E. S. Cardoso, M. C. de Oliveira, K. Furuya
Quantification of entanglement against mixing is given for a system of coupled qubits under a phase damping channel. A family of pure initial joint states is defined, ranging from pure separable states to maximally entangled state. An ordering of entanglement measures is given for well defined initial state amount of entanglement.
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For a class of mixed two -qubit states we show that it is not possible to discriminate between states violating or non - violating Bell - CHSH inequalities, knowing only their entanglement and mixedness. For a large set of possible values of these quantities, we construct pairs of states with the same entanglement and mixedness such that one state is violating but the other is non - violating Bell - CHSH inequality.
Maximally entangled mixed states are those states that, for a given mixedness, achieve the greatest possible entanglement. For two-qubit systems and for various combinations of entanglement and mixedness measures, the form of the corresponding maximally entangled mixed states is determined primarily analytically. As measures of entanglement, we consider entanglement of formation, relative entropy of entanglement, and negativity; as measures of mixedness, we consider linear and von Neumann entropies. We show that the forms of the maximally entangled mixed states can vary with the combination of…
Quantum Imaginarity-Mixedness Trade-off: Characterizing Maximally Imaginary Mixed States
研究了任意 $d$ 维量子系统中虚部与混合度的权衡关系，定义并刻画了最大虚部混合态（MIMS），揭示了多种范数与熵之间的互补关系，并分析了单量子比特在四种马尔可夫信道下的演化。
We study entanglement properties of all eigenstates of the Heisenberg XXX model, and find that the entanglement and mixedness for a pair of nearest-neighbor qubits are completely determined by the corresponding eigenenergies. Specifically, the negativity of the eigenenergy implies pairwise entanglement. From the relation between entanglement and eigenenergy, we obtain finite-size behaviors of the entanglement. We also study entanglement and mixedness versus energy in the quantum Heisenberg XY model.
Wave-particle-mixedness redistribution in Schwarzschild spacetime
该研究探讨史瓦西时空中霍金辐射与通道噪声对两量子比特各向同性态波粒特征及混合度分布的影响，发现三者间的三元关系不受这类噪声影响。
The relation between the violation of the Bell-CHSH inequalities and entanglement properties of quantum states is not clear so one may consider the mixedness of the system to understand the entanglement properties better than the Bell-CHSH inequality. In this respect, we prove that if the mixedness of the state measured by the linear entropy is less than 2/3 but strictly greater than zero then the two qubit states are entangled. But if the linear entropy is greater or equal to 2/3 then the state may or may not be entangled. Further we show that our entanglement criterion detects larger set of …
We investigate the system-environment information flow from the point of view ofcomplete complementarity relations. We consider some commonly used noisy quantum channels:Amplitude damping, phase damping, bit flip, bit-phase flip, phase flip, depolarizing, and correlatedamplitude damping. By starting with an entangled bipartite pure quantum state, with the linearentropy being the quantifier of entanglement, we study how entanglement is redistributed and turnedinto general correlations between the degrees of freedom of the whole system. For instance, it ispossible to express the entanglement ent…
The effect of noise on various protocols of secure quantum communication has been studied. Specifically, we have investigated the effect of amplitude damping, phase damping, squeezed generalized amplitude damping, Pauli type as well as various collective noise models on the protocols of quantum key distribution, quantum key agreement,quantum secure direct quantum communication and quantum dialogue. From each type of protocol of secure quantum communication, we have chosen two protocols for our comparative study; one based on single qubit states and the other one on entangled states. The compar…
Zero- Versus Infinite-Temperature Damping in Variational Quantum Circuits: Feature Scale, Sampling Cost, and Frame Gauge
该研究比较变分量子电路中零温振幅阻尼与其无限温泡利twirl，隔离零温偏置对特征尺度的影响，发现可训练输出尺度可消除精度差异但增加测量采样成本，并指出阻尼方向在特定条件下为规范。
By means of two simple examples: phase and amplitude damping, the impact of decoherence on the dynamical Casimir effect is investigated. Even without dissipating energy (i.e., pure phase damping), the amount of created particles can be diminished significantly via the coupling to the environment (reservoir theory) inducing decoherence. For a simple microscopic model, it is demonstrated that spontaneous decays within the medium generate those problems -- Rabi oscillations are far more advantageous in that respect. These findings are particularly relevant in view of a recently proposed experimen…
Single-qubit channels are studied under two broad classes: amplitude damping channels and generalized depolarizing channels. A canonical derivation of the Kraus representation of the former, via the Choi isomorphism is presented for the general case of a system's interaction with a squeezed thermal bath. This isomorphism is also used to characterize the difference in the geometry and rank of these channel classes. Under the isomorphism, the degree of decoherence is quantified according to the mixedness or separability of the Choi matrix. Whereas the latter channels form a 3-simplex, the former…
We study the possibility of exploiting superpositions of coherent states to encode qubit. A comparison between the use of deformed and undeformed bosonic algebra is made in connection with the amplitude damping errors.
There is current interest in investigating which variables play an important role in the physical processes with an open composite quan- tum system that ranges from the foundational issues to the tasks of diverse applications in quantum physics and technology. In this paper we contrast the local versus the collective classical-like behavior of a pair of interacting qubits immersed in the mutually independent thermal baths. The qubits can be locally subjected to any of the standard, microscopically modelled, generalized amplitude damping and phase damping channel, as well as to the recently int…
Geometry versus excitation sector in the decoherence of asymmetric $N$-qubit $W$ states
该研究对比非对称N量子比特W态退相干中网络几何与激发扇区对两体纠缠的影响，推导噪声模型下的并发度动力学，明确两者为纠缠鲁棒性的独立控制要素。
The dynamics of entanglement between three - level atoms coupled to the common vacuum is investigated. We show that the collective effects such as collective damping, dipole - dipole interaction and the cross coupling between orthogonal dipoles, play a crucial role in the process of creation of entanglement. In particular, the additional cross coupling enhances the production of entanglement. For the specific initial states we find that the effect of delayed sudden birth of entanglement, recently invented by Ficek and Tanas [Phys. Rev. A 77, o54301(2008)] in the case of two - level atoms, can …
Decoherence Mitigation with Local NOT Gates in Multipartite Systems
研究2-3-4量子比特贝尔态和GHZ态在幅值阻尼通道中的纠缠动力学，通过真多体纯度（GMC）和最优量子 teleportation 保真度评估其用途，发现局部NOT操作能有效将退相干导致的纠缠突然死亡转化为渐进衰减。
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