arXiv subjects

Ping Gao

Publications and source records attributed to Ping Gao.

At least 19 recordsLinked to original sources

arXiv2025

Probing Stringy Horizons with Pole-Skipping in Non-Maximal Chaotic Systems

In this paper, we study pole-skipping in non-maximally quantum chaotic systems. Using Rindler conformal field theories and the large-$q$ SYK chain as illustrative examples, we argue that the pole-skipping points of few-body operators organize into trajectories in the complex frequency-momentum plane, with the leading trajectory encoding the quantum Lyapunov exponent. We further propose that these trajectories admit a natural interpretation as Regge trajectories of stringy excitations in a dual stringy black hole geometry. From this perspective, pole-skipping for an individual operator can be viewed as tracking the stringy horizon through the response of a single excitation. Our results suggest that pole-skipping reflects intrinsic properties of quantum chaotic systems and may be deeply connected to the structure of horizons in the stringy regime.

hep-th↗

arXiv2025

Single-Sided Black Holes in Double-Scaled SYK Model and No Man's Island

We study a single-sided black hole with an end-of-the-world (EoW) brane behind the horizon in the double-scaled SYK (DSSYK). The new Hamiltonian is a deformation of the original DSSYK Hamiltonian with an extra exponential wormhole length operator, which leads to a new chord diagram rule. The boundary algebra is defined as generated by the new Hamiltonian and boundary matter. There is an alternative but equivalent definition with a $q$-coherent state due to a nontrivial isomorphism of the vN algebra of DSSYK. This isomorphism induces a unitary equivalence, which yields a surprising result that the boundary algebra of a single-sided black hole in DSSYK has a non-trivial commutant and is a type II$_1$ vN factor. It follows that the full bulk reconstruction from the boundary is impossible, and there is a ``no man's island" behind the horizon in the semiclassical JT limit. Inspired by the EoW brane, we construct a family of matter-brane states with an arbitrary number of matter chords and behaving like an EoW brane. They exactly solve the full spectrum of DSSYK. We take different ways to understand the nontrivial commutant. We show that the commutant is complex on chord number basis and thus non-geometric. In the semiclassical JT limit, the commutant becomes the canonical purification of the boundary algebra and claims the no man's island. In the context of Hawking radiation after Page time, the unitary equivalence is interpreted as encoding the canonical purification into the old Hawking radiation, and the no man's island has the same essence as the island. Including the exponential wormhole length operator independently, the boundary algebra is extended to all bounded operators and reconstructs the no man's island. This can be regarded as a different choice for the definition of boundary algebra. This type I$_\infty$ algebra is closely related to the EoW brane in Kourkoulou-Maldacena.

hep-th↗

arXiv2024

D-commuting SYK model: building quantum chaos from integrable blocks

We construct a new family of quantum chaotic models by combining multiple copies of integrable commuting SYK models. As each copy of the commuting SYK model does not commute with others, this construction breaks the integrability of each commuting SYK and the family of models demonstrates the emergence of quantum chaos. We study the spectrum of this model analytically in the double-scaled limit. As the number of copies tends to infinity, the spectrum becomes compact and equivalent to the regular SYK model. For finite $d$ copies, the spectrum is close to the regular SYK model in UV but has an exponential tail $e^{E/T_c}$ in the IR. We identify the reciprocal of the exponent in the tail as a critical temperature $T_c$, above which the model should be quantum chaotic. $T_c$ monotonically decreases as $d$ increases, which expands the chaotic regime over the non-chaotic regime. We propose the existence of a new phase around $T_c$, and the dynamics should be very different in two phases. We further carry out numeric analysis at finite $d$, which supports our proposal. Given any finite dimensional local Hamiltonian, by decomposing it into $d$ groups, in which all terms in one group commute with each other but terms from different groups may not, our analysis can give an estimate of the critical temperature for quantum chaos based on the decomposition. We also comment on the implication of the critical temperature to future quantum simulations of quantum chaos and quantum gravity.

