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The optical Spin-Hall effect originates from the interaction between the spin angular momentum (SAM) and extrinsic orbital angular momentum (OAM) of light, leading to mutual interrelations between the polarization and trajectory of light in case of non-paraxial fields. Here, we extensively study the SHE and the resultant Spin-Hall shifts (SHS) in optical tweezers (OT) by varying the numerical aperture of objective lenses, and the refractive index (RI) stratification of the trapping medium. Indeed, we obtain much larger values of the SHS for particular combinations of NA and stratification compared to the sub-wavelength orders typically reported. We also observe that the longitudinal component of the spin angular momentum (SAM) density - which is responsible for the spin of birefringent particles in optical tweezers - changes more-or-less monotonically with the lens numerical aperture, except around values of the latter where the angle subtended by the focused light equals the critical angle for a particular RI interface. Our results may find applications in designing experiments for tuning the SHS and SAM induced due to SOI to generate exotic optomechanics of trapped particles in optical tweezers., Comment: 10 pages, 7 figures

Coherent perfect absorption (CPA) has been a topic of considerable contemporary research interest. However, its implementation in practical applications has been limited, since it has been demonstrated only for plane waves till now. The issue for beams with finite confinement -- characterized by a collection of plane waves -- is that complete destructive interference is not feasible for all the plane waves simultaneously. In this paper, we study the absorption characteristics of two counter-propagating structured beams, e.g., Gaussian and Laguerre-Gaussian (LG) beams with and without orbital angular momentum respectively, incident normally on a composite slab from both sides by fulfilling the CPA condition exclusively for the central plane waves. We show that though perfect absorption is not achievable, there can be a substantial reduction of the scattered light. We also consider CPA for oblique incidence and discuss the difficulties., Comment: 5 pages, 6 figures, Comments are appreciated!

We introduce a new class of optical micromotors driven by the spin-orbit interaction of light and spin-driven fluid flows leading to simultaneous rotation and revolution of the micromotors. The micromotors are essentially birefringent liquid crystal particles (LC) that can efficiently convert the angular momentum of light into high-frequency rotational motion. By tightly focusing circularly polarized Gaussian beams through a high numerical aperture objective into a refractive index stratified medium, we create a spherically aberrated intensity profile where the spinning motion of a micromotor optically trapped at the centre of the profile induces fluid flows that causes orbiting motion of the off-axially trapped surrounding particles (secondary micromotors). In addition, the interaction between the helicity of light and the anisotropic properties of the LC medium leads to the breaking of the input helicity and drives the conversion of right to left-circular polarization and vice-versa. This spin-to-spin conversion, causes the orbiting secondary micromotors to spin in certain cases as well so that the entire system of spinning primary micromotor and revolving and spinning secondary micromotors is reminiscent of planetary motion at mesoscopic scales. Our findings, supported by both theoretical modeling and experimental validation, advance the understanding of light-matter interactions at the microscale., Comment: 14 figures and 17 pages

We demonstrate an effective and optimal strategy for generating spatially resolved longitudinal spin angular momentum (LSAM) in optical tweezers by tightly focusing first-order azimuthally radially polarized (ARP) vector beams with zero intrinsic angular momentum into a refractive index (RI) stratified medium. The stratified medium gives rise to a spherically aberrated intensity profile near the focal region of the optical tweezers, with off-axis intensity lobes in the radial direction possessing opposite LSAM (helicities corresponding to $\sigma = +1$ and -1) compared to the beam centre. We trap mesoscopic birefringent particles in an off-axis intensity lobe as well as at the beam center by modifying the trapping plane, and observe particles spinning in opposite directions depending on their location. The direction of rotation depends on particle size with large particles spinning either clockwise (CW) or anticlockwise (ACW) depending on the direction of spirality of the polarization of the ARP vector beam after tight focusing, while smaller particles spin in both directions depending on their spatial location. Numerical simulations support our experimental observations. Our results introduce new avenues in spin-orbit optomechanics to facilitate novel yet straightforward avenues for exotic and complex particle manipulation in optical tweezers., Comment: 10 pages, 6 figures

