arXiv subjects

Guang-Can Guo

Publications and source records attributed to Guang-Can Guo.

At least 127 records · Page 7Linked to original sources

arXiv2025

Position-correlated biphoton wavefront sensing for quantum adaptive imaging

Quantum imaging with spatially entangled photons offers advantages such as enhanced spatial resolution, robustness against noise, and counter-intuitive phenomena, while a biphoton spatial aberration generally degrades its performance. Biphoton aberration correction has been achieved by using classical beams to detect the aberration source or scanning the correction phase on biphotons if the source is unreachable. Here, a new method named position-correlated biphoton Shack-Hartmann wavefront sensing is introduced, where the phase pattern added on photon pairs with a strong position correlation is reconstructed from their position centroid distribution at the back focal plane of a microlens array. Experimentally, biphoton phase measurement and adaptive imaging against the disturbance of a plastic film are demonstrated. This single-shot method is a more direct and efficient approach toward quantum adaptive optics, suitable for integration into quantum microscopy, remote imaging, and communication.

quant-ph↗

arXiv2025

Topological resilience of optical skyrmions in local decoherence

The topologically protected configuration embedded in skyrmions has prompted some investigations into their fundamental properties and versatile applications, sparking interest and guiding ongoing development. The topological protection associated with skyrmions was initially observed in systems with interactions. It is widely believed that skyrmions are stable yet relevant confirmation and empirical research remain limited. A pertinent question is whether skyrmion configurations formed by a single classical beam with two coupled degrees of freedom also exhibit topological stability. In this study, we affirm this hypothesis by investigating the effects of local decoherence. We analytically and numerically demonstrate the topological resilience of skyrmions and the occurrence of transition points of skyrmion numbers in local decoherence across three typical decoherence channels. On the other hand, we show that these qualities are independent of the initial state. From the numerical results, we find that inhomogeneous but continuous decoherence channels also have the same behaviors and maintain topological stability of skyrmions as homogeneous decoherence channels do. These properties of skyrmions contribute to further applications in various areas, including communication and imaging.

physics.optics↗

arXiv2025

A hybrid-frequency on-chip programmable synthetic-dimension simulator with arbitrary couplings

High-performance photonic chips provide a powerful platform for analog computing, enabling the simulation of high-dimensional physical systems using low-dimensional devices with additional synthetic dimensions. The realization of large-scale complex simulations necessitates an architecture capable of arbitrary coupling configurations (encompassing symmetric, asymmetric and long-range coupling schemes) which is also crucial for scaling up. Previous approaches rely on excessive physical components to introduce asymmetric coupling, however, are restricted in reconfiguring and scaling by the relatively complicated structures. Here, to solve this problem, we propose a hybrid-frequency synthetic-dimension simulator architecture that combines both intra-resonant and inter-resonant frequency-lattice sites, and experimentally demonstrate it using the thin-film lithium niobate (TFLN) photonic chip. Employing this hybrid programmable architecture, we are able to simulate both the regular and long-range coupled forms of diverse compound-lattice models, such as the Hall ladder, Creutz ladder (symmetric) and Su-Schrieffer-Heeger (SSH, asymmetric) model, on a single chip, simultaneously reducing the experimental requirements significantly. As results, the direct readout of the bandstructure of the SSH model is able to be achieved, to be distinguished from all previous works, and important phenomena such as spin-momentum locking, topological flat band and Aharonov-Bohm cage effect are also observed with lower experimental requirements. Furthermore, applications like piecewise-continuous optical frequency shifting can be enabled by cascading our devices. Our results offer promising insights for future large-scale complex on-chip simulators with arbitrary couplings.

physics.optics↗

arXiv2025

Versatile photonic frequency synthetic dimensions using a single Mach-Zehnder-interferometer-assisted device on thin-film lithium niobate

