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Closed-loop calculations of electronic structure on a quantum processor and a classical supercomputer at full scale
Authors:
Tomonori Shirakawa,
Javier Robledo-Moreno,
Toshinari Itoko,
Vinay Tripathi,
Kento Ueda,
Yukio Kawashima,
Lukas Broers,
William Kirby,
Himadri Pathak,
Hanhee Paik,
Miwako Tsuji,
Yuetsu Kodama,
Mitsuhisa Sato,
Constantinos Evangelinos,
Seetharami Seelam,
Robert Walkup,
Seiji Yunoki,
Mario Motta,
Petar Jurcevic,
Hiroshi Horii,
Antonio Mezzacapo
Abstract:
Quantum computers must operate in concert with classical computers to deliver on the promise of quantum advantage for practical problems. To achieve that, it is important to understand how quantum and classical computing can interact together, and how one can characterize the scalability and efficiency of hybrid quantum-classical workflows. So far, early experiments with quantum-centric supercompu…
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Quantum computers must operate in concert with classical computers to deliver on the promise of quantum advantage for practical problems. To achieve that, it is important to understand how quantum and classical computing can interact together, and how one can characterize the scalability and efficiency of hybrid quantum-classical workflows. So far, early experiments with quantum-centric supercomputing workflows have been limited in scale and complexity. Here, we use a Heron quantum processor deployed on premises with the entire supercomputer Fugaku to perform the largest computation of electronic structure involving quantum and classical high-performance computing. We design a closed-loop workflow between the quantum processors and 152,064 classical nodes of Fugaku, to approximate the electronic structure of chemistry models beyond the reach of exact diagonalization, with accuracy comparable to some all-classical approximation methods. Our work pushes the limits of the integration of quantum and classical high-performance computing, showcasing computational resource orchestration at the largest scale possible for current classical supercomputers.
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Submitted 31 October, 2025;
originally announced November 2025.
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Quantum-Centric Algorithm for Sample-Based Krylov Diagonalization
Authors:
Jeffery Yu,
Javier Robledo Moreno,
Joseph T. Iosue,
Luke Bertels,
Daniel Claudino,
Bryce Fuller,
Peter Groszkowski,
Travis S. Humble,
Petar Jurcevic,
William Kirby,
Thomas A. Maier,
Mario Motta,
Bibek Pokharel,
Alireza Seif,
Amir Shehata,
Kevin J. Sung,
Minh C. Tran,
Vinay Tripathi,
Antonio Mezzacapo,
Kunal Sharma
Abstract:
Approximating the ground state of many-body systems is a key computational bottleneck underlying important applications in physics and chemistry. The most widely known quantum algorithm for ground state approximation, quantum phase estimation, is out of reach of current quantum processors due to its high circuit-depths. Subspace-based quantum diagonalization methods offer a viable alternative for…
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Approximating the ground state of many-body systems is a key computational bottleneck underlying important applications in physics and chemistry. The most widely known quantum algorithm for ground state approximation, quantum phase estimation, is out of reach of current quantum processors due to its high circuit-depths. Subspace-based quantum diagonalization methods offer a viable alternative for pre- and early-fault-tolerant quantum computers. Here, we introduce a quantum diagonalization algorithm which combines two key ideas on quantum subspaces: a classical diagonalization based on quantum samples, and subspaces constructed with quantum Krylov states. We prove that our algorithm converges in polynomial time under the working assumptions of Krylov quantum diagonalization and sparseness of the ground state. We then demonstrate the scalability of our approach by performing the largest ground-state quantum simulation of impurity models using a Heron quantum processors and the Frontier supercomputer. We consider both the single-impurity Anderson model with 41 bath sites, and a system with 4 impurities and 7 bath sites per impurity. Our results are in excellent agreement with Density Matrix Renormalization Group calculations.
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Submitted 17 September, 2025; v1 submitted 16 January, 2025;
originally announced January 2025.
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Maximum limit of connectivity in rectangular superconducting films with an oblique weak link
Authors:
F. Colauto,
D. Carmo,
A. M. H. de Andrade,
A. A. M. Oliveira,
M. Motta,
W. A. Ortiz
Abstract:
A method for measuring the electrical connectivity between parts of a rectangular superconductor was developed for weak links making an arbitrary angle with the long side of the sample. The method is based on magneto-optical observation of characteristic lines where the critical current makes discontinuous deviations in the flow direction to adapt to the non-uniform condition created by the presen…
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A method for measuring the electrical connectivity between parts of a rectangular superconductor was developed for weak links making an arbitrary angle with the long side of the sample. The method is based on magneto-optical observation of characteristic lines where the critical current makes discontinuous deviations in the flow direction to adapt to the non-uniform condition created by the presence of the weak link. Assuming the Bean critical state model in the full penetration regime for a sample submitted to a perpendicular magnetic field, the complete flow pattern of screening currents is reconstructed, from which the transparency of the weak link, i.e., the ratio between its critical current and that of the pristine sample, $τ= \frac{J_i}{J_c}$, is then related to the angle $θ$ formed by two characteristic discontinuity lines which, in turn, are intimately associated to the presence of the weak link. The streamline distribution is compared with magneto-optical observations of the flux penetration in Nb superconducting films, where a weak link was created using focused ion beam milling. The present work generalizes previous analyses in which the weak link was perpendicular to the long sides of the rectangular sample. Equations and measurements demonstrate that the relationship between the transparency and the angle $θ$ is not affected by the tilting of the weak link. Noticeably, in order to attain optimum connectivity, the weak link critical current can be less than that of the pristine sample, namely, $τ_{max}=\sin Φ$, where $Φ$ is the tilt angle of the weak link. This expression generalizes the previous result of $τ_{max}=1$ for $Φ=$ 90$^\circ$.
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Submitted 13 November, 2024;
originally announced November 2024.
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Quantum-centric computation of molecular excited states with extended sample-based quantum diagonalization
Authors:
Stefano Barison,
Javier Robledo Moreno,
Mario Motta
Abstract:
The simulation of molecular electronic structure is an important application of quantum devices. Recently, it has been shown that quantum devices can be effectively combined with classical supercomputing centers in the context of the sample-based quantum diagonalization (SQD) algorithm. This allowed the largest electronic structure quantum simulation to date (77 qubits) and opened near-term device…
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The simulation of molecular electronic structure is an important application of quantum devices. Recently, it has been shown that quantum devices can be effectively combined with classical supercomputing centers in the context of the sample-based quantum diagonalization (SQD) algorithm. This allowed the largest electronic structure quantum simulation to date (77 qubits) and opened near-term devices to practical use cases in chemistry toward the hundred-qubit mark. However, the description of many important physical and chemical properties of those systems, such as photo-absorption/-emission, requires a treatment that goes beyond the ground state alone. In this work, we extend the SQD algorithm to determine low-lying molecular excited states. The extended-SQD method improves over the original SQD method in accuracy, at the cost of an additional computational step. It also improves over quantum subspace expansion based on single and double electronic excitations, a widespread approach to excited states on pre-fault-tolerant quantum devices, in both accuracy and efficiency. We employ the extended SQD method to compute the first singlet (S$_1$) and triplet (T$_1$) excited states of the nitrogen molecule with a correlation-consistent basis set, and the ground- and excited-state properties of the [2Fe-2S] cluster.
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Submitted 1 November, 2024;
originally announced November 2024.
