arXiv subjects

Haifeng Dong

Publications and source records attributed to Haifeng Dong.

14 recordsLinked to original sources

arXiv2026

Semidefinite-programming hierarchies for classically simulable state families

Identifying whether a state family admits an irreducible quantum advantage is a fundamental task in quantum resource theory and quantum information processing. Here we study classically simulable state families, namely those residing within the convex hull of pairwise commuting families and therefore admitting a classical explanation. We develop a complete semidefinite-programming (SDP) hierarchy characterizing the set of classically simulable state families in arbitrary finite dimension. The key step is to reformulate classical simulability as a feasibility problem over deterministic response functions and auxiliary positive-operator-valued measures (POVMs) simulable by rank-one projective measurements. We establish a complete SDP hierarchy for rank-one projectively simulable POVMs and transfer the resulting characterization to state families, yielding both primal feasibility tests and dual affine witnesses certifying failure of classical simulability. Applying the hierarchy to state families mixed with depolarizing noise gives computable upper bounds on the critical classical visibility, which are matched by explicit classical simulations in several symmetric examples. These results provide a systematic convex-optimization framework for certifying classical simulability of quantum state families.

quant-ph↗

arXiv2026

Geometric Construction of Optimal Teleportation Witnesses

Not all entangled states are useful for quantum teleportation. We present a geometric method to construct optimal teleportation witnesses, which provide operational necessary and sufficient criteria for identifying the teleportation usefulness of arbitrary two-qudit entangled states. Specifically, by developing a two-layer iterative cutting-plane algorithm to solve the shortest distance problem from the target state $\rho$ to the convex set $S$ of useless states, we obtain the projection point $\sigma^* \in S$ and then construct the optimal teleportation witness from the projection geometry. Moreover, the shortest distance $D(\rho)$ obtained during this construction also serves as a necessary and sufficient criterion for usefulness. We apply our method to identify the teleportation usefulness of three classes of entangled states.

quant-ph↗

arXiv2026

Semi-device-independent certification of high-dimensional quantum channels

Certifying high-dimensional quantum channels is essential for ensuring the reliability of quantum communication protocols. Existing certification schemes often rely on fully trusted internal devices, which is difficult to achieve in realistic scenarios. Here, we propose a semi-device-independent framework for certifying channel properties directly from observed statistics, assuming only that the system dimension is known. By explicitly incorporating the full set of structural constraints inherent to Choi states, our approach exploits the Choi-Jamio{\l}kowski isomorphism for rigorous certification of quantum channels. The entanglement dimensionality of quantum channels is first certified by introducing a witness and numerically determining its Schmidt-number-dependent bounds. This certification method reproduces known analytical benchmarks and is applied to dephasing and depolarizing noise channels, thereby confirming its validity. To provide a more complete assessment of channel performance, the entanglement fidelity of quantum channels is also certified using a hierarchy of semidefinite programming relaxations based on localizing matrices. Lower bounds on the entanglement fidelity are obtained that are compatible with either the full set of observed statistics or a single witness value.

quant-ph↗

arXiv2025

A General Framework for Constructing Local Hidden-state Models to Determine the Steerability

Not all entangled states can exhibit quantum steering, and determining whether a given entangled state is steerable is a crucial problem in quantum information theory. The main challenge lies in verifying the existence of a local hidden-state (LHS) model capable of reproducing all post-measurement assemblages generated by arbitrary measurements. To address this, we propose a machine learning-based framework that employs batch sampling of measurements and gradient-based optimization to construct an optimal LHS model. We validate our method by analyzing the steerability of two-qubit Werner and two-qutrit isotropic states. For Werner states, our approach saturates the analytical visibility bounds under three Pauli measurements, arbitrary projective measurements (PVMs), and arbitrary positive operator-valued measurements (POVMs). For isotropic states, we achieve the known analytical bounds under arbitrary PVMs. We further investigate the steerability of this class of states under arbitrary POVMs, and our results suggest that POVMs can offer an advantage over PVMs in revealing the steerability of such states.

quant-ph↗

arXiv2025

Unbounded-input explicit Bell inequalities for general quantum networks

Quantum nonlocality in networks featuring multiple independent sources underpins large-scale quantum communication and poses fundamental challenges for its characterization. In this work, we construct a family of explicit nonlinear Bell inequalities to verify the nonlocality across the general multi-input quantum networks. The construction of these inequalities relies on the number of leaf nodes, a network parameter that can be identified by a linear-time algorithm. Our approach establishes a structural connection between bipartite full-correlation Bell inequalities and network Bell inequalities, enabling the analytical derivation of optimal quantum violations and the conditions under which they occur. We further quantify the upper bound on maximal violations achievable by arbitrary two-qubit mixed states in such networks, under separable measurements, and evaluate the noise robustness of the proposed inequalities via the visibilities of Werner states. Finally, we demonstrate that these inequalities can, in a device-independent manner, distinguish between network topologies of equal size that differ in the number of leaf nodes.