We have developed a rectangular loop interferometer (RLI) that confines light in a rectangular path and facilitates various interesting applications. Such a device can yield the sum of numerous geometric series converging to different values between zero and one by the use of simple intra-cavity beam splitters - both polarization-independent and dependent. Losses - principally due to alignment issues of the beam in the RLI - limit the average accuracy of the series sum value to be between 90 - 98\% with the computation speed determined by the bandwidth of the detectors. In addition, with a circularly polarized input Gaussian beam, and a combination of half-wave plate and q-plate inserted into the interferometer path, the device can generate a vortex beam that carries orbital angular momentum (OAM) of all orders of topological charge. The OAM is generated due to the spin-orbit interaction of light, and the topological charge increases with each successive pass of the beam inside the interferometer. However, experimentally, only the third order of OAM could be measured since projecting out individual orders entailed a slight misalignment of the interferometer, which caused higher orders to go out of resonance. Furthermore, with input linear polarization, the device can generate a vector beam bearing a superposition of polarization states resembling the multipole expansion of a charge distribution. Even here, experimentally, we were able to quantify the polarization distribution up to the third order using a Stokes vector analysis of the vector beam, with the size of the polarization singularity region increasing as the polarization states evolve inside the interferometer. Our work demonstrates the ubiquitous nature of loop interferometers in modifying the scalar and vector properties of light to generate simple mathematical results and other complex but useful applications., Comment: 22 pages, 9 figures

Reflectionless potentials following the prescription of Kay and Moses allow for total transmission of incoming waves of any kinetic energy. The optical analogue of such potentials occur as dielectric stratified media that can offer null reflectivity and near total transmission over a large range of incidence angles and wavelengths. In a previous work (S. Dutta Gupta and G. S. Agarwal, Opt. Express 15, 9614-9624, 2007), this was demonstrated for linearly polarized plane waves. We extend the earlier work valid for plane waves to structured beams to show near-total transmission of beams across the reflectionless dielectric profile. The analysis is based on the angular spectrum decomposition treating the beam as a collection of plane waves. Gaussian and Laguerre-Gaussian beams are shown to be transmitted through the film with <1% reflection in most scenarios. We also discuss the superlative performance of our proposed profile in preserving the beam shape during transmission comparing these results to a conventional lambda/2 antireflection coating.

We report the observation of two additional sub-natural line width quantum interference in the $D_2$ manifold of $^{39}K$ vapor, in addition to the usual single Electromagnetically induced transparency peak. The other two features appear exclusively because $^{39}K$ ground hyperfine splitting is smaller than the Doppler broadened absorption profile. This allows probe and control beams to swap their transition pathways. The control beam detuning captures the nature of the coherence, therefore an unusual phenomenon of conversion from perfect transparency to enhanced absorption is observed and explained by utilizing adiabatic elimination of the excited state in the Master equation. Controlling such dark and bright resonances leads to new applications in quantum technologies viz. frequency offset laser stabilization and long-lived quantum memory., Comment: 16 pages, 11 figures

Spin orbit interaction (SOI) due to tight focusing of light in optical tweezers has led to exciting and exotic avenues towards inducing rotation in microscopic particles. However, instances where the back action of the particles influences and modifies SOI effects so as to induce rotational motion are rarely known. Here, we tightly focus a vector beam having radial/azimuthal polarization carrying no intrinsic angular momentum, into a refractive index stratified medium, and observe orbital rotation of birefringent particles around the beam propagation axis. In order to validate our experimental findings, we perform numerical simulations of the underlying equations. Our simulations reveal that the interaction of light with a birefringent particle gives rise to inhomogeneous spin currents near the focus, resulting in a finite spin momentum. This spin momentum combines with the canonical momentum to finally generate an origin-dependent orbital angular momentum which is manifested in the rotation of the birefringent particles around the beam axis. Our study describes a unique modulation of the SOI of light due to interaction with anisotropic particles that can be used to identify new avenues for exotic and complex particle manipulation in optical tweezers., Comment: 7 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:2302.14443

We observe clear precessional motion of highly birefringent liquid crystal (LC) particles trapped in a spherically aberrated optical trap which is built around a tilted refractive index stratified medium. For input circularly polarized light, the breaking of azimuthal symmetry induced by the tilt leads to an asymmetric intensity distribution in the radial direction near the trap focal plane, which - in combination with the spin-orbit conversion effects for input circularly polarized light - results in non-uniform canonical and spin momentum densities in those regions. In addition, while the canonical momentum remains always oriented towards the axial direction, the spin momentum reverses direction along spatial loops in the radial direction. As a consequence, the total momentum precesses around the canonical momentum vector along elliptical spatial loops - akin to a Larmor-like precession of magnetic moment (total momentum in our case) around a magnetic field (canonical momentum). We probe this precession experimentally using the single trapped LC particles - with the direction of precession determined by the helicity of the input light and the precession frequency varying linearly with the laser power. Our experimental results are validated by numerical simulations of the system where we employ the Debye-Wolf theory for tight focusing in the presence of a tilted stratified media., Comment: 6 pages, 3 figures, Comments are appreciated

