The quantum computing revolution is on the horizon.

But what does that mean for you—or your company? While a fully viable quantum computer hasn’t been built yet, understanding the implications is important (and exciting). From the effects it could have on cybersecurity, detailed problem solving, the drug industry and even personalized medications––here’s the context you need to understand what a future with quantum computing could be.

To understand where we’re going, we need to understand where we’ve been. For classical computers, that’s the same place for nearly the last 70 years. It’s called the transistor and it’s been the basic building block of any computer since the 50’s. Manufacturing and engineering have certainly improved since then, but the basic functionality has not.

A transistor is like a light switch—either on or off. And it’s the combination of multiple switches that allows us to make logic gates and computing. You increase your computing power by adding more transistors or switches. Let’s look at an example.

Classical computers increase their computing power by increasing the number of transistors. Since a transistor can only hold one state at a time, more and more transistors need to be used to compute on all possible states. This is why the most powerful chips in the world cram billions of transistors on a single chip—it’s the only way to realize more and more computing power.

As great as our classical computers are, they have limitations. Richard Feynman, arguably the greatest physicist since Einstein, posed a simple question in one of his famous lectures: “Can a quantum system be probabilistically simulated by a classical universal computer?”

In other words, can something inherently quantum like, say, most of nature be completely simulated by a computer that is not also quantum? I bet you can guess his answer: “If you take the computer to be the classical kind, and there are no changes in any laws, and there's no hocus-pocus, the answer is certainly no!”

Now you may think that classical computers will eventually be powerful enough as long as they continue growing in power. Unfortunately, Feynman disagrees with you:

“This is called the hidden-variable problem: it is impossible to represent the results of quantum mechanics with a classical universal device.”

If you’ve forgotten the hidden-variable problem from physics class, here’s a quick refresher. In the quantum world, there are inherent indeterminisms, mostly stemming from Heisenberg’s uncertainty principle; you could say the state of a physical system does not give a complete description of the system. If that makes your head hurt, you’re not alone! The key is that we have an incomplete model of the ultra small and seemingly a barrier in understanding it.

Another limitation is directly related to the previous one. The way to increase computing power is to increase the number of transistors, and the top chips today have an almost incomprehensible number of transistors on a single chip. So, can we continue cramming more and more transistors on a chip? No. The smallest transistors today are just a dozen atoms and that’s pushing the limit on how small you can go before quantum effects and, therefore, unpredictability take effect. So far, we’ve been clever engineers in finding new ways to avoid this problem. But the day will come when transistors can’t get any smaller.

Now that we’ve seen where we’ve been, let’s see where (we think) we’re going. If the transistor (or bit) is the basic unit of classical computing, then the qubit is the basic unit of quantum computing. I won’t get into the math behind what a qubit is, but the key difference is that unlike a two state system in the transistor, a qubit is a three state system.

If a transistor is like a light switch (either on or off), a qubit is like a dimmer light switch in that it can be on, off or both. Let’s look at another example.

And this continues to scale. If you wanted to classically represent all 16 possible states of 4 transistors or bits, you would need 64 transistors, but to represent those same states you would only need 4 qubits. 

What about an amount more comparable to today’s computers? If you had a quantum computer comprised of just 300 qubits, how many transistors would that translate to? That quantum computer would be able to simultaneously represent about 2 x 10^90 bits. That’s a 2 with 90 zeros behind it and is more than the number of known atoms in the universe.

In contrast, one of the best classical computer chips we have today, the Everest FPGA by Xilinx, has 50 billion transistors. That would mean that our theoretical 300 qubit quantum computer would be able to out simulate one of our best classical computers today by about 10^81. This would be like trying to compare the performance speed of a tricycle and a Bugatti Veyron.

It’s important to note here though that while incredible to think about, quantum computers will probably not replace classical computers. This is because quantum computers are known to be able to work on only certain types of problems like large optimizations. And, for the foreseeable future, they’re prohibitively expensive to run. (You wouldn’t want to use a quantum computer to watch cat videos, no matter how hilarious.)

With a high level understanding of how both classical and quantum computers work, the question is: what will a quantum computer be able to do that a classical computer will not? While there are many theories, the simple answer is we just don’t know (yet). A fully viable quantum computer hasn’t been built yet. But there are some good theories.

One of the most talked about applications of a quantum computer is wreaking havoc on our cybersecurity friends. Many, but not all, public-private key standards rely on mathematically hard integer factorization. Think 300+ digit prime numbers multiplied together. Classical computers can’t solve this problem in a reasonable amount of time, but a sufficiently large quantum computer could—effectively unlocking a significant amount of internet traffic.

Another application is in the drug industry. Right now drugs are manufactured and then tested. As part of that testing, any potential interactions with other drugs must be considered. Since these interactions are chemical, they’re also quantum, and, as we’ve seen, we can’t model them accurately. Because of this, many drug interaction work is either based on assumptions or trial and error. A quantum computer though could effectively model the quantum states of such chemical reactions. This could lead to a world with personalized medications.

We’re on the cusp of understanding what a quantum computer might be able to do in the future. We’ve seen that quantum computers have exponential potential over classical computers, but it’s important to note that quantum computers will most likely be domain specific in the problems they solve. As for now, we can anticipate a world that includes the use of both classical and quantum computers in our daily lives.

It’s not only possible but probable that there are many applications or problems that quantum computers will be able to solve that we haven’t or can’t comprehend.

That said, it’s not only possible but probable that there are many applications or problems that quantum computers will be able to solve that we haven’t or can’t comprehend. Where the quantum revolution will take us is yet to be fully realized, but the prospects are deeply exciting. Want to learn more about the concepts of quantum computing? Check out the course Quantum Computing: The Big Picture.