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Topological phase transitions of Thouless charge pumping realized in helical organic molecules with long-range hopping

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Physical Review B 2020年第15期102卷 155402-155402页

作者： Ai-Min Guo Pei-Jia Hu Xiao-Hui Gao Tie-Feng Fang Qing-Feng Sun Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha 410083 China Key Laboratory for Magnetism and Magnetic Materials of MOE School of Physical Science and Technology Lanzhou University Lanzhou 730000 China International Center for Quantum Materials School of Physics Peking University Beijing 100871 China Collaborative Innovation Center of Quantum Matter Beijing 100871 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing 100190 China

Recent studies indicated that helical organic molecules, such as DNA and the α-helical protein, can behave as Thouless quantum pumps when a rotating electric field is applied perpendicularly to their helical axes. Here we investigate the influence of long-range hoppings on this topological pumping of electrons in single-helical organic molecules. Under variation of the long-range hoppings governed by a decay exponent μ, we find an energy gap in the molecular band structure closes at a critical value μc of the decay exponent and reopens for μ deviating from μc. The relevant bulk bands in a pumping cycle acquire different Chern numbers in the strong (μ<μc) and weak (μ>μc) long-range hopping regimes, with a sudden jump at criticality. This topological phase transition is also shown to separate two distinct behaviors of the midgap end states in the pumping process. The end states carry quantized current pumped by the rotating electric field, and the current forms a plateau by sweeping the Fermi energy over the gap. In the strong-hopping phase, the quantized current plateau is positive, which is reversed to a negative one with smaller amplitude in the weak-hopping phase. However, the reversal is a smooth crossover, not a sharp transition, due to the finite sizes of the molecules. We show that these transport characteristics of the topological phase transition could also be observed at finite temperatures.

关键词： Topological phase transition Biomolecules Topological materials

Running of effective dimension and cosmological entropy in early universe

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arXiv 2020年

作者： Xiao, Yong Key Laboratory of High-precision Computation and Application of Quantum Field Theory of Hebei Province College of Physical Science and Technology Hebei University Baoding071002 China Department of Physics and Astronomy University of Sussex BrightonBN1 9QH United Kingdom

In this paper, we suggest that the early universe starts from a high-energetic state with a two dimensional description and the state recovers to be four dimensional when the universe evolves into the radiation dominated phase. This scenario is consistent with the recent viewpoint that quantum gravity should be effectively two dimensional in the ultraviolet and recovers to be four dimensional in the infrared. A relationship has been established between the running of effective dimension and that of the entropy inside particle horizon of the universe, i.e., as the effective dimension runs from two to four, the corresponding entropy runs from the holographic entropy to the normal entropy appropriate to radiation. These results can be generalized to higher dimensional cases. Copyright © 2020, The Authors. All rights reserved.

关键词： Entropy

Discrete Time Crystals Enforced by Floquet-Bloch Scars

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Physical Review Letters 2022年第13期129卷 133001-133001页

作者： Biao Huang Tsz-Him Leung Dan M. Stamper-Kurn W. Vincent Liu Kavli Institute for Theoretical Sciences University of Chinese Academy of Sciences Beijing 100190 China Department of Physics University of California Berkeley California 94720 USA Challenge Institute for Quantum Computation University of California Berkeley California 94720 USA Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA Department of Physics and Astronomy and IQ Initiative University of Pittsburgh Pittsburgh Pennsylvania 15260 USA Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 China

We analytically identify a new class of quantum scars protected by spatiotemporal translation symmetries, dubbed Floquet-Bloch scars. They are distinguished from previous (quasi-)static scars by a rigid spectral pairing only possible in Floquet systems, where strong interaction and drivings equalize the quasienergy corrections to all scars and maintain their spectral spacings against generic bilinear perturbations. Scars then enforce the spatial localization and rigid discrete time crystal (DTC) oscillations as verified numerically in a trimerized kagome lattice model relevant to recent cold atom experiments. Our analytical solutions offer a potential scheme to understand the mechanisms for more generic translation-invariant DTCs.

