arXiv subjects

Chi Xiong

Publications and source records attributed to Chi Xiong.

At least 19 recordsLinked to original sources

arXiv2025

Feeding a Kerr black hole with quantized vortices

By solving a nonlinear Klein-Gordon equation in Kerr geometry, we uncover new phenomena and key characteristics of quantized vortices in quantum fluids near a Kerr black hole. The formation of these vortices induces rotational or turbulent flows, which profoundly alter the fluid properties and revise those dark matter models describing axion condensates, ultralight boson clouds, and other scalar fields in the vicinity of spinning black holes. As macroscopic, quantum, and topological defects, these vortices can stably orbit the black hole over extended periods, establishing their viability as novel probes for investigating black hole physics. For instance, we calculate the angular velocities of orbiting vortices to quantitatively characterize the frame-dragging effect, a classic prediction of general relativity. Additionally, we observe that relatively large vortices are accreted onto the black hole, wrapping around it while undergoing splitting and reconnecting processes. In quantum fluids with high vortex densities, turbulent flows emerge, accompanied by the formation of a vortex boundary layer near the event horizon. Beyond the ergosphere, we find vortex emissions and energetic outbursts, which may provide crucial insights into analogous astrophysical events recently discovered by the XRISM satellite.

gr-qc↗

arXiv2025

Distilled remote entanglement between superconducting qubits across optical channels

A promising quantum computing architecture comprises modules of superconducting quantum processors linked via optical channels using quantum transducers. As quantum transducer hardware improves, a need has arisen to understand the quantitative relationship between transducer-device characteristics and the strength of the resulting remote entanglement. Using Monte Carlo simulations that incorporate 2-to-1 and 3-to-1 entanglement distillation methods, our model maps transducer device performance up to system-level channel performance, thereby allowing the performance of remote entanglement approaches to be compared and optimized. We find the extreme photon loss (EPL) distillation protocol to be particularly high performing. Moreover, even without distillation, present-day transducers with added noise of photons are at the threshold of enabling remote Bell pairs with fidelities exceeding 50%. If the next generation of transducers can improve by 3 orders of magnitude in added noise, efficiency, and repetition rates, then they would allow for remote two-qubit gates achieving 99.7% fidelities at MHz rates. These results set practical targets for transducers to be ready for deployment into modular quantum computing systems.

quant-ph↗

arXiv2024

Mechanically-intermixed indium superconducting connections for microwave quantum interconnects

Superconducting coaxial cables represent critical communication channels for interconnecting superconducting quantum processors. Here, we report mechanically-intermixed indium joins to aluminum coaxial cables for low loss quantum interconnects. We describe an ABCD matrix formalism to characterize the total resonator internal quality factor ($Q_i$) and any contact ($R_{cont}$) or shunt resistance ($R_{shunt}$) associated with the mechanically-intermixed indium joins. We present four resonator test systems incorporating three indium join methods over the typical frequency range of interest (3-5.5GHz) at temperatures below $20mK$. We measure high internal quality factor aluminum cables ($Q_i = 1.55 \pm 0.37 x 10^6$) through a push-to-connect indium join of the outer conductor that capacitively couples the inner conductor for reflection measurements. We then characterize the total internal quality factors of modes of a cable resonator with a push-to-connect superconducting cable-splice at the midpoint to find mean $Q_i = 1.40 x 10^6$ and $Q_i = 9.39 x 10^5$ for even and odd-modes respectively and use an ABCD matrix model of the system to extract $R_{cont} = 6x10^{-4} Ω$ for the indium join of the inner conductor. Finally, we demonstrate indium press-mold cable-to-chip connections where the cable-to-chip join is placed at a current node and voltage node through varying on-chip waveguide lengths with mean $Q_i = 1.24 x 10^6$ and $Q_i = 1.07 x 10^6$ respectively to extract $R_{cont} = 8.5x10^{-4} Ω$ and $R_{shunt} = 1.3x10^7 Ω$ for the interface. With these techniques, we demonstrate a set of low-loss methods to join superconducting cables for future quantum

quant-ph↗

arXiv2023

Thermal conductivity in one-dimensional nonlinear disordered lattices: Two kinds of scattering effects of hard-type and soft-type anharmonicities

