Experimental study of modified Tavis-Cummings model with directly-coupled superconducting artificial atoms.

The Tavis-Cummings model is intensively investigated in quantum optics and has important applications in generation of multi-atom entanglement. Here, we employ a superconducting circuit quantum electrodynamic system to study a modified Tavis-Cummings model with directly-coupled atoms. In our device, three superconducting artificial atoms are arranged in a chain with direct coupling through fixed capacitors and strongly coupled to a transmission line resonator. By performing transmission spectrum measurements, we observe different anticrossing structures when one or two qubits are resonantly coupled to the resonator. In the case of the two-qubit Tavis-Cummings model without qubit-qubit interaction, we observe two dips at the resonance point of the anticrossing. The splitting of these dips is determined by Δ λ=2g12+g32, where g1 and g3 are the coupling strengths between Qubit 1 and the resonator, and Qubit 3 and the resonator, respectively. The direct coupling J12 between the two qubits results in three dressed states in the two-qubit Tavis-Cummings model at the frequency resonance point, leading to three dips in the transmission spectrum. In this case, the distance between the two farthest and asymmetrical dips, arising from the energy level splitting, is larger than in the previous case. The frequency interval between these two dips is determined by the difference in eigenvalues (Δ λ=ε 1+-ε 1-), obtained through numerical calculations. What we believe as novel and intriguing experimental results may potentially advance quantum optics experiments, providing valuable insights for future research.

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.

[Effect of Transcutaneuos Acupoint Electrostimulation on Serum Sex Hormone Levels and Expression of Ovarian Steroid Hormone Metabolic Enzymes in Polycystic Ovary Syndrome Rats].

OBJECTIVE: To observe the effect of transcutaneuos acupoint electrostimulation(TAES) on ovarian serum sex hormone levels and ovarian follicle granular cell aromatase cytochrome P 450 (P 450 arom) protein and follicle theca cell cytochrome P 450 17 α-hydroxylase/c 17-20 lyase cytochrome P 450 (P 450 c 17 α) protein expression in polycystic ovary syndrome (PCOS)rats, so as to explore its mechanisms underlying improvement of PCOS. METHODS Forty SD rats were randomly divided into four groups: normal control, model, medication and TAES (10 rats/group). The PCOS model was established by giving (gavage) the animals with letrozole solution (1.0 mg/kg, once daily for 21 consecutive days). Rats of the medication group were treated with Clomiphene (1 mg/kg) once daily for 7 days, and those of the TAES group were treated with electrical stimulation (2 Hz, 3 mA) of "Guanyuan" (CV 4) and "Sanyinjiao" (SP 6) areas for 30 min, once daily for 7 consecutive days. The rats body weight and bilateral ovarian weight were detected, and the ovarian structure and follicular development degree were observed under light microscope after H. E. stain, and the serum testosterone (T), estradiol (E2), luteotrophic hormone (LH) and follicle-stimulating hormone (FSH) contents were detected using radioimmunoassay. The expression of ovarian P 450 arom (for production of estrogen)protein and P 450 c 17 α (for production of androgen) protein was detected by using immunohistochemical stain and Western blot, respectively. RESULTS: The body weight, bilateral ovary weight, serum T and LH contents, and ratio of LH/FSH, and ovarian P 450 c 17 α immunoactivity and protein expression levels in the model group were all significantly increased compared with the normal control group (P < 0.01), and the levels of serum E2 and ovarian P 450 arom immunoactivity and protein expression were significantly decreased after modeling (P < 0.01). Following the treatment, the increased body weight, ovary weight, serum T and LH contents, ratio of LH/FSH, and ovarian P 450 c 17 α immunoactivity and protein expression levels, and the decreased ovarian P 450 arom immunoactivity and protein expression levels were reversed in the TAES group (P < 0.01, P < 0.05) rather than in the medication group, except serum T and ratio of LH/FSH in the medication group. No significant differences were found between the medication and TAES groups in the serum T and ratio of LH/FSH (P > 0.05). In addition, the increased vesicular follicle number, the decreased corepus luteum number and the thickness of granular cell layer were markedly improved in the TAES group. CONCLUSION: TAES intervention can reduce both body weight and ovarian weight and regulate the levels of serum sex hormones and ovarian P 450 c 17 α and P 450 arom protein expression levels in PCOS rats, which may contribute to its effect in improving PCOS.