quant-ph↗

arXiv2025

A compact unshielded optically-pumped magnetic gradiometer

Optically-pumped magnetic gradiometers (OPGs) play a crucial role in applications such as magnetic anomaly detection and bio-magnetic measurements. This study classifies current OPGs into four types based on their differential modes: voltage, frequency, optical rotation, and magnetic field differential modes. We introduce the concept of inherent Common-Mode Rejection Ratio (CMRR) and analyze the differences between the inherent CMRR and the measured CMRR, as well as the upper limit of inherent CMRR. We point out that although magnetic field differential method has the potential to increase inherent CMRR by a factor of 1+AF, the difference between the feedback gains is often neglected, which may set the limit of inherent CMRR. We designed and fabricated a compact, unshielded OPG with a specially designed scheme to minimize the distance between the sensing heads and the magnetic source. Measurement results demonstrate a measured CMRR of 1200@1Hz and a sensitivity of approximately 5 pT/cm/\sqrt{Hz} from 1 Hz to 100 Hz.

physics.optics↗

arXiv2025

Measuring network quantum steerability utilizing artificial neural networks

Network quantum steering plays a pivotal role in quantum information science, enabling robust certification of quantum correlations in scenarios with asymmetric trust assumptions among network parties. The intricate nature of quantum networks, however, poses significant challenges for the detection and quantification of steering. In this work, we develop a neural network-based method for measuring network quantum steerability, which can be generalized to arbitrary quantum networks and naturally applied to standard steering scenarios. Our method provides an effective framework for steerability analysis, demonstrating remarkable accuracy and efficiency in standard bipartite and multipartite steering scenarios. Numerical simulations involving isotropic states and noisy GHZ states yield results that are consistent with established findings in these respective scenarios. Furthermore, we demonstrate its utility in the bilocal network steering scenario, where an untrusted central party shares two-qubit isotropic states of different visibilities, $\nu$ and $\omega$, with trusted endpoint parties and performs a single Bell state measurement. Through explicit construction of a network local hidden state model derived from numerical results and incorporation of the entanglement properties of network assemblages, we analytically demonstrate that the network steering thresholds are determined by the curve $\nu \omega = {1}/{3}$ under the corresponding configuration.

quant-ph↗

arXiv2024

Characterizing the set of quantum correlations in prepare-and-measure quantum chain-shaped networks

We introduce a hierarchy of tests satisfied by any probability distribution $P$ that represents the quantum correlations generated in prepare-and-measure (P\&M) quantum chain-shaped networks, assuming only the inner-product information of the non-orthogonal quantum states. The P\&M quantum chain-shaped networks involve multiple measurement parties, each measurement party potentially having multiple sequential receivers. Specifically, we adapt the original NPA-hierarchy by incorporating a finite number of linear and positive semi-definite constraints to characterize the quantum correlations in P\&M quantum chain-shaped networks. These constraints in each hierarchy are derived from sequential measurement operators and the inner-product matrix of the non-orthogonal quantum states. We apply the adapted NPA-hierarchy to tackle some quantum information tasks, including sequential quantum random access codes (QRACs) and randomness certification. First, we derive the optimal trade-off between the two sequential receivers in the $2 \to 1$ sequential QRACs. Furthermore, we have investigated semi-device-independent randomness certification in the double violation region of $2 \to 1$ sequential QRACs. Second, considering the presence of eavesdropper (Eve) in actual communication, we show how much global and local randomness can be certified using the optimal trade-off of $2 \to 1$ sequential QRACs. Additionally, we quantify the amount of local and global randomness that can be certified from the complete probabilities generated by the two sequential receivers. We conclude that utilizing the complete set of probabilities certifies more local and global randomness than relying solely on the optimal trade-off relationship.

quant-ph↗

arXiv2024

Sharing tripartite nonlocality sequentially using only projective measurements

Bell nonlocality is a valuable resource in quantum information processing tasks. Scientists are interested in whether a single entangled state can generate a long sequence of nonlocal correlations. Previous work has accomplished sequential tripartite nonlocality sharing through unsharp measurements. In this paper, we investigate the sharing of tripartite nonlocality using only projective measurements and sharing classical randomness. For the generalized GHZ state, we have demonstrated that using unbiased measurement choices, two Charlies can share the standard tripartite nonlocality with a single Alice and a single Bob, while at most one Charlie can share the genuine tripartite nonlocality with a single Alice and a single Bob. However, with biased measurement choices, the number of Charlies sharing the genuine tripartite nonlocality can be increased to two. Nonetheless, we find that using biased measurements does not increase the number of sequential observers sharing the standard tripartite nonlocality. Moreover, we provide the feasible range of double violation for the parameters of the measurement combination probability with respect to the state.

