ABSTRACT: The presence of two degenerate unconventional quantum states, known as valleys, in two- dimensional materials is often regarded as analogous to binary operational units – representing 0 and 1. These valley states can also exist in superposition, effectively functioning as qubits. The unique properties of valleys make two-dimensional (2D) materials a viable possibility for integration into devices designed for coherent encoding, processing and reading of both classical and quantum information. To realize such applications, precise control over valley states is essential, enabling the implementation of valley-based devices for practical purposes. In this talk, I will discuss how valley-selective excitation in graphene with zero bandgap can be achieved by an all-optical means. Ultrashort laser pulses are employed to obtain a desire control over valley polarisation. By tailoring the waveforms of the laser pulses to the symmetry of the graphene’s sub-lattice, first I will demonstrate that it is possible to induce and read valley polarization in 2D materials including graphene -- a medium where light-driven valleytronics was thought to be impossible. Subsequently, I will show a coherent protocol to initiate valley-selective excitation, de-excitation and switch the excitation to another valley within tens of femtoseconds -- timescale faster than any valley decoherence time. If time permits, I will introduce a novel approach to exercise necessary control in achieving valley polarization using a nonresonant, linearly polarized laser pulse without requiring carrier-envelope-phase stabilization. By exploiting the asymmetric waveform of the amplitude-polarized linear pulse, valley polarization is achieved successfully. The asymmetric waveform also generates a valley current, which serves as a quantifiable marker for induced valley polarization. Our approach provides a means to induce valley polarization, achieve its complete reversal, and quantify it through the associated valley current.

BIO: After earning my Ph.D. in Atomic and Molecular Physics from IIT Kharagpur and TU Munich, I worked at CFEL in Hamburg from 2011 to 2013. Subsequently, I joined the Max Born Institute in Berlin, where I continued my research from 2013 to 2015. Following my time in Berlin, I joined the Department of Physics at IIT Bombay, where I currently serve as an Associate Professor. Presently, I am on sabbatical leave, serving as a Visiting Professor at the PULSE Institute. This seminar is sponsored by the Department of Applied Physics and the Ginzton Laboratory