arXiv subjects

Qing Ai

Publications and source records attributed to Qing Ai.

At least 19 recordsLinked to original sources

arXiv2026

Numerically-Exact Quantum-Simulation Approach for Two-Dimensional Spectroscopy of Open Quantum Systems

Two-dimensional spectroscopy (2DS) is a powerful ultrafast technique for probing electronic and vibrational dynamics in complex microscopic systems. Extracting detailed information on system dynamics and system-bath interactions from 2DS experiments requires precise theoretical simulations for comparison, which motivates the development of numerically-exact and computationally-efficient simulation approaches. Here, we propose a quantum-simulation approach for 2DS based on the bath-engineering technique (BET), which has been successfully employed in quantum simulations of open quantum dynamics. To demonstrate our approach, we first simulate the 2DS of a driven four-level system in chiral enantiodetection, where we also assess the applicability of the center-line slope (CLS) method for extracting time correlation functions (TCFs) from the 2DS. We further apply our approach to the 2DS of ${\rm Rh(CO)_2C_5H_7O_2}$ (RDC) dissolved in chloroform, where the results reproduce the main spectral patterns observed in experiments. Our work provides a numerically-exact and efficient framework for simulating 2DS, and can offer additional insight into the dynamics of open quantum systems.

quant-ph↗

arXiv2026

Investigating Lipkin-Meshkov-Glick Model and Criticality-Enhanced Metrology in a Coherent Ising Machine

Quantum criticality has received extensive attention due to its ability to significantly enhance quantum sensing. But its realization and control in many-body quantum systems remain challenging. We present an effective scheme to simulate the Lipkin-Meshkov-Glick (LMG) model using a coherent Ising machine (CIM) composed of a network of degenerate optical parametric oscillators (DOPO). In our work, the spin variables of the LMG model are mapped onto the phases of DOPO pulses, and the spin-spin interactions are realized by all-to-all couplings among them. Through our investigation of the critical behavior in the antiferromagnetically coupled LMG model in the thermodynamic limit, i.e., $N\rightarrow\infty$, and its application in quantum sensing near the critical point, we verify that the CIM does not only effectively capture the second-order quantum phase transition (QPT) at the critical point but also reconstructs its complete phase diagram under ferromagnetic coupling. Furthermore, we demonstrate how the critical dynamics of this simulation platform can be utilized for quantum-enhanced metrology, achieving a measurement precision that diverges near the critical point of the LMG model. These results highlight the capability of the CIM as a flexible experimental platform for investigating the QPT in the fundamental quantum magnetic models, providing valuable insights into quantum simulation and critical phenomena.

quant-ph↗

arXiv2025

Electromagnetically-Induced Transparency Bridges Disconnected Light-Harvesting Networks

The energy-transfer efficiency of the natural photosynthesis system seems to be perfectly optimized during the evolution for millions of years. However, how to enhance the efficiency in the artificial light-harvesting systems is still unclear. In this paper, we investigate the energy-transfer process in the photosystem I (PSI). When there is no effective coupling between the outer antenna (OA) and the reaction center (RC), the two light-harvesting networks are disconnected and thus the energy transfer is inefficient. In order to repair these disconnected networks, we introduce a bridge with three sites between them. We find that by modulating the level structure of the 3-site bridge to be resonant, the energy transfer via the dark state will be enhanced and even outperform the original PSI. Our discoveries may shed light on the designing mechanism of artificial light-harvesting systems.

physics.optics↗

arXiv2025

Quantum Phase Transitions in Coherent Ising Machines: XY Model for Demonstration

In this work, we study the detection of quantum phase transitions (QPTs) in coherent Ising machines (CIMs) through a spectral mapping between the one-dimensional XY spin model and a network of degenerate optical parametric oscillators (DOPOs). This exact correspondence reveals that the DOPO spectrum faithfully encodes the critical behavior of anisotropic and isotropic XY chains, while a strongly anisotropic regime provides a controlled near-transverse-field-Ising realization, with the energy gap closing precisely at the critical point. The ground-state energy density and its derivatives are analyzed, and the resulting singularities in magnetic susceptibility accurately pinpoint the quantum critical points of the corresponding spin model. These results show that CIMs not only serve as powerful platforms for solving combinatorial optimization problems but also provide a versatile tool for probing universal quantum critical phenomena, bridging quantum-spin models and photonic quantum systems.

