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Journal articles on the topic 'TWO-QUBIT SYSTEM'

Author: Grafiati

Published: 11 September 2023

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1

Zhao, Chao-Ying, Qi-Zhi Guo, and Wei-Han Tan. "A simple entanglement criterion of two-qubit system." International Journal of Modern Physics B 33, no. 18 (July 20, 2019): 1950197. http://dx.doi.org/10.1142/s0217979219501972.

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We present a novel method to judge the entanglement of two-qubit system, the density matrix of a two-qubit system can be constituted by the principle density matrix [Formula: see text] and the separable density matrices [Formula: see text]–[Formula: see text]. The necessary and sufficient conditions for the two-qubit system, the three involved coefficients p [Formula: see text] 0, p [Formula: see text] 0, p [Formula: see text] 0, and the principal density matrix [Formula: see text] being separable, then the two-qubit system is separable, otherwise the two-qubit system is entangled. Finally, the criterion for several known density matrices have been verified in this way.

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2

Kato, Akihito, and Yoshitaka Tanimura. "Quantum heat transport of a two-qubit system: Interplay between system-bath coherence and qubit-qubit coherence." Journal of Chemical Physics 143, no. 6 (August 14, 2015): 064107. http://dx.doi.org/10.1063/1.4928192.

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3

Khalil, E. M., and A. B. A. Mohamed. "Dynamics of entanglement and population inversion of two qubits in a hybrid nonlinear system." Modern Physics Letters A 36, no. 06 (January 15, 2021): 2150037. http://dx.doi.org/10.1142/s0217732321500371.

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An analytical solution is obtained when the Kerr medium and Stark shift are considered as nonlinear interaction terms to the system containing two-qubit and two-mode electromagnetic field from the parametric amplifier. Dynamics of the population inversion, cavity–qubit and qubit–qubit entanglements are analyzed under the unitary cavity–qubit interaction, the Kerr medium and the Stark shift. The population inversion of a qubit presents periodic revivals and collapses. The results show that the entanglement and the population inversion as well as the inversion have the same stable intervals, that is, the collapse intervals. It is found that the Kerr medium and the Stark shift may lead to reduction of the periods and the amplitudes of the population inversion and the cavity–qubit/qubit–qubit entanglement. The deteriorated qubit–qubit/cavity–qubit entanglement and the population inversion, due to the Kerr medium, may be increased by increasing the Stark shift and vice versa.

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4

Zhao, Chao-Ying, Qi-Zhi Guo, and Wei-Han Tan. "A novel entanglement criterion of two-qubit system." International Journal of Modern Physics B 34, no. 05 (February 17, 2020): 2050022. http://dx.doi.org/10.1142/s0217979220500228.

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The “separability problem” in quantum information theory is a quite important and well-known hard problem. The low-dimensional system satisfies the PPT criterion. However, the high-dimensional system problem has been shown to be NP-hard problem. In general, it is very difficult to find the analytic solution of the density matrix for the high-dimensional system. Therefore, getting an analytic solution for two-qubit system is an interesting and useful problem. We propose a novel criterion for separability and entanglement-verification of two-qubit system. We expressed the density matrix by a sum of a principal density matrix and six separable density matrices. The necessary and sufficient conditions for the two-qubit system include that if the four involved coefficients [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and the principal density matrix [Formula: see text] are separable, then the two-qubit system is separable, otherwise the two-qubit system is entangled. Finally, our criterion results in a totally different conclusion compared to Horodecki’s criterion. We believe that the new criterion is more stringent than existing PPT methods.

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5

ADHIKARI, SATYABRATA. "ENTANGLEMENT AND TELEPORTATION IN BIPARTITE SYSTEM." International Journal of Quantum Information 08, no. 07 (October 2010): 1153–67. http://dx.doi.org/10.1142/s0219749910006411.

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We present a mathematical formulation of old teleportation protocol (original teleportation protocol introduced by Bennett et al.) for mixed state and study in detail the role of mixedness of the two-qubit quantum channel in a teleportation protocol. We show that maximally entangled mixed state described by the density matrix of rank-4 will be useful as a two-qubit teleportation channel to teleport a single qubit mixed state when the teleportation channel parameter p1 > 1/2. Also we discuss the case when p1 ≤ 1/2.

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6

FRYDRYSZAK, ANDRZEJ M. "NILPOTENT QUANTUM MECHANICS." International Journal of Modern Physics A 25, no. 05 (February 20, 2010): 951–83. http://dx.doi.org/10.1142/s0217751x10047786.

