# Quantum Computing 101

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I remember my obsession with maze puzzles as a kid. They were the most incredible thing ever. Trying to figure out how to get to point A to point B with no obstacles along with way.

Back then, my strategy was to go through every single route I saw and whenever I’d reach a dead-end, I’d just try an alternative path. That explains why certain mazes took me hours to complete.

Think of a maze like a more high-level problem (such as our supply chain system) — except we don’t have to use my *time-consuming *strategy when we’ve got our **quantum computers**.

Q

uantum computing isa way to solve problems that are too large or too complex for our conventional computers using the law of quantum mechanics— which is the physics of extremely small matter.

In 1965, Gordon Moore suggested that roughly every 2 years, the number of transistors (the little device that controls the flow of electric signals) on microchips will double. This is why our devices keep getting smaller and smaller — *think about how we went from a computer that occupied the entire room to one that fits in our pockets.*

But** the second we hit the atomic level, things change… **we can’t use the physics we usually do but instead have to work with *quantum* physics.

*Note:** This article is written with the intention of being a very simple and basic walk-through of the emerging technology, Quantum Computing. It’s meant to expose readers to the fundamentals of QC plus its applications & value, and is not meant to be technical. If you’re looking for a more specific algorithm walk-through, I’ve written a couple more articles you can check out on my Medium profile **here** — but if you’re simply here to learn something new, read along and I hope you enjoy! :)*

# Bits vs. Qubits

In order to process information to the simplest level, classical computers use something called *bits.* **Bits are a binary system where everything gets translated to either a state of 0 or 1.** It’s the unit of information that classical computers use to send and receive information, store data and do calculations. Basically, to do all the functions your devices perform at the moment. **It’s because of this certainty that classical computers can only perform one operation at a time.**

Think about a typical on/off light switch that’s most likely on your wall. You can either turn it on *or* off. That’s exactly how bits work* — a value either exists in the state of 0 or 1.* But what if I told you to keep it in the middle of on and off? What would you classify it as —* is the light on or off?*

*Qubits* work in the same way. **Qubits **— or also known as *quantum bits — *are similar to bits as they have the ability to process information but instead of definitive states, **they can exist in-between 0 and 1.** This is called *superposition**…*

# Superposition

**Superposition is what differs a bit from a qubit — ***and a classical computer vs. a quantum computer. *This aspect of quantum mechanics allows qubits to be in-between two states, so **qubits can be in a state somewhere between 0 and 1.** Since the nature of qubits isn’t definitive, you can perform *multiple* functions at a time — *this is why quantum computers are much faster in performing certain tasks.*

# Representation of Qubits

One way that we express the state of qubits is through a geometrical-representation called a **bloch sphere. ***It looks like this…*

In quantum computing, we use linear algebra to calculate and manipulate the states, so vectors are commonly used to describe the state of a qubit — but, the main takeaway from the image above is that |Ψ**⟩** basically represents the state of the qubit.

# Measurement

Superposition doesn’t exist forever though. It’s important to note that the second you **measure** a qubit, superposition disappears since that’s when the quantum system will collapse and the qubit will *pick* a state to be in.

**It will choose based on the probabilities of its superposition.** *Not to get too mathematical but the equation looks like this…*

Each qubit has something called an *amplitude *which refers to the probability of it falling into each computational basis state — which are what ‘alpha’ (α) and ‘beta’ (β) stand for in the equation.

We have the ability to manipulate the probability of a qubit collapsing into a particular state through **quantum logic gates**. There are many different kinds of gates, each with a unique function, but for now it’s important to know that gates are a way to control the qubits for a desired result.

# Entanglement

If I told you that two particles are connected, even if they were light years apart, you would probably be quick to call that a lie. Well, I don’t blame you — after all, even Albert Einstein initially rejected this idea by calling it a *“spooky-action-at-a-distance.”*

**Quantum entanglement is when two qubits link together in a certain way, in which no matter how far apart they are, information about one qubit will tell you something about the other qubit.**

My favourite way to explain this is through a story by Dr. Brian Greene at Columbia University:

Pretend that you and a friend bought a pair of gloves. You place one glove inside one box and the other glove inside another box. You take one box and travel to one side of the universe. Your friend takes the other box and travels to the other side. You open your box, and find the left glove. You know immediately that your friend is going to open the box and find the right glove. You don’t need to call your friend on the telephone. Nor do you need to see inside the second box to confirm this fact. The gloves are, in a sense, entangled. One glove can tell you all you need to know about the other.

The phenomena of quantum entanglement can allow us to cut down on both the necessary time and computing power to process the transfer of information between qubits.

# Applications of Quantum Computers

Over the last few years, quantum computing has emerged to be considered as an innovative technology. Today it’s reached a stage where it can potentially solve a significant number of problems, in a way that classical computers cannot.

*Some of the areas of problems that quantum computers can solve include:*

**Optimization Problems**— when you’re looking for an optimal solution, you typically need an analysis of every single potential option… quantum computers (more specifically, quantum annealers) can speed up this process exponentially.**Finance**— quantum machine learning can handle these large amounts of data in the finance industry for real-time data insights and predictions.**Cybersecurity**— in order to secure data in a way that cannot be encrypted, quantum cryptography employs aspects of quantum physics.**Drug Discovery**— by utilizing quantum computers, we can gain better insights about shared characteristics between molecules and expedite the process of drug discovery.**Data Analysis**— quantum computing allows high-speed detection, analysis, integration, and diagnosis capabilities when working with huge, scattered data sets.

# Current State of Quantum Computing

There’s a reason why companies all over the world invest millions of dollars into quantum computing research but its’ potential cannot be blindsided by the limitations currently present.

Quantum computers are still in a stage where they’re unstable and not reliable. They’re prone to errors — due to the nature of quantum physics — so the computers don’t always produce the most accurate results.

## Decoherence

One of the greatest problems in quantum computing is defined as **decoherence ***— exactly where these mysterious errors come from.*

Since qubits are extremely tiny, they’re also sensitive to compute on. This is because the external environment of the qubits can often interfere and mess-up the existing quantum states… which causes information stored by the quantum computer to be lost.

*Some environmental factors that may cause or contribute to decoherence are:*

- Changing Magnetic and Electric Fields
- Radiation from Warm Objects Nearby
- Interference between Qubits

# Key Takeaways

- Quantum computers take advantage of
*quantum physics* **Superposition**is what differs a qubit from a bit, as a qubit can exist in a state that is in-between 0 and 1 — rather than always being a definitive state. It disappears when**measuring**a qubit and the qubit will then choose one particular state to be in, which is based off its’ probability.**Quantum entanglement**is the idea that, when two qubits are linked, information about one will reveal information about the other, regardless of the distance between them.**Decoherence**refers to external factors in a qubits’ environment which can negatively impact the existing quantum systems.

*Hey, I’m Priyal, a 16-year-old driven to impact the world using emerging technologies. If you enjoyed my article or learned something new, feel free to subscribe to my **monthly newsletter** to keep up with my progress in quantum computing exploration and an insight into everything I’ve been up to. You can also connect with me on **LinkedIn** and follow my **Medium** for more content! Thank you so much for reading.*