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arXiv 2024年

作者： Midha, Siddhant Singh, Roshni Gharavi, Kaveh Baugh, Jonathan Muralidharan, Bhaskaran Department of Electrical Engineering Indian Institute of Technology Bombay Powai Mumbai400076 India Department of Physics Indian Institute of Technology Bombay Powai Mumbai400076 India Institute for Quantum Computing University of Waterloo Canada Center of Excellence in Quantum Information Computing Science and Technology Indian Institute of Technology Bombay Powai Mumbai400076 India

Investigating the microscopic details of the proximity effect is crucial for both key experimental applications and fundamental inquiries into nanoscale devices featuring superconducting elements. In this work, we develop a framework motivated by experiments to study induced superconducting correlations in hybrid nanoscale devices featuring layered superconductor-normal heterostructures using the Keldysh non-equilibrium Green’s functions. Following a detailed method for analyzing the induced pair amplitude in a prototypical one-dimensional hybrid, we provide insights into the proximity effect within and outside the Andreev approximation. Our analysis also uncovers a disorder-induced crossover in the correlation patterns of the system. By elucidating the spectral distribution of the induced pair amplitude, we investigate the pair correlations established in a recent experiment [***.128,127701], providing a theoretical basis for the enhanced Cooper pair injection demonstrated through the lens of the induced pair correlations, thereby establishing the promise of our methods in guiding new experiments in hybrid quantum devices. © 2024, CC BY.

关键词： Superconducting devices

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Mining Top-k Frequent Patterns over Streaming Graphs 28th

Mining Top-k Frequent Patterns over Streaming Graphs

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28th International Conference on Database Systems for Advanced Applications, DASFAA 2023

作者： Wang, Xi Zhang, Qianzhen Guo, Deke Zhao, Xiang Institute for Quantum Information and State Key Laboratory of High Performance Computing National University of Defense Technology Changsha China Science and Technology on Information Systems Engineering Laboratory National University of Defense Technology Changsha China Laboratory for Big Data and Decision National University of Defense Technology Changsha China

ISBN: (纸本)9783031306747

Mining top-k frequent patterns is an important operation on graphs, which is defined as finding k interesting subgraphs with the highest frequency. Most existing work assumes a static graph. However, graphs are dynamic in nature, which is described as streaming graphs. Mining top-k frequent patterns in streaming graphs is challenging due to the streaming nature of the input and the exponential time complexity of the problem. A naive solution is to calculate approximations of the frequent patterns in the streaming graph and then find the top-k answers, which is a memory- and time-consuming method. In this paper, we design a novel auxiliary data structure, FPC, to detect valid subgraph patterns and their frequency in real-time. We first convert each newly produced subgraph into a sequence and then map it into corresponding tracks in FPC based on hash functions. We theoretically prove that FPC can provide unbiased estimation and then give an error bound of our algorithm. In addition, we propose a vertical hashing and candidate buckets sampling technique to further improve FPC with higher space utilization and higher accuracy. Extensive experiments confirm that our approach generates high-quality results compared to the baseline method. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

关键词： Hash functions

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Distributed exact Grover’s algorithm

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Frontiers of physics 2023年第5期18卷 255-279页

作者： Xu Zhou Daowen Qiu Le Luo Institute of Quantum Computing and Computer Theory School of Computer Science and EngineeringSun Yat-sen UniversityGuangzhou 510006China The Guangdong Key Laboratory of Information Security Technology Sun Yat-sen UniversityGuangzhou 510006China School of Physics and Astronomy Sun Yat-sen UniversityZhuhai 519082China QUDOOR Co Ltd.Beijing 100089China

Distributed quantum computation has gained extensive *** this paper,we consider a search problem that includes only one target item in the unordered *** that,we propose a distributed exact Grover’s algorithm(DEGA),which decomposes the original search problem into■n/2■***,(i)our algorithm is as exact as the modified version of Grover’s algorithm by Long,which means the theoretical probability of finding the objective state is 100%;(ii)the actual depth of our circuit is 8(n mod 2)+9,which is less than the circuit depths of the original and modified Grover’s algorithms,1+8■π/4√2^(n)■and 9+8■π/4√2^(n)-1/2■,*** only depends on the parity of n,and it is not deepened as n increases;(iii)we provide particular situations of the DEGA on Mindquantum(a quantum software)to demonstrate the practicality and validity of our *** our circuit is shallower,it will be more resistant to the depolarization channel noise.