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We develop a generalized quantum mechanical formalism based on the nilpotent commuting variables (η-variables). In the nonrelativistic case such formalism provides natural realization of a two-level system (qubit). Using the space of η-wavefunctions, η-Hilbert space and generalized Schrödinger equation we study properties of pure multiqubit systems and also properties of some composed, hybrid models: fermion–qubit, boson–qubit. The fermion–qubit system can be truly supersymmetric, with both SUSY partners having identical spectra. It is a novel feature that SUSY transformations relate here only nilpotent object. The η-eigenfunctions of the Hamiltonian for the qubit–qubit system give the set of Bloch vectors as a natural basis.

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7

MAZIERO, JONAS, and ROBERTO M. SERRA. "CLASSICALITY WITNESS FOR TWO-QUBIT STATES." International Journal of Quantum Information 10, no. 03 (April 2012): 1250028. http://dx.doi.org/10.1142/s0219749912500281.

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In the last few years one realized that if the state of a bipartite system can be written as ∑i,j pij|ai〉〈ai| ⊗ |bj〉〈bj|, where {|ai〉} and {|bj〉} form orthonormal basis for the subsystems and {pij} is a probability distribution, then it possesses at most classical correlations. In this article we introduce a nonlinear witness providing a sufficient condition for classicality of correlations (absence of quantum discord) in a broad class of two-qubit systems. Such witness turns out to be necessary and sufficient condition in the case of Bell-diagonal states. We show that the witness introduced here can be readily experimentally implemented in nuclear magnetic resonance setups.

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8

Ntalaperas, Dimitrios, and Nikos Konofaos. "Encoding Two-Qubit Logical States and Quantum Operations Using the Energy States of a Physical System." Technologies 10, no. 1 (December 22, 2021): 1. http://dx.doi.org/10.3390/technologies10010001.

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In this paper, we introduce a novel coding scheme, which allows single quantum systems to encode multi-qubit registers. This allows for more efficient use of resources and the economy in designing quantum systems. The scheme is based on the notion of encoding logical quantum states using the charge degree of freedom of the discrete energy spectrum that is formed by introducing impurities in a semiconductor material. We propose a mechanism of performing single qubit operations and controlled two-qubit operations, providing a mechanism for achieving these operations using appropriate pulses generated by Rabi oscillations. The above architecture is simulated using the Armonk single qubit quantum computer of IBM to encode two logical quantum states into the energy states of Armonk’s qubit and using custom pulses to perform one and two-qubit quantum operations.

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9

von Kugelgen, Stephen, Matthew D. Krzyaniak, Mingqiang Gu, Danilo Puggioni, James M. Rondinelli, Michael R. Wasielewski, and Danna E. Freedman. "Spectral Addressability in a Modular Two Qubit System." Journal of the American Chemical Society 143, no. 21 (May 20, 2021): 8069–77. http://dx.doi.org/10.1021/jacs.1c02417.

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10

Tzemos, A. C., G. Contopoulos, and C. Efthymiopoulos. "Bohmian trajectories in an entangled two-qubit system." Physica Scripta 94, no. 10 (August 7, 2019): 105218. http://dx.doi.org/10.1088/1402-4896/ab2445.

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11

Orszag, Miguel, and Maritza Hernandez. "Coherence and entanglement in a two-qubit system." Advances in Optics and Photonics 2, no. 2 (March 17, 2010): 229. http://dx.doi.org/10.1364/aop.2.000229.

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12

Jakóbczyk, L., and M. Siennicki. "Geometry of Bloch vectors in two-qubit system." Physics Letters A 286, no. 6 (August 2001): 383–90. http://dx.doi.org/10.1016/s0375-9601(01)00455-8.

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13

Zhu, Guo-Qiang. "Off-diagonal Geometric Phase of Two-Qubit System." International Journal of Theoretical Physics 49, no. 11 (August 18, 2010): 2672–79. http://dx.doi.org/10.1007/s10773-010-0459-2.

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14

Hieu, Nguyen Van, Nguyen Bich Ha, and Le Thi Ha Linh. "Quantum dynamics of a two-atom-qubit system." Journal of Physics: Conference Series 187 (September 1, 2009): 012010. http://dx.doi.org/10.1088/1742-6596/187/1/012010.

