arXiv subjects

Qin Liao

Publications and source records attributed to Qin Liao.

15 recordsLinked to original sources

arXiv2026

Breaking the trade-off between invisibility and sensitivity in electromagnetic sensing

Weak electromagnetic signals demand highly sensitive sensors, yet increasing a sensor's sensitivity inevitably strengthens its interaction with the surrounding field, producing scattering that perturbs the very signals being measured. Conversely, existing cloaking strategies suppress scattering only by isolating the sensor from incident waves, thereby compromising signal reception. Resolving this long-standing trade-off between invisibility and sensitivity has remained an outstanding challenge. Here we overcome this dilemma through an integrated transformation-optical architecture that co-designs the entire sensing system, including the electrically large sensor body, the subwavelength sensing probe, and their electrical interconnection. The proposed multifunctional core-shell structure guides incident waves around the sensor body while simultaneously concentrating them into the sensing region without disturbing the external electromagnetic field. A deep-subwavelength aperture preserves electrical connectivity without degrading either cloaking or field concentration, enabling invisible sensing within a single platform. A microwave prototype based on practical optic-null-medium metamaterials experimentally demonstrates broadband scattering suppression exceeding 3 dB together with an average sixfold enhancement of the detected signal over 4.9-5.1 GHz. By simultaneously eliminating measurement-induced field perturbation and amplifying the local sensing field, our approach establishes a general framework for invisible yet highly responsive electromagnetic sensors, opening new opportunities for weak-signal detection in biomedical diagnostics, secure communications, quantum technologies, and deep-space exploration.

physics.optics↗

arXiv2026

Quantum multi-label k-nearest neighbor

Although multi-label k-nearest neighbor (ML-kNN) is able to effectively solve multi-label learning (MLL) problem with local neighborhood similarity, its time complexity is nearly unacceptable with large-scale datasets. To solve this issue, we propose a novel ML-kNN algorithm with quantum computing techniques, which called quantum multi-label k-nearest neighbor (QML-kNN). In particular, we first accelerate the calculation of the prior probability by taking advantage of quantum phase estimation and Grover's amplitude amplification. Then, a controlled-SWAP test and a quantum k-maximal similarity search are used for efficiently identifying the neighbors. Subsequently, a quantum parallel counting circuit (QPCC) is designed to rapidly calculate the posterior probabilities. Experimental results demonstrate that QML-kNN is able to significantly reduce the time complexity of solving multi-label problems with performance improvement, achieving a substantial speedup over the classical MLL algorithm.

quant-ph↗

arXiv2026

Decoupling heat and electricity: A thermal invisible gateway

The Wiedemann-Franz law couples electrical and thermal conductivity, making high electrical conduction with low thermal conduction a major challenge. To overcome this, we designed an active thermal metasurface (ATMS) - based thermal invisible gateway that decouples thermal and electrical paths. Built on a copper substrate with a dumbbell-shaped bridge, the structure suppresses heat flow via directional compensation while allowing unimpeded electrical conduction. Room-temperature experiments show an effective thermal conductivity below 10^-3 W m^-1 K^-1 (near zero, air-like insulation) and an electrical conductivity up to 2.8x10^7 S m^-1 (metal-level). Unlike conventional material-modification approaches, our work uses macroscopic structural design to break the intrinsic coupling, offering a promising solution for applications like on-chip interconnects and wearable electronics.

physics.app-ph↗

arXiv2026

Deep Learning-Enabled Invisible Electromagnetic Scattering Amplifier

With the rapid development of micro-electro-mechanical systems, electrically small micro-targets, such as subwavelength micro unmanned aerial vehicles and bionic mosquito robots, exhibit ultra-low scattering cross section, which brings severe challenges to their effective detection. To address this problem, an Invisible Electromagnetic Scattering Amplifier (IESA) is designed by combining finite-element electromagnetic simulation with a forward lossless tandem neural network. The IESA realizes the dual-functional integration of intrinsic electromagnetic invisibility (near-zero scattering) for itself and significant scattering amplification for subwavelength targets entering its air sensing region. Electromagnetic simulations verify that the designed IESA can achieve a stable scattering amplification effect on subwavelength targets with a characteristic size of approximately 0.1λ0, regardless of their spatial positions or geometric shapes, with a maximum scattering cross section amplification factor of 8.58. The IESA breaks the technical bottleneck of the separate design of electromagnetic invisibility and scattering amplification functions. It shows potential for applications in the fields of radar detection, anti-terrorism security, micro-target monitoring, and adaptive electromagnetic sensing.

