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Superconductivity in topological semimetals

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National Science Review 2019年第2期6卷 199-202页

作者： Jian Wang International Center for quantum Materials School of Physics Peking University Collaborative Innovation Center of quantum Matter CAS Center for Excellence in Topological quantum computation University of Chinese Academy of Sciences Beijing Academy of quantum information Sciences

Topological superconductors, where the bulk state shows superconducting gap and Majorana fermions constitute gapless edge states, have become one of the most important topics in physical sciences. Majorana fermions are their own antiparticles and Majorana quasiparticles in a solid-state system obey non-Abelian statistics, and thus can be used for faulttolerant topological quantum computation.

关键词： As Superconductivity in topological semimetals

Photoionisation detection of a single Er3+ ion with sub-100-ns time resolution

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National Science Review 2024年第4期11卷 38-45页

作者： Yangbo Zhang Wenda Fan Jiliang Yang Hao Guan Qi Zhang Xi Qin Changkui Duan Gabriele G.de Boo Brett C.Johnson Jeffrey C.Mc Callum Matthew J.Sellars Sven Rogge Chunming Yin Jiangfeng Du CAS Key Laboratory of Microscale Magnetic Resonance and School of Physical Sciences University of Science and Technology of China CAS Center for Excellence in quantum information and quantum Physics University of Science and Technology of China Hefei National Laboratory University of Science and Technology of China Centre of Excellence for quantum computation and Communication Technology School of Physics University of New South Wales Centre of Excellence for quantum computation and Communication Technology School of Engineering RMIT University Centre of Excellence for quantum computation and Communication Technology School of Physics University of Melbourne Centre of Excellence for quantum computation and Communication Technology Research School of Physics and Engineering Australian National University

Efficient detection of single optical centres in solids is essential for quantum information processing, sensing and single-photon generation *** this work,we use radio-frequency（RF） reflectometry to electrically detect the photoionisation induced by a single Er3+ion in *** high bandwidth and sensitivity of the RF reflectometry provide sub-100-ns time resolution for the photoionisation *** this technique,the optically excited state lifetime of a single Er3+ion in a Si nano-transistor is measured for the first time to be 0.49±0.04μ*** results demonstrate an efficient approach for detecting a charge state change induced by Er excitation and *** approach could be used for fast readout of other single optical centres in solids and is attractive for large-scale integrated optical quantum systems thanks to the multi-channel RF reflectometry demonstrated with frequency multiplexing techniques.

关键词： single optical centres erbium ions RF reflectometry photoionisation detection

Topological phases of quantized light

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National Science Review 2021年第1期8卷 69-80页

作者： Han Cai Da-Wei Wang Interdisciplinary Center for quantum information and State Key Laboratory of Modern Optical Instrumentation Zhejiang Province Key Laboratory of Quantum Technology and Device and Department of Physics Zhejiang University CAS Center for Excellence in Topological quantum computation University of Chinese Academy of Sciences

Topological photonics is an emerging research area that focuses on the topological states of classical *** we reveal the topological phases that are intrinsic to the quantum nature of light, i.e. solely related to the quantized Fock states and the inhomogeneous coupling strengths between them. The Hamiltonian of two cavities coupled with a two-level atom is an intrinsic one-dimensional Su-Schriefer-Heeger model of Fock states. By adding another cavity, the Fock-state lattice is extended to two dimensions with a honeycomb structure, where the strain due to the inhomogeneous coupling strengths of the annihilation operator induces a Lifshitz topological phase transition between a semimetal and three band insulators within the lattice. In the semimetallic phase, the strain is equivalent to a pseudomagnetic field, which results in the quantization of the Landau levels and the valley Hall effect. We further construct an inhomogeneous Fock-state Haldane model where the topological phases can be characterized by the topological *** d cavities being coupled to the atom, the lattice is extended to d-1 dimensions without an upper limit. In this study we demonstrate a fundamental distinction between the topological phases in quantum and classical optics and provide a novel platform for studying topological physics in dimensions higher than three.

