The main characteristic of quantum computing compared to classical computing is its use of quantum bits or qubits. Unlike classical bits, which exist as either 0 or 1, qubits can exist in multiple states simultaneously due to the principles of superposition and entanglement. This allows quantum computers to perform complex calculations at unprecedented speeds, making them potentially far more powerful for specific tasks, such as cryptography and optimization problems. Quantum computing's unique properties could revolutionize various fields by solving problems that are currently computationally infeasible.