关键词： distributed quantum computation search problem distributed exact Grover’s algorithm(DEGA) Mindquantum the depolarization channel noise

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Programmable Photonic Nonlinearity for quantum Simulation

Programmable Photonic Nonlinearity for Quantum Simulation

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2024 Asia Communications and Photonics Conference, ACP 2024 and International Conference on Information Photonics and Optical Communications, IPOC 2024

作者： Wang, Ying Nielsen, Kasper H. Deacon, Edward Sund, Patrik I. Liu, Zhe Scholz, Sven Ludwig, Arne Midolo, Leonardo Sørensen, Anders S. Paesani, Stefano Lodahl, Peter Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen2100 Denmark Quantum Engineering and Technology Laboratories School of Physics Department of Electrical and Electronic Engineering University of Bristol Bristol United Kingdom Lehrstuhl für Angewandte Festkörperphysik Ruhr-Universität Bochum Universitätsstrasse 150 BochumD-44780 Germany NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen2100 Denmark

ISBN: (纸本)9798350379266

Light-matter interaction at the quantum level provides a versatile interface driving photonic quantum technologies toward practical applications. We demonstrate multi-mode photonic circuits that enable precise programming of linear and nonlinear phase configurations at the single-photon level. The nonlinearity operation is realized using a solid-state quantum emitter, a self-assembled quantum dot, integrated into a nanophotonic device. The quantum dot interfaces with a temporal linear optical interferometer, creating a programmable nonlinear photonic platform that is necessary for implementing quantum protocols that require strong nonlinearities, such as the quantum simulation of anharmonic molecular dynamics. © 2024 IEEE.

关键词： Nanocrystals

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Reachability deficit of variational Grover search

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Physical Review A 2024年第1期109卷 012414-012414页

作者： Xiao-Wei Li Xiao-Ming Zhang Bin Cheng Man-Hong Yung Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 China Department of Physics Southern University of Science and Technology Shenzhen 518055 China Center on Frontiers of Computing Studies Peking University Beijing 100871 China Centre for Quantum Software and Information Faculty of Engineering and Information Technology University of Technology Sydney New South Wales 2007 Australia Guangdong Provincial Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 China Shenzhen Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 China

The quantum approximate optimization algorithm (QAOA) is promising for achieving quantum computational advantage with near-term quantum devices. It was numerically shown that the QAOA cost functions exhibit a phenomenon called reachability deficit (RD), where the success probability cannot reach unity until the circuit depth exceeds a certain critical value. However, an in-depth theoretical understanding of RD remains lacking. Here we focus on a variational variant of Grover search on multiple marked solutions as a prototype for analyzing the RD problem, where we further relax the criterion of reachability by tolerating a certain probability of failure. Specifically, we obtain a general analytical expression relating the critical depth of the quantum circuit to the solution density. In the dilute limit, the critical depth is consistent with the Grover bound, exhibiting a robust quadratic scaling that is insensitive to the failure probability. Moreover, we also find that the projective mixing Hamiltonian performs significantly better than the traditional mixing Hamiltonian in the QAOA, although it is less favorable in terms of physical implementation. However, by taking into account two-body interactions in the mixing Hamiltonian, the performance becomes on par with the projective mixing Hamiltonian at the cost of O(n2) additional terms. These results represent a simplified but insightful model of the QAOA, fully addressing the dependence of required circuit depth over the ground-state degeneracy.