quant-ph↗

arXiv2023

A general approach to improve the bias stability of NMR gyroscope

In recent years, progress in improving the bias stability of NMR gyroscopes has been hindered. Taking inspiration from the core idea of rotation modulation in the strapdown inertial navigation system, we propose a general approach to enhancing the bias stability of NMR gyroscopes that does not require consideration of the actual physical sources. The method operates on the fact that the sign of the bias does not follow that of the sensing direction of the NMR gyroscope, which is much easier to modulate than with other types of gyroscopes. We conducted simulations to validate the method's feasibility.

physics.ins-det↗

arXiv2021

The sub-millimetre non-uniformity measurement of residual and coil-generated field in the magnetic shield using atomic vapor cell

Magnetic field source localization and imaging happen at different scales. The sensing baseline ranges from meter scale such as magnetic anomaly detection, centimeter scale such as brain field imaging to nanometer scale such as the imaging of magnetic skyrmion and single cell. Here we show how atomic vapor cell can be used to realize a baseline of 109.6 μm with a magnetic sensitivity of 10pT/sqrt(Hz)@0.6-100Hz and a dynamic range of 2062-4124nT.We use free induction decay (FID) scheme to suppress low-frequency noise and avoid scale factor variation for different domains due to light non-uniformity. The measurement domains are scanned by digital micro-mirror device (DMD). The currents of 22mA, 30mA, 38mA and 44mA are applied in the coils to generate different fields along the pumping axis which are measured respectively by fitting the FID signals of the probe light. The residual fields of every domain are obtained from the intercept of linearly-fitting of the measurement data corresponding to these four currents. The coil-generated fields are calculated by deducting the residual fields from the total fields. The results demonstrate that the hole of shield affects both the residual and the coil-generated field distribution. The potential impact of field distribution measurement with an outstanding comprehensive properties of spatial resolution, sensitivity and dynamic range is far-reaching. It could lead to capability of 3D magnetography for small stuffs and/or organs in millimeter or even smaller scale.

physics.atom-ph↗

arXiv2019

Spin image of an atomic vapor cell with a resolution smaller than the diffusion crosstalk free distance

The diffusion crosstalk free distance is an important parameter for spin images in atomic vapor cells and is also regarded as a limit on the spatial resolution. However, by modulating the pumping light both spatially and temporally using a digital micromirror device, a spin image of a vapor cell has been obtained with a distinguishable stripe width of 13.7~$μ$m, which is much smaller than the corresponding diffusion crosstalk free distance of $\sim$138~$μ$m. The fundamental limit on the spatial resolution as determined by diffusion and the uncertainty principle is analyzed.

physics.atom-ph↗

arXiv2018

Comparison of Compensation Mechanism Between an NMR Gyroscope and an SERF Gyroscope -- Equivalence of NMR and SERF gyroscopes

There are two kinds of atomic vapor cell gyroscopes, one is nuclear-magnetic-resonance (NMR) gyroscope and the other is spin-exchange-relaxation-free (SERF) gyroscope. We demonstrate that there is a common model for these two kinds of gyroscope. The output signals of NMR and SERF gyroscopes are compared directly, which provides an important guidance for the scheme choosing and optimization of atomic gyroscope. Although this expose of the equivalence cannot solve the current problems of atomic gyroscopes, such as the narrow response bandwidth of SERF gyroscope and the drift due to the different Fermi-contact interaction coefficient in NMR gyroscope, it provides a simple understanding of atomic gyroscopes and may inspire new schemes combining advantages of both NMR and SERF gyroscopes.

quant-ph↗

arXiv2012

Atomic-signal-based zero field finding technique for unshielded laser-pumped atomic magnetometer

We described a novel technique that can find the zero-field for unshielded laser-pumped atomic magnetometer using atomic signal itself. By comparing light density of pump beam after atomic vapor cell, it is decided which direction to move the compensation magnetic field and whether to increase or decrease the converging step length. The zero-field is found in less than 18s and the step length after converging is smaller than 10nT, 10nT and 40nT for x, y and z axes, respectively, limited by 50Hz noise in the lab environment.

physics.atom-ph↗