Cross-Kerr nonlinearity between continuous-mode coherent states and single photons

Weak cross-Kerr nonlinearities between single photons and coherent states are the basis for many applications in quantum information processing. These nonlinearities have so far mainly been discussed in terms of highly idealized single-mode models. We develop a general theory of the interaction between continuous-mode photonic pulses and apply it to the case of a single photon interacting with a coherent state. We quantitatively study the validity of the usual single-mode approximation using the concepts of fidelity and conditional phase. We show that high fidelities, non-zero conditional phases and high photon numbers are compatible, under conditions where the pulses fully pass through each other and where unwanted transverse-mode effects are suppressed.Comment: 8 pages, 2 figures, more general results in section V

Control of photon propagation via electromagnetically induced transparency in lossless media

We study the influence of a lossless material medium on the coherent storage and quantum state transfer of a quantized probe light in an ensemble of $\Lambda$-type atoms. The medium is modeled as uniformly distributed two-level atoms with same energy level spacing, coupling to a probe light. This coupled system can be simplified to a collection of two-mode polaritons which couple to one transition of the $\Lambda$-type atoms. We show that, when the other transition of $\Lambda$-type atoms is controlled by a classical light, the electromagnetically induced transparency can also occur for the polaritons. In this case the coherent storage and quantum transfer for photon states are achievable through the novel dark states with respect to the polaritons. By calculating the corresponding dispersion relation, we find the ensemble of the three-level atoms with $\Lambda$-type transitions may serve as quantum memory for it slows or even stops the light propagation through the mechanism of electromagnetically induced transparency. the corresponding dispersion relation, we find the ensemble of the three-level atoms with $\Lambda$-type transitions may serve as quantum memory for it slows or even stops the light propagation through the mechanism of electromagnetically induced transparency.Comment: 10 pages, 5 figure

Coherent Control of Magneto-optical Rotation in Inhomogeneously Broadened Medium

We extend our earlier investigations [Opt. Commun. {\bf 179}, 97 (2000)] on the enhancement of magneto-optical rotation (MOR) to include inhomogeneous broadening. We introduce a control field that counter-propagates with respect to the probe field. We derive analytical results for the susceptibilities corresponding to the two circular polarization components of the probe field. From the analytical results we identify and numerically demonstrate the region of parameters where significantly large magneto-optical rotation (MOR) can be obtained. From the numerical results we isolate the significance of the magnetic field and the control field in enhancement of MOR. The control field opens up many new regions of the frequencies of the probe where large magneto-optical rotation occurs. We also report that a large enhancement of MOR can be obtained by operating the probe and control field in two-photon resonance condition.Comment: REVTex format, 14 pages including 6 figures, to be published in Optics Communication

Coherent versus Incoherent Light Scattering from a Quantum Dot

We analyze the light scattered by a single InAs quantum dot interacting with a resonant continuous-wave laser. High resolution spectra reveal clear distinctions between coherent and incoherent scattering, with the laser intensity spanning over four orders of magnitude. We find that the fraction of coherently scattered photons can approach unity under sufficiently weak or detuned excitation, ruling out pure dephasing as a relevant decoherence mechanism. We show how spectral diffusion shapes spectra, correlation functions, and phase-coherence, concealing the ideal radiatively-broadened two-level system described by Mollow.Comment: to appear in PRB 85, 23531

Far-off resonance conditional phase-shifter using the ac-Stark shift

We propose a simple technique that achieves a conditional phase shift of pi radians between two weak lasers with energies at the 1000-photon level. The key idea is to set up a V-system with two far-off resonant lasers by coupling the ground state to two excited electronic states. The lasers interact through the ac Stark shift of the ground state and thereby acquire a large conditional phase shift.Comment: 4 pages, 3 figure

A protective role for BRCA2 at stalled replication forks

The hereditary breast and ovarian cancer predisposition genes BRCA1 and BRCA2 account for the lion's share of heritable breast cancer risk in the human population. Loss of function of either gene results in defective homologous recombination (HR) and triggers genomic instability, accelerating breast tumorigenesis. A long-standing hypothesis proposes that BRCA1 and BRCA2 mediate HR following attempted replication across damaged DNA, ensuring error-free processing of the stalled replication fork. A recent paper describes a new replication fork protective function of BRCA2, which appears to collaborate with its HR function to suppress genomic instability

