Ultrafast phenomena in weak and strong light-matter interaction limits: nonlinear spectroscopy and imaging with quantum light and high harmonic regimes

The progress in quantum optics utilizes a unique photon state configuration for engineering of the ultimate light-matter interactions with relatively simple material systems. It results in a broad range of photonic applications including radiation sources, quantum communication, information, computing and nanotechnology. The development of the ultrafast multidimensional nonlinear spectroscopy that has been enabled by progress in ultrafast optical technology provides a unique tool for probing complex molecules, semiconductors, nanomaterials by classical light fields. I will show how new quantum phenomena in complex systems can be studied and controlled using advances in both quantum optics and nonlinear spectroscopy. In particular, I investigate how to probe, control, and image the dynamics of these complex systems using quantum light and reveal the material information, which is not accessible by conventional classical photonics tools. In the second part of the talk I will discuss a novel method for monitoring electronic coherences using ultrafast spectroscopy in high harmonic regime. This method is based on the time-domain high-order harmonic spectroscopy where a coherent superpostion of the electronic states is first prepared by the strong optical laser pulse using a three-step mechanism introduced by Lewenstein and Corkum. The coherent dynamics can then be probed by the higher order harmonics generated by the delayed probe pulse. The main advantage of the method is that only optical (non X-ray) laser is needed. In addition, a semi-perturbative model based on the Liouville space superoperator approach is developed for the bookkeeping of the different orders of the nonlinear response for the high-order harmonic generation using multiple pulses. Coherence between bound electronic states is monitored in the harmonic spectra from both the first and the second order responses.

Reference:
K.E. Dorfman, F. Schlawin, and S. Mukamel, Rev. Mod. Phys. 88, 045008 (2016).
F. Schlawin, F. Schlawin, and S. Mukamel, Acc. Chem. Res. 51, 2207 (2018).
K.E. Dorfman, P. Wei, J. Liu, and R. Li, Optics Express 27, 7147 (2019).

Bottom-up engineering of new electronic and structural effects with atomic layers

Van der Waals heterostructures represent a new paradigm of material design, where two atomic or molecular planes of different chemical origin are brought together within the sub-nanometer van der Waals distance. When two atomic layers are placed so close their electronic states may hybridize, and the physical properties are modified by the rules of momentum conservation and structural commensurability. In this talk I shall present several new physical phenomena, in multiple domains ranging from electronic, opto-electronic to thermoelectric properties, that emerge as a result of van der Waals heterostructuring of two-dimensional (2D) materials. Apart from achieving high carrier mobility and ultra-low noise in electrical transport, encapsulating graphene by boron nitride leads to manifestation of edge transport and trigonal warping at low energies. Optoelectronic properties are strongly enhanced on graphene and transition metal dichalcogenide heterostructures, that can be extended to single photon detection. I shall also show new phenomena in thermoelectric transport in twisted bilayer graphene, where the Seebeck coefficient is strongly determined by the angular misorientation between the graphene layers in the van der Waals stack.

Optical vortices and entanglement duality

Optical vortices also called light whirlpools are structures in light very similar to water whirlpools. Due to the helical wavefront, just as in water whirlpools, the light and consequently photons acquire orbital angular momentum that is different from spin angular momentum associated with circularly polarized light. We will discuss methods to generate these structures in the lab followed by their properties which are finding a variety of applications including the ones in classical and quantum communication.
Entanglement being a great resource for quantum information processing, we will see how these structures can help in achieving different kinds of entanglements leading to duality of entanglement.

Quantum phases of canted dipolar bosons in optical lattices

In this talk, we shall discuss on a minimal model to describe the quantum phases of ultracold polarized dipolar bosons in two-dimensional square optical lattice. The polarization axis of the dipoles can be canted with respect to the lattice plane by the external magnetic field. We study the quantum phases of the system arising from the variation in the tilt angle.Our study reveals that due to the anisotropic nature of the dipole-dipole interaction, the system can undergo a structural phase transition between two quantum phases with different orders, checkerboard and striped. In addition, we shall discuss on the phase diagrams of the system illustrating the parameter regions of the quantum phases.

