Abstract
<jats:p>Quantum computing is transitioning from theory to engineered reality. This chapter examines key technological advances driving this shift, focusing on qubit architectures, quantum error correction (QEC), variational algorithms, and early fault-tolerant applications in drug discovery and financial optimization. Recent milestones—including error rates below the surface code threshold, high-threshold low-density parity-check codes, and logical processors using reconfigurable neutral-atom arrays—indicate that fault-tolerant quantum computation is approaching practicality. Variational algorithms such as VQE and QAOA provide utility on near-term noisy devices, despite challenges like barren plateaus and hardware noise. This chapter situates these developments within a layered architectural framework and assesses the path toward a post-binary computational era, where quantum-enhanced AI transforms high-dimensional optimization, molecular simulation, and machine learning at scale.</jats:p>