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Chemistry Beyond the Scale of Exact Diagonalization on a Quantum-Centric Supercomputer
Authors:
Javier Robledo-Moreno,
Mario Motta,
Holger Haas,
Ali Javadi-Abhari,
Petar Jurcevic,
William Kirby,
Simon Martiel,
Kunal Sharma,
Sandeep Sharma,
Tomonori Shirakawa,
Iskandar Sitdikov,
Rong-Yang Sun,
Kevin J. Sung,
Maika Takita,
Minh C. Tran,
Seiji Yunoki,
Antonio Mezzacapo
Abstract:
A universal quantum computer can simulate diverse quantum systems, with electronic structure for chemistry offering challenging problems for practical use cases around the hundred-qubit mark. While current quantum processors have reached this size, deep circuits and large number of measurements lead to prohibitive runtimes for quantum computers in isolation. Here, we demonstrate the use of classic…
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A universal quantum computer can simulate diverse quantum systems, with electronic structure for chemistry offering challenging problems for practical use cases around the hundred-qubit mark. While current quantum processors have reached this size, deep circuits and large number of measurements lead to prohibitive runtimes for quantum computers in isolation. Here, we demonstrate the use of classical distributed computing to offload all but an intrinsically quantum component of a workflow for electronic structure simulations. Using a Heron superconducting processor and the supercomputer Fugaku, we simulate the ground-state dissociation of N$_2$ and the [2Fe-2S] and [4Fe-4S] clusters, with circuits up to 77 qubits and 10,570 gates. The proposed algorithm processes quantum samples to produce upper bounds for the ground-state energy and sparse approximations to the ground-state wavefunctions. Our results suggest that, for current error rates, a quantum-centric supercomputing architecture can tackle challenging chemistry problems beyond sizes amenable to exact diagonalization.
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Submitted 13 July, 2025; v1 submitted 8 May, 2024;
originally announced May 2024.
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Distinguishing homolytic versus heterolytic bond dissociation of phenyl sulfonium cations with localized active space methods
Authors:
Qiaohong Wang,
Valay Agarawal,
Matthew R. Hermes,
Mario Motta,
Julia E. Rice,
Gavin O. Jones,
Laura Gagliardi
Abstract:
Modeling chemical reactions with quantum chemical methods is challenging when the electronic structure varies significantly throughout the reaction, as well as when electronic excited states are involved. Multireference methods such as complete active space self-consistent field (CASSCF) can handle these multiconfigurational situations. However, even if the size of needed active space is affordabl…
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Modeling chemical reactions with quantum chemical methods is challenging when the electronic structure varies significantly throughout the reaction, as well as when electronic excited states are involved. Multireference methods such as complete active space self-consistent field (CASSCF) can handle these multiconfigurational situations. However, even if the size of needed active space is affordable, in many cases the active space does not change consistently from reactant to product, causing discontinuities in the potential energy surface. The localized active space SCF (LASSCF) is a cheaper alternative to CASSCF for strongly correlated systems with weakly correlated fragments. The method is used for the first time to study a chemical reaction, namely the bond dissociation of a mono-, di-, and triphenylsulfonium cation. LASSCF calculations generate smooth potential energy scans more easily than the corresponding, more computationally expensive, CASSCF calculations, while predicting similar bond dissociation energies. Our calculations suggest a homolytic bond cleavage for di- and triphenylsulfonium, and a heterolytic pathway for monophenylsulfonium.
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Submitted 22 April, 2024;
originally announced April 2024.
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Quantum-centric Supercomputing for Materials Science: A Perspective on Challenges and Future Directions
Authors:
Yuri Alexeev,
Maximilian Amsler,
Paul Baity,
Marco Antonio Barroca,
Sanzio Bassini,
Torey Battelle,
Daan Camps,
David Casanova,
Young Jai Choi,
Frederic T. Chong,
Charles Chung,
Chris Codella,
Antonio D. Corcoles,
James Cruise,
Alberto Di Meglio,
Jonathan Dubois,
Ivan Duran,
Thomas Eckl,
Sophia Economou,
Stephan Eidenbenz,
Bruce Elmegreen,
Clyde Fare,
Ismael Faro,
Cristina Sanz Fernández,
Rodrigo Neumann Barros Ferreira
, et al. (102 additional authors not shown)
Abstract:
Computational models are an essential tool for the design, characterization, and discovery of novel materials. Hard computational tasks in materials science stretch the limits of existing high-performance supercomputing centers, consuming much of their simulation, analysis, and data resources. Quantum computing, on the other hand, is an emerging technology with the potential to accelerate many of…
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Computational models are an essential tool for the design, characterization, and discovery of novel materials. Hard computational tasks in materials science stretch the limits of existing high-performance supercomputing centers, consuming much of their simulation, analysis, and data resources. Quantum computing, on the other hand, is an emerging technology with the potential to accelerate many of the computational tasks needed for materials science. In order to do that, the quantum technology must interact with conventional high-performance computing in several ways: approximate results validation, identification of hard problems, and synergies in quantum-centric supercomputing. In this paper, we provide a perspective on how quantum-centric supercomputing can help address critical computational problems in materials science, the challenges to face in order to solve representative use cases, and new suggested directions.
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Submitted 19 September, 2024; v1 submitted 14 December, 2023;
originally announced December 2023.
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Quantum algorithm for imaginary-time Green's functions
Authors:
Diksha Dhawan,
Dominika Zgid,
Mario Motta
Abstract:
Green's function methods lead to ab initio, systematically improvable simulations of molecules and materials while providing access to multiple experimentally observable properties such as the density of states and the spectral function. The calculation of the exact one-particle Green's function remains a significant challenge for classical computers and was attempted only on very small systems. H…
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Green's function methods lead to ab initio, systematically improvable simulations of molecules and materials while providing access to multiple experimentally observable properties such as the density of states and the spectral function. The calculation of the exact one-particle Green's function remains a significant challenge for classical computers and was attempted only on very small systems. Here, we present a hybrid quantum-classical algorithm to calculate the imaginary-time one-particle Green's function. The proposed algorithm combines variational quantum eigensolver and quantum subspace expansion to calculate Green's function in Lehmann's representation. We demonstrate the validity of this algorithm by simulating H$_2$ and H$_4$ on quantum simulators and on IBM's quantum devices.
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Submitted 18 September, 2023;
originally announced September 2023.
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Using quantitative magneto-optical imaging to reveal why the ac susceptibility of superconducting films is history-independent
Authors:
Davi A. D. Chaves,
J. C. Corsaletti Filho,
E. A. Abbey,
D. Bosworth,
Z. H. Barber,
M. G. Blamire,
T. H. Johansen,
A. V. Silhanek,
W. A. Ortiz,
M. Motta
Abstract:
Measurements of the temperature-dependent ac magnetic susceptibility of superconducting films reveal reversible responses, i.e., irrespective of the magnetic and thermal history of the sample. This experimental fact is observed even in the presence of stochastic and certainly irreversible magnetic flux avalanches which, in principle, should randomly affect the results. In this work, we explain suc…
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Measurements of the temperature-dependent ac magnetic susceptibility of superconducting films reveal reversible responses, i.e., irrespective of the magnetic and thermal history of the sample. This experimental fact is observed even in the presence of stochastic and certainly irreversible magnetic flux avalanches which, in principle, should randomly affect the results. In this work, we explain such an apparent contradiction by exploring the spatial resolution of magneto-optical imaging. To achieve this, we successfully compare standard frequency-independent first harmonic ac magnetic susceptibility results for a superconducting thin film with those obtained by ac-emulating magneto-optical imaging (acMOI). A quantitative analysis also provides information regarding flux avalanches, reveals the presence of a vortex-antivortex annihilation zone in the region in which a smooth flux front interacts with pre-established avalanches, and demonstrates that the major impact on the flux distribution within the superconductor happens during the first ac cycle. Our results establish acMOI as a reliable approach for studying frequency-independent ac field effects in superconducting thin films while capturing local aspects of flux dynamics, otherwise inaccessible via global magnetometry techniques.