Fractionalization of Integer Quantum Hall state

Integer quantum Hall (IQH) states which are well understood in terms of non-interacting electrons are expected to have dissipation-less edge states transport from protected integer charge modes with conductance of e2/h. However, in strong Coulomb interaction regime, nucleation of dominant fractional quantum Hall (FQH) gaps at filling ν = 1/3 and 2/3 gives rise to incompressible strips around the smooth boundary of IQH system. As a consequence, edge states of IQH system become fractionalized into three downstream charge modes of conductance /3h each. In this talk I shall present the edge state fractionalization at long mesa boundary of ν = 1 IQH states in high mobility 2DEG. We experimentally demonstrate that ν = 1 IQH edge state is composed of three robust downstream fractional 1/3 charge modes. Equilibration between the modes can be controlled by tuning the magnetic field within the extent of ν = 1 IQH plateau. In our experiment, we could unveil the equilibration properties of the modes and this finding is linked to formation of the two set of fractional conductance plateaus of values 1/9, 2/9, 4/9 and 1/6, 1/3, 2/3 at the two ends of ν = 1 IQH plateau under selective excitation and detection of the fractionalized 1/3 modes.

Colloids in complex and dynamic environments

Topological defects have been objects of intense studies in various disciplines starting from cosmology to condensed matter, optics and more recently in active matter. In liquid crystals (LCs) they are produced during the symmetry breaking phase transition. Such defects can be induced by dispersing foreign nano- and micro-particles in LCs. The embedded particles create elastic distortions in the LC medium inducing topological defects, and interact via long-range anisotropic elastic forces so generated. These forces obviously have no analogues in regular colloidal systems in an isotropic dispersive medium. An interesting manifestation of such novel forces is the ability of the colloidal system to self-assemble. In an experiment, such a process can be conveniently guided to create 2D and 3D colloidal crystals, with complex architectures.
In this talk, I will present some of our recent studies on particle induced defects and transformations of such defects across the phase transitions in liquid crystals. We show that the elastic properties and the emergence of smectic layering have profound effects on these defects, in terms of the colloidal pair-interactions and their resulting two-dimensional assemblies. Finally, I will present some recent results on the electric field driven transport properties of Janus particles. In a striking departure from conventional electrophoresis, we show that metal-dielectric Janus particles can be piloted at will through a nematic liquid crystal film, in the plane perpendicular to an imposed AC electric field. We achieve complete command over particle trajectories by varying field amplitude and frequency, exploiting the sensitivity of electro-osmotic flow to the asymmetries of particle and defect structure. We propose a new method for measuring the induced electrostatic dipole moment of the Janus particles, through competition between elastic and electrostatic interactions. These findings open unexplored directions for the use of colloids and liquid crystals in controlled transport, assembly and dynamical topology.

Bacterial Turbulence: Collective motion in suspensions of microswimmers

I will begin by briefly summarizing our recent work on the spatial migration of microswimmers (bacteria and algae) in shearing flows, emphasizing the range of behaviour possible depending on swimmer shape and shear rate, and pointing towards the possibility of hydrodynamic focusing of swimmer populations. Thereafter, my main focus will be on the development of a novel stochastic kinetic theory framework to characterize the transition to collective motion in a dilute suspension of persistent swimmers. The fundamental equation underlying this approach is the fluctuating run-and-tumble equation - the kinetic equation for the probability density of run-and-tumble swimmers in position-orientation space driven by a noise arising from fluctuations inherent in the Poisson statistics governing the tumbles. Combining the fluctuating run-and-tumble equation with the Stokes equations that include a swim stress, allows one to examine the effects of long-wavelength velocity fluctuations, that emerge close to the onset of collective motion, on tracer diffusion. We derive an expression for the diffusivity of spherical tracers over the entire range of swimmer volume fractions, from its known plateau value in the non-interacting dilute limit to its divergence at the collective motion threshold.

