Today, one of my close friends Jason was on a rant about "Are we living in a simulation" and "Quantum Superposition". So I was in the mood to write an essay. This was because Jason also wrote an essay and I had a school project called the ICE (In Class Essay) which I could not attend. This essay gives a thorough and concise definition of what quantum superposition is. Quantum superposition is a fundemental principle of quatum mechanics. A common misconception is that quantum superposition and quantum entanglement are the same thing. They are not the same thing, as one is 2 separate things, and one is about 2 things that are 1.
In classical physics, momentum, inertia, and position are well-defined. While in Quantum physics, those definitions get a little "indirect". Qunatum superposition in simple terms can be explained as a physical object existing in more than 1 position at once. It can be "not-excited"(negative) and "excited"(positive) at a given moment of time, quantum physicists say. Quantum superposition is very similar to that of the supercritical state in thermodynamics. The supercritical state is the state in which most substances (all pure substances inclusive) go above their critical state which is a state where vapourization stops happening. When a substance is supercritical it is in both its gaseous, and liquid state. Some could also say that when a substance is supercritical the differences between the liquid and gas phases disappear. Below is a graph showing the P-T Diagram. (P - Pressure, T - Temperature)
Quantum superposition can apply to any quantum particle. Such as protons, electrons, molecules, spin, magnetism, and much more. An atom with quantum superposition can be in both a positive and negative energy level as I mentioned above. A great analogy for this is square roots. A negative atom is -6 and a positive atom +6. The square root of 36 can either be -6 or +6, but we don't know, when someone tries to figure out the value, it can only be either -6 or +6. Just like the square root of 36, an atom with quantum superposition can be +-6, but when trying to measure the energy level, it can only be one of the energy levels is randomly observed.
"How does one observe a physical object in quantum superposition? some may be asking. To observe an object in a quantum superposition, you need to beam an electromagnetic wave at it. With the right frequency, you can see the object alternate in its positive and negative state. If the state of the atom is averaged being measured and graphed many times, "Rabbi oscillations" appear (looks like sin/cos waves). In real life, quantum objects are never alone, so they are constantly being hit by other non-quantum objects all the time. This causes a change in the electromagnetic wave response, thus why we need to take an average. During when the quantum object is hit by other non-quantum objects, the superposition slowly fades away. At the start, an object can be in multiple positions/states at the same time, but at the end, it will slowly fade away into a randomly chosen definite one. The time that is taken for quantum superposition to fade away is called the decoherence time. Below is a graph of the electromagnetic wave for light. The amplitude and frequency will be different for each object in quantum superposition. We can expect similar waves of that which correspond to an object in quantum superposition, just that, at the end, there will be a slow decay.
Quantum superposition in quantum computing is described by bits and qubits. A bit is either a 1 or a 0 and is the smallest piece of information. Bits are transistors, which can either block or open the way for information to pass, and multiple bits together are what we call binary code. A qubit is a bit in quantum superposition, it is both 1 and 0. A qubit can be any proportion of 1s and 0s, such as 1/3rd 1 and 2/3rds 0. The instant you measure a qubit it collapses into one of the definite values such as 0 or 1. Think of it like this, 4 bits can have 16 possible combinations, and 4 qubits can be in all of those configurations/combinations at once, thanks to superposition. 20 yes, only 20 qubits are needed to have over 1,000,000 values at once. Now's a good time to explain what quantum entanglement is. Quantum entanglement is when an object is in sync with another no matter how far away it is. Imagine this: A star dies on the other side of the universe, instantaneously in sync, your dog dies, or vice versa. Using quantum entanglement a qubit can turn on or off and possibly 4 other qubits turn on or off at the same time instantaneously. This means that you only have to measure one qubit to change another qubit's value to that of a definite one. This can all be done in sync with no delay.
Inside computers exists multiple circuit chips, which contain multiple basic modules, which contain multiple logic gates, which contain multiple transistors. Due to this reason, the smaller the transistor, the less space it takes. The less space a transistor takes, the more you can fit in a small space. The more transistors you fit in a small space, the more power it gives you (considering that you don't want to have 0.1cm^3 transistors and carry 5,000 pounds just to store 5 MB). A normal logic gate, gets a set amount of inputs and produces 1 output. A quantum gate takes an unknown number of qubits (in superposition), scrambles and processes it, and gives another qubit as its output.
What I just explained in the past 2 paragraphs means that you can complete A LOT of calculations at the same time. But you can only measure one result, and it may be the one you want, so you may have to try again. But by cleverly manipulating these superpositions and entanglements, it will be exponentially more efficient than normal computations. Let's say that you are searching for something specific in a database (I assume you know what those are), a normal computer may check all the results/inputs to finally give your desired output. A quantum computer instantly checks all the results at once and then gives your desired output.
Another use of quantum computing is hacking đź« . Let's say your trying to hack someone's email, you would first need an email from them. Using the email you got from them, you'll have their public key. A public key is what allows only you to read the email, instead of everyone else. The sender, let's say it is Jason, uses a private key to send his emails (Only he has access to the private key). This is so that Jason only sends it to the desired person who wants to read it. When he is sending an email, he will use his private key (which is used to encrypt) to send the email. Along with the email, will be sent the public key (which is used to decrypt), which will be combined together to create a key that will allow you to read the email. Let's say a hacker tried to hack into Jason's email so he can read an email, he can't because it is encrypted and he will only see a bunch of gibberish along with the public key, what he doesn't have is the private key. What many people don't know is that you can use the public key to decipher the private key. The deciphering process would take hundreds/millions of years on the latest most powerful PC (that is not quantum). Using a quantum computer, you can calculate the private key, and it will be a breeze. Wow, I didn't think I would be explaining what end-to-end encryption was in this essay.
So yeah, that's what quantum entanglement, superposition, and computing is for a dummy.
Why is this useful? For hacking, sience, and many of things.
Contributors to Wikimedia projects. “Quantum Superposition.” Wikipedia, 29 June 2023, https://en.wikipedia.org/wiki/Quantum_superposition.
Kurzgesagt - In a Nutshell. “Quantum Computers Explained – Limits of Human Technology.” YouTube, 8 Dec. 2015, https://www.youtube.com/watch?v=JhHMJCUmq28.
Medielab HVL. “Thermodynamics - Explaining the Critical Point.” YouTube, 14 Jan. 2016, https://www.youtube.com/watch?v=RmaJVxafesU.