The promise of quantum computing is its ability to derive answers for problems which are currently computationally prohibitive. Of the many open issues surrounding the successful delivery of mass-market quantum computers two of note are the vagueness of what they will be useful for and if quantum computers can be scaled in a manner to solve hard problems? It is uncertain as to if there are answers to these questions.
By modelling the natural world in a processor, as opposed to digital operations in current processors, the assumption is we will have the ability to quickly simulate the interaction of particles in the real world. Our current computing model built as it is on zero and one’s is inadequate for these use cases as in the natural world things are not binary. Traditional computers are built on the bit, it has a state of 0 or 1 and never anything else. The qubit, the building block of quantum computing, is capable of operating in intermediate states. Imagine it as always operating from 0 to 1, and qubits only deliver an output of 0 or 1 when you take a measurement of their current state.
To give an inaccurate accounting of quantum computing that I'll tell you right now is incorrect but does not require an understanding of quantum mechanics or linear algebra, imagine that when simulating something using bits that you sequentially cycle through every outcome until you deliver an answer. For some workloads this can be done quickly, for others, usually involving an examination of the building blocks of reality, the computational time required can be measured in thousands of years. With qubits you can check multiple outcomes in parallel because what you’re using for your computation more accurately reflects the phenomena you are looking to examine. When you take a measurement, you have an answer and the answer is not derived from a binary simulation of reality painfully stepped through one option at a time but from the effect of computation on reality as it exists.
This isn’t to say that quantum computing will solve all problems, it is not administration rights to the knowledge of the universe, nor might it solve problems faster than traditional computing. It is expected quantum computing will have applications in physics and mathematical factorisation (for example cryptography and breaking cryptography), but there is still a realm of hard problems expected to be well beyond the capability of quantum computing.
To date we are unsure as to what quantum computers will be useful for as the hardware is experimental, small scale and provides results of questionable accuracy. If chip designers can crack the tough problems around the development of quantum processors and qubits the end goal will be discreet quantum processor unit cards (QPUs) available as accelerator cards the way graphics processors are delivered today. Today however quantum computers are big, qubits requiring isolation as to not negatively interact with one another, and require cryogenic cooling to ensure stability.
Right now Intel, IBM and Google have fabricated double-digit qubit chips but Intel admit these are probably not good enough for operation at scale as these qubits have a high error rate. The fact the hardware returns an unacceptable number of incorrect answers to be useful for computation has not slowed down the search for new quantum accelerated algorithms. With a lack of production grade hardware, software developers have turned to simulating qubits on traditional computers. Microsoft has released a preview of their Q# programming language which comes packaged with their quantum processor simulator and there are extensions for Java and Python which do the same thing.
As qubits in the real world may not be performing as expected how accurate software simulations running on traditional computers will turn out to be is also a question yet to be answered. There may be a discovery or two yet to be found not reflected in the software and when the hardware and software are delivered the systems may just fail to live up to their promises.
The quantum computing breakthrough has been five years away since the first time you heard the phrase “quantum computing” and its success is still not inevitable. While the technology industry is like the fashion industry in the sense there is hype, trends and seasons when it comes to new offerings it would be unwise to be cynical about a new technology in its formative state. That said, controlling expectations would be prudent until you can rent millions of qubits from your favourite cloud computing provider or add a QPU to your desktop.
Just be sure to keep a can of liquid nitrogen close to hand if you buy your own QPU.