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15

Ramos, R. C., F. W. Strauch, P. R. Johnson, A. J. Berkley, H. Xu, M. A. Gubrud, J. R. Anderson, C. J. Lobb, A. J. Dragt, and F. C. Wellstood. "Capacitively coupled josephson junctions: A two-qubit system." IEEE Transactions on Appiled Superconductivity 13, no. 2 (June 2003): 994–1000. http://dx.doi.org/10.1109/tasc.2003.814122.

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16

Singh, Manu P., and B. S. Rajput. "Maximally Entangled States of a Two-Qubit System." International Journal of Theoretical Physics 52, no. 12 (August 2, 2013): 4237–55. http://dx.doi.org/10.1007/s10773-013-1736-7.

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17

Algarni, Mariam, Kamal Berrada, Sayed Abdel-Khalek, and Hichem Eleuch. "Coherence Trapping in Open Two-Qubit Dynamics." Symmetry 13, no. 12 (December 17, 2021): 2445. http://dx.doi.org/10.3390/sym13122445.

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In this manuscript, we examine the dynamical behavior of the coherence in open quantum systems using the l1 norm. We consider a two-qubit system that evolves in the framework of Kossakowski-type quantum dynamical semigroups (KTQDSs) of completely positive maps (CPMs). We find that the quantum coherence can be asymptotically maintained with respect to the values of the system parameters. Moreover, we show that the quantum coherence can resist the effect of the environment and preserve even in the regime of long times. The obtained results also show that the initially separable states can provide a finite value of the coherence during the time evolution. Because of such properties, several states in this type of environments are good candidates for incorporating quantum information and optics (QIO) schemes. Finally, we compare the dynamical behavior of the coherence with the entire quantum correlation.

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18

GÜN, A., and A. GENÇTEN. "THREE-QUBIT QUANTUM ENTANGLEMENT FOR SI (S = 3/2, I = 1/2) SPIN SYSTEM." International Journal of Quantum Information 09, no. 07n08 (October 2011): 1635–42. http://dx.doi.org/10.1142/s0219749911008313.

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In quantum information processing, spin-3/2 electron or nuclear spin states are known as two-qubit states. For SI (S = 3/2, I = 1/2) spin system, there are eight three-qubit states. In this study, first, three-qubit CNOT logic gates are obtained. Then three-qubit entangled states are obtained by using the matrix representation of Hadamard and three-qubit CNOT logic gates. By considering single 31P@C60 molecule as SI (S = 3/2, I = 1/2) spin system, three-qubit entangled states are also obtained using the magnetic resonance pulse sequences of Hadamard and CNOT logic gates.

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19

XU, JIN-SHI, and CHUAN-FENG LI. "QUANTUM DISCORD UNDER SYSTEM–ENVIRONMENT COUPLING: THE TWO-QUBIT CASE." International Journal of Modern Physics B 27, no. 01n03 (November 26, 2012): 1345054. http://dx.doi.org/10.1142/s0217979213450549.

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Open quantum systems have attracted great attention, since inevitable coupling between quantum systems and their environment greatly affects the features of interest of these systems. Quantum discord, is a measure of the total nonclassical correlation in a quantum system that includes, but is not exclusive to, the distinct property of quantum entanglement. Quantum discord can exist in separated quantum states and plays an important role in many fundamental physics problems and practical quantum information tasks. There have been numerous investigations on quantum discord and its counterpart classical correlation. This short review focuses on highlighting the system–environment dynamics of two-qubit quantum discord and the influence of initial system–environment correlations on the dynamics of open quantum systems. The external control effect on the dynamics of open quantum systems are involved. Several related experimental works are discussed.

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20

Cai, Xiaoya, Hui Pan, and Z. S. Wang. "Geometric phase of two-qubit system in dephasing environment." International Journal of Modern Physics B 29, no. 32 (December 17, 2015): 1550236. http://dx.doi.org/10.1142/s0217979215502367.

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We investigated the geometric phase for interaction between superconducting two-qubit system in dephased environment. The Pancharatnam phase and the Berry phase are studied. Numerical results are discussed. By considering the differently initial conditions, we find that the time-dependent Pancharatnam phase keeps the initial entangling message. On the other hand, the transition of Pancharatnam phase is dependent of the phase change in the superconducting two-qubit coupling system. Our results may be helpful to implement the time-dependent geometric quantum computation.