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Submitted 14 September, 2023;
originally announced September 2023.
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Magnetic field-induced weak-to-strong-link transformation in patterned superconducting films
Authors:
D. A. D. Chaves,
M. I. Valerio-Cuadros,
L. Jiang,
E. A. Abbey,
F. Colauto,
A. A. M. Oliveira,
A. M. H. Andrade,
L. B. L. G. Pinheiro,
T. H. Johansen,
C. Xue,
Y. -H. Zhou,
A. V. Silhanek,
W. A. Ortiz,
M. Motta
Abstract:
Ubiquitous in most superconducting materials and a common result of nanofabrication processes, weak-links are known for their limiting effects on the transport of electric currents. Still, they are at the root of key features of superconducting technology. By performing quantitative magneto-optical imaging experiments and thermomagnetic model simulations, we correlate the existence of local maxima…
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Ubiquitous in most superconducting materials and a common result of nanofabrication processes, weak-links are known for their limiting effects on the transport of electric currents. Still, they are at the root of key features of superconducting technology. By performing quantitative magneto-optical imaging experiments and thermomagnetic model simulations, we correlate the existence of local maxima in the magnetization loops of FIB-patterned Nb films to a magnetic field-induced weak-to-strong-link transformation increasing their critical current. This phenomenon arises from the nanoscale interaction between quantized magnetic flux lines and FIB-induced modifications of the device microstructure. Under an ac drive field, this leads to a rectified vortex motion along the weak-link. The reported tunable effect can be exploited in the development of new superconducting electronic devices, such as flux pumps and valves, to attenuate or amplify the supercurrent through a circuit element, and as a strategy to enhance the critical current in weak-link-bearing devices.
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Submitted 9 October, 2023; v1 submitted 7 May, 2023;
originally announced May 2023.
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High-fidelity dimer excitations using quantum hardware
Authors:
Norhan M. Eassa,
Joe Gibbs,
Zoe Holmes,
Andrew Sornborger,
Lukasz Cincio,
Gavin Hester,
Paul Kairys,
Mario Motta,
Jeffrey Cohn,
Arnab Banerjee
Abstract:
Many-body entangled quantum spin systems exhibit emergent phenomena such as topological quantum spin liquids with distinct excitation spectra accessed in inelastic neutron scattering (INS) experiments. Here we simulate the dynamics of a quantum spin dimer, the basic quantum unit of emergent many-body spin systems. While canonical Trotterization methods require deep circuits precluding long time-sc…
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Many-body entangled quantum spin systems exhibit emergent phenomena such as topological quantum spin liquids with distinct excitation spectra accessed in inelastic neutron scattering (INS) experiments. Here we simulate the dynamics of a quantum spin dimer, the basic quantum unit of emergent many-body spin systems. While canonical Trotterization methods require deep circuits precluding long time-scale simulations, we demonstrate 'direct' Resource-Efficient Fast-forwarding (REFF) measurements with short-depth circuits that can be used to capture longer time dynamics on quantum hardware. The temporal evolution of the 2-spin correlation coefficients enabled the calculation of the dynamical structure factor $S(\mathbf{Q},ω)$ - the key component of the neutron scattering cross-section. We simulate the triplet gap and the triplet splitting of the quantum dimer with sufficient fidelity to compare to experimental neutron data. Our results on current circuit hardware pave an important avenue to benchmark, or even predict, the outputs of the costly INS experiments.
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Submitted 12 April, 2023;
originally announced April 2023.
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Enhancing the Expressivity of Variational Neural, and Hardware-Efficient Quantum States Through Orbital Rotations
Authors:
Javier Robledo Moreno,
Jeffrey Cohn,
Dries Sels,
Mario Motta
Abstract:
Variational approaches, such as variational Monte Carlo (VMC) or the variational quantum eigensolver (VQE), are powerful techniques to tackle the ground-state many-electron problem. Often, the family of variational states is not invariant under the reparametrization of the Hamiltonian by single-particle basis transformations. As a consequence, the representability of the ground-state wave function…
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Variational approaches, such as variational Monte Carlo (VMC) or the variational quantum eigensolver (VQE), are powerful techniques to tackle the ground-state many-electron problem. Often, the family of variational states is not invariant under the reparametrization of the Hamiltonian by single-particle basis transformations. As a consequence, the representability of the ground-state wave function by the variational ansatz strongly dependents on the choice of the single-particle basis. In this manuscript we study the joint optimization of the single-particle basis, together with the variational state in the VMC (with neural quantum states) and VQE (with hardware-efficient circuits) approaches. We show that the joint optimization of the single-particle basis with the variational state parameters yields significant improvements in the expressive power and optimization landscape in a variety of chemistry and condensed matter systems. We also realize the first active-space calculation using neural quantum states, where the single-particle basis transformations are applied to all of the orbitals in the basis set.
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Submitted 9 October, 2023; v1 submitted 22 February, 2023;
originally announced February 2023.
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Hierarchical Clifford transformations to reduce entanglement in quantum chemistry wavefunctions
Authors:
Ryan V. Mishmash,
Tanvi P. Gujarati,
Mario Motta,
Huanchen Zhai,
Garnet Kin-Lic Chan,
Antonio Mezzacapo
Abstract:
The performance of computational methods for many-body physics and chemistry is strongly dependent on the choice of basis used to cast the problem; hence, the search for better bases and similarity transformations is important for progress in the field. So far, tools from theoretical quantum information have been not thoroughly explored for this task. Here we take a step in this direction by prese…
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The performance of computational methods for many-body physics and chemistry is strongly dependent on the choice of basis used to cast the problem; hence, the search for better bases and similarity transformations is important for progress in the field. So far, tools from theoretical quantum information have been not thoroughly explored for this task. Here we take a step in this direction by presenting efficiently computable Clifford similarity transformations for quantum chemistry Hamiltonians, which expose bases with reduced entanglement in the corresponding molecular ground states. These transformations are constructed via block diagonalization of a hierarchy of truncated molecular Hamiltonians, preserving the full spectrum of the original problem. We show that the bases introduced here allow for more efficient classical and quantum computation of ground state properties. First, we find a systematic reduction of bipartite entanglement in molecular ground states as compared to standard problem representations. This entanglement reduction has implications in classical numerical methods such as ones based on the density matrix renormalization group. Then, we develop variational quantum algorithms that exploit the structure in the new bases, showing again improved results when the hierarchical Clifford transformations are used.
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Submitted 18 January, 2023;
originally announced January 2023.
