lattice is characterized by different configurations of exceptional points in the Brillouin zone. The topology of the anisotropic non-Hermitian Lieb lattices can be verified in many experimental platforms including the optical waveguide lattices, photonic crystals, and electronic circuits., Comment: 11 pages, 9 figures

The cooperation between non-Hermiticity and interaction brings about a lot of counterintuitive behaviors, which are impossible to exist in the framework of the Hermitian system. We study the effect of a non-Hermitian impurity on the Hubbard model in the context of $\ensuremath{\eta}$ symmetry. We show that the non-Hermitian Hubbard Hamiltonian can respect a full real spectrum even if a local non-Hermitian impurity is applied to. The balance between dissipation of single fermion and on-site pair fluctuation results in a highest-order coalescing state with off-diagonal long-range order (ODLRO). Based on the characteristic of high-order EP, the critical non-Hermitian Hubbard model allows the generation of such a steady superconducting-like state through the time evolution from an arbitrary initial state, including the vacuum state. Remarkably, this dynamic scheme is insensitive to the on-site interaction and entirely independent of the locations of particle dissipation and pair fluctuation. Our results lay the groundwork for the dynamical generation of a steady ODLRO state through the critical non-Hermitian strongly correlated system.

We report a global effect induced by the local complex field, associated with the spin-exchange interaction. High-order exceptional point up to ($N+1$)-level coalescence is created at the critical local complex field applied to the $N$-size quantum spin chain. The ($N+1$)-order coalescent level is a saturated ferromagnetic ground state in the isotropic spin system. Remarkably, the final state always approaches the ground state for an arbitrary initial state with any number of spin flips; even if the initial state is orthogonal to the ground state. Furthermore, the switch of macroscopic magnetization is solely driven by the time and forms a hysteresis loop in the time domain. The retentivity and coercivity of the hysteresis loop mainly rely on the non-Hermiticity. Our findings highlight the cooperation of non-Hermiticity and the interaction in quantum spin system, suggest a dynamical framework to realize magnetization, and thus pave the way for the non-Hermitian quantum spin system., Comment: 10 pages, 4 figures

International audience; To investigate the hot electron population and the appearance of kinetic instabilities in highly charged electron cyclotron resonance ion source (ECRIS), the axially emitted bremsstrahlung spectra and microwave bursts emitted from ECRIS plasma were synchronously measured on SECRAL-II (Superconducting ECR ion source with Advanced design in Lanzhou No. II) ion source with various magnetic field configurations. The experimental results show that when the ratio of the minimum field to the resonance field (i.e. Bmin/Becr ) is less than ~0.8, the bremsstrahlung spectral temperature Ts increases linearly with the Bmin/Becr –ratio when the injection, extraction and radial mirror fields are kept constant. Above this threshold Ts saturates and the electron cyclotron instability appears simultaneously. This study has also demonstrated that Ts decreases linearly with the increase of the average gradient over the ECR surface when the on-axis gradient and hexapole field strengths are constant. In addition, it is found that Ts decreases with the increase of the gradient at the resonance zone (∇Becr on axis and ) at relatively low mirror ratio and is insensitive to the gradient at high mirror ratio when Bmin is constant. Compared to a recent study taken on a fully superconducting ECRIS (Benitez et al 2017 IEEE Trans. Plasma Sci. 45 1746–54), in which it was concluded that Ts is only sensitive with Bmin , this article shows different results discussing the mechanisms behind the correlation of magnetic field parameters to Ts .

Unlike a Chern number in $2$D and $3$D topological system, Zak phase takes a subtle role to characterize the topological phase in $1$D. On the one hand, it is not a gauge invariant, on the other hand, the Zak phase difference between two quantum phases can be used to identify the topological phase transitions. A non-Hermitian system may inherit some characters of a Hermitian system, such as entirely real spectrum, unitary evolution, topological energy band, etc. In this paper, we study the influence of non-Hermitian term on the Zak phase for a class of non-Hermitian systems. We show exactly that the real part of the Zak phase remains unchanged in a bipartite lattice. In a concrete example, $1$D Su-Schrieffer-Heeger (SSH) model, we find that the real part of Zak phase can be obtained by an adiabatic process. To demonstrate this finding, we investigate a scattering problem for a time-dependent scattering center, which is a magnetic-flux-driven non-Hermitian SSH ring. Owing to the nature of the Zak phase, the intriguing features of this design are the wave-vector independence and allow two distinct behaviors, perfect transmission or confinement, depending on the timing of a flux impulse threading the ring. When the flux is added during a wavepacket travelling within the ring, the wavepacket is confined in the scatter partially. Otherwise, it exhibits perfect transmission through the scatter. Our finding extends the understanding and broaden the possible application of geometric phase in a non-Hermitian system., Comment: 11 pages, 7 figures