关键词： quantum algorithms Search strategy

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Simultaneous information and energy transmission through quantum channels

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Physical Review A 2025年第1期111卷 012609-012609页

作者： Bishal Kumar Das Lav R. Varshney Vaibhav Madhok Department of Physics Indian Institute of Technology Madras Chennai 600036 India Centre for Quantum Information Communication and Computing (CQuICC) Indian Institute of Technology Madras Chennai 600036 India Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Urbana Illinois 61801 USA

The optimal rate at which information can be sent through a quantum channel when the transmitted signal must simultaneously carry some minimum amount of energy is characterized. To do so, we introduce the quantum-classical analog of the capacity-power function, and we generalize results in classical information theory for transmitting classical information through noisy channels. We show that the capacity-power function for a classical-quantum channel, for both unassisted and private protocol, is concave, and we also prove additivity for unentangled and uncorrelated ensembles of input signals for such channels. This implies that we do not need regularized formulas for calculation. We show that these properties also hold for all noiseless channels when we restrict the set of input states to be pure quantum states. For general channels, we geometrically prove that the capacity-power function is piecewise concave, with further support from numerical simulations. Further, we connect channel capacity to properties of random quantum states. In particular, we obtain analytical expressions for the capacity-power function for the case of noiseless channels using properties of random quantum states under an energy constraint and concentration phenomena in large Hilbert spaces.

关键词： quantum channel

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Deep Learning for Channel Prediction in Non-Stationary Wireless Fading Environments

Deep Learning for Channel Prediction in Non-Stationary Wirel...

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2024 IEEE International Conference on Intelligent Signal Processing and Effective Communication Technologies, INSPECT 2024

作者： Upadhyay, Deepak Sharma, Kunj Bihari Gupta, Mridul Upadhyay, Abhay Venu, Nookala Graphic Era Hill University Dept. of Computer Science and Engineering Dehradun India Graphic Era deemed to be University Dept. of Computer Science and Engineering Dehradun India Graphic Era deemed to be University Dept. of Electronics and Communication Engineering Dehradun India Data Science and Quantum Computing ABV Indian Institute of Information Technology and Management Gwalior India

ISBN: (纸本)9798350379525

In non-stationary wireless fading channels deep learning models are effective in predicting channel states as indicated by this study. This work compared the LSTM and GRU models with autoregressive methods or Kalman filter, implying that deep learning is indeed able to capture temporal dependence between variables and was likely more adapted than linear method when dealing with many changes in dynamics. From the perspective of pre-processing data, keys like attention mechanism and transfer learning were decisive elements in helping them to improve prediction scores and make models more robust. These results showed that these enhanced procedures allow the models to generalise over a wide range of non-stationary situations, generating consistent performance in various diverse environments. This study indicates the promise of deep learning for enhancing wireless network operation, which could lead to greater self-awareness and utilization features in emerging future-generation wireless systems. © 2024 IEEE.

关键词： Prediction models

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Clifford-Deformed Surface Codes

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PRX quantum 2024年第1期5卷 010347-010347页

作者： Arpit Dua Aleksander Kubica Liang Jiang Steven T. Flammia Michael J. Gullans Department of Physics and Institute for Quantum Information and Matter California Institute of Technology Pasadena California 91125 USA AWS Center for Quantum Computing Pasadena California 91125 USA California Institute of Technology Pasadena California 91125 USA Pritzker School of Molecular Engineering The University of Chicago Illinois 60637 USA Joint Center for Quantum Information and Computer Science NIST/University of Maryland College Park Maryland 20742 USA

Various realizations of Kitaev’s surface code perform surprisingly well for biased Pauli noise. Attracted by these potential gains, we study the performance of Clifford-deformed surface codes (CDSCs) obtained from the surface code by the application of single-qubit Clifford operators. We first analyze CDSCs on the 3×3 square lattice and find that, depending on the noise bias, their logical error rates can differ by orders of magnitude. To explain the observed behavior, we introduce the effective distance d′, which reduces to the standard distance for unbiased noise. To study CDSC performance in the thermodynamic limit, we focus on random CDSCs. Using the statistical mechanical mapping for quantum codes, we uncover a phase diagram that describes random CDSC families with 50% threshold at infinite bias. In the high-threshold region, we further demonstrate that typical code realizations outperform the thresholds and subthreshold logical error rates, at finite bias, of the best-known translationally invariant codes. We demonstrate the practical relevance of these random CDSC families by constructing a translation-invariant CDSC belonging to a high-performance random CDSC family. We also show that our translation-invariant CDSC outperforms well-known translation-invariant CDSCs, such as the XZZX and XY codes.