physics.optics↗

arXiv2025

Broadband Simultaneous Beam Steering and Compressing Device Based on Subwavelength Protrusion Metallic Tunnels

Beam steering and beamwidth compressing play a role in steering the beam and narrowing its half-power beamwidth, respectively, which are both widely applied in extending the effective operational range of 6G communications, IoT devices, and antenna systems. However, research on wave manipulation devices capable of simultaneously achieving both functionalities remains limited, despite their great potential for system miniaturization and functional integration. In this study, we design and realize a broadband device capable of simultaneously steering and compressing the TM-polarized EM waves using subwavelength protrusion metallic tunnels. The underlying physical mechanisms are quantitatively explained through wave optics and optical surface transformation, indicating the size ratio between the incident and output surface governs both the steering angle and the compression ratio. Numerical simulations demonstrate its outstanding performance, achieving a maximum steering angle of 40{\deg} and a compression ratio of 0.4 across 3 to 12 GHz, with averaged energy transmittance above 80%. The experiments further validate its effectiveness by measuring the magnetic field distributions of the output beam at various frequencies. The excellent beam steering and compressing effects make the proposed device highly promising for next-generation multifunctional wave manipulation in advanced communication systems.

physics.optics↗

arXiv2025

Surpassing the PLOB bound in continuous-variable quantum secret sharing using a state-discrimination detector

Continuous-variable quantum secret sharing (CVQSS) is a promising approach to ensuring multi-party information security. While CVQSS offers practical ease of implementation, its present performance remains limited. In this paper, we propose a novel CVQSS protocol integrated with a state-discrimination detector (SDD), dubbed SDD-CVQSS. In particular, we first develop the detailed procedure of SDD-CVQSS, which replaces the traditional coherent detector with an SDD and eliminates the long-standing necessary step of establishing multiple point-to-point quantum key distribution links between all users and the dealer. We then elaborate on the principle of the specifically designed SDD, which can efficiently discriminate mixed states with a much lower error probability. Finally, we construct a security model for SDD-CVQSS and derive its security bound against beam-splitting collective attacks. Numerical simulations show that SDD-CVQSS outperforms conventional CVQSS in both maximum transmission distance and secret key rate, even surpassing the PLOB bound. Additionally, we find that the performance degradation of SDD-CVQSS in long-distance transmission scenarios can be effectively compensated for using a post-selection scheme, providing a feasible way to achieve high-performance CVQSS.

quant-ph↗

arXiv2025

Implementation of ultra-broadband optical null media via space-folding

Optical null medium (ONM) has garnered significant attention in electromagnetic wave manipulation. However, existing ONM implementations suffer from either narrow operational bandwidths or low efficiency. Here, we demonstrate an ultra-broadband ONM design that simultaneously addresses both challenges - achieving broad bandwidth while preserving perfect impedance matching with air for near-unity transmittance. The proposed space-folding ONM is realized by introducing precisely engineered folds into a metal channel array, creating an effective dispersion-free medium that enables independent phase control in each channel. The design incorporates optimized boundary layers implemented through gradually tapered folding structures, achieving perfect impedance matching with the surrounding medium. Beam bending effect and broadband beam focusing effect are experimentally verified using the proposed space-folding ONM. Due to its simple material requirements, broadband characteristics, and high transmittance, the proposed space-folding ONM shows potential for applications in electromagnetic camouflage, beam steering devices and ultra-compact microwave components.

physics.optics↗

arXiv2024

Practical continuous-variable quantum secret sharing using local local oscillator