We study the dynamical behavior of a non-Hermitian moire superlattice system, which consists of two-coupled SSH chains with staggered imaginary on-site potentials. There are two main spatial regions, in which systems are in unbroken symmetric phases with fully real spectrum, appearing periodically along the ladder. We show that the two quantum phases are dimerized and tetramerized, which determine the distinct dynamical behaviors. Dirac probability can oscillate periodically, increase quadratically and increase exponentially, which correspond to the unbroken phase, exceptional point and the broken phase of the tetramerized region. In comparison, the Dirac probability can exhibit high-frequency oscillation in the dimerized region. These phenomena demonstrate the dynamical signature and provide insightful information of the moire pattern in the non-Hermitian regime., 10 pages, 5 figures

A degeneracy line in parameter space, at which the energy gap closes up, can be the boundary separating either two topological quantum phases or two conventional phases, depending on the surface containing the line. We study the topological feature of degeneracy line in parameter space via a dimerized Kitaev spin chain with staggered transverse field, which can be mapped onto the system of dimerized spinless fermions with $p$-wave superconductivity. The quantum phase boundaries are straight crossing degeneracy lines in three-dimensional (3D) parameter space. We show that the degeneracy line acts as a vortex filament associated with a vector field, which is generated from the Zak phase of the Bogoliubov--de Gennes band. We also investigate the topological invariant in Majorana fermion representation for open chains. The edge modes are not the zero mode but are still protected by the energy gap. The exact midgap states of the Majorana lattice allow us to obtain the corresponding Majorana probability distribution for the whole 3D parameter space, which can establish a scalar field to identify the topological feature of the degeneracy lines. Furthermore, when we switch on a weak tunneling between two ends of the Majorana lattice, the topological invariants of the degeneracy lines can be obtained by the pumped Majorana probability from an adiabatic passage encircling the lines. Numerical simulations of quasiadiabatic time evolution are performed in a small system. We compute the current to monitor the transport of the Majorana fermion, which exhibits an evident character of topological pumping. Our results link the bulk topological invariant to the dynamical behavior of the edge mode, extending the concept of bulk-edge correspondence.

We systematically study a Kitaev chain with imbalanced pair creation and annihilation, which is introduced by non-Hermitian pairing terms. Exact phase diagram shows that the topological phase is still robust under the influence of the conditional imbalance. The gapped phases are characterized by a topological invariant, the extended Zak phase, which is defined by the biorthonormal inner product. Such phases are destroyed at the points where the coalescence of groundstates occur, associating with the time-reversal symmetry breaking. We find that the Majorana edge modes also exist for the open chain within unbroken time-reversal symmetric region, demonstrating the bulk-edge correspondence in such a non-Hermitian system., 8 pages, 4 figures

We study an optomechanical transistor, where an input field can be transferred and amplified unidirectionally in a cyclic three-mode optomechanical system. In this system, the mechanical resonator is coupled simultaneously to two cavity modes. We show that it only requires a finite mechanical gain to achieve the nonreciprocal amplification. Here the nonreciprocity is caused by the phase difference between the linearized optomechanical couplings that breaks the time-reversal symmetry of this system. The amplification arises from the mechanical gain, which provides an effective phonon bath that pumps the mechanical mode coherently. This effect is analogous to the stimulated emission of atoms, where the probe field can be amplified when its frequency is in resonance with that of the anti-Stokes transition. We show that by choosing optimal parameters, this optomechanical transistor can reach perfect unidirectionality accompanied with strong amplification. In addition, the presence of the mechanical gain can result in ultra-long delay in the phase of the probe field, which provides an alternative to controlling light transport in optomechanical systems., 8 pages, 5 figures

Moving target detection is important for the application of target tracking and remote surveillance in active range-gated laser imaging. This technique has two operation modes based on the difference of the number of pulses per frame: stroboscopic mode with the accumulation of multiple laser pulses per frame and flash mode with a single shot of laser pulse per frame. In this paper, we have established a range-gated laser imaging system. In the system, two types of lasers with different frequency were chosen for the two modes. Electric fan and horizontal sliding track were selected as the moving targets to compare the moving blurring between two modes. Consequently, the system working in flash mode shows more excellent performance in motion blurring against stroboscopic mode. Furthermore, based on experiments and theoretical analysis, we presented the higher signal-to-noise ratio of image acquired by stroboscopic mode than flash mode in indoor and underwater environment.

