Tighter constraints of multiqubit entanglement in terms of Renyi-α entropy

Quantum entanglement plays essential roles in quantum information processing.The monogamy and polygamy relations characterize the entanglement distributions in the multipartite systems.We present a class of monogamy inequalities related to theµ-th power of the entanglement measure based on Renyi-αentropy,as well as polygamy relations in terms of theµ-th power of Renyi-αentanglement of assistance.These monogamy and polygamy relations are shown to be tighter than the existing ones.

Discrimination of coherent states via atom–field interaction without rotation wave approximation

Quantum state discrimination is an important part of quantum information processing.We investigate the discrimination of coherent states through a Jaynes-Cummings(JC)model interaction between the field and the ancilla without rotation wave approximation(RWA).We show that the minimum failure probability can be reduced as RWA is eliminated from the JC model and the non-RWA terms accompanied by the quantum effects of fields(e.g.the virtualphoton process in the JC model without RWA)can enhance the state discrimination.The JC model without RWA for unambiguous state discrimination is superior to ambiguous state discrimination,particularly when the number of sequential measurements increases.Unambiguous state discrimination implemented via the non-RWA JC model is beneficial to saving resource costs.

Dynamics of coherence-induced state ordering under Markovian channels

We study the dynamics of coherence-induced state ordering under incoherent channels, particularly four specific Markovian channels： amplitude damping channel, phase damping channel, depolarizing channel and bit flit channel for single-qnbit states. We show that the amplitude damping channel, phase damping channel, and depolarizing channel do not change the coherence-induced state ordering by l1 norm of coherence, relative entropy of coherence, geometric measure of coherence, and Tsallis relative α-entropies, while the bit flit channel does change for some special cases.

Maximum relative entropy of coherence for quantum channels

Based on the resource theory for quantifying the coherence of quantum channels, we introduce a new coherence quantifier for quantum channels via maximum relative entropy. We prove that the maximum relative entropy for coherence of quantum channels is directly related to the maximally coherent channels under a particular class of superoperations, which results in an operational interpretation of the maximum relative entropy for coherence of quantum channels. We also introduce the conception of subsuperchannels and sub-superchannel discrimination. For any quantum channels, we show that the advantage of quantum channels in sub-superchannel discrimination can be exactly characterized by the maximum relative entropy of coherence for quantum channels. Similar to the maximum relative entropy of coherence for channels, the robustness of coherence for quantum channels has also been investigated. We show that the maximum relative entropy of coherence for channels provides new operational interpretations of robustness of coherence for quantum channels and illustrates the equivalence of the dephasing-covariant superchannels,incoherent superchannels, and strictly incoherent superchannels in these two operational tasks.

Experimental detection of quantum entanglement

In this review, we introduce some methods for detecting or measuring entanglement. Several non- linear entanglement witnesses are presented. We derive a series of Bell inequalities whose maximally violations for any multipartite qubit states can be calculated by using our formulas. Both the non- linear entanglement witnesses and the Bell inequalities can be operated experimentally. Thus they supply an effective way for detecting entanglement. We also introduce some experimental methods to measure the entanglement of formation, and the lower bound of the convex-roof extension of negativity.

Quantum Fisher information and coherence in one-dimensional XY spin models with Dzyaloshinsky-Moriya interactions

We investigate quantum phase transitions in XY spin models using Dzyaloshinsky-Moriya(DM) interactions. We identify the quantum critical points via quantum Fisher information and quantum coherence, finding that higher DM couplings suppress quantum phase transitions. However, quantum coherence(characterized by the l_1-norm and relative entropy) decreases as the DM coupling increases. Herein, we present both analytical and numerical results.