arXiv subjects

Hui Sun

Publications and source records attributed to Hui Sun.

119 records · Page 7Linked to original sources

arXiv2017

Computational Study on Hysteresis of Ion Channels: Multiple Solutions to Steady-State Poisson--Nernst--Planck Equations

The steady-state Poisson-Nernst-Planck (ssPNP) equations are an effective model for the description of ionic transport in ion channels. It is observed that an ion channel exhibits voltage-dependent switching between open and closed states. Different conductance states of a channel imply that the ssPNP equations probably have multiple solutions with different level of currents. We propose numerical approaches to study multiple solutions to the ssPNP equations with multiple ionic species. To find complete current-voltage (I-V ) and current-concentration (I-C) curves, we reformulate the ssPNP equations into four different boundary value problems (BVPs). Numerical continuation approaches are developed to provide good initial guesses for iteratively solving algebraic equations resulting from discretization. Numerical continuations on V , I, and boundary concentrations result in S-shaped and double S-shaped (I-V and I-C) curves for the ssPNP equations with multiple species of ions. There are five solutions to the ssPNP equations with five ionic species, when an applied voltage is given in certain intervals. Remarkably, the current through ion channels responds hysteretically to varying applied voltages and boundary concentrations, showing a memory effect. In addition, we propose a useful computational approach to locate turning points of an I-V curve. With obtained locations, we are able to determine critical threshold values for hysteresis to occur and the interval for V in which the ssPNP equations have multiple solutions. Our numerical results indicate that the developed numerical approaches have a promising potential in studying hysteretic conductance states of ion channels.

math.NA↗

arXiv2017

Spin-dependent Optical Superlattice

We propose and implement a lattice scheme for coherently manipulating atomic spins. Using the vector light shift and a superlattice structure, we demonstrate experimentally the capability on parallel spin addressing in double-wells and square plaquettes with subwavelength resolution. Quantum coherence of spin manipulations is verified through measuring atom tunneling and spin exchange dynamics. Our experiment presents a building block for engineering many-body quantum states in optical lattices for realizing quantum simulation and computation tasks.

cond-mat.quant-gas↗

arXiv2017

Observation of Quantum Criticality and Luttinger Liquid in One-dimensional Bose Gases

We experimentally investigate the quantum criticality and Tomonaga-Luttinger liquid (TLL) behavior within one-dimensional (1D) ultracold atomic gases. Based on the measured density profiles at different temperatures, the universal scaling laws of thermodynamic quantities are observed. The quantum critical regime and the relevant crossover temperatures are determined through the double-peak structure of the specific heat. In the TLL regime, we obtain the Luttinger parameter by probing sound propagation. Furthermore, a characteristic power-law behavior emerges in the measured momentum distributions of the 1D ultracold gas, confirming the existence of the TLL.

cond-mat.quant-gas↗

arXiv2017

X-ray counterpart of gravitational waves due to binary neutron star mergers: light curves, luminosity functions, and event rate densities

Zhang (2013) proposed a type of GRB-less X-ray transient associated with double neutron star (NS-NS) mergers under the conjecture of a rapidly-spinning magnetar merger product with the line of sight off the short GRB jet. We investigate possible light curves of these transients by considering different observer's viewing angles. We perform Monte Carlo simulations to calculate the peak luminosity function (LF) and event rate density of these X-ray transients. By considering that a fraction of massive neutron stars may be supra-massive and later collapse into black holes after spinning down, we investigate how the predicted LF depends on the equation of state (EoS) of the central object and the geometry of the system. In general, the LF can be fit by two log-normal distributions peaking around $10^{46.4}$ and $10^{49.6}$ $\rm erg\,s^{-1}$, corresponding to the trapped and free zones, respectively. For the majority of the EoS models, the current non-detection is consistent with having a free zone solid angle at most a few times of the solid angle of the short GRB jet. The event rate density of these X-ray transients is around a few tens of $\rm Gpc^{-3}yr^{-1}$ for luminosity above $10^{45}$ $\rm erg\,s^{-1}$. We predict that future X-ray telescopes (such as Einstein Probe) with sensitivity $\sim 10^{-11}$ $\rm erg\,s^{-1}\,cm^{-2}$ would detect as many as several tens of such transients per year per steradian. Within 200 Mpc, the aLIGO average range for NS-NS mergers, the estimated event rate of these transients is about 1 transient per year all sky.

astro-ph.HE↗

arXiv2016

Magnetar central engine and possible gravitational wave emission of nearby short GRB 160821B

GRB 160821B is a short gamma-ray burst (GRB) at redshift $z=0.16$, with a duration less than 1 second and without detection of any "extended emission" up to more than 100 seconds in both {\em Swift}/BAT and {\em Fermi}/GBM bands. An X-ray plateau with a sharp drop 180 seconds after the BAT trigger was observed with {\em Swift}/XRT. No supernova or kilo-nova signature was detected. Assuming the central engine of this SGRB is a recently born supra-massive magnetar, we can explain the SGRB as jet radiation and its X-ray plateau as the internal energy dissipation of the pulsar wind as it spins down. We constrain its surface magnetic field as $B_{\rm p}<3.12\times 10^{16}$ G and initial spin period as $P_0< 8.5\times 10^{-3}$ seconds. Its equation of state is consistent with the GM1 model with $M_{\rm TOV} \sim 2.37 M_\odot$ and ellipticity $ε<0.07$. Its gravitational wave (GW) radiation may be detectable with the future Einstein Telescope, but is much weaker than the current detectability limit of advanced-LIGO. The GW radiation of such an event would be detectable by advanced-LIGO if it occurred at a distance of 100 Mpc ($z=0.023$).

