The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
Masanao Yamaoka - One of the best experts on this subject based on the ideXlab platform.
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A 2 $\times$ 30k-Spin Multi-Chip Scalable CMOS Annealing Processor Based on a Processing-in-Memory Approach for Solving Large-Scale Combinatorial Optimization Problems
IEEE Journal of Solid-State Circuits, 2020Co-Authors: Takashi Takemoto, Masato Hayashi, Chihiro Yoshimura, Masanao YamaokaAbstract:The world's first 2 x 30k-Spin multi-chip CMOS annealing processor (AP)-based on the processing-in-memory approach for solving large-scale combinatorial optimization problem-was developed. To expand the bit width of coefficients and enhance the scalability of the AP, it has three key features: an expandable and high-accuracy Spin Operator for local communication, a highly integrated Spin circuit using direct access to SRAM, and a low-latency inter-chip interface that does not affect the runtime or results of the annealing process. The AP is fabricated on the basis of 40-nm CMOS technology. It was experimentally demonstrated that the Spin-flip ratio of the processor agrees well with theoretical values based on the Gibbs distribution over a wide temperature range. As a result, under two-chip operation with 2 x 30k Spins, the AP achieves an annealing time of 22 μs, which is 455 times and 2.6 x 104 times faster than those achieved by our previous CMOS-AP and a conventional CPU, respectively. Moreover, its energy efficiency is 1.75 x 105 times higher than that of a conventional CPU-based algorithm.
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2.6 A 2 ×30k-Spin Multichip Scalable Annealing Processor Based on a Processing-In-Memory Approach for Solving Large-Scale Combinatorial Optimization Problems
2019 IEEE International Solid- State Circuits Conference - (ISSCC), 2019Co-Authors: Takashi Takemoto, Masato Hayashi, Chihiro Yoshimura, Masanao YamaokaAbstract:The last decade has seen impressive progress in the development of a new computer architecture, commonly known as annealing processor [1, 2]. An annealing processor provides a fast means for finding the ground state of an Ising model; thus, it can efficiently solve NP-hard combinatorial optimization problems [3]. In addition to quantum annealers based on superconducting circuits [1], annealing processors based on CMOS technology have received increased interest and are being developed on the basis of simulated annealing (SA) [2]. However, these CMOS annealing processors (CMOS-APs) have room for improvement, such as: i) expanding the bit widths of coefficients, and ii) increasing the number of Spins handled by the processor. To address these challenges, a CMOS-AP based on the processing-in-memory approach (where CMOS circuits and an SRAM are tightly coupled [4]) has been developed. Its key features are threefold: a Spin Operator (processing local memory) which provides coefficients with expandable bit width and fast parallel Spin updates according to the Gibbs distribution; a low-latency inter-chip interface (I/F) connecting two Ising chips, resulting in an increased number of Spins; and a highly integrated Spin circuit which directly connects the Spin Operator with the SRAM cell. Installed in a 2×30k Spin system, the CMOS-AP demonstrates the capability for multi-chip operation with energy efficiency 1.75×105 higher than running SA on a CPU.
R Grobe - One of the best experts on this subject based on the ideXlab platform.
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Spin dynamics in relativistic light-matter interaction
Proceedings of SPIE, 2015Co-Authors: Heiko Bauke, Sven Ahrens, Christoph H Keitel, R GrobeAbstract:Various Spin effects are expected to become observable in light-matter interaction at relativistic intensities. Relativistic quantum mechanics equipped with a suitable relativistic Spin Operator forms the theoretical foundation for describing these effects. Various proposals for relativistic Spin Operators have been offered by different authors, which are presented in a unified way. As a result of the Operators’ mathematical properties only the Foldy-Wouthuysen Operator and the Pryce Operator qualify as possible proper relativistic Spin Operators. The ground states of highly charged hydrogen-like ions can be utilized to identify a legitimate relativistic Spin Operator experimentally. Subsequently, the Foldy-Wouthuysen Spin Operator is employed to study electron-Spin precession in high-intensity standing light waves with elliptical polarization. For a correct theoretical description of the predicted electron-Spin precession relativistic effects due to the Spin angular momentum of the electromagnetic wave has to be taken into account even in the limit of low intensities.
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what is the relativistic Spin Operator
New Journal of Physics, 2014Co-Authors: Heiko Bauke, Sven Ahrens, Christoph H Keitel, R GrobeAbstract:Although the Spin is regarded as a fundamental property of the electron, there is no universally accepted Spin Operator within the framework of relativistic quantum mechanics. We investigate the properties of different proposals for a relativistic Spin Operator. It is shown that most candidates are lacking essential features of proper angular momentum Operators, leading to spurious zitterbewegung (quivering motion) or violation of the angular momentum algebra. Only the Foldy–Wouthuysen Operator and the Pryce Operator qualify as proper relativistic Spin Operators. We demonstrate that ground states of highly charged hydrogen-like ions can be utilized to identify a legitimate relativistic Spin Operator experimentally.