The amorphous solids can be theoretically modeled by anharmonic disordered lattices. However, most of theoretical studies on thermal conductivity in anharmonic disordered lattices only focus on the potentials of hard-type (HT) anharmonicity. Here we study the thermal conductivity $κ$ of one-dimensional (1D) disordered lattices with both hard- and soft-type (ST) anharmonic on-site potentials. It is found, via both direct molecular dynamic simulations and theoretical method, that the anharmonicity dependence of $κ$ in the HT model is nonmonotonous, while in the ST model is monotonously increased. This provides a new way to enhance thermal conductivity in disordered systems. Furthermore, $κ$ of the HT model is consistent with the prediction of the quasi-harmonic Green-Kubo (QHGK) method in a wide range of anharmonicity, while for the ST model, the numerical results seem largely deviated from the theoretical predictions as the anharmonicity becomes soft. This new and peculiar feature of the ST model may root in the fact that only delocalization effect exists, different from the competing roles that both delocalization and localization play in the counterpart HT model.

cond-mat.stat-mech↗

arXiv2022

Unusual slow energy relaxation induced by mobile discrete breathers in one-dimensional lattices with next-nearest-neighbor coupling

We study the energy relaxation process in one-dimensional (1D) lattices with next-nearest-neighbor (NNN) couplings. This relaxation is produced by adding damping (absorbing conditions) to the boundary (free-end) of the lattice. Compared to the 1D lattices with on-site potentials, the properties of discrete breathers (DBs) that are spatially localized intrinsic modes are quite unusual with the NNN couplings included, i.e., these DBs are mobile, and thus they can interact with both the phonons and the boundaries of the lattice. For the interparticle interactions of harmonic and Fermi-Pasta-Ulam-Tsingou-$β$ (FPUT-$β$) types, we find two crossovers of relaxation in general, i.e., a first crossover from the stretched-exponential to the regular exponential relaxation occurring in a short timescale, and a further crossover from the exponential to the power-law relaxation taking place in a long timescale. The first and second relaxations are universal, but the final power-law relaxation is strongly influenced by the properties of DBs, e.g. the scattering processes of DBs with phonons and boundaries in the FPUT-$β$ type systems make the power-law decay relatively faster than that in the counterparts of the harmonic type systems under the same coupling. Our results present new information and insights for understanding the slow energy relaxation in cooling the lattices.

nlin.CD↗

arXiv2021

Ultrahigh-$Q$ on-chip silicon-germanium microresonators

We demonstrate fully crystalline, single-mode ultrahigh quality factor integrated microresonators comprising epitaxially grown Si$_{0.86}$Ge$_{0.14}$ waveguide cores with silicon claddings. These waveguides support resonances with internal $Q >10^8$ for both polarization modes, a nearly order-of-magnitude improvement over that seen in prior integrated Si photonics platforms. The maximum $Q$ is $1.71\pm0.06 \times 10^8$ for the transverse magnetic (TM) polarization mode, corresponding to a loss of $0.39\pm0.02$ dB/m. Together with silicon's strong Kerr nonlinearity and low losses in the optical, microwave and acoustic regimes, our results could lead to the Si$_{1-x}$Ge$_x$/Si architecture unlocking important new avenues for Kerr frequency combs, optomechanics, and quantum transduction.

physics.optics↗

arXiv2021

Relativistic quantum information as radiation reaction: entanglement entropy and self-force of a moving mirror analog to the CGHS black hole

The CGHS black hole has a spectrum and temperature that corresponds to an accelerated reflecting boundary condition in flat spacetime. The beta coefficients are identical to a moving mirror model where the acceleration is exponential in laboratory time. The center and the event horizon of the black hole are at the same location modeled by the perfectly reflecting regularity condition that red-shifts the field modes. In addition to computing the energy flux, we find the corresponding parameter associated with the black hole mass and the cosmological constant in the gravitational analog system. Generalized to any mirror trajectory we derive the self-force (Lorentz-Abraham-Dirac) and express it and the power (Larmor) in connection with entanglement entropy, inviting an interpretation of acceleration radiation in terms of information flow. The mirror self-force and radiative power are applied to the particular CGHS black hole analog moving mirror which reveals the physics of information at the horizon during asymptotic approach to thermal equilibrium.

gr-qc↗

arXiv2019

Axionic excitation from QCD Condensate

A complex order parameter is used for describing inhomogeneous quark condensate and its phase is decomposed into a regular part and a singular part. An emergent gauge symmetry is found to connect these two parts. The singular part plays the role of an emergent gauge field while the regular part can be considered as an axionic excitation, provided that the chromoelectric flux tube is capable of inducing a vortex configuration in the quark condensate, with the help of axial anomaly.

