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Author: Subject: Claimed quantum computer breakthough
leau
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[*] posted on 25-2-2022 at 10:51


Conference 10082: Solid State Lasers XXVI: Technology and Devices

SPIE Photonics West 2017

Part of Proceedings of SPIE Vol. 10082 Solid State Lasers XXVI: Technology and Devices


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leau
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[*] posted on 26-2-2022 at 11:12


UTe 2 : a nearly insulating half-filled j =25f 3 heavy fermion metal

Alexander B. Shick, Shin-ichi Fujimori, Warren E. Pickett

Phys. Rev. B 103, 125136 (2021)
https://doi.org/10.48550/arXiv.2103.11410

Correlated band theory implemented as a combination of density functional theory with exact diagonalization [DFT+U(ED)] of the Anderson impurity term with Coulomb repulsion U in the open 14-orbital 5f shell is applied to UTe 2 . The small gap for U =0, evidence of the half-filled j = 52 subshell of 5f 3 uranium, is converted for U =3 eV to a flat band semimetal with small heavy-carrier Fermi surfaces that will make properties sensitive to pressure, magnetic field, and off-stoichiometry, as observed experimentally. Two means of identification from the Green’s function give a mass enhancement of the order of 12 for already heavy (flat) bands, consistent with the common heavy fermion characterization of UTe 2 . The predicted Kondo temperature around 100 K matches the experimental values from resistivity. The electric field gradients for the two Te sites are calculated by DFT+U(ED) to differ by a factor of seven, indicating a strong site distinction, while the anisotropy factor η = 0.18 is similar for all three sites. The calculated uranium moment < M 2 > 1/2 of 3.5µ B is roughly consistent with the published experimental Curie-Weiss values of 2.8µ B and 3.3µ B (which are field-direction dependent), and the calculated separate spin and orbital moments are remarkably similar to Hund’s rule values for an f 3 ion. The U =3 eV spectral density is compared with angle-integrated and angle-resolved photoemission spectra, with agreement that there is strong 5f character at, and for several hundred meV below, the Fermi energy. Our results support the picture that the underlying ground state of UTe 2 is that of a half-filled j = 52 subshell with two half-filled m j = ± 2 1 orbitals forming a narrow gap by hybridization, then driven to a conducting state by configuration mixing (spin-charge fluctuations). UTe 2 displays similarities to UPt 3 with its 5f dominated Fermi surfaces rather than a strongly localized Kondo lattice system.


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[Edited on 26-2-2022 by leau]
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[*] posted on 27-2-2022 at 10:24


Quantum restricted Boltzmann machine universal for quantum computation

Yusen Wu, Chunyan Wei, Sujuan Qin, Qiaoyan Wen, Fei Gao

https://arxiv.org/abs/2005.11970
https://doi.org/10.48550/arXiv.2005.1197

The challenge posed by the many-body problem in quantum physics originates from the difficulty of describing the nontrivial correlations encoded in the many-body wave functions with high complexity. Quantum neural network provides a powerful tool to represent the large-scale wave function, which has aroused widespread concern in the quantum superiority era. A significant open problem is what exactly the representational power boundary of the single-layer quantum neural network is. In this paper, we design a 2-local Hamiltonian and then give a kind of Quantum Restricted Boltzmann Machine (QRBM, i.e. single-layer quantum neural network) based on it. The proposed QRBM has the following two salient features. (1) It is proved universal for implementing quantum computation tasks. (2) It can be efficiently implemented on the Noisy Intermediate-Scale Quantum (NISQ) devices. We successfully utilize the proposed QRBM to compute the wave functions for the notable cases of physical interest including the ground state as well as the Gibbs state (thermal state) of molecules on the superconducting quantum chip. The experimental results illustrate the proposed QRBM can compute the above wave functions with an acceptable error.


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[*] posted on 28-2-2022 at 11:03


Quantum Humanities: A First Use Case for Quantum-ML in Media Science

Johanna Barzen & Frank Leymann

https://doi.org/10.1007/s42354-019-0243-2 .

Quantum computers are becoming real. Therefore, it is promising to use their potentials in different applications areas, which includes research in the humanities.Due to an increasing amount of data that needs to be processed in the digital humanities the use of quantum computers can contribute to this research area. To give an impression on how beneficial such involvement of quantum computers can be when analyzing data from the humanities, a use case from the media science is presented. Therefore, both the theoretical basis and the tooling support for analyzing the data from our digital humanities project MUSE is described. This includes a data analysis pipeline, containing e.g. various approaches for data preparation, feature engineering, clustering, and classification where several steps can be realized classically, but also supported by quantum computers.


