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Triangle-like inequalities related to coherence and entanglement negativity
摘要： Quantum coherence and entanglement are two key features in quantum mechanics and play important roles in quantum information processing and quantum computation. We provide a general triangle-like inequality satisfied by the l1-norm measure of coherence for convex combination of arbitrary n pure states of a quantum state ρ. Furthermore, we present triangle-like inequality for the convex-roof extended negativity for any states of rank 2, which gives a positive answer to a conjecture raised in Dai et al. (Phys. Rev. A 96:062308, 2017). Detailed examples are given to illustrate the relations characterized by the triangle-like inequalities.
关键词： Convex-roof extended negativity,Triangle-like inequality,Quantum coherence
更新于2025-09-10 09:29:36
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Dynamics of Kerr-like medium with two-mode intensity-dependent cavity fields
摘要： The dynamics of an effective two-level atom coupled to two-mode intensity-dependent quantized cavity fields via a ladder process in the presence of a Kerr medium has been investigated. Eigenfunctions and eigenvalues of the Hamiltonian of the interacting system have been obtained using a unitary transformation method. The cavity field statistics and non-classical properties are investigated numerically through second-order correlation functions. The effect of detuning and the Kerr medium on the non-classical features of the atom-field state has been analyzed. We find that the presence of Kerr non-linearity enhances the non-classical correlation between the correlated beams at short time intervals and increases antibunching at short time intervals.
关键词： intensity-dependent coupling,antibunching,photon statistics,Kerr non-linearity,two-mode ladder model,Cauchy–Schwartz inequality,second-order correlation functions
更新于2025-09-09 09:28:46
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Experimental observation of the Leggett-Garg inequality violation in classical light
摘要： Leggett-Garg inequalities (LG inequalities) have been derived to clarify the validity of generalizing quantum mechanics to macroscopic systems more than thirty years. They have been used as tools to investigate the existence of quantum coherence in the macroscopic systems. Here we show that such inequalities violation can also be observed in classical optical systems. Using the linear polarization degree of freedom as the dichotomic observables, in classical optical experiment we have observed the violation of LG inequality by implementing the non-invasive measurement. Furthermore, the coherence witness, which is analogy of the quantum witness, has also been observed in the classical optical experiment. Our results not only provide new physical insights into the macroscopic quantum correlation and quantum witness, but also show their potential applications in correlated information processes.
关键词： classical optical correlation,Leggett-Garg inequality
更新于2025-09-09 09:28:46
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Various angle periods of parabolic coincidence fringes in violation of the Bell inequality with high-dimensional two-photon entanglement
摘要： Two quantum states of two half-charge optical vortexes with relative azimuthal angle π are orthogonal, by which two half-charge spiral phase plates with intersection angle π can be used to demonstrate a parabolic coincident fringe in the Bell inequality experiment with high-dimensional two-photon orbital angular momentum entanglement and to thereby obtain a strong Bell parameter of 3 1/5. I theoretically demonstrate various orthogonal relations between two quantum states, each of which is a state with a rotational symmetry superposition made up of n fractional orbital angular momentum states, where n ∈ N. I propose a Bell inequality experiment with two n-section spiral phase plates that have these two quantum states, whereby various angle periods with parabolic coincident fringes 2π/n and Bell’s parameter 3 1/5 in each period can be obtained.
关键词： Bell inequality,orbital angular momentum,spiral phase plates,high-dimensional entanglement,parabolic coincident fringes
更新于2025-09-09 09:28:46
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Response in the violation of the Bell inequality to imperfect photon addition and subtraction in noisy squeezed states of light
摘要： Violation of Bell inequality is a prominent detection method for quantum correlations present in composite quantum systems, both in finite and infinite dimensions. We investigate the consequence of the violation of local realism based on pseudospin operators when photons are added or subtracted in a single mode or in both the modes of the two-mode squeezed states of light in the presence of noise. In the noiseless situation, we show that for addition (subtraction) of photons in a single mode, there is an overall enhancement in the maximal violation, although we observe an interplay between monotonicity and nonmonotonicity in the violation of Bell inequality depending on the squeezing strength. Moreover, we report that for low squeezing or low number of photons added or subtracted, subtraction in both the modes can lead to higher violation of local realism than that in the case of addition. For any choice of parameters, such ordering is not seen if one compares their entanglement contents. In the event of a faulty twin-beam generator, we obtain a lower than expected squeezing in the state. In such a case, or in imperfect photon addition (subtraction) or under local noise, we find that the violation of local realism by the noise-affected two-mode squeezed states always decreases. Interestingly, however, we notice that photon addition (subtraction) can in general help to conquer the ill effects of noise by enhancing the violation of local realism or by transforming nonviolating states to violating ones, thereby acting as an activating agent.
关键词： two-mode squeezed states,photon subtraction,local realism,photon addition,quantum correlations,Bell inequality,noise
更新于2025-09-09 09:28:46
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Finer distribution of quantum correlations among multiqubit systems
摘要： We study the distribution of quantum correlations characterized by monogamy relations in multipartite systems. By using the Hamming weight of the binary vectors associated with the subsystems, we establish a class of monogamy inequalities for multiqubit entanglement based on the αth (α ≥ 2) power of concurrence, and a class of polygamy inequalities for multiqubit entanglement in terms of the βth (0 ≤ β ≤ 2) power of concurrence and concurrence of assistance. Moveover, we give the monogamy and polygamy inequalities for general quantum correlations. Application of these results to quantum correlations like squared convex-roof extended negativity, entanglement of formation and Tsallis-q entanglement gives rise to either tighter inequalities than the existing ones for some classes of quantum states or less restrictions on the quantum states. Detailed examples are presented.
关键词： Polygamy inequality,Hamming weight,Multiqubit systems,Monogamy relation
更新于2025-09-04 15:30:14