We study a non-Hermitian Rice-Mele model without breaking time-reversal symmetry, with the non-Hermiticity arising from imbalanced hopping rates. The Berry connection, Berry curvature, and Chern number are introduced in the context of biorthonormal inner product. It is shown that for a bulk system, although the Berry connection can be complex numbers, the Chern number is still quantized, as a topological invariant. For an opened chain system, the midgap edge modes are obtained exactly, obeying the bulk-edge correspondence. Furthermore, we also introduce a local current in the context of biorthonormal inner product to measure the pumping charge generated by a cyclic adiabatic evolution. Analytical analysis and numerical simulation of the time evolution of the midgap states show that the pumping charge can be a dynamical topological invariant in correspondence with the Chern number. It indicates that the geometric concepts for Hermitian topological insulator can be extended to the non-Hermitian regime.

Author(s): Zhao, HW; Sun, LT; Guo, JW; Lu, W; Xie, DZ; Hitz, D; Zhang, XZ; Yang, Y | Abstract: The superconducting electron cyclotron resonance ion source with advanced design in Lanzhou (SECRAL) is a superconducting-magnet-based electron cyclotron resonance ion source (ECRIS) for the production of intense highly charged heavy ion beams. It is one of the best performing ECRISs worldwide and the first superconducting ECRIS built with an innovative magnet to generate a high strength minimum-B field for operation with heating microwaves up to 24-28 GHz. Since its commissioning in 2005, SECRAL has so far produced a good number of continuous wave intensity records of highly charged ion beams, in which recently the beam intensities of Ar4012+ and Xe12926+ have, for the first time, exceeded 1 emA produced by an ion source. Routine operations commenced in 2007 with the Heavy Ion accelerator Research Facility in Lanzhou (HIRFL), China. Up to June 2017, SECRAL has been providing more than 28,000 hours of highly charged heavy ion beams to the accelerator demonstrating its great capability and reliability. The great achievement of SECRAL is accumulation of numerous technical advancements, such as an innovative magnetic system and an efficient double-frequency (24+18 GHz) heating with improved plasma stability. This article reviews the development of SECRAL and production of intense highly charged ion beams by SECRAL focusing on its unique magnet design, source commissioning, performance studies and enhancements, beam quality and long-term operation. SECRAL development and its performance studies representatively reflect the achievements and status of the present ECR ion source, as well as the ECRIS impacts on HIRFL.

We study inter-chain pair tunnelling dynamics based on an exact two-particle solution for a two-leg ladder. We show that the Hermitian Hamiltonian shares a common two-particle eigenstate with a corresponding non-Hermitian Hubbard Hamiltonian in which the non-Hermiticity arises from an on-site interaction of imaginary strength. Our results provides that the dynamic processes of two-particle collision and across-legs tunnelling are well described by the effective non-Hermitian Hubbard Hamiltonian based on the eigenstate equivalence. We also find that any common eigenstate is always associated with the emergence of spectral singularity in the non-Hermitian Hubbard model. This result is valid for both Bose and Fermi systems and provides a clear physical implication of the non-Hermitian Hubbard model., Comment: 10 pages, 4 figures

We investigate herein the existence of spectral singularities (SSs) in composite systems that consist of two separate scattering centers A and B embedded in one-dimensional free space, with at least one scattering center being non-Hermitian. We show that such composite systems have an SS at $k_{c}$ if the reflection amplitudes $r^{A}\left( k_{c}\right) $ and $r^{B}\left( k_{c}\right) $ of the two scattering centers satisfy the condition $r_{\mathrm{R}% }^{A}\left( k_{c}\right) r_{\mathrm{L}}^{B}\left( k_{c}\right) e^{i2k_{c}\left( x_{B}-x_{A}\right) }=1$. We also extend the condition to the system with multi-scattering centers. As an application, we construct a simple system to simulate a resonant lasing cavity., Comment: 12 pages, 5 figures

We study the physical and chemical properties of the molecular clump hosting a young stellar cluster, IRAS 20160+3636, which is believed to have formed via the “collect and collapse” process. Physical parameters of the UC Hii region associated with the embedded cluster are measured from the radio continuum observations. This source is found to be a typical Galactic UC Hii region, with a B0.5 type exciting star, if it is ionized by a single star. We derive a CN/HCN abundance ratio larger than 1 over this region, which may suggest that this clump is being affected by the UV radiation from the Hii region.

