arXiv subjects

Jiangbin Gong

Publications and source records attributed to Jiangbin Gong.

At least 37 records · Page 2Linked to original sources

arXiv2025

Breaking Peierls theorem in polyacetylene chains via topological design

Peierls theorem postulates that a one-dimensional (1D) metallic chain must undergo a metal-to-insulator transition via lattice distortion, resulting in bond length alternation (BLA) within the chain. The validity of this theorem has been repeatedly proven in practice, as evidenced by the absence of a metallic phase in low-dimensional atomic lattices and electronic crystals, including conjugated polymers, artificial 1D quantum nanowires, and anisotropic inorganic crystals. Overcoming this transition enables realizing long-sought organic quantum phases of matter, including 1D synthetic organic metals and even high-temperature organic superconductors. Herein, we demonstrate that the Peierls transition can be globally suppressed by employing lattice topology engineering of classic trans-polyacetylene chains connected to open-shell nanographene terminals. The appropriate topology connection enables an effective interplay between the zero-energy modes (ZMs) of terminal and the finite odd-membered polyacetylene (OPA) chains. This creates a critical topology-defined highest occupied molecular orbital (HOMO) that compensates for bond density variations, thereby suppressing BLA and reestablishing their quasi-1D metallic character. Moreover, it also causes the formation of an unconventional boundary-free resonance state, being delocalized over the entire chain with non-decaying spectral weight, distinguishing them from traditional solitons observed in polyacetylene. Our finding sets the stage for pioneering the suppression of material instability and the creation of synthetic organic quantum materials with unconventional quantum phases previously prohibited by the Peierls transition.

cond-mat.mes-hall↗

arXiv2025

Non-Hermitian entanglement dip from scaling-induced exceptional criticality

It is well established that the entanglement entropy of a critical system generally scales logarithmically with system size. Yet, in this work, we report a new class of non-Hermitian critical transitions that exhibit dramatic divergent dips in their entanglement entropy scaling, strongly violating conventional logarithmic behavior. Dubbed scaling-induced exceptional criticality (SIEC), it transcends existing non-Hermitian mechanisms such as exceptional bound states and non-Hermitian skin effect (NHSE)-induced gap closures, which are nevertheless still governed by logarithmic entanglement scaling. Key to SIEC is its strongly scale-dependent spectrum, where eigenbands exhibit an exceptional crossing only at a particular system size. As such, the critical behavior is dominated by how the generalized Brillouin zone (GBZ) sweeps through the exceptional crossing with increasing system size, and not just by the gap closure per se. We provide a general approach for constructing SIEC systems based on the non-local competition between heterogeneous NHSE pumping directions, and show how a scale-dependent GBZ can be analytically derived to excellent accuracy. Beyond 1D free fermions, SIEC is expected to occur more prevalently in higher-dimensional or even interacting systems, where antagonistic NHSE channels generically proliferate. SIEC-induced entanglement dips generalize straightforwardly to kinks in other entanglement measures such as Renyi entropy, and serve as spectacular demonstrations of how algebraic and geometric singularities in complex band structures manifest in quantum information.

quant-ph↗

arXiv2025

Aperiodic Dissipation as a Mechanism for Steady-State Localization

Dissipation is traditionally regarded as a disruptive factor in quantum systems because it often leads to decoherence and delocalization. However, recent insights into engineered dissipation reveal that it can be tuned to facilitate various quantum effects, from state stabilization to phase transitions. In this work, we identify aperiodic dissipation as a mechanism for inducing steady-state localization, independent of disorder or a quasiperiodic potential in the Hamiltonian. This localization arises from long-range phase correlations introduced by a spatially varying dissipation phase parameter, which enables nontrivial interference in the steady-state. By systematically comparing two classes of aperiodic dissipation (defined as commensurate and incommensurate cases), we find that incommensurate modulation plays the most efficient role in stabilizing a localized steady-state. Our analysis, based on coherence measures, purity, and participation ratio, reveals a direct link between eigenstate coherence and real-space localization, showing that dissipation can actively shape localization rather than simply causing decoherence. These findings highlight aperiodic dissipation as a viable approach to controlling localization in open quantum systems, potentially enabling new ways to manipulate quantum states and design dissipation-driven phases.

quant-ph↗

arXiv2025

Microscopic theory of a precessing ferromagnet for ultrasensitive magnetometry

Levitated systems have great potential in quantum sensing and exploring quantum effects at the macroscopic scale. Of particular interest are recent works suggesting that a levitated ferromagnet can beat the standard quantum limit of magnetometry. This work offers a theoretical model to analyze and understand critical features of the precessing dynamics of a levitated ferromagnetic needle, indeed much like a macrospin, in the presence of a weak magnetic field. The dynamics from the atomic scale reveals how the standard quantum limit is surpassed, thus verifying sensing advantages when compared with a collection of independent spins. Our theory further takes us to two additional experimental designs of immediate interest: measurement of the celebrated Berry phase with a precessing ferromagnetic needle and the use of its nutation motion to sense a low-frequency oscillating magnetic field. With a microscopic theory established for levitated ferromagnetic needles, future studies of macroscopic quantum effects and the associated quantum-classical transition also become possible.

