arXiv subjects

Chuan-Feng Li

Publications and source records attributed to Chuan-Feng Li.

At least 55 records · Page 3Linked 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

Remote Quantum Networks based on Quantum Memories

Quantum networks, capable of transmitting arbitrary quantum states, provide a foundation for a wide range of quantum applications, including distributed quantum computing, distributed quantum sensing, and quantum communication. Photons are the natural carrier of information in quantum networks, but the exponential loss of optical fiber channels prevents the construction of large-scale quantum networks. A potential solution is implementing quantum repeaters based on quantum memories, which can efficiently establish long-distance entanglement from short-distance entanglement. In the past decades, intense efforts have been devoted to constructing large-scale quantum networks based on various atomic quantum memories. In this Perspective, we present a concise overview of current advancements in remote quantum networks, elucidate the imminent challenges that must be addressed, and discuss the future directions.

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

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

Quantum Quenches from the Critical Point: Theory and Experimental Validation in a Trapped-Ion Quantum Simulator

We investigate quantum quenches starting from a critical point and experimentally probe the associated defect statistics using a trapped-ion quantum simulator of the transverse-field Ising model. The cumulants of the defect number distribution exhibit universal scaling with quench depth, featuring Gaussian behavior at leading order and systematic subleading corrections. Our results are in excellent agreement with both exact and approximate theoretical predictions, establishing quench-depth scaling as a powerful and precise experimental benchmark for nonequilibrium quantum critical dynamics.

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

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

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↗

arXiv2025

Low-crosstalk optical addressing system for atomic qubits based on multiple objectives and acousto-optic deflectors

Large-scale programmable trapped ion hardware, featuring high gate fidelity and long coherence times, is promising for realizing a practical fault-tolerant quantum computer (FTQC). However, individual addressing (IA) methods, which are important for implementing programmable gates in near-term quantum devices, can lead to undesired errors between the target ions and neighboring ions. In this work, we present a low-crosstalk optical addressing system based on multiple optical objectives and acousto-optic deflectors (AODs) with a symmetrical configuration. Two counter-propagating Raman operation beams are both tightly focused, generating an overlapping spot with a waist radius of approximately $1~\upmu\mathrm{m}$, to address the target ion. As a result, IA crosstalk, characterized by Rabi rate crosstalk on the spectator ion, is measured to be $1.19(5)\times10^{-3}$, with the two ions separated by approximately 5.5~$\upmu\mathrm{m}$. This low-crosstalk optical addressing system holds promise for high-fidelity entangling operations, and the symmetrically-configured AODs in our method can be readily extended to two dimensions to address a two-dimensional ion crystal.

quant-ph↗

arXiv2025

Cold hybrid electrical-optical ion trap

Advances in research such as quantum information and quantum chemistry require subtle methods for trapping particles (including ions, neutral atoms, molecules, etc.). Here we propose a hybrid ion trapping method by combining a Paul trap with optical tweezers. The trap combines the advances of the deep-potential feature for the Paul trap and the micromotion-free feature for the optical dipole trap. By modulating the optical-dipole trap synchronously with the radio frequency voltage of the Paul trap, the alternating electrical force in the trap center is fully counteracted, and the micromotion temperature of a cold trapped ion can reach the order of nK while the trap depth is beyond 300K. These features will enable cold collisions between an ion and an atom in the $s$-wave regime and stably trap the produced molecular ion in the cold hybrid system. This will provide a unique platform for probing the interactions between the ions and the surrounding neutral particles and enable the investigation of new reaction pathways and reaction products in the cold regime.

physics.atom-ph↗

arXiv2025

Observation of Genuine High-dimensional Multi-partite Non-locality in Entangled Photon States

