Entanglement, Qubits, and Quantum Computing, Simplified

What’s Up with Quantum Computers?

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I wouldn’t have the patience to use my old high school laptop today. Like many people, I’ve become accustomed to fast downloads, non-buffering videos, and instantaneous answers to pressing questions (Is the dress gold and white, or blue and black?). But our ability to make everyday computers faster and more powerful is reaching a threshold. Our computers are limited because they process information using “bits,” the 1s and 0s we abstractly associate with computer code. 

Enter the quantum computer. In 2016, a major company made its quantum computer prototype available for public tinkering. The device has helped stoke curiosity in the applications of quantum technologies, which include communication, cryptography, and finance, to name a few. 

Quantum computers process information using quantum bits, or “qubits.” Instead of being represented as either a 1 or 0, a qubit exists as both a 1 and a 0—and different states in between—at the same time. Remember in high school chemistry when you learned that light could be both a particle and a wave? Or when you puzzled over that optical illusion that looks like both a rabbit and a duck? This is called superposition, the concept of existing in multiple states at once. A qubit is a tiny object, like an atom or electron, that can exhibit superposition. 

Now, what if I told you that the many simultaneous states of a qubit can be harnessed to process information? With clever algorithms, computer scientists showed that qubits will process information faster than bits…exponentially faster, it turns out, if you “entangle” qubits together. Quantum entanglement means that qubits can be linked across distances, such that the state of one is tied to the state of the other.  

Confused? Think of it this way. Two baseball games are happening in New York City, one in the Bronx and one in Flushing. Different in-game scenarios will lead to different winning teams, so—while in progress—the games exist in multiple states. But if a thunderstorm suddenly pauses over the city, both games—our qubits—stop immediately, and each leading team is declared the winner. Let’s take the example one step further: imagine if baseball games across the country were to stop when it rains in New York. Despite the distance, the games would all be affected in the same way by the weather, just like entangled qubits.

You might have noticed, though, that the games no longer exist in multiple states after their winners are declared. They fall out of superposition and become standard bits instead of qubits, because they can be represented as either a 1 or 0.  

So, when developing a quantum computer, we find ourselves in a catch-22. Entangling more qubits together gives us greater computing power, but if one qubit falls out of superposition, they all do. As it turns out, it’s also really hard to keep even a few qubits in superposition in the first place. The scenario is like building a house of cards…how many cards can you add until it falls?  

This challenge is driving a lot of current research, which includes finding new qubit materials and figuring out how to maintain their superposition. If researchers are successful, the possibilities of what we could do with quantum computers are profound. Pharmaceutical discovery could be sped up, revolutionizing disease treatment. Codebreaking, which relies on factoring enormous numbers, could be simplified. Quantum encryption could make your online shopping more secure. Even combing through massive datasets would be streamlined; instead of examining pieces of hay one by one, we would simultaneously search multiple bales when looking for the needle in a haystack.  

While quantum computing with two qubits was first reported in 1998, and a 72-qubit case was announced a few years ago, we’re still nowhere near having a fully functional quantum computer at our fingertips. And that’s exactly why companies, venture capitalists, and even federal governments are investing in quantum research and development. Continued leadership in a broad range of quantum technologies—like computing, communication, and sensing—is a U.S. Government priority, as evidenced by the signing of the National Quantum Initiative Act in December 2018.  

The future economic and social impacts of quantum computing, both in the United States and around the world, are transformative and diverse. How would quantum computers change your life? 

About the Author: Aubrey R. Paris, Ph.D., is a Science and Technology Policy Adviser in the Office of the Science and Technology Adviser to the U.S. Secretary of State (STAS). She received her Ph.D. in Chemistry and Materials Science from Princeton University and B.S. in Chemistry and Biology from Ursinus College. 

Image Credit: Michael S. Helfenbein/Yale University

Source:  U.S. Department of State.  Aubrey R. Paris, Ph.D.,  What’s Up with Quantum Computers?

Content may have been edited for style and clarity.