Short-range interaction among the spins can not only results in the rich phase diagram but also brings about fascinating phenomenon both in the contexts of quantum computing and information. In this paper, we investigate the quantum correlation of the system coupled to a surrounding environment with short-range anisotropic interaction. It is shown that the decay of quantum correlation of the central spins measured by pairwise entanglement and quantum discord can serve as a signature of quantum phase transition. In addition, we study the decoherence factor of the system when the environment is in the vicinity of the phase transition point. In the strong coupling regime, the decay of the decoherence factor exhibits Gaussian envelop in the time domain. However, in weak coupling limit, the quantum correlation of the system is robust against the disturbance of the magnetic field through optimal control of the anisotropic short-range interaction strength. Based on this, the effects of the short-range anisotropic interaction on the sudden transition from classical to quantum decoherence are also presented.

In contrast to a Hermitian system, in which zero modes are usually degenerate and localized edge state in the thermodynamic limit, the zero mode of a finite non-Hermitian system can be a single nontrivial long-range entangled state at the exceptional point (EP). In this work, we demonstrate this feature with a concrete example based on exact solutions. Numerical simulations show that the entangled state can be generated through the dynamic process with a high fidelity.

A new heavy-ion linac within a continuous-wave (CW) 4-rod radio-frequency quadrupole (RFQ) was designed and constructed as the injector for the separated-sector cyclotron (SSC) at the Heavy Ion Research Facility at Lanzhou (HIRFL). In this paper, we present the development of and the beam commissioning results for the 53.667 MHz CW RFQ. In the beam dynamics design, the transverse phase advance at zero current, sigma(0 perpendicular to), is maintained at a relatively high level compared with the longitudinal phase advance (sigma(0 parallel to)) to avoid parametric resonance. A quasi-equipartitioning design strategy was applied to control the emittance growth and beam loss. The installation error of the electrodes was checked using a FARO 3D measurement arm during the manufacturing procedure. This method represents a new approach to measuring the position shifts of electrodes in a laboratory environment and provides information regarding the manufacturing quality. The experimental results of rf measurements exhibited general agreement with the simulation results obtained using CST code. During on-line beam testing of the RFQ, two kinds of ion beams (Ar-40(8+) and O-16(5+)) were transported and accelerated to 142.8 keV/u, respectively. These results demonstrate that the SSC-Linac has made a significant progress. And the design scheme and technology experiences developed in this work can be applied to other future CW RFQs.

Phase transitions of first and second order can easily be distinguished in small systems in the microcanonical ensemble. Configurations of phase coexistence, which are suppressed in the canonical formulation, carry important information about the main characteristics of first order phase transitions like the transition temperature, the latent heat, and the interphase surface tension. The characterisitc backbending of the micro- canonical caloric equation of state T(E) (not to be confused with the well known Van der Waals loops in ordinary thermodynamics) leading to a negative specific heat is intimatly linked to the interphase surface entropy., Latex, 4 eps-figures, graphicx.sty

The performance of a louver-cooling scheme on a flat plate was analyzed using a detached-eddy-simulation turbulence model. It was assumed that the louver-cooling scheme was tested in a wind tunnel with the mainstream flow velocity of 20 m/s, equivalent to a Reynolds number of 16,200, based on the jet diameter. Turbulence closure was achieved by a realizable k-e-based detached-eddy-simulation turbulence model. Solutions of two blowing ratios of 0.5 and 1 were successfully obtained by running parallel on 16 nodes on a computer cluster. The flowfields were found to be highly unsteady and oscillatory in nature, with the maximum fluctuation of the adiabatic effectiveness as high as 15% of the time-averaged value. It is shown that the fluctuations in the adiabatic effectiveness are mainly caused by the spanwise fluctuation of the coolant jet and the unsteady vortical structures created by the interaction of the jet and the mainstream.

In the Hermitian regime, the Berry phase is always a real number. It may be imaginary for a non-Hermitian system, which leads to amplitude amplification or attenuation of an evolved quantum state. We study the dynamics of the non-Hermitian Rice-Mele model driven by a time-dependent external field. The exact results show that it can have a full real spectrum for any value of the field. Several rigorous results are presented for the Berry phase with respect to the varying field. We demonstrate that the Berry phase is the same complex constant for any initial state in a single sub-band. Numerical simulation indicates that the amplitude control of a state can be accomplished by a quasiadiabatic process within a short time.