Novel Titanium Niobium Oxide (TNO) thin films for High Energy Storage Solid-State Thin Film Batteries

Complex metal oxides-based materials and devices based on their nanostructurd thin films & heterostructures provide a plethora of applications and are considered as promising next-generation devices. Among them, titanium niobium oxide (TNO) materials found growing interest due to their complex disorder layered structures which offer unique functional properties. Nonetheless, the synthesis (growth) of quality titanium niobium oxide thin films is not realized until recently. The fundamental understanding and growth of these exotic complex oxide systems could lead to the development of next generation high energy storage & conversion systems like solid-state batteries, photoanodes, and transparent oxide electronics devices.

Towards this, we have been developing TiNb₂O₇ oxides in thin film form using physical vapor deposition methods for the first time and successfully demonstrated their usage as negative electrodes in rechargeable Li-ion thin film (micro) batteries. Moreover, the amorphous of TNO thin films also offering superior energy storage properties over their crystalline TNO and commercial Li₄Ti₅O₁₂ (LTO) negative electrodes, with remarkable high initial discharging capacity ≈ 226 μAh/μm¹cm² (≈ 460 mAh/g) at 17 μA /cm² current density, excellent coulombic efficiency (> 99%), reversible kinetics and stable crystal structures in the operating voltage window of 0.1−3.0 V.  This research opened up a new research paradigm for developing novel solid-state thin film (micro) batteries, coupled with suitable electrodes (for ex. Li-metal based solid state batteries) and solid oxide electrolyte materials; thus, very much promising for powering next generation CMOS, integrating with RFID, portable-wearable technology and IoT sensors applications. In my talk, I will discuss the important concepts of all solid-state thin film batteries using our research findings and discuss challenges that need to be addressed further.

References:

[1] J.T. Han, Y.H. Huang, and J.B. Goodenough., Chem. Mater. 23,2027 (2011)
[2] V. Daramalla and S.B.Krupandihi., MRS Proceedings 1805, mrss15-2128679 (2015)
[3] V. Daramalla, Tirupathi Rao Penki, N Munichandraiah, and S. B. Krupanidhi., Materials Science & Engineering. B, 213, 90–97 (2016)
[4] V. Daramalla, G Venkatesh, B Kishore, N Munichandraiah, SB Krupanidhi, Journal of Electrochemical Society, 165 (5), A764–A772 (2018).
[5] V. Daramalla*, S. Dutta*, S. B. Krupanidhi, Journal of European Ceramic Society (2019), accepted
[6] V. Daramalla, S. B. Krupanidhi, Thin Solid Films (2019), under revision
[7] E. Burns, D. Pergolesi, Thomas J. Schmidt, T. Lippert, and V. Daramalla, submitted 2019(under review)

Generalized Gaussian Wave Packet Dynamics and Semiclassical Physics

The ultimate semiclassical wave packet propagation technique is a complex, time-dependent Wentzel-Kramers-Brillouin method known as generalized Gaussian wave packet dynamics (GGWPD). It requires overcoming many technical difficulties in order to be carried out fully in practice. In its place roughly twenty years ago, linearized wave packet dynamics was generalized to methods that include sets of off-center, real trajectories for both classically integrable and chaotic dynamical systems that completely capture the dynamical transport. The connections between those methods and GGWPD are developed in a way that enables a far more practical implementation of GGWPD. The generally complex saddle-point trajectories at its foundation are found using a multidimensional Newton-Raphson root search method that begins with the set of off-center, real trajectories. This is possible because there is a one-to-one correspondence. The neighboring trajectories associated with each off-center, real trajectory form a path that crosses a unique saddle; there are exceptions that are straightforward to identify. The method is applied to the kicked rotor to demonstrate accuracy improvement as a function of ℏ that comes with using the saddle-point trajectories.

Drive-specific adaptation in disordered mechanical networks of bistable springs

Systems with many stable configurations abound in nature, both in living and inanimate matter. Their inherent nonlinearity and sensitivity to small perturbations make them challenging to study, particularly in the presence of external driving, which can alter the relative stability of different attractors. Under such circumstances, one may ask whether any clear relationship holds between the specific pattern of external driving and the particular attractor states selected by a driven multi-stable system. To gain insight into this question, I will present a numerical study of driven disordered mechanical networks of bistable springs which possess a vast number of stable configurations arising from the two stable rest lengths of each spring, thereby capturing the essential physical properties of a broad class of multi-stable systems. I will show that the attractor states of driven disordered multi-stable mechanical networks are fine-tuned with respect to the pattern of external forcing to have atypically low work absorption from it. Furthermore, I will demonstrate that these drive-specific attractor states are even more stable than expected for a given level of work absorption.