Taeseung Choi - One of the best experts on this subject based on the ideXlab platform.
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Spin Operators and representations of the Poincar\'e group
arXiv: General Physics, 2018Co-Authors: Taeseung ChoiAbstract:We present the rigorous derivation of Spin Operators whose square is the second Casimir invariant of the Poincare group. It is shown that only two Spin Operators, of all that are general linear combinations of the components of Pauli-Lubanski vector with momentum-dependent coefficients, satisfy the Spin algebra and transform properly under the Lorentz transformation. They provide the two inequivalent representations, i.e., the left-handed and the right-handed representation of the Poincare group, in which the base states describe free massive chiral fields with integer or half-integer Spin $s$. In case that the Poincare group is extended by parity operation, a massive elementary Spin $s$ field should be represented by the direct sum of the left-handed and the right-handed representation. The two Spin Operators providing the left-handed and the right-handed representation are not axial and not Hermitian as themselves. This implies that the two Spin Operators are not observables as themselves. The Spin Operator in the direct sum representation is axial and also becomes Hermitian acting on either a positive or a negative energy representation space. Therefore, the physical theory with a Spin as an observable is provided from the parity-extended Poinare group, not just the Poincare group. For Spin $1/2$, the parity operation expressed by the Lorentz boost in the direct sum representation naturally leads to the fundamental dynamical equation that is shown to be equal to the covariant equation for free Dirac field, which was originally derived from the homogeneous Lorentz symmetry. However, the equality of the two dynamical equations does not mean that the two theories are equivalent in physical aspect because, for instance, the Spin Operators in the two theories are different, and the Spin in the new theory is conserved by itself but is not in the usual Dirac theory.
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Newton-Wigner position Operator and the corresponding Spin Operator in relativistic quantum mechanics
Journal of the Korean Physical Society, 2015Co-Authors: Taeseung ChoiAbstract:A relativistic Spin Operator is the difference between the total and the orbital angular momentum. As the unique position Operator for a localized state, the remarkable Newton-Wigner position Operator, which has all the desirable commutation relations of a position Operator, can give a proper Spin Operator. Historically, the three important Spin Operators proposed by Bogolubov et al., Pryce, and Foldy-Woutheysen, respectively were investigated to manifest a Spin Operator corresponding to the Newton-Wigner position Operator. We clarify a unique Spin Operator in relativistic quantum mechanics, which can be described by using the Dirac Hamiltonian.
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Newton-Wigner position Operator and its corresponding Spin Operator in relativistic quantum mechanics
arXiv: Quantum Physics, 2014Co-Authors: Taeseung ChoiAbstract:A relativistic Spin Operator is to be the difference between the total and orbital angular momentum. As the unique position Operator for a localized state, the remarkable Newton-Wigner position Operator, which has all desirable commutation relations as a position Operator, can give a proper Spin Operator. Historically important three Spin Operators respectively proposed by Bogolubov et al., Pryce, and Foldy-Woutheysen are investigated to manifest a corresponding Spin Operator to the Newton-Wigner position Operator. We clarify a unique Spin Operator in relativistic quantum mechanics described by the Dirac Hamiltonian.
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Spin Operators for Massive Particles
arXiv: Quantum Physics, 2014Co-Authors: Taeseung ChoiAbstract:Since the discovery a century ago, Spin describing the intrinsic angular momentum of massive elementary particles has exposed its nature and significant roles in wide ranges of (relativistic) quantum phenomena and practical applications for future quantum technology. Emerging inconsistencies have also disclosed its telltale incomplete description. Finding relativistic Spins (Operators) of massive particles is a long-standing fundamental problem from the beginning of relativistic quantum mechanics. Here we present the rigorous derivation and the representation of Spin Operators from the spacetime symmetry. The covariant parity operation, defined by the Spin Operators, naturally leads to a fundamental equation equivalent to the covariant Dirac equation, which manifests existent relativistic Spins. Proper understanding position Operator in the Dirac theory on account of the Spin Operator through total angular momentum predicts no Zitterbewegung as well as conserving orbital and Spin currents. The Spin Operators can be applicable for unraveling the inconsistencies and for exploring unveiled physics of massive particles.
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Relativistic Spin Operator and Lorentz transformation of the Spin state of a massive Dirac particle
Journal of the Korean Physical Society, 2013Co-Authors: Taeseung ChoiAbstract:We have shown that the covariant relativistic Spin Operator is equivalent to the Spin Operator commuting with the free Dirac Hamiltonian. This implies that the covariant relativistic Spin Operator is a good quantum observable. The covariant relativistic Spin Operator has a pure quantum contribution that does not exist in the classical covariant Spin Operator. Based on this equivalence, reduced Spin states can be clearly defined. We have shown that depending on the relative motion of an observer, the change in the entropy of a reduced Spin density matrix sweeps through the whole range.
