arXiv subjects

Jian Leng

Publications and source records attributed to Jian Leng.

10 recordsLinked to original sources

arXiv2025

Channel-loss-independent quantum-enhanced interferometer

We propose a channel-loss-independent quantum-enhanced interferometer. In our scheme, the Fisher information for phase difference of weak light from a remote star remains constant under arbitrarily large channel loss, and the angular resolution of our method is better than that of prior quantum-enhanced methods in the long-baseline regime. Moreover, our method requires only threshold detectors and tunable coherent state or two-mode squeezed state sources, both of which are matured technologies nowadays.

quant-ph↗

arXiv2025

Piecemeal method revisited

Detecting the angles and orbits of remote targets precisely has been playing crucial roles in astrophysical research. Due to the resolution limitations imposed by the Airy disk in a single telescope, optical interferometric schemes with at least two telescopes have received considerable attention. We have extended the piecemeal method to reduce the required number of baselines for observation. Through the analysis of its performance under practical conditions, we demonstrate that both the original and extended piecemeal methods exhibit strong robustness against errors in baseline lengths and orientations. Under the same practical conditions, our approach achieves higher precision than other existing weak-light interference-based methods.

astro-ph.IM↗

arXiv2024

Piecemeal Telescope Array: Exponential Precision with Strong Robustness and High Efficiency

Optical telescopes are powerful eyes for terrestrial and astronomical detection. Here we propose a new detection method with high efficiency, strong robustness and super precision, as an enhanced technique for optical telescopes in angular locating. In detail, our method requests only small number of incident single-photons, holds strong fault tolerance to any noise and improves the precision by magnitude orders comparing with current optical telescopes. Given these advantages, our method promises an important progress in remote sensing and astrometry, especially in locating the very dark object.

quant-ph↗

arXiv2023

Quantum Advantage of Noisy Grover's Algorithm

Quantum advantage is the core of quantum computing. Grover's search algorithm is the only quantum algorithm with proven advantage to any possible classical search algorithm. However, realizing this quantum advantage in practice is quite challenging since Grover's algorithm is very sensitive to noise. Here we present a noise-tolerant method that exponentially improves the noise threshold of Grover's algorithm. We present a lower bound for average fidelity of any quantum circuit with O(log D log D) cost under time-independent noise, where D is the dimension of Hilbert space. According to this bound value, we determine the number of iterates which will be applied in Grover's algorithm. Numerical simulation shows that the noise threshold of quantum advantage of Grover's algorithm by our noise-tolerant method is improved by an exponential factor with qubit amount rise.

quant-ph↗

arXiv2023

Modifying $n$-qubit controlled-$ZX$ gate to be $n$-qubit Toffoli gate

The decomposition for controlled-$ZX$ gate in [Phys. Rev. A, 87, 062318 (2013)] has a shallow circuit depth $8n-20$ with no ancilla. Here we modify this decomposition to decompose $n$-qubit Toffoli gate with only $2n-3$ additional single-qubit gates. The circuit depth is unchanged and no ancilla is needed. We explicitly show that the circuit after decomposition can be easily constructed in present physical systems.

quant-ph↗

arXiv2023

Improving D2p Grover's algorithm to reach performance upper bound under phase noise

The original Grover's algorithm has a success probability to output a correct solution, while deterministic Grover's algorithms improve the success probability to 100%. However, the success probability of deterministic Grover's algorithm decreases in noisy environment. Here we improve the deterministic two-parameter (D2p) Grover's algorithm to reach the upper bound for success probability under phase noise. We prove that it is not possible to design any deterministic Grover's algorithm whose success probability is higher than our improved D2p protocol's under phase noise.

quant-ph↗

arXiv2021

Nuclear electric resonance

Nuclear-spin qubits have long coherence time and are desirably applied into quantum information processing. However, the existing methods either fail to address single nucleus (such as nuclear magnetic resonance), or severely affect nuclear coherence time (such as electrical nuclear manipulation based on hyperfine stark effect, ENMHSE). Here we propose an electrical nuclear manipulation called nuclear electric resonance which can on the one hand address the single nuclear qubit, and on the other keep the long coherence time. Applying this, we construct universal quantum gates with external electric field. These universal gates are practicable for arbitrary $S\ge 1$ spin nuclei. Given the much longer coherence time of nuclear electric resonance, we improve the number of single-qubit operations by three orders of magnitude compared with that of ENMHSE.

quant-ph↗

arXiv2020

Fragment-synthesis-based multiparty cryptographic key distribution over a public network

A secure optical communication requires both high transmission efficiency and high authentication performance, while existing cryptographic key distribution protocols based on ghost imaging have many shortcomings. Here, based on computational ghost imaging, we propose an interactive protocol that enables multi-party cryptographic key distribution over a public network and self-authentication by setting an intermediary that shares partial roles of the server. This fragment-synthesis-based authentication method may facilitate the remote distribution of cryptographic keys.

eess.IV↗

arXiv2019

Unified probability explanation for ghost imaging with thermal light

Ghost imaging (GI) is an intriguing imaging technology which achieves the object images through intensity correlation between reference patterns and bucket signal. Here, we propose a probability model to explain the imaging mechanism of this modality, by assuming that the reference patterns fulfill an arbitrary identical distribution and that the objects are of gray-scale. We have proven that the probability of the reconstructed pixel values in the pixel region of the same original gray value obeys a Gaussian distribution, no matter which functional form of the reference patterns is used in correlation calculation. Both simulation and experiments have demonstrated that the probability of recovered pixel values are highly consistent with their Gaussian theoretical distribution, while their variance explains the appearance of reconstruction noise. In addition, we have also extend this theory to other classic correlation functions, e.g., normalized GI and differential GI. The results have shown that there is a linear relationship between reconstruction means in specified pixel regions and original gray values, which might provide a unified explanation for GI with thermal light.

eess.IV↗

arXiv2019

Formation mechanism of correspondence imaging with thermal light

Correspondence imaging can achieve positive-negative ghost images by just conditional averaging of partial patterns, without treating bucket intensities as weights. To explain its imaging mechanism, we develop a probability theory assuming the targets are of gray-scale and the thermal reference speckles obey an arbitrary independent and identical distribution. By both simulation and experiments, we find that the recovered values in each region of the same original gray value conditionally obey a Gaussian distribution. A crosspoint-to-standard-deviation ratio is used as the figure of merit to prove that the patterns with respect to larger bucket values generate a positive image with a higher quality, vice versa for negative one. This work complements the theory of ghost imaging.

physics.optics↗