hep-ph↗

arXiv2019

Vectorizing Quantum Turbulence Vortex-Core Lines for Real-Time Visualization

Vectorizing vortex-core lines is crucial for high-quality visualization and analysis of turbulence. While several techniques exist in the literature, they can only be applied to classical fluids. Recently, quantum fluids with turbulence get more and more attention in physics. It is thus desirable that vortex-core lines can also be well extracted and visualized for quantum fluids. In this paper, we aim for this goal and developed an efficient vortex-core line vectorization method for quantum fluids, which enables real-time visualization of high-resolution quantum turbulence structure. Given the datasets by simulation, our technique is developed from the vortices identified by the circulation-based method. To vectorize the vortex-core lines enclosed by those vortices, we propose a novel graph-based data structure, with iterative graph reduction and density-guided local optimization, to locate more precisely sub-grid-scale vortex-core line samples, which are then vectorized by continuous curves. This not only represents vortex-core line structures continuously, but also naturally preserves complex topology, such as branching during reconnection. By vectorization, the memory consumption can be largely reduced by orders of magnitude, enabling real-time rendering performance. Different types of interactive visualizations are demonstrated to show the effectiveness of our technique, which could assist further research on quantum turbulence.

cs.GR↗

arXiv2018

QCD strings and the U(1) problem

We promote the usual QCD $θ$-parameter to a field and interpret it as the phase of the quark condensate, which becomes nontrivial when topological defects, vortices in our formulation, are induced in the quark condensate by the QCD strings (chromoelectric flux tubes). The QCD topological term emerges naturally as a derivative coupling between the Chern-Simons current and a supercurrent in the quark condensate. This new formulation can address the $U_A(1)$ problem and leads to the chiral magnetic effects. It is possible that in this formulation the strong CP problem can be avoided without the axion particle.

hep-ph↗

arXiv2017

Towards High-quality Visualization of Superfluid Vortices

Superfluidity is a special state of matter exhibiting macroscopic quantum phenomena and acting like a fluid with zero viscosity. In such a state, superfluid vortices exist as phase singularities of the model equation with unique distributions. This paper presents novel techniques to aid the visual understanding of superfluid vortices based on the state-of-the-art non-linear Klein-Gordon equation, which evolves a complex scalar field, giving rise to special vortex lattice/ring structures with dynamic vortex formation, reconnection, and Kelvin waves, etc. By formulating a numerical model with theoretical physicists in superfluid research, we obtain high-quality superfluid flow data sets without noise-like waves, suitable for vortex visualization. By further exploring superfluid vortex properties, we develop a new vortex identification and visualization method: a novel mechanism with velocity circulation to overcome phase singularity and an orthogonal-plane strategy to avoid ambiguity. Hence, our visualizations can help reveal various superfluid vortex structures and enable domain experts for related visual analysis, such as the steady vortex lattice/ring structures, dynamic vortex string interactions with reconnections and energy radiations, where the famous Kelvin waves and decaying vortex tangle were clearly observed. These visualizations have assisted physicists to verify the superfluid model, and further explore its dynamic behavior more intuitively.

physics.flu-dyn↗

arXiv2017

A unified composite model of inflation and dark matter in the Nambu-Jona-Lasinio theory

In this work, we propose a cosmological scenario inherently based on the effective Nambu-Jona-Lasinio (NJL) model that cosmic inflation and dark matter can be successfully described by a single framework. On the one hand, the scalar channel of the NJL model plays a role of the composite inflaton (CI) and we show that it is viable to achieve successful inflation via a non-minimal coupling to gravity. For model of inflation, we compute the inflationary parameters and confront them with recent Planck 2015 data. We discover that the predictions of the model are in excellent agreement with the Planck analysis. We also present in our model a simple connection of physics from the high scales to low scales via renormalization group equations of the physical parameters. On the other hand, the pseudoscalar channel can be assigned as a candidate for composite dark matter (CD). For model of dark matter, we couple the pseudoscalar to the Higgs sector of the standard model with the coupling strength $κ$ and estimate its thermally-averaged relic abundance. We discover that the CD mass is strongly sensitive to the coupling $κ$. We find in case of light CD, $M_{s} M_{W,\,Z}$ (or $>M_{h}$), the required relic abundance can be satisfied for value of the CD mass $M_{s}\sim 410\,{\rm GeV}$ for $κ= 0.5$. In contradiction to the light mass case, however, the CD mass in this case can even be heavier when the coupling is getting larger.

