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Tuesday, 29 November 2022

Tarak Nath Dey
Title: Structured beam propagation through atomic media

In this tutorial, we explore the propagation of Laguerre-Gaussian beam through the atomic medium. Linear and non-linear atom-field interaction used to control polarization, phase and amplitude of the beam, gives complete freedom to manipulate structured light. Therefore, the mechanism of efficient control of beam parameters can open up new avenues for high-resolution microscopy, high-density optical communication, the realization of optical tweezers for controlled manipulation and trapping of particles, and in micromachining.

G K Samanta
Title: Nonlinear interaction and the generation of structured beams

Laser once considered as problem seeking solutions have become solutions to many problems in science and technology. However, most of the scientific and technological applications use a laser beam in the Gaussian spatial structure (fundamental mode). As such, many of the scientific and technical applications require laser beams in different spatial structures. For example, optical vortices, having phase singularities (phase dislocations) in the wavefront, carry vanishing intensity at the singular point. Due to the screw-like (helical) phase structure around the point of singularity, such beams carry orbital angular momentum (OAM) [1]. The OAM associated with optical vortices is important for high-resolution microscopy [2], quantum information [3], optical communication, material processing [4], and particle micro-manipulation and lithography [5]. Similarly, the Bessel beams have peculiar properties of non-diffraction and self-healing. In our group, we have been working for more than a decade to understand the nonlinear interaction of the various spatial structured beams, and devise new mechanisms and strategies for the active control and transfer the properties of the input structured beams through nonlinear interaction. In this talk, we will discuss some of our recent results on classical and quantum optics experiments with spatial structured beams for the realization of Hilbert hotel paradox, generation of OAM spectrum from a single mode converter and the transfer of classical non-separable state into hybrid entangled states and the increasing the dimensionality of the entangled states [6-8].

[1] L. Allen, M. W. Beijersbergen, R. J. Spreeuw, and J. P. Woerdman, “Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes,” Phys. Rev. A 45, 8185 (1992).
[2] S. Fürhapter, A. Jesacher, S. Bernt, and M. Ritsch-Marte, “Spiral phase contrast imaging in microscopy,” Opt. Express 13, 689 (2005)
[3] A. Mair, A. Vaziri, G. Weihs, and A. Zeilinger, “Entanglement of the orbital angular momentum states of photons,” Nature 412, 313–316 (2001).
[4] K. Toyoda, K. Miyamoto, N. Aoki, R. Morita and T. Omatsu, “Using optical vortex to control the chirality of twisted metal nanostructures” Nano letters 12, 7, 3645-3649 (2012)
[5] T. F. Scott, B. A. Kowalski, A. C. Sullivan, C. N. Bowman, and R. R. McLeod, “Two-color single-photon photoinitiation and photoinhibition for subdiffraction photolithography,” Science 324, 913–917 (2009).
[6] M. V. Jabir, N. Apurv Chaitanya, Manoj Mathew, and G. K. Samanta, “Direct transfer of classical non-separable states into hybrid entangled two photon states,” Scientific Reports 7, 7331 (2017).
[7] M. V. Jabir, N. Apurv Chaitanya, A. Aadhi, and G. K. Samanta “Generation of "perfect" vortex of variable size and its effect in angular spectrum of the down-converted photons”, Scientific Reports, 6, 21877 (2016).
[8] M. V. Jabir, Ali Anwar, and G. K. Samanta, “Controlling the bi-photon orbital angular momentum eigenmodes using asymmetric pump vortex beam,” Journal of Optics 21, 055201 (2019).

Federico Capasso
Title: Structured Light and Singularity Engineering by Meta-optics (Online)

Metaoptics offer fresh opportunities for structuring light as well as dark. I will discuss metasurfaces that enable light’s spin and OAM to evolve, simultaneously, from one state to another along the propagation direction1,2, along with nonlocal supercell designs that demonstrate multiple independent optical functions at arbitrary large deflection angles with high efficiency.3 In one implementation the incident laser is simultaneously diffracted into Gaussian, helical and Bessel beams over a large angular range and in another one a compact wavelength-tunable external cavity laser with arbitrary beam control capabilities including hologram lasing is demonstrated. We also propose a new class of computer-generated holograms whose far-fields have designer-specified polarization response, dubbed Jones matrix holograms.3 We provide a simple procedure for their implementation using form-birefringent metasurfaces. In particular, we demonstrate holograms whose far-fields implement parallel polarization analysis and custom waveplate-like behavior. The realization of 2D phase and polarization singularities and the unique applications that they will open will be discussed4 ,along with recent results on the realization of an equally spaced liner array of 0D phase singularities using inversed designed cylindrically symmetric phase only metasurfaces. Finally, a complete, topologically protected polarization singularity has been reported for the first time; it is located in the 4D space spanned by the three spatial dimensions and the wavelength and is created in the focal region of a lens using a metasurface.5 The field Jacobian plays a key role in the design of such higher dimensional singularities, which can be extended to multidimensional wave phenomena, and pave the way to novel applications in topological photonics.