The interaction of light beams with resonant structures has led to the development of various optical platforms for sensing, particle manipulation, and strong light-matter interaction. In the current study, we investigate the manifestations of the bound states in continuum (BIC) on the in plane and out of plane shifts (referred to as Goos-Hanchen (GH) and Imbert-Fedorov (IF) shifts, respectively) of a finite beam with specific polarization incident at an arbitrary angle. Based on the angular spectrum decomposition, we develop a generic formalism for understanding the interaction of the finite beam with an arbitrary stratified medium with isotropic and homogeneous components. it is applied to the case of a Gaussian beam with p and circularly polarized light incident on a symmetric structure containing two polar dielectric layers separated by a spacer layer. For p-polarized plane wave incidence one of the coupled Berreman modes of the structure was recently shown to evolve to the bound state with infinite localization and diverging quality factor coexisting with the other mode with large radiation leakage (Remesh et al. Optics Communications, 498:127223, 2021). A small deviation from the ideal BIC resonance still offers resonances with very high quality factors and these are exploited in this study to report giant GH shifts. A notable enhancement in the IF shift for circularly polarized light is also shown. Moreover, the reflected beam is shown to undergo distortion leading to a satellite spot. The origin of such a splitting of the reflected beam is traced to a destructive interference due to the left and right halves of the corresponding spectra.

The spin-orbit interaction (SOI) of light generated by tight focusing in optical tweezers has been regularly employed in generating angular momentum - both spin and orbital - in trapped mesoscopic particles. Specifically, the transverse spin angular momentum (TSAM), which arises due to the longitudinal component of the electromagnetic field generated by tight focusing, is of special interest, both in terms of fundamental studies and associated applications. We provide an effective and optimal strategy for generating TSAM in optical tweezers by tightly focusing radially and azimuthally polarized first-order Laguerre Gaussian beams with no intrinsic angular momentum, into a refractive index stratified medium. Our choice of such input fields ensures that the longitudinal spin angular momentum (LSAM) arising from the electric (magnetic) field for the radial (azimuthal) component is zero, which leads to the separate and exclusive effects of the electric and magnetic TSAM in the case of input radially and azimuthally polarized beams on single birefringent particles. We also observe the emergence of origin-dependent intrinsic orbital angular momentum causing the rotation of birefringent particles around the beam axis for both input beam types, which opens up new and simple avenues for exotic and complex particle manipulation in optical tweezers., Comment: 10 pages, 5 figures

We demonstrate theoretically the feasibility of correlated entangled photon-pair generation with vanishing threshold in a bimodal cavity setup that uses a single V-type three level atom pumped by dual incoherent sources and driven by two coherent fields. The photon-pair is shown to be entangled only for low levels of the incoherent pumps and owes its origin solely to the coherent drives. Our results show that the dual incoherent pumping with no coherent drive can lead to amplification of the cavity fields with strong inter-mode antibunching but no entanglement. Though only coherent drives with no incoherent pumping can produce entangled photon-pairs, the entangled cavity fields can not be amplified beyond a certain limit using only coherent drives. However, the use of even small incoherent pumping in the presence of the coherent drives can amplify the generated entangled photon-pairs significantly. We analyse our results in terms of an interplay between coherent and incoherent processes involving cavity-dressed states. Both the inter- and intra-mode HBT functions exhibit temporal oscillations in the strong-coupling cavity QED regime. Our theoretical scheme for the generation of nonclassical and entangled photon pairs may find interesting applications in quantum metrology and quantum information science., Comment: 13 pages, 13 figures

Manifestations of orbital angular momentum induced effects in the diffraction of a radially polarized vector beam by an off-axis tilted aperture are studied both experimentally and theoretically. Experiments were carried out to extract the degree of circular polarization, which was shown to be proportional to the on-axis component of the spin angular momentum density. We report a clear separation of the regions of dominance of the right and left circular polarizations associated with positive and negative topological charges respectively, which is reminiscent of the standard vortex-induced transverse shift, albeit in the diffraction scenario. The experimental results are supported by model simulations and the agreement is quite satisfactory. The results are useful to appreciate the orbit-orbit related effects due to unavoidable misalignment problems (especially for vortex beams).