Investigating physical models with photonic synthetic dimensions has been generating great interest in vast fields of science. The rapid developing thin-film lithium niobate (TFLN) platform, for its numerous advantages including high electro-optic coefficient and scalability, is well compatible with the realization of synthetic dimensions in the frequency together with spatial domain. While coupling resonators with fixed beam splitters is a common experimental approach, it often lacks tunability and limits coupling between adjacent lattices to sites occupying the same frequency domain positions. Here, on the contrary, we conceive the resonator arrays connected by electro-optic tunable Mach-Zehnder interferometers in our configuration instead of fixed beam splitters. By applying bias voltage and RF modulation on the interferometers, our design extends such coupling to long-range scenario and allows for continuous tuning on each coupling strength and synthetic effective magnetic flux. Therefore, our design enriches controllable coupling types that are essential for building programmable lattice networks and significantly increases versatility. As the example, we experimentally fabricate a two-resonator prototype on the TFLN platform, and on this single chip we realize well-known models including tight-binding lattices, topological Hall ladder and Creutz ladder. We directly observe the band structures in the quasi-momentum space and important phenomena such as spin-momentum locking and the Aharonov-Bohm cage effect. These results demonstrate the potential for convenient simulations of more complex models in our configuration.

physics.optics↗

arXiv2025

Quantum synchronization at the critical point of Floquet driven Rydberg atoms

The criticality enhanced correlations and susceptibility allow weak periodic driving to induce collective synchronization due to critical slowing down, providing a unique platform to study non-equilibrium order emergence. This establishes a powerful paradigm for investigating non-equilibrium order formation, yet the fundamental mechanisms of critical-point synchronization remain poorly understood. Here, we utilize a microwave pulse as a seed to induce quantum synchronization at the critical point of Floquet driven Rydberg atoms. In the experiment, the microwave periodic driving on Rydberg states acts as a seeded temporal order in subspace, which triggers synchronization across the entire ensemble. The behavior of the emergent synchronized oscillation is elaborately linked to alterations in the seed, such as the relative phase shift and the frequency difference, which result in phase-dependent seeding and embryonic synchronization. This result opens up new possibilities for studying and harnessing time-dependent quantum many-body phenomena, offering insight into the behavior of complex many-body systems under seeding.

cond-mat.quant-gas↗

arXiv2025

Experimental investigation of uncertainty relations for non-Hermitian operators

Uncertainty relations for Hermitian operators have been confirmed through many experiments. However, previous experiments have only tested the special case of non-Hermitian operators, i.e., uncertainty relations for unitary operators. In this study, we explore uncertainty relations for general non-Hermitian operators, which include Hermitian and unitary operators as special cases. We perform experiments with both real and complex non-Hermitian operators for qubit states, and confirm the validity of the uncertainty relations within the experimental error. Our results provide experimental evidence of uncertainty relations for non-Hermitian operators. Furthermore, our methods for realizing and measuring non-Hermitian operators are valuable in characterizing open-system dynamics and enhancing parameter estimation.

quant-ph↗

arXiv2025

Characterizing Topological Phase Transition in Non-Hermitian Systems

We propose and present a concept of Topological Distance (TD), obtained from the integration of trace distance over the generalized Brillouin zone, in order to characterize the topological transitions of non-Hermitian systems. Specifically, such a quantity is used to measure the overall dissimilarity between eigen wavefunctions upon traversing all possible matter states, and confirms the phase boundaries through observing the divergences of both TD and its partial derivatives; we clarify its origin and also offer a theoretical explanation. The method is developed to characterize the non-Hermitian topology in a novel way, and shows its generality and effectiveness in 1D non-Hermitian Kitaev systems, non-Hermitian Hamiltonians under periodic or open boundary conditions, and even generalizable to higher-order topological systems, providing a novel perspective to understand topological physics.