quant-ph↗

arXiv2025

Quantum batteries in coherent Ising machine

With intensive studies of quantum thermodynamics, quantum batteries (QBs) have been proposed to store and transfer energy via quantum effects. Despite many theoretical models, decoherence remains a severe challenge and practical platforms are still rare. Here, we propose a QB based on the coherent Ising machine, in which the signal field acts as the core energy-storage unit. To clarify the role of quantum coherence in resisting dissipation, we decompose the ergotropy, i.e., the maximum extractable work from the QB, into its coherent and incoherent components. We find that the coherent part decays at a rate roughly half that of the incoherent part, exhibiting much stronger robustness against decoherence. More importantly, the coherent ergotropy and the average charging power reach their respective maxima at essentially the same moment, which defines the optimal instant to switch off the pump field. Finally, by coupling the QB to a two-level system as the load, we demonstrate an efficient energy discharge process of the proposed QB. Our work establishes a realistic and immediately-implementable QB architecture on a mature optical platform, laying a foundation for experimental exploration of quantum energy storage.

quant-ph↗

arXiv2025

Guest metal-driven quantum anharmonic effects on stability and two-gap superconductivity in carbon-boron clathrates

Traditionally, strong quantum anharmonic effects have been considered a characteristic of hydrogen-rich compounds. Here we propose that these effects also play a decisive role in boron-carbon clathrates. The stability and superconducting transition temperature (Tc) of carbon-boron clathrates XYB6C6, whose metal atoms have an average oxidation state of +1.5, have long remained under debate. At this oxidation state, some combinations (e.g., RbSrB6C6) are dynamically stable, whereas others (e.g., RbPbB6C6) are not. Using the stochastic self-consistent harmonic approximation combined with machine learning, we find that the anharmonicity originates primarily from guest metal atoms. For comparison, we find that quantum fluctuations have negligible influence on SrB3C3, but remove the lattice instability of RbPbB6C6. The predicted Tc of RbPbB6C6 (88 K) is nearly twice that of SrB3C3. Moreover, RbPbB6C6 exhibits two-gap superconductivity due to the higher C/B ratio in the density of states at the Fermi level compared to SrB3C3, weakening the sp3 hybridization. These findings demonstrate that quantum anharmonicity crucially governs the stability and superconductivity of XYB6C6 clathrates.

cond-mat.supr-con↗

arXiv2025

Quantum Jump Approach for Photosynthetic Energy Transfer with Chemical Reaction and Fluorescence Loss

Recently, the coherent modified Redfield theory (CMRT) has been widely used to simulate the excitation-energy-transfer (EET) processes in photosynthetic systems. However, the numerical simulation of the CMRT is computationally expensive when dealing with large-scale systems, e.g. photosystem I (PSI) and II (PSII). On the other hand, the chemical reaction and fluorescence loss traditionally treated by the non-Hermitian Hamiltonian approach may result in significantly error in a wide range of parameters. To address these issues, we introduce a quantum jump approach (QJA) based on the CMRT to simulate the evolution of photosynthetic complexes including both the chemical reaction and fluorescence loss. The QJA shows higher accuracy and efficiency in simulating the EET processes. The QJA-CMRT approach may provide a powerful tool to design and optimize artificial photosynthetic systems, which benefits future innovation in the field of energy.

physics.chem-ph↗

arXiv2025

Quantum Biology, Quantum Simulation and Quantum Coherent Devices

Many living organisms can exploit quantum mechanical effects to gain distinct biological advantages. In plants, photosynthesis uses quantum coherence to achieve near 100% efficiency in energy transfer. With advances in experimental techniques, two-dimensional electronic spectroscopy can reveal dynamic processes such as coherence and coupling within a system, and it plays an important role in studying energy transfer in photosynthesis. On the theory side, methods such as the generalized Bloch-Redfield theory and the hierarchical equations of motion are used to model photosynthetic systems. Quantum simulation, as a high-efficiency and low-complexity approach, has also made progress across various platforms in the study of photosynthesis. In recent years, a series of studies has introduced quantum coherence into artificial systems to enhance energy transfer efficiency, laying the groundwork for the design of coherent devices with efficient energy transport. Birds can use the weak geomagnetic field and spin-dependent chemical reactions to detect direction. Theoretical frameworks for animal navigation include magnetite-based mechanisms, magnetoreceptor genes, and the radical-pair mechanism. Quantum simulations of navigation have also advanced on multiple platforms. Inspired by animal navigation, diverse quantum effects have been applied to improve sensing and to support navigation tasks. This paper presents a comprehensive review of progress on quantum coherence in photosynthesis and avian navigation, along with related theoretical methods, quantum simulation approaches, and research on quantum coherent devices.

