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# Quantum Mechanics

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by

## Issy Wall

on 18 May 2015

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#### Transcript of Quantum Mechanics

Schrodinger's cat
Quantum Mechanics

To Schrodinger put a cat in a box. He also put poison in the same box. Half the time, when the box is opened the poison is set off and it kills the cat and the other half of time the box is opened and the poison isn't set off(the cat doesn't get killed). Whilst the cat is in the box you are not able to tell whether the cat is alive or dead, so the cat is in a weird state where it is both alive and dead at the same time, this is called
superposition
. It is only when you open the box that you know whether the cat is alive or dead.
Quantum
Schrodinger's Cat
If there were two boxes with cats in each of them there are four possible outcomes in Classical Mechanics but in Quantum Mechanics they are
entangled
, therefore, there are only two possible outcomes:

Classical Mechanics: Quantum Mechanics:
[Box1] [Box2] [Box1] [Box2]
0 0 0 1
0 1 1 0
1 1
1 0
The meaning of Quanta comes from the Latin word "Quantus" meaning "how many".
Einstein
and
Planck
named sub-atomic particles Quanta and Quantum is what they called the plural of Quanta.
Quantum mechanics is what very small things at sub-atomic level behave according to.
Two sub-atomic particles created together are entangled
e.g when you point a laser beam(photons) at something the photons get absorbed by electrons and then eventually the electron emits the photon and returns to its original state.
BUT
when you point a laser beam at a special crystal occasionally a photon will split into two photons. The split photons are like two halves of a photon because together the two split protons have the properties of one whole photon.
THE SPLIT PHOTONS ARE ENTANGLED!!!
So, take the example of the photons, if you send one of the entangled photons to the other side of the universe and do something to one of the entangled photons(and observe it), the other will respond instantly and it will do the exact opposite of what the other photon did e.g if one photon was made to spin clockwise the other photon will instantly spin anti-clockwise.
This defies the laws of physics, space and time!
Quantum Entanglement
Gallery of cats:
What is a Qubit?
How is a Qubit different to a bit?
A bit is the smallest unit of data in a computer which can either be 1 or 0 (on or off). Whereas, a qubit can be both 1 and 0 and in a
superposition
state (all of the numbers between 1 and 0 at the same time), like Schrodinger's cat in the superposition state(dead and alive at the same time). The fact that a qubit is able to be in this superposition state allows a quantum computer to work on many computations at once; a computer using bytes can only work on one computation at a time. This means that quantum computers work at an extremely fast pace. Qubits can use
superdense coding
which makes them able to work fast and store lots of data.
A qubit is another word for a quantum bit. It can be 1 or 0 or in state of superposition. It is the basic unit of data in a quantum computer. This unit of data is called a qubit because of its similarity to a cubit(an ancient measurement of length).
superdense coding
= a technique that is used to send two bits of data using one qubit. This requires quantum entanglement. (the opposite of quantum teleportation.)
D-wave
D-wave was made in Canada by the company D-wave Systems. The D-wave computer is a quantum computer that has 128 qubits. Whereas, D-wave two has 512 qubits so it is able to work even faster. This means that D-wave can pick out the best possible outcome, out of many, in a very short amount of time. Quantum computers like D-wave use quantum superposition, quantum entanglement, quantum tunneling to enable them to manipulate all the combitations of bits simultaniously.
Quantum computers are much faster that the traditional computers because they are able to compare all possible solutions at once, whereas a traditional computer does them one at a time.
Traditional computer calculations are done essentially by hand, therefore are easy to understand. But quantum computers use something called unitary transformation and they also use superposition. This creates possibilities that we are not able to do using hand calcultions - in other words they are super intelligent!
What is Encryption?

Encryption is the direct application of cryptography.
Data is encrypted by using an encryption key and a encryption algorithm. Data is often called plaintext and after the process of encryption the encrypted data is called cipher text. To decrypt a message the computer that is recieving the message needs to have the correct encryption key. Encryption uses very advanced mathematics. We have two types of encryption algorithms: symmetric and asymmetric.

Encryption has been around for a long time. For example in Ancient Greece, someone sent a solider to pass on a secret message. He did this by shaving the soldier's hair off and writing a message on his head. They waited until the soldier's hair grew back. This helped because if the soldier was captured they wouldn't be able to find the message. When he delievered the message, he just shaved off his hair to reveal the message.

Now, we use encryption in lots of ways, such as passwords or when we go onto a website we have https://. The 's' shows that it is safe and it stands for secure socket layer. Sometimes instead of having the 's' websites have a lock sign before the address.

What is photonic computing?
What is Cryptography?
What is quantum cryptography?

Cryptography is the science of encrypting data. Cryptography uses ciphers. This allows people to scramble and descramble messages so that, if someone intercepted the message, it would appear meaningless. Cryptography is uses by banks and governments to ensure that documents remain confidential.
Quantum cryptography can also be refered to as Quantum key distribrution. Quantum cryptography uses quantum mechanics. Quantum cryptography relies more on physics to develop cryptosystems, rather than mathematics. It enables two particles to produce the same random key that only they both know. Quantum cryptography provides long-term secrecy whereas classical cryptography only provides secrecy for a limited period of time.
Photonic computers, also called optical computers, use photons of infrared beams or visible light beams to perform digital computations. The aim of photonic computers is to make a computer that relies entirely on photons instead of electrons. A downside to photonic computing is that it takes more energy to send a signal with photons than it does when you use electrons. In theory, photonic computing could produce computers of an extremely high speed; much faster than today's computers.
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