We study the effect of PT-symmetric imaginary potentials embedded in the two arms of an Aharonov-Bohm interferometer on the transmission phase by finding an exact solution for a concrete tight-binding system. It is observed that the spectral singularity always occurs at k=${\pm}${\pi}/2 for a wide range of fluxes and imaginary potentials. Critical behavior associated with the physics of the spectral singularity is also investigated. It is demonstrated that the quasi-spectral singularity corresponds to a transmission maximum and the transmission phase jumps abruptly by {\pi} when the system is swept through this point. Moreover, We find that there exists a pulse-like phase lapse when the imaginary potential approaches the boundary value of the spectral singularity., Comment: 8 pages, 4 figures, Accepted by PRA

Isospin dependence of polarization charges in O isotopes is studied based on a microscopic particle-vibration coupling model in which the Hartree–Fock single-particle wavefunctions and RPA quadrupole strengths are used. Both isoscalar and isovector parts are included in the vertex of particle-vibration coupling. The effects of the different possible dynamical structures at a given excitation energy on polarization charges are also discussed. A large quenching of the polarization charges is found with a large value of (N − Z)/A for most single particle orbits. It is also found that the polarization charges are sensitive to the binding energy of the single particle orbit.

Structure of carbon and neon isotopes is investigated by deformed Skyrme Hartree-Fock and shell model calculations. We point out that the quadrupole deformations of C and Ne isotopes have strong isotope dependence as a typical example of the evolution of deformations in nuclei. It is shown also that the quadrupole moments and the magnetic moments of the odd C isotopes depend clearly on assigned configurations, and their experimental data will be useful to determine the spin-parities and the deformations of the ground states of these nuclei. The electric quadrupole (E2) transitions in even C and Ne isotopes are also studied. The isotope dependence of the E2 transition strength is reproduced properly, although the calculated strength overestimates an extremely small observed value in 16C.

Intense heavy ion beams have been produced from IMP 14.5 GHz LECR3 by optimization of the ion source conditions and transmission efficiency. Highly charged stable beams, such as 325 eμA of Ar11+, 95 eμA of Xe26+, 7 eμA of Xe30+, 140 eμA of Fe13+, and 75 eμA of Ni12+, were obtained by 14.5 GHz rf power 800–1000 W. Furthermore, an advanced superconducting ECR ion source named SECRAL is being constructed. SECRAL is designed to operate at rf frequency 18–28 GHz with axial mirror magnetic fields 4.0 T at injection, 2.2 T at extraction, and sextupole field 2.0 T at the plasma chamber wall. The unique feature of this superconducting ECR source is that the sextupole is located outside of the three axial solenoid coils to reduce the interaction force and make the source more compact. Fabrications of the superconducting coils, cryostat, beam transmission line, and other components are almost completed. Tests of the superconducting magnet with sextupole and solenoid coils are under way.

The octupole strengths of $\beta$-stable nucleus $^{208}_{82}Pb_{126}$, a neutron skin nucleus $^{60}_{20}Ca_{40}$ and a neutron drip line nucleus $^{28}_{8}O_{20}$ are studied by using the self-consistent Hartree-Fock calculation plus the random phase approximation (RPA) with Skyrme interaction. The collective properties of low-lying excitations are analyzed by using particle-vibration coupling. The results show that the lowest isoscalar states above threshold in $^{60}_{20}Ca_{40}$ and $^{28}_{8}O_{20}$ are the superpositions of collective excitations and unperturbed transitions from bound state to nonresonance states. For these three nuclei, both the low-lying isoscalar states and giant isoscalar resonance carry isovector strength. The ratio B(IV)/B(IS) is checked. It is found that, for $^{208}_{82}Pb_{126}$, the ratios are equal to $(\frac{N-Z}{A})^2$ in good accuracy, while for $^{60}_{20}Ca_{40}$ and $^{28}_{8}O_{20}$, the ratios are much larger than $(\frac{N-Z}{A})^2$. This results from the excess neutrons with small binding energies in $^{60}_{20}Ca_{40}$ and $^{28}_{8}O_{20}$., Comment: 14 pages, 10 figures

The high resolution Fly’s Eye (HiRes) detector in Dugway, Utah, is an air fluorescence detector designed for the measurement of the energy and arrival direction of cosmic ray particles with energy E >10 18 eV. HiRes monitors the night sky for fluorescence light from air shower cascades induced by cosmic ray primaries. The light is collected by mirrors and projected onto arrays of photomultiplier tubes that provide an image of the air shower. HiRes is an astronomical instrument, and the accuracy of the mirror pointing and understanding of the optical properties of the mirror–camera units is crucial. We present a method to cross-check and monitor the mirror pointing by using star light. A star crossing the field of view of a photomultiplier tube causes a temporary increase in the total light detected by the tube. Using UV bright stars, we analyze the pointing accuracy of the HiRes 2 detector, and evaluate the shape of a point-like object as a function of distance to the mirror axis.