quant-ph↗

arXiv2025

Suppressing Degradation in Quantum Batteries by Electromagnetically-induced Transparency

Quantum batteries (QBs), as emerging quantum devices for energy storage and transfer, have attracted significant attention due to their potential to surpass classical batteries in charging efficiency and energy density. However, interactions between a QB and its environment result in decoherence, which significantly reduces its operational lifespan. In this work, we propose suppressing the aging of QBs by introducing the electromagnetically-induced transparency (EIT). Specifically, we model a four-level atom as a QB with an effective two-level system enabled by the EIT, while the photons in the cavity serve as the energy charger. By comparing the energy and extractable work of the QB with and without the EIT effect, we demonstrate that the QBs incorporating the EIT exhibit enhanced resistance to spontaneous decay as compared to their counterparts without the EIT. We believe that our findings may provide valuable insights and shed the light on the design principles for mitigating the degradation of the QBs.

quant-ph↗

arXiv2025

Electromagnetically Induced Transparency Effect Improves Quantum Battery Lifetime

Quantum battery (QB) is an application of quantum thermodynamics which uses quantum effects to store and transfer energy, overcoming the limitations of classical batteries and potentially improving performance. However, due to the interaction with the external environment, it will lead to decoherence and thus reduce the lifetime of QBs. Here, we propose suppressing the environmental dissipation in the energy-storage process of the QB by exploiting the electromagnetically-induced transparency (EIT) and bound states. By constructing a hybrid system composed of a four-level atom and a coupled-cavity array, two bound states are formed in the system when the energy of the QB is in the energy band of the cavity array. Due to the bound states and the EIT effect, the ambient dissipation is significantly suppressed, which improves the lifetime of the QB. In addition, we show that when the energy of the QB is in resonance with the cavity, the ergotropy of the QB reaches the maximum. Furthermore, there exists an optimal coupling strength between two neighbouring cavities which helps improve the performance of the QB. These discoveries may shed the light on the design of high-efficiency QBs.

quant-ph↗

arXiv2024

Non-Hermitian Hamiltonian Approach for Two-Dimensional Coherent Spectra of Driven Systems

Two-dimensional coherent spectroscopy (2DCS) offers significant advantages in terms of high temporal and frequency resolutions and signal-to-noise ratio. Until now, the response-function (RF) formalism has been the prevalent theoretical description. In this study, we compare the non-Hermitian Hamiltonian (NHH) method with the RF formalism in a three-level system with a constant control field. We obtain the signals from both approaches and compare their population dynamics and 2DCS. We propose the quasi-Green functions for the NHH method, which allows all dominant Liouville paths to be inferred. We further simulate the 2DCS of Rh(CO)$_2$C$_5$H$_7$O$_2$ (RDC) dissolved in hexane with the NHH method, which is in good agreement with the previous experiments. Although the NHH method overestimates relaxations, it provides all important paths by analytical solutions, which are different from the four paths used in the RF formalism. Our results demonstrate that the NHH method is more suitable than the RF formalism for investigating the systems including relaxation and control fields via the 2DCS.

quant-ph↗

arXiv2024

Finite-temperature topological invariant for higher-order topological insulators

We investigate the effects of temperature on the higher-order topological insulators (HOTIs). The finite-temperature topological invariants for the HOTIs can be constructed by generalizing the Resta's polarization for the ground state to the ensemble geometric phase (EGP) for the mixed states, [C.-E. Bardyn, L. Wawer, A. Altland, M. Fleischhauer, and S. Diehl, PhysRevX.8.011035}{Phys. Rev. X 8, 011035 (2018)}]. The EGP is consistent with the Resta's polarization both at zero temperature and at finite temperatures in the thermodynamic limit. {We find that the temperature can change the critical point and thus induces a phase transition from a topologically-trivial phase to a nontrivial phase in a finite-size system, manifesting changes in the winding of the EGP.

cond-mat.stat-mech↗

arXiv2024

Anomalously reduced homogeneous broadening of two-dimensional electronic spectroscopy at high temperature by detailed balance

Dissipation and decoherence of quantum systems in thermal environments is important to various spectroscopies. It is generally believed that dissipation can broaden the line shape of spectroscopies, and thus stronger system-bath interaction can result in more significant homogeneous broadening of two-dimensional electronic spectroscopy (2DES). Here we show that the case can be the opposite in the regime of electromagnetically induced transparency (EIT). We predict that assisted by EIT, the homogeneous broadening of the 2DES at a higher temperature can be significantly reduced due to the detailed balance. This anomalous effect is due to the long-lasting off-diagonal peaks in 2DES.