hep-th↗

arXiv2024

Invisible sweat sensor: ultrathin membrane mimics skin for stress monitoring

Epidermal skin sensors have emerged as a promising approach for continuous and noninvasive monitoring of vital health signals, but to maximize their performance, these sensors must integrate seamlessly with the skin, minimizing impedance while maintaining the skin's natural protective and regulatory functions.In this study, we introduce an imperceptible sweat sensor that achieves this seamless skin integration through interpenetrating networks formed by a porous, ultra-thin, ultra-high molecular weight polyethylene (UHMWPE) nanomembrane. Upon attachment to the skin by van der Waals force, the amphiphilic sweat extrudates infuse into the interconnected nanopores inside the hydrophobic UHWMPE nanomembrane, forming "pseudo skin" nanochannels for continuous sweat perspiration. This integration is further enhanced by the osmotic pressure generated during water evaporation. Leveraging the efficient transport of biomarkers through the "skin" channels within the porous membrane, we developed an organic electrochemical transducer (OECT) cortisol sensor via in-situ synthesis of a molecularly imprinted polymer (MIP) and poly(3,4 ethylenedioxythiophene) (PEDOT) within the nanomembrane. This demonstrates the capability to detect cortisol concentrations from 0.05 to 0.5 {\mu}M for seamless monitoring of stress levels. This work represents a significant advancement in self-adhesive sweat sensors that offer imperceptible and real-time non-invasive health monitoring capabilities.

cond-mat.mtrl-sci↗

arXiv2024

Modular flow in JT gravity and entanglement wedge reconstruction

It has been shown in recent works that JT gravity with matter with two boundaries has a type II$_\infty$ algebra on each side. As the bulk spacetime between the two boundaries fluctuates in quantum nature, we can only define the entanglement wedge for each side in a pure algebraic sense. As we take the semiclassical limit, we will have a fixed long wormhole spacetime for a generic partially entangled thermal state (PETS), which is prepared by inserting heavy operators on the Euclidean path integral. Under this limit, with appropriate assumptions of the matter theory, geometric notions of the causal wedge and entanglement wedge emerge in this background. In particular, the causal wedge is manifestly nested in the entanglement wedge. Different PETS are orthogonal to each other, and thus the Hilbert space has a direct sum structure over sub-Hilbert spaces labeled by different Euclidean geometries. The full algebra for both sides is decomposed accordingly. From the algebra viewpoint, the causal wedge is dual to an emergent type III$_1$ subalgebra, which is generated by boundary light operators. To reconstruct the entanglement wedge, we consider the modular flow in a generic PETS for each boundary. We show that the modular flow acts locally and is the boost transformation around the global RT surface in the semiclassical limit. It follows that we can extend the causal wedge algebra to a larger type III$_1$ algebra corresponding to the entanglement wedge. Within each sub-Hilbert space, the original type II$_\infty$ reduces to type III$_1$.

hep-th↗

arXiv2023

Photochemical Upcycling of Ultrastrong Polyethylene Nanomembranes into Fibrous Carbon at Ambient Conditions

The escalating global issue of plastic waste accumulation, specifically polyolefins, necessitates an urgent solution for upcycling these materials into beneficial compounds. Yet, achieving such upcycling without introducing carbon dioxide into the environment remains a formidable challenge. In this study, we demonstrate an eco-friendly approach for the photochemical conversion of ultrastrong, ultratransparent, and ultrathin polyethylene membrane into fibrous carbon nanomembrane at ambient conditions. The membrane was sputter-coated with platinum and cuprous oxide nanoparticles and exposed to simulated sunlight, resulting in a porous carbon membrane decorated with Pt nanoparticles. The new carbonized nanomembrane maintained the pristine membrane's morphology. The membrane exhibited high activity (2.11 mA/cm2) for electrochemical ethanol oxidation with stability over 1000 cycles. This work holds significance for sustainable plastic waste management and the design of new polyolefin materials in a circular economy.

