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Recent numerical and experimental works have revealed a disorder-free many-body localization (MBL) in an interacting system subjecting to a linear potential, known as the Stark MBL. The conventional MBL, induced by disorder, has been widely studied by using quantum simulations based on superconducting circuits. Here, we consider the Stark MBL in two types of superconducting circuits, i.e., the 1D array of superconducting qubits, and the circuit where non-local interactions between qubits are mediated by a resonator bus. We calculate the entanglement entropy and participate entropy of the highly-excited eigenstates, and obtain the lower bound of the critical linear potential $\gamma_{c}$, using the finite-size scaling collapse. Moreover, we study the non-equilibrium properties of the Stark MBL. In particular, we observe an anomalous relaxation of the imbalance, dominated by the power-law decay $t^{-\xi}$. The exponent $\xi$ satisfies $\xi\propto|\gamma-\gamma_{c}|^{\nu}$ when $\gamma, Comment: 9+7 pages, 10+7 figures, 2 tables

We experimentally study the ergodic dynamics of a 1D array of 12 superconducting qubits with a transverse field, and identify the regimes of strong and weak thermalization with different initial states. We observe convergence of the local observable to its thermal expectation value in the strong-thermalizaion regime. For weak thermalization, the dynamics of local observable exhibits an oscillation around the thermal value, which can only be attained by the time average. We also demonstrate that the entanglement entropy and concurrence can characterize the regimes of strong and weak thermalization. Our work provides an essential step towards a generic understanding of thermalization in quantum systems., Comment: 6+6 pages, 4+8 figures

Two new excited bands built on the πh11/2 configuration have been identified in Nd135 in addition to the known πh11/2 band. The energy spectra of the excited bands and the available electromagnetic transition probabilities are in good agreement with theoretical results obtained using quasiparticle-plus-triaxial-rotor model calculations. The properties of the bands identify them as tilted precession bands instead of wobbling bands. Our results give a new insight into the interpretation of the low-lying bands in odd-A mass nuclei, and can stimulate future studies to address the nuclear triaxiality.

The authors present a method of charactering many-body localization transition via the quench dynamics of diagonal entropy, as an experimentally feasible quantity. The critical point of many-body localization transition can be efficiently detected. The adopted scaling ansatz respects the Harris-Luck bound, and the scaling exponent can provide information for the universality class of many-body localization transition.

The very first in-ring reaction experiment at the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR), namely proton elastic scattering on stable $^{58}\mathrm{Ni}$ nuclei, is presented. The circulating $^{58}\mathrm{Ni}^{19+}$ ions with an energy of 95 MeV/u were interacting repeatedly with an internal hydrogen gas target in the experimental storage ring (CSRe). Low-energy proton recoils from the elastic collisions were measured with an ultra-high vacuum compatible silicon-strip detector. Deduced differential cross sections were normalized by measuring $k$-shell x rays from $^{58}\mathrm{Ni}^{19+}$ projectiles due to the $^{58}\mathrm{Ni}^{19+}\text{\ensuremath{-}}{\mathrm{H}}_{2}$ ionization collisions. Compared to the experimental cross sections, a good agreement has been achieved with the theoretical predictions in the measured region, which were obtained by using the global phenomenological optical model potentials. Our results enable new research opportunities for optical model potential studies on exotic nuclides by using the in-ring reaction setup at the HIRFL-CSR facility.

The cross section for one-proton knockout from $^{16}\mathrm{C}$ with a large neutron-proton separation energy asymmetry on a carbon target has been measured at an intermediate beam energy of around 240 MeV/nucleon. The measured cross section is compared to the predictions based on the eikonal reaction model with shell-model structure inputs. The beam-energy dependence of the reduction on the extracted spectroscopic strength for strongly bound nucleon removal is derived from combining the existing intermediate-energy data with the present measurement. The deduced reduction factor ${R}_{s}$, defined as the ratio of the measured and theoretical cross sections, for the strongly bound nucleon removal at around 240 MeV/nucleon is consistent with the systematics observed from knockout reactions induced by light nuclear targets at intermediate energies of around 80 MeV/nucleon.

The cross sections for two-neutron removal from $^{15,16}\mathrm{C}$ on a carbon target have been measured at around 240 MeV/nucleon. The measured cross section for $^{15}\mathrm{C}$ is smaller than for $^{16}\mathrm{C}$. The trends of the cross sections for $^{15,16}\mathrm{C}$ are inconsistent with the previously reported experimental data, but in agreement with the theoretical predictions based on eikonal-model calculations. Based on the present results of $^{15,16}\mathrm{C}$ combined with the available experimental data on $^{17--20}\mathrm{C}$, an odd-even staggering of the two-neutron removal cross sections along the neutron-rich carbon isotopic chain from $^{15}\mathrm{C}$ to $^{20}\mathrm{C}$ is observed, and this feature is well reproduced by the theoretical calculations.

