This seminar journeys through three captivating frontiers of quantum information: classical channel capacity with output constraints, quantum-to-classical transition, and efficient simulation of quantum computations. First, we delve into the classical capacity of quantum channels under specific state constraints. By analytically proving the intriguing properties of concavity and additivity, verified numerically also, we propose to study new avenues for exploration. By providing an analytical form of such capacity energy function for noiseless channels, we proposed to derive such expression for any noisy channel. Next, we embark on a path integral exploration of the quantum-to-classical transition. We investigate how continuous measurements nudge quantum systems towards classical behavior, uncovering the conditions under which macroscopic systems recover classicality and how measurement strengths trigger this fascinating shift? Finally, we confront the challenge of efficiently simulating quantum computations on classical computers. We highlight the unexpected hurdle posed by "concordant" states, devoid of entanglement and discord. What hidden "quantumness" remains within these states, and how can we formalise it and use this to quantify the ability of classical computers to simulate quantum algorithms?