Thermodynamics of quantum systems under dynamical control

In this review the debated rapport between thermodynamics and quantum mechanics is addressed in the framework of the theory of periodically-driven/controlled quantum-thermodynamic machines. The basic model studied here is that of a two-level system (TLS), whose energy is periodically modulated while the system is coupled to thermal baths. When the modulation interval is short compared to the bath memory time, the system-bath correlations are affected, thereby causing cooling or heating of the TLS, depending on the interval. In steady state, a periodically-modulated TLS coupled to two distinct baths constitutes the simplest quantum heat machine (QHM) that may operate as either an engine or a refrigerator, depending on the modulation rate. We find their efficiency and power-output bounds and the conditions for attaining these bounds. An extension of this model to multilevel systems shows that the QHM power output can be boosted by the multilevel degeneracy. These results are used to scrutinize basic thermodynamic principles: (i) Externally-driven/modulated QHMs may attain the Carnot efficiency bound, but when the driving is done by a quantum device ("piston"), the efficiency strongly depends on its initial quantum state. Such dependence has been unknown thus far. (ii) The refrigeration rate effected by QHMs does not vanish as the temperature approaches absolute zero for certain quantized baths, e.g., magnons, thous challenging Nernst's unattainability principle. (iii) System-bath correlations allow more work extraction under periodic control than that expected from the Szilard-Landauer principle, provided the period is in the non-Markovian domain. Thus, dynamically-controlled QHMs may benefit from hitherto unexploited thermodynamic resources

The Apoptotic Effect of the Hexane Extract of Rheum undulatum L. in Oral Cancer Cells through the Down-regulation of Specificity Protein 1 and Survivin

The hexane extract of Rheum undulatum L. (HERL) has been shown to have anti-cancer activity in several cancers in vivo and in vitro. However, the anti-cancer activity of HERL and its molecular mechanism in human oral cancer cells has not been explored. Thus, the aim of this study was to elucidate the growth-inhibitory and apoptosis-inducing effects of HERL in HN22 and SCC15 oral cancer cell lines. This study shows that HERL inhibits oral cancer growth, decreases cell viability, and causes apoptotic cell death in HN22 and SCC15 cells, as characterized by morphological changes, nuclear condensation and fragmentation, the cleavage of PARP and the accumulation of cells in the sub-G1 phase. The treatment of oral cancer cells with HERL also resulted in decreased expression of specificity protein (Sp1) and its downstream protein, survivin. Therefore, our results suggest that the regulation of Sp1 and survivin plays a critical role in HERL-induced apoptosis in human oral cancer cells

Quantifying vertical mixing in estuaries

© 2008 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution Noncommercial License. The definitive version was published in Environmental Fluid Mechanics 8 (2008): 495-509, doi:10.1007/s10652-008-9107-2.Estuarine turbulence is notable in that both the dissipation rate and the buoyancy frequency extend to much higher values than in other natural environments. The high dissipation rates lead to a distinct inertial subrange in the velocity and scalar spectra, which can be exploited for quantifying the turbulence quantities. However, high buoyancy frequencies lead to small Ozmidov scales, which require high sampling rates and small spatial aperture to resolve the turbulent fluxes. A set of observations in a highly stratified estuary demonstrate the effectiveness of a vessel-mounted turbulence array for resolving turbulent processes, and for relating the turbulence to the forcing by the Reynolds-averaged flow. The observations focus on the ebb, when most of the buoyancy flux occurs. Three stages of mixing are observed: (1) intermittent and localized but intense shear instability during the early ebb; (2) continuous and relatively homogeneous shear-induced mixing during the mid-ebb, and weakly stratified, boundary-layer mixing during the late ebb. The mixing efficiency as quantified by the flux Richardson number Rf was frequently observed to be higher than the canonical value of 0.15 from Osborn (J Phys Oceanogr 10:83–89, 1980). The high efficiency may be linked to the temporal–spatial evolution of shear instabilities.The funding for this research was obtained from ONR Grant N00014-06-1-0292 and NSF Grant OCE-0729547