astro-ph.HE↗

arXiv2016

High sensitivity optical Faraday-magnetometry with intracavity electromagnetically induced transparency

We suggest a multiatom cavity quantum electrodynamics system for the weak magnetic field detection based on Faraday rotation with intracavity electromagnetically induced transparency. Our study demonstrates that the collective coupling between the cavity modes and the atomic ensemble can be used to improve the sensitivity. With single probe photon input, the sensitivity is inversely proportional to the number of atoms, and the sensitivity with 0.7(5)~nT/$\sqrt{\rm Hz}$ could be attained. With multiphoton measurement, our numerical calculations show that the magnetic field sensitivity can be improved to 4.7(9)~fT/$\sqrt{\rm Hz}$.

quant-ph↗

arXiv2016

Observation of Four-body Ring-exchange Interactions and Anyonic Fractional Statistics

Ring exchange is an elementary interaction for modeling unconventional topological matters which hold promise for efficient quantum information processing. We report the observation of four-body ring-exchange interactions and the topological properties of anyonic excitations within an ultracold atom system. A minimum toric code Hamiltonian in which the ring exchange is the dominant term, was implemented by engineering a Hubbard Hamiltonian that describes atomic spins in disconnected plaquette arrays formed by two orthogonal superlattices. The ring-exchange interactions were resolved from the dynamical evolutions in the spin orders, matching well with the predicted energy gaps between two anyonic excitations of the spin system. A braiding operation was applied to the spins in the plaquettes and an induced phase $1.00(3)π$ in the four-spin state was observed, confirming $\frac{1}{2}$-anynoic statistics. This work represents an essential step towards studying topological matters with many-body systems and the applications in quantum computation and simulation.

cond-mat.quant-gas↗

arXiv2015

Extra-galactic high-energy transients: event rate densities and luminosity functions

Several types of extra-galactic high-energy transients have been discovered, which include high-luminosity and low-luminosity long-duration gamma-ray bursts (GRBs), short-duration GRBs, supernova shock breakouts (SBOs), and tidal disruption events (TDEs) without or with an associated relativistic jet. In this paper, we apply a unified method to systematically study the redshift-dependent event rate densities and the global luminosity functions (ignoring redshift evolution) of these transients. We introduce some empirical formulae for the redshift-dependent event rate densities for different types of transients, and derive the local specific event rate density, which also represents its global luminosity function. Long GRBs have a large enough sample to reveal features in the global luminosity function, which is best characterized as a triple power law. All the other transients are consistent with having a single power law luminosity function. The total event rate density depends on the minimum luminosity, and we obtain the following values in units of ${\rm Gpc^{-3}~yr^{-1}}$: $0.8^{+0.1}_{-0.1}$ for high-luminosity long GRBs above $ 10^{50}~{\rm erg~s^{-1}}$, $164^{+98}_{-65}$ for low-luminosity long GRBs above $5\times 10^{46}~{\rm erg~s^{-1}}$, $1.3^{+0.4}_{-0.3}$, $1.2^{+0.4}_{-0.3}$, and $3.3^{+1.0}_{-0.8}$ above $ 10^{50}~ {\rm erg~s^{-1}}$ for short GRBs with three different merger delay models (Gaussian, log-normal, and power law), $1.9^{+2.4}_{-1.2}\times 10^4$ above $ 10^{44}~{\rm erg~s^{-1}}$ for SBOs, $ 4.8^{+3.2}_{-2.1}\times10^2 $ for normal TDEs above $10^{44}~ {\rm erg~s^{-1}}$, and $0.03^{+0.04}_{-0.02}$ above $ 10^{48}~ {\rm erg~s^{-1}}$ for TDE jets as discovered by Swift. Intriguingly, the global luminosity functions of different kinds of transients, which cover over 12 orders of magnitude, are consistent with a single power law with an index of -1.6.

astro-ph.HE↗

arXiv2012

Tunneling-induced high efficiency four-wave mixing in an asymmetric quantum wells

An asymmetric double quantum wells (QWs) structure with resonant tunneling is suggested to achieve high efficient four wave mixing (FWM). We analytically demonstrate that the resonant tunneling can induce high efficient mixing wave in such a semiconductor structure with a low light pump wave. In particular, the FWM conversion efficiency can be enhanced dramatically in the vicinity of the center frequency. This interesting scheme may be used to generate coherent long-wavelength radiation in solid-state system.

quant-ph↗

arXiv2011

Strongly interacting and highly entangled photons in asymmetric quantum well with resonant tunneling

We propose an asymmetric quantum well structure to realize strong interaction between two slow optical pulses. The linear optical properties and nonlinear optical responses associated with cross-Kerr nonlinearity are analyzed. Combining the resonant tunneling and the advantages of inverted-Y type scheme, giant cross-Kerr nonlinearity can be achieved with vanishing absorptions. Based on the unique feature, we demonstrate that highly entangled photons can be produced and photonic controlled phase gate can be constructed. In this construction, the scheme is symmetric for the probe and signal pulses. Consequently, the condition of group velocity matching can be fulfilled by adjusting the initial electron distribution.

physics.optics↗

arXiv2009

Optical rotation of heavy hole spins by non-Abelian geometrical means

A non-Abelian geometric method is proposed for rotating of heavy hole spins in a singly positive charged quantum dot in Voigt geometry. The key ingredient is the delay-dependent non-Abelian geometric phase, which is produced by the nonadiabatic transition between the two degenerate dark states. We demonstrate, by controlling the pump, the Stokes and the driving fields, that the rotations about $y$- and $z$-axes with arbitrary angles can be realized with high fidelity. Fast initialization and heavy hole spin state readout are also possible.

quant-ph↗