In the analysis of quantum discord, the minimization of average entropy traditionally involved over orthogonal projective measurements may be attained at more optimal decompositions by using the positive-operator-valued measure（POVM）measurements. Taking advantage of the quantum steering ellipsoid in combination with three-element POVM optimization,we show that, for a family of two-qubit X states locally interacting with Markovian non-dissipative environments, the decay rates of quantum discord show smooth dynamical evolutions without any sudden change. This is in contrast to two-element orthogonal projective measurements, in which case the sudden change of the decay rates of quantum and classical decoherences may be a common phenomenon. Notwithstanding this, we find that a subset of X states（including the Bell diagonal states） involving POVM optimization can still preserve the sudden change character as usual.
A symmetric measure of quantum correlation based on the Hilbert–Schmidt distance is presented in this paper. For two-qubit states, we considerably simplify the optimization procedure so that numerical evaluation can be performed efficiently. Analytical expressions for the quantum correlation are attained for some special states. We further investigate the dynamics of quantum correlation of the system qubits in the presence of independent dissipative environments. Several nontrivial aspects are demonstrated. We find that the quantum correlation can increase even if the system state is suffering from dissipative noise. Sudden changes occur, even twice, in the time evolution of quantum correlation. There exists a certain correspondence between the evolution of quantum correlation in the systems and that in the environments, and the quantum correlation in the systems will be transferred into the environments completely and asymptotically.
We carried out a proof-of-principle demonstration of the reconstruction of a static vector magnetic field involving adjacent three nitrogen-vacancy(NV) sensors with corresponding different NV symmetry axes in a bulk diamond. By means of optical detection of the magnetic resonance(ODMR) techniques, our experiment employs the continuous wave(CW) to monitor resonance frequencies and it extracts the information of the detected field strength and polar angles with respect to each NV frame of reference. Finally, the detected magnetic field relative to a fixed laboratory reference frame was reconstructed from the information acquired by the multi-NV sensor.
The radiation and ionization energy loss are presented for single arm Monte Carlo simulation for the GDH sum rule experiment in Hall-A at the Jefferson Lab. Radiation and ionization energy loss are discussed for12 C elastic scattering simulation. The relative momentum ratio△p pand12 C elastic cross section are compared without and with radiative energy loss and a reasonable shape is obtained by the simulation. The total energy loss distribution is obtained, showing a Landau shape for12 C elastic scattering. This simulation work will give good support for radiation correction analysis of the GDH sum rule experiment.
We perform a proof-of-principle experiment that uses a single negatively charged nitrogen–vacancy（NV） color center with a nearest neighbor ^13C nuclear spin in diamond to detect the strength and direction（including both polar and azimuth angles） of a static vector magnetic field by optical detection magnetic resonance（ODMR） technique. With the known hyperfine coupling tensor between an NV center and a nearest neighbor ^13C nuclear spin, we show that the information of static vector magnetic field could be extracted by observing the pulsed continuous wave（CW） spectrum.
Feng-Jian JiangJian-Feng YeZheng JiaoJun Jiang Kun MaXin-Hu YanHai-Jiang Lv
We suggest an experimental scheme that a single nitrogen-vacancy（NV） center coupled to a nearest neighbor ^13C nucleus as a sensor in diamond can be used to detect a static vector magnetic field. By means of optical detection magnetic resonance（ODMR） technique, both the strength and the direction of the vector field could be determined by relevant resonance frequencies of continuous wave（CW） and Ramsey spectrums. In addition, we give a method that determines the unique one of eight possible hyperfine tensors for an（NV–^13C） system. Finally, we propose an unambiguous method to exclude the symmetrical solution from eight possible vector fields, which correspond to nearly identical resonance frequencies due to their mirror symmetry about ^14N–Vacancy–^13 C（^14N–V–^13C） plane.