Local and intrinsic quantum coherence, as two contributions of total quantum coherence, have been introduced by Radhakrishnan et al. [C. Radhakrishnan, M. Parthasarathy, S. Jambulingam, and T. Byrnes, Phys. Rev. Lett. 116, 150504 (2016)]. In the present work we study the property of local, intrinsic, and total quantum coherence in critical systems such as the $XY$ model, extended $XY$ model, and Ashkin-Teller model to analyze their capability in identifying the second-order, infinite-order quantum phase transitions, as well as the topological quantum phase transitions. It is shown that not only the total coherence, but also the local and intrinsic coherence can spotlight the critical points efficiently. Moreover, the long-range properties of total and local coherence, and the short-range properties of intrinsic coherence are analyzed. The total and local coherence for spin-pairs farther than nearest neighbors can highlight the critical points while the intrinsic coherence is absent for long-distance spin-pairs.

The longitudinal momentum distributions of $^{7}\mathrm{Be}$ fragments in the breakup of $^{8}\mathrm{B}$ on a carbon target have been measured at 36 MeV/u. The different mechanisms have been distinguished by coincidence measurements. The longitudinal momentum distributions of $^{7}\mathrm{Be}$ fragments from both the stripping and the diffraction mechanisms are consistent with the results of noneikonal calculations and CDCC calculations. The full widths at half maximum of the longitudinal momentum distributions are $124\ifmmode\pm\else\textpm\fi{}17$ and $92\ifmmode\pm\else\textpm\fi{}7$ MeV/$c$ for the stripping and diffraction components, respectively. The comparison with the different model calculations is discussed. It is crucial to separate the different reaction mechanisms experimentally to benchmark nuclear reaction theories.

Strong odd-even staggering (OES) of the yields of fragments, produced by fragmenting Kr78 projectiles, has been measured by employing the combination of an in-flight fragment separator and a storage ring. It is shown that the OES of fragment yields of Tz=−1/2 and Tz=1/2 mirror nuclei critically depends on both pairing and shell structure, especially at the closed shells Z=20 and 28. A comparison of the relative OES of yields and of particle-emission threshold energies reveals unambiguously that the origin of the OES of fragment yields is mainly determined by the OES of the particle-emission threshold energies, which contain both pairing and shell effects.

To improve the effective interactions in the $pf$ shell, it is important to measure the single-particle and single-hole states near the $N$ $=$ 28 shell gap. In this paper, the neutron spectroscopic factors of hole states from the unstable neutron-rich ${}^{45}$Ar ($Z$ $=$ 18,$N$ $=$ 27) nucleus have been studied using the ${}^{1}$H(${}^{46}$Ar,$d$) ${}^{45}$Ar transfer reaction in inverse kinematics. Comparison of our results with the particle states of ${}^{45}$Ar produced in ${}^{2}$H(${}^{44}$Ar, $p$) ${}^{45}$Ar reaction shows that the two reactions populate states with different angular momenta. Using the angular distributions, we are able to confirm the spin assignments of four low-lying states of ${}^{45}$Ar. These are the ground state (${f}_{7/2}$), the first-excited state (${p}_{3/2}$), and the ${s}_{1/2}$ and ${d}_{3/2}$ states. While large basis shell-model predictions describe spectroscopic properties of the ground and ${p}_{3/2}$ states very well, they fail to describe the ${s}_{1/2}$ and ${d}_{3/2}$ hole states.

The projectile fragmentation reactions of ${}^{40}$Ar at 57 MeV/nucleon on ${}^{9}$Be and ${}^{181}$Ta targets have been studied by the Radioactive Ion Beam Line in Lanzhou (RIBLL) at the Heavy-Ion Research Facility in Lanzhou (HIRFL). The momentum distributions of fragments have been measured and the competition between different mechanisms are observed. The production cross sections have been obtained and compared with the empirical parametrization of fragmentation cross section (EPAX), abrasion-ablation (AA), and heavy-ion phase space exploration (HIPSE) models, and the target dependence of fragment cross sections has also been discussed.

The breakup reactions of Cl-31 + C-12 at 44A MeV are investigated experimentally. The longitudinal momentum distribution of S-30 after one-proton removal from Cl-31 has been obtained. By assuming core plus a valence proton structure, the momentum distribution is studied using the few-body Glauber model. The calculation shows that the width of momentum distribution for a valence proton with l = 2 is consistent with the experimental data, which indicates a dominant d-wave component for the valence proton in Cl-31.

Mass excesses of short-lived $A=2Z\ensuremath{-}1$ nuclei $^{63}\mathrm{Ge}$, $^{65}\mathrm{As}$, $^{67}\mathrm{Se}$, and $^{71}\mathrm{Kr}$ have been directly measured to be $\ensuremath{-}46\text{ }921(37)$, $\ensuremath{-}46\text{ }937(85)$, $\ensuremath{-}46\text{ }580(67)$, and $\ensuremath{-}46\text{ }320(141)\text{ }\text{ }\mathrm{keV}$, respectively. The deduced proton separation energy of $\ensuremath{-}90(85)\text{ }\text{ }\mathrm{keV}$ for $^{65}\mathrm{As}$ shows that this nucleus is only slightly proton unbound. X-ray burst model calculations with the new mass excess of $^{65}\mathrm{As}$ suggest that the majority of the reaction flow passes through $^{64}\mathrm{Ge}$ via proton capture, indicating that $^{64}\mathrm{Ge}$ is not a significant $rp$-process waiting point.

