Week 10 - my notes

Week 10 - Quantum Key Distribuition: Part 1

In X basis, we can only get \(|+\rangle\) or \(|-\rangle\) as a result
- \(|1\rangle\) state measured in the X basis will be either \(|+\rangle\) or \(|-rangle\), half the time one of these states when measured.
In Z basis, we can only get \(|0\rangle\) or \(|1\rangle\) as a result
- \(|+\rangle\) state measured in the Z basis will be either \(|1\rangle\) or \(|0\rangle\), half the time one of these states when measured.

Algorithm: A specific set os steps for solving a computational problem
Protocol: Set of rules that allow electronic devices to communicate with each other.
- Quantum Protocol: Set of rules that uses properties of quantum physics to allow electronic devices to communicate with each other.

Criptography is a sub-field of cybersecurity
- Using protocols a criptography professional can secure someone’s cellphone.

Encryption: enconding/scramble a message so that it can only be read by desired parties.
Descryption: the process of converting the encrypted message back into a readable form.
The key: the peice of information you need to encrypt and decrypt a message.
- Quantum Key Distrubution is just a smart way of distrubiting a key!

A protocol that uses quantum properties to help us securely share a key.
Using QKD we can figure out if there is someone eavesdroping, therefore making the actual key only shared between the sender and the receiver.
- Quantum Measurement is the way to make this happen.
- Someone eavesdroping will change the key!
The key itself is a series of classical bits, the way we share it tho, we use qubits.

The purpose of QKD is to test if your quantum communication channel is truly secure
In QKD, we use four quantum states \(|0\rangle\), \(|1\rangle\), \(|+\rangle\), \(|-\rangle\) to create a predetermined code
Before running the protocol, we need to decide on the two measurement basis, which one to use
Then we assign a value of each classical bit in a qubit state in each basis that will be used.
Classical bit 0: In Z basis it is a \(|0\rangle\). In X basis it is a \(|+\rangle\)
Classical bit 1: In Z basis it is a \(|1\rangle\). In X basis it is a \(|-\rangle\)
- You can use any other order for this!

Sender randomly picks some classical bits
Sender randomly chooses a basis (Z or X) to each bit.
Sender encondes each classical bit in a qubit using the rules the party agreed on.
Sender sends the qubits using a quantum channel

Receiver ramdonly picks bases
Receiver measures the qubits with his/her chosen bases to get new quantum states
Receiver decodes the states of his measured qubits into bits

Sender and receiver compare bases using the classical channel and eliminate the ones that their bases didn’t match up.
Sender and receiver compare bits over the classical channel