Quantum computers are an active area of research and development, and significant progress has been made in recent years. However, the timeline for when we will see a fully functional, large-scale, fault-tolerant quantum computer is difficult to predict with certainty. It depends on various factors, including technological advancements, overcoming technical challenges, and further understanding of quantum phenomena.
Currently, quantum computers exist in the form of small-scale devices with limited qubits (quantum bits), which are the basic units of quantum information. These early quantum computers have demonstrated capabilities like quantum supremacy, which means they can perform specific tasks faster than classical computers.
However, building a large-scale, error-corrected quantum computer capable of solving complex problems that are currently intractable for classical computers remains a significant challenge. One of the main hurdles is preserving the delicate quantum states, known as quantum coherence, for a sufficiently long time to perform meaningful computations.
Researchers are actively working on various approaches to improve qubit stability, develop error correction techniques, and scale up the number of qubits. There are different technologies being explored, such as superconducting circuits, trapped ions, topological qubits, and more.
While it is challenging to provide a precise timeline, some experts estimate that a fully mature, fault-tolerant quantum computer may still be several decades away. However, it's important to note that intermediate milestones and advancements in quantum computing are likely to occur before reaching that ultimate goal. These advancements can have significant implications for fields like cryptography, optimization, material science, and drug discovery, among others.
In summary, while the development of a legitimate, large-scale quantum computer is an ongoing effort, its exact timeline and realization depend on numerous factors and are subject to further advancements and breakthroughs in the field.