Correlations in atomic systems: Diagnosing coherent superpositions

While investigating quantum correlations in atomic systems, we note that single measurements contain information about these correlations. Using a simple model of measurement -- analogous to the one used in quantum optics -- we show how to extract higher order correlation functions from individual "phtotographs" of the atomic sample. As a possible application we apply the method to detect a subtle phase coherence in mesoscopic superpostitions.Comment: 4 pages, 2 figures, provisionally accepted to Physical Review Letter

Extracting molecular Hamiltonian structure from time-dependent fluorescence intensity data

We propose a formalism for extracting molecular Hamiltonian structure from inversion of time-dependent fluorescence intensity data. The proposed method requires a minimum of \emph{a priori} knowledge about the system and allows for extracting a complete set of information about the Hamiltonian for a pair of molecular electronic surfaces.Comment: 7pages, no figures, LaTeX2

High-efficiency, high-power difference-frequency generation of 0.9–1.5 μm light in BBO

An efficient method for generation of high energy pulsed ir light between 0.9 and 1.5 μm is described. The technique uses difference frequency mixing of pulsed, visible dye and Nd:YAG laser light in a 10 mm long BBO crystal. Quantum efficiencies of up to 23% and ir pulse energies up to 4.5 mJ are demonstrated. The low shot-to-shot fluctuations of difference frequency generation in BBO make this technique an attractive alternative to the conventional optical parametric oscillator or Raman shifting methods that are currently used to access this spectral region

Duplex formation between the template and the nascent strand in the transcription-regulating sequences is associated with the site of template switching in SARS - CoV-2.

Funder: Clinical Academic ReserveFunder: NUS Department of MedicineFunder: Biomedical Research CentreRecently published transcriptomic data of the SARS-CoV-2 coronavirus show that there is a large variation in the frequency and steady state levels of subgenomic mRNA sequences. This variation is derived from discontinuous subgenomic RNA synthesis, where the polymerase switches template from a 3' proximal genome body sequence to a 5' untranslated leader sequence. This leads to a fusion between the common 5' leader sequence and a 3' proximal body sequence in the RNA product. This process revolves around a common core sequence (CS) that is present at both the template sites that make up the fusion junction. Base-pairing between the leader CS and the nascent complementary minus strand body CS, and flanking regions (together called the transcription regulating sequence, TRS) is vital for this template switching event. However, various factors can influence the site of template switching within the same TRS duplex. Here, we model the duplexes formed between the leader and complementary body TRS regions, hypothesizing the role of the stability of the TRS duplex in determining the major sites of template switching for the most abundant mRNAs. We indicate that the stability of secondary structures and the speed of transcription play key roles in determining the probability of template switching in the production of subgenomic RNAs. We speculate on the effect of reported variant nucleotide substitutions on our models

Quantum State Tomography of Complex Multimode Fields using Array Detectors

We demonstrate that it is possible to use the balanced homodyning with array detectors to measure the quantum state of correlated two-mode signal field. We show the applicability of the method to fields with complex mode functions, thus generalizing the work of Beck (Phys. Rev. Letts. 84, 5748 (2000)) in several important ways. We further establish that, under suitable conditions, array detector measurements from one of the two outputs is sufficient to determine the quantum state of signals. We show the power of the method by reconstructing a truncated Perelomov state which exhibits complicated structure in the joint probability density for the quadratures.Comment: 14 pages text and 3 figures. To be submitted to PR

Complete characterization of weak, ultrashort near-UV pulses by spectral interferometry

We present a method for a complete characterization of a femtosecond ultraviolet pulse when a fundamental near-infrared beam is also available. Our approach relies on generation of second harmonic from the pre-characterized fundamental, which serves as a reference against which an unknown pulse is measured using spectral interference (SI). The characterization apparatus is a modified second harmonic frequency resolved optical gating setup which additionally allows for taking SI spectrum. The presented method is linear in the unknown field, simple and sensitive. We checked its accuracy using test pulses generated in a thick nonlinear crystal, demonstrating the ability to measure the phase in a broad spectral range, down to 0.1% peak spectral intensity as well as retrieving pi leaps in the spectral phase

The SARS-CoV-2 spike protein binds and modulates estrogen receptors

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein binds angiotensin-converting enzyme 2 as its primary infection mechanism. Interactions between S and endogenous proteins occur after infection but are not well understood. We profiled binding of S against >9000 human proteins and found an interaction between S and human estrogen receptor alpha (ER alpha). Using bioinformatics, supercomputing, and experimental assays, we identified a highly conserved and functional nuclear receptor coregulator (NRC) LXD-like motif on the S2 sub-unit. In cultured cells, S DNA transfection increased ER alpha cytoplasmic accumulation, and S treatment induced ER-dependent biological effects. Non-invasive imaging in SARS-CoV-2-infected hamsters localized lung pathology with increased ER alpha lung levels. Postmortem lung experiments from infected hamsters and humans confirmed an increase in cytoplasmic ER alpha and its colocalization with S in alveolar macrophages. These findings describe the discovery of a S-ER alpha interaction, imply a role for S as an NRC, and advance knowledge of SARS-CoV-2 biology and coronavirus disease 2019 pathology

Polaritonic molecular clock for all-optical ultrafast imaging of wavepacket dynamics without probe pulses

Conventional approaches to probing ultrafast molecular dynamics rely on the use of synchronized laser pulses with a well-defined time delay. Typically, a pump pulse excites a molecular wavepacket. A subsequent probe pulse can then dissociate or ionize the molecule, and measurement of the molecular fragments provides information about where the wavepacket was for each time delay. Here, we propose to exploit the ultrafast nuclear-position-dependent emission obtained due to large light–matter coupling in plasmonic nanocavities to image wavepacket dynamics using only a single pump pulse. We show that the time-resolved emission from the cavity provides information about when the wavepacket passes a given region in nuclear configuration space. This approach can image both cavity-modified dynamics on polaritonic (hybrid light–matter) potentials in the strong light–matter coupling regime and bare-molecule dynamics in the intermediate coupling regime of large Purcell enhancements, and provides a route towards ultrafast molecular spectroscopy with plasmonic nanocavitiesThis work has been funded by the European Research Council grant ERC-2016-STG-714870 and the Spanish Ministry for Science, Innovation, and Universities—AEI grants RTI2018-099737-B-I00, PCI2018-093145 (through the QuantERA program of the European Commission), and CEX2018-000805-M (through the María de Maeztu program for Units of Excellence in R&D