Today, normal computers store information using binary digits or bits, which is simply one digit in the binary number system. Most people are familiar with the decimal number system, the system most commonly used in everyday life. This is base ten, meaning each digit can be any number from 1 through 9. Binary is base two, so each digit can be a one or a zero. This means that every digit represents a power of 2. For example, 1011 in binary would be (1⋅2³) + (0⋅2²) + (1⋅2¹) + (1⋅2⁰) or 11 in decimal. Computers use the binary system because the fundamental building block of a computer is a transistor. Transistors are binary switches, which can take an on or off input, like a light switch. "On" means that the transistor is allowing energy to pass through it, while "off" means it blocks the energy. If a zero signal is applied to a transistor, the energy is blocked. If a one signal is applied to a transistor, the energy can pass through. This is used to create logic switches, like the switch that requires two conditions to be true (1=true and 0=false) before the entire output is true. Sets of these switches give addition and subtraction, which lead to multiplication and division, allowing you to do tons of different things.

Over time, transistors have been getting smaller and smaller, because smaller transistors are faster and take up less energy. Now, the typical transistor is around 14 nanometers long, only 14 times as wide as a DNA molecule. If the transistors get small enough, quantum tunneling comes into effect. Basically, this means that electrons, the energy for circuits, will pass through a barrier that it wouldn’t classically be able to pass through, like a transistor in its "off" position. This happens because in the world of quantum mechanics, electrons act like waves, not abruptly stopping at a barrier, but rather tapering off quickly. With enough energy, these electrons can pass through a barrier, because it is too thin to get them to completely stop. This is a huge problem in computers because circuits rely on an on and off position to work. If we make transistors too small, then the electrons can tunnel through, rendering the circuits useless.

The solution to this is quantum computing, possibly the smallest we can ever make these electronics. In addition to being smaller, quantum computers are also much quicker, because they utilize quantum bits or qubits, instead of bits. Different objects can be used as a qubit such as a photon or an electron. All electrons have small magnetic fields, meaning that they will align with the magnetic field that they are placed in. When an electron is aligned, it is in the lowest energy position, also called spin down. With energy, you can put it in spin up, which is the highest energy position. The difference between this and regular bits is that qubits can be in a quantum superposition, which is a combination between one and zero (one being spin up and zero being spin down). When measured, the qubit will be either one or zero and cannot be in a superposition. The chance that the qubit will be one or zero depends on the spin of the object. The closer a particle's spin is to spin up or spin down, the greater the chance it will be that when measured. For example, if a particle’s spin was perpendicular to the magnetic field, it would be a 50% chance the particle would be measured as one or zero.

A qubit can actually store more information than a regular bit. Imagine two different qubits interacting with each other. While two regular bits could give you the binary numbers 11, 10, 01, and 00, a pair of qubits can be all of those at the same time. This means that they can run more complicated algorithms much faster because qubits can try every single possibility of something at one time, while a normal computer would have to try everything one by one. While this is great because it means computers can make advanced models and simulation quickly, it also brings a large problem to encryption, the process of scrambling data to prevent unauthorized access.

With regular computers, our current method of encryption works well, but quantum computers might pose a threat. Our system today works by a server that you send your information to, making a private and public key. The public key is used to only scramble the information and cannot be used to figure out the information. The server can send you the public key because it doesn’t matter if someone who is trying to steal your data gets it. Your computer uses the key to scramble your message and you send the scrambled message back to the server. A data stealer can steal both the public key and the scrambled message, but they won’t be able to get the real message without the key to unscramble the message. This is why the server never sends the private key anywhere, so no one but the server can decrypt your data. One private key will only be able to unscramble messages scrambled by the public key that correlates to it. In other words, one key can only scramble, and the other can only scramble information scrambled by the first one.

In order for the server to be able to send you private information, you have to generate your own key. You then encrypt the key using the servers’ public key, so the only the server can unscramble it with its private key. Your key can be used to both scramble and unscramble messages, but eavesdroppers cannot get the key because it was scrambled when you sent it to the server. It is possible for an eavesdropper computer to try tons of different private keys until it matches the public key, but the keys are specially designed for this to take forever. No computer today can try enough possibilities quickly enough to guess the key in a reasonable amount of time. The problem is that quantum computers can try out many different possibilities at once because of superpositioning. This means that they can use algorithms to try out tons of different possibilities at one time in order to guess the key in less time than a normal computer.

Our best solution to this is quantum cryptography, using quantum computers themselves. You can measure qubits in any orientation you want to, meaning you could make the spin up and spin down the top and bottom, the left and right side, or anything in between. You cannot measure a qubit based on its orientation, because you won’t know it's orientation. If you tried to measure the orientation of the qubit then you might end up changing it.

One protocol for quantum encryption is called BB84. To encrypt a code using quantum computers, the server first generates a random string of ones and zeros which will be used as a key. Then, the server encodes the bits into qubits by randomly choosing a vertical or horizontal orientation to measure the qubits by. The server then sends you the qubits, but you don’t know they were measured, so you randomly guess. You and the server then compare your results and throw out the bits you guessed wrong, giving both you and the server a key. If an eavesdropper intercepted the qubits that the server sent to you, they couldn’t guess the orientation and then send a copy to you because the qubits would change before you got them. The eavesdropper couldn’t send a copy of the original qubits to you because the no-cloning theorem states that you can't make copies of qubits if you don’t already know what they are. To make sure an eavesdropper didn’t change your qubits, you send half of your qubits to the server and you compare. The eavesdropper won’t be able to know the other half of the qubits so they can’t do anything with that information. Chances are, if half of the qubits are correct, the whole thing probably is too. To increase your chance of the eavesdropper's mistakes being caught when you send them to the server, more qubits are used. If any mistake is caught the qubits are thrown out and the process is restarted. If there are mistakes in the qubits a second time you switch communication channels.

There are still problems with protocols like these, such as the eavesdropper changing the information every time. They will be detected, but it will cut off safe communication between you and the server. Also, the current infrastructure of the internet cannot even send qubits, although there are some small quantum networks being built. Lastly, people with quantum computers will be able to successfully eavesdrop on anyone with a regular computer, meaning that if you can’t afford or just don’t have a quantum computer, you will be very prone to getting your information stolen.