What is the meaning of coherent states of mean photon number

In summary, coherent states are a type of quantum state that describes the behavior of light in a quantum system and are characterized by a specific mean photon number. The mean photon number can be measured using various techniques and coherent states are important in quantum optics due to their simple and intuitive description of light, as well as their applications in quantum information processing. These states can only have integer mean photon numbers and differ from other types of quantum states by having well-defined classical-like properties and forming a complete basis for describing quantum states of light.
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Nur Ziadah
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I am studying Quantum Cryptography and I am quite new in Quantum area. I have read an article and I found this confusing statement:
upload_2018-5-17_17-19-48.png

My questions:
1. The three stage protocol implementing multiphoton. What is the meaning of coherent states of mean photon number?
2. How to describe the quantum state by density matrix?

Hopefully that anyone can help me to clarify on this