arXiv subjects

Yu Jia

Publications and source records attributed to Yu Jia.

At least 55 records · Page 3Linked to original sources

arXiv2023

Quantum computation in silicon-vacancy centers based on nonadiabatic geometric gates protected by dynamical decoupling

Due to strong zero-phonon line emission, narrow inhomogeneous broadening, and stable optical transition frequencies, the quantum system consisting of negatively charged silicon-vacancy (SiV) centers in diamond is highly expected to develop universal quantum computation. We propose to implement quantum computation for the first time using SiV centers placed in a one-dimensional phononic waveguide, for which quantum gates are realized in a nonadiabatic geometric way and protected by dynamical decoupling (DD). The scheme has the feature of geometric quantum computation that is robust to control errors and the advantage of DD that is insensitive to environmental impact. Furthermore, the encoding of qubits in long-lifetime ground states of silicon-vacancy centers can reduce the effect of spontaneous emission. Numerical simulations demonstrate the practicability of the SiV center system for quantum computation and the robustness improvement of quantum gates by DD pulses. This scheme may provide a promising path toward high-fidelity geometric quantum computation in solid-state systems.

quant-ph↗

arXiv2023

Optimized ${\cal O}(α_s^2)$ correction to exclusive double $J/ψ$ production at $B$ factories

The failure of observing the $e^+ e^- \to J/ψ+J/ψ$ events at $B$ factories to date is often attributed to the significant negative order-$α_s$ correction. In this work we compute the ${\cal O}(α^2_s)$ correction to this process for the first time. The magnitude of the next-to-next-to-leading order (NNLO) perturbative correction is substantially negative so that the standard NRQCD prediction would suffer from an unphysical, negative cross section. This dilemma may be traced in the fact that the bulk contribution of the fixed-order radiative corrections stems from the perturbative corrections to the $J/ψ$ decay constant. We thus implement an improved NRQCD factorization framework, by decomposing the amplitude into the photon-fragmentation piece and the non-fragmentation piece. With the measured $J/ψ$ decay constant as input, which amounts to resumming a specific class of radiative and relativistic corrections to all orders, the fragmentation-induced production rate can be predicted accurately and serves a benchmark prediction. The non-fragmentation type of the amplitude is then computed through NNLO in $α_s$ and at lowest order in velocity. Both the ${\cal O}(α_s)$ and ${\cal O}(α^2_s)$ corrections in the interference term become positive and exhibit a decent convergence behavior. Our finest prediction is $σ(e^+ e^- \to J/ψ+J/ψ)= 2.13^{+0.30}_{-0.06}$ fb at $\sqrt{s}=10.58$ GeV. With the projected integrated luminosity of 50 ${\rm ab}^{-1}$, the prospect to observe this exclusive process at \texttt{Belle} 2 experiment appears to be bright.

hep-ph↗

arXiv2023

Inclusive production of fully-charmed tetraquarks at LHC

The $X(6900)$ resonance, originally discovered by the \texttt{LHCb} collaboration and later confirmed by both \texttt{ATLAS} and \texttt{CMS} experiments, has sparked broad interests in the fully-charmed tetraquark states. Relative to the mass spectra and decay properties of fully-heavy tetraquarks, our knowledge on their production mechanism is still rather limited. In this work we investigate the inclusive production of fully-charmed $S$-wave tetraquarks at \texttt{LHC} within the nonrelativistic QCD (NRQCD) factorization framework. The partonic cross sections are computed at lowest order in $α_s$ and velocity, while the long-distance NRQCD matrix elements are estimated from phenomenological potential models. We predict the differential $p_T$ spectra of various fully-charmed $S$-wave tetraquarks at the \texttt{LHC}, and compare with the results predicted from the fragmentation mechanism at large $p_T$ end.

hep-ph↗

arXiv2023

Soft pattern of Rutherford scattering from heavy target mass expansion

We investigate the soft behavior of the tree-level Rutherford scattering process. We consider two types of Rutherford scattering, a low-energy massless point-like projectile (say, a spin-${1\over 2}$ or spin-$0$ electron) to hit a static massive composite target particle carrying various spins (up to spin-$2$), and a slowly-moving light projectile hits a heavy static composite target. For the first type, the unpolarized cross sections in the laboratory frame are found to exhibit universal forms in the first two orders of $1/M$ expansion, yet differ at the next-to-next-to-leading order (though some terms at this order still remain to be universal or depend on the target spin in a definite manner). For the second type, at the lowest order in electron velocity expansion, through all orders in $1/M$, the unpolarized cross section is universal (also not sensitive to the projectile spin). The universality partially breaks down at relative order-$v^2/M^2$, though some terms at this order are still universal or depend on the target spin in a specific manner. We also employ the effective field theory approach to reproduce the soft behavior of the differential cross sections for the target particle being a composite Dirac fermion.

