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An actively correlated Mach-Zehnder interferometer (ACMZI) renders a number of significant advantages over a conventional Mach-Zehnder interferometer (MZI) with a squeezed vacuum state input such as an active output readout, loss tolerant detection, and multiarms for multiparameter estimation. We theoretically studied the quantum Cram\'er-Rao bound of an ACMZI, where the quantum Fisher information obtained by the phase-averaging method can give the conclusive phase-sensing sensitivity without any external phase reference. We numerically calculate the phase sensitivities with the method of homodyne detection and intensity detection in the presence of losses. Under lossless and very low loss conditions, the ACMZI is operated in a balanced case to beat the standard quantum limit (SQL). As the loss increases, the reduction in sensitivity increases. Fortunately, within a certain range, we can adjust the gain parameters of the beam recombination process to reduce the reduction in sensitivity and realize the sensitivity can continue to beat the SQL in an unbalanced situation. Our scheme provides an optimization method of phase estimation in the presence of losses.

Quantum non-demolition (QND) measurement is an important tool in the fields of quantum information processing and quantum optics. The atom-light hybrid interferometer is of great interest due to its combination of an atomic spin wave and an optical wave, which can be utilized for photon number QND measurement via the AC-Stark effect. In this paper, we present an SU(1,1)-SU(2)-concatenated atom-light hybrid interferometer, and theoretically study QND measurement of the photon number. Compared to the traditional SU(2) interferometer, the signal-to-noise ratio in a balanced case is improved by a gain factor of the nonlinear Raman process (NRP) in this proposed interferometer. Furthermore, the condition of high-quality QND measurement is analyzed. In the presence of losses, the measurement quality is reduced. We can adjust the gain parameter of the NRP in the readout stage to reduce the impact due to losses. Moreover, this scheme is a multiarm interferometer, which has the potential of multiparameter estimation with many important applications in the detection of vector fields, quantum imaging, and so on.

A nonlinear phase shift is introduced to a Mach-Zehnder interferometer (MZI), and we present a scheme for enhancing the phase sensitivity. In our scheme, one input port of a standard MZI is injected with a coherent state and the other input port is injected with one mode of a two-mode squeezed-vacuum state. The final interference output of the MZI is detected with the method of active correlation output readout. Based on the optimal splitting ratio of beam splitters, the phase sensitivity can beat the standard quantum limit and approach the quantum Cram\'{e}r-Rao bound. The effects of photon loss on phase sensitivity are discussed. Our scheme can also provide some estimates for units of $\chi^{(3)}$, due to the relation between the nonlinear phase shift and the susceptibility $\chi^{(3)}$ of the Kerr medium., Comment: 4 figures

We theoretically study angular displacement estimation based on a modified Mach-Zehnder interferometer (MZI), in which two optical parametric amplifiers (PAs) are introduced into two arms of the standard MZI, respectively. The employment of PAs can both squeeze the shot noise and amplify the photon number inside the interferometer. When the unknown angular displacements are introduced to both arms, we derive the multiparameter quantum Cramér-Rao bound (QCRB) using the quantum Fisher information matrix approach, and the bound of angular displacement difference between the two arms is compared with the sensitivity of angular displacement using the intensity detection. On the other hand, in the case where the unknown angular displacement is in only one arm, we give the sensitivity of angular displacement using the method of homodyne detection. It can surpass the standard quantum limit (SQL) and approach the single parameter QCRB. Finally, the effect of photon losses on sensitivity is discussed.

We theoretically investigate the frequency-nondegenerate and frequency degenerate squeezed lights with a four-wave mixing process (4WM) driven by two pump fields crossing at a small angle. Different from a 4WM process driven by a single pump field, the refractive index of the corresponding probe field, n p, can be converted to a value that is greater than 1 or less than 1 by an angle adjustment. In the new region with n p < 1, the bandwidth of the gain is relatively large due to the slow change in the refractive index with the two-photon detuning. In this region with an exchange of the roles of the pump and probe beams, the frequency degenerate and spatial nondegenerate twin beams can be generated, which has potential application in quantum information and quantum metrology.

The strengthening abilities of NbTi for 6-filamentary MgB1.9(TiC)0.08/Nb/Cu wires and the electrical properties have been investigated. The NbTi reinforcing core was suitable for manufacturing MgB2 wires. It was observed that with the sintering temperature increasing, the yield strength decreased. The plasticity improved while the strength changed little by introduction of intermediate annealing during the cold processing of the wires. The transport properties of the wire degraded to some degree due to intermediate annealing. The mechanical properties have already met the application requirements of superconducting magnets in low field with the critical engineering current Ic above 90 A (Jce exceeding 7.9×103 A/cm2) at 35 K in self-field.

In this paper, we propose a modified bidimensional empirical mode decomposition (BEMD) algorithm where the interpolation method is based on radial basis function interpolation using blocking technique combined with natural mosaicing. We can get ride of solving large linear equations and calculating huge matrix. It is proved that the modified method has faster calculating speed. At the same time, it reduces the border error problem as a result of blocking. Experimental results demonstrate that it is feasible and effective.