quant-ph↗

arXiv2025

Nonadiabatic braiding of Majorana modes

The realization and manipulation of Majorana zero modes have drawn significant attention for their crucial role in enabling topological quantum computation. Conventional approaches to the braiding of Majorana zero modes rely on adiabatic processes. In this work, using a composite 2-Kitaev-chain system accommodating Majorana zero modes as a working example, we propose a nonadiabatic and non-Abelian geometry phase-based protocol to execute operations on these Majorana zero modes. This is possible by locally coupling the edge sites of both quantum chains with an embedded lattice defect, successfully simulating the braiding operation of two Majorana modes in a highly nonadiabatic fashion. To further enhance the robustness against control imperfections, we apply a multiple-pulse composite strategy to our quantum chain setting for second-order protection of the braiding operations. Our proposal can also support the fast and robust realization of the π/8 gate, an essential ingredient for universal quantum computation. This work hence offers a potential pathway towards the nonadiabatic and fault-tolerant control of Majorana zero modes.

quant-ph↗

arXiv2025

Critical Dynamics of the Anderson Transition on Small-World Graphs

The Anderson transition on random graphs draws interest through its resemblance to the many-body localization (MBL) transition with similarly debated properties. In this Letter, we construct a unitary Anderson model on Small-World graphs to characterize long time and large size wave-packet dynamics across the Anderson transition. We reveal the logarithmically slow non-ergodic dynamics in the critical regime, confirming recent random matrix predictions. Our data clearly indicate two localization times: an average localization time that diverges, while the typical one saturates. In the delocalized regime, the dynamics are initially non-ergodic but cross over to ergodic diffusion at long times and large distances. Finite-time scaling then allows us to characterize the critical dynamical properties: the logarithm of the average localization time diverges algebraically, while the ergodic time diverges exponentially. Our results could be used to clarify the dynamical properties of MBL and could guide future experiments with quantum simulators.

cond-mat.dis-nn↗

arXiv2025

Higher-order protection of quantum gates: Hamiltonian engineering coordinated with dynamical decoupling

Dynamical decoupling represents an active approach towards the protection of quantum memories and quantum gates. Because dynamical decoupling operations can interfere with a system's own time evolution, the protection of quantum gates is more challenging than that of quantum states. In this work, we put forward a simple but general approach towards the realization of higher-order protection of quantum gates and further execute the first cloud-based demonstration of dynamical-decoupling-protected quantum gates at the first order and the second order. The central idea of our approach is to engineer (hence regain the control of) the gate Hamiltonian in coordination with higher-order dynamical decoupling sequences originally proposed for the protection of quantum memories. The physical demonstration on an IBM quantum processor indicates the effectiveness and potential of our approach on noisy intermediate scale quantum computers.

quant-ph↗

arXiv2025

Universal fluctuations of localized two interacting particles in one dimension

We investigate the universal fluctuations of localized wavefunction in the Fock space of two interacting particles in one-dimensional disordered systems, focusing on the interplay between random potentials and random long-range interactions. By mapping the system onto a directed polymer problem, we show that random potentials alone produce correlated energies for the sites in the Fock space, giving rise to the fluctuation growth exponent 1/2. Introducing random long-range interactions alters these correlations and drives the system's fluctuations into the Kardar-Parisi-Zhang universality class in (1+1)D with the exponent 1/3. To validate the universality of the observed fluctuation scaling, we study a complex directed polymer model with competing point and columnar disorder. Our results confirm that columnar disorder corresponds to on-site energies in the Fock space from the random potentials, while point disorder models the effects of random long-range interactions between the two particles. These findings provide new insights into the Fock-space perspective for examining disordered quantum many-body systems, and emphasize the critical role of disorder structure in determining the universality class of fluctuations in localized quantum systems.