hep-ph↗

arXiv2023

Origin of the large differences in high-pressure stability and superconductivity between ThH9 and ThH18

Recently, the thorium hydride ThH9 possessing an H-rich clathrate structure has been experimentally synthesized to exhibit a superconducting transition temperature Tc of 146 K at 170-175 GPa, while the more H-rich clathrate thorium hydride ThH18 was theoretically predicted to reach a Tc of 296 K at 400 GPa. Using first-principles calculations, we find that ThH9 has a more ionic character between Th atoms and H cages than ThH18 and that the latter has a more substantial hybridization of the Th 6p semicore and H 1s states than the former. These different bonding characteristics of ThH9 and ThH18 are associated with their stability at very different pressures. Furthermore, we reveal that (i) the H-derived density of states at the Fermi level Ef is about two times larger in ThH18 than in ThH9. (ii) the average squared phonon frequency of H atoms is about 29% higher in ThH18 than in ThH9, and (iii) the Fermi surface average squared electron-phonon matrix element is similar between the two hydrides. Consequently, the electron-phonon coupling constant of ThH18 becomes much greater than that of ThH9, leading to a significant Tc difference between the two thorium hydrides. Our findings not only provide an explanation for the very large differences in the stabilization pressure and superconducting transition temperature between ThH9 and ThH18 but also have important implications for the design of H-rich, high-Tc clathrate metal hydrides.

cond-mat.supr-con↗

arXiv2023

Parton distribution of intrinsic charm in two dimensional QCD

We present a detailed investigation on the intrinsic charm content in a light meson within the 't Hooft model, namely, the two-dimensional QCD in large $N_c$ limit. The intrinsic charm parton distribution function (PDF) of a light meson, which first arises at order $N_c^{-1}$, is explicitly expressed in terms of the 't Hooft wave functions of the light meson and an infinite towers of excited charmed mesons. We also derive the functional forms from the two-dimensional counterparts of the meson cloud model (MCM) and Brodsky-Hoyer-Peterson-Sakai (BHPS) model. We then make a quantitative comparison between our rigorous results and model predictions. We also study how the profile of the intrinsic charm PDF varies with charm quark mass. The average momentum fraction carried by the charm quark inside a light meson is found to decrease faster than $m_c^{-4}$ with increasing charm quark mass.

hep-ph↗

arXiv2022

Surface-induced ferromagnetism and anomalous Hall transport at Zr2S(001)

Two-dimensional layered electrides possessing anionic excess electrons in the interstitial spaces between cationic layers have attracted much attention due to their promising opportunities in both fundamental research and technological applications. Using first-principles calculations, we predict that the layered bulk electride Zr2S is nonmagnetic with massive Dirac nodal-line states arising from Zr-4d cationic and interlayer anionic electrons. However, the Zr2S(001) surface increases the density of states at the Fermi level caused by the surface potential, thereby inducing a ferromagnetic order at the outermost Zr layer via the Stoner instability. Consequently, the time-reversal symmetry breaking at the surface not only generates highly spin-polarized topological surface states with intricate helical spin textures, but also hosts an intrinsic anomalous Hall effect originating from the Berry curvature generated by spin-orbit coupling. Our findings offer a playground to investigate the emergence of ferromagnetism and anomalous Hall transport at the surface of nonmagnetic topological electrides.

cond-mat.mtrl-sci↗

arXiv2022

Next-to-next-to-leading-order QCD corrections to $e^+e^-\to J/ψ+η_c$ at $B$ factories

Within the nonrelativistic QCD (NRQCD) factorization framework, we compute the long-awaited ${\mathcal O}(α_s^2)$ correction for the exclusive double charmonium production process at $B$ factories, {\it i.e.}, $e^+e^-\to J/ψ+η_c$ at $\sqrt{s}=10.58$ GeV. For the first time, we confirm that NRQCD factorization does hold at next-to-next-to-leading-order (NNLO) for exclusive double charmonium production. It is found that including the NNLO QCD correction considerably reduces the renormalization scale dependence, and also implies the reasonable perturbative convergence behavior for this process. Our state-of-the-art prediction is consistent with the BaBar measurement within errors.

hep-ph↗

arXiv2022

New Physics Opportunities in Triangle Singularity

We show that loop-induced processes involving new physics particles can readily satisfy Landau Equation and trigger triangular singularities at high energy colliders, leading to fully visible Standard Model final states. Four-particle vertices in new physics allow triangular singularity diagrams to evade large virtuality suppression. In addition, a $t$-channel triangular singularity can also occur in particle scattering processes that may extend to low momentum exchange. We discuss several typical scenarios in supersymmetric and extended Higgs models, then identify the singular component in the loop-integral amplitude at specific external momentum points.

