arXiv subjects

Jingen Xiang

Publications and source records attributed to Jingen Xiang.

13 recordsLinked to original sources

arXiv2025

Enhanced Distributed Variational Quantum Eigensolver for Large-Scale MaxCut Problem

MaxCut is a canonical NP-hard combinatorial optimization problem in graph theory with broad applications ranging from physics to bioinformatics. Although variational quantum algorithms offer promising new approaches that may eventually outperform classical schemes, they suffer from resource constraints and trainability issues such as barren plateaus, making large-scale instances intractable on noisy intermediate-scale quantum devices. In this paper, we propose an enhanced distributed variational quantum eigensolver for large-scale MaxCut problems, which extends our prior distributed variational quantum eigensolver framework by integrating a novel hybrid classical-quantum perturbation strategy, enhances optimization scalability and efficiency. Our algorithm solves weighted MaxCut instances with up to 1000 vertices using only 10 qubits, and numerical results indicate that it consistently outperforms the Goemans-Williamson algorithm. We further employ a warm-start initialization strategy, seeding the algorithm with high-quality solutions from the Goemans-Williamson algorithm, with results confirming that the optimal classical solution can be effectively further improved. The practical utility of the proposed algorithm is further validated through its application to haplotype phasing on genome sequencing data of the human ABCA1 gene, producing high-quality haplotypes that rival those obtained by the Goemans-Williamson algorithm with $10^6$ projections. These results establish the proposed algorithm as a scalable, NISQ-compatible framework for near-term quantum-enhanced large-scale combinatorial optimization.

quant-ph↗

arXiv2025

Realization of Thread Level Parallelism on Quantum Devices

Scaling up quantum devices is a central challenge for realizing practical quantum computation. Modular quantum architectures promise scalability, yet experiments to date have relied on either $\sim\!10^{3}$-qubit monolithic chips or fragile interconnects with high loss. Here, we introduce a classical linkage scheme that merges multiple independent quantum processing units (QPUs) into a single logical device, enabling thread-level parallelism (TLP). Theoretically, we show that quantum routines with product-state inputs and low-rank entangling layers can be re-expressed in an efficient parallelizable form. Experimentally, we validate this architecture on clusters comprising up to sixteen benchtop nuclear magnetic resonance (NMR) quantum nodes. A four-qubit Greenberger-Horne-Zeilinger (GHZ) state is partitioned into parallel two-qubit subcircuits, achieving a fidelity of $93.8\,\%$ with respect to the ideal state. A non-Hermitian evolution, implemented via a truncated Cauchy integral on Hermitian Hamiltonians, reproduces exact observables with high accuracy. Our results demonstrate that classical links suffice to scale up the logical size of quantum computations and realize general, non-unitary channels on today's hardware, opening an experimentally accessible route toward software-defined, clustered quantum accelerators.

quant-ph↗

arXiv2022

SpinQ Triangulum: a commercial three-qubit desktop quantum computer

SpinQ Triangulum is the second generation of the desktop quantum computers designed and manufactured by SpinQ Technology. SpinQ's desktop quantum computer series, based on room temperature NMR spectrometer, provide light-weighted, cost-effective and maintenance-free quantum computing platforms that aim to provide real-device experience for quantum computing education for K-12 and college level. These platforms also feature quantum control design capabilities for studying quantum control and quantum noise. Compared with the first generation product, the two-qubit SpinQ Gemini, Triangulum features a three-qubit QPU, smaller dimensions (61 * 33 * 56 cm^3) and lighter (40 kg). Furthermore, the magnetic field is more stable and the performance of quantum control is more accurate. This paper introduces the system design of Triangulum and its new features. As an example of performing quantum computing tasks, we present the implementation of the Harrow-Hassidim-Lloyd (HHL) algorithm on Triangulum, demonstrating Triangulum's capability of undertaking complex quantum computing tasks. SpinQ will continue to develop desktop quantum computing platform with more qubits. Meanwhile, a simplified version of SpinQ Gemini, namely Gemini Mini (https://www.spinq.cn/products#geminiMini-anchor) , has been recently realised. Gemini Mini is much more portable (20* 35 * 26 cm^3, 14 kg) and affordable for most K-12 schools around the world.

