Quantum simulation of tunable and ultrastrong mixed-optomechanics.

We propose a reliable scheme to simulate tunable and ultrastrong mixed (first-order and quadratic optomechanical couplings coexisting) optomechanical interactions in a coupled two-mode bosonic system, in which the two modes are coupled by a cross-Kerr interaction and one of the two modes is driven through both the single- and two-excitation processes. We show that the mixed-optomechanical interactions can enter the single-photon strong-coupling and even ultrastrong-coupling regimes. The strengths of both the first-order and quadratic optomechanical couplings can be controlled on demand, and hence first-order, quadratic, and mixed optomechanical models can be realized. In particular, the thermal noise of the driven mode can be suppressed totally by introducing a proper squeezed vacuum bath. We also study how to generate the superposition of coherent squeezed state and vacuum state based on the simulated interactions. The quantum coherence effect in the generated states is characterized by calculating the Wigner function in both the closed- and open-system cases. This work will pave the way to the observation and application of ultrastrong optomechanical effects in quantum simulators.

Spectrometric detection of weak forces in cavity optomechanics.

We propose a spectrometric method to detect a classical weak force acting upon the moving end mirror in a cavity optomechanical system. The force changes the equilibrium position of the end mirror, and thus the resonance frequency of the cavity field depends on the force to be detected. As a result, the magnitude of the force can be inferred by analyzing the single-photon emission and scattering spectra of the optomechanical cavity. Since the emission and scattering processes are much faster than the characteristic mechanical dissipation, the influence of the mechanical thermal noise is negligible in this spectrometric detection scheme. We also extent this spectrometric method to detect a monochromatic oscillating force by utilizing an optomechanical coupling modulated at the same frequency as the force.

Quantum entanglement maintained by virtual excitations in an ultrastrongly-coupled-oscillator system.

We study the effect of quantum entanglement maintained by virtual excitations in an ultrastrongly-coupled harmonic-oscillator system. Here, the quantum entanglement is caused by the counterrotating interaction terms and hence it is maintained by the virtual excitations. We obtain the analytical expression for the ground state of the system and analyze the relationship between the average excitation numbers and the ground-state entanglement. We also study the entanglement dynamics between the two oscillators in both the closed- and open-system cases. In the latter case, the quantum master equation is microscopically derived in the normal-mode representation of the coupled-oscillator system. This work will open a route to the study of quantum information processing and quantum physics based on virtual excitations.

Genome shuffling and ribosome engineering of Streptomyces virginiae for improved virginiamycin production.

The production of virginiamycin (VGM) from Streptomyces virginiae was improved by genome shuffling and ribosome engineering companied with a high-throughput screening method integrating deep-well cultivation and the cylinder-plate detecting. First, a novel high-throughput method was developed to rapidly screen large numbers of VGM-producing mutants. Then, the starting population of genome shuffling was obtained through ultraviolet (UV) and microwave mutagenesis, and four mutants with higher productivity of VGM were selected for genome shuffling. Next, the parent protoplasts were inactivated by UV and heat when a fusant probability was about 98%. Streptomycin resistance was used as an evolutionary pressure to extend positive effects on VGM synthesis. Finally, after five rounds of genome shuffling, a genetically stable strain G5-103 was obtained and characterized to be able to yield 251 mg/L VGM, which was 3.1- and 11.6-fold higher than that of the mutant strain UV 1150 and the wild-type strain, respectively.

Identification of three antigen epitopes on the nucleocapsid protein of the genotype C of bovine parainfluenza virus type 3.

Bovine parainfluenza virus type 3 (BPIV3) is an important respiratory tract pathogen for both young and adult cattle. So far, three genotypes A, B and C of BPIV3 have been described on the basis of genetic and phylogenetic analysis. But fine mapping of epitopes of BPIV3 is scant and the antigenic variations among the three genotypes of BPIV3 have not been reported. Nucleocapsid protein (NP) is the most abundant protein in the virion and highly conserved in BPIV3, which is crucial for the induction of protective immunity in host. To identify antigenic determinants of BPIV3 NP, a panel of monoclonal antibodies (mAbs) was tested against a series of overlapping recombinant NP fragments expressed in Escherichia coli. Firstly, six monoclonal antibodies (mAbs) against NP of the genotype C of BPIV3 (BPIV3c) were generated by using the purified BPIV3c strain SD0835 as immunogen and the recombinant NP of SD0835 as screening antigen. Then three antigen epitopes were identified with the six mAbs. One epitope (91)GNNADVKYVIYM(102) was recognized by mAb 5E5. The mAbs 7G5, 7G8, 7G9, and 7H5 were reactive with another epitope (407)FYKPTGG(413). The third epitope (428)ESRGDQDQ(435) was reactive with mAb 6F8. Further analysis showed that the epitope (91-102 amino acids [aa]) was the most conserved and reactive with mAb 5E5 for all three genotypes of BPIV3 and HPIV3. The epitope (407-413 aa) was relatively conserved and reactive with mAbs 7G5, 7G8, 7G9, and 7H5 for BPIV3a, BPIV3c and HPIV3, but not reactive with BPIV3b. The epitope (428-435 aa) was less conserved and was reactive only with mAb 6F8 for BPIV3a and BPIV3c. These results suggested that there were evident antigenic variations among the three genotypes of BPIV3 and HPIV3. The mAb 6F8 could be used to detect BPIV3a and BPIV3c. The mAbs 7G5, 7G8, 7G9, and 7H5 might be used for differentiate BPIV3a, BPIV3c and HPIV3 from BPIV3b. The mAb 5E5 might be used for detecting all three types of BPIV3 and HPIV3. The results in this study would have potential applications in the development of suitable diagnostic techniques for BPIV3, which was prevalent in China.