We study the directional amplification of an optical probe field in a three-mode optomechanical system, where the mechanical resonator interacts with two linearly-coupled optical cavities and the cavities are driven by strong optical pump fields. The optical probe field is injected into one of the cavity modes, and at the same time, the mechanical resonator is subject to a mechanical drive with the driving frequency equal to the frequency difference between the optical probe and pump fields. We show that the transmission of the probe field can be amplified in one direction and de-amplified in the opposite direction. This directional amplification or de-amplification results from the constructive or destruction interference between different transmission paths in this three-mode optomechanical system., Comment: 8 pages, 4 figures

The Gamow-Teller (GT) strength distributions and isobaric analog resonance (IAR) states of several N = Z + 2 nuclei with mass number A = 42 – 58 are studied by using a self-consistent Skyrme Hartree-Fock-Bogoliubov method plus quasiparticle random phase approximation (HFB+QRPA) formalism. The isoscalar spin-triplet pairing interaction is included in QRPA on top of the isovector spin-singlet one in the HFB method. It is found that the isoscalar pairing correlations mix largely the ( ν j > → π j ) configurations into the low-energy states, and this mixing plays an important role in the formation and in the collectivity of these low-energy states. Furthermore, the observed excitation energy of the low-energy GT state with respect to the IAR can be well reproduced when the strength of isoscalar pairing is about 1.0 – 1.05 times that of the isovector pairing, irrespective of the adopted Skyrme interactions. In N = Z + 2 nuclei in the middle of the p f -shell, a mutual cooperative effect of isoscalar pairing and tensor interaction is found; namely, the tensor force reduces the spin-orbit splittings and enhances the effect of the isoscalar pairing.

We study the possibility of asymmetric transmission induced by a non-Hermitian scattering center embedded in a one-dimensional waveguide, motivated by the aim of realizing quantum diode in a non-Hermitian system. It is shown that a $\mathcal{PT}$ symmetric non-Hermitian scattering center always has symmetric transmission although the dynamics within the isolated center can be unidirectional, especially at its exceptional point. We propose a concrete scheme based on a flux-controlled non-Hermitian scattering center, which comprises a non-Hermitian triangular ring threaded by an Aharonov-Bohm flux. The analytical solution shows that such a complex scattering center acts as a diode at the resonant energy level of the spectral singularity, exhibiting perfect unidirectionality of the transmission. The connections between the phenomena of the asymmetric transmission and reflectionless absorption are also discussed., 6 pages, 5 figures

A conventional quantum phase transition (QPT) can be accessed by varying a real parameter at absolute zero temperature. Motivated by the discovery of the pseudo-Hermiticity of non-Hermitian systems, we explore the QPT in non-Hermitian PT-symmetric Ising model, which is driven by a staggered complex transverse field. Exact solution shows that the Laplacian of the groundstate energy density, with respect to real and imaginary components of the transverse field, diverges on the boundary in the complex plane. The phase diagram indicate that the imaginary transverse field has the effect of shrinking the paramagnet phase. In addition, we also investigate the connection between the geometric phase and the QPT., Comment: 7 pages,4 figures

Superconducting ECR ion sources can produce intense highly charged ion beams for the application in heavy ion accelerators. Superconducting Electron Resonance ion source with Advanced Design (SECRAL) is one of the few fully superconducting ECR ion sources that has been successfully built and put into routine operation for years. With enormous efforts and RD work, promising results have been achieved with the ion source. Heated by the microwave power from a 7 kW/24 GHz gyrotron microwave generator, very intense highly charged gaseous ion beams have been produced, such as 455 eμA Xe(27+), 236 eμA Xe(30+), and 64 eμA Xe(35+). Since heavy metallic ion beams are being more and more attractive and important for many accelerator projects globally, intensive studies have been made to produce highly charged heavy metal ion beams, such as those from bismuth and uranium. Recently, 420 eμA Bi(30+) and 202 eμA U(33+) have been produced with SECRAL source. This paper will present the latest results with SECRAL, and the operation status will be discussed as well. An introduction of recently started SECRAL II project will also be given in the presentation.