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21

USHA DEVI, A. R., M. S. UMA, R. PRABHU, and SUDHA. "LOCAL INVARIANTS AND PAIRWISE ENTANGLEMENT IN SYMMETRIC MULTIQUBIT SYSTEM." International Journal of Modern Physics B 20, no. 11n13 (May 20, 2006): 1917–33. http://dx.doi.org/10.1142/s0217979206034406.

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Pairwise entanglement properties of a symmetric multi-qubit system are analyzed through a complete set of two-qubit local invariants. Collective features of entanglement, such as spin squeezing, are expressed in terms of invariants and a classification scheme for pairwise entanglement is proposed. The invariant criteria given here are shown to be related to the recently proposed (Phys. Rev. Lett.95, 120502 (2005)) generalized spin squeezing inequalities for pairwise entanglement in symmetric multi-qubit states.

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22

Chen, Mingli, Haonan Chen, Tao Han, and Xiangji Cai. "Disentanglement Dynamics in Nonequilibrium Environments." Entropy 24, no. 10 (September 21, 2022): 1330. http://dx.doi.org/10.3390/e24101330.

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We theoretically study the non-Markovian disentanglement dynamics of a two-qubit system coupled to nonequilibrium environments with nonstationary and non-Markovian random telegraph noise statistical properties. The reduced density matrix of the two-qubit system can be expressed as the Kraus representation in terms of the tensor products of the single qubit Kraus operators. We derive the relation between the entanglement and nonlocality of the two-qubit system which are both closely associated with the decoherence function. We identify the threshold values of the decoherence function to ensure the existences of the concurrence and nonlocal quantum correlations for an arbitrary evolution time when the two-qubit system is initially prepared in the composite Bell states and the Werner states, respectively. It is shown that the environmental nonequilibrium feature can suppress the disentanglement dynamics and reduce the entanglement revivals in non-Markovian dynamics regime. In addition, the environmental nonequilibrium feature can enhance the nonlocality of the two-qubit system. Moreover, the entanglement sudden death and rebirth phenomena and the transition between quantum and classical nonlocalities closely depend on the parameters of the initial states and the environmental parameters in nonequilibrium environments.

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23

Mohamed, A. B. A., E. M. Khalil, M. F. Yassen, and H. Eleuch. "Two-Qubit Local Fisher Information Correlation beyond Entanglement in a Nonlinear Generalized Cavity with an Intrinsic Decoherence." Entropy 23, no. 3 (March 6, 2021): 311. http://dx.doi.org/10.3390/e23030311.

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In this paper, we study a Hamiltonian system constituted by two coupled two-level atoms (qubits) interacting with a nonlinear generalized cavity field. The nonclassical two-qubit correlation dynamics are investigated using Bures distance entanglement and local quantum Fisher information under the influences of intrinsic decoherence and qubit–qubit interaction. The effects of the superposition of two identical generalized coherent states and the initial coherent field intensity on the generated two-qubit correlations are investigated. Entanglement of sudden death and sudden birth of the Bures distance entanglement as well as the sudden changes in local Fisher information are observed. We show that the robustness, against decoherence, of the generated two-qubit correlations can be controlled by qubit–qubit coupling and the initial coherent cavity states.

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24

Metwally, N., and F. Ebrahim. "Fisher information of accelerated two-qubit system in the presence of the color and white noisy channels." International Journal of Modern Physics B 34, no. 05 (February 18, 2020): 2050027. http://dx.doi.org/10.1142/s0217979220500277.

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In this paper, an accelerated two-qubit system initially prepared in maximum or partial entangled state, which interacts locally with white/color or white-color noises, is considered. Due to the acceleration process and the noise effect, the entanglement degraded. Therefore, the effect of noise strength, initial state settings and the acceleration on the survival entanglement are investigated by means of the concurrence. Moreover, the initial parameters that describe this system are estimated by using the quantum Fisher information, where two forms are considered, namely by using a single and two-qubit forms. It is shown that, by using the two-qubit form, the estimation degree of these parameters is larger than that displayed by using a single-qubit form.

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25

JORRAND, PHILIPPE, and MEHDI MHALLA. "SEPARABILITY OF PURE N-QUBIT STATES: TWO CHARACTERIZATIONS." International Journal of Foundations of Computer Science 14, no. 05 (October 2003): 797–814. http://dx.doi.org/10.1142/s0129054103002035.

