With the advent of digital computing (classic computers) in the 1940s, we thought that computers should solve all the problems which were too complex or compute-intensive for humans. Digital computing made tremendous progress both in terms of hardware and software. 5×10−1 is the speed of the average human mental calculation for multiplication using pen and paper. The number referred to here is the digital computing power in instructions per second organized by order of magnitude in FLOPS. Today we have compute capability to the tune 1×1018, and 1×1021 is the compute capability expected to be achieved by 2035. So, does this mean that in the future humans can solve all the computation problems in the world using this digital computer? Well, the answer is no. Our problem space, including nature, is too complex and classical computers can’t solve all of them within a finite time frame (or within some predefined time limits). That’s why scientists have been looking for more advanced, faster digital computing technologies.
Quantum computing is the new-age technology proposed by scientists. Quantum computing taps into the fundamental quantum nature of matter at subatomic levels to offer the possibility of vastly increased digital computing power. The fundamental computational unit of quantum computing is the quantum circuit, an arrangement of qubits into quantum gates and measurements. The more qubits a quantum processor possesses, the more complex and valuable the quantum circuits it can run.
IBM recently announced its new 127-quantum bit (qubit) 'Eagle' quantum processor at the IBM Quantum Summit 2021. We don’t measure the computational power of a quantum system computer in terms of flops (as we do for classic computers).
Does it mean quantum computers are faster than classic computers, and in future, quantum computers will replace our conventional computers (laptops, supercomputers, etc.)?
Any computational problem that can be solved by a classical computer can also be solved by a quantum computer. Conversely, any problem that can be solved by a quantum computer can also be solved by a classical computer, at least in principle given enough time. Quantum computers obey the Church–Turing thesis. This means that while quantum computers provide no additional advantages over classical computers in terms of computability, quantum algorithms for certain problems have significantly lower time complexities than corresponding known classical algorithms. Notably, quantum computers are believed to quickly solve certain problems that no classical computer could solve in any feasible amount of time—a feat known as ‘quantum supremacy.’
In simple words, quantum computing, by its design, doesn’t perform the “basic operations” any faster or slower compared to the classic computer. But, there are certain problems that if given to the classic computer, can be solved, but the time to solve is un-deterministic. The same problem, when given to quantum computers, in a special implemented form of quantum algorithms, can solve the problem faster (time) and more efficiently (space). That does not mean that all applications will or should be moved to quantum computers.
The class of problems that can be efficiently solved by a quantum computer with bounded error is called BQP, for "bounded error, quantum, polynomial time".
Integer factorization and the discrete logarithm problem are known to be in BQP. Some applications which are best suited for quantum computing are as below:
- Cryptography
- Search problems
- Simulation of quantum systems
- Artificial intelligence
Another point to note is that quantum computers cannot solve undecidable problems like the halting problem. Neither the classic computers can solve the undecidable problems.
Conclusion
For all the computer applications, the classic computer will not only continue to co-exist with quantum computing but also dominate in most of the application areas. Quantum computing, by its dependency on quantum physics concepts and other technological limitations, will mostly be limited to certain sub-area of application such as financial, cryptography, simulation, and chemical engineering. That too, more around research and development but not into a daily application and end-user usage. Your laptops would not be replaced by quantum chips, but we will have quantum computers on the cloud to solve your complex problems, accessed via classical laptops.
Even if we look at the maturity of quantum computing for research labs, then we can see it progressing but still far away from reaching the stage that could make it available for industries and labs across the world. The very nature of quantum computing to store qubit is error-prone and hence requires a lot of refinement to make it feasible for real-world problems and wide usage.
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