Single-neutron-transfer measurements using (p,d) reactions have been performed at 33 MeV per nucleon with proton-rich Ar-34 and neutron-rich Ar-46 beams in inverse kinematics. The extracted spectroscopic factors are compared to the large-basis shell-model calculations. Relatively weak quenching of the spectroscopic factors is observed between Ar-34 and Ar-46. The experimental results suggest that neutron correlations have a weak dependence on the asymmetry of the nucleus over this isotopic region. The present results are consistent with the systematics established from extensive studies of spectroscopic factors and dispersive optical-model analyses of Ca40-49 isotopes. They are, however, inconsistent with the trends obtained in knockout-reaction measurements.

Two-{alpha} emission from high-lying excited states of {sup 18}Ne was studied by complete-kinematics measurements. The {sup 18}Ne beam at the energy of 51.8 MeV/u was bombarding a {sup 197}Au target to populate the excited states via Coulomb excitation. Products of two-{alpha} emission, {sup 10}C-{alpha}-{alpha}, were measured by an array of silicon strip detectors and a CsI + PIN telescope. With the help of Monte Carlo simulations, the experimental results show the characteristics of sequential two-{alpha} emission via {sup 14}O excited states. Sequential two-{alpha} and two-proton emissions from {sup 18}Ne via one-particle daughter states are compared and the distinction of the opening angles of these two modes originates from the difference of the mass ratio of emitted particles to daughter nuclei.

An experiment to study exotic two-proton emission from excited levels of the odd-$Z$ nucleus $^{28}\mathrm{P}$ was performed at the National Laboratory of Heavy Ion Research-Radioactive Ion Beam Line (HIRFL-RIBLL) facility. The projectile $^{28}\mathrm{P}$ at the energy of $46.5$ MeV/$u$ was bombarding a $^{197}\mathrm{Au}$ target to populate the excited states via Coulomb excitation. Complete-kinematics measurements were realized by the array of silicon strip detectors and the $\mathrm{CsI}+\mathrm{PIN}$ telescope. Two-proton events were selected and the relativistic-kinematics reconstruction was carried out. The spectrum of relative momentum and opening angle between two protons was deduced from Monte Carlo simulations. Experimental results show that two-proton emission from $^{28}\mathrm{P}$ excited states less than $17.0$ MeV is mainly two-body sequential emission or three-body simultaneous decay in phase space. The present simulations cannot distinguish these two decay modes. No obvious diproton emission was found.

Spectroscopic factors have been extracted for proton rich 34Ar and neutron rich 46Ar using the (p,d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton rich nucleus 34Ar compared to that of 46Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements., Comment: 11 pages, 2 figures. submitted to PRL

An experiment of a $^{29}\mathrm{S}$ beam bombarding a $^{197}\mathrm{Au}$ target at an energy of 49.2 MeV/u has been performed to study the two-proton correlated emission from $^{29}\mathrm{S}$ excited states. Complete-kinematics measurements were carried out in the experiment. The relative momentum, opening angle, and relative energy of two protons, as well as the invariant mass of the final system, were deduced by relativistic-kinematics reconstruction. The $^{27}\mathrm{Si}$-$p\text{\ensuremath{-}}p$ coincident events were picked out under strict conditions and the phenomenon of $p\text{\ensuremath{-}}p$ correlations was observed among these events. The mechanisms of two-proton emission were analyzed in a simple schematic model, in which the extreme decay modes like $^{2}\mathrm{He}$ cluster emission, three-body phase-space decay, and two-body sequential emission were taken into account. Associated with the Monte Carlo simulations, the present results show that two protons emitted from the excited states between 9.6 MeV and 10.4 MeV exhibit the features of $^{2}\mathrm{He}$ cluster decay with a branching ratio of ${29}_{\ensuremath{-}11}^{+10}%$.

The {beta}-decay of {sup 18}N has been studied using {beta}-n and {beta}-{gamma} coincidence methods. The {sup 18}N ions were produced by the fragmentation of the E/A=68.8 MeV {sup 22}Ne beam on a thick beryllium target. A newly constructed neutron detector system with wide energy detection range and low-energy detection threshold was used. The 619 {+-} 2 ms half-life of the {sup 18}N {beta}-decay was found to be in very good agreement with the previous measurements. Transitions to 11 {beta}-delayed neutron emitting states in {sup 18}O have been observed with a total branching ratio of 6.98 {+-} 1.46%. The Gamow-Teller {beta}-decay strengths of {sup 18}N to these levels were deduced and compared with the shell model calculations. The intensities of the strong {gamma}-ray transitions in {sup 18}O were found to be consistent with recent work.