In the recent past, optical tweezers incorporating a stratified medium have been exploited to generate complex translational and rotational dynamics in mesoscopic particles due to the coupling between the spin and orbital angular momentum of the light, generated as a consequence of the tight focusing of light by a high numerical aperture objective lens into the stratified medium. Here, we consider an optical tweezers system with a tilted stratified medium (direction of stratification at an angle with the axis of the incident beam), and show that for input circularly polarized Gaussian beams, the resulting spin-orbit interaction deeply influences the generation of transverse spin angular momentum (TSAM) and Belinfante momentum of light, and allows additional control on their magnitude. Importantly, the TSAM generated in our system consists of both the orthogonal components, which is in sharp contrast to the case of evanescent waves and surface plasmons, where only one of the TSAM components are generated. The broken symmetry due to the tilt ensures that, depending upon the helicity of the input beam, the magnitude of the mutually orthogonal components of the TSAM depend entirely on the tilt angle. This may prove to be an effective handle in exotic spin-controlled manipulation of particles in experiments., Comment: 10 pages, 10 figures

Simultaneous manifestation of both forward and inverse photonic Spin Hall effect in geometrically tailored anisotropic waveguided plasmonic crystal system is observed through the excitation of the leaky hybridized quasiguided modes. The quasiguided modes of the plasmonic crystal manifested in the far-field momentum (Fourier) domain as circular ring-like intensity distributions, and the different spin orbit interaction (SOI) effects revealed their exclusive signature as polarization-dependent azimuthal intensity lobes on top of it. Using a darkfield Fourier domain polarization Mueller matrix platform, we have observed input spin (circular polarization)- dependent trajectory of the leaky quasiguided modes in the momentum domain (forward spin Hall effect) and its reciprocal effect as the wave vector-controlled spin selection of quasiguided modes (inverse spin Hall effect). These effects are separately manifested in characteristic Mueller matrix elements enabling their interpretation as geometrical circular anisotropy effects. Resonance-enabled enhancement and control of these effects are also demonstrated by exploiting the spectral Fano-type resonance. The far-field manifestation of spin-directional excitation of leaky quasiguided modes, their unique interpretation through momentum domain Mueller matrix, regulation and control of the SOI effects in plasmonic-photonic crystal systems, opens up exciting avenues in spin-orbit photonic research.

We study coupling of leaky Berreman modes in polar dielectric films (SiO2) through a thin metallic layer (gold) and show the familiar signatures of normal mode splitting. Due to very large negative real part of the dielectric function of gold, the splitting shows up only for extremely thin coupling layers. In contrast, coupling of Berreman modes through a dielectric spacer layer reveals novel possibilities of having bound states in continuum, albeit in the limit of vanishing losses. It is shown that the corresponding dispersion branches of the symmetric and antisymmetric modes can cross. BIC is shown to occur on one of these branches which is characterized by lower loss. In fact the BIC corresponds to the point where the radiative losses are minimized. For thicker layers (both spacer and the polar dielectric) BIC is shown to occur on the higher order dispersion branches. The origin of BIC is traced to the Fabry-Perot type mechanism due to the excitation of the leaky guided modes in the central layer.

Spin-to-orbit conversion of light is a dynamical optical phenomenon in non-paraxial fields leading to various manifestations of the spin and orbital Hall effect. However, effects of spin-orbit interaction (SOI) have not been explored extensively for higher order Gaussian beams carrying no intrinsic orbital angular momentum. Indeed, the SOI effects on such structured beams can be directly visualized due to azimuthal rotation of their transverse intensity profiles - a phenomenon we call the rotational Hall effect. In this paper, we show that for an input circularly polarized (right/left) $HG_{10}$ mode, SOI leads to a significant azimuthal rotation of the transverse intensity distribution of both the orthogonal circularly polarized (left/right) component, and the transverse component of the longitudinal field intensity with respect to the input intensity profile. We validate our theoretical and numerically simulated results experimentally by tightly focusing a circularly polarized $HG_{10}$ beam in an optical tweezers configuration, and projecting out the opposite circular polarization component and the transverse component of the longitudinal field intensity at the output of the tweezers. We also measure the rotational shift as a function of the refractive index contrast in the path of the tightly focused light, and in general observe a proportional increase. The enhanced spin-orbit conversion in these cases may lead to interesting applications in inducing complex dynamics in optically trapped birefringent particles using higher order Gaussian beams with no intrinsic orbital angular momentum., Comment: 11 pages with SI, 3+3 figs