quant-ph↗

arXiv2024

Observing Quantum Coherent Oscillations in a Three-Level Atoms via Electromagnetically Induced Transparency by Two-Dimensional Spectroscopy

Two-dimensional electronic spectroscopy (2DES) has high spectral resolution and is a useful tool for studying atom dynamics. In this paper, we show a smallest unit of electromagnetically induced transparency (EIT) for 2DES, that is, a three-level system. It is found that the original main peak is split into four small ones due to the introduction of the EIT. It suggests that the homogeneous broadening of 2DES can be effectively reduced by the EIT. Moreover, in sharp contrast to a constant height, the height of the peaks will manifest a damped oscillation with respect to the population time. It seems that the quantum-beat phenomenon appears. These findings may help us obtain more information about the dynamics of excited states.

quant-ph↗

arXiv2023

Optical Non-Reciprocity in Coupled Resonators Inspired by Photosynthetic Energy Transfer

Inspired by the photosynthetic energy transfer process, we theoretically propose a method to realize non-reciprocal optical transmission in an array of coupled resonators. The optical non-reciprocity of the coupled resonators arises from the frequency gradient between adjacent cavities and the interaction with the environment, which is similar to photosynthetic energy transfer. An increase in the frequency gradient or the number of the cavities can lead to better non-reciprocity. However, although a higher environment temperature will increase the total photon number in the coupled cavities, non-reciprocity will be weakened. All these findings can be well described by the detailed balance. Our discovery reveals the similarity between the noise-induced optical non-reciprocity and exciton energy transfer in natural photosynthesis.

physics.optics↗

arXiv2023

Quantum Simulation of Bound-State-Enhanced Quantum Metrology

Quantum metrology explores quantum effects to improve the measurement accuracy of some physical quantities beyond the classical limit. However, due to the interaction between the system and the environment, the decoherence can significantly reduce the accuracy of the measurement. Many methods have been proposed to restore the accuracy of the measurement in the long-time limit. Recently, it has been found that the bound state can assist the error-free measurement and recover the $t^{-1}$ scaling [K. Bai, Z. Peng, H. G. Luo, and J. H. An, Phys. Rev. Lett. 123, 040402 (2019)]. Here, by using $N$-qubits, we propose a method to simulate the open quantum dynamics of the hybrid system including one atom and coupled resonators. We find that the error of the measurement can vanish as the time increases due to the existence of the bound state. By both analytical and numerical simulations, we prove the $t^{-1}$ scaling of the measurement error can be recovered when there is a bound state in the hybrid system. Interestingly, we observe that there are perfect oscillations which can be used for the evaluation of the atomic transition frequency. For a finite-$N$, the duration of the perfect oscillations doubles as one more qubit is involved.

quant-ph↗

arXiv2023

Sudden death of entanglement with Hamiltonian ensemble assisted by auxiliary qubits

In this paper, we theoretically propose a method to simulate the longitudinal relaxation of a single qubit by coupling it to an auxiliary qubit. In order to mimic the finite-temperature relaxation, we utilize the Hamiltonian-ensemble approach [Kropf, Gneiting, and Buchleitner, Phys. Rev. X 6, 031023 (2016)] and in each realization the auxiliary qubit possesses a random level spacing. The longitudinal relaxation arises as a consequence of the ensemble average and the interaction between the working qubit and the auxiliary qubit. Furthermore, we apply this approach to investigate the influence of the longitudinal relaxation and the transverse relaxation on the entanglement dynamics of two qubits. It is discovered that the sudden death of the entanglement will occur as long as the longitudinal relaxation is present. The transverse relaxation assists the longitudinal relaxation and thus accelerates the finite-time disentanglement.

quant-ph↗

arXiv2023

Universal quantum gates by nonadiabatic holonomic evolution for the surface electron

The nonadiabatic holonomic quantum computation based on the geometric phase is robust against the built-in noise and decoherence. In this work, we theoretically propose a scheme to realize nonadiabatic holonomic quantum gates in a surface electron system, which is a promising two-dimensional platform for quantum computation. The holonomic gate is realized by a three-level structure that combines the Rydberg states and spin states via an inhomogeneous magnetic field. After a cyclic evolution, the computation bases pick up different geometric phases and thus perform a geometric gate. Only the electron with spin up experiences the geometric gate, while the electron with spin down is decoupled from the state-selective driving fields. The arbitrary controlled-U gate encoded on the Rydberg states and spin states can then be realized. The fidelity of the output state exceeds 0.99 with experimentally achievable parameters.

quant-ph↗