quant-ph↗

arXiv2021

SpinQ Gemini: a desktop quantum computer for education and research

SpinQ Gemini is a commercial desktop quantum computer designed and manufactured by SpinQ Technology. It is an integrated hardware-software system. The first generation product with two qubits was launched in January 2020. The hardware is based on NMR spectrometer, with permanent magnets providing $\sim 1$ T magnetic field. SpinQ Gemini operates under room temperature ($0$-$30^{\circ}$C), highlighting its lightweight (55 kg with a volume of $70\times 40 \times 80$ cm$^3$), cost-effective (under $50$k USD), and maintenance-free. SpinQ Gemini aims to provide real-device experience for quantum computing education for K-12 and at the college level. It also features quantum control design capabilities that benefit the researchers studying quantum control and quantum noise. Since its first launch, SpinQ Gemini has been shipped to institutions in Canada, Taiwan and Mainland China. This paper introduces the system of design of SpinQ Gemini, from hardware to software. We also demonstrate examples for performing quantum computing tasks on SpinQ Gemini, including one task for a variational quantum eigensolver of a two-qubit Heisenberg model. The next generations of SpinQ quantum computing devices will adopt models of more qubits, advanced control functions for researchers with comparable cost, as well as simplified models for much lower cost (under $5$k USD) for K-12 education. We believe that low-cost portable quantum computer products will facilitate hands-on experience for teaching quantum computing at all levels, well-prepare younger generations of students and researchers for the future of quantum technologies.

quant-ph↗

arXiv2011

The Extreme Spin of the Black Hole in Cygnus X-1

The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observations. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole's accretion disk by fitting its thermal continuum spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-1 contains a near-extreme Kerr black hole with a spin parameter a/M>0.95 (3σ). For a less probable (synchronous) dynamical model, we find a/M>0.92 (3σ). In our analysis, we include the uncertainties in black hole mass, orbital inclination angle and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disk's low luminosity.

astro-ph.HE↗

arXiv2011

Using the X-ray Dust Scattering Halo of Cygnus X-1 to determine distance and dust distributions

We present a detailed study of the X-ray dust scattering halo of the black hole candidate \cygx1 based on two \chandra\ HETGS observations. Using 18 different dust models, including one modified by us (dubbed XLNW), we probe the interstellar medium between us and this source. A consistent description of the cloud properties along the line of sight that describes at the same time the halo radial profile, the halo lightcurves, and the column density from source spectroscopy is best achieved with a small subset of these models. Combining the studies of the halo radial profile and the halo lightcurves, we favor a geometric distance to \cygx1 of $d=1.81\pm{0.09}$\,kpc. Our study also shows that there is a dense cloud, which contributes $\sim$50% of the dust grains along the line of sight to \cygx1, located at $\sim1.6$ kpc from us. The remainder of the dust along the line of sight is close to the black hole binary.

astro-ph.HE↗

arXiv2009

Condensed Matter Astrophysics: A Prescription for Determining the Species-Specific Composition and Quantity of Interstellar Dust using X-rays

We present a new technique for determining the *quantity and composition* of dust in astrophysical environments using <6keV X-rays. We argue that high resolution X-ray spectra as enabled by the Chandra and XMM-Newton gratings should be considered a powerful and viable new resource for delving into a relatively unexplored regime for directly determining dust properties: composition, quantity, and distribution. We present initial cross-section measurements of astrophysically likely iron-based dust candidates taken at the Lawrence Berkeley National Laboratory Advanced Light Source synchrotron beamline, as an illustrative tool for the formulation of our methodology. Focused at the 700eV Fe LIII and LII photoelectric edges, we discuss a technique for modeling dust properties in the soft X-rays using L-edge data, to complement K-edge X-ray absorption fine structure analysis techniques discussed in Lee & Ravel 2005. This is intended to be *a techniques paper* of interest and usefulness to both condensed matter experimentalists and astrophysicists. For the experimentalists, we offer a new prescription for normalizing relatively low S/N L-edge cross section measurements. For astrophysics interests, we discuss the use of X-ray absorption spectra for determining dust composition in cold and ionized astrophysical environments, and a new method for determining *species-specific gas-to-dust ratios*. Possible astrophysical applications of interest, are offered. Prospects for improving on this work with future X-ray missions with higher throughput and spectral resolution are presented in the context of spectral resolution goals for gratings and calorimeters, for proposed and planned missions such as Astro-H and the International X-ray Observatory.