Although continuous-variable quantum secret sharing (CVQSS) has been theoretically proven to be secure, it may still be vulnerable to various local oscillator (LO)-aimed attacks. To close this loophole, we propose a practical CVQSS scheme using local LO (LLO), which is called LLO-CVQSS. In this scheme, LO is no longer generated by each user but can be locally generated by the legitimate party, i.e., the dealer. This waives the necessity that all LOs have to be transmitted through an untrusted channel, which makes CVQSS system naturally immune to all LO-aimed attacks, greatly enhancing its practical security. We also develop a specially designed phase compensation method for LLO-CVQSS so that the phase noise of the whole system can be eliminated. We finally construct a noise model for LLO-CVQSS and derive its security bound against both eavesdroppers and dishonest users. Numerical simulation shows that LLO-CVQSS is able to support 30 users at the same time and its maximal transmission distance reaches 112 km, revealing that LLO-CVQSS is not only has the ability to defend itself against all LO-aimed attacks but also has the potential for building large-scale practical quantum communication networks.

quant-ph↗

arXiv2023

Security boundaries of an optical power limiter for protecting quantum key distribution systems

Unauthorized light injection has always been a vital threat to the practical security of a quantum key distribution (QKD) system. An optical power limiter (OPL) based on the thermo-optical defocusing effect has been proposed and implemented, limiting the injected hacking light. As a hardware countermeasure, the performance of the OPL under various light-injection attacks shall be tested to clarify the security boundary before being widely deployed. To investigate the OPL's security boundary in quantum cryptography, we comprehensively test and analyse the behavior of OPL under continuous-wave (c.w.) light-injection attacks and pulse illumination attacks with pulses' repetition rate at $0.5$-$\hertz$, $40$-$\mega\hertz$, and $1$-$\giga\hertz$. The testing results illuminate the security boundary of the OPL, which allows one to properly employ the OPL in the use cases. The methodology of testing and analysis proposed here is applicable to other power-limitation components in a QKD system.

quant-ph↗

arXiv2023

High-rate discretely-modulated continuous-variable quantum key distribution using quantum machine learning

We propose a high-rate scheme for discretely-modulated continuous-variable quantum key distribution (DM CVQKD) using quantum machine learning technologies, which divides the whole CVQKD system into three parts, i.e., the initialization part that is used for training and estimating quantum classifier, the prediction part that is used for generating highly correlated raw keys, and the data-postprocessing part that generates the final secret key string shared by Alice and Bob. To this end, a low-complexity quantum k-nearest neighbor (QkNN) classifier is designed for predicting the lossy discretely-modulated coherent states (DMCSs) at Bob's side. The performance of the proposed QkNN-based CVQKD especially in terms of machine learning metrics and complexity is analyzed, and its theoretical security is proved by using semi-definite program (SDP) method. Numerical simulation shows that the secret key rate of our proposed scheme is explicitly superior to the existing DM CVQKD protocols, and it can be further enhanced with the increase of modulation variance.

quant-ph↗

arXiv2020

Multi-label learning for improving discretely-modulated continuous-variable quantum key distribution

Discretely-modulated continuous-variable quantum key distribution (CVQKD) is more suitable for long-distance transmission compared with its Gaussian-modulated CVQKD counterpart. However, its security can only be guaranteed when modulation variance is very small, which limits its further development. To solve this problem, in this work, we propose a novel scheme for discretely-modulated CVQKD using multi-label learning technology, called multi-label learning-based CVQKD (ML-CVQKD). In particular, the proposed scheme divides the whole quantum system into state learning and state prediction. The former is used for training and estimating quantum classifier, and the latter is used for generating final secret key. A quantum multi-label classification (QMLC) algorithm is also designed as an embedded classifier for distinguishing coherent state. Feature extraction for coherent state and related machine learning-based metrics for the quantum classifier are successively suggested. Security analysis shows that QMLC-embedded ML-CVQKD is able to immune intercept-resend attack so that small modulation variance is no longer compulsively required, thereby improving the performance of discretely-modulated CVQKD system.