cond-mat.dis-nn↗

arXiv2025

Enhancing Quantum Metrology by Quantum Resonance Dynamics

Quantum effects in metrology can in principle enhance measurement precision from the so-called standard quantum limit to the Heisenberg Limit. Further advancements in quantum metrology largely rely on innovative metrology protocols that can avoid a number of known obstacles, including the challenge of preparing entangled states with sufficient fidelity, the readout noise in measuring highly entangled states, and no-go theorems for quantum metrology under noisy environments. In this Letter, exploiting some peculiar but experimentally feasible dynamical features of a collection of spins with all-to-all time-periodic interactions, we propose a metrology protocol that can circumvent all the three mentioned obstacles and yet still make good use of time as a resource for metrology. Specifically, by mapping the dynamics of such a periodically driven spin system to that of a paradigm of quantum chaos but tuned to some high-order quantum resonance, it is shown that a simple $SU(2)$ coherent state can, after evolving to highly entangled states in the ensuing dynamics, be dynamically brought back to the same initial coherent state. The associated quantum Fisher information is found to exhibit quadratic scaling with both the number of spins and the duration of the metrology protocol. The achieved Heisenberg scaling can also largely survive in the presence of Markovian noise. Representing a previously unknown strategy for quantum metrology, the protocol proposed here can be tested on available experimental platforms.

quant-ph↗

arXiv2024

Topological edge states at Floquet quantum criticality

Topologically protected edge states exactly at topological phase boundaries challenge the conventional belief that topological states must be associated with a bulk energy gap. Because periodically driven (Floquet) systems host unusually intricate topological phase boundaries, topological edge states can be prolific at such Floquet quantum criticality. Working on a class of chiral-symmetric, Floquet-driven Majorana fermion chains, we analytically and computationally show that the precise boundaries between different Floquet topological gapped phases can accommodate topological edge modes, including the so-called Majorana $π$ modes. We also identify a general bulk-edge correspondence formula to predict and understand the emergence of topological edge modes at Floquet quantum criticality. Of direct interest to quantum simulation experiments, our results break new grounds for studies of nonequilibrium topological phases of matter undergoing topological phase transitions.

cond-mat.stat-mech↗

arXiv2024

Mitigation of systematic amplitude error in nonadiabatic holonomic operations

Nonadiabatic holonomic operations are based on nonadiabatic non-Abelian geometric phases, hence possessing the inherent geometric features for robustness against control errors. However, nonadiabatic holonomic operations are still sensitive to the systematic amplitude error induced by imperfect control of pulse timing or laser intensity. In this work, we present a scheme of nonadiabatic holonomic operations in order to mitigate the said systematic amplitude error. This is achieved by introducing a monitor qubit along with a conditional measurement on the monitor qubit that serves as an error correction device. We shall show how to filter out the undesired effect of the systematic amplitude error, thereby improving the performance of nonadiabatic holonomic operations.

quant-ph↗

arXiv2024

Multiple topological transitions and spectral singularities in non-Hermitian Floquet systems

The interplay between Floquet driving and non-Hermitian gain/loss could give rise to intriguing phenomena including topological funneling of light, edge-state delocalization, anomalous topological transitions and Floquet non-Hermitian skin effects. In this work, we uncover two unique phenomena in Floquet systems caused by gain and loss. First, multiple topological transitions from anomalous Floquet second-order topological insulators to anomalous Floquet first-order topological insulators and then to normal insulators can be induced by gain and loss. Interestingly, the resulting anomalous Floquet insulators further carry hybrid skin-topological boundary modes, which could either be fully localized or localized to different edges at different time slices and traversing along all edges in a single driving period. The topological phase transitions are also shown to be detectable through studies of transmission properties in the setting of coupled ring resonators. Second, gain and loss are found to induce singularities in the Floquet spectral, around which anomalous transmissions at flat quasienergy bands are predicted. These discoveries not only enhanced our understanding of topological matter and phase transitions in driven non-Hermitian systems, but also promoted their experimental realizations in optical and acoustic settings.

physics.app-ph↗

arXiv2024

Direct Probe of Topology and Geometry of Quantum States on IBM Q

The concepts of topology and geometry are of critical importance in exploring exotic phases of quantum matter. Though they have been investigated on various experimental platforms, to date a direct probe of topological and geometric properties on a universal quantum computer even for a minimum model is still in vain. In this work, we first show that a density matrix form of the quantum geometric tensor (QGT) can be explicitly re-constructed from Pauli operator measurements on a quantum circuit. We then propose two algorithms, suitable for IBM quantum computers, to directly probe QGT. The first algorithm is a variational quantum algorithm particularly suitable for Noisy Intermediate-Scale Quantum (NISQ)-era devices, whereas the second one is a pure quantum algorithm based on quantum imaginary time evolution. Explicit results obtained from IBM Q simulating a Chern insulator model are presented and analysed. Our results indicate that transmon qubit-based universal quantum computers have the potential to directly simulate and investigate topological and geometric properties of a quantum system.

quant-ph↗

arXiv2024

Describing the critical behavior of the Anderson transition in infinite dimension by random-matrix ensembles: logarithmic multifractality and critical localization

