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1.
We present a computer simulation of exciton–exciton scattering in a quantum well. Specifically, we use quantum Monte Carlo techniques to study the bound and continuum states of two excitons in a 10 nm wide GaAs/Al0.3Ga0.7As quantum well. From these bound and continuum states we extract the momentum-dependent phase shifts for s-wave scattering. A surprising finding of this work is that a commonly studied effective-mass model for excitons in a 10 nm quantum well actually supports two bound biexciton states. The second, weakly bound state may dramatically enhance exciton–exciton interactions. We also fit our results to a hard-disk model and indicate directions for future work. 相似文献
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电子-声子相互作用对柱形量子线中光学克尔效应的影响 总被引:3,自引:2,他引:1
本文利用密度矩阵方法研究了柱形量子线中的光学克尔效应, 重点讨论了电子-声子相互作用对其的影响,并以GaAs量子线为例进行了数值计算。结果显示,随着量子线半径R0的减小,光学克尔效应会逐渐增强;考虑了电子-声子相互作用时的光学克尔效应比未考虑电子-声子相互作用时的大20%多;量子线半径R0越小,峰越尖锐,峰值越强;当量子线半径R0大〖WTBZ〗于40 nm时,峰会逐渐消失. 相似文献
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The charged Dirac oscillator on a noncommutative plane coupling to a uniform perpendicular magnetic field is studied in this paper. We map the noncommutative plane to a commutative one by means of Bopp shift and study this problem on the commutative plane. We find that this model can be mapped onto a quantum optics model which contains Anti-Jaynes-Cummings (AJC) or Jaynes-Cummings (JC) interactions when a dimensionless parameter ζ (which is the function of the intensity of the magnetic field) takes values in different regimes. Furthermore, this model behaves as experiencing a chirality quantum phase transition when the dimensionless parameter ζ approaches the critical point. Several evidences of the chirality quantum phase transition are presented. We also study the non-relativistic limit of this model and find that a similar chirality quantum phase transition takes place in its non-relativistic limit. 相似文献
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Gerd Niestegge 《Foundations of Physics》2008,38(3):241-256
The well-known proposal to consider the Lüders-von Neumann measurement as a non-classical extension of probability conditionalization
is further developed. The major results include some new concepts like the different grades of compatibility, the objective
conditional probabilities which are independent of the underlying state and stem from a certain purely algebraic relation
between the events, and an axiomatic approach to quantum mechanics. The main axioms are certain postulates concerning the
conditional probabilities and own intrinsic probabilistic interpretations from the very beginning. A Jordan product is derived
for the observables, and the consideration of composite systems leads to operator algebras on the Hilbert space over the complex
numbers, which is the standard model of quantum mechanics. The paper gives an expository overview of the results presented
in a series of recent papers by the author. For the first time, the complete approach is presented as a whole in a single
paper. Moreover, since the mathematical proofs are already available in the original papers, the present paper can dispense
with the mathematical details and maximum generality, thus addressing a wider audience of physicists, philosophers or quantum
computer scientists. 相似文献
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Deng-Yu Zhang Shi-Qing Tang Li-Jun Xie Xiao-Gui Zhan Kai-Ming You Feng Gao 《International Journal of Theoretical Physics》2009,48(9):2685-2691
We propose a model to implement the two-qubit quantum logic gates, i.e., the quantum phase gate and the Controlled-NOT gate,
and generate the atomic qubits cluster states with a large detuned interaction between four-level atoms and a single-mode
cavity field. In the presented protocol, the quantum information is encoded on the stable ground states of the atoms, and
the effect of decoherence from atomic spontaneous emission is negligible. In addition, the interaction between atoms and the
cavity is large detuned, and the cavity is only virtually excited. Therefore, the scheme is insensitive to the cavity decay.
The experimental feasibility of our proposal is also discussed. 相似文献
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The effective theories for many quantum phase transitions can be mapped onto those of classical transitions. Here we show that the naive mapping fails for the sub-Ohmic spin-boson model which describes a two-level system coupled to a bosonic bath with power-law spectral density, J(omega) proportional, variantomega(s). Using an epsilon expansion we prove that this model has a quantum transition controlled by an interacting fixed point at small s, and support this by numerical calculations. In contrast, the corresponding classical long-range Ising model is known to display mean-field transition behavior for 0 < s < 1/2, controlled by a noninteracting fixed point. The failure of the quantum-classical mapping is argued to arise from the long-ranged interaction in imaginary time in the quantum model. 相似文献
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A theoretical framework is demonstrated to evaluate the degree of entanglement of bit states in quantum computing. Separability
of general superposition of Hilbert space unit vectors is discussed, and criteria in amplitude as well as in phase are derived.