关键词： topological phases Su-Schriefer-Heeger model Jaynes-Cummings model strain-induced magnetic field Haldane model

Spectroscopic Evidence for Electron Correlations in Epitaxial Bilayer Graphene with Interface-Reconstructed Superlattice Potentials

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Chinese Physics Letters 2022年第7期39卷 74-80页

作者： Chaofei Liu Jian Wang International Center for quantum Materials School of PhysicsPeking UniversityBeijing 100871China CAS Center for Excellence in Topological quantum computation University of Chinese Academy of SciencesBeijing 100190China Beijing Academy of quantum information Sciences Beijing 100193China

Superlattice potentials are theoretically predicted to modify the single-particle electronic structures. The resulting Coulomb-interaction-dominated low-energy physics would generate highly novel many-body phenomena. Here,by in situ tunneling spectroscopy, we show the signatures of superstructure-modulated correlated electron states in epitaxial bilayer graphene(BLG) on 6H-Si C(0001). As the carrier density is locally quasi-‘tuned’ by the superlattice potentials of a 6 × 6 interface reconstruction phase, the spectral-weight transfer occurs between the two broad peaks flanking the charge-neutral point. Such a detected non-rigid band shift beyond the single-particle band description implies the existence of correlation effects, probably attributed to the modified interlayer coupling in epitaxial BLG by the 6×6 reconstruction as in magic-angle BLG by the moiré potentials. Quantitative analysis suggests that the intrinsic interface reconstruction shows a high carrier tunability of ~1/2 filling range, equivalent to the back gating by a voltage of ~70 V in a typical gated BLG/SiO_(2)/Si device. The finding in interfacemodulated epitaxial BLG with reconstruction phase extends the BLG platform with electron correlations beyond the magic-angle situation, and may stimulate further investigations on correlated states in graphene systems and other van der Waals materials.

关键词： BLG red profile STM Spectroscopic Evidence for Electron Correlations in Epitaxial Bilayer Graphene with Interface-Reconstructed Superlattice Potentials Graphene

Realization of -bit semiclassical quantum Fourier transform on IBM's quantum cloud computer

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Chinese Physics B 2019年第2期28卷 117-122页

作者： Xiang-Qun Fu Wan-Su Bao He-Liang Huang Tan Li Jian-Hong Shi Xiang Wang Shuo Zhang Feng-Guang Li Henan Key Laboratory of quantum information and Cryptography Information Engineering University Synergetic Innovation Center of quantum information and quantum Physics University of Science and Technology of China

To overcome the difficulty of realizing large-scale quantum Fourier transform(QFT) within existing technology, this paper implements a resource-saving method(named t-bit semiclassical QFT over Z_(2~n)), which could realize large-scale QFT using an arbitrary-scale quantum register. By developing a feasible method to realize the control quantum gate Rk, we experimentally realize the 2-bit semiclassical QFT over Z_(2~3) on IBM's quantum cloud computer, which shows the feasibility of the method. Then, we compare the actual performance of 2-bit semiclassical QFT with standard QFT in the *** squared statistical overlap experimental data shows that the fidelity of 2-bit semiclassical QFT is higher than that of standard QFT, which is mainly due to fewer two-qubit gates in the semiclassical QFT. Furthermore, based on the proposed method, N = 15 is successfully factorized by implementing Shor's algorithm.

关键词： quantum cloud computation quantum Fourier transform semiclassical quantum Fourier transform Shor’s algorithm

Unconventional Geometric Phase-Shift Gates Based on Superconducting quantum Interference Devices Coupled to a Single-Mode Cavity

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Communications in Theoretical Physics 2006年第4X期46卷 631-634页

作者： SONG Ke-Hui ZHOU Zheng-Wei GUO Guang-Can Key Laboratory of quantum Communication and quantum computation University of Science and Technology of China Hefei 230026 China Department of Electronic information Science and Physics Huaihua University Huaihua 418008China

We present a scheme to realize geometric phase-shift gate for two superconducting quantum interference device （SQUID） qubits coupled to a single-mode microwave field. The geometric phase-shift gate operation is performed in two lower flux states, and the excited state [2〉 would not participate in the procedure. The SQUIDs undergo no transitions during the gate operation. Thus, the docoherence due to energy spontaneous emission based on the levels of SQUIDs are suppressed. The gate is insensitive to the cavity decay throughout the operation since the cavity mode is displaced along a circle in the phase space, acquiring a phase conditional upon the two lower flux states of the SQUID qubits, and the cavity mode is still in the original vacuum state. Based on the SQUID qubits interacting with the cavity mode, our proposed approach may open promising prospects for quantum iogic in SQUID-system.