Yuri Tykhyy - One of the best experts on this subject based on the ideXlab platform.
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Spin Operator matrix elements in the quantum ising chain fermion approach
Journal of Statistical Mechanics: Theory and Experiment, 2011Co-Authors: Nikolai Iorgov, V N Shadura, Yuri TykhyyAbstract:Using some modification of the standard fermion technique we derive factorized formulas for Spin Operator matrix elements (form factors) between general eigenstates of the Hamiltonian of the quantum Ising chain in a transverse field of finite length. The derivation is based on the approach recently used to derive factorized formulas for ZN-Spin Operator matrix elements between ground eigenstates of the Hamiltonian of the ZN-symmetric superintegrable chiral Potts quantum chain. The obtained factorized formulas for the matrix elements of the Ising chain coincide with the corresponding expressions obtained by the separation of variables method.
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Spin Operator Matrix Elements in the Superintegrable Chiral Potts Quantum Chain
Journal of Statistical Physics, 2010Co-Authors: Nikolai Iorgov, V N Shadura, Yuri Tykhyy, S. Pakuliak, G. GehlenAbstract:We derive Spin Operator matrix elements between general eigenstates of the superintegrable ℤ_ N -symmetric chiral Potts quantum chain of finite length. Our starting point is the extended Onsager algebra recently proposed by Baxter. For each pair of spaces (Onsager sectors) of the irreducible representations of the Onsager algebra, we calculate the Spin matrix elements between the eigenstates of the Hamiltonian of the quantum chain in factorized form, up to an overall scalar factor. This factor is known for the ground state Onsager sectors. For the matrix elements between the ground states of these sectors we perform the thermodynamic limit and obtain the formula for the order parameters. For the Ising quantum chain in a transverse field ( N =2 case) the factorized form for the matrix elements coincides with the corresponding expressions obtained recently by the Separation of Variables method.
Takashi Takemoto - One of the best experts on this subject based on the ideXlab platform.
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A 2 $\times$ 30k-Spin Multi-Chip Scalable CMOS Annealing Processor Based on a Processing-in-Memory Approach for Solving Large-Scale Combinatorial Optimization Problems
IEEE Journal of Solid-State Circuits, 2020Co-Authors: Takashi Takemoto, Masato Hayashi, Chihiro Yoshimura, Masanao YamaokaAbstract:The world's first 2 x 30k-Spin multi-chip CMOS annealing processor (AP)-based on the processing-in-memory approach for solving large-scale combinatorial optimization problem-was developed. To expand the bit width of coefficients and enhance the scalability of the AP, it has three key features: an expandable and high-accuracy Spin Operator for local communication, a highly integrated Spin circuit using direct access to SRAM, and a low-latency inter-chip interface that does not affect the runtime or results of the annealing process. The AP is fabricated on the basis of 40-nm CMOS technology. It was experimentally demonstrated that the Spin-flip ratio of the processor agrees well with theoretical values based on the Gibbs distribution over a wide temperature range. As a result, under two-chip operation with 2 x 30k Spins, the AP achieves an annealing time of 22 μs, which is 455 times and 2.6 x 104 times faster than those achieved by our previous CMOS-AP and a conventional CPU, respectively. Moreover, its energy efficiency is 1.75 x 105 times higher than that of a conventional CPU-based algorithm.
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2.6 A 2 ×30k-Spin Multichip Scalable Annealing Processor Based on a Processing-In-Memory Approach for Solving Large-Scale Combinatorial Optimization Problems
2019 IEEE International Solid- State Circuits Conference - (ISSCC), 2019Co-Authors: Takashi Takemoto, Masato Hayashi, Chihiro Yoshimura, Masanao YamaokaAbstract:The last decade has seen impressive progress in the development of a new computer architecture, commonly known as annealing processor [1, 2]. An annealing processor provides a fast means for finding the ground state of an Ising model; thus, it can efficiently solve NP-hard combinatorial optimization problems [3]. In addition to quantum annealers based on superconducting circuits [1], annealing processors based on CMOS technology have received increased interest and are being developed on the basis of simulated annealing (SA) [2]. However, these CMOS annealing processors (CMOS-APs) have room for improvement, such as: i) expanding the bit widths of coefficients, and ii) increasing the number of Spins handled by the processor. To address these challenges, a CMOS-AP based on the processing-in-memory approach (where CMOS circuits and an SRAM are tightly coupled [4]) has been developed. Its key features are threefold: a Spin Operator (processing local memory) which provides coefficients with expandable bit width and fast parallel Spin updates according to the Gibbs distribution; a low-latency inter-chip interface (I/F) connecting two Ising chips, resulting in an increased number of Spins; and a highly integrated Spin circuit which directly connects the Spin Operator with the SRAM cell. Installed in a 2×30k Spin system, the CMOS-AP demonstrates the capability for multi-chip operation with energy efficiency 1.75×105 higher than running SA on a CPU.