astro-ph.IM↗

arXiv2009

The accretion disk corona and disk atmosphere of 4U 1624-490 as viewed by the Chandra-HETGS

We present a detailed spectral study (photoionization modelling and variability) of the "Big Dipper" 4U 1624-490 based on a \chandra-High Energy Transmission Gratings Spectrometer (HETGS) observation over the $\sim76$ ks binary orbit of 4U 1624-490. While the continuum spectrum can be modeled using a blackbody plus power-law, a slightly better fit is obtained using a single $Γ=2.25$ power-law partially (71%) covered by a local absorber of column density $N_{\rm H, Local}=8.1_{-0.6}^{+0.7}\times 10^{22} \rm cm^{-2}$. The data show a possible quasi-sinusoidal modulation with period $43_{-9}^{+13}$ ks that might be due to changes in local obscuration. Photoionization modeling with the {\sc xstar} code and variability studies of the observed strong \ion{Fe}{25} and \ion{Fe}{26} absorption lines point to a two-temperature plasma for their origin: a highly ionized component of ionization parameter $ξ_{\rm hot} \approx 10^{4.3} {\rm ergs cm s^{-1}}$ ($T\sim 3.0\times 10^{6}$ K) associated with an extended accretion disk corona of radius $R \sim3\times10^{10}$ cm, and a less ionized more variable component of $ξ\approx 10^{3.4} {\rm ergs cm s^{-1}}$ ($T\sim 1.0\times 10^{6}$ K) and $\rm ξ\approx 10^{3.1} ergs cm s^{-1}$ ($T\sim 0.9\times 10^{6}$ K) coincident with the accretion disk rim. We use this, with the observed \ion{Fe}{25} and \ion{Fe}{26} absorption line variations (in wavelength, strength, and width) to construct a viewing geometry that is mapped to changes in plasma conditions over the 4U 1624-490 orbital period.

astro-ph.HE↗

arXiv2008

A Study of the X-Ray Dust Scattering Halo of Cyg X-1 with a Cross-Correlation Method

X-ray photons scattered by the interstellar medium carry information about dust distribution, dust grain model, scattering cross section, and the distance of the source; they also take longer time than unscattered photons to reach the observer. Using a cross-correlation method, we study the light curves of the X-ray dust scattering halo of Cyg X-1, observed with the \textit{Chandra X-ray Observatory}. Significant time lags are found between the light curves of the point source and its halo. This time lag increases with the angular distance from Cyg X-1, implying a dust concentration at a distance along the line of sight (LOS) of 2.0 kpc $\times$ (0.876 $\pm$ 0.002) from the Earth. By fitting the observed light curves of the halo at different radii with simulated light curves, we obtain a width of $\mathit{ΔL}=33_{-13}^{+18}$ pc of this dust concentration. The origin of this dust concentration is still not clearly known. The advantage of our method is that we need no assumption of scattering cross section, dust grain model, or dust distribution along the LOS. Combining the derived dust distribution from the cross-correlation study with the surface brightness distribution of the halo, we conclude that the two commonly accepted models of dust grain size distribution need to be modified significantly.

astro-ph↗

arXiv2008

Time lag in the X-ray Dust Scattering Halo of Cyg X-1

This paper has been withdrawn temporarily by the authors, because we are waiting for referee report of the paper submitted to ApJ.

astro-ph↗

arXiv2007

Using the X-ray Dust Scattering Halo of 4U 1624-490 to determine distance and dust distributions