cond-mat.mes-hall↗

arXiv2025

Measurement-device-independent quantum key distribution with asymmetric sources

Measurement-device-independent quantum key distribution (MDI-QKD), which eliminates all the attacks from the eavesdropper to the measurement party, has been one of the most promising technology for the implementation of end-to-end quantum networks. In practice, the asymmetry of both sources and channels is generally inevitable. Therefore, we propose a theory to analyze the performance when any two MDI users in networks communicates using asymmetric sources in distinct single or multiple temporal modes. As a specific application, we model to obtain the key rate of MDI-QKD with weak coherent pulse source and spontaneous parametric down-conversion source, and compare the performance to the cases with symmetric (i.e. identical) sources. The result demonstrates that the actual performance does not degrade due to the asymmetry of sources. In contrary, it maintains at a good level over the entire distance we study. This work provides a theoretical basis for analyzing and optimizing MDI-QKD networks with asymmetric sources, and thus paving the way for the practical deployment of completely asymmetric MDI-QKD networks.

quant-ph↗

arXiv2025

Efficient single-atom transfer from an optical conveyor belt to a tightly confined optical tweezer

Efficient loading of single atoms into tightly confined traps is crucial for advancing quantum information processing and exploring atom-photon interactions. However, directly loading atoms from a magneto-optical trap (MOT) into static tweezers in cavity-based systems and hybrid atom-photon interfaces remains a challenge. Here, we demonstrate atom loading in a tightly confined optical tweezer 0.6mm away from MOT by an optical conveyor belt. By employing real-time feedback control of the atom number in the overlapping region between the conveyor belt and the tweezer, we enhance a single-atom loading probability to 77.6%. Our technique offers a versatile solution for deterministic single-atom loading in various experimental settings and paves the way for diverse applications based on hybrid photonic-atom structures.

physics.atom-ph↗

arXiv2025

Generation of Near-ideal Indistinguishable Two-Photon State by Incoherent Light

High-quality quantum states lie at the heart of advanced quantum information processing. The degree of photon indistinguishability is critical for applications from photonic quantum computation to precision metrology. The two-photon Hong-Ou-Mandel (HOM) interference effect provides a rigorous quantification method, with its visibility serving as the ultimate benchmark for source quality. Generally, the coherent pumping is widely regarded as indispensable for the preparation of quantum sources. As a result, incoherent light sources have seen limited applications in the current quantum technologies. In this work, we generate an indistinguishable two-photon state by incoherent light generated by frequency doubling of Amplified Spontaneous Emission light. The theoretical analysis indicates that phase randomization of the pumping does not affect the coincidence visibility in two-photon intensity interference. Moreover, temporal incoherence further enhances the symmetry of the generated spectrum in second-harmonic generation. In the experiment, the incoherently pumped photon sources exhibit a heralding efficiency of approximately 60\% and a coincidence-to-accidental ratio exceeding 15000. The observed HOM interference fringes show the visibility of 99.1\% without any spectrum filtering, confirming the near-ideal indistinguishability of the photons. Our study reveals the role of temporal coherence in second-order nonlinear interactions, it provide a potential approach to use an easily accessible incoherent light for engineering high-quality quantum sources.

quant-ph↗

arXiv2025

Secure quantum key distribution against correlated leakage source

Quantum key distribution (QKD) provides information theoretic security based on quantum mechanics, however, its practical deployment is challenged by imperfections of source devices. Among various source loopholes, correlations between transmitted pulses pose a significant yet underexplored security risk, potentially compromising QKD's theoretical guarantees. In this work, we propose a security analysis framework for QKD under correlations, enabling finite-key analysis for the first time by extending and rearranging QKD rounds and leveraging the generalized chain rule. Based on this framework, and inspired by the idea of side-channel-secure QKD, we develop a secure QKD against correlated leakage source only need the characterization of correlation range and the lower bound on the vacuum component of the prepared states. Additionally, our framework can be extended to other QKD protocols, offering a general approach to consider correlation induced security vulnerabilities. The simulation results demonstrate the effectiveness of our protocol and its significantly superior tolerance to imperfect parameters compared to existing protocols. This work provides a crucial step toward closing security loopholes in QKD, enhancing its practicality, and ensuring long-distance,high-performance secure communication under real-world constraints.

