The operational speed of semiconductors in various electronic and optoelectronic devices is limited to several gigahertz (a billion oscillations per second). This constrains the upper limit of the operational speed of computing. Light waves perform several hundred trillion oscillations per second. Hence, it is natural to envision employing light oscillations to drive the electronic motion. Unlike conventional techniques, light waves not only initiate the electronic motion but also control it on its natural timescale, i.e., the attosecond timescale (one attosecond is one quintillionth of a second). This can potentially increase the operational speed of devices and computing by orders of magnitude and opens an avenue for petahertz electronics. Under this approach, we employ a laser to trigger and control the current in solids. One of our recent examples includes the role of defects in solids and their consequences in Petahertz Electronics.
Discoveries of topological materials, such as topological insulators, Dirac, and Weyl semimetals, have revolutionized contemporary physics. Moreover, these materials hold promises for upcoming technologies based on quantum science and electronics. One of the remarkable properties of these materials is the robustness of the electronic states against perturbations, which has catalyzed a plethora of interesting phenomena. Recently, we got interested in light-induced valleytronics. Similar to the charge and spin, the electron can also have another degree of freedom: valley pseudospin, which determines the valley the electron occupies. Valleys are local minima in the energy bands of solids. Similar to 1 and 0, two valleys can be seen as two units of operations. Not only that, operations in between the two units, i.e., the superposition of 1 and 0, can also be realized using two valleys. The superposition principle is an essential ingredient for quantum technology. Therefore, these valleys may be used to encode, process, and store quantum information at room temperature – A holy grail for quantum computing. Recently, we have shown that laser not only controls the asymmetry between the two valleys, but also wiggle the electron several hundred trillion times in one second. This opens a door to perform valleytronics at a petahertz rate - a million times faster than the conventional speed today. By exploiting the light-driven valley-operations in graphene, quantum computers operating at ambient temperature, just like ordinary computers, might one day become possible.
Electrons are the glue that keeps atoms in matter together, and their motion plays a vital role in the function and transformation of materials. During complex chemical and biological reactions, electrons undergo ultrafast rearrangements, such as in photoinduced exciton dynamics, bond formation and breakage, conformational changes, and charge migration. The motion of atoms within molecules and solids associated with chemical transformations occurs on the femtosecond (1 fs = 10-15 s) timescale. The timescale of electronic motion can be even faster, on the order of attoseconds (1 as = 10-18 s). We apply pump-probe approach to film moving electrons in matter. In this approach, first a pump pulse activates the dynamics, and subsequently, the activated dynamics is investigated by the probe pulse at a precise instant. A series of signals, obtained by varying the pump-probe time-delay, may be stitched together to make a movie of the electronic motion with atomic- scale spatial and temporal resolution. In recent years, we have applied time-resolved x-ray diffraction to understand bond-breaking and making during a pericyclic reaction, to image the flow of electrons in benzene, understand and induce chirality in molecules are name to few examples.