Quantum resources can enhance the sensitivity of a device beyond the classical shot noise limit and, as a result, revolutionize the field of metrology through the development of quantum-enhanced sensors. In particular, plasmonic sensors, which are widely used in biological and chemical sensing applications, offer a unique opportunity to bring such an enhancement to real-life devices. Here, we use bright entangled twin beams to enhance the sensitivity of a plasmonic sensor used to measure local changes in refractive index. We demonstrate a 56% quantum enhancement in the sensitivity of state-of-the-art plasmonic sensor with measured sensitivities on the order of 10 −10 RIU/ √ Hz, nearly 5 orders of magnitude better than previous proof-of-principle implementations of quantumenhanced plasmonic sensors. These results promise significant enhancements in ultratrace label free plasmonic sensing and will find their way into areas ranging from biomedical applications to chemical detection.

Spatial quantum correlations in the transverse degree of freedom promise to enhance optical resolution, image detection, and quantum communications through parallel quantum information encoding. In particular, the ability to observe these spatial quantum correlations in a single shot will enable such enhancements in applications that require real time imaging, such as particle tracking and in-situ imaging of atomic systems. Here, we report on measurements in the far-field that show spatial quantum correlations in single images of bright twin-beams with 10 8 photons in a 1 µs pulse using an electron-multiplying charge-coupled device camera. A four-wave mixing process in hot rubidium atoms is used to generate narrowband-bright pulsed twin-beams of light. Owing to momentum conservation in this process, the twin-beams are momentum correlated, which leads to spatial quantum correlations in the far field. We show around 2 dB of spatial quantum noise reduction with respect to the shot noise limit. The spatial squeezing is present over a large range of total number of photons in the pulsed twin-beams.PACS numbers: 42.50. Dv, 42.50.Ar, Under certain conditions, the quantum fluctuations in beams of light can be reduced below the shot noise limit (SNL) not only in the temporal domain, but also in the transverse spatial degree of freedom [1]. To date, most of the attention has focused on the study of quantum noise reduction, or squeezing, in the temporal domain [2][3][4][5][6][7][8][9][10][11][12]. Nevertheless, many areas in quantum optics, specifically quantum metrology and quantum imaging, could greatly benefit from the study of the quantum correlations directly in the spatial domain [13][14][15]. This would make it possible to take advantage of the spatial quantum properties of light, such as spatial squeezing, for enhanced spatial resolution and sub shot noise imaging [14].With this in mind, a few groups have recently experimentally demonstrated sub-shot noise spatial correlations using an electron-multiplying charge-coupled device (EMCCD) camera in photon pairs generated through spontaneous parametric down conversion (SPDC) [16][17][18]. As a proof of principle of a potential application of spatial quantum correlations in quantum imaging, Brida et al.[19] imaged a weak absorbing object with significantly higher signal-to-noise ratio than what is possible with classical light. However, the intensity levels were limited by the source and are orders of magnitude lower than what is used in standard imaging techniques. While these initial experiments provided an indication that spatial quantum correlations can lead to significant enhancements, many applications in quantum imaging and quantum metrology require real time imaging and, as such, require the ability to observe the spatial quantum correlations in a single shot with a controllable and macroscopic number of photons. In addition, the use of such a large number of photons can lead to a more sig- * ashok@ou.edu † marino@ou.edu nificant sensitivity enhancement due to t...

We have experimentally generated higher order optical vortices and scattered them through a ground glass plate that results in speckle formation. Intensity autocorrelation measurements of speckles show that their size decreases with an increase in the order of the vortex. It implies an increase in the angular diameter of the vortices with their order. The characterization of vortices in terms of their annular bright ring also helps us to understand these observations. The results may find applications in stellar intensity interferometry and thermal ghost imaging.

We introduce an asymmetry in the core of a high charge optical vortex by using an appropriate computer generated hologram. The splitting of a high charge optical vortex core into unit charge vortices has been found to depend on the extent of the asymmetry. For a second order vortex, the trajectories of the split unit charged vortices and their separation have been recorded as a function of change in the asymmetry of the core. We find a good agreement between the experimentally obtained and numerically calculated results.

We study, experimentally as well as theoretically, the spatial coherence function and the Wigner distribution function for one-dimensional projections of optical vortices of different orders. The information entropy derived from the spatial coherence functions has been used to quantify the information content of the vortices and compared with those obtained for the Gaussian beam. The experimental results verify the theoretical findings of Agarwal and Banerji [Opt. Lett. 27, 800 (2002)].