关键词： Cold gases in optical lattices Eigenstate thermalization Time crystals Atomic gases Floquet systems Kagome lattice Exact diagonalization Hubbard model

All-electron ab-initio hyperfine coupling of Si-, Ge- and Sn-vacancy defects in diamond

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arXiv 2023年

作者： Karim, Akib Vallabhapurapu, Harish H. Adambukulam, Chris Laucht, Arne Russo, Salvy P. Peruzzo, Alberto Quantum Photonics Laboratory Centre for Quantum Computation and Communication Technology School of Engineering RMIT University MelbourneVIC3000 Australia School of Electrical Engineering and Telecommunications University of New South Wales SydneyNSW2052 Australia ARC Centre of Excellence in Exciton Science School of Science RMIT University MelbourneVIC3001 Australia Chemical and Quantum Physics School of Science RMIT University MelbourneVIC3001 Australia Quantum Photonics Laboratory Centre for Quantum Computation and Communication Technology School of Engineering RMIT University MelbourneVIC3000 Australia

Colour centres in diamond are attractive candidates for numerous quantum applications due to their good optical properties and long spin coherence times. They also provide access to the even longer coherence of hyperfine coupled nuclear spins in their environment. While the NV centre is well studied, both in experiment and theory, the hyperfine couplings in the more novel centres - SiV, GeV, and SnV - are still largely unknown. Here we report on the first all-electron ab-initio calculations of the hyperfine constants for SiV, GeV, and SnV defects in diamond, both for the respective defect atoms (29Si, 73Ge, 117Sn, 119Sn), as well as for the surrounding 13C atoms. Furthermore, we calculate the nuclear quadrupole moments of the GeV defect. We vary the Hartree-Fock mixing parameter for Perdew-Burke-Ernzerhof (PBE) exchange correlation functional and show that the hyperfine couplings of the defect atoms have a linear dependence on the mixing percentage. We calculate the inverse dielectric constant to predict an ab-initio mixing percentage. The final hyperfine coupling predictions are close to the experimental values available in the literature. Our results will help to guide future novel experiments on these defects. Copyright © 2023, The Authors. All rights reserved.

关键词： Atoms

Focused ion beam polishing based optimization of high-Q silica microdisk resonators

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arXiv 2024年

作者： Eswaramoorthy, Lekshmi Sharma, Parul Kumar, Brijesh Abhay Anand, V.S. Singh, Anuj Kumar Mandal, Kishor Kumar Mokkapati, Sudha Kumar, Anshuman Laboratory of Optics of Quantum Materials Department of Physics Indian Institute of Technology Bombay Powai Mumbai400076 India Department of Materials Science and Engineering Monash University ClaytonVIC3800 Australia IITB-Monash Research Academy Indian Institute of Technology Bombay Powai Mumbai400076 India Centre of Excellence in Quantum Information Computation Science and Technology Indian Institute of Technology Bombay Powai Mumbai400076 India

Whispering gallery mode (WGM) microdisk resonators are promising optical devices that confine light efficiently and enable enhanced nonlinear optical effects. This work presents a novel approach to reduce sidewall roughness in SiO2 microdisk resonators using focused ion beam (FIB) polishing. The microdisks, with varying diameter ranging from 5 to 20 µm are fabricated using a multi-step fabrication scheme. However, the etching process introduces significant sidewall roughness, which increases with decreasing microdisk radius, degrading the resonators’ quality. To address this issue, a FIB system is employed to polish the sidewalls, using optimized process parameters to minimize Ga ion implantation. White light interferometry measurements reveal a significant reduction in surface roughness from 7 nm to 20 nm for a 5 µm diameter microdisk, leading to a substantial enhancement in the scattering quality factor (Qss) from 3 × 102 to 2 × 106. These findings demonstrate the effectiveness of FIB polishing in improving the quality of microdisk resonators and open up new possibilities for the fabrication of advanced photonic devices. Copyright © 2024, The Authors. All rights reserved.

关键词： Whispering gallery modes

Quantum Induced Coherence Light Detection and Ranging

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Physical Review Letters 2023年第3期131卷 033603-033603页

作者： Gewei Qian Xingqi Xu Shun-An Zhu Chenran Xu Fei Gao V. V. Yakovlev Xu Liu Shi-Yao Zhu Da-Wei Wang Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation and Zhejiang Province Key Laboratory of Quantum Technology and Device School of Physics Zhejiang University Hangzhou 310027 Zhejiang Province China ZJU-Hangzhou Global Science and Technology Innovation Center College of Information Science and Electronic Engineering Zhejiang University Hangzhou 310027 China Texas A&M University 3120 TAMU College Station Texas 77843 USA Hefei National Laboratory Hefei 230088 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing 100190 China

Quantum illumination has been proposed and demonstrated to improve the signal-to-noise ratio (SNR) in light detection and ranging (LiDAR). When relying on coincidence detection alone, such a quantum LiDAR is limited by the timing jitter of the detector and suffers from jamming noise. Inspired by the Zou-Wang-Mandel experiment, we design, construct, and validate a quantum induced coherence (QuIC) LiDAR which is inherently immune to ambient and jamming noises. In traditional LiDAR the direct detection of the reflected probe photons suffers from deteriorating SNR for increasing background noise. In QuIC LiDAR we circumvent this obstacle by only detecting the entangled reference photons, whose single-photon interference fringes are used to obtain the distance of the object, while the reflected probe photons are used to erase path information of the reference photons. In consequence, the noise accompanying the reflected probe light has no effect on the detected signal. We demonstrate such noise resilience with both LED and laser light to mimic the background and jamming noise. The proposed method paves a new way of battling noise in precise quantum electromagnetic sensing and ranging.