We present X-ray dust scattering halo results based on our 76 ks {\it Chandra} ACIS-S/HETGS observation of the LMXB dipping source 4U 1624-490. Through analysis of the halo light curves with 2-6 keV spectra over the persistent and dipping periods, we estimate a geometric distance of $\sim$15 kpc to 4U 1624-490. We also fit halo radial profiles with different ISM dust grain models to assess the location, uniformity, and density of the halo. Our analysis shows that the dust spatial distribution is not uniform along the line-of-sight; rather, it is consistent with the spiral arm structure mapped in {\sc Hii}. The large difference between the absorption Hydrogen column ($N_{\rm H}^{abs} \sim 8 \times10^{22} \rm cm^{-2}$; probes all gas along the line-of-sight) derived from broadband spectral fitting, and the scattering Hydrogen column ($N_{\rm H}^{sca} \sim 4 \times10^{22} \rm cm^{-2}$; probes only Galactic gas) derived from our studies of the 4U 1624-490 X-ray halo suggests that a large fraction of the column is local to the X-ray binary. We also present (and apply) a new method for assessing the {\it Chandra} point spread function at large ($> 50''$) angles, through use of the time delays from the observed dips.

astro-ph↗

arXiv2005

Probing the Spatial Distribution of the Interstellar Dust Medium by High Angular Resolution X-ray Halos of Point Sources

We studied the X-ray dust scattering halos around 17 bright X-ray point sources using {\it Chandra} data. We use an iterative method to resolve the halos at small scattering angles from the zeroth order data in CC-mode or the first order data in TE-mode which is not or less piled-up. Using the halo models of Weingartner $&$ Draine (2001, WD01) and Mathis, Rumpl $&$ Nordsieck (1977, MRN) to fit the halo profiles, we get the hydrogen column densities and the spatial distributions of the scattering dust grains along the line of sights (LOS) to these sources. We find that the scattering dust density very close to these sources is much higher than the normal interstellar medium. For X-ray pulsars GX 301-2 and Vela X-1 with companions of strong stellar winds, the X-ray absorption column densities are much higher than the derived scattering column densities, because of the dense media around the X-ray sources produce extremely small angle scatterings which are indistinguishable from the point sources even with \textit{Chandra}'s angular resolution. For LMC X-1, most of the scattering and absorption occur in Large Magellanic Cloud, rather than in the Milky Way. From the obtained X-rays spectra, the cold gas absorption and thus the quivalent hydrogen column is determined. We have obtained the linear correlation between $N_{H}$ derived from spectral fits and the one derived from the halo model WD01 and MRN (except for GX 301-2 and Vela X-1): $N_{H,WD01} = (0.720\pm0.009) \times N_{H,abs} + (0.051\pm0.013)$ and $N_{N, MRN} = (1.156\pm0.016) \times N_{H,abs} + (0.062\pm0.024)$ in the units $10^{22}$ cm$^{-2}$. High angular resolution X-ray dust scattering halos offer an excellent potential for probing the spatial distributions of interstellar dust medium.

astro-ph↗

arXiv2005

Study the X-ray Dust Scattering Halos with Chandra Observations of Cygnus X-3 and Cygnus X-1

We improve the method proposed by Yao \emph{et al} (2003) to resolve the X-ray dust scattering halos of point sources. Using this method we re-analyze the Cygnus X-1 data observed with {\it Chandra} (ObsID 1511) and derive the halo radial profile in different energy bands and the fractional halo intensity (FHI) as $I(E)=0.402\times E_{\rm keV}^{-2}$. We also apply the method to the Cygnus X-3 data ({\it Chandra} ObsID 425) and derive the halo radial profile from the first order data with the {\it Chandra} ACIS+HETG. It is found that the halo radial profile could be fit by the halo model MRN (Mathis, Rumpl $&$ Nordsieck, 1977) and WD01 (Weingartner $&$ Draine, 2001); the dust clouds should be located at between 1/2 to 1 of the distance to Cygnus X-1 and between 1/6 to 3/4 (from MRN model) or 1/6 to 2/3 (from WD01 model) of the distance to Cygnus X-3, respectively.

astro-ph↗