Unless you’ve been living under a rock (or don’t enjoy sci-fi/superhero movies), you’ve probably come across something to do with quantum. A lot of futuristic pop culture contains quantum science as an explanation for weird and wondrous occurrences, from time travel to telepathy. Quantum science, especially quantum computing, has often been depicted as the wave of the future (no pun intended). But have you ever stopped to consider why that might be so?
What is Quantum?
We know that the first question on your mind is: what is quantum? Merriam-Webster Dictionary defines “quantum” as “of, or relating to, the principles of quantum mechanics.” Well, gee. That’s helpful, isn’t it? Let’s break it down. Say you’re two meters tall. Now, imagine yourself shrinking by one order of magnitude every second (you’ll be 2×10^-1m tall after one second and 2×10^-2m tall after two seconds). Everything seems normal within the first few seconds, and you’re okay. But once you hit the ten-second mark, things begin to get weird.
At this moment, you are the size of an atom; what you see is mostly empty space. Actually, you can’t see much of anything at all. Then you remember from chemistry class that atoms are mostly empty space, and you’re okay again. But after five more seconds, you’re the size of a proton and things really start acting up. You can’t really tell what’s going on around you. It’s chaotic and confusing. Finally, you get to the size of an electron. Electrons are so itty-bitty tiny that they have no known radius; their size is determined by their wavefunction. They’re just points in space with mass, charge, and spin.
Let’s pause here, in this strange electron land. Nothing works like it did when you were your normal size. High-energy systems occupy multiple states at the same time but collapse on themselves when you try to observe them. This is called superposition. These systems can also interact with each other in such a way that their individual states cannot henceforth be described independently of the other, a process called entanglement. The inner workings of this world are what the quantum mechanics field strives to understand, and the driving force at the heart of quantum computers.
Quantum Computers vs. Classical Computers
The first thing to get straight about quantum computers is that they are not at all like the computers we see every day. While classical computers use binary bits that can only occupy states of 1 or 0, quantum bits (or qubits) harness the quantum-mechanical property of superposition to occupy the states of both 1 and 0 at the same time. The ingenuity of quantum computers is at the heart of the quantum-mechanical qubit: a small particle. Remember the crazy electron world from before? The particles at the heart of the qubit are the same ones found in the electron world; they display quantum-mechanical properties that are then harnessed by qubits. This feature enables quantum computers to process problems that classical computers can’t even comprehend at a fraction of the time, even with fewer bits.
Quantum computers are also used for different purposes than classical computers; you’ll never have one in your smartphone or on your desk because they’re not meant to perform the same functions as classical computers. While a classical computer may help you browse memes or predict traffic, a quantum computer is meant for more big-picture things such as simulating quantum-mechanical systems, increasing the effectiveness of artificial intelligence, and creating uncrackable security. Since classical computers can’t simulate quantum superposition, it’s impossible for them to perform these tasks.
Furthermore, classical computers adhere to something called Moore’s Law, which states that as time goes on, transistors will decrease in size and become cheaper. We are unfortunately approaching the point where computers can’t get smaller or less expensive; this was the very problem that prompted computer scientists to look to quantum science to perform more complex tasks. In quantum computers, however, the addition of a new qubit (quantum bit) will actually double the processing capacity of the computer in the right conditions. This means that Moore’s Law doesn’t apply to quantum computers and they have virtually inexhaustible computational capabilities.
Quantum computers have the potential to accurately model chemical reactions, increase the security of blockchain, boost artificial intelligence, and create more effective medications than ever before. Classical computers are Toyotas and quantum computers are Marty McFly’s DeLorean. Huge difference.
Problems with Quantum
Now you might be thinking: If quantum computers are so great, then why aren’t they commonplace? Well, when taking properties that belong in the electron-sized world and applying them to the normal-sized world, there are bound to be some problems.
The first problem that we encounter is decoherence. It’s very difficult to keep qubits in a superposition because they require extremely low temperatures (near absolute zero) and a vacuum-sealed chamber in order to work. Decoherence occurs when small changes in the environment ruin the superposition of a qubit, which restricts the quantum computer from performing any further computations. Simply put, one foreign vibration could render an entire qubit useless. The high costs associated with creating qubits and maintaining such precise conditions prevent quantum computers from being widespread, not to mention the fact that quantum computers are extremely bulky and heavy.
Another problem with qubits is the difficulty of maintaining superposition long enough for it to actually be useful. Andrew Houck, inaugural director of the National Quantum Initiative, says, “Quantum states are incredibly fragile. Real progress is keeping these quantum mechanical properties ‘alive’ for as long as possible so that you can do the kinds of computations, sensing or communications that you want to do before all this falls apart.”
In order for qubits to effectively communicate with each other and form quantum circuits, they must entangle with each other. However, entangling several qubits together is an enormous challenge, especially since entanglement rarely lasts more than a minute in human-sized quantum systems.
Scientific leaders from around the world are attempting to combat these problems in several ways, including fortifying circuits and using atoms instead of quantum particles. Companies like Google and IBM, Rigetti, and D-Wave are getting in on the action, and every new breakthrough brings us closer to our ideal quantum computer.
The universal quantum computer that we are one day hoping to build, one containing at least 100,000 qubits, would solve extremely complex problems with unprecedented accuracy. Such a computer would have the computational power to model the entire universe, allowing us to take giant leaps forward in astronomy and space exploration. So, yes: there is a very important reason backing the use of the word “quantum” in pop culture. Today, quantum computing sounds cool, science-y, and futuristic. But tomorrow, it will be breaking barriers we haven’t even dreamed of discovering yet.