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Nanobridge SQUIDs as multilevel memory elements
Authors:
Davi A. D. Chaves,
Lukas Nulens,
Heleen Dausy,
Bart Raes,
Donghua Yue,
Wilson A. Ortiz,
Maycon Motta,
Margriet J. Van Bael,
Joris Van de Vondel
Abstract:
With the development of novel computing schemes working at cryogenic temperatures, superconducting memory elements have become essential. In this context, superconducting quantum interference devices (SQUIDs) are promising candidates, as they may trap different discrete amounts of magnetic flux. We demonstrate that a field-assisted writing scheme allows such a device to operate as a multilevel mem…
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With the development of novel computing schemes working at cryogenic temperatures, superconducting memory elements have become essential. In this context, superconducting quantum interference devices (SQUIDs) are promising candidates, as they may trap different discrete amounts of magnetic flux. We demonstrate that a field-assisted writing scheme allows such a device to operate as a multilevel memory by the readout of eight distinct vorticity states at zero magnetic field. We present an alternative mechanism based on single phase slips which allows to switch the vorticity state while preserving superconductivity. This mechanism provides a possibly deterministic channel for flux control in SQUID-based memories, under the condition that the field-dependent energy of different vorticity states are nearby.
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Submitted 15 November, 2022;
originally announced November 2022.
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Magnetic flux penetration in nanoscale wedge-shaped superconducting thin films
Authors:
L. B. L. G. Pinheiro,
L. Jiang,
E. A. Abbey,
Davi A. D. Chaves,
A. J. Chiquito,
T. H. Johansen,
J. Van de Vondel,
C. Xue,
Y. -H. Zhou,
A. V. Silhanek,
W. A. Ortiz,
M. Motta
Abstract:
Thickness uniformity is regarded as an important parameter in designing thin film devices. However, some applications based on films with non-uniform thickness have recently emerged, such as gas sensors and optimized materials based on the gradual change of film composition. This work deals with superconducting Pb thin films with a thickness gradient prepared with the aid of a diffuse stencil mask…
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Thickness uniformity is regarded as an important parameter in designing thin film devices. However, some applications based on films with non-uniform thickness have recently emerged, such as gas sensors and optimized materials based on the gradual change of film composition. This work deals with superconducting Pb thin films with a thickness gradient prepared with the aid of a diffuse stencil mask. Atomic Force Microscopy and Energy-Dispersive X-ray Spectroscopy show variations ranging from 90~nm to 154~nm. Quantitative magneto-optical images reveal interesting features during both the abrupt and the smooth penetration regimes of magnetic flux, as well as the thickness-dependent critical current density ($J_c$). In addition, we observe a gradual superconducting transition as the upper critical field is progressively reached for certain thicknesses. Furthermore, the hysteresis observed for triggering flux avalanches when increasing and decreasing magnetic fields is also accounted for by the $J_c$ profile evolution along the thickness gradient. Numerical simulations based on the Thermomagnetic Model are in fair agreement with the experimental data. These findings demonstrate that wedge-shaped films are a viable approach to investigate, in a continuous fashion, thickness-dependent properties of a superconducting materials.
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Submitted 18 October, 2022;
originally announced October 2022.
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Quantum-enhanced Markov chain Monte Carlo
Authors:
David Layden,
Guglielmo Mazzola,
Ryan V. Mishmash,
Mario Motta,
Pawel Wocjan,
Jin-Sung Kim,
Sarah Sheldon
Abstract:
Sampling from complicated probability distributions is a hard computational problem arising in many fields, including statistical physics, optimization, and machine learning. Quantum computers have recently been used to sample from complicated distributions that are hard to sample from classically, but which seldom arise in applications. Here we introduce a quantum algorithm to sample from distrib…
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Sampling from complicated probability distributions is a hard computational problem arising in many fields, including statistical physics, optimization, and machine learning. Quantum computers have recently been used to sample from complicated distributions that are hard to sample from classically, but which seldom arise in applications. Here we introduce a quantum algorithm to sample from distributions that pose a bottleneck in several applications, which we implement on a superconducting quantum processor. The algorithm performs Markov chain Monte Carlo (MCMC), a popular iterative sampling technique, to sample from the Boltzmann distribution of classical Ising models. In each step, the quantum processor explores the model in superposition to propose a random move, which is then accepted or rejected by a classical computer and returned to the quantum processor, ensuring convergence to the desired Boltzmann distribution. We find that this quantum algorithm converges in fewer iterations than common classical MCMC alternatives on relevant problem instances, both in simulations and experiments. It therefore opens a new path for quantum computers to solve useful--not merely difficult--problems in the near term.
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Submitted 23 March, 2022;
originally announced March 2022.
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Influence of pinning centers of different natures onsurrounding vortices
Authors:
Rodolfo Carvalho dos Santos,
Elwis Carlos Sartorelli Duarte,
Danilo Okimoto,
Alice Presotto,
Edson Sardella,
Maycon Motta,
Rafael Zadorosny
Abstract:
Studies involving vortex dynamics and their interaction with pinning centers are an important ingredient to reach higher critical currents in superconducting materials. The vortex distribution around arrays of engineered defects, such as blind and through holes, may help to improve the superconducting properties. Thus, in this work, we used the time-dependent Ginzburg-Landau theory to investigate…
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Studies involving vortex dynamics and their interaction with pinning centers are an important ingredient to reach higher critical currents in superconducting materials. The vortex distribution around arrays of engineered defects, such as blind and through holes, may help to improve the superconducting properties. Thus, in this work, we used the time-dependent Ginzburg-Landau theory to investigate the vortex dynamics in superconductors of mesoscopic dimensions with a large central square defect with three different configurations: (i) a hole which passes through the sample (interface with the vacuum); (ii) a superconducting region with lower critical temperature (Tc); and (iii) a region with a more robust superconductivity, i.e., with a higherTc. Such systems can be envisaged as elementary building blocks of a macroscopic decorated specimen. Therefore, we evaluated the influence of different interfaces on the vortex dynamics and their effects in the field-dependent magnetization and time-dependent induced electric potential variation. The results show that the lower critical field is independent from the nature of the defect. However, the currents crowd at the vertices of the through hole producing a lower degradation of the local superconductivity, which may increase the upper critical field. On the other hand, the last type of defect can be used to control the vortex dynamics in the main superconducting region around the defect with more accuracy. Whereas the first two defects are attractive for the vortices, the third type is repulsive for them, being needed several vortices penetrated in the superconducting matrix to have vortices penetrated into it.
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Submitted 27 January, 2022;
originally announced January 2022.
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Enhancing the effective critical current density in a Nb superconducting thin film by cooling in an inhomogeneous magnetic field
Authors:
D. A. D. Chaves,
I. M. de Araújo,
D. Carmo,
F. Colauto,
A. A. M. de Oliveira,
A. M. H. de Andrade,
T. H. Johansen,
A. V. Silhanek,
W. A. Ortiz,
M. Motta
Abstract:
Quantitative magneto-optical imaging of a type-II superconductor thin film cooled under zero, homogeneous, and inhomogeneous applied magnetic fields, indicates that the latter procedure leads to an enhancement of the screening capacity. Such an observation is corroborated by both B-independent and B-dependent critical state model analyses. Furthermore, repulsive (attractive) vortex-(anti)vortex in…
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Quantitative magneto-optical imaging of a type-II superconductor thin film cooled under zero, homogeneous, and inhomogeneous applied magnetic fields, indicates that the latter procedure leads to an enhancement of the screening capacity. Such an observation is corroborated by both B-independent and B-dependent critical state model analyses. Furthermore, repulsive (attractive) vortex-(anti)vortex interactions were found to have a decisive role in the shielding ability, with initial states prepared with vortices resulting in a shorter magnetic flux front penetration depth than those prepared with antivortices. The proposed strategy could be implemented to boost the performance of thin superconducting devices.