We propose a coherent optical method for creating negative refractive index (NRI) for a gaseous ensemble of ground-state polar molecules possessing both permanent electric and magnetic moments. Exploiting the pure rotational transition between the two lowest rotational levels of the ground vibrational state one can generate two dressed states of mixed parity using a microwave laser. These dressed states are then used as the two lower states of a {\Lambda}-type three-level scheme using two infrared lasers to couple them to another ro-vibrational level in the ground-state manifold. One of the infrared lasers is used as a weak probe and the other as a control field with a fixed detuning. We take into account local-field effects on the dielectric response of the medium at the probe frequency in terms of Clausius-Mossoti relation. We extract magnetic response out of purely dielectric response and calculate the magnetic permeability of the medium in terms of dielectric susceptibility. Our results show that there is a small frequency window near the two-photon resonance where both electric permittivity and magnetic permeability are negative with vanishingly small absorption. The figure of merit for the medium is shown to exceed unity. We interpret our results in terms of the proximity of EIT and quantum interference. We discuss the possible realization of our method using cold polar molecules that are recently experimentally produced., Comment: 16 pages, 4 figures. Version-2 is substantially modified following referees comments

We demonstrate that tight focusing of a circularly polarized Gaussian beam in optical tweezers leads to spin-momentum locking - with the transverse spin angular momentum density being independent of helicity, while the transverse momentum (Poynting vector) becomes helicity dependent. Our theoretical calculations, numerical simulations, and experiments reveal that the presence of a stratified medium in the path of the trapping beam significantly enhances the magnitude of transverse momentum in the radial direction with respect to the beam axis, and likewise, also leads to high off-axial intensity. This overlap allows us to experimentally observe the circular motion of a birefringent particle, trapped off-axis, in response to an input circularly polarized fundamental Gaussian beam carrying no intrinsic orbital angular momentum. The circular motion is dependent on the helicity of the input beam, so that we can identify it to be the signature of the elusive Belinfante spin in propagating light beams obtained in our optical tweezers setup. Our work can be extended to higher-order beams carrying intrinsic orbital angular momentum leading to simple routes of achieving complex particle manipulation using optical tweezers., Comment: 15 pages, 6 figures

The extraordinary concept of weak value amplification has attracted considerable attention for addressing foundational questions in quantum mechanics and for metrological applications in high precision measurement of small physical parameters. Here, we experimentally demonstrate a fundamental relationship between the weak value of an observable and complex zero of the response function of a system by employing weak value amplification of spin Hall shift of a Gaussian light beam. Using this relationship, we show that arbitrarily large weak value amplification far beyond the conventional weak measurement limit can be experimentally obtained from the position of the minima of the pointer intensity profile corresponding to the real part of the complex zero of the response function. The imaginary part of the complex zero, on the other hand, is related to the spatial gradient of geometric phase of light, which in this particular scenario evolves due to the weak interaction and the pre and post selections of the polarization states. These universal relationships between the weak values and the complex zeros of the response function may provide new insights on weak measurements in a wide class of physical systems. Extremely large weak value amplification and extraction of system parameters outside the region of validity of conventional weak measurements may open up a new paradigm of weak measurement enhancing its metrological applications.