Quantum information science has leaped forward with the exploration of high-dimensional quantum systems, offering greater potential than traditional qubits in quantum communication and quantum computing. To advance the field of high-dimensional quantum technology, a significant effort is underway to progressively enhance the entanglement dimension between two particles. An alternative effective strategy involves not only increasing the dimensionality but also expanding the number of particles that are entangled. We present an experimental study demonstrating multi-partite quantum non-locality beyond qubit constraints, thus moving into the realm of strongly entangled high-dimensional multi-particle quantum systems. In the experiment, quantum states were encoded in the path degree of freedom (DoF) and controlled via polarization, enabling efficient operations in a two-dimensional plane to prepare three- and four-particle Greenberger-Horne-Zeilinger (GHZ) states in three-level systems. Our experimental results reveal ways in which high-dimensional systems can surpass qubits in terms of violating local-hidden-variable theories. Our realization of multiple complex and high-quality entanglement technologies is an important primary step for more complex quantum computing and communication protocols.

quant-ph↗

arXiv2025

Surpassing the Global Heisenberg Limit Using a High-effciency Quantum Switch

Indefinite causal orders have been shown to enable a precision of inverse square N in quantum parameter estimation, where N is the number of independent processes probed in an experiment. This surpasses the widely accepted ultimate quantum precision of the Heisenberg limit, 1/N. While a recent laboratory demonstration highlighted this phenomenon, its validity relies on postselection for it only accounted for a subset of the resources used. Achieving a true violation of the Heisenberg limit-considering photon loss, detection ineffciency, and other imperfections-remains an open challenge. Here, we present an ultrahigh-effciency quantum switch to estimate the geometric phase associated with a pair of conjugate position and momentum displacements embedded in a superposition of causal orders. Our experimental data demonstrate precision surpassing the global Heisenberg limit without artificially correcting for losses or imperfections. This work paves the way for quantum metrology advantages under more general and realistic constraints.

quant-ph↗

arXiv2025

Practical Advantage of Classical Communication in Entanglement Detection

Entanglement is the cornerstone of quantum communication, yet conventional detection relies solely on local measurements. In this work, we present a unified theoretical and experimental framework demonstrating that one-way local operations and classical communication (1-LOCC) can significantly outperform purely local measurements in detecting high-dimensional quantum entanglement. By casting the entanglement detection problem as a semidefinite program (SDP), we derive protocols that minimize false negatives at fixed false-positive rates. A variational generative machine-learning algorithm efficiently searches over high-dimensional parameter spaces, identifying states and measurement strategies that exhibit a clear 1-LOCC advantage. Experimentally, we realize a genuine event-ready protocol on a three-dimensional photonic entanglement source, employing fiber delays as short-lived quantum memories. We implement rapid, FPGA-based sampling of the optimized probabilistic instructions, allowing Bob's measurement settings to adapt to Alice's outcomes in real time. Our results validate the predicted 1-LOCC advantage in a realistic noisy setting and reduce the experimental trials needed to certify entanglement. These findings mark a step toward scalable, adaptive entanglement detection methods crucial for quantum networks and computing, paving the way for more efficient generation and verification of high-dimensional entangled states.

quant-ph↗

arXiv2025

A millisecond integrated quantum memory for photonic qubits

Quantum memories for light are essential building blocks for quantum repeaters and quantum networks. Integrated operations of quantum memories could enable scalable application with low-power consumption. However, the photonic quantum storage lifetime in integrated optical waveguide has so far been limited to tens of microseconds, falling short of the requirements for practical applications. Here, we demonstrate quantum storage of photonic qubits for 1.021 ms based on a laser-written optical waveguide fabricated in a 151Eu3+:Y2SiO5 crystal. Spin dephasing of 151Eu3+ is mitigated through dynamical decoupling applied via on-chip electric waveguides and we obtain a storage efficiency of 12.0(0.5)% at 1.021 ms, which is a demonstration of integrated quantum memories that outperforms the efficiency of a simple fiber delay line. Such long-lived waveguide-based quantum memory could support applications in quantum repeaters, and further combination with critical magnetic fields could enable potential application as transportable quantum memories.

quant-ph↗