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Fundamental Research 2024年第3期4卷 706-707页

At present,we are in the noisy-intermediate-scale-quantum era of quantum information science and technology[1],in which there are relatively large numbers of qubits with noise.For instance,the error rate of current superconducting qubits is orders of magnitude away from practical application.To solve this problem,various methods have been used,such as holonomic quantum gate[2],dynamical decoupling[3],entanglement purification[4],and quantum error correction[5].

关键词： quantum correction error

A new twist to the interplay between superconductivity and Kondo correlation

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Science China(Physics,Mechanics & Astronomy) 2024年

作者： gui-lu long Department of Physics Tsinghua University Beijing Academy of Quantum Information Sciences

Recently, Deng et al.[1] found a new twist to the intriguing physics resulting from the interplay between Kondo correlation and superconductivity.Kondo correlation [2,3] and superconductivity [4,5] are two fundamental phenomena in condensed matter physics, and various novel physics have been discovered from their interplay. Superconductivity occurs when electrons in the material form Cooper pairs and can thus move through the material without resistance. In a primary s-wave superconductor, Cooper pairs can be disrupted by the presence of magnetic impurities or other interactions. Kondo correlation is a type of interaction between localized magnetic moments and conduction electrons. This correlation can significantly modify the electrical conductivity of a normal state quantum-dot system.

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A new scheme of fully stabilized soliton microcombs

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Science China(Physics,Mechanics & Astronomy) 2024年第2期67卷 1-1页

作者： gui-lu long Department of Physics Tsinghua UniversityBeijing 100084China Beijing Academy of Quantum Information Sciences Beijing 100193China

More stable frequency standard has been the focus of studies for a long time^([1,2]).Dissipative Kerr solitons(DKSs)in microresonators have attracted much interest for their potential in on-chip frequency standards^([1]).DKSs provide frequency combs characterized by high coherence,expansive bandwidth,and microwave-repetition rates.

关键词： soliton stabilized scheme

Suppressing noisy features with quantum filters for efficient encoded images with high signal to noise ratios

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Science China(Physics,Mechanics & Astronomy) 2024年

作者： gui-lu long Department of Physics Tsinghua University Beijing Academy of Quantum Information Sciences

Image processing is fundamental in computer vision and imaging research [1,2]. Most image processing algorithms rely on Fourier transform. It is well-known that quantum Fourier transform (QFT) offers exponential speedup compared to their classical counterpart and serves as a crucial component in quantum algorithms such as Shor’s factoring algorithm [3] and the HHL algorithm [4] to realize exponential speedup. This has led researchers to investigate whether image processing can also achieve exponential speedup on quantum processors. However, this is not as straightforward as it may seem. Broadly speaking,quantum image processing faces three main challenges:Efficient quantum-state initialization to encode the image, efficient image processing using quantum circuit, and efficient decoding of the resulting image information from the output state. None of these challenges have been satisfactorily solved so far.

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Interfacing superconducting and atomic qubits via unconventional geometric quantum operations

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Science China(Physics,Mechanics & Astronomy) 2022年第4期65卷 1-2页

作者： gui-lu long Department of Physics Tsinghua UniversityBeijing100084China

Interfacing or entanglement between spatially separated quantum systems,such as superconducting qubits,semiconductor quantum dots,atomic qubits,and solid-state color centers,is crucial in quantum networks and distributed quantum computation[1].Significant progress has been made in generating entanglement between spatially separated quantum systems via optical links[2],while remote superconducting chips,whose quantum states are easily spoiled by optical photons,have been entangled via cryogenic microwave links[3].

关键词： quantum superconducting spatially

Realization of quantum secure direct communication over 100 km fiber with time-bin and phase quantum states

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Light(Science & Applications) 2022年第5期11卷 787-795页

作者： Haoran Zhang Zhen Sun Ruoyang Qi Liuguo Yin gui-lu long Jianhua lu State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua UniversityBeijingChina Beijing Academy of Quantum Information Science BeijingChina School of Information and Technology Tsinghua UniversityBeijingChina Beijing Institute of Spacecraft System Engineering BeijingChina Frontier Science Center for Quantum Information BeijingChina Beijing National Research Center for Information Science and Technology BeijingChina

Rapid progress has been made in quantum secure direct communication in recent years.For practical application,it is important to improve the performances,such as the secure information rate and the communication distance.In this paper,we report an elaborate physical system design and protocol with much enhanced performance.This design increased the secrecy capacity greatly by achieving an ultra-low quantum bit error rate of<0.1%,one order of magnitude smaller than that of existing systems.Compared to previous systems,the proposed scheme uses photonic time-bin and phase states,operating at 50 MHz of repetition rate,which can be easily upgraded to over 1 GHz using current on-the-shelf technology.The results of our experimentation demonstrate that the proposed system can tolerate more channel loss,from 5.1 dB,which is about 28.3 km in fiber in the previous scheme,to 18.4 dB,which corresponds to fiber length of 102.2 km.Thus,the experiment shows that intercity quantum secure direct communication through fiber is feasible with present-day technology.