1. Ahmed H. Dorrah, Noah A. Rubin, Aun Zaidi, Michele Tamagnone & Federico Capasso
Nature Photonics 15, 287 (2021)
2. Ahmed H Dorrah, Noah A Rubin, Michele Tamagnone, Aun Zaidi, & Federico Capasso Nature Communications 12, 6249 (2021)
3. Noah A. Rubin, Aun Zaidi, Ahmed H. Dorrah, Zhujun Shi, & Federico Capasso Science Advances, 7, eabg7488 (2021)
4. Soon Wei Daniel Lim, Joon-Suh Park, Maryna L. Meretska, Ahmed H. Dorrah, & Federico Capasso Nature Communications, 12, 4190 (2021)
5. Christina M. Spaegele, Michele Tamagnone, Soon Wei Daniel Lim, Marcus Ossiander, Maryna Meretska, Federico Capasso arXiv:2208.09054 (2022)

Nirmalya Ghosh
Title: Angular momentum, Geometric phase and spin orbit interaction of Light

The spin angular momentum (SAM) and orbital angular momentum (OAM) of light, which are associated with the circular (elliptical) polarization and helical phase fronts, have been widely studied in the domain of classical and quantum optics for both fundamental interests and numerous applications. In this regard, coupling and mutual influence of the SAM, OAM and linear momentum degrees of freedom of light have led to a number of fundamental photonic SOI effects in various light-matter interactions. Classical light beams carry both spin (SAM, circular / elliptical polarization) and orbital angular momentum (OAM). While the former (SAM) is intrinsic, the latter can have both intrinsic and extrinsic contributions. From a fundamental point of view, coupling and interconversion between the spin and orbital AM degrees of freedom of light is expected under certain circumstances, leading to the so-called Spin orbit interaction (SOI) of light. Accordingly, the evolution of polarized light in a trajectory mimics the SOI effect of a massless spin 1 particle (photon).
The SOI of light is associated with two interdependent effects –
(i) evolution of geometric phase due to the effect of the trajectory on the state of polarization of light, leading to intrinsic SAM to intrinsic OAM inter-conversion and its various intriguing manifestations (such as formation of polarization controlled vortices); and (ii) the reverse effect of polarization on the trajectory of light, leading to intrinsic SAM to extrinsic OAM inter-conversion and manifesting as the so-called Spin Hall effect (SHE) of light and its different other variants. In this lecture, I shall aim to provide a unified framework for describing a variety of SOI phenomena using the same underlying concept of angular momenta and geometric phase of light. SOI of light emerging in a variety of light-matter interactions will be discussed, which includes propagation of light in inhomogeneous anisotropic medium, reflection / refraction of light beams at dielectric interfaces, high numerical aperture imaging and focusing of fundamental or higher order Gaussian beams, scattering from micro/nano scale optical systems, propagation of light in nano-structured metamaterials, meta-surfaces and so forth. Illustrative examples of SOI of light and the discussions will be restricted to propagating waves only. In this regard, the concept of geometrical phase of light and the mathematical framework of polarized light, which are intimately related to the SOI of light, will be briefly covered.
The second part of the lecture will be dealing with the concept of weak measurements and weak value amplification in the domain of classical optics and spin-orbit photonics. The weak value amplification (WVA) concept, introduced by Aharonov, Albert, and Vaidman, has proven to be fundamentally important and extremely useful for numerous applications. This quantum mechanical concept can be understood using the wave interference phenomena and can therefore be realized in classical optical settings also. In this talk, I shall illustrate how the WVA concept can be formulated within the realm of classical electromagnetic theory of light and discuss its use for the amplification of tiny spin orbit interaction effects of classical light beam.