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Given a pure state |ψN>∈ℋN of a quantum system composed of n qubits, where ℋN is the Hilbert space of dimension N=2n, this paper answers two questions: what conditions should the amplitudes in |ψN> satisfy for this state to be separable (i) into a tensor product of n qubit states |ψ2>0⊗ |ψ2>1 ⊗⋯⊗ |ψ2>n-1, and (ii), into a tensor product of two subsystems states |ψP> ⊗ |ψQ> with P=2p and Q=2q such that p+q=n? For both questions, necessary and sufficient conditions are proved, thus characterizing at the same time families of separable and entangled states of n qubit systems. A number of more refined questions about separability in n qubit systems can be studied on the basis of these results.

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26

Cabot, Albert, Gian Luca Giorgi, and Roberta Zambrini. "Synchronization and coalescence in a dissipative two-qubit system." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 477, no. 2249 (May 2021): 20200850. http://dx.doi.org/10.1098/rspa.2020.0850.

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The possibility of detuned spins displaying synchronous oscillations in local observables is analysed in the presence of coupling, collective dissipation and incoherent pumping. We show that there exist two distinct scenarios in which synchronization can emerge, related respectively to the presence of a non-degenerate long-lived eigenmode and to the presence of a single-frequency regime. Both scenarios can arise by tuning parameters in this system, owing to the presence of coalascence. The former, known as transient synchronization, is here generalized in the presence of incoherent pumping, and is due to long-lasting coherences leading to a progressive frequency selection. On the other hand, in spite of the spins detuning, the dynamics can be governed by a single frequency. Still, we show that synchronization can be established only after a transient, when phase-locking arises. Spectral features of synchronization in these two scenarios are analysed for two-time correlations.

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27

Jie Zhao, Yang Yu, and Biao-Bing Jin. "Transmission Properties of a Qubit-Coupled-Two-Resonator System." IEEE Transactions on Applied Superconductivity 23, no. 3 (June 2013): 1701705. http://dx.doi.org/10.1109/tasc.2013.2243197.

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28

Zhang, Qiang, Alexander Goebel, Claudia Wagenknecht, Yu-Ao Chen, Bo Zhao, Tao Yang, Alois Mair, Jörg Schmiedmayer, and Jian-Wei Pan. "Experimental quantum teleportation of a two-qubit composite system." Nature Physics 2, no. 10 (September 17, 2006): 678–82. http://dx.doi.org/10.1038/nphys417.

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29

Łuczak, Jakub, and Bogdan R. Bułka. "Two-qubit logical operations in three quantum dots system." Journal of Physics: Condensed Matter 30, no. 22 (May 4, 2018): 225601. http://dx.doi.org/10.1088/1361-648x/aabe50.

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30

Ban, Masashi. "Disentanglement of two-qubit system in the Bloch channel." Optics Communications 283, no. 19 (October 2010): 3812–17. http://dx.doi.org/10.1016/j.optcom.2010.05.030.

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31

Devi, A. R. Usha, M. S. Uma, R. Prabhu, and Sudha. "Non-local properties of a symmetric two-qubit system." Journal of Optics B: Quantum and Semiclassical Optics 7, no. 12 (November 23, 2005): S740—S744. http://dx.doi.org/10.1088/1464-4266/7/12/042.

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32

Yang, Xiong, and Jia-hua Xiao. "Dynamics of quantum discord for a two-qubit system." Optoelectronics Letters 9, no. 1 (January 2013): 69–72. http://dx.doi.org/10.1007/s11801-013-2289-y.

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33

Li, Xiu-feng, and Mao-fa Fang. "Geometric Phase of Two-Qubit System with Dissipative Effects." International Journal of Theoretical Physics 53, no. 6 (January 22, 2014): 2075–81. http://dx.doi.org/10.1007/s10773-014-2013-0.

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34

Ma, Tiantian, Jun Jing, Yi Guo, and Ting Yu. "Quantum feedback control for qubit-qutrit entanglement." Quantum Information and Computation 16, no. 7&8 (May 2016): 597–614. http://dx.doi.org/10.26421/qic16.7-8-3.

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We study a hybrid quantum open system consisting of two interacting subsystems formed by one two-level atom (qubit) and one three-level atom (qutrit). The quantum open system is coupled to an external environment (cavity) via the qubit-cavity interaction. It is found that the feedback control on different parts of the system (qubit or qutrit) gives dramatically different asymptotical behaviors of the open system dynamics. We show that the local feedback control mechanism acting on the qutrit subsystem is superior than that on the qubit in the sense of improving the entanglement. Particularly, the qutrit-control scheme may result in an entangled steady state, depending on the initial state.