quant-ph↗

arXiv2025

Nonlinear Enhancement of Measurement Precision via a Hybrid Quantum Switch

Quantum metrology promises measurement precision beyond the classical limit by using suitably tailored quantum states and detection strategies. However, scaling up this advantage is experimentally challenging, due to the difficulty of generating high-quality large-scale probes. Here, we build a photonic setup that achieves enhanced precision scaling by manipulating the probe's dynamics through operations performed in a coherently controlled order. Our setup applies an unknown rotation and a known orbital angular momentum increase in a coherently controlled order, in a way that reproduces a hybrid quantum SWITCH involving gates generated by both discrete and continuous variables. The unknown rotation angle $θ$ is measured with precision scaling as $1/4ml$ when a photon undergoes a rotation of $2mθ$ and an angular momentum shift of $2l \hbar$. With a practical enhancement factor as high as 2317, the ultimate precision in our experiment is $0.0105^{\prime \prime}$ when using $7.16\times10^7$ photons, corresponding to a normalized precision of $\approx 10^{-4}$rad per photon. No photon interaction occurs in our experiment, and the precision enhancement consumes only a linearly increasing amount of physical resources while achieving a nonlinear scaling of the precision. We further indicate that this nonlinear enhancement roots in an in-depth exploration of the Heisenberg uncertainty principle (HUP), and our findings not only deepen the understanding of the HUP but also pave a pathway for advancements in quantum metrology.

quant-ph↗

arXiv2025

Thermalization of Quantum Many-Body Scars in Kinetically Constrained Systems

The phenomenon of quantum many-body scars (QMBS) has been studied both theoretically and experimentally, due to its unusual violation of the eigenstate thermalization hypothesis (ETH). In this paper, we extend the ETH to a new description based on the grand canonical ensemble to depict the thermal properties of QMBS models. For this purpose, we embed the dynamics of kinetically constrained systems within the Lindblad-like master equation, and demonstrate that the violation of the ETH by scar eigenstates is related to their slow decay in the corresponding dissipative process. Within this open system description, we reformulate the ETH to demonstrate that both scar eigenstates and thermal ones exhibit thermalization governed by grand canonical statistics. Consequently, our revised ETH unifies scars and thermal states under a cohesive thermodynamic rule. Our work resolves the fundamental tension between constraint-induced non-ergodicity and thermalization paradigms, establishing a unified route to generalized thermalization for quantum many-body systems.

quant-ph↗

arXiv2025

Transverse Polarization Gradient Entangling Gates for Trapped-Ion Quantum Computation

The construction of entangling gates with individual addressing capability represents a crucial approach for implementing quantum computation in trapped ion crystals. Conventional entangling gate schemes typically rely on laser beam wave vectors to couple the ions' spin and motional degrees of freedom. Here, we experimentally demonstrate an alternative method that employs a polarization gradient field generated by a tightly focused laser beam, previously proposed as a Magnus-type quantum logic gate. Using this technique, we perform Raman operations on nuclear spin qubits encoded in 171Yb+ ions, generating spin-dependent forces along axial motional modes in a linear trap. By utilizing an acousto-optic deflector to create arbitrary spot pairs for individual ion addressing in two-ion (four-ion) chains, we achieve MS gates with fidelities exceeding 98.5% (97.2%). Further improvements in numerical aperture and laser power could reduce gate durations while enhancing fidelity. This method is compatible with, and can significantly simplify, optical tweezer gate proposals, where motional mode engineering enables scalable trapped-ion quantum computation. The technique can be extended to two-dimensional ion crystals, representing a key step toward large-scale trapped-ion quantum processors.