1. K. Y. Bliokh, F. J. Rodríguez-Fortuño, F. Nori & A. V. Zayats, Nature Photonics 9, 796–808 (2015).
2. Andrea Aiello, Peter Banzer, Martin Neugebauer and Gerd Leuchs, Nature Photonics 9, 789 (2015).
3. S. Dutta Gupta, N. Ghosh and A. Banerjee, Wave Optics: Basic concepts and contemporary trends, CRC Press, Taylor and Francis (2015).
4. K. Y. Bliokh, A. Niv, V. Kleiner and E. Hasman, Nature Photonics, 2, 748 (2008).
5. O. Hosten and P. Kwiat, Science, 319, 787 (2008).
6. S. Dutta Gupta, N. Ghosh and A. Banerjee, Wave Optics: Basic concepts and contemporary trends, CRC Press, Taylor and Francis (2015).
7. K. Y. Bliokh, D. Smirnova and F. Nori, Science 348, 1448 (2015).
8. Y. Aharonov, D. Z. Albert, and L. Vaidman, Phys. Rev. Lett. 60, 1351 (1988).
9. J. Dressel et al, Rev. Mod. Phys., 86, 307-315 (2014).
10. G.C. Knee, J. Combes, C. Ferrie, E.M. Gauger, Quantum Meas. Quatum Metrol., 3, 32-37 (2016).
11. A.G. Kofman, S. Ashhab, F. Nori, Physics Reports, 520, 43-133 (2012).
12. O. Hosten and P. Kwiat, Science, 319, 787 (2008).

Wednesday, 30 November 2022

Subhasish Dutta Gupta
Title: Transverse spin with structured light

The usual spin angular momentum (SAM) associated with featureless plane polarized light is
longitudinal, parallel or antiparallel to the direction of propagation depending on its helicity.
We look into the genesis of transverse spin in guided wave optics and plasmonics to expose
the nontrivial elusive effects of structured light. The structuring can be engineered in standard
waveguide or surface plasmon geometries, or using focused Gaussian and vector beams. We
explore various different optical systems (both planar and spherical) to enhance the elusive
effects. In particular, we exploit coupled modes, coherent perfect absorption, PT-symmetry to
enhance the transverse SAM.

Ayan Banerjee
Title: Focusing light till it spins particles: Spin orbit interaction of light in optical tweezers

Engineering the angular momentum of light in optical tweezers using spin orbit interaction

In this talk, I shall describe our experiments over the last several years on generating rotational dynamics in microscopic particles trapped by optical tweezers by exploiting the spin orbit interaction and the spin Hall effect of light. Using the formalism developed in the tutorial, I shall show how the introduction of a refractive index stratified medium in the path of the input light, causes a spherically aberrated intensity profile near the focal region of the tweezers. The large z-component which arises due to the tight focusing, leads to the spin-Hall effect of light which causes the generation of spatially separated regions of opposite helicity near the focal region – where particles can be trapped and rotate (along the body-axis of the particles) according to the helicity they encounter. The rotation – which is a manifestation of the longitudinal spin angular momentum (LSAM) of the light – can also be switched on and off using a second optical tweezers, which demonstrates the flexibility and power of this technique towards optical micromanipulation [1]. I shall then move on to observations of orbital angular momentum (OAM) on birefringent micro-particles – which, intriguingly are dependent on the input helicity of circularly polarized light containing no intrinsic OAM – and thus, are manifestations of the elusive Belinfante spin momentum [2]. Finally, I shall describe our recipe towards generating clear signatures of transverse spin angular momentum (TSAM) in birefringent micro-particles, where we use a radially polarized LG beam having zero topological charge, and thus no intrinsic OAM [3]. The radial polarization implies zero LSAM, so that the spin angular momentum generated is entirely transverse, and leads to exotic rotation of the particles with the magnitude of TSAM also controllable by the refractive index contrast of the stratified medium. Fascinatingly, we elicit signatures of TSAM originating from solely the electric and magnetic fields of light by using radially and azimuthally polarized input beams, respectively – which is a rare demonstration of work done by these components of light individually in optical tweezers. Our design also leads to orbital motion of the trapped particles due to the Poynting vector – so that the experiment demonstrates a unique engineering of spin angular momentum using a combination of input polarization (which leads to TSAM) and refractive index stratification which leads to an extended intensity profile near the trap center that is capable of trapping particles off-axis to the beam and observing their rotational motion around the beam center.


  1. Manifestations of geometric phase and enhanced topological phase and spin Hall shifts in an optical trap, Basudev Roy, Nirmalya Ghosh, Ayan Banerjee, S. Dutta Gupta, and Soumyajit Roy, New Journal of Physics 16, 083037 (2014).
  2. Direct observation of the effects of spin dependent momentum of light in optical tweezers, Debapriya Pal, Subhasish Dutta Gupta, Nirmalya Ghosh, and Ayan Banerjee, APL Photonics 5, 086106 (2020).
  3. Using a structured vector beam to reveal intriguing angular momentum dynamics exploiting spin-orbit interaction, Ram Nandan Kumar, Subhasish Dutta Gupta, Nirmalya Ghosh, and Ayan Banerjee, manuscript under preparation.