physics.app-ph↗

arXiv2023

Commuting SYK: a pseudo-holographic model

In this work, we study a type of commuting SYK model in which all terms in the Hamiltonian are commutative to each other. Because of the commutativity, this model has a large number of conserved charges and is integrable. After the ensemble average of random couplings, we can solve this model exactly in any $N$. Though this integral model is not holographic, we do find that it has some holography-like features, especially the near-perfect size winding in high temperatures. Therefore, we would like to call it pseudo-holographic. We also find that the size winding of this model has a narrowly peaked size distribution, which is different from the ordinary SYK model. We apply the traversable wormhole teleportation protocol in the commuting SYK model and find that the teleportation has a few features similar to the semiclassical traversable wormhole but in different parameter regimes. We show that the underlying physics is not entirely determined by the size-winding mechanism but involves the peaked-size mechanism and thermalization. Lastly, we comment on the recent simulation of the dynamics of traversable wormholes on Google's quantum processor.

hep-th↗

arXiv2023

Geometric and Dynamic Properties of Entangled Polymer Chains in Athermal Solvents: A Coarse-Grained Molecular Dynamics Study

We used a coarse-grained model to study the geometric and dynamic properties of flexible entangled polymer chains dissolved in explicit athermal solvents. Our simulations successfully reproduced the geometrical properties including the scaling relationships between mean-square end-to-end distance $ $, chain entanglement lengths $N_{e}$ and concentration $\Phi$. Specifically, we find that $ \sim N*\Phi^{-1/4}$,$N_{e} = 30.01\Phi^{-5/4}+31.23$. Dynamically, our model confirmed the ratio of the dynamic critical entanglement $N_{c}$ and the geometric entanglement length $N_{e}$ is constant, with $N_{c}/N_{e} = 5\sim 6$. To account for the local swelling effect for chains confined in athermal solvents, we treated the chains using the concept of blobs where each blob occupies a volume $\Omega_{b}$, with length $g$. Direct MD simulations and scaling analysis showed that $g \sim \Phi^{-25/36}$, $\Omega_{b}\sim\Phi^{-5/4}$. Using these together with the concentration dependent packing length $p \sim \Phi^{-5/12}$, we obtained a modified the Lin-Noolandi ansatz for concentrated flexible polymer chains in athermal solvents: $G \sim \frac{\Phi}{\left(N_{e} / g\right) \Omega_{b}} \sim \Phi^{-2.28}$. We demonstrate this modified ansatz agrees well with our coarse-grained numerical simulations.

cond-mat.soft↗

arXiv2023

An effective field theory for non-maximal quantum chaos

In non-maximally quantum chaotic systems, the exponential behavior of out-of-time-ordered correlators (OTOCs) results from summing over exchanges of an infinite tower of higher "spin" operators. We construct an effective field theory (EFT) to capture these exchanges in $(0+1)$ dimensions. The EFT generalizes the one for maximally chaotic systems, and reduces to it in the limit of maximal chaos. The theory predicts the general structure of OTOCs both at leading order in the $1/N$ expansion ($N$ is the number of degrees of freedom), and after resuming over an infinite number of higher order $1/N$ corrections. These general results agree with those previously explicitly obtained in specific models. We also show that the general structure of the EFT can be extracted from the large $q$ SYK model.

hep-th↗

arXiv2021

Seeing behind black hole horizons in SYK

We present an explicit reconstruction of the interior of an AdS$_2$ black hole in Jackiw-Teitelboim gravity, that is entirely formulated in the dual SYK model and makes no direct reference to the gravitational bulk. We do this by introducing a probe "observer" in the right wormhole exterior and using the prescription of [arXiv:2009.04476] to transport SYK operators along the probe's infalling worldline and into the black hole interior, using an appropriate SYK modular Hamiltonian. Our SYK computation recovers the precise proper time at which signals sent from the left boundary are registered by our observer's apparatus inside the wormhole. The success of the computation relies on the universal properties of SYK and we outline a promising avenue for extending it to higher dimensions and applying it to the computation of scattering amplitudes behind the horizon.

hep-th↗

arXiv2021

An effective matrix model for dynamical end of the world branes in Jackiw-Teitelboim gravity