关键词： fiber communication quantum

Toward applications of cloud quantum computation

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Science China(Physics,Mechanics & Astronomy) 2022年第11期65卷 82-83页

作者： gui-lu long State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua UniversityBeijing100084China Beijing Academy of Quantum Information Science Beijing100193China Frontier Science Center for Quantum Information Beijing100084China Beijing National Research Center Information Science and Technology and School of Information Tsinghua UniversityBeijing100084China

Quantum computation has attracted much attention from both academia and the public due to its great achievements. Along with its fast development and increasing investment, a series of problems are raised. For example, can quantum supremacy be realized? Recently, several results have been reported to address the problem of sampling random circuits, accompanied by classical improvements [1-3]. Another problem worthy of note is how to use a quantum computer. Irrelevant to specific problems that can be solved by a quantum computer, this is actually a problem about how many users can conveniently access quantum computation resources.

关键词： quantum computation conveniently

Lithium niobate microresonator-based spectrally multiplexed entangled photon pairs

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Science China(Physics,Mechanics & Astronomy) 2022年第9期65卷 1-2页

作者： gui-lu long Department of Physics Tsinghua UniversityBeijing 100084China

Integrated quantum photonics combining the micron-scale fabrication technique and quantum information carriers promises a new platform for quantum computation and communication systems [1,2]. Integrated chips remarkably reduce the footprint of the quantum processor and make complicated quantum networks into reality. Nevertheless, to fulfill the increasing need of massive qubits in quantum networks, quantum sources of multiple qubits are widely requested [3].

关键词： quantum remarkably networks

Variational quantum attacks threaten advanced encryption standard based symmetric cryptography

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Science China(Information Sciences) 2022年第10期65卷 31-42页

作者： Zeguo WANG Shijie WEI gui-lu long Lajos HANZO State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua University Beijing Academy of Quantum Information Sciences Beijing National Research Center for Information Science and Technology School of Information Tsinghua University Frontier Science Center for Quantum Information Department of Electronics and Computer Science (ECS) University of Southampton

We propose a variational quantum attack algorithm(VQAA) for classical advanced encryption standard(AES)-like symmetric cryptography, as exemplified by the simplified-data encryption standard(S-DES). In the VQAA, the known ciphertext is encoded as the ground state of a Hamiltonian that is constructed through a regular graph, and the ground state can be found using a variational approach. We designed the ansatz and cost function for the S-DES’s variational quantum attack. It is surprising that sometimes the VQAA is even faster than Grover’s algorithm as demonstrated by our simulation results. The relationships of the entanglement entropy, concurrence, and the cost function are investigated, which indicate that entanglement plays a crucial role in the speedup.

关键词： S-DES VQA ansatz cost function optimization

The circuit design and optimization of quantum multiplier and divider

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Science China(Physics,Mechanics & Astronomy) 2022年第6期65卷 11-25页

作者： Hai-Sheng Li Ping Fan Haiying Xia gui-lu long College of Electronic Engineering Guangxi Normal UniversityGuilin 541004China College of Information Engineering East China JiaoTong UniversityNanchang 330013China Department of Physics Tsinghua UniversityBeijing 100084China State Key Laboratory of Low-Dimensional Quantum Physics Tsinghua UniversityBeijing 100084China Beijing National Research Center for Information Science and Technology Beijing 100084China Beijing Academy of Quantum Information Sciences Beijing 100193China

A fault-tolerant circuit is required for robust quantum computing in the presence of noise.Clifford+T circuits are widely used in fault-tolerant implementations.As a result,reducing T-depth,T-count,and circuit width has emerged as important optimization goals.A measure-and-fixup approach yields the best T-count for arithmetic operations,but it requires quantum measurements.This paper proposes approximate Toffoli,TR,Peres,and Fredkin gates with optimized T-depth and T-count.Following that,we implement basic arithmetic operations such as quantum modular adder and subtractor using approximate gates that do not require quantum measurements.Then,taking into account the circuit width,T-depth,and T-count,we design and optimize the circuits of two multipliers and a divider.According to the comparative analysis,the proposed multiplier and divider circuits have lower circuit width,T-depth,and T-count than the current works that do not use the measure-and-fixup approach.Significantly,the proposed second multiplier produces approximately 77%T-depth,60%T-count,and 25%width reductions when compared to the existing multipliers without quantum measurements.

关键词： quantum multiplier quantum divider quantum fault-tolerant circuit quantum computing