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Submitted 3 June, 2021;
originally announced June 2021.
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Ab initio electronic density in solids by many-body plane-wave auxiliary-field quantum Monte Carlo calculations
Authors:
Siyuan Chen,
Mario Motta,
Fengjie Ma,
Shiwei Zhang
Abstract:
We present accurate many-body results of the electronic densities in several solid materials, including Si, NaCl, and Cu. These results are obtained using the ab initio auxiliary-field quantum Monte Carlo (AFQMC) method working in a plane-wave basis with norm-conserving, multiple-projector pseudopotentials. AFQMC has been shown to be an excellent many-body total energy method. Computation of obser…
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We present accurate many-body results of the electronic densities in several solid materials, including Si, NaCl, and Cu. These results are obtained using the ab initio auxiliary-field quantum Monte Carlo (AFQMC) method working in a plane-wave basis with norm-conserving, multiple-projector pseudopotentials. AFQMC has been shown to be an excellent many-body total energy method. Computation of observables and correlation functions other than the ground-state energy requires back-propagation, whose adaption and implementation in the plane-wave basis AFQMC framework are discussed in the present paper. This development allows us to compute correlation functions, electronic densities and interatomic forces, paving the way for geometry optimizations and calculations of thermodynamic properties in solids. Finite supercell size effects are considerably more subtle in the many-body framework than in independent-electron calculations. We analyze the convergence of the electronic density, and obtain best estimates for the thermodynamic limit. The densities from several typical density functionals are benchmarked against our near-exact results. The electronic densities we have obtained can also be used to help construct improved density functionals.
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Submitted 22 February, 2021; v1 submitted 16 November, 2020;
originally announced November 2020.
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Optimum heat treatment to enhance the weak-linkresponse of Y123 nanowires prepared by SolutionBlow Spinning
Authors:
Ana M. Caffer,
Davi A. D. Chaves,
Alexsander L. Pessoa,
Claudio L. Carvalho,
Wilson A. Ortiz,
Rafael Zadorosny,
Maycon Motta
Abstract:
Although the production of YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (Y123) has been extensively reported, there is still a lack of information on the ideal heat treatment to produce this material in the form of one dimension nanostructures. Thus, by means of the Solution Blow Spinning technique, metals embedded in polymer fibers were prepared. These polymer composite fibers were fired and then investigated by t…
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Although the production of YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (Y123) has been extensively reported, there is still a lack of information on the ideal heat treatment to produce this material in the form of one dimension nanostructures. Thus, by means of the Solution Blow Spinning technique, metals embedded in polymer fibers were prepared. These polymer composite fibers were fired and then investigated by thermogravimetric analysis. The maximum sintering temperatures of heat treatment were chosen in the interval \SI{850}{\celsius}-\SI{925}{\celsius} for one hour under oxygen flux. SEM images allowed us to determine the wire diameter as approximately 350~nm for all samples, as well as to map the evolution of the entangled wire morphology with the sintering temperature. XRD analysis indicated the presence of Y123 and secondary phases in all samples. Ac magnetic susceptibility and dc magnetization measurements demonstrated that the sample sintered at \SI{925}{\celsius}/1h is the one with the highest weak-link critical temperature and the largest diamagnetic response.
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Submitted 6 October, 2020;
originally announced October 2020.
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Quantum algorithms for quantum chemistry and quantum materials science
Authors:
Bela Bauer,
Sergey Bravyi,
Mario Motta,
Garnet Kin-Lic Chan
Abstract:
As we begin to reach the limits of classical computing, quantum computing has emerged as a technology that has captured the imagination of the scientific world. While for many years, the ability to execute quantum algorithms was only a theoretical possibility, recent advances in hardware mean that quantum computing devices now exist that can carry out quantum computation on a limited scale. Thus i…
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As we begin to reach the limits of classical computing, quantum computing has emerged as a technology that has captured the imagination of the scientific world. While for many years, the ability to execute quantum algorithms was only a theoretical possibility, recent advances in hardware mean that quantum computing devices now exist that can carry out quantum computation on a limited scale. Thus it is now a real possibility, and of central importance at this time, to assess the potential impact of quantum computers on real problems of interest. One of the earliest and most compelling applications for quantum computers is Feynman's idea of simulating quantum systems with many degrees of freedom. Such systems are found across chemistry, physics, and materials science. The particular way in which quantum computing extends classical computing means that one cannot expect arbitrary simulations to be sped up by a quantum computer, thus one must carefully identify areas where quantum advantage may be achieved. In this review, we briefly describe central problems in chemistry and materials science, in areas of electronic structure, quantum statistical mechanics, and quantum dynamics, that are of potential interest for solution on a quantum computer. We then take a detailed snapshot of current progress in quantum algorithms for ground-state, dynamics, and thermal state simulation, and analyze their strengths and weaknesses for future developments.
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Submitted 10 July, 2020; v1 submitted 10 January, 2020;
originally announced January 2020.
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Ground-state properties of the hydrogen chain: insulator-to-metal transition, dimerization, and magnetic phases
Authors:
Mario Motta,
Claudio Genovese,
Fengjie Ma,
Zhi-Hao Cui,
Randy Sawaya,
Garnet Kin-Lic Chan,
Natalia Chepiga,
Phillip Helms,
Carlos Jimenez-Hoyos,
Andrew J. Millis,
Ushnish Ray,
Enrico Ronca,
Hao Shi,
Sandro Sorella,
Edwin M. Stoudenmire,
Steven R. White,
Shiwei Zhang
Abstract:
Accurate and predictive computations of the quantum-mechanical behavior of many interacting electrons in realistic atomic environments are critical for the theoretical design of materials with desired properties, and require solving the grand-challenge problem of the many-electron Schrodinger equation. An infinite chain of equispaced hydrogen atoms is perhaps the simplest realistic model for a bul…
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Accurate and predictive computations of the quantum-mechanical behavior of many interacting electrons in realistic atomic environments are critical for the theoretical design of materials with desired properties, and require solving the grand-challenge problem of the many-electron Schrodinger equation. An infinite chain of equispaced hydrogen atoms is perhaps the simplest realistic model for a bulk material, embodying several central themes of modern condensed matter physics and chemistry, while retaining a connection to the paradigmatic Hubbard model. Here we report a combined application of cutting-edge computational methods to determine the properties of the hydrogen chain in its quantum-mechanical ground state. Varying the separation between the nuclei leads to a rich phase diagram, including a Mott phase with quasi long-range antiferromagnetic order, electron density dimerization with power-law correlations, an insulator-to-metal transition and an intricate set of intertwined magnetic orders.
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Submitted 13 July, 2020; v1 submitted 4 November, 2019;
originally announced November 2019.