quant-ph↗

arXiv2025

Tunable Antichiral Hinge State in Photonic Synthetic Dimensions

Recent research in 2-dimensional (2D) topological matter has generalized the notion of edge states from chiral to antichiral configurations with the same propagating direction at parallel edges, revealing a rich variety of robust transport phenomena. Here, we propose that antichiral hinge states can emerge in a 3D higher-order topological insulator/semimetal, where two surface/bulk Dirac points are connected by the hinge states. The band dispersion can be controlled and tilted independently for each hinge using properly designed tunnelings, resulting in tunable antichiral hinge states with programmable propagation direction and velocity. Moreover, we propose experimental realization schemes based on a 1D coupled cavity array with additional synthetic dimensions represented by the photonic orbital angular momentum and frequency. We innovatively introduce both longitudinal and transversal electro-optic modulators to generate the desired tunable tunnelings along the synthetic dimensions, which significantly reduce the experimental complexity by eliminating the need for beam splittings and auxiliary cavities. The tunable antichiral hinge states are confirmed by the photonic transmission spectra. Our work presents the robust and tunable antichiral hinge-state transports which paves the way for exploring novel topological matter and their device applications.

quant-ph↗

arXiv2025

Temperature dependent single- and double-quantum relaxation of negatively charged boron vacancies in hexagonal boron nitride

The negatively charged boron vacancy in two-dimensional hexagonal boron nitride has emerged as a promising candidate for quantum sensing. The coherence time of this defect spins which coherent quantum sensing resides in is limited spin-phonon interactions, while the underlying physical mechanism of the corresponding high-temperature behavior is still not fully understood. Here, we probe the single- and double-quantum relaxation rates on this center over the temperature range from 293 to 393 K. The results show that both relaxation rates increase with increasing temperature, and the double-quantum relaxation rate significantly increases rapidly. At high temperature (above 400 K), the double-quantum relaxation rate is much greater than single-quantum relaxation rate, and may dominate the decoherence channel of spin-phonon interactions. Using a theoretical model of second-order spin-phonon interactions, we attribute the high-temperature spin relaxation rates to interactions with higher-energy effective phonon mode, aiding the further understanding and guiding high-temperature sensing applications.

quant-ph↗

arXiv2025

Experimental Realization of Genuine Three-copy Collective Measurements for Optimal Information Extraction

Nonclassical phenomena tied to entangled states are the focus of foundational studies and powerful resources in many applications. By contrast, the counterparts in quantum measurements are still poorly understood. Notably, genuine multipartite nonclassicality is barely discussed, let alone its experimental realization. Here we experimentally demonstrate the power of genuine tripartite nonclassicality in quantum measurements based on a simple estimation problem. To this end we realize an optimal genuine three-copy collective measurement via a nine-step two-dimensional photonic quantum walk with 30 elaborately designed coin operators. Then we realize an optimal estimation protocol and achieve an unprecedented high estimation fidelity, which can beat all strategies based on restricted collective measurements by more than 11 standard deviations. These results clearly demonstrate that genuine collective measurements can extract more information than local measurements and restricted collective measurements. Our work opens the door for exploring genuine multipartite nonclassical measurements and their power in quantum information processing.

quant-ph↗

arXiv2025

Experimental Verification of Entangled States in the Adversarial Scenario

Efficient verification of entangled states is crucial to many applications in quantum information processing. However, the effectiveness of standard quantum state verification (QSV) is based on the condition of independent and identical distribution (IID), which impedes its applications in many practical scenarios. Here we demonstrate a defensive QSV protocol, which is effective in all kinds of non-IID scenarios, including the extremely challenging adversarial scenario. To this end, we build a high-speed preparation-and-measurement apparatus controlled by quantum random-number generators. Our experiments clearly show that standard QSV protocols often provide unreliable fidelity certificates in non-IID scenarios. In sharp contrast, the defensive QSV protocol based on a homogeneous strategy can provide reliable and nearly tight fidelity certificates at comparable high efficiency, even under malicious attacks. Moreover, our scheme is robust against the imperfections in a realistic experiment, which is very appealing to practical applications.

quant-ph↗