The question of whether a general-purpose, fault-tolerant quantum computer is possible or not is a topic of debate among researchers. While the majority of experts in the field believe that it is theoretically possible to build a quantum computer, there are also some researchers who hold the view that quantum computers may be fundamentally impossible to realize.
One prominent argument against the feasibility of quantum computers is based on the concept of the Church-Turing thesis, which states that any function computable by an algorithm can be computed by a Turing machine. Some researchers argue that since quantum mechanics does not violate the Church-Turing thesis, quantum computers cannot offer computational capabilities beyond what classical computers can achieve.
However, the majority of researchers in the field of quantum computing argue that this view is based on a limited understanding of quantum mechanics and the potential of quantum computation. Quantum computers have the potential to solve certain problems more efficiently than classical computers through phenomena such as superposition, entanglement, and quantum interference. Many quantum algorithms, such as Shor's algorithm for factoring large numbers, demonstrate the potential for exponential speedup compared to classical algorithms.
Furthermore, experimental progress in the field of quantum computing has been significant, with various approaches showing promise, including gate-based quantum computers, adiabatic (annealing) quantum computers, and photonic quantum computers. While current quantum computers are still in the early stages and face numerous technical challenges, they have already demonstrated limited computational capabilities.
It is important to note that the feasibility of quantum computers is an active area of research, and our understanding of their potential and limitations is continuously evolving. While some researchers have expressed skepticism, the prevailing consensus among experts is that building a practical, fault-tolerant quantum computer is indeed possible, albeit a challenging task that requires substantial technological advancements.