We study Jackiw-Teitelboim gravity with dynamical end of the world branes in asymptotically nearly AdS$_2$ spacetimes. We quantize this theory in Lorentz signature, and compute the Euclidean path integral summing over topologies including dynamical branes. The latter will be seen to exactly match with a modification of the SSS matrix model. The resolution of UV divergences in the gravitational instantons involving the branes will lead us to understand the matrix model interpretation of the Wilsonian effective theory perspective on the gravitational theory. We complete this modified SSS matrix model nonperturbatively by extending the integration contour of eigenvalues into the complex plane. Furthermore, we give a new interpretation of other phases in such matrix models. We derive an effective $W(\Phi)$ dilaton gravity, which exhibits similar physics semiclassically. In the limit of a large number of flavors of branes, the effective extremal entropy $S_{0,\text{eff}}$ has the form of counting the states of these branes.

hep-th↗

arXiv2021

Many-body quantum teleportation via operator spreading in the traversable wormhole protocol

By leveraging shared entanglement between a pair of qubits, one can teleport a quantum state from one particle to another. Recent advances have uncovered an intrinsically many-body generalization of quantum teleportation, with an elegant and surprising connection to gravity. In particular, the teleportation of quantum information relies on many-body dynamics, which originate from strongly-interacting systems that are holographically dual to gravity; from the gravitational perspective, such quantum teleportation can be understood as the transmission of information through a traversable wormhole. Here, we propose and analyze a new mechanism for many-body quantum teleportation -- dubbed peaked-size teleportation. Intriguingly, peaked-size teleportation utilizes precisely the same type of quantum circuit as traversable wormhole teleportation, yet has a completely distinct microscopic origin: it relies upon the spreading of local operators under generic thermalizing dynamics and not gravitational physics. We demonstrate the ubiquity of peaked-size teleportation, both analytically and numerically, across a diverse landscape of physical systems, including random unitary circuits, the Sachdev-Ye-Kitaev model (at high temperatures), one-dimensional spin chains and a bulk theory of gravity with stringy corrections. Our results pave the way towards using many-body quantum teleportation as a powerful experimental tool for: (i) characterizing the size distributions of operators in strongly-correlated systems and (ii) distinguishing between generic and intrinsically gravitational scrambling dynamics. To this end, we provide a detailed experimental blueprint for realizing many-body quantum teleportation in both trapped ions and Rydberg atom arrays; effects of decoherence and experimental imperfections are analyzed.

quant-ph↗

arXiv2020

Ultrastrong, Ultraflexible, and Ultratransparent Polyethylene Cellular Nanofilms

Light weight and mechanically robust cellular polymer nanofilms provide materials solutions to many cutting-edge technologies, such as high-flux membrane filtration, ultrathin flexible energy storage, and skin-conformable devices. However, it remains challenging to fabricate hand manipulatable cellular polymer nanofilms for use as self-standing structural materials. Herein, we used a sequential planar extension approach to transform low-entanglement ultrahigh molecular weight polyethylene (UHMWPE) gel films dispersed in porogenic polyethylene oligomers into cellular nanofilms consisting of stretch-dominated triangular cells of molecularly anisotropic cell edges. The microstructure afforded the cellular nanofilm, which had a thickness down to 20 nm, with a unique combination of ultratransparency (>98.5%), ultrahigh in-plane tensile strength (1071 MPa.cm^3.g^(-1)), and ultrahigh flexibility: a 43 nm thick film can deflect reversibly up to 8.0 mm in depth (185,000 times) under a spherical indentation load. As an application, we fabricated the nanofilm into a freestanding ultratransparent respiratory face covering. The new polyethylene cellular nanofilms are expected to represent a new class of platform membranes for advancing fundamental and technological development.