hep-ph↗

arXiv2022

Three-loop QCD corrections to the decay constant of $B_c$

Within the framework of nonrelativistic QCD (NRQCD) factorization, we compute the three-loop QCD corrections to the decay constant of $B_c$. We reconstruct the analytical expressions for the three-loop renormalization constant and the corresponding anomalous dimension affiliated with the pseudoscalar current composed of two different heavy flavors in NRQCD, which are functions of the ratio between the charm and bottom quark masses. Meanwhile, the short-distance coefficient is obtained with very high numerical accuracy. The three-loop QCD correction turns out to be overwhelmingly large. The phenomenological implication of this new piece of radiative corrections for the $B_c$ leptonic decay is also addressed.

hep-ph↗

arXiv2022

Complete three-loop QCD corrections to leptonic width of vector quarkonium

Within the nonrelativistic QCD (NRQCD) factorization framework, we compute the order-$α_s^3$ perturbative corrections to the leptonic decay of the $Υ$ and $J/ψ$ with high numerical accuracy, at the lowest order in velocity expansion. We confirm the existing three-loop results in literature. Furthermore, we explicitly consider the complex-valued light-by-light (singlet) contributions. We for the first time also consider the finite charm quark mass effect for $Υ$ leptonic decay, and obtain a new piece of 3-loop contribution to the anomalous dimension related to the composite NRQCD bilinear of vector current that arises from the nonzero charm quark mass. Based on the complete three-loop NRQCD short-distance coefficients, we also present a comprehensive phenomenological analysis for $Υ(J/ψ)$ leptonic width.

hep-ph↗

arXiv2022

Photoproduction of C-even quarkonia at EIC and EicC

The $η_c$ photoproduction in $ep$ collision has long been proposed as an ideal process to probe the existence of odderon. In the current work, we systematically investigate the photoproduction of various $C$-even heavy quarkonia (exemplified by $η_{c(b)}$, and $χ_{c(b)J}$ with $J=0,1,2$) via one-photon exchange channel, at the lowest order in $α_s$ and heavy quark velocity in the context of NRQCD factorization. We find that the photoproduction rates of the $C$-even quarkonia through this mechanism are comparable in magnitude with that through the odderon-initiated mechanism, even in the Regge limit ($s\gg -t$), though the latter types of predictions suffers from considerable theoretical uncertainties. The future measurements of these types of quarkonium photoproduction processes in \texttt{EIC} and \texttt{EicC} are crucial to ascertain which mechanism plays the dominant role.

hep-ph↗

arXiv2022

Charge density wave and superconductivity in the kagome metal CsV$_3$Sb$_5$ around a pressure-induced quantum critical point

Using first-principles density functional theory calculations, we investigate the pressure-induced quantum phase transition (QPT) from the charge density wave (CDW) to the pristine phase in the layered kagome metal CsV$_3$Sb$_5$ consisting of three-atom-thick Sb$-$V$_3$Sb$-$Sb and one-atom-thick Cs layers. The CDW structure having the formation of trimeric and hexameric V atoms with buckled Sb honeycomb layers features an increase in the lattice parameter along the $c$ axis, compared to its counterpart pristine structure having the ideal V$_3$Sb kagome and planar Sb honeycomb layers. Consequently, as pressure increases, the relatively smaller volume of the pristine phase contributes to reducing the enthalpy difference between the CDW and pristine phases, yielding a pressure-induced QPT at a critical pressure $P_c$ of ${\sim}$2 GPa. Furthermore, we find that (i) the superconducting transition temperature $T_c$ increases around $P_c$ due to a phonon softening associated with the periodic lattice distortion of V trimers and hexamers and that (ii) above $P_c$, optical phonon modes are hardened with increasing pressure, leading to monotonous decreases in the electron-phonon coupling constant and $T_c$. Our findings not only demonstrate that the uniaxial strain along the $c$ axis plays an important role in the QPT observed in CsV$_3$Sb$_5$, but also provide an explanation for the observed superconductivity around $P_c$ in terms of a phonon-mediated superconducting mechanism.

cond-mat.mtrl-sci↗

arXiv2021

Gluon fragmentation into $B_c^{(*)}$ in NRQCD factorization

The universal fragmentation functions of gluon into the flavored quarkonia $B_c$ and (polarized) $B_c^*$ are computed within NRQCD factorization framework, at the lowest order in velocity expansion and strong coupling constant. It is mandatory to invoke the DGLAP renormalization program to render the NRQCD short-distance coefficients UV finite in a point-wise manner. The calculation is facilitated with the sector decomposition method, with the final results presented with high numerical accuracy. This knowledge is useful to enrich our understanding toward the large-$p_T$ behavior of $B_c^{(*)}$ production at LHC experiment.