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Electronic structure of bulk manganese oxide and nickel oxide from coupled cluster theory
Authors:
Yang Gao,
Qiming Sun,
Jason M. Yu,
Mario Motta,
James McClain,
Alec F. White,
Austin J. Minnich,
Garnet Kin-Lic Chan
Abstract:
We describe the ground- and excited-state electronic structure of bulk MnO and NiO, two prototypical correlated electron materials, using coupled cluster theory with single and double excitations (CCSD). As a corollary, this work also reports the first implementation of unrestricted periodic ab initio equation-of motion CCSD. Starting from a Hartree-Fock reference, we find fundamental gaps of 3.46…
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We describe the ground- and excited-state electronic structure of bulk MnO and NiO, two prototypical correlated electron materials, using coupled cluster theory with single and double excitations (CCSD). As a corollary, this work also reports the first implementation of unrestricted periodic ab initio equation-of motion CCSD. Starting from a Hartree-Fock reference, we find fundamental gaps of 3.46 eV and 4.83 eV for MnO and NiO respectively for the 16 unit supercell, slightly overestimated compared to experiment, although finite-size scaling suggests that the gap is more severely overestimated in the thermodynamic limit. From the character of the correlated electronic bands we find both MnO and NiO to lie in the intermediate Mott/charge-transfer insulator regime, although NiO appears as a charge transfer insulator when only the fundamental gap is considered. While the lowest quasiparticle excitations are of metal 3d and O 2p character in most of the Brillouin zone, near the Γ point, the lowest conduction band quasiparticles are of s character. Our study supports the potential of coupled cluster theory to provide high level many-body insights into correlated solids.
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Submitted 8 October, 2019; v1 submitted 4 October, 2019;
originally announced October 2019.
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Direct comparison of many-body methods for realistic electronic Hamiltonians
Authors:
Kiel T. Williams,
Yuan Yao,
Jia Li,
Li Chen,
Hao Shi,
Mario Motta,
Chunyao Niu,
Ushnish Ray,
Sheng Guo,
Robert J. Anderson,
Junhao Li,
Lan Nguyen Tran,
Chia-Nan Yeh,
Bastien Mussard,
Sandeep Sharma,
Fabien Bruneval,
Mark van Schilfgaarde,
George H. Booth,
Garnet Kin-Lic Chan,
Shiwei Zhang,
Emanuel Gull,
Dominika Zgid,
Andrew Millis,
Cyrus J. Umrigar,
Lucas K. Wagner
Abstract:
A large collaboration carefully benchmarks 20 first principles many-body electronic structure methods on a test set of 7 transition metal atoms, and their ions and monoxides. Good agreement is attained between the 3 systematically converged methods, resulting in experiment-free reference values. These reference values are used to assess the accuracy of modern emerging and scalable approaches to th…
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A large collaboration carefully benchmarks 20 first principles many-body electronic structure methods on a test set of 7 transition metal atoms, and their ions and monoxides. Good agreement is attained between the 3 systematically converged methods, resulting in experiment-free reference values. These reference values are used to assess the accuracy of modern emerging and scalable approaches to the many-electron problem. The most accurate methods obtain energies indistinguishable from experimental results, with the agreement mainly limited by the experimental uncertainties. Comparison between methods enables a unique perspective on calculations of many-body systems of electrons.
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Submitted 5 October, 2019; v1 submitted 30 September, 2019;
originally announced October 2019.
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One-pot synthesis: a simple and fast method to obtain ceramic superconducting materials
Authors:
Maycon Rotta,
Maycon Motta,
Alexsander L Pessoa,
Claudio L Carvalho,
Cesar V Deimling,
Paulo N Lisboa-Filho,
Wilson A Ortiz,
Rafael Zadorosny
Abstract:
The one-pot method focuses on the reduction of the number of steps or chemical reactions in the synthesis of materials, and it is very appealing in terms of sustainability. In addition to this point of view, superconductors are desired materials due to their unusual properties, such as the zero resistivity and the perfect diamagnetism. One-pot, Thus, in this work, we described the one-pot synthesi…
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The one-pot method focuses on the reduction of the number of steps or chemical reactions in the synthesis of materials, and it is very appealing in terms of sustainability. In addition to this point of view, superconductors are desired materials due to their unusual properties, such as the zero resistivity and the perfect diamagnetism. One-pot, Thus, in this work, we described the one-pot synthesis of YBa2Cu3O7-δ superconducting ceramic. In just two steps and a few hours, a polymer composite solution was prepared, which originates a powder after burning the polymer out with pure phase and with superconducting properties better than those produced by other techniques.
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Submitted 26 August, 2019;
originally announced August 2019.
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Quantitative magneto-optical investigation of superconductor/ferromagnet hybrid structures
Authors:
G. Shaw,
J. Brisbois,
L. B. G. L. Pinheiro,
J. Müller,
S. Blanco Alvarez,
T. Devillers,
N. M. Dempsey,
J. E. Scheerder,
J. Van de Vondel,
S. Melinte,
P. Vanderbemden,
M. Motta,
W. A. Ortiz,
K. Hasselbach,
R. B. G. Kramer,
A. V. Silhanek
Abstract:
We present a detailed quantitative magneto-optical imaging study of several superconductor/ferromagnet hybrid structures, including Nb deposited on top of thermomagnetically patterned NdFeB, and permalloy/niobium with erasable and tailored magnetic landscapes imprinted in the permalloy layer. The magneto-optical imaging data is complemented with and compared to scanning Hall probe microscopy measu…
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We present a detailed quantitative magneto-optical imaging study of several superconductor/ferromagnet hybrid structures, including Nb deposited on top of thermomagnetically patterned NdFeB, and permalloy/niobium with erasable and tailored magnetic landscapes imprinted in the permalloy layer. The magneto-optical imaging data is complemented with and compared to scanning Hall probe microscopy measurements. Comprehensive protocols have been developed for calibrating, testing, and converting Faraday rotation data to magnetic field maps. Applied to the acquired data, they reveal the comparatively weaker magnetic response of the superconductor from the background of larger fields and field gradients generated by the magnetic layer.
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Submitted 15 February, 2018; v1 submitted 11 December, 2017;
originally announced December 2017.
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Computation of ground-state properties in molecular systems: back-propagation with auxiliary-field quantum Monte Carlo
Authors:
Mario Motta,
Shiwei Zhang
Abstract:
We address the computation of ground-state properties of chemical systems and realistic materials within the auxiliary-field quantum Monte Carlo method. The phase constraint to control the fermion phase problem requires the random walks in Slater determinant space to be open-ended with branching. This in turn makes it necessary to use back-propagation (BP) to compute averages and correlation funct…
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We address the computation of ground-state properties of chemical systems and realistic materials within the auxiliary-field quantum Monte Carlo method. The phase constraint to control the fermion phase problem requires the random walks in Slater determinant space to be open-ended with branching. This in turn makes it necessary to use back-propagation (BP) to compute averages and correlation functions of operators that do not commute with the Hamiltonian. Several BP schemes are investigated and their optimization with respect to the phaseless constraint is considered. We propose a modified BP method for the computation of observables in electronic systems, discuss its numerical stability and computational complexity, and assess its performance by computing ground-state properties for several substances, including constituents of the primordial terrestrial atmosphere and small organic molecules.
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Submitted 9 July, 2017;
originally announced July 2017.