A mechanistic model of the cellular resource allocation strategy in bacteria

Bacterial growth requires protein synthesis. It is carried out by cellular machines called ribosomes which polymerize amino acids into proteins. However, being made up of protein sub-units themselves the ribosomes not only have to synthesize other proteins, like the metabolic proteins converting environmental nutrients into amino acids, but also their own sub-units. Therefore, a bacterial cell is faced with this interesting trade-off of how much of its ribosomes should it allocate to producing more ribosomes as opposed to producing other proteins, so as to optimize the utilization of the machines and the nutrient resources. We present a simple, mechanistic model which demonstrates this trade-off,and show that there exists an optimal allocation parameter which maximizes the growth rate of the cell. Moreover, bacteria must dynamically adapt their growth to changes in the environment. We show how the bacterial cell uses a simple feedback mechanism to achieve this, by dynamically driving this allocation parameter towards the optimal value for different environments. The resultant model is consequently capable of explaining various experimental results pertaining to the effect of nutrient,antibiotic and other such perturbations under one unified framework.

Laser Materials Processing: A contemporary Overview

Lasers is undoubtedly one of the path breaking discoveries of the last century, which is revolutionizing a myriad of technologies during this century. In this lecture we will discuss the growth of laser materials processing with an objective to review the ongoing research and development in this field. We will get an essence of the emerging areas of laser-based materials processing technologies such as laser additive manufacturing, ultra-short pulsed laser peening, laser forming etc.

Lithium-Sulfur Batteries: the Next Frontier in Energy Storage

Lithium-sulfur (Li-S) batteries offer a theoretical energy density of ~2600 Wh/kg (compared to ~387 Wh/kg for Li-ion technology) and therefore offer great potential as a next generation energy storage device. However there are two major barriers to realization of high performance Li-S batteries: (1) poor cycle stability caused by dissolution of intermediate lithium polysulfides from the S cathode into the electrolyte and (2) nucleation and growth of dendritic structures on the Li metal anode, which can electrically short the battery. In this talk, I will discuss some possible solutions to these problems. Specifically, I will show that two-dimensional (2D) sheets of black phosphorous (i.e. phosphorene) are highly effective as a lithium polysulfide trapping agent. I will further show that the Li dendrite problem can be addressed by using self (Joule) heating to accelerate surface diffusion processes to heal (smoothen) the dendrites in situ. Such advances show potential in enabling the successfully deployment of Li-S batteries with breakthrough improvements in performance as compared to the incumbent Li-ion technology.

Quantum Field Theory: Dualities and What They're Good For

Quantum field theory is hard. It's especially hard when the interactions between particles become strong. I'll describe recent progress in understanding this issue, and show how various ideas from condensed matter physics, high energy physics, and string theory have converged to give us new and surprising insights into the behaviour of quantum fields.

Numerical investigations of SO(4) emergent extended symmetry in spin-1/2 Heisenberg antiferromagnetic chains

The antiferromagnetic Heisenberg chain is expected to have an extended symmetry, [SU(2)×SU(2)]/Z2, in the infrared limit whose physical interpretation is that the spin and dimer order parameters form the components of a common four-dimensional pseudovector. Here we numerically investigate this emergent symmetry using quantum Monte Carlo simulations of a modified Heisenberg chain (the J/Q model) in which the logarithmic scaling corrections of the conventional Heisenberg chain can be avoided. We show how the two- and three-point spin and dimer correlation functions approach their forms constrained by conformal field theory as the system size increases and numerically confirm the expected effects of the extended symmetry on various correlation functions. We stress that sometimes the leading power laws of three-point (and higher) correlations are not given simply by the scaling dimensions of the lattice operators involved but can be faster decaying because of exact cancellations of contributions from the fields and currents under conformal symmetry.