cond-mat.mtrl-sci↗

arXiv2020

Towards Scalable Distributed Training of Deep Learning on Public Cloud Clusters

Distributed training techniques have been widely deployed in large-scale deep neural networks (DNNs) training on dense-GPU clusters. However, on public cloud clusters, due to the moderate inter-connection bandwidth between instances, traditional state-of-the-art distributed training systems cannot scale well in training large-scale models. In this paper, we propose a new computing and communication efficient top-k sparsification communication library for distributed training. To further improve the system scalability, we optimize I/O by proposing a simple yet efficient multi-level data caching mechanism and optimize the update operation by introducing a novel parallel tensor operator. Experimental results on a 16-node Tencent Cloud cluster (each node with 8 Nvidia Tesla V100 GPUs) show that our system achieves 25%-40% faster than existing state-of-the-art systems on CNNs and Transformer. We finally break the record on DAWNBench on training ResNet-50 to 93% top-5 accuracy on ImageNet.

cs.DC↗

arXiv2019

A Traversable Wormhole Teleportation Protocol in the SYK Model

In this paper, we propose a concrete teleportation protocol in the SYK model based on a particle traversing a wormhole. The required operations for the communication, and insertion and extraction of the qubit, are all simple operators in terms of the basic qubits. We determine the effectiveness of this protocol, and find a version achieves almost perfect fidelity. Many features of semiclassical traversable wormholes are manifested in this setup.

hep-th↗

arXiv2019

Flexible Ultrastrong 100-nm Polyethylene Membranes with Polygonal Pore Structures

Robust nanoporous polymer films with approximate 100-nm thicknesses would be broadly applicable in technological areas such as flexible sensors, artificial skins, separators, antireflection and self-cleaning films. However, the creation of these films has been extremely challenging. To date, all reported ultrathin films are of insufficient mechanical strength for use without substrate supports. We describe here the fabrication of a new ultrastrong and highly flexible ultrahigh molecular weight polyethylene (UHMWPE) 100-nm porous membrane. Scanning and transmission electron microscopy evaluations of film microstructures reveal a planar fibrous structure with randomly oriented polygonal interconnected pores. Moreover, the tensile strength of this film is twice as strong as that of solid stainless steel, with a measured in-plane tensile strength and ductility of approximately 900 MPa and 26%, respectively. We further coated our newly developed film with a monolayer graphene to invent an optically transparent and fully conformable piezoresistive skin sensor and thus demonstrated a potential application.

physics.app-ph↗

arXiv2018

Regenesis and quantum traversable wormholes

Recent gravity discussions of a traversable wormhole indicate that in holographic systems signals generated by a source could reappear long after they have dissipated, with the need of only performing some simple operations. In this paper we argue the phenomenon, to which we refer as "regenesis", is universal in general quantum chaotic many-body systems, and elucidate its underlying physics. The essential elements behind the phenomenon are: (i) scrambling which in a chaotic system makes out-of-time-ordered correlation functions (OTOCs) vanish at large times; (ii) the entanglement structure of the state of the system. The latter aspect also implies that the regenesis phenomenon requires fine tuning of the initial state. Compared to other manifestations of quantum chaos such as the initial growth of OTOCs which deals with early times, and a random matrix-type energy spectrum which reflects very large time behavior, regenesis concerns with intermediate times, of order the scrambling time of a system. We also study the phenomenon in detail in general two-dimensional conformal field theories in the large central charge limit, and highlight some interesting features including a resonant enhancement of regenesis signals near the scrambling time and their oscillations in coupling. Finally, we discuss gravity implications of the phenomenon for systems with a gravity dual, arguing that there exist regimes for which traversability of a wormhole is quantum in nature, i.e. cannot be associated with a semi-classical spacetime causal structure.

hep-th↗

arXiv2018

Ghostbusters: Unitarity and Causality of Non-equilibrium Effective Field Theories

For a non-equilibrium physical system defined along a closed time path (CTP), a key constraint is the so-called largest time equation, which is a consequence of unitarity and implies causality. In this paper, we present a simple proof that if the propagators of a non-equilibrium effective action have the proper pole structure, the largest time equation is obeyed to all loop orders. Ghost fields and BRST symmetry are not needed. In particular, the arguments for the proof can also be used to show that if ghost fields are introduced, their contributions vanish.

hep-th↗