Focusing light till it spins particles: Spin orbit interaction of light in optical tweezers


The paraxial approximation, which is the simple-most mathematical treatment required to produce light beams from plane waves, suppreses several interesting and exotic properties of structured light. Note that this approximation stems from the fact that the very act of confining light in the transverse direction immediately causes the plane wave solution of the wave equation to collapse – since the intensity becomes spatially dependent. What is often overlooked here is that this, in turn, breaks the transversality condition that lies at the heart of plane waves – namely that there can be no component of electric field in the direction of propagation of the wave (i.e. the  z  direction, along the wave vector k). The requirement that Gauss’s law needs to be satisfied for a source free region, and the fact that the electric field in the transverse directions are spatially varying, necessitates the existence of a longitudinal (z) component of the field – which leads to intriguing consequences. The most important consequence is the evolution of transverse components in the Poynting vector or the direction of energy/momentum flow. Now, the z component keeps on increasing as light is focused tightly using a microscope objective lens to produce optical tweezers – which have the ability of confining and manipulating mesoscopic particles. Indeed, optical tweezers also manipulate the properties of light significantly – since the transverse components of the Poynting vector increase significantly – so that the trajectory of circularly polarized light undergoes a transverse shift according to the direction of helicity – something known as the Spin-Hall effect of light. Other than this, tight focusing by a lens having high numerical aperture causes the k-vectors of an incident polarized Gaussian beam to bend differentially and follow different trajectories towards the focal region, so that an inhomogeneous spin-redirectional geometric phase is generated. The azimuthal gradient of this geometric phase causes the generation of an intrinsic orbital angular momentum (OAM), and the condition of conservation of total angular momentum causes different spin (or helicity) components to be associated with different OAM modes. This is called the spin-orbit interaction of light, which leads to different exotic effects in optical tweezers depending on the input state of polarization of light before tight focusing.


In this tutorial, I shall walk the students along this entire journey, and introduce them to the properties of light not regulated by the paraxial approximation. The dropping of this approximation immediately complicates the wave equation, which now needs to be solved in its entirety (without the second derivative of the field in the z direction being neglected). This is carried out using the angular spectrum method – where an input beam is decomposed in Fourier space into its spatial frequency components, and the real-space electric field near the focal region is determined by the interference of the constituent partial plane waves having different k vectors. Additionally, the action of the tight focusing lens is represented as a rotational transformation of the input electric field by an appropriate rotation matrix, with the polarization characteristics of the medium where the light propagates also being mapped by the Fresnel coefficients of the latter. I shall present in detail this vector diffraction theory, and demonstrate how this formalism beautifully explains spin-orbit interaction, and can be used to determine the electric field intensity in the vicinity of the focus, with the light propagating through a refractive index stratified medium after the focusing lens.


I shall also provide an understanding of the spin and OAM of light in terms of the Poynting vector, where the latter, which represents the total momentum, can be considered to be made up of two components – a canonical momentum which is proportional to the local phase gradient of the wave and thus may be associated with the OAM, and a spin momentum – which arises due to non-vanishing circulating currents at the boundary of confined light. This spin momentum, also known as Belinfante momentum – is a virtual quantity with zero energy flow, but generates spin angular momentum (SAM) density – both longitudinal and transverse. The effects of both OAM and SAM can be experimentally probed by mesoscopic particles trapped in optical tweezers, which I shall describe briefly. I shall elaborate more on the transverse SAM (TSAM) – which causes spinning motion of particles akin to a wheel. The TSAM is again a direct consequence of the large z component which tight focusing generates, and has been observed recently in experiments using interesting configurations of the input light.


Reading material:

  1. Controlled transportation of mesoscopic particles by enhanced spin orbit interaction of light in an optical trap, Basudev Roy, Nirmalya Ghosh, S. Dutta Gupta, Prasanta K. Panigrahi, Soumyajit Roy, and Ayan Banerjee, Physical Review A 87, 043823 (2013).
  2. Manifestations of geometric phase and enhanced topological phase and spin Hall shifts in an optical trap, Basudev Roy, Nirmalya Ghosh, Ayan Banerjee, S. Dutta Gupta, and Soumyajit Roy, New Journal of Physics 16, 083037 (2014).
  3. Extraordinary momentum and spin in evanescent waves, Konstantin Y. Bliokh, Aleksandr Y. Bekshaev, and Franco Nori, Nature Communications, 5:3300, DOI: 10.1038/ncomms4300 (2014).
  4. Direct observation of the effects of spin dependent momentum of light in optical tweezers, Debapriya Pal, Subhasish Dutta Gupta, Nirmalya Ghosh, and Ayan Banerjee, APL Photonics 5, 086106 (2020).
Pankaj Kumar Mishra
Title: Excitation spectrum of spin-orbit coupled spinor Bose-Einstein condensate

