Efficient scheme for realizing a multiplex-controlled phase gate with photonic qubits in circuit quantum electrodynamics

We propose an efficient scheme to implement a multiplex-controlled phase gate with multiple photonic qubits simultaneously controlling one target photonic qubit based on circuit quantum electrodynamics(QED).For convenience,we denote this multiqubit gate as MCP gate.The gate is realized by using a two-level coupler to couple multiple cavities.The coupler here is a superconducting qubit.This scheme is simple because the gate implementation requires only one step of operation.In addition,this scheme is quite general because the two logic states of each photonic qubit can be encoded with a vacuum state and an arbitrary non-vacuum state|φ>(e.g.,a Fock state,a superposition of Fock states,a cat state,or a coherent state,etc.)which is orthogonal or quasi-orthogonal to the vacuum state.The scheme has some additional advantages:because only two levels of the coupler are used,i.e.,no auxiliary levels are utilized,decoherence from higher energy levels of the coupler is avoided;the gate operation time does not depend on the number of qubits;and the gate is implemented deterministically because no measurement is applied.As an example,we numerically analyze the circuit-QED based experimental feasibility of implementing a three-qubit MCP gate with photonic qubits each encoded via a vacuum state and a cat state.The scheme can be applied to accomplish the same task in a wide range of physical system,which consists of multiple microwave or optical cavities coupled to a two-level coupler such as a natural or artificial atom.

A novel method of polarization state control for polarization division multiplexing system

We describe a new algorithm in a cost effective polarization division multiplexing （PDM） system. Without modifying the existing transmitter, receiver electronics, or softwares, we use a special optical scheme to demultiplex the signal multiplexed and improve it with a conjugated gradient algorithm. We experimentally resume the polarization state with a deviation under 5% and the power loss less than 20 dB which proves the feasibility of the polarization control algorithm in the new polarization multiplexing system.

Ripple-based matrix modeling and cross-coupling effect analysis of double-input DC-DC Boost converters

This paper deals with the modeling and cross-coupling effect analysis in double-input Boost converters with multiplex current control. A ripple-based multiplex current controlled matrix model is proposed to restore the system's high-frequency domain dynamics information and resolve the coexistence problem of the sample-and-hold effect in multiplex current controllers, which significantly improves the resolution of the conventional average model. Based on the proposed model, both sub-harmonic and low-frequency oscillations are identified in terms of stability analysis, and the inherent mechanism of these complicated nonlinear dynamic behavior is revealed, which not only illustrates the origin of the oscillations but also points out the dominant factors in diverse types of instability situation. Besides, cross-coupling effect analysis is performed to study the interaction between the input ports with the help of the Gershgorin band, and the mechanism of the special unbalanced oscillation phenomenon is revealed. Furthermore, the sensitivity analysis approach is used to identify the key parameters with respect to the cross-coupling effect, which provides more design-oriented knowledge for practical engineering. In addition, the benefits of the proposed model are further illustrated through a comparative analysis. Finally, these theoretical results are verified by experimental ones. These results are beneficial to the improvement of performance as well as the understanding of the cross-coupling effect of multi-input converters.