Recent measurements using two-dimensional electronic spectroscopy (2D ES) have shown that the initial dynamic response of photosynthetic proteins can involve quantum coherence. We show how electronic coherence can be differentiated from vibrational coherence in 2D ES. On that basis we conclude that both electronic and vibrational coherences are observed in the phycobiliprotein light-harvesting complex PC645 from Chroomonas sp. CCMP270 at ambient temperature. These light-harvesting antenna proteins of the cryptophyte algae are suspended in the lumen, where the pH drops significantly under sustained illumination by sunlight. Here we measured 2D ES of PC645 at increasing levels of acidity to determine if the change in pH affects the quantum coherence; quantitative analysis reveals that the dynamics are insensitive to the pH change.

We have measured whole-pulse photon statistics of macroscopic twin pulses of light generated by coherently seeding a two-mode optical parametric amplifier equally in each mode. We are able to produce 300 ps, near-transform-limited twin pulses ( -10^ photons) with a difference photon number having a variance measured to be 73% below the shot-noise level. We have measured probability distributions of the photoelectron difference number, which are the only photoelectron distributions in the macroscopic regime which cannot be explained using standard semiclassical detection theory.

Stimulated emission depletion (STED) fluorescence microscopy squeezes an excited spot well below the wavelength scale using a doughnut-shaped depletion beam. To generate a doughnut, a scale-free vortex phase modulation (2D-STED) is often used because it provides maximal transverse confinement and radial-aberration immunity (RAI) to the central dip. However, RAI also means blindness to a defocus term, making the axial origin of fluorescence photons uncertain within the wavelength scale provided by the confocal detection pinhole. Here, to reduce the uncertainty, we perturb the 2D-STED phase mask so as to change the sign of the axial concavity near focus, creating a dilated dip. By providing laser depletion power, the dip can be compressed back in three dimensions to retrieve lateral resolution, now at a significantly higher contrast. We test this coherent-hybrid STED (CH-STED) mode in x-y imaging of complex biological structures, such as the dividing cell. The proposed strategy creates an orthogonal direction in the STED parametric space that uniquely allows independent tuning of resolution and contrast using a single depletion beam in a conventional (circular polarization-based) STED setup.

We have studied one-body and two-body correlation functions in a ballistically expanding, noninteracting atomic cloud in the presence of gravity. We find that the correlation functions are equivalent to those at thermal equilibrium in the trap with an appropriate rescaling of the coordinates. We derive simple expressions for the correlation lengths and give some physical interpretations. Finally a simple model to take into account finite detector resolution is discussed.

New efficient and thermally stable NLO-chromophores 4-5 based on a thienylpyrrolyl donor πconjugated bridge and a benzimidazolyl acceptor moieties were developed by a one step Na 2 S 2 O 4 reduction of substituted o-nitroanilines in the presence of formyl-thienylpyrroles. Abstract -A new series of thermally stable benzimidazole-based nonlinear optical (NLO)chromophores 4-5 has been developed. These chromophores possess a thienylpyrrolyl πconjugated system attached to functionalized benzimidazole heterocycles. This feature leads to robust chromophores with excellent solvatochromic properties, high thermal stabilities and good molecular optical nonlinearities.