关键词： Photon pairs & parametric down-conversion Quantum metrology Quantum optics Imaging & optical processing

Ancilla dimensions needed to carry out positive-operator-valued measurement

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Physical Review A 2007年第6期76卷 060303(R)-060303(R)页

作者： Ping-Xing Chen János A. Bergou Shi-Yao Zhu Guang-Can Guo Department of Physics Hong Kong Baptist University Kowloon Tong Hong Kong People’s Republic of China Key Laboratory of Quantum Communication and Quantum Computation University of Science and Technology of China Hefei 230026 People’s Republic of China Department of Physics National University of Defense Technology Changsha 410073 People’s Republic of China Department of Physics and Astronomy Hunter College City University of New York 695 Park Avenue New York NY 10021 USA Institute of Theoretical Physics Chinese University of Hong Kong Hong Kong People’s Republic of China

To implement a positive-operator-valued measurement (POVM), which is defined on the dS-dimensional Hilbert space of a physical system, one has to extend the Hilbert space to include dA additional dimensions (called the ancilla). This is done via either the tensor product extension (TPE) or the direct sum extension (DSE). The implementation of a POVM utilizes the available resources more efficiently if it requires fewer additional dimensions. To determine how to implement a POVM with the least additional dimensions is, therefore, an important task in quantum information. We have determined the necessary and sufficient (hence minimal) number of the additional dimensions needed to implement the same POVM by the TPE and the DSE, respectively. If the POVM has n elements and ri is the rank of the ith element, then the dimension of the minimal ancilla is dA=∑i=1nri−dS for the DSE implementation, and this represents a lower bound for the added dimensions in the TPE implementation. In the proof, we explicitly construct the DSE implementation of a general POVM with elements of arbitrary rank. As an example, we determine dA for the unambiguous discrimination of N linearly independent states and provide the full DSE implementation of a state-discriminating POVM for N=2.

关键词： Mathematical operators

Machine learning cryptanalysis of a quantum random number generator

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arXiv 2019年

作者： Truong, Nhan Duy Haw, Jing Yan Assad, Syed Muhamad Lam, Ping Koy Kavehei, Omid Nano-Neuro-inspired Research Laboratory School of Electrical and Information Engineering University of Sydney SydneyNSW2006 Australia Centre for Quantum Computation and Communication Technology Department of Quantum Science Research School of Physics and Engineering Australian National University CanberraACT2601 Australia

Random number generators (RNGs) that are crucial for cryptographic applications have been the subject of adversarial attacks. These attacks exploit environmental information to predict generated random numbers that are supposed to be truly random and unpredictable. Though quantum random number generators (QRNGs) are based on intrinsic indeterministic nature of quantum properties, the presence of classical noise in the measurement process compromises the integrity of a QRNG. In this paper, we develop a predictive machine learning analysis to investigate the impact of deterministic classical noise in different stages of an optical continuous variable QRNG. Our machine learning (ML) model successfully detects inherent correlations when the deterministic noise sources are prominent. After appropriate filtering and randomness extraction processes are introduced, our QRNG system, in turn, demonstrates its robustness against ML. We further demonstrate the robustness of our machine learning approach by applying it to uniformly distributed random numbers from the QRNG and a congruential RNG. Hence, our result shows that machine learning has potentials in benchmarking the quality of RNG devices. Copyright © 2019, The Authors. All rights reserved.

关键词： Random number generation

A microscopic derivation of the Bekenstein-Hawking entropy for Schwarzschild black holes

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arXiv 2019年

In this paper, we successfully derive the Bekenstein-Hawking entropy for Schwarzschild black holes in various dimensions by using a non-trivial phase space. It is appealing to notice that the thermodynamics of a Schwarzschild black hole actually behaves like that of a 1-dimensional quantum mechanical system. Our result suggests that black hole should be viewed as a system with the equation of state P = ρ, and it also suggests that a holographic stage should exist in the early universe. Copyright © 2019, The Authors. All rights reserved.

关键词： Gravitation