Since its first realization in the laboratory experiment in 2011, spin-orbit coupled Bose-Einstein condensates (BECs) have been an active area of research in the condensed matter Physics. In general, the spin-orbit (SO) coupling, which emerges due to interaction between the intrinsic spin of an electron and the magnetic field induced by its motion, plays a prominent role in understanding the underlying mechanism of different fields of physics ranging from a single atom, for example, hydrogen atom to bulk materials like semiconductors. In condensed matter, the effect of SO coupling can lead to a variety of novel quantum phenomena such as topological insulators, topological superconductors, topological semimetals, and anomalous Hall effect.  However, studying the effect of SO coupling in these naturally occurring systems faces serious challenges owing to its extreme difficulty in controlling the magnitude of SO coupling. In that case, SO coupling in BECs helps one to overcome this caveat since SO coupling in BECs is highly tunable [1,2].

The aim of this tutorial is to introduce the methodology based on Bogoliubov de Gennes theory to calculate the collective excitation spectrum for the SO coupled spin-1/2 BEC. We begin the calculation of the collective excitation spectrum for scalar BECs. After setting up the formalism we will demonstrate the excitation spectrum calculation for one-dimension SO coupled spin-1/2 BEC. The analysis will be extended for two-dimension. Further we will discuss the different kind of excitations modes that appear upon varying the spin-orbit coupling parameters for two-dimension BECs as reported in [3] .  We will discuss many interesting phases like phonon, maxon and rotons using the analysis of eigenenergy of the excitation spectrum. Behaviour of eigenvector upon change of Rashba coupling suggests interesting manifestation of the density-like and spin-like modes in the stability and instability regime of the excitation spectrum respectively. We will show that the increase in Rashba coupling destabilizes the system while increase in Rabi coupling leads stabilization of the condensates. 


[1] Y. J. Lin, K. J. Garcia and I. B. Spielman, Nature 471,  83-86 (2011).

[2] R. Ravisankar, T. Sriraman, R. Kishor Kumar, P. Muruganandam, and P. K. Mishra,  J. Phys. B: At. Mol. Opt. Phys. 54, 225301 (2021).

[3] R. Ravisankar , H. Fabrelli,  A. Gammal, P. Muruganandam ,  and P. K. Mishra, Phys. Rev. A 104, 053315 (2021). 

Nikolay I Zheludev
Title: The Technology of Optical Superoscillations (Online)

The lecture will focus on history of superoscillations in optics and recent advances in applications of artificial intelligence and superoscillatory light to far-field non-destructive localization and metrology with deeply subwavelength resolution

Andrea Aiello
Title: On the helicity decomposition of spin and orbital optical currents (Online)

The helicity representation of the linear momentum density of a light wave is well understood for monochromatic optical fields in both paraxial and non-paraxial regimes of propagation.
Recently, we have generalized such representation to  nonmonochromatic optical  fields (see, Andrea Aiello, J. Phys. A: Math. Theor. 55 244004 (2022)).  In this talk we show that, differently from the monochromatic case, the linear momentum density, aka the Poynting vector divided by the square of the speed of light, does not separate into the sum of right-handed and left-handed terms, even when the so-called electric-magnetic democracy in enforced by averaging the electric and magnetic contributions. However, for  quasimonochromatic light, such a separation is approximately restored after time-averaging.

Thursday, 01 December 2022

Mishkatul Bhattacharya
Title: Cavity Optomechanical Sensing and Manipulation of an Atomic Persistent Current

In this talk I will describe our recent theoretical work showing how several problems in atomic superfluid rotation can be addressed using the versatile toolbox of cavity optomechanics [1]. We consider an annular Bose-Einstein condensate, which exhibits dissipationless flow and is a paradigm of rotational quantum physics, inside a cavity excited by optical fields carrying orbital angular momentum. We show that this configuration provides the first platform that can sense ring Bose-Einstein condensate rotation with minimal destruction, in situ and in real time, unlike demonstrated techniques, all of which involve fully destructive measurement. It also shows how light can actively manipulate rotating matter waves by optomechanically entangling persistent currents. Our work opens up a novel and useful direction in the sensing and manipulation of atomic superflow.