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Dynamical structure factor of one-dimensional hard rods
Authors:
M. Motta,
E. Vitali,
M. Rossi,
D. E. Galli,
G. Bertaina
Abstract:
The zero-temperature dynamical structure factor $S(q,ω)$ of one-dimensional hard rods is computed using state-of-the-art quantum Monte Carlo and analytic continuation techniques, complemented by a Bethe Ansatz analysis. As the density increases, $S(q,ω)$ reveals a crossover from the Tonks-Girardeau gas to a quasi-solid regime, along which the low-energy properties are found in agreement with the n…
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The zero-temperature dynamical structure factor $S(q,ω)$ of one-dimensional hard rods is computed using state-of-the-art quantum Monte Carlo and analytic continuation techniques, complemented by a Bethe Ansatz analysis. As the density increases, $S(q,ω)$ reveals a crossover from the Tonks-Girardeau gas to a quasi-solid regime, along which the low-energy properties are found in agreement with the nonlinear Luttinger liquid theory. Our quantitative estimate of $S(q,ω)$ extends beyond the low-energy limit and confirms a theoretical prediction regarding the behavior of $S(q,ω)$ at specific wavevectors $\mathcal{Q}_n=n 2 π/a$, where $a$ is the core radius, resulting from the interplay of the particle-hole boundaries of suitably rescaled ideal Fermi gases. We observe significant similarities between hard rods and one-dimensional $^4$He at high density, suggesting that the hard-rods model may provide an accurate description of dense one-dimensional liquids of quantum particles interacting through a strongly repulsive, finite-range potential.
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Submitted 27 August, 2016;
originally announced August 2016.
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Linear response of one-dimensional liquid $^4$He to external perturbations
Authors:
M. Motta,
G. Bertaina,
E. Vitali,
D. E. Galli,
M. Rossi
Abstract:
We study the response of one-dimensional liquid $^4$He to weak perturbations relying on the dynamical structure factor, $S(q,ω)$, recently obtained via ab-initio techniques [Phys. Rev. Lett. 116, 135302 (2016)]. We evaluate the drag force, $F_v$, experienced by an impurity moving along the system with velocity $v$ and the static response function, $χ(q)$, describing the density modulations induced…
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We study the response of one-dimensional liquid $^4$He to weak perturbations relying on the dynamical structure factor, $S(q,ω)$, recently obtained via ab-initio techniques [Phys. Rev. Lett. 116, 135302 (2016)]. We evaluate the drag force, $F_v$, experienced by an impurity moving along the system with velocity $v$ and the static response function, $χ(q)$, describing the density modulations induced by a periodic perturbation with wave vector $q$.
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Submitted 25 November, 2016; v1 submitted 18 July, 2016;
originally announced July 2016.
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Roton excitations and the fluid-solid phase transition in superfluid 2D Yukawa Bosons
Authors:
S. Molinelli,
D. E. Galli,
L. Reatto,
M. Motta
Abstract:
We compute several ground state properties and the dynamical structure factor of a 0-temperature system of Bosons interacting with the 2D screened Coulomb (2D-SC) potential. We resort to the exact shadow path integral ground state (SPIGS) quantum Monte Carlo method to compute the imaginary-time correlation function of the model, and to the genetic algorithm via falsification of theories (GIFT) to…
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We compute several ground state properties and the dynamical structure factor of a 0-temperature system of Bosons interacting with the 2D screened Coulomb (2D-SC) potential. We resort to the exact shadow path integral ground state (SPIGS) quantum Monte Carlo method to compute the imaginary-time correlation function of the model, and to the genetic algorithm via falsification of theories (GIFT) to retrieve the dynamical structure factor. We provide a detailed comparison of ground state properties and collective excitations of 2D-SC and 4He atoms. The roton energy of the 2D-SC system is an increasing function of density, and not a decreasing one as in 4He. This result is in contrast with the view that the roton is the soft mode of the fluid-solid transition. We uncover a remarkable quasi-universality of backflow and of other properties when expressed in terms of the amount of short range order as quantified by the height of the first peak of the static structure factor.
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Submitted 4 May, 2016;
originally announced May 2016.
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Imaginary Time Correlations for a High-Density two-dimensional Electron Gas
Authors:
M. Motta,
D. E. Galli,
S. Moroni,
E. Vitali
Abstract:
We evaluate imaginary time density-density correlation functions for a two-dimensional homogeneous electron gas using the phaseless auxiliary field quantum Monte Carlo method. We show that such methodology, once equipped with suitable numerical stabilization techniques necessary to deal with exponentials, products and inversions of large matrices, gives access to the calculation of imaginary time…
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We evaluate imaginary time density-density correlation functions for a two-dimensional homogeneous electron gas using the phaseless auxiliary field quantum Monte Carlo method. We show that such methodology, once equipped with suitable numerical stabilization techniques necessary to deal with exponentials, products and inversions of large matrices, gives access to the calculation of imaginary time correlation functions for medium-sized systems; we present simulations of a number up to 42 correlated fermions in the continuum, using up to 300 plane waves as basis set elements. We discuss the numerical stabilization techniques and the computational complexity of the methodology. We perform the inverse Laplace transform of the obtained density-density correlation functions, assessing the ability of the phaseless auxiliary field quantum Monte Carlo method to evaluate dynamical properties of many-fermion systems.
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Submitted 28 July, 2015;
originally announced September 2015.
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One-dimensional liquid $^4$He: dynamical properties beyond Luttinger liquid theory
Authors:
G. Bertaina,
M. Motta,
M. Rossi,
E. Vitali,
D. E. Galli
Abstract:
We compute the zero-temperature dynamical structure factor of one-dimensional liquid $^4$He by means of state-of-the-art Quantum Monte Carlo and analytic continuation techniques. By increasing the density, the dynamical structure factor reveals a transition from a highly compressible critical liquid to a quasi-solid regime. In the low-energy limit, the dynamical structure factor can be described b…
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We compute the zero-temperature dynamical structure factor of one-dimensional liquid $^4$He by means of state-of-the-art Quantum Monte Carlo and analytic continuation techniques. By increasing the density, the dynamical structure factor reveals a transition from a highly compressible critical liquid to a quasi-solid regime. In the low-energy limit, the dynamical structure factor can be described by the quantum hydrodynamic Luttinger liquid theory, with a Luttinger parameter spanning all possible values by increasing the density. At higher energies, our approach provides quantitative results beyond the Luttinger liquid theory. In particular, as the density increases, the interplay between dimensionality and interaction makes the dynamical structure factor manifest a pseudo {\it{particle-hole}} continuum typical of fermionic systems. At the low-energy boundary of such region and moderate densities, we find consistency, within statistical uncertainties, with predictions of a power-law structure by the recently-developed non-linear Luttinger liquid theory. In the quasi-solid regime we observe a novel behavior at intermediate momenta, which can be described by new analytical relations that we derive for the hard-rods model.
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Submitted 10 March, 2016; v1 submitted 22 December, 2014;
originally announced December 2014.
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Implementation of the Linear Method for the optimization of Jastrow-Feenberg and Backflow Correlations
Authors:
M. Motta,
G. Bertaina,
D. E. Galli,
E. Vitali
Abstract:
We present a fully detailed and highly performing implementation of the Linear Method [J. Toulouse and C. J. Umrigar (2007)] to optimize Jastrow-Feenberg and Backflow Correlations in many-body wave-functions, which are widely used in condensed matter physics. We show that it is possible to implement such optimization scheme performing analytical derivatives of the wave-function with respect to the…
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We present a fully detailed and highly performing implementation of the Linear Method [J. Toulouse and C. J. Umrigar (2007)] to optimize Jastrow-Feenberg and Backflow Correlations in many-body wave-functions, which are widely used in condensed matter physics. We show that it is possible to implement such optimization scheme performing analytical derivatives of the wave-function with respect to the variational parameters achieving the best possible complexity O(N^3) in the number of particles N.