quant-ph↗

arXiv2018

Continuous-variable quantum key distribution with non-Gaussian quantum catalysis

The non-Gaussian operation can be used not only to enhance and distill the entanglement between Gaussian entangled states, but also to improve quantum communications. In this paper, we propose an non-Gaussian continuous-variable quantum key distribution (CVQKD) by using quantum catalysis (QC), which is an intriguing non-Gaussian operation in essence that can be implemented with current technologies. We perform quantum catalysis on both ends of the Einstein-Podolsky-Rosen (EPR) pair prepared by a sender, Alice, and find that for the single-photon QC-CVQKD, the bilateral symmetrical quantum catalysis (BSQC) performs better than the single-side quantum catalysis (SSQC). Attributing to characteristics of integral within an ordered product (IWOP) of operators, we find that the quantum catalysis operation can improve the entanglement property of Gaussian entangled states by enhancing the success probability of non-Gaussian operation, leading to the improvement of the QC-CVQKD system. As a comparison, the QC-CVQKD system involving zero-photon and single-photon quantum catalysis outperforms the previous non-Gaussian CVQKD scheme via photon subtraction in terms of secret key rate, maximal transmission distance and tolerable excess noise.

quant-ph↗

arXiv2018

Dual-phase-modulated plug-and-play measurement-device-independent continuous-variable quantum key distribution

We suggest an improved plug-and-play measurement-device-independent (MDI) continuous-variable quantum key distribution (CVQKD) via the dual-phase modulation (DPM), aiming to solve an implementation problem with no extra performance penalty. The synchronous loophole of different lasers from Alice and Bob can be elegantly eliminated in the plug-and-play configuration, which gives birth to the convenient implementation when comparing to the Gaussian-modulated coherent-state protocol. While the local oscillator (LO) can be locally generated by the trusted part Charlie, the LO-aimed attacks can be accurately detected in the data post-processing. We derive the security bounds of the DPM-based MDI-CVQKD against optimal Gaussian collective attacks. Taking the finite-size effect into account, the secret key rate can be increased due to the fact that almost all raw keys of the MDI-CVQKD system can be fully exploited for the final secret key generation without sacrificing raw keys in parameter estimation. Moreover, we give an experimental concept of the proposed scheme which can be deemed guideline for final implementation.

quant-ph↗

arXiv2017

Long-distance continuous-variable quantum key distribution using non-Gaussian state-discrimination detection

We propose a long-distance continuous-variable quantum key distribution (CVQKD) with four-state protocol using non-Gaussian state-discrimination detection. A photon subtraction operation, which is deployed at the transmitter, is used for splitting the signal required for generating the non-Gaussian operation to lengthen the maximum transmission distance of CVQKD. Whereby an improved state-discrimination detector, which can be deemed as an optimized quantum measurement that allows the discrimination of nonorthogonal coherent states beating the standard quantum limit, is applied at the receiver to codetermine the measurement result with conventional coherent detector. By tactfully exploiting multiplexing technique, the resulting signals can be simultaneously transmitted through an untrusted quantum channel, and subsequently sent to the state-discrimination detector and coherent detector respectively. Security analysis shows that the proposed scheme can lengthen the maximum transmission distance up to hundreds of kilometers. Furthermore, by taking finite-size effect and composable security into account we obtain the tightest bound of the secure distance, which is more practical than that obtained in the asymptotic limit.

quant-ph↗

arXiv2017

Composable security of unidimensional continuous-variable quantum key distribution

We investigate the composable security of unidimensional contin- uous variable quantum key distribution (UCVQKD), which is based on the Gaussian modulation of a single quadrature of the coherent-state of light, aiming to provide a simple implementation of key distribution compared to the symmetrically modulated Gaussian coherent-state protocols. This protocol neglects the necessity in one of the quadrature modulation in coherent-states and hence reduces the system complexity. To clarify the influence of finite-size effect and the cost of performance degeneration, we establish the relation- ship of the balanced parameters of the unmodulated quadrature and estimate the precise secure region. Subsequently, we illustrate the composable security of the UCVQKD protocol against collective attacks and achieve the tightest bound of the UCVQKD protocol. Numerical simulations show the asymptotic secret key rate of the UCVQKD protocol, together with the symmetrically modulated Gaussian coherent-state protocols.

quant-ph↗