It has been recently recognized that in addition to the conventional longitudinal angular momentum, structured (inhomogeneous) optical fields exhibit helicity-independent transverse spin angular momentum (SAM) and an unusual spin (circular polarization)- dependent transverse momentum, the so-called Belinfante's spin momentum. Such highly nontrivial structure of the momentum and the spin densities in the structured optical fields (e.g., evanescent fields) has led to a number of fundamentally interesting and intricate phenomena, e.g., the quantum spin Hall effect of light and the optical spin-momentum locking in surface optical modes similar to that observed for electrons in topological insulators. In this review, we introduce the basic concepts and look into the genesis of transverse SAM and transverse spin momentum in structured light. We then discuss few illustrative examples of micro and nano optical systems where these illusive entities can be observed. The studied systems include planar and spherical micro and nano structures. We also investigate the ways and means of enhancing the elusive extraordinary spin. In particular, we show that dispersion management leading to avoided crossing along with perfect absorption mediated by recently discovered coherent perfect absorption can positively influence the resonant enhancement of the transverse spin and spin momentum. The role of mode mixing and interference of neighboring TE and TM scattering modes of diverse micro and nano optical systems are illustrated with the selected examples. The results demonstrate possibilities for the enhancement of not only the magnitudes but also the spatial extent of transverse SAM and the transverse momentum components, which opens up interesting avenues for experimental detection of these illusive fundamental entities and may enhance the ensuing spin-based photonic applications.

We study the effect of focusing of the radially and azimuthally polarized vector beams on the spin angular momentum (SAM) density and Poynting vector of scattered waves from a Mie particle. Remarkably, the study reveals that the SAM density of the scattered field is solely transverse in nature for radially and azimuthally polarized incident vector beams; however the Poynting vector shows usual longitudinal character. We also demonstrate that the transverse SAM density can further be tuned with wavelength and focusing of the incident beam by exploiting the interference of different scattering modes. These results may stimulate further experimental technique of detecting the transverse spin and Belinfante's spin-momentum densities.

We define the standard quantum limit (SQL) for phase and number fluctuations, and describe two-mode squeezing for number and phase variables. When phase is treated as a unitary quantum-mechanical operator, number and phase operators satisfy an uncertainty relation. As a result, the usual definition of number squeezing parameter becomes modified. Two-mode number squeezing occurs when the number fluctuation goes below the SQL at the cost of enhanced phase fluctuation. As an application of number-phase uncertainty, we consider bosons or fermions trapped in a quasi-one dimensional double-well (DW) potential interacting via a 3D finite-range two-body interaction potential with large scattering length $a_s$. Under tight-binding or two-mode approximation, we describe in detail the effects of the range of interaction on the quantum dynamics and number-phase uncertainty in the strongly interacting or unitarity regime $a_s \rightarrow \pm \infty$. Our results show intriguing coherent dynamics of number-phase uncertainty with number-squeezing for bosons and phase squeezing for fermions. Our results may be important for exploring new quantum interferometry, Josephson oscillations, Bose-Hubbard and Fermi-Hubbard physics with ultracold atoms in DW potentials or DW optical lattices. Particularly interesting will be the question of the importance of quantum phase operators in two-atom interferometry and entanglement., Comment: 20 pages, 5 figures

Interference of orthogonal modes in a birefringent crystal is known to lead to interesting physical effects (Solli et al., Phys. Rev. Lett. 91, 143906 (2003)). In this paper we show that the cavity with an intra-cavity rotator can enhance the mixing to the extent of normal mode splitting and avoided crossing depending on the orientation of the rotator with respect to the optic axis of the crystal. A high finesse cavity is shown to be capable of resolving small angles. The results are based on direct calculations of the cavity transmissions along with an analysis of its dispersion relation.

We study transverse spin in a sub-wavelength metal-dielectric-metal (MDM) sphere when the MDM sphere exhibits avoided crossing due to hybridization of the surface plasmon with the Mie localized plasmon. We show that the change in the absorptive and dipersive character near the crossing can have significant effect on the transverse spin. An enhancement in the transverse spin is shown to be possible associated with the transparency (suppression of extinction) of the MDM sphere. The effect is attributed to the highly structured field emerging as a consequence of competition of the electric and magnetic modes.

We study the truncated Kramers-Kronig (KK) medium to reveal the effects of nonreciprocity in reflection on the scattering and the wave guiding properties. We focus on the simplest possible spatial profile mimicking the dielectric response. We show that a finite slab of KK medium can support only one sided null scattering under bidirectional identical illumination. However, for a phase lag between the two incident beams it is possible to have null scattering on the other side. This is shown to be a consequence of the nonreciprocity in reflection due to the inherent asymmetry of the KK medium. We further look at the possibility of surface modes for unidirectional illumination. For specific range of parameters, we show the existence of TM polarized surface plasmons only for illumination from one side. The origin of such modes is traced to the inhomogeneous metal like layer with negative real part of the permittivity in the KK medium.