hep-ph↗

arXiv2021

Equally Spaced Quantum States in van der Waals Epitaxy-Grown Nanoislands

Pursuing the confinement of linearly dispersive relativistic fermions is of interest in both fundamental physics and potential applications. Here, we report strong STM evidence for the equally spaced, strikingly sharp, and densely distributed quantum well states (QWSs) near Fermi energy in Pb(111) nanoislands, van-der-Waals epitaxially grown on graphitized 6H-SiC(0001). The observations can be explained as the quantized energies of confined linearly dispersive [111] electrons, which essentially 'simulate' the out-of-plane relativistic quasiparticles. The equally spaced QWSs with an origin of confined relativistic electrons are supported by phenomenological simulations and Fabry-Perot fittings based on the relativistic fermions. First-principles calculations further reveal that the spin-orbit coupling strengthens the relativistic nature of electrons near Fermi energy. Our finding uncovers the unique equally spaced quantum states in electronic systems beyond Landau levels, and may inspire future studies on confined relativistic quasiparticles in flourishing topological materials and applications in structurally simpler quantum cascade laser.

cond-mat.mes-hall↗

arXiv2021

Four-lepton decays of neutral vector mesons

We investigate the rare electromagnetic decays of neutral vector mesons (exemplified by $J/ψ$, $Υ$, $ρ^0$, $ω,ϕ$, \ldots) into four charged leptons ($2(e^+e^-)$, $2(μ^+μ^-)$, $2(τ^+τ^-)$, $e^+e^-μ^+μ^-$, $e^+e^-τ^+τ^-$, \ldots) at lowest order in QED. In contrast to the case of vector meson decay into a single pair of leptons, the lepton mass must be retained in these four-lepton decay channels to cutoff the mass singularity. Owing to more pronounced collinear enhancement, the branching fractions of vector mesons decays into $ 2(e^+e^-)$ are considerably greater than those for decays into $2(μ^+μ^-)$. The decay channels $J/ψ(Υ)\to 2(e^+e^-), e^+e^-μ^+μ^-$ are predicted to have branching fractions of order $10^{-5}$, which appear to have bright observation prospect at {\tt BESIII}, {\tt Belle 2} and {\tt LHC} experiments.

hep-ph↗

arXiv2021

Magnetic moment preservation and emergent Kondo resonance of Co-phthalocyanine on semimetallic Sb(111)

Magnetic molecules on surfaces have been widely investigated to reveal delicate interfacial couplings and for potential technological applications. In these endeavors, one prevailing challenge is how to preserve or recover the molecular spins, especially on highly metallic substrates that can readily quench the magnetic moments of the ad-molecules. Here we use scanning tunneling microscopy/spectroscopy to exploit the semimetallic nature of antimony and observe, surprisingly yet pleasantly, that the spin of Co-phthalocyanine is well preserved on Sb(111), as unambiguously evidenced by the emergent strong Kondo resonance across the molecule. Our first-principles calculations further confirm that the optimal density of states near the Fermi level of the semimetal is a decisive factor, weakening the overall interfacial coupling, while still ensuring sufficiently effective electron-spin scattering in the many-body system. Beyond isolated ad-molecules, we discover that each of the magnetic moments in a molecular dimer or a densely packed island is distinctly preserved as well, rendering such molecular magnets immense potentials for ultra-high density memory devices.

cond-mat.mtrl-sci↗

arXiv2021

Surface Van Hove Singularity Enabled Efficient Catalysis: The Cases of CO Oxidation and Hydrogen Evolution Reactions

Surface Van Hove singularity (SVHS), defined as the surface states near the Fermi level (EF) in low-dimensional systems, triggers exciting physical phenomena distinct from bulk. We herein explore theoretically the potential role of SVHS in catalysis taking CO oxidation reaction as prototype over graphene/Ca2N (Gra/Ca2N) heterojunction and Pt2HgSe3 (001) surface. It is demonstrated that both systems with SVHS could serve as an electron bath to promote O2 adsorption and subsequent CO oxidation with low energy barriers of 0.2 ~ 0.6 eV for Gra/Ca2N and Pt2HgSe3 (001) surface. Importantly, the catalytically active sites associated with SVHS are well-defined and uniformly distributed over the whole surface plane, which is superior to the commonly adopted defect or doping strategy, and further the chemical reactivity of SVHS also can be tuned easily via adjusting its position with respect to EF. Our study demonstrates the enabling power of SVHS, and provides novel physical insights into the promising potential role of VHS in designing high-efficiency catalysts.

cond-mat.mtrl-sci↗