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Submitted 10 December, 2014; v1 submitted 1 December, 2014;
originally announced December 2014.
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First observation of flux avalanches in a-MoSi superconducting thin films
Authors:
F. Colauto,
M. Motta,
A. Palau,
M. G. Blamire,
T. H. Johansen,
W. A. Ortiz
Abstract:
We have observed the occurrence of dendritic flux avalanches in an amorphous film of Mo$_{84}$Si$_{16}$. These events are understood to have a thermomagnetic origin and involve the abrupt penetration of bursts of magnetic flux taking place within a limited window of temperatures and magnetic fields. While dc-magnetometry allows one to determine the threshold fields for the occurrence of the thermo…
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We have observed the occurrence of dendritic flux avalanches in an amorphous film of Mo$_{84}$Si$_{16}$. These events are understood to have a thermomagnetic origin and involve the abrupt penetration of bursts of magnetic flux taking place within a limited window of temperatures and magnetic fields. While dc-magnetometry allows one to determine the threshold fields for the occurrence of the thermomagnetic instabilities, magneto-optical imaging reveals the spatial distribution of magnetic flux throughout the sample. Conducting appropriate experiments, typical for this goal, avalanches were confirmed to be a characteristic of this material, ruling out the otherwise admissible possibility of an experimental artifact or a feature related to defects in the film. After the present observation, a-MoSi can be included in the gallery of superconducting materials exhibiting flux avalanches when in the form of thin films, a characteristic that must be carefully taken into consideration when one plans to employ films of those materials in applications.
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Submitted 20 August, 2014;
originally announced August 2014.
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Classical analogy for the deflection of flux avalanches by a metallic layer
Authors:
J. Brisbois,
B. Vanderheyden,
F. Colauto,
M. Motta,
W. A. Ortiz,
J. Fritzsche,
N. D. Nguyen,
B. Hackens,
O. -A. Adami,
A. V. Silhanek
Abstract:
Sudden avalanches of magnetic flux bursting into a superconducting sample undergo deflections of their trajectories when encountering a conductive layer deposited on top of the superconductor. Remarkably, in some cases flux is totally excluded from the area covered by the conductive layer. We present a simple classical model that accounts for this behaviour and considers a magnetic monopole approa…
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Sudden avalanches of magnetic flux bursting into a superconducting sample undergo deflections of their trajectories when encountering a conductive layer deposited on top of the superconductor. Remarkably, in some cases flux is totally excluded from the area covered by the conductive layer. We present a simple classical model that accounts for this behaviour and considers a magnetic monopole approaching a semi-infinite conductive plane. This model suggests that magnetic braking is an important mechanism responsible for avalanche deflection.
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Submitted 11 August, 2014;
originally announced August 2014.
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Imaginary Time Correlations and the phaseless Auxiliary Field Quantum Monte Carlo
Authors:
M. Motta,
D. E. Galli,
S. Moroni,
E. Vitali
Abstract:
The phaseless Auxiliary Field Quantum Monte Carlo method provides a well established approximation scheme for accurate calculations of ground state energies of many-fermions systems. Here we apply the method to the calculation of imaginary time correlation functions. We give a detailed description of the technique and we test the quality of the results for static and dynamic properties against exa…
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The phaseless Auxiliary Field Quantum Monte Carlo method provides a well established approximation scheme for accurate calculations of ground state energies of many-fermions systems. Here we apply the method to the calculation of imaginary time correlation functions. We give a detailed description of the technique and we test the quality of the results for static and dynamic properties against exact values for small systems.
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Submitted 5 November, 2013;
originally announced November 2013.
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Enhancement of pinning properties of superconducting thin films by graded pinning landscapes
Authors:
M. Motta,
F. Colauto,
W. A. Ortiz,
J. Fritzsche,
J. Cuppens,
W. Gillijns,
V. V. Moshchalkov,
T. H. Johansen,
A. Sanchez,
A. V. Silhanek
Abstract:
A graded distribution of pinning centers (antidots) in superconducting MoGe thin films has been investigated by magnetization and magneto-optical imaging. The pinning landscape has maximum density at the border, decreasing progressively towards the center. At high temperatures and low fields, where this landscape mimics the vortex distribution predicted by the Bean model, an increase of the critic…
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A graded distribution of pinning centers (antidots) in superconducting MoGe thin films has been investigated by magnetization and magneto-optical imaging. The pinning landscape has maximum density at the border, decreasing progressively towards the center. At high temperatures and low fields, where this landscape mimics the vortex distribution predicted by the Bean model, an increase of the critical current is observed. At low temperatures and fields, the superconducting performance of the non-uniform sample is also improved due to suppression of thermomagnetic avalanches. These findings emphasize the relevance of non-uniform pinning landscapes, so far experimentally unexplored, on the enhancement of pinning efficiency.
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Submitted 26 January, 2013;
originally announced January 2013.
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Superconducting properties of corner-shaped Al microstrips
Authors:
O. -A. Adami,
D. Cerbu,
D. Cabosart,
M. Motta,
J. Cuppens,
W. A. Ortiz,
V. V. Moshchalkov,
B. Hackens,
R. Delamare,
J. Van de Vondel,
A. V. Silhanek
Abstract:
The electrical transport properties of corner-shaped Al superconducting microstrips have been investigated. We demonstrate that the sharp turns lead to asymmetric vortex dynamics, allowing for easier penetration from the inner concave angle than from the outer convex angle. This effect is evidenced by a strong rectification of the voltage signal otherwise absent in straight superconducting strips.…
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The electrical transport properties of corner-shaped Al superconducting microstrips have been investigated. We demonstrate that the sharp turns lead to asymmetric vortex dynamics, allowing for easier penetration from the inner concave angle than from the outer convex angle. This effect is evidenced by a strong rectification of the voltage signal otherwise absent in straight superconducting strips. At low magnetic fields, an enhancement of the critical current with increasing magnetic field is observed for a particular combination of field and current polarity, confirming a recently theoretically predicted competing interplay of superconducting screening currents and applied currents at the inner side of the turn.
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Submitted 17 January, 2013; v1 submitted 11 January, 2013;
originally announced January 2013.
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Anomalous flux avalanche morphology in a a-MoGe superconducting film with a square antidot lattice - experiment and simulation
Authors:
M. Motta,
F. Colauto,
W. A. Ortiz,
J. I. Vestgarden,
T. H. Johansen,
J. Cuppens,
V. V. Moshchalkov,
A. V. Silhanek
Abstract:
We have employed magneto-optical imaging to visualize the occurrence of flux avalanches in a superconducting film of a-MoGe. The specimen was decorated with square antidots arranged in a square lattice. We observed avalanches with the anomalous habit of forming trees where the trunk is perpendicular to the main axis of the square lattice, whereas the branches form angles of 45 degrees. The overall…
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We have employed magneto-optical imaging to visualize the occurrence of flux avalanches in a superconducting film of a-MoGe. The specimen was decorated with square antidots arranged in a square lattice. We observed avalanches with the anomalous habit of forming trees where the trunk is perpendicular to the main axis of the square lattice, whereas the branches form angles of 45 degrees. The overall features of the avalanches, and in particular the 45 degree direction of the branches, were confirmed by numerical simulations.
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Submitted 12 September, 2011;
originally announced September 2011.