Motivated by the physical relevance of a spectral singularity of interacting many-particle system, we explore the dynamics of two bosons as well as fermions in one-dimensional system with imaginary delta interaction strength. Based on the exact solution, it shows that the two-particle collision leads to amplitude-reduction of the wave function. For fermion pair, the amplitude-reduction depends on the spin configuration of two particles. In both cases, the residual amplitude can vanish when the relative group velocity of two single-particle Gaussian wave packets with equal width reaches the magnitude of the interaction strength, exhibiting complete particle-pair annihilation at the spectral singularity., Comment: 8 pages, 2 figures

We study the spectrum and average mass composition of cosmic rays with primary energies between 10^{17} eV and 10^{18} eV using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum as a function of energy. A complete Monte Carlo simulation of the detector response and comparisons with shower simulations leads to the conclusion that the cosmic ray intensity is changing f rom a heavier to a lighter composition in this energy range. The spectrum is consistent with earlier Fly's Eye measurements and supports the previously found steepening near 4 \times 10^{17} eV .

The average mass composition of cosmic rays with primary energies between ${10}^{17}$ and ${10}^{18}\mathrm{eV}$ has been studied using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum and the muon density as a function of energy. The results show that the composition is changing from a heavy to lighter mix as the energy increases.

We study giant resonances using the self-consistent Hartree-Fock calculation plus the random phase approximation with Skyrme interactions. Including simultaneously both the isoscalar and the isovector correlation the RPA response function is calculated in the coordinate space so as to take properly into account the continuum effect. Giant monopole states are discussed in relation with the nuclear compression modulus of the nuclear matter K nm . The core polarization charges are also discussed in comparison with recent empirical data in 100 Sn region.

We study displacement fields of multipole excitations in a halo nucleus 4 11 Be 7 and a skin nucleus 20 60 Ca 40 in comparison with those of collective states in a β-stable nucleus 82 208 Pb 126 . The self-consistent Hartree-Fock calculation plus the random phase approximation with Skyrme interactions is performed in the coordinate space, taking into account the proton and neutron degree of freedom. Transition densities, radial current components and displacement fields of giant resonances in drip-line nuclei are found very similar to those in β stable nuclei. The isovector giant resonances are not properly understood in terms of any available collective models, while the isoscalar giant resonances are in a good approximation expressed by collective models. It is found that the radial velocity of the highest-lying peak of isovector giant multipole resonances vanishes at a radius slightly outside the surface. It is shown that transition densities and current components of the excitations just above the threshold of the drip-line nuclei are extended to far outside the nuclear surface, where the displacement fields show a simple pattern.

It is shown that the isoscalar (isovector) strength in the energy region just above the low-energy threshold, which is created by exciting particles to the continuum in nuclei far from \ensuremath{\beta}-stability lines, can be reduced (increased) by the attractive (repulsive) coupling to isoscalar (isovector) shape oscillations. This is in contrast to the well-known fact that in \ensuremath{\beta}-stable nuclei low-lying isoscalar (isovector) particle-hole strengths are increased (reduced) by the attractive (repulsive) isoscalar (isovector) coupling. We also study the core-polarization effect on one-particle operators for bound particles, of which separation energies are appreciably smaller than those in \ensuremath{\beta}-stable nuclei.

We study monopole states in nuclei near drip lines by using the self-consistent response function. The random phase approximation (RPA) response function is solved in coordinate space including the full momentum-dependent isoscalar and isovector Skyrme interactions simultaneously. It is shown in drip-line nuclei that strong peaks appear at the excitation energies not only in the giant resonance region but also just above the threshold of the RPA response. The nuclear compression modulus is studied comparing the RPA results with experiment data in . The symmetry term of the nuclear compression modulus is also discussed from the mass-number dependence of monopole giant resonances in Ca isotopes.

Taking the Gamow-Teller -decay operator as well as isoscalar and isovector multipole operators, the characteristic features of the response function in nuclei far from the -stability line are illustrated. The Hartree-Fock plus the random phase approximation (RPA) with Skyrme interactions is solved, taking into account simultaneously both the isoscalar and isovector correlation in the self-consistent RPA, which is solved in the coordinate space by the Green's function method. Displacement fields of some collective modes are also shown in order to obtain a deeper understanding of the dynamics.

The isoscalar and the isovector dipole mode of drip line and \ensuremath{\beta}-stable nuclei are investigated, using the self-consistent Hartree-Fock plus the random-phase approximation with Skyrme interactions. Including simultaneously both the isoscalar and the isovector correlation, the RPA response function is estimated in the coordinate space so as to take into account properly the continuum effect. The spurious component is carefully taken away from the calculated strength. In \ensuremath{\beta}-stable nuclei such as ${}^{208}\mathrm{Pb}$ the frequency of the isovector giant dipole resonance (IVGDR) is lower than that of the isoscalar giant dipole resonance (compression mode). In contrast, in lighter drip line nuclei a major part of the isoscalar compression dipole strength lies at an energy much lower than the energy of the IVGDR.