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[*] posted on 1-3-2022 at 11:59


Feature Learning with Gaussian Restricted Boltzmann Machine for Robust Speech Recognition

Xin Zheng, Zhiyong Wu, Helen Meng, Weifeng Li, Lianhong Cai

https://arxiv.org/abs/1309.6176

In this paper, we first present a new variant of Gaussian restricted Boltzmann machine (GRBM) called multivariate Gaussian restricted Boltzmann machine (MGRBM), with its definition and learning algorithm. Then we propose using a learned GRBM or MGRBM to extract better features for robust speech recognition. Our experiments on Aurora2 show that both GRBM-extracted and MGRBM-extracted feature performs much better than Mel-frequency cepstral coefficient (MFCC) with either HMM-GMM or hybrid HMM-deep neural network (DNN) acoustic model, and MGRBM-extracted feature is slightly better.


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[*] posted on 2-3-2022 at 10:35


An Algorithm of Quantum Restricted Boltzmann Machine Network Based on Quantum Gates and Its Application

Peilin Zhang, Sheng Li and Yu Zhou

https://doi.org/10.1155/2015/756969

We present an algorithm of quantum restricted Boltzmann machine network based on quantum gates. The algorithm is used to initialize the procedure that adjusts the qubit and weights. After adjusting, the network forms an unsupervised generative model that gives better classification performance than other discriminative models. In addition, we show how the algorithm can be constructed with quantum circuit for quantum computer.


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[*] posted on 4-3-2022 at 12:21


Multiorbital spin-triplet pairing and spin resonance in the heavy-fermion superconductor UTe 2

Lei Che, Haoyu Hu, Christopher Lane, Emilian M. Nica, Jian-Xin Zhu, and Qimiao

https://arxiv.org/abs/2112.14750
https://doi.org/10.48550/arXiv.2112.14750

The heavy-fermion system UTe 2 is a candidate for spin-triplet superconductivity, which is of considerable interest to quantum engineering. Among the outstanding issues is the nature of the pairing state. A recent surprising discovery is the observation of a resonance in the spin excitation spectrum at an antiferromagneticwavevector [C. Duan et al., Nature 600, 636 (2021)], which stands in apparent contrast to the ferromagnetic nature of the interactions expected in this system. We show how the puzzle can be resolved by a multiorbitalspin-triplet pairing constructed from local degrees of freedom. Because it does not commute with the kinetic part of the Hamiltonian, the pairing contains both intra- and inter- band terms in the band basis. We demonstrate that the intraband pairing component naturally yields a spin resonance at the antiferromagnetic wavevector. Our work illustrates how orbital degrees of freedom can enrich the nature and properties of spin-triplet superconductivity of strongly-correlated quantum materials.


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[*] posted on 5-3-2022 at 13:53


Implementation of a Walsh-Hadamard Gate in a Superconducting Qutrit

M A Yurtalan, J Shi, M Kononenko, A Lupascu & S Ashhab

DOI: 10.1103/PhysRevLett.125.180504
Phys Rev Lett. 2020 Oct 30;125(18):180504
https://arxiv.org/abs/2003.04879

We have implemented a Walsh-Hadamard gate, which performs a quantum Fourier transform, in a superconducting qutrit. The qutrit is encoded in the lowest three energy levels of a capacitively shunted flux device, operated at the optimal flux-symmetry point. We use an efficient decomposition of the Walsh-Hadamard gate into two unitaries, generated by off-diagonal and diagonal Hamiltonians, respectively. The gate implementation utilizes simultaneous driving of all three transitions between the three pairs of energy levels of the qutrit, one of which is implemented with a two-photon process. The gate has a duration of 35 ns and an average fidelity over a representative set of states, including preparation and tomography errors, of 99.2%, characterized with quantum-state tomography. Compensation of ac-Stark and Bloch-Siegert shifts is essential for reaching high gate fidelities.


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[*] posted on 6-3-2022 at 12:26


Generalized Optical Signal Processing Based on Multi-Operator Metasurfaces Synthesized by Susceptibility Tensors

