Bits & Bytes

Classical or traditional computing uses binary digits, or bits, to store information in the form of a 1 or 0, corresponding to either one of two possible physical states. Bits are the smallest unit of data a computer can store. Think of this as how a light switch can either be on and off, or how a factual statement can be either true or false. 

A sequence of eight bits treated as a single unit is called a byte, which is how we tend to think about a computer’s memory or storage. 

Bits are stored as an electrical charge in capacitors; transistors take those 1’s and 0’s to turn the flow of electricity on or off, respectively. Transistors and capacitors can be arranged in different configurations to create circuits and logic gates that perform different operations within the computer. Bits, capacitors, and transistors are three of the components that make up the microchips that enable much of the technology around us. Combinations of microchips in integrated circuits are called processors.  Processors, also known as central processing units (CPUs), are the brains of computers that tells the other parts what to do.

Today, almost every aspect of our lives revolves around classical computing. Our smartphones, laptops, and cars are all filled with microchips using billions and billions of classical bits. For example, you might have a phone with 164 gigabytes of memory, which is 164,000,000,000 bytes!  Even the Frontier supercomputer at Oak Ridge National Laboratory, considered the most advanced operational computing system in the world, still uses classical computing and classical bits (1’s and 0’s). Classical computing has enabled many amazing technological advances during our lifetimes. But now we are entering the age of quantum computing, where quantum mechanics and computing combine to allow even more new capabilities.         

Quantum Computing

In quantum computing, the basic unit of information is referred to as a quantum bit, or qubit. Qubits represent atoms, ions, photons, or electrons and their respective control devices, which work together to act as both computer memory and processor. Unlike their classical computing counterparts, qubits are not limited to only one of two physical states (0 or 1); instead, they can exist as mixtures of states, with any proportion of 0 and 1 in a superposition of both states at the same time. Superposition is the ability of a quantum system to be in multiple states at the same time until it is measured; this is one of the unique properties that sets qubits apart from classical bits and allows them to store and process information more efficiently. Superposition isn’t an in-between state like one-half or two-thirds; rather it is a probability like 50% likely to be 1 or 0, or 30% likely to be 0 and 70% likely to be 1. 

One of the cool things computers are able to do is to perform tasks in parallel, which means that many calculations or processes can be carried out simultaneously. Large problems are broken down into simpler ones, which are solved all at the same time instead of one-by-one. Superposition of qubits enables quantum computers to do parallel processing even faster than classical computers. 

Another unique property of qubits is their ability to undergo quantum entanglement.¹ Entanglement occurs when the state of one particle belonging to a pair or group of particles cannot be described independently of the state of the other particle(s). Qubits, like particles, can become entangled with one another. When two qubits are entangled, there is a special connection between them that correlates measurements made on them. For example, we can consider a particle characteristic called spin: when the spin of one particle is measured to be clockwise, entanglement means the spin of the other is guaranteed to be measured as counterclockwise. The total spin of the set of particles is zero, but entanglement causes the particles to “feel” that a measurement is made and to somehow “know” what the outcome should be. No information is exchanged between the particles, and entanglement persists even at infinite distances between particles! Entanglement ultimately enhances processing time for computers, since qubits automatically “know” information about each other and there is no time required to transfer that information; by measuring the properties of one qubit, we automatically know the information about its entangled partner. This has important applications in superdense coding, quantum cryptography, and even quantum teleportation!  

Overall, the entanglement and superposition properties of qubits give quantum computers the ability to store and process large amounts of data with less time and effort, significantly enhancing computer power to solve complex problems. Without entanglement and superposition, quantum computing wouldn’t be “quantum”! 

Quantum computing is such a powerful tool that the US government has created special research centers devoted to its development and applications. The Co-design Center for Quantum Advantage (C²QA) at Brookhaven National Laboratory (BNL) is one of five National Quantum Information Science Centers established in 2020, supported by the National Quantum Initiative. Scientists in C²QA are studying how to leverage quantum computing to solve scientific problems that would be impossible for classical computers. They are also working on solving challenges such as quantum decoherence, where qubits lose their information due to interactions with the environment or material defects. 

Quantangled Pet

Quantum computing can be hard to explain even to adults (including fellow scientists!) but that didn’t stop Dr. Alexei Tkachenko from working on explaining it in a way that even young kids can understand. As a staff scientist at BNL, he developed an application called Quantangled Pet: Adopt a Pet from Quantum Realm. The app was unveiled during one of BNL’s Summer Sundays, where different departments opened their doors to the community and shared posters and demonstrations to explain some of their science. Dr. Tkachenko’s goal was to create an app-based demonstration on quantum mechanics principles that could be used and understood by anyone. The development of the Quantangled Pet app was a team effort for Dr. Tkachenko and his family, combining his knowledge of quantum science, his son’s experience in building apps, and his wife’s expertise in programming. 