Isoscalar and isovector monopole responses of Ca isotopes towards drip lines are studied in comparison with those of stable nuclei, {sup 40}Ca, {sup 90}Zr, and {sup 208}Pb, using the self-consistent Hartree-Fock calculation plus the random phase approximation with Skyrme interactions. Including simultaneously both the isoscalar and the isovector correlation the RPA response function is calculated in the coordinate space so as to take properly into account the continuum effect. The distribution of the monopole strength is much affected by the presence of the low-energy threshold strength in both proton and neutron drip line nuclei, while the isoscalar monopole strength is concentrated in one giant peak in the heavy {beta}-stable nucleus {sup 208}Pb. It is found that in drip line nuclei the transition density and the displacement field of protons are very different from those of neutrons, especially around the nuclear surface. The relation between the compression modulus of the nuclear matter K{sub nm} and that of finite nuclei K{sub A} is also discussed by using the energy moments estimated in RPA. {copyright} {ital 1997} {ital The American Physical Society}

Using the self-consistent Hartree-Fock calculation plus RPA with Skyrme interactions, the RPA quadrupole strength function is estimated in the coordinate space, including simulataneously both the isoscalar and the isovector correlation. We discuss the result of the isoscalar, the isovector and the electric quadrupole polarization of the Ca-isotopes from the proton drip line towards the neutron drip line. We study also the comparison of the polarizations in the A = 48 mirror nuclei, 2848Ni20 and 2048Ca28, and the dependence of the polarizations of 828O20 on various Skyrme interactions.

We study the giant quadrupole resonances in the neutron drip line nucleus, {sub 8}{sup 28}O{sub 20}, using the self-consistent Hartree-Fock calculation plus the random-phase approximation (RPA) with Skyrme interactions. Including simultaneously both the isoscalar and the isovector correlation, the RPA response function is calculated in the coordinate space so as to take into account properly the continuum effect. Though in neutron drip line nuclei the distribution of the quadrupole strength is much affected by the presence of the low-energy threshold strength, the isoscalar and the isovector correlation structure as well as the transition densities of the isoscalar giant resonance are in good agreement with those given by the collective model. In contrast, the transition density of the isovector giant resonance shows a clear deviation from that of the liquid-drop polarization mode. {copyright} {ital 1997} {ital The American Physical Society}

We study the geometric phase for the ground state of a generalized one-dimensional non-Hermitian quantum XY model, which has transverse-field-dependent intrinsic rotation-time reversal symmetry. Based on the exact solution, this model is shown to have full real spectrum in multiple regions for the finite size system. The result indicates that the phase diagram or exceptional boundary, which separates the unbroken and broken symmetry regions corresponds to the divergence of the Berry curvature. The scaling behaviors of the groundstate energy and Berry curvature are obtained in an analytical manner for a concrete system., Comment: 6 pages, 3 figures

We theoretically study the non-Hermitian systems, the non-Hermiticity of which arises from the unequal hopping amplitude (UHA) dimers. The distinguishing features of these models are that they have full real spectra if all of the eigenvectors are time-reversal (T) symmetric rather than parity-time-reversal (PT) symmetric, and that their Hermitian counterparts are shown to be an experimentally accessible system, which have the same topological structures as that of the original ones but modulated hopping amplitudes within the unbroken region. Under the reflectionless transmission condition, the scattering behavior of momentum-independent reflectionless transmission (RT) can be achieved in the concerned non-Hermitian system. This peculiar feature indicates that, for a certain class of non-Hermitian systems with a balanced combination of the RT dimers, the defects can appear fully invisible to an outside observer., 9 pages, 4 figures. arXiv admin note: text overlap with arXiv:1008.5306 by other authors

A low energy beam transport (LEBT) system has been built for a compact pulsed hadron source (CPHS) at Tsinghua University in China. The LEBT, consisting of two solenoids and three short-drift sections, transports a pulsed proton beam of 60 mA of energy of 50 keV to the entrance of a radio frequency quadrupole (RFQ). Measurement has shown a normalized RMS beam emittance less than 0.2 π mm mrad at the end of the LEBT. Beam simulations were carried out to compare with the measurement and are in good agreement. Based on the successful CPHS LEBT development, a new LEBT for a China ADS projector has been designed. The features of the new design, including a beam chopper and beam simulations of the LEBT are presented and discussed along with CPHS LEBT development in this article.