We study the near field to the far field evolution of spin angular momentum (SAM) density and the Poynting vector of the scattered waves from spherical scatterers. The results show that at the near field, the SAM density and the Poynting vector are dominated by their transverse components. While the former (transverse SAM) is independent of the helicity of the incident circular polarization state, the latter (transverse Poynting vector) depends upon the polarization state. It is further demonstrated that the magnitudes and the spatial extent of the transverse SAM and the transverse momentum components can be controllably enhanced by exploiting the interference of the transverse electric and transverse magnetic scattering modes.

Spectral singularities are ubiquitous with PT-symmetry leading to infinite transmission and reflection coefficients. Such infinities imply the divergence of the fields in the medium thereby breaking the very assumption of the linearity of the medium used to obtain such singularities. We identify saturable nonlinearity retaining contributions from all orders of the field to limit the infinite growth and regularize the spectral singularity. We present explicit numerical results to demonstrate regularization. The all order nonlinear PT-symmetric device is shown to exhibit very effective isolation or optical diode action, since transmission through such a system is nonreciprocal. In contrast, a linear system or a system with Kerr nonlinearity is known to have only reciprocal transmission. Further we demonstrate optical bistability for such a system with high contrast., Comment: 5 pages, 5 figures

The spin orbit interaction (SOI) of light has been in the focus in recent times because of fundamental consequences and potential applications in diverse systems ranging from inhomogeneous anisotropic media to engineered plasmonics and metamaterial strutures. Here we demonstrate perhaps one of the simplest means to realize SOI and the Spin Hall Shift (SHS) using a standard Gaussian TEM$_{00}$ beam in an optical trap. Our system exploits the versatility and interference generated in a stratified medium to control and manipulate SOI and transfer the resulting angular momentum to optically trapped micro-particles. We show that even such a simple setup can lead to an order of magnitude enhancement in the SHS compared to the sub-wavelength shifts typically obtained. Importantly, this leads to controlled rotation of mesoscopic particles using a fundamental Gaussian beam lacking any intrinsic angular momentum., Comment: 13 pages, 4 figures

We introduce unitary quantum phase operators for material particles. We carry out a model study on quantum phases of interacting bosons in a symmetric double-well potential in terms of unitary and commonly-used non-unitary phase operators and compare the results for different number of bosons. We find that the results for unitary quantum phase operators are significantly different from those for non-unitary ones especially in the case of low number of bosons. We introduce unitary operators corresponding to the quantum phase-difference between two single-particle states of fermions. As an application of fermionic phase operators, we study a simple model of a pair of interacting two-component fermions in a symmetric double-well potential. We also investigate quantum phase and number fluctuations to ascertain number-phase uncertainty in terms of unitary phase operators., Comment: 22 pages 11 figures

We study the effects of the spin orbit interaction (SOI) of light in an optical trap and show that the propagation of the tightly focused trapping beam in a stratified medium can lead to significantly enhanced SOI. For a plane polarized incident beam the SOI manifests itself by giving rise to a strong anisotropic linear diattenuation effect which produces polarization-dependent off-axis high intensity side lobes near the focal plane of the trap. Single micron-sized asymmetric particles can be trapped in the side lobes, and transported over circular paths by a rotation of the plane of input polarization. We demonstrate such controlled motion on single pea-pod shaped single soft oxometalate (SOM) particles of dimension around $1\times 0.5\mu$m over lengths up to $\sim$15 $\mu$m . The observed effects are supported by calculations of the intensity profiles based on a variation of the Debye-Wolf approach. The enhanced SOI could thus be used as a generic means of transporting mesoscopic asymmetric particles in an optical trap without the use of complex optical beams or changing the alignment of the beam into the trap., Comment: 9 pages, 7 figures

We study the reflection of a Hermite-Gaussian beam at an interface between two dielectric media. We show that unlike Laguerre-Gaussian beams, Hermite-Gaussian beams undergo no significant distortion upon reflection. We report Goos-H\"anchen shift for all the spots of a higher order Hermite Gaussian beam near the critical angle. The shift is shown to be insignificant away from the critical angle. The calculations are carried out neglecting the longitudinal component along the direction of propagation for a spatially finite, s-polarized, full 3-d vector beam. We briefly discuss the difficulties associated with the paraxial approximation pertaining to a vector Gaussian beam., Comment: Accepted for publication in Journal of Physics - Pramana. 4 figures, 13 pages