## Menace or Miracle: The dawn of quantum computing

You trust the encryption systems that your bank uses to secure your accounts and that your doctor uses to keep your medical records confidential, right? These encryption systems are great at guarding against almost all attacks by modern computers, but there’s a new type of computer on the rise: the quantum computer. Not only can quantum computers easily break current encryption systems, but they also have the potential to revolutionize the way computers process information and the way scientists model natural phenomena.

**What does “ quantum”really mean?**

“Quantum” is a scary word, especially when you apply it to the inner mechanism of a computer which is complicated enough as is. Here’s what you need to know about the quantum realm: the term “quantum,” like in “quantum physics,” applies to the study of *very small things*, like the interactions of individual atoms and light particles. The cool and perplexing part of quantum physics is that in the quantum realm, a particle or piece of information can be in two different states *at the exact same time*. When a quantum system is in two states at the same time, the system is said to be in a state of superposition. Superposition is very important for quantum computing. (If you want to learn more about superposition, click __here __and __here__).

**How is a quantum computer different from a classical computer?**

Modern computers, like your Mac or PC, are ‘classical computers’ that use bits to store one piece of information: either a 0 or 1. In a quantum computer, information is stored in a quantum bit, or a ‘qubit.’ Qubits also store 0s and 1s, but their quantum nature means that the piece of information can be either a 0, a 1, or some combination of __both at the same time__.^{[1]}For example, the qubit could be 20% a 0 and 80% a 1.

Qubits can be made out of many different natural systems that have two possible states (0 and 1). Here is an analogy to help you picture a qubit: think of the hydrogen atom that has one proton and one electron. When the electron is in the ground state (the least energetic orbital), it is a zero. When the electron is in the excited state (the next orbital up that has more energy), it is a 1. When the electron is in a superposed quantum state, it is simultaneously in the ground and excited state. Quantum computation scientists don’t actually use hydrogen atoms to make qubits, but it is a good model to understand the principle.

The most commonly used and effective qubits today are oscillating, superconducting electrical circuits. When this type of qubit is put together on to a computer chip in a quantum computer, it can be controlled by microwave pulses that are shot at the chip.^{[2] }

So what makes quantum computers more powerful than classical computers? Here’s an example: you have to solve a problem in which there are many possible answers. In a classical computer, you have to run the calculation over and over again for each possible answer, which may take a very long time. But because of superposition in a quantum computer (where a qubit can be both a 0 and a 1 simultaneously), the quantum computer can calculate all of those possible answers at the same time. Of course, in real quantum computers, there are many additional complexities that are not taken into account in this example. ^{[2]}

Because a quantum computer can store data in a superimposed way (the data can be in two states at the same time), the computational power of a quantum computer increases exponentially as the number of qubits increases linearly, which is a capability not wielded by classical computers. This exponential nature of data storage allows quantum computers to process extremely large numbers and data. This ability allows quantum computers to recognize repeating patterns very quickly, even if those repeating patterns are very long. For example, quantum computers can factor very large numbers using an algorithm that detects large patterns, while classical computers do not have this computational capability. This may seem like a trivial ability of quantum computers, but it is actually the key to how quantum computers decrypt security systems!

**Menace or Miracle?**

Most modern encryptions systems–like the ones that secure our bank accounts or personal computers–rely on the fact that classical computers cannot factor very large numbers, as mentioned above. The encryption codes include very large numbers that normal computers cannot process. But near-future quantum computers will make these security systems obsolete when they breeze right by those large numbers. So why are quantum computers not a bigger deal, especially if they could end modern security as we know it?

Because this threat isn’t as big of a deal as it seems. In the past decade, the field of post-quantum cryptography (encoding and decoding) has been growing. If quantum computers become regularly used, post-quantum cryptographic algorithms will undoubtedly be implemented in place of our current security systems, and the world will go back to running smoothly. To learn more, read __Chandler’s article on post-quantum cryptography__.

So if the most well known application of quantum computers – hacking encryptions –is not actually that useful or threatening in the long run, then are quantum computers still a big deal? Absolutely. Quantum computers can model natural phenomena in realistic ways that classical computers cannot. This application of quantum computers is extremely useful in scientific pursuits. For example, in the areas of quantum chemistry, medicine, material science, and high-energy physics, the way particles interact with each other is usually quantum in nature. Thus, these interactions can be much better modeled by a device that is also quantum in nature. We will be able to model quantum physics using quantum physics, so to say.

Quantum computers will give us a peek into how the universe works at its most basic level, and hopefully will help physicists solve some of the mysteries of the universe. There is also speculation that quantum computers will be useful in machine learning in the future.^{[3] }In an application that is much more applicable to our everyday lives, quantum computers may help create new materials like medical drugs that could cure diseases.^{[2]}

**The future of quantum computing**

So when will quantum computing become a part of our daily lives? Right now, companies like IBM, Microsoft, and Google are building quantum computers, but they have limited capabilities and there are only a few of them. There are still many challenges facing quantum computers.

The most significant challenge that the development of quantum computers faces is creating computer chips that can hold enough qubits to perform meaningful calculations, according to Dr. Patrick Hayden, a professor of physics at Stanford University who studies the role of quantum computing in fundamental physics. Currently, IBM has a 20 qubit quantum computer. Qubits on the order of thousands are needed to solve realistic scientific problems.^{[2]}

Despite such challenges, Dr. Hayden estimates that quantum computers will be used for scientific purposes within the next decade. Google and IBM also envision using quantum computers as a cloud service, where you would access a quantum computer through the internet. IBM even currently has a small quantum computer that you can play with on their __website__. With the constantly evolving technological world, it is entirely possible that in the future, your laptop will have a small quantum computer inside it.

The fate of quantum computers is still uncertain, but if and when realized, they will have the potential to revolutionize our daily lives and our understanding of the world. In a future where our computers are made of qubits instead of bits, we may have to move onto new systems to secure our confidential information. However, more importantly, we will have the ability to understand the world around us at a greater level and to solve problems in entirely new ways.

**References:**

- Hayden, P. (2018, November 1) Decoding Spacetime: The Quantum Computational Universe [Powerpoint Lecture]
- Hayden, P. (2018, Nov 16) Personal Interview.
- (2018, March 27)
*Future Focus: Quantum Computing in Next Generation AI Research*[Video File] Retrieved from: https://www.technologyreview.com/video/610678/future-focus-quantum-computing-in-next-generation-ai-research/