The time optimal problem for a two level quantum system is studied. We compare two different control strategies of bangbang control and the geometric control, respectively, especially in the case of minimizing the time of steering the state from North Pole to South Pole on the Bloch sphere with bounded control. The time performances are compared for different parameters by the individual numerical simulation experiments, and the experimental results are analyzed. The results show that the geometric control spends less time than the bangbang control does.
The quantum swap gate is one of the most useful gates for quantum computation. Two-qubit entanglement and a controlled-NOT quantum gate in a neutral Rydberg atom system have been achieved in recent experiments. It is therefore very interesting to propose a scheme here for swapping a quantum state between two trapped neutral atoms via the Rydberg blockade mechanism. The atoms interact with a sequence of laser pulses without individual addressing. The errors of the swap gate due to imprecision of pulse length, finite Rydberg interaction, and atomic spontaneous emission are discussed.
During the past few years, researchers have made significant progress on quantum information processing in gate controlled semiconductor quantum dots. We review the global research efforts, including works by our group, which provides pathways towards applications in quantum computation.
We investigate the possibility of observing in integrated solid-state systems the dynamical Casimir effect,in which photons are created out of vacuum.We use a transmission line resonator on a superconducting chip as the microwave cavity and modulate its properties by coupling it to carefully designed Josephson devices.We evaluate the effect of main decoherence sources and show that our design offers a promising system for experimentally demonstrating the dynamical Casimir effect.Moreover,we also study the squeezing properties of the created photon field and how they depend on the dissipation.
In an optomechanical resonator, the optical and mechanical excitations can be coherently converted, which induces a transparency window for a weak probe laser beam. Here, we report an experimental study of transient optomechanically induced transparency(OMIT) using the silica microsphere with the breathing modes. The transient OMIT behavior obtained are in good agreement with theoretical calculations. In addition, the coherent interconversion between optical and mechanical excitations that can be used for light storage and readout has also been studied here. Our experimental results indicate that the light storage is closely related to the process of OMIT, and the photon-phonon conversion can be further applied to optical wavelength or optical mode conversion.
Using first-principles calculations within the generalized gradient approximation (GGA) +U framework, we investigate the effect of C doping on the structural and electronic properties of LiFePO 4 . The calculated formation energies indicate that C doped at O sites is energetically favoured, and that C dopants prefer to occupy O 3 sites. The band gap of the C doped material is much narrow than that of the undoped one, indicating better electro- conductive properties. To maintain charge balance, the valence of the Fe nearest to C appears as Fe 3+ , and it will be helpful to the hopping of electrons.
Quantum key distribution(QKD)provides an unconditional secure key generation method between two distant legitimate parties Alice and Bob based on the fundamental properties of quantum mechanics,in the presence of an eavesdropper Eve.Since key reconciliation cannot always assure that the reconciled keys between Alice and Bob are identical,error verification is an important step in QKD.In this paper,we propose a scheme of delayed error verification using extra keys gained by privacy amplification with an arbitrarily small failure probability.The proposed scheme simplifies the post-processing procedure in QKD,which can be applied in practical QKD systems.
Chun-Mei ZhangXiao-Tian SongPatcharapong TreeviriyanupabMo LiChao WangHong-Wei LiZhen-Qiang YinWei ChenZheng-Fu Han