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35

Yan-liang ZHANG, 张延亮, 周清平 Qing-ping ZHOU, and 阳汝昭 Ru-zhao YANG. "The Study of Dynamics of Quantum Memory Assisted Entropic Uncertainty of the Two-qubit System Under Decoherence." Acta Sinica Quantum Optica 26, no. 2 (2020): 114. http://dx.doi.org/10.3788/jqo20202602.0103.

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LASTRA, F., G. ROMERO, C. E. LÓPEZ, and J. C. RETAMAL. "CLASSICAL NOISE INDUCED DECOHERENCE EFFECTS ON THE ENTANGLEMENT IN A TWO-QUBIT SYSTEM." International Journal of Quantum Information 05, no. 04 (August 2007): 457–68. http://dx.doi.org/10.1142/s0219749907003006.

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In this work we study entanglement properties of a two-qubit system being affected by a classical noisy environment and coupled through exchange interaction. We study the dynamical generation of entanglement considering different initial conditions for the two-qubit system. We evaluate the rate at which entanglement is lost by calculating the concurrence as a function of time.

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37

Essammouni, K., A. Chouikh, T. Said, and M. Bennai. "niSWAP and NTCP gates realized in a circuit QED system." International Journal of Geometric Methods in Modern Physics 14, no. 07 (March 7, 2017): 1750100. http://dx.doi.org/10.1142/s0219887817501006.

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Based on superconducting qubit coupled to a resonator driven by a strong microwave field, we propose a method to implement two quantum logic gates ([Formula: see text]SWAP and NTCP gates) of one qubit simultaneously controlling [Formula: see text] qubits selected from [Formula: see text] qubits in a circuit QED [Formula: see text] by introducing qubit–qubit interaction. The interaction between the qubits and the circuit QED can be achieved by tuning the gate voltage and the external flux. The operation times of the logic gates are much smaller than the decoherence time and dephasing time. Moreover, the numerical simulation under the influence of the gates operations shows that the scheme could be achieved efficiently with presently available techniques.

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38

Almarashi, Abdullah, Sayed Abdel-Khalek, and Debasis Kundu. "Photon statistics and non-local properties of a two-qubit-field system in the excited negative binomial distribution." Thermal Science 26, Spec. issue 1 (2022): 239–46. http://dx.doi.org/10.2298/tsci22s1239a.

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In this paper, a quantum scheme for a two-qubit system (2QS) and field initially prepared in the excited negative binomial distribution is presented. The field photon statistics is detected from the evolution of the Mandel parameter, while the evolution of von Neumann entropy detects the nonlocal correlation between the 2QS and radiation field. The concurrence is used to detect the qubit-qubit entanglement during the time evolution. The dynamical properties of single-qubit and two-qubit quantum Fisher information are investigated. We visualize the number of photon excitations on the field in negative binomial states with influence of photon success probability. A connection is provided between the dynamical behaviors of these statistical quantities. We have found that the proposed quantities are strongly influenced by the number of excited photons of the field in negative binomial states and photon success probability.

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39

Kuzmak, A. R. "Implementation of a two-qubit state by an auxiliary qubit on the three-spin system." Physica Scripta 95, no. 3 (February 3, 2020): 035403. http://dx.doi.org/10.1088/1402-4896/ab4b40.

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40

Mohamed, A.-B. A., H. A. Hessian, and H. Eleuch. "Generation of quantum coherence in two-qubit cavity system: qubit-dipole coupling and decoherence effects." Physica Scripta 95, no. 7 (May 18, 2020): 075104. http://dx.doi.org/10.1088/1402-4896/ab8f41.

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41

Shi, Jianxin. "Entanglement Research for the Coupled Superconducting Phase Qubit and a Two-Level System." Advances in Condensed Matter Physics 2020 (September 21, 2020): 1–8. http://dx.doi.org/10.1155/2020/3838106.

