Two-colour high-purity Einstein-Podolsky-Rosen photonic state.

We report a high-purity Einstein-Podolsky-Rosen (EPR) state between light modes with the wavelengths separated by more than 200 nm. We demonstrate highly efficient EPR-steering between the modes with the product of conditional variances [Formula: see text]. The modes display - 7.7 ± 0.5 dB of two-mode squeezing and an overall state purity of 0.63 ± 0.16. EPR-steering is observed over five octaves of sideband frequencies from RF down to audio-band. The demonstrated combination of high state purity, strong quantum correlations, and extended frequency range enables new matter-light quantum protocols.

Quantum frequency conversion of vacuum squeezed light to bright tunable blue squeezed light and higher-order spatial modes.

Quantum frequency conversion, the process of shifting the frequency of an optical quantum state while preserving quantum coherence, can be used to produce non-classical light at otherwise unapproachable wavelengths. We present experimental results based on highly efficient sum-frequency generation (SFG) between a vacuum squeezed state at 1064 nm and a tunable pump source at 850 nm ± 50 nm for the generation of bright squeezed light at 472 nm ± 4 nm, currently limited by the phase-matching of the used nonlinear crystal. We demonstrate that the SFG process conserves part of the quantum coherence as a 4.2(±0.2) dB 1064 nm vacuum squeezed state is converted to a 1.6(±0.2) dB tunable bright blue squeezed state. We furthermore demonstrate simultaneous frequency- and spatial-mode conversion of the 1064-nm vacuum squeezed state, and measure 1.1(±0.2) dB and 0.4(±0.2) dB of squeezing in the TEM01 and TEM02 modes, respectively. With further development, we foresee that the source may find use within fields such as sensing, metrology, spectroscopy, and imaging.

Cavity-enhanced sum-frequency generation of blue light with near-unity conversion efficiency.

We report on double-resonant highly efficient sum-frequency generation in the blue range. The system consists of a 10-mm-long periodically poled KTP crystal placed in a double-resonant bow-tie cavity and pumped by a fiber laser at 1064.5 nm and a Ti:sapphire laser at 849.2 nm. An optical power of 375 mW at 472.4 nm in a TEM00 mode was generated with pump powers of 250 mW at 849.2 nm and 200 mW at 1064.5 nm coupled into the double-resonant ring resonator with 88% mode-matching. The resulting internal conversion efficiency of 95(±3)% of the photons mode-matched to the cavity constitutes, to the best of our knowledge, the highest overall achieved quantum conversion efficiency using continuous-wave pumping. Very high conversion efficiency is rendered possible due to very low intracavity loss on the level of 0.3% and high nonlinear conversion coefficient up to 0.045(0.015) W-1. Power stability measurements performed over one hour show a stability of 0.8%. The generated blue light can be tuned within 5 nm around the center wavelength of 472.4 nm, limited by the phase-matching of our nonlinear crystal. This can however be expanded to cover the entire blue spectrum (420 nm to 510 nm) by proper choice of nonlinear crystals and pump lasers. Our experimental results agree very well with analytical and numerical simulations taking into account cavity impedance matching and depletion of the pump fields.

Continuous-wave coherent Raman spectroscopy for improving the accuracy of Raman shifts.

Raman spectroscopy is an appealing technique that probes molecular vibrations in a wide variety of materials with virtually no sample preparation. However, accurate and reliable Raman measurements are still a challenge and require more robust and practical calibration methods. We demonstrate the implementation of a simple low-cost continuous-wave (cw) stimulated Raman spectroscopy scheme for accurate and high-resolution spectroscopy. We perform shot noise-limited cw stimulated Raman scattering as well as cw coherent anti-Stokes Raman scattering on polystyrene samples. Our method enables accurate determination of Raman shifts with an uncertainty below 0.1 cm-1. The setup is used for the characterization of reference materials required for the calibration of Raman spectrometers. Compared with existing standards, we provide an order of magnitude improvement of the uncertainty of Raman energy shifts in a polystyrene reference material.