I had the opportunity to speak with Dr. Tkachenko to discuss his app in further detail and see how it works. (I’m a postdoctoral scholar at Brookhaven National Lab and work down the hall from him!) When asked about his motivation for creating the app, Dr. Tkachenko responded, “Quantum mechanics is very cool, and I keep rediscovering it for myself all of the time!” 

When you first open the app, it prompts you to name your qubit Quantum Pet and then you are told about the different things (or states) the pet can be: Cat or Dog and Happy or Sad. Because the Quantum Pet is a qubit, it can be multiple things at once and in a mixture of states!  

Scrolling through the pages using the green arrow, you are met with explanations on entanglement and instructions on “How to use this App?”. When you click the blue magnifying glass icon, you can check what your pet looks like OR measure what state your pet is in: cat or dog, happy or sad, or mixtures of Saddish Doggish and Happyish Cattish and vice versa. 

This is where the idea of superposition comes in: Happyish Cattish is not the same thing as Happy Cat. Happyish Cattish means that the pet is in a state that is mostly Cat and mostly Happy, but there’s also a small probability that the pet is Dog and Sad. Moreover, although you know it’s mostly Happy, you can’t confirm the final state unless you check (observe) it, and checking one property means you can’t know the other! So if you check on your pet’s mood when it is in the Happyish Cattish state, the state is most likely to result in a Happy pet, but we lose track of whether it’s a Cat or a Dog when that mood observation is made. This all may seem very confusing, but using these in-between states is part of what makes quantum computation so powerful.

This phenomenon in which observing one property makes it harder to nail down another one is based on the Uncertainty Principle, which basically says that once we measure one property with certainty, the less certain we can be on the other properties, because the act of measurement can change them. In quantum mechanics, we tend to think of the Uncertainty Principle in terms of knowing the position or momentum of a particle. In other words, we can know either where a particle is or how it’s moving, but not both at the same time. 

As Dr. Tkachenko says, “We introduce the very mysterious phenomenon called quantum entanglement though a game.” You can also play  by “quantangling” your own pet with pets of other app users or with the virtual pets Schroedinger or Einstein. Once two pets are connected, or quantangled, you can choose which state to measure – Happy/Sad or Cat/Dog – by rotating your phone. If the other user checks the same state on their pet by holding their phone in the same way, they are guaranteed to get the same result because they are entangled. 

Here’s where the game play comes in: you are given a challenge to either MAXIMIZE or MINIMIZE the match with the other pet. By manipulating the orientation that you hold your phone, you choose which property to measure; when you tap the Check icon, the state is locked and compared to the other pet, giving a matching percentage and an associated score. For example, if your and your partner’s pets are entangled and you both hold your phones vertically to measure if the pet is Happy or Sad, your results will match 100%. Change the way you hold your phone and then check the state again, and you will either increase or decrease your match depending on how the other user is holding their phone. You can continue to play the entanglement game with this partner or choose a different one, incrementally increasing or decreasing your overall score.   

As someone who struggled with physics during my education, I found this app incredibly helpful to actually show how quantum mechanics works! Quantum mechanics has this air of mysticism surrounding it, so having ways to demonstrate different concepts helps to lift the veil and makes it more approachable. I appreciated that Dr. Tkachenko used the idea of a “pet” as opposed to trying to explain things in terms of particles and their properties. Qubits are the workhorse of quantum computing, and I think this app helps demonstrate the underlying principles that control their properties and applications. Today, it takes time to transfer information throughout a computer system and over the internet; entangled qubits allow for an instantaneous transfer of knowledge, which will drastically improve processing and communication speeds. Quantum computing is still a long way from being present in our everyday lives in the way that classical computing is, but, with continued advances in algorithms and materials discovery, their implementation is on the horizon!   

The Quantangled Pet demonstrates several principles from quantum mechanics for players of all ages: the Uncertainty Principle, Superposition, and Entanglement. The Quantangled Pet application is available for free download on both the iOS App and Google Play stores. 

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REFERENCES

1. Peacock, K.A., The Quantum Revolution: A Historical Perspective. 2007: Bloomsbury Publishing. ISBN: 9780313334481
2. Ladd, T.D., et al., Quantum computers. Nature, 2010. 464 (7285): 45-53. DOI: 10.1038/nature08812