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Entanglement can exist not only in the microscopic system (e.g., atom, photon, and ion trap) but also in macroscopic systems. According to recent research, entanglement can be achieved and controlled in superconducting devices. The quantum dynamics and entanglement mechanism of the coupled superconducting phase qubit and a two-level system (TLS) were demonstrated when the bipartite system was under microwave driving. Besides, the results reveal that when the system was experiencing decoherence, entanglement (concurrence) of the coupled superconducting phase qubit and TLS would oscillate damply with microwave driving time, even exhibiting concurrence sudden death and revival. The coupling effect of the superconducting qubit and TLS system and the resonant microwave together help to achieve entanglement, while concurrence death and concurrence revival are dependent on the decoherence source and mechanism, for example, the resonant microwave driving time acting on the bipartite coupling system. Furthermore, the simulation results show the entanglement of the coupled qubit and TLS system also depends on the purity of the initial states of the system. The article carried out a numerical simulation on the entanglement of different initial states, and the results showed that the entanglement of the coupled system changes with different initial states. For different initial states, entanglement, sudden death, and rejuvenation are still visible.

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42

Metwally, N. "Fisher information of accelerated two-qubit systems." International Journal of Modern Physics B 32, no. 05 (February 2018): 1850050. http://dx.doi.org/10.1142/s0217979218500509.

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In this paper, Fisher information for an accelerated system initially prepared in the X-state is discussed. An analytical solution, which consists of three parts: classical, the average over all pure states and a mixture of pure states, is derived for the general state and for Werner state. It is shown that the Unruh acceleration has a depleting effect on the Fisher information. This depletion depends on the degree of entanglement of the initial state settings. For the X-state, for some intervals of Unruh acceleration, the Fisher information remains constant, irrespective to the Unruh acceleration. In general, the possibility of estimating the state’s parameters decreases as the acceleration increases. However, the precision of estimation can be maximized for certain values of the Unruh acceleration. We also investigate the contribution of the different parts of the Fisher information on the dynamics of the total Fisher information.

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METWALLY, N., M. ABDEL-ATY, and A. S. OBADA. "COHERENT AND INCOHERENT BEHAVIORS OF QUBITS INTERACTING WITH A SPIN-PATH PARTICLE." International Journal of Modern Physics B 27, no. 17 (July 3, 2013): 1350076. http://dx.doi.org/10.1142/s0217979213500768.

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We analyze a crucial effect of the spin-path environment on a single and maximum entangled two-qubit systems. For a single qubit, we investigate the coherent loss by means of coherent-vectors' dynamics and the interacted qubits' fidelity. We used entanglement and population dynamics to investigate the coherent loss of the two-qubit system. We show and numerically verify that the effect of the detuning and coupling parameters in the negativity can be mapped onto the maximum and minimum values of the entanglement.

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Zheng, Chao, Jin Tian, Daili Li, Jingwei Wen, Shijie Wei, and Yansong Li. "Efficient Quantum Simulation of an Anti-P-Pseudo-Hermitian Two-Level System." Entropy 22, no. 8 (July 24, 2020): 812. http://dx.doi.org/10.3390/e22080812.

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Besides Hermitian systems, quantum simulation has become a strong tool to investigate non-Hermitian systems, such as PT-symmetric, anti-PT-symmetric, and pseudo-Hermitian systems. In this work, we theoretically investigate quantum simulation of an anti-P-pseudo-Hermitian two-level system in different dimensional Hilbert spaces. In an arbitrary phase, we find that six dimensions are the minimum to construct the anti-P-pseudo-Hermitian two-level subsystem, and it has a higher success probability than using eight dimensions. We find that the dimensions can be reduced further to four or two when the system is in the anti-PT-symmetric or Hermitian phase, respectively. Both qubit-qudit hybrid and pure-qubit systems are able to realize the simulation, enabling experimental implementations in the near future.

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Bhandari, Bibek, Robert Czupryniak, Paolo Andrea Erdman, and Andrew N. Jordan. "Measurement-Based Quantum Thermal Machines with Feedback Control." Entropy 25, no. 2 (January 20, 2023): 204. http://dx.doi.org/10.3390/e25020204.

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We investigated coupled-qubit-based thermal machines powered by quantum measurements and feedback. We considered two different versions of the machine: (1) a quantum Maxwell’s demon, where the coupled-qubit system is connected to a detachable single shared bath, and (2) a measurement-assisted refrigerator, where the coupled-qubit system is in contact with a hot and cold bath. In the quantum Maxwell’s demon case, we discuss both discrete and continuous measurements. We found that the power output from a single qubit-based device can be improved by coupling it to the second qubit. We further found that the simultaneous measurement of both qubits can produce higher net heat extraction compared to two setups operated in parallel where only single-qubit measurements are performed. In the refrigerator case, we used continuous measurement and unitary operations to power the coupled-qubit-based refrigerator. We found that the cooling power of a refrigerator operated with swap operations can be enhanced by performing suitable measurements.