Quantification of microwave-induced amorphization of celecoxib in PVP tablets using transmission Raman spectroscopy.

In this study, the influence of drug load on the microwave-induced amorphization of celecoxib (CCX) in polyvinylpyrrolidone (PVP) tablets was investigated using quantitative transmission Raman spectroscopy. A design of experiments (DoE) setup was applied for developing the quantitative model using two factors: drug load (10, 30, and 50% w/w) and amorphous fraction (0, 25, 50, 75 and 100%). The data was modeled using partial least-squares (PLS) regression and resulted in a robust model with a root mean-square error of prediction of 2.5%. The PLS model was used to study the amorphization kinetics of CCX-PVP tablets with different drug content (10, 20, 30, 40 and 50% w/w). For this purpose, transition Raman spectra were collected in 60 s intervals over a total microwave time of 10 min with an energy input of 1000 W. Using the quantitative model it was possible to measure the amorphous fraction of the tablets and follow the amorphization as a function of microwaving time. The relative amorphous fraction of CCX increased with increasing microwaving time and decreasing drug load, hence 90 ±â€¯7% of the drug was amorphized in the tablets with 10% drug load whereas only 31 ±â€¯7% of the drug was amorphized in the 50% CCX tablets. It is suggested that the degree of amorphization depends on drug loading. The likelihood of drug particles being in direct contact with the polymer PVP is a requirement for the dissolution of the drug into the polymer upon microwaving, and this is reduced with increasing drug load. This was further supported by polarized light microscopy that revealed evidence of crystalline particles and clusters in all the microwaved tablets.

Compact and versatile laser system for polarization-sensitive stimulated Raman spectroscopy.

We demonstrate a compact and versatile laser system for stimulated Raman spectroscopy (SRS). The system is based on a tunable continuous wave (CW) probe laser combined with a home-built semi-monolithic nanosecond pulsed pump Nd:YVO4 laser at 1064 nm. The CW operation of the probe laser offers narrow linewidth, low noise and the advantage that temporal synchronization with the pump is not required. The laser system enables polarization-sensitive stimulated Raman spectroscopy (PS-SRS) with fast high resolution measurement of the depolarization ratio by simultaneous detection of Raman scattered light in orthogonal polarizations, thus providing information about the symmetry of the Raman-active vibrational modes. Measurements of the depolarization ratios of the carbon-hydrogen (CH) stretching modes in two different polymer samples in the spectral range of 2825-3025 cm-1 were performed. Raman spectra are obtained at a sweep rate of 20 nm/s (84 cm-1/s) with a resolution of 0.65 cm-1. A normalization method is introduced for the direct comparison of the simultaneously acquired orthogonal polarized Raman spectra.

Quantum enhanced feedback cooling of a mechanical oscillator using nonclassical light.

Laser cooling is a fundamental technique used in primary atomic frequency standards, quantum computers, quantum condensed matter physics and tests of fundamental physics, among other areas. It has been known since the early 1990s that laser cooling can, in principle, be improved by using squeezed light as an electromagnetic reservoir; while quantum feedback control using a squeezed light probe is also predicted to allow improved cooling. Here we show the implementation of quantum feedback control of a micro-mechanical oscillator using squeezed probe light. This allows quantum-enhanced feedback cooling with a measurement rate greater than it is possible with classical light, and a consequent reduction in the final oscillator temperature. Our results have significance for future applications in areas ranging from quantum information networks, to quantum-enhanced force and displacement measurements and fundamental tests of macroscopic quantum mechanics.

Quantum-enhanced micromechanical displacement sensitivity.

We report on a hitherto unexplored application of squeezed light: for quantum-enhancement of mechanical transduction sensitivity in microcavity optomechanics. Using a toroidal silica microcavity, we experimentally demonstrate measurement of the transduced phase modulation signal in the frequency range 4-5.8 MHz with a sensitivity -0.72(±0.01) dB below the shot noise level. This is achieved for resonant probing in the highly undercoupled regime, by preparing the probe in a weak coherent state with phase squeezed vacuum states at sideband frequencies.