User:Ssabir19/sandbox

Article Evaluation: Greenberger-Horne-Zeilinger State

Content: In the introduction, a GHZ state is introduced as a certain type of entangled quantum state, but they do not define entanglement or the definition of a qubit. This may confuse a reader who is not previously familiar with quantum mechanics. In the second paragraph of the Properties section, I would like if the article went into more depth on how the GHZ states lead to a violation of Bell's Inequality. This displays the inconsistency between classical theory and quantum theory. The section Pairwise Entanglement is extremely clear and well-written: this was the most comprehensive section of the article in my opinion. The applications section should be added to with more specific applications. This section is very vague.

Tone: The tone is neutral throughout. The Applications section is extremely short and vague. This is by far the weakest section of the article. The previous three sections are clear.

Source: The second source does not seem to be a source. It is a sentence restating where it was quoted. The fourth article also does not appear to be a source. It is a sentence describing its own reference. They do not have titles, authors, or URLs. I am a bit confused as to why these are on the references list.

Article Selection

Bell States has decent content, but it is extremely disorganized. The intro is confusing and goes back and forth between history and math. The section on Bell measurement does not make much sense, because its listing recent applications rather than explaining the properties of Bell State Measurement. The sources are reliable. We also added a few sources, of which are listed in the references section of this sandbox.

The Bell States

The Bell states, a concept in quantum information science, are specific quantum states of two qubits that represent the simplest (and maximal) examples of quantum entanglement. The Bell states are a form of entangled and normalized basis vectors. This normalization implies that the overall probability of the particle being in one of the mentioned states is 1: <Φ|Φ> = 1. Entanglement is a basis-independent result of superposition, a principle in which a particle is in multiple states at once. Due to this superposition, measurement of the qubit will collapse it into one of its basis states with a given probability. Because of the entanglement, measurement of one qubit will assign one of two possible values to the other qubit instantly, where the value assigned depends on which Bell state the two qubits are in.

Understanding of the Bell states is essential in analysis of quantum communication (such as superdense coding) and quantum teleportation. The no-communication theorem prevents this behavior from transmitting information faster than the speed of light, because there is a need for A to communicate information to B.

Quantum Teleportation

Quantum teleportation is the transfer of a quantum state over a distance.  It is facilitated by entanglement between A, the giver and B, the receiver of this quantum state.  The process of quantum teleportation is defined as the following:

Alice and Bob share an EPR pair and each took one qubit before they became separated.  Alice must deliver a qubit of information to Bob, but she does not know the state of this qubit and can only send classical information to Bob.  

It is performed step by step as the following:

1. Alice sends her qubits through a CNOT gate.  
2. Alice then sends the first qubit through a Hadamard gate.  
3. Alice measures her qubits, obtaining one of four results, and sends this information to Bob.  
4. Given Alice’s measurements, Bob performs one of four operations on his half of the EPR pair and recovers the original quantum state.  

The following quantum circuit describes teleportation:

Quantum Circuit for Teleporting a qubit

Quantum Cryptography

Quantum cryptography is the use of quantum mechanical properties in order to encode and send information safely. The theory behind this process is the fact that it is impossible to measure a quantum state of a system without disturbing the system. This can be used to detect eavesdropping within a system.

The most common form of quantum cryptography is quantum key distribution. It enables two parties to produce a shared random secret key that can be used to encrypt messages. Its private key can be created between the two parties through a public channel and still remain secure.

Quantum cryptography can be considered a state of entanglement between two multi-dimensional systems, also known as two-qudit entanglement.

Response to Peer Reviews

I have not seen any comments or peer reviews from a classmate. But we made sure to address critiques in the talk page of the article when we first began our edits of the Bell States. Hopefully, these issues have all been addressed. The comments left on the talk page by David Boden were extremely helpful when we began editing.