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López-Saldívar, Julio A., Octavio Castaños, Margarita A. Man’ko, and Vladimir I. Man’ko. "A New Mechanism of Open System Evolution and Its Entropy Using Unitary Transformations in Noncomposite Qudit Systems." Entropy 21, no. 8 (July 27, 2019): 736. http://dx.doi.org/10.3390/e21080736.

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The evolution of an open system is usually associated with the interaction of the system with an environment. A new method to study the open-type system evolution of a qubit (two-level atom) state is established. This evolution is determined by a unitary transformation applied to the qutrit (three-level atom) state, which defines the qubit subsystems. This procedure can be used to obtain different qubit quantum channels employing unitary transformations into the qutrit system. In particular, we study the phase damping and spontaneous-emission quantum channels. In addition, we mention a proposal for quasiunitary transforms of qubits, in view of the unitary transform of the total qutrit system. The experimental realization is also addressed. The probability representation of the evolution and its information-entropic characteristics are considered.

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Algarni, Mariam, Kamal Berrada, Sayed Abdel-Khalek, and Hichem Eleuch. "Parity Deformed Tavis-Cummings Model: Entanglement, Parameter Estimation and Statistical Properties." Mathematics 10, no. 17 (August 24, 2022): 3051. http://dx.doi.org/10.3390/math10173051.

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In this paper, we introduce the parity extension of the harmonic oscillator systems to develop the generalized Tavis-Cummings model (T-CM) based on a specific deformation of the Heisenberg algebra. We present a quantum scheme of a two-qubit system (TQS) interacting with a quantized field that is initially prepared in parity deformed coherent states (PDCSs). The dynamical features of the considered system are explored in the presence of parity deformed parameter (PDP) and time-dependent coupling (t-dc). In particular, we examine the amount of the entanglement formed in the qubit–field and qubit–qubit states. We find that the maximal amount of the entanglement may be occurred periodically during the time evolution. Finally, we investigate the influence of PDP on the Fisher information and the photon statistics of the deformed field with respect to the main parameters of the system.

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Plesch, M., and V. Buzek. "Entangled graphs." Quantum Information and Computation 2, Special (November 2002): 530–39. http://dx.doi.org/10.26421/qic2.s-3.

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We study how bi-partite quantum entanglement (measured in terms of a concurrence) can be shared in multi-qubit systems. We introduce a concept of the entangled graph such that each qubit of a multi-partite system is associated with a vertex while a bi-partite entanglement between two specific qubits is represented by an edge. We prove that any entangled graph can be associated with a pure state of a multi-qubit system. We also derive bounds on the concurrence for some weighted entangled graphs (the weight corresponds to the value of concurrence associated with the given edge).

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Bertoni, A., P. Bordone, R. Brunetti, C. Jacoboni, and S. Reggiani. "Numerical Simulation of Quantum Logic Gates Based on Quantum Wires." VLSI Design 13, no. 1-4 (January 1, 2001): 97–102. http://dx.doi.org/10.1155/2001/86126.

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A system based on frontier mesoscopic semiconductor technology, able to perform the basic quantum operations needed for quantum computation, is proposed. The elementary quantum bit (qubit) is defined as the state of an electron running along a couple of quantum wires coupled through a potential barrier with variable height and/ or width. A proper design of the system, together with the action of Coulomb interaction of two electrons representing two different qubits, allows the implementation of basic one-qubit and two-qubit quantum logic gates. Numerical simulations confirm the correctness of the hypothesis.

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Duan, Junjun, Lin Zhang, Quan Qian, and Shao-Ming Fei. "A Characterization of Maximally Entangled Two-Qubit States." Entropy 24, no. 2 (February 7, 2022): 247. http://dx.doi.org/10.3390/e24020247.

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As already known by Rana’s result, all eigenvalues of any partial-transposed bipartite state fall within the closed interval [−12,1]. In this note, we study a family of bipartite quantum states where the minimal eigenvalues of partial-transposed states are −12. For a two-qubit system, we find that the minimal eigenvalue of its partial-transposed state is −12 if and only if such a two-qubit state is maximally entangled. However this result does not hold in general for a two-qudit system when the dimensions of the underlying space are larger than two.

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