关键词： geometric phase-shift gate superconducting quantum interference device cavity-QED

Observation of 1D Fermi arc states in Weyl semimetal TaAs

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National Science Review 2022年第8期9卷 62-70页

作者： Xiaohu Zheng Qiangqiang Gu Yiyuan Liu Bingbing Tong Jian-Feng Zhang Chi Zhang Shuang Jia Ji Feng Rui-Rui Du International Center for quantum Materials School of PhysicsPeking University Collaborative Innovation Center of quantum Matter State Key Laboratory of Superlattices and Microstructures Institute of SemiconductorsChinese Academy of Sciences CAS Center for Excellence in Topological quantum computation University of Chinese Academy of Sciences Beijing Academy of quantum information Sciences

Fermi arcs on Weyl semimetals exhibit many exotic quantum phenomena. Usually found on atomically flat surfaces with approximate translation symmetry, Fermi arcs are rooted in the peculiar topology of bulk Bloch bands of 3D crystals. The fundamental question of whether a 1D Fermi arc can be probed remains unanswered. Such an answer could significantly broaden potential applications of Weyl semimetals. Here,we report a direct observation of robust edge states on atomic-scale ledges in TaAs using low-temperature scanning tunneling microscopy/spectroscopy. Spectroscopic signatures and theoretical calculations reveal that the 1D Fermi arcs arise from the chiral Weyl points of bulk crystals. The crossover from 2D Fermi arcs to eventual complete localization on 1D edges was arrested experimentally on a sequence of surfaces. Our results demonstrate extreme robustness of the bulk-boundary correspondence, which offers topological protection for Fermi arcs, even in cases in which the boundaries are at the atomic-scale. The persistent 1D Fermi arcs can be profitably exploited in miniaturized quantum devices.

关键词： Weyl semimetals Fermi arc edge states chiral Weyl points TaAs scanning tunneling microscopy/spectroscopy

Taking tomographic measurements for photonic qubits 88 ns before they are created

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Chinese Physics B 2021年第4期30卷 55-60页

作者： Zhibo Hou Qi Yin Chao Zhang Han-Sen Zhong Guo-Yong Xiang Chuan-Feng Li Guang-Can Guo Geoff J.Pryde Anthony Laing Key Laboratory of quantum information University of Science and Technology of ChinaCASHefei 230026China Synergetic Innovation Center of quantum information and quantum Physics University of Science and Technology of ChinaHefei 230026China Centre for quantum computation and Communication Technology(CQC2T)and Centre for quantum Dynamics Griffith UniversityBrisbane4111Australia quantum Engineering and Technology Laboratories School of Physics and Department of Electrical and Electronic EngineeringUniversity of BristolUK

We experimentally demonstrate that tomographic measurements can be performed for states of qubits before they are prepared.A variant of the quantum teleportation protocol is used as a channel between two instants in time,allowing measurements for polarization states of photons to be implemented 88 ns before they are *** data taken at the early time and later unscrambled according to the results of the protocol’s Bell measurements,produces density matrices with an average fidelity of 0.90±0.01 against the ideal states of photons created at the later *** tomography of the time reverse quantum channel finds an average process fidelity of 0.84±*** our proof-of-principle implementation necessitates some post-selection,the general protocol is deterministic and requires no post-selection to sift desired states and reject a larger ensemble.

关键词： teleportation tomography time reverse

Realization of arbitrary two-qubit quantum gates based on chiral Majorana fermions

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Chinese Physics B 2021年第4期30卷 43-54页

作者： Qing Yan Qing-Feng Sun International Center for quantum Materials School of PhysicsPeking UniversityBeijing 100871China CAS Center for Excellence in Topological quantum computation University of Chinese Academy of SciencesBeijing 100190China Collaborative Innovation Center of quantum Matter Beijing 100871China Beijing Academy of quantum information Sciences Beijing 100193China

quantum computers are in hot-spot with the potential to handle more complex problems than classical computers *** the quantum computation requires the universal quantum gate set {T,H,CNOT} so as to perform any unitary transformation with arbitrary *** we first briefly review the Majorana fermions and then propose the realization of arbitrary two-qubit quantum gates based on chiral Majorana *** cells consist of a quantum anomalous Hall insulator surrounded by a topological superconductor with electric gates and quantum-dot structures,which enable the braiding operation and the partial exchange *** defining a qubit by four chiral Majorana fermions,the singlequbit T and H quantum gates are realized via one partial exchange operation and three braiding operations,*** entangled CNOT quantum gate is performed by braiding six chiral Majorana ***,we design a powerful device with which arbitrary two-qubit quantum gates can be realized and take the quantum Fourier transform as an example to show that several quantum operations can be performed with this space-limited ***,our proposal could inspire further utilization of mobile chiral Majorana edge states for faster quantum computation.

关键词： quantum computation T gate CNOT gate braiding chiral Majorana fermions