[1] P. Kumar, T. Biswas, K. Feliz, R. Kanamoto, M.-S. Chang, A. K. Jha and M. Bhattacharya, Phys. Rev. Lett. 127, 113601 (2021).

Bio: Mishkat Bhattacharya is a Professor of physics at the Rochester Institute of Technology, Rochester, NY. His interests lie in theoretical quantum optics. His research has been recognized with an NSF Career award (2015) and was selected as one of the Breakthroughs of the Year by Optics and Photonics magazine (2019).

Zubin Jacob
Title: Quantum magnetometry of photonic spin density with NV centers in diamond

This talk will consist of two parts. The first part will be theoretical. I will provide a quantum field theoretic derivation of photonic spin density. This derivation will settle the long standing questionon the commutation relations for the SAM and OAM of a photon.
 I will discuss the SAM and OAM of a single photon from quantum field theory and show the unique noise properties which have no classical counterpart.  

The second part of the talk will be experimental. I will discuss the progress we have made in multiple platforms to study the nanoscale photonic spin texture. In particular, I will explain how the photonic spin leads to an effective magnetic field for light and how it can be measured using quantum magnetometry. 

More details can be found here

P. Senthilkumaran
Title: Topological constructs and phases on polarization singularities

Poincare sphere can be used to represent all conceivable states of polarization as points on it.  It is now well known that any adiabatic transport of the state of polarization of light over a closed geodesic path on Poincare sphere using unitary elements leads to the realization of Pancharatnam phase.  Similarly Berry phase exhibited by light adiabatically transported in the momentum phase in a closed path using coiled optical fibers is topological in nature.  Starting from Pancharatnam circuit also called Simon-Mukunda gadget, comprising of quarter wave plate – half wave plate and quarter wave plate, we move on to deal with inhomogenous polarization distributions.  Of special interest are the fields having circulating polarization azimuth distributions.  These polarization structured optical fields are basically polarization singularities with defined topological indices.   Some recent published work on topological phases in Lemon, Star, Spider web and flower polarization patterns will be discussed.  In this talk, modal spheres useful in representing Hermite Gaussian modes as superposition of Laguerre Gaussian modes and the effect of topological phases on these modes will be touched upon.  New topological constructs such as higher order Poincare spheres and Hybrid order Poincare spheres and Pancharatnam-Berry phases realization in these spheres will be presented.  Introduction of other spheres such as Hybrid order Poincare sphere for Stokes singularities and some of our recent research work will also be discussed in this presentation.

G. V. Pavan Kumar
Title: Structured-Light Scattering : Implication in Momentum Space

We will discuss two classes of experiments. First is the momentum (k) space discrimination of spin and orbital angular momentum of light scattered from a metallic-silver nanowire. We will specifically highlight how k-space scattering patterns have one-to-one correspondence with magnitude and sign of topological charge of an optical vortex beam. Second class of experiment is the evolutionary assembly of thermally active colloids in a structured optical trap. We will discuss light scattering and absorption effects in dynamic assemblies, and the possibility of k-space measurements in determining optical forces and torques.

Achanta Venugopal
Title: Light-matter interaction in metamaterials

Light-matter interaction has evolved from perturbative regimes of weak and strong coupling to the non-perturbative regimes of ultra-strong and deep strong coupling regimes [1,2]. To reach these regimes for their exotic physics and novel phenomena, one needs to realize very high quality factors or utilize cooperativity. In this talk, I will give two examples. One is an unpublished work on plasmonic quasicrystal (PlQC) structure with quantum dots (QDs) on it and the other is bound state in continuum (BIC) structures.

In the PlQC-QD structure, we performed detailed time resolved measurements that showed features of long range plasmon mediated exciton-exciton coupling [3]. These features include oscillations in temporal domain lasting much longer than the plasmon lifetime and shift in the photoluminescence (PL) spectra. The density dependent studies showed these features for very high density QDs indicating cooperativity. Estimates showed the plasmon-exciton coupling in the ultrastrong coupling regime with g/w > 0.1. In addition to the far-field measurements in the equilibrium state (cw PL and Goos-Hanchen (GH) shift) and temporal domain with 45 fsec time resolution, near-field studies showed emission from QDs far from the excitation spot and within the G-H shift.

Bound states in continuum are mathematical abstractions with zero linewidth or infinite quality factor resonances [4]. Recently, polarization vortex at a BIC resonance was reported [5]. We numerically studied the near- and far-field profiles of the reflected light beam from a designed metasurface at BIC resonance. The designed structures were fabricated and studied the response. We observed polarization independent BIC resonance as well as conversion of a gaussian beam to a Bessel-Gauss beam on reflection [6,7].