Due to their analytical tractability, random matrix ensembles serve as robust platforms for exploring exotic phenomena in systems that are computationally demanding. Building on a companion letter [arXiv:2312.17481], this paper investigates two random matrix ensembles tailored to capture the critical behavior of the Anderson transition in infinite dimension, employing both analytical techniques and extensive numerical simulations. Our study unveils two types of critical behaviors: logarithmic multifractality and critical localization. In contrast to conventional multifractality, the novel logarithmic multifractality features eigenstate moments scaling algebraically with the logarithm of the system size. Critical localization, characterized by eigenstate moments of order $q>1/2$ converging to a finite value indicating localization, exhibits characteristic logarithmic finite-size or time effects, consistent with the critical behavior observed in random regular and Erdös-Rényi graphs of effective infinite dimensionality. Using perturbative methods, we establish the existence of logarithmic multifractality and critical localization in our models. Furthermore, we explore the emergence of novel scaling behaviors in the time dynamics and spatial correlation functions. Our models provide a valuable framework for studying infinite-dimensional quantum disordered systems, and the universality of our findings enables broad applicability to systems with pronounced finite-size effects and slow dynamics, including the contentious many-body localization transition, akin to the Anderson transition in infinite dimension.

cond-mat.dis-nn↗

arXiv2024

Quantum machine learning with indefinite causal order

In a conventional circuit for quantum machine learning, the quantum gates used to encode the input parameters and the variational parameters are constructed with a fixed order. The resulting output function, which can be expressed in the form of a restricted Fourier series, has limited flexibility in the distributions of its Fourier coefficients. This indicates that a fixed order of quantum gates can limit the performance of quantum machine learning. Building on this key insight (also elaborated with examples), we introduce indefinite causal order to quantum machine learning. Because the indefinite causal order of quantum gates allows for the superposition of different orders, the performance of quantum machine learning can be significantly enhanced. Considering that the current accessible quantum platforms only allow to simulate a learning structure with a fixed order of quantum gates, we reform the existing simulation protocol to implement indefinite causal order and further demonstrate the positive impact of indefinite causal order on specific learning tasks. Our results offer useful insights into possible quantum effects in quantum machine learning.

quant-ph↗

arXiv2024

Spontaneous superradiant photon current

This work reports the spontaneous emergence of a photon current in a class of spin-cavity systems, where an assemble of quantum emitters interact with distinct photon modes confined in tunneling-coupled cavities. Specifically, with necessary symmetry breaking, photons in a superradiant phase afforded by coherent photon-emitter interaction spontaneously flow from a cavity with a lower resonance frequency to a different cavity with a higher resonance frequency. Theoretical analysis reveals that cavity dissipation is the key to alter spin-cavity coherence, which then makes it possible to extract photons from, and later return photons to the vaccum through the cavities. The interplay between photon loss and emitter coherence hence sustains a counter-intuitive steady current of photons between cavities without an external pumping field.

quant-ph↗

arXiv2023

Quantum logarithmic multifractality

Through a combination of rigorous analytical derivations and extensive numerical simulations, this work reports an exotic multifractal behavior, dubbed "logarithmic multifractality", in effectively infinite-dimensional systems undergoing the Anderson transition. In marked contrast to conventional multifractal critical properties observed at finite-dimensional Anderson transitions or scale-invariant second-order phase transitions, in the presence of logarithmic multifractality, eigenstate statistics, spatial correlations, and wave packet dynamics can all exhibit scaling laws which are algebraic in the logarithm of system size or time. Our findings offer crucial insights into strong finite-size effects and slow dynamics in complex systems undergoing the Anderson transition, such as the many-body localization transition.

cond-mat.dis-nn↗

arXiv2023

Experimental study on the principle of minimal work fluctuations

The central quantity in the celebrated quantum Jarzynski equality is $e^{-βW}$, where $W$ is work and $β$ is the inverse temperature. The impact of quantum randomness on the fluctuations of $e^{-βW}$ and hence on the predictive power of the Jarzynski estimator is an important problem. Working on a single nitrogen-vacancy center in diamond and riding on an implementation of two-point measurement of non-equilibrium work with single-shot readout, we have conducted a direct experimental investigation of the relationship between the fluctuations of $e^{-βW}$ and adiabaticity of non-equilibrium work protocols. It is observed that adiabatic processes minimize the variance of $e^{-βW}$, thus verifying an early theoretical concept, the so-called principle of minimal work fluctuations. Furthermore, it is experimentally demonstrated that shortcuts-to-adiabaticity control can be exploited to minimize the variance of $e^{-βW}$ in fast work protocols. Our work should stimulate further experimental studies of quantum effects on the bias and error in the estimates of free energy differences based on the Jarzynski equality.

quant-ph↗