Ali Momeni, Hamid Rajabalipanah, Ali Abdolali, Karim Achouri

https://doi.org/10.48550/arXiv.1811.02618
https://arxiv.org/abs/1811.02618

This paper theoretically proposes a multichannel functional metasurface computer characterized by Generalized Sheet Transition Conditions (GSTCs) and surface susceptibility tensors. The study explores a polarization- and angle-multiplexed metasurfaces enabling multiple and independent parallel analog spatial computations when illuminated by differently polarized incident beams from different directions. The proposed synthesis overcomes substantial restrictions imposed by previous designs such as large architectures arising from the need of additional subblocks, slow responses, and most importantly, supporting only the even reflection symmetry operations for normal incidences, working for a certain incident angle or polarization, and executing only single mathematical operation. The versatility of the design is demonstrated in a way that an ultra-compact, integrable and planar metasurface-assisted platform can execute a variety of optical signal processing operations such as spatial differentiation and integration. It is demonstrated that a metasurface featuring non-reciprocal property can be thought of as a new paradigm to break the even symmetry of reflection and perform both even- and odd-symmetry mathematical operations at normal incidences. Numerical simulations also illustrate different aspects of multichannel edge detection scheme through projecting multiple images on the metasurface from different directions. Such appealing findings not only circumvent the major potential drawbacks of previous designs but also may offer an efficient, easy-to-fabricate, and flexible approach in wave-based signal processing, edge detection, image contrast enhancement, hidden object detection, and equation solving without any Fourier lens.


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[*] posted on 7-3-2022 at 11:34


Biology begins to tangle with quantum computing

Vivien Marx

Nat Methods 18, 715–719 (2021).

https://doi.org/10.1038/s41592-021-01199-z


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[*] posted on 8-3-2022 at 07:49


Quantum circuit architecture search on a superconducting processor

Kehuan Linghu, Yang Qian, Ruixia Wang, Meng-Jun Hu, Zhiyuan Li, Xuegang Li, Huikai Xu, Jingning Zhang, Teng Ma, Peng Zhao, Dong E. Liu, Min-Hsiu Hsieh, Xingyao Wu, Yuxuan Du, Dacheng Tao, Yirong Jin & Haifeng Yu

https://arxiv.org/abs/2201.00934
https://doi.org/10.48550/arXiv.2201.00934

Variational quantum algorithms (VQAs) have shown strong evidences to gain provable computational advantages for diverse fields such as finance, machine learning, and chemistry. However, the heuristic ansatz exploited in modern VQAs is incapable of balancing the tradeoff between expressivity and trainability, which may lead to the degraded performance when executed on the noisy intermediate-scale quantum (NISQ) machines. To address this issue, here we demonstrate the first proof-of-principle experiment of applying an efficient automatic ansatz design technique, i.e., quantum architecture search (QAS), to enhance VQAs on an 8-qubit superconducting quantum processor. In particular, we apply QAS to tailor the hardware-efficient ansatz towards classification tasks. Compared with the heuristic ansatze, the ansatz designed by QAS improves test accuracy from 31% to 98%. We further explain this superior performance by visualizing the loss landscape and analyzing effective parameters of all ansatze. Our work provides concrete guidance for developing variable ansatze to tackle various large-scale quantum learning problems with advantages.


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[*] posted on 9-3-2022 at 09:41


Reciprocal space study of Heisenberg exchange interactions in ferromagnetic metals

I. V. Kashin, A. Gerasimov, V. V. Mazurenko

https://arxiv.org/abs/2112.13016
https://doi.org/10.48550/arXiv.2112.13016

The modern quantum theory of magnetism in solids is getting commonly derived using Green's functions formalism. The popularity draws itself from remarkable opportunities to capture the microscopic landscape of exchange interactions, starting from a tight-binding representation of the electronic structure. Indeed, the conventional method of infinitesimal spin rotations, considered in terms of local force theorem, opens vast prospects of investigations regarding the magnetic environment, as well as pairwise atomic couplings. However, this theoretical concept practically does not devoid of intrinsic inconsistencies. In particular, naturally expected correspondence between single and pairwise infinitesimal spin rotations is being numerically revealed to diverge. In this work, we elaborate this question on the model example and canonical case of bcc iron. Our analytical derivations discovered the principal preference of on-site magnetic precursors if the compositions of individual atomic interactions are in focus. The problem of extremely slow or even absent spatial convergence while considering metallic compounds was solved by suggesting the original technique, based on reciprocal space framework. Using fundamental Fourier transform-inspired interconnection between suggested technique and traditional spatial representation, we shed light on symmetry breaking in bcc Fe on the level of orbitally decomposed total exchange surrounding.


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[*] posted on 10-3-2022 at 10:31


PREPARING FOR Q-DAY

Davide Castelvecchi

Nature, Vol 602, 10 February 2022 pp 198-201

The quantum-computer revolution could give hackers superpowers. New encryption algorithms will keep them at bay.


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[*] posted on 11-3-2022 at 09:19


Quantum Computing: How to Address the National Security Risk

Dr. Arthur Herman & Idalia Friedson

2018 Hudson Institute


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