hep-ph↗

arXiv2016

Relativistic two-fluid hydrodynamics with quantized vorticity from the nonlinear Klein-Gordon equation

We consider a relativistic two-fluid model of superfluidity, in which the superfluid is described by an order parameter that is a complex scalar field satisfying the nonlinear Klein-Gordon equation (NLKG). The coupling to the normal fluid is introduced via a covariant current-current interaction, which results in the addition of an effective potential, whose imaginary part describes particle transfer between superfluid and normal fluid. Quantized vorticity arises in a class of singular solutions and the related vortex dynamics is incorporated in the modified NLKG, facilitating numerical analysis which is usually very complicated in the phenomenology of vortex filaments. The dual transformation to a string theory description (Kalb-Ramond) of quantum vorticity, the Magnus force and the mutual friction between quantized vortices and normal fluid are also studied.

hep-th↗

arXiv2016

Fantasia of a Superfluid Universe -- In memory of Kerson Huang

This article introduces Kerson Huang's theory on superfluid universe in these aspects: I. choose the asymptotically free Halpern-Huang scalar field(s) to drive inflation; II. use quantum turbulence to create matter; III. consider dark energy as the energy density of the cosmic superfluid and dark matter the deviation of the superfluid density from its equilibrium value; IV. use quantum vorticity to explain phenomena such as the non-thermal filaments at the galactic center, the large voids in the galactic distribution, and the gravitational collapse of stars to fast-rotating blackholes.

astro-ph.CO↗

arXiv2016

Geometric creation of quantum vorticity

We consider superfluidity and quantum vorticity in rotating spacetimes. The system is described by a complex scalar satisfying a nonlinear Klein-Gordon equation. Rotation terms are identified and found to lead to the transfer of angular momentum of the spacetime to the scalar field. The scalar field responds by rotating, physically behaving as a superfluid, through the creation of quantized vortices. We demonstrate the vortex nucleation through numerical simulation.

gr-qc↗

arXiv2016

A monolithic 56 Gb/s silicon photonic pulse-amplitude modulation transmitter

Silicon photonics promises to address the challenges for next-generation short-reach optical interconnects. Growing bandwidth demand in hyper-scale data centers and high-performance computing motivates the development of faster and more-efficient silicon photonics links. While it is challenging to raise the serial line rate, further scaling of the data rate can be realized by, for example, increasing the number of parallel fibers, increasing the number of wavelengths per fiber, and using multi-level pulse-amplitude modulation (PAM). Among these approaches, PAM has a unique advantage because it does not require extra lasers or a costly overhaul of optical fiber cablings within the existing infrastructure. Here, we demonstrate the first fully monolithically integrated silicon photonic four-level PAM (PAM-4) transmitter operating at 56 Gb/s and demonstrate error-free transmission (bit-error-rate < 10$^{-12}$) up to 50 Gb/s without forward error correction. The superior PAM-4 waveform is enabled by optimization of silicon traveling wave modulators and monolithic integration of the CMOS driver circuits. Our results show that monolithic silicon photonics technology is a promising platform for future ultrahigh data rate optical interconnects.

physics.optics↗

arXiv2016

A de-gauging approach to physics beyond the Standard Model

By studying the t-J model for superconductivity, the Pati-Salam model and the Haplon model for particle unifications, we extract their common feature which is the spin-charge separation of fermions. This becomes a de-gauging process for charged fermions by considering them as bound states of a neutral fermion and charged or neutral bosons. We present a few examples including the weak-charge-spin separation for the leptons in the Standard Model. Some fundamental fermions can be obtained by continuing this de-gauging process for different kinds of charges. Finally the binding forces of the bound states might be provided by interactions related to spacetime symmetries such as supersymmetry.

hep-ph↗

arXiv2016

Dark fermions from the Standard Model via spin-charge separation

We study a new composite scenario of the lepton sector in the Standard Model by a de-gauging procedure called spin-charge separation and propose that leptons are bound states of some neutral fermions and Higgs bosons. Continuing this procedure we may obtain more fundamental dark fermions. They become the physical leptons by acquiring both charges and masses from some Higgs fields.

hep-ph↗