By these criteria the possibility of different quantum gates such as controlled not (CN), controlled controlled not (CCN),
controlled rotation (CR), and controlled phase shift (CPS), to create the entanglement is examined. Furthermore, the selection
of measurement mode external to the quantum system is incorporated in the formula using Kronecker delta (δ
kx
), introducing the concept of dynamic entanglement. With this the process of wavefunction collapse upon measurement is understood as the result of the activation of the dynamic
entanglement. A firefly in a box model is used to show a pure state of ontological uncertainty, which is in a dynamically
entangled state in Hilbert space. 相似文献
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A new model of quantum computation is considered, in which the connections between gates are programmed by the state of a quantum register. This new model of computation is shown to be more powerful than the usual quantum computation, e.g. in achieving the programmability of permutations of N different unitary channels with 1 use instead of N uses per channel. For this task, a new elemental resource is needed, the quantum switch, which can be programmed to switch the order of two channels with a single use of each one. 相似文献
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The Mechanism of Quantum Computation 总被引:1,自引:1,他引:0
Giuseppe Castagnoli 《International Journal of Theoretical Physics》2008,47(8):2181-2194
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《Physics letters. A》2020,384(16):126333
We investigate the diagonal entropy(DE) of the ground state for quantum many-body systems, including the XY model and the Ising model with next nearest neighbor interactions. We focus on the DE of a subsystem of L continuous spins. We show that the DE in many-body systems, regardless of integrability, can be represented as a volume term plus a logarithmic correction and a constant offset. Quantum phase transition points can be explicitly identified by the three coefficients thereof. Besides, by combining entanglement entropy and the relative entropy of quantum coherence, as two celebrated representatives of quantumness, we simply obtain the DE, which naturally has the potential to reveal the information of quantumness. More importantly, the DE is concerning only the diagonal form of the ground state reduced density matrix, making it feasible to measure in real experiments, and therefore it has immediate applications in demonstrating quantum supremacy on state-of-the-art quantum simulators. 相似文献
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We elaborate on the distinction between geometric and dynamical phase in quantum theory and we show that the former is intrinsically linked to the quantum mechanical probabilistic structure. In particular, we examine the appearance of the Berry phase in the consistent histories scheme and establish that it is the basic building block of the decoherence functional. These results are consequences of the novel temporal structure of histories-based theories. 相似文献
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Duality Quantum Computers and Quantum Operations 总被引:1,自引:0,他引:1
Stan Gudder 《International Journal of Theoretical Physics》2008,47(1):268-279
We present a mathematical theory for a new type of quantum computer called a duality quantum computer that is similar to one
that has recently been proposed. We discuss the nonunitarity of certain circuits of a duality quantum computer. We then discuss
the relevance of this work to quantum operations and their convexity theory. This discussion is based upon isomorphism theorems
for completely positive maps. 相似文献
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M. Wilkens H. -J. Sommers M. Lewenstein F. Haake 《Zeitschrift für Physik B Condensed Matter》1989,77(1):141-150
The mapping of random onto nonrandom competing bonds recently suggested is here implemented for spin glasses of long-ranged interactions. Exact results are obtained which support previous conclusions from high-temperature series. 相似文献
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Belief Propagation algorithms acting on Graphical Models of classical probability distributions, such as Markov Networks, Factor Graphs and Bayesian Networks, are amongst the most powerful known methods for deriving probabilistic inferences amongst large numbers of random variables. This paper presents a generalization of these concepts and methods to the quantum case, based on the idea that quantum theory can be thought of as a noncommutative, operator-valued, generalization of classical probability theory. Some novel characterizations of quantum conditional independence are derived, and definitions of Quantum n-Bifactor Networks, Markov Networks, Factor Graphs and Bayesian Networks are proposed. The structure of Quantum Markov Networks is investigated and some partial characterization results are obtained, along the lines of the Hammersley–Clifford theorem. A Quantum Belief Propagation algorithm is presented and is shown to converge on 1-Bifactor Networks and Markov Networks when the underlying graph is a tree. The use of Quantum Belief Propagation as a heuristic algorithm in cases where it is not known to converge is discussed. Applications to decoding quantum error correcting codes and to the simulation of many-body quantum systems are described. 相似文献
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O.G. Zabaleta 《Physica A》2010,389(14):2858-1220
We consider the dating market decision problem under the quantum mechanics point of view. Quantum states whose associated amplitudes are modified by men strategies are used to represent women. The Grover quantum search algorithm is used as a playing strategy. Success is more frequently obtained by playing quantum than playing classic. 相似文献
20.
It is quite relevant the extension of decoration transformation for quantum spin models since most of the real materials could be well described by Heisenberg type models. Here we propose an exact quantum decoration transformation and also showing interesting properties such as the persistence of symmetry and the symmetry breaking during this transformation. Although the proposed transformation, in principle, cannot be used to map exactly a quantum spin lattice model into another quantum spin lattice model, since the operators are non-commutative. However, it is possible the mapping in the “classical” limit, establishing an equivalence between both quantum spin lattice models. To study the validity of this approach for quantum spin lattice model, we use the Zassenhaus formula, and we verify how the correction could influence the decoration transformation. But this correction could be useless to improve the quantum decoration transformation because it involves the second-nearest-neighbor and further nearest neighbor couplings, which leads into a cumbersome task to establish the equivalence between both lattice models. This correction also gives us valuable information about its contribution, for most of the Heisenberg type models, this correction could be irrelevant at least up to the third order term of Zassenhaus formula. This transformation is applied to a finite size Heisenberg chain, comparing with the exact numerical results, our result is consistent for weak xy-anisotropy coupling. We also apply to bond-alternating Ising–Heisenberg chain model, obtaining an accurate result in the limit of the quasi-Ising chain. 相似文献