关键词： Classical statistical mechanics Critical phenomena Order parameters Percolation theory Phase diagrams Phase transitions by order quantum error correction quantum memories

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Secrecy Capacity Optimization in RF/FSO Systems: Impact of Mixed Rayleigh and Log-Normal Fading with Atmospheric Turbulence

Secrecy Capacity Optimization in RF/FSO Systems: Impact of M...

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2024 IEEE International Conference on Intelligent Signal Processing and Effective Communication Technologies, INSPECT 2024

作者： Upadhyay, Deepak Sharma, Kunj Bihari Gupta, Mridul Upadhyay, Abhay Venu, Nookala Graphic Era Hill University Dept. of Computer Science and Engineering Dehradun India Graphic Era deemed to be University Dept. of Computer Science and Engineering Dehradun India Graphic Era deemed to be University Dept. of Electronics and Communication Engineering Dehradun India ABV Indian Institute of Information Technology and Management Data Science and Quantum Computing Gwalior India

ISBN: (纸本)9798350379525

This paper investigates the secrecy capacity optimization in RF/FSO systems with mixed Rayleigh and log-normal fading, while masking eavesdroppers channel state information () as well as suffering from atmospheric turbulence. We explore the impact of several parameters including beamforming angles, modulation schemes and hybrid RF/FSO link configurations through a combination of simulations as well as analytical models. Secrecy capacity is enhanced for an improved SNR and vice versa under higher turbulence conditions and cooler influents eavesdropped scenarios. Performance of the hybrid RF/FSO systems dominates considerably over single-link solutions, especially at longer distances. All these mechanisms appreciably increase the secrecy capacity, while beamforming and advanced modulation techniques offer most of the improvement. The study also demonstrates the interdependencies of system parameters, providing guidelines for designing secure communication systems under different environmental and operational conditions. © 2024 IEEE.

关键词： Beamforming

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High dynamic-range and portable magnetometer using ensemble nitrogen-vacancy centers in diamond

arXiv

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arXiv 2024年

作者： Kumar, Himanshu Shishir, Dasika Mangat, Maheshwar Tallur, Siddharth Saha, Kasturi Department of Electrical Engineering Indian Institute of Technology Bombay Mumbai India Center of Excellence in Quantum Information Computing Science and Technology Indian Institute of Technology Bombay Mumbai India Indian Institute of Technology Bombay Mumbai India

Nitrogen vacancy (NV) centers in diamonds have been explored for realizing a wide range of sensing applications in the last decade due to their unique quantum properties. Here we realize a compact and portable magnetometer with an ensemble of NV centers which we call the quantum MagPI (quantum Magnetometer with Proportional Integral control). Including the sensor head and associated electronics, our sensor assembly can fit inside 10 cm × 10 cm × 7 cm box_ and control electronics in 30 cm × 25 cm × 5 cm box. We achieve a bandwidth normalized sensitivity of ∼ 10 nT/√Hz. Using closed-loop feedback for locking to the resonance frequency, we extend the linear dynamic range to 200 µT (20× improvement compared to the intrinsic dynamic range) without compromising the sensitivity. We report a detailed performance analysis of the magnetometer through measurements of noise spectra, Allan deviation, and tracking of nT-level magnetic fields in real-time. Additionally, we demonstrate the utility of such a magnetometer by real-time tracking the movement of the elevator car and door opening by measuring the projection of the magnetic field along one of the NV-axes under ambient temperature and humidity. © 2024, CC BY.

关键词： Magnetic fields

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