Acknowledgments : The works being presented have contributions from my group members and collaborators including, Banoj Kumar, Nayak, Abhinav Kala, Pravin Vaity, Harshavardhan Gupta, Shilpa Samdhani, Ajith P. Ravishankar, Ch. N. Rao, S. Dutta Gupta, Yuri S Kivshar, and Vladimir R Tuz.


References :

  1. A. F. Kockum, A. Miranowicz, S. De Liberato, S. Savasta, F. Nori, “Ultrastrong Coupling between Light and Matter” Nature Rev. Phys. 1, 19 (2019).
  2. P. Forn-Diaz, L. Lamata, E. Rico, J. Kono, E. Solano, “Ultrastrong Coupling Regimes of Light-Matter Interaction” Rev. Mod. Phys. 91, 025005 (2019).
  3. B. K. Nayak, A. Kala, S. Samdani, A. P. Ravishankar, Ch. N. Rao, Venu Gopal Achanta, “Long range dipole-dipole coupling mediated by surface plasmon polaritons” (To be submitted).
  4. K. Koshelev, G. Favraud, A. Bogdanov, Y. Kivshar, and A. Fratalocchi,"Nonradiating photonics with resonant dielectric nanostructures," Nanophotonics 8, 725 2019.
  5. H. M. Doeleman, "Experimental observation of a polarization vortex at an optical bound state in the continuum," Nature Photonics 12, 397 (2018).
  6. P. Vaity, and Venu Gopal Achanta, “Angular Spectrum of Bound State in the Continuum for Near and Far Field Analysis”, JW1A.177, CLEO 2021.
  7. P. Vaity, H. Gupta, A. Kala, S. Dutta Gupta, Y. S. Kivshar, V. R. Tuz, and Venu Gopal Achanta, “Polarization-Independent Quasibound States in the Continuum”
Ranjan Singh
Title: Topological states of light on a silicon chip for 6G communication and beyond

Global digitalization and the recent rise of artificial intelligence-based data-driven applications have directed their vectors towards terabits per second (Tbps) communication links. The fast-evolving 5G communication network cannot fulfill this demand due to several technological challenges, including bandwidth scarcity, which has stimulated innovative technologies with a vision of 6G communication. Terahertz (THz) micro-nanotechnologies have been identified as a critical candidate for the emerging 6G communication with the potential to provide ubiquitous connectivity and remove the barrier between the physical, digital, and biological worlds. Nonetheless, the existing THz photonic on-chip communication devices suffer from backscattering, bending loss, limited data speed, and lack of active tunability. Here, I will describe a new class of quantum-inspired on-chip THz photonic topological devices consisting of low-loss, broadband single channel 160 Gbit/s interconnect devices and critically coupled high-Q cavities built on Silicon Valley-Hall Photonic Crystal. Silicon topological photonics will pave the path for augmentation of CMOS-compatible hybrid electronic-photonic-spintronic driven terahertz technologies, vital for accelerating the development of 6G and 7G communications that would empower societies with real-time terabits per second wireless connectivity for network sensing, holographic communication, cognitive internet of everything, and massive digital cloning of the physical and the biological world.

Sanjukta Roy
Title: Quantum Interference with cold Rydberg atoms

Atoms excited to Rydberg states with high principal quantum numbers have exaggerated properties such as strong dipole-dipole interaction, large values of polarisability and longer lifetimes compared to atoms in their ground state. These exotic characteristics and a high degree of controllability make ultra-cold Rydberg atoms versatile atomic building blocks for a variety of quantum technologies such as scalable quantum information networks, precision electrometry as well as a single-photon source for secure quantum communications.

In this talk, I will give an overview of Quantum Technologies with Rydberg atoms and describe the recent results from our experiments on Quantum Interference with thermal and cold Rydberg atoms. Finally, I will give future perspectives on Quantum Information and Quantum Sensing with ultra-cold Rydberg atoms.

Dibyendu Roy
Title: Light-matter interactions in waveguide quantum electrodynamic systems

Waveguide quantum electrodynamic (QED) systems can realize strong light-matter interactions in one-dimensional waveguides with no optical confinement along the propagation direction. Waveguides with linear or nonlinear energy-momentum dispersions and topological properties have been employed in experiments. These cavity-free systems feature intrinsically nonequilibrium, quantum many-body dynamics. The input field is driven by a laser or microwave generator, imposing a nonequilibrium boundary condition on the propagating photons. I shall describe our research to theoretically study photon-photon correlation mediated by local light-matter coupling in waveguide QED systems for coherent and single-photon beams. I shall further discuss the physical mechanisms behind various applications of these systems in recent years and current trends and future possibilities in this rapidly developing discipline.

References: (1) Strongly interacting photons in one-dimensional continuum, Dibyendu Roy, Chris M. Wilson, and Ofer Firstenberg, Rev. Mod. Phys. 89, 021001 (2017), 

(2) Single photons versus coherent state input in waveguide quantum electrodynamics: light scattering, Kerr and cross-Kerr effect, Athul Vinu and Dibyendu Roy, arXiv:2209.03418 (2022)


Omar S. Magana Loaiza
Title: Multiparticle interactions in plasmonic nanostructures (Online)

The additional interference paths provided by plasmonic waves enable the use of optical near fields to control complex quantum mechanical interactions in metallic nanostructures [1,2]. Interestingly, the spinorbit interactions supported by plasmonic nanostructures permit for an unprecedented level of quantum control through the manipulation of polarization [3]. In this talk, I will describe the first demonstration of the modification of the quantum statistical fluctuations of multiparticle systems in plasmonic platforms [4].

I will discuss how our findings are contributing to change old paradigms that led researchers to believe that the quantum statistical properties of bosons were always conserved in plasmonic systems [5]. I will conclude my talk by presenting the quantum simulation of fermionic interactions in a plasmonic system with ten interacting photons. The implications of our work for diverse fields ranging from condensed matter to high-energy physics will also be discussed.

[1] O. S. Magaña-Loaiza et al., “Exotic Looped Trajectories of Photons in Three-Slit Interference”, Nature Communications, 7, 13987 (2016).
[2] A. Safari, R. Fickler, E. Giese, O. S.Magana-Loaiza, and R. W. Boyd, “Measurement of the Photon- Plasmon Coupling Phase Shift”, Physical Review Letters, 122, 133601 (2019).
[3] C. You, A. C. Nellikka, I. De Leon, and O. S. Magaña-Loaiza, “Multiparticle quantum plasmonics”, Nanophotonics, 9(3) 0517 (2020).
[4] C. You, M. Hong, N. Bhusal, J. Chen, M. A. Quiroz-Juarez, F. Mostafavi, J. Guo, I. De Leon, R. J. Leon- Montiel and O. S. Magaña-Loaiza, “Observation of the Modification of Quantum Statistics of Plasmonic Systems”, Nature Communications, 12, 5161 (2021).
[5] M. Tame “Mix and match” Nature Physics, 17, 1198 (2021).

Friday, 02 December 2022

R P Singh
Title: Quantum signature of photons with orbital angular momentum

We produce light beams with orbital angular momentum (OAM) using spiral phase plates by imprinting helical phase fronts to a gaussian beam. A classical experiment with two similar beams of light derived from a single beam using a beam splitter and a quantum experiment with two indistinguishable photons produced through Hong Ou Mandel interferometer shows that OAM of light manifests itself in different ways in classical and quantum domains. We explain the results using indistinguishability, intrinsic to the quantum mechanics, and conservation of OAM. The results indicate that indistinguishability can be a great resource for many quantum information processing protocols akin to entanglement.

Saptarishi Chaudhuri
Title: A Mixture of cold atoms in a structured optical potential

Experimental and theoretical developments in the active field of ultra-cold atoms in optical and magnetic potentials have opened up several new avenues to study many body physics among other disciplines. In this seminar, I shall indicate some examples in the recent past where ultra-cold atoms and atom-light interactions have been used successfully to explore exotic phenomena in quantum mechanics – a class of study known as “quantum simulations”. Thereafter, I shall present the performance of our newly built experimental system to study a mixture of mass and spin-imbalanced ultra-cold atoms at Raman Research Institute. The focus will be on the many body physics and dynamics of cold atoms in optical and magnetic fields. A major new direction of the study of many body physics is using arbitrary shape of the trapping potential. I shall show the “structured” optical tweezers for atoms being developed in our laboratory at RRI to explore the truly exotic light matter interactions.

Lab website:

Shashi Prabhakar
Title: Spatial modes of light in turbulence and their quantum effects

The spatial degree of freedom of photons, orbital angular momentum (OAM), as an example, are suitable for implementing quantum systems for application in high-dimensional quantum key distribution. Unlike the polarization of light, which offers a two-level Hilbert space, the OAM of photons provides an infinite-dimensional Hilbert space. The effect of atmospheric turbulence on such high-dimensional OAM entanglement and two-photon Hong-Ou-Mandel interference will be presented. The discussion will be primarily focused on the challenges posed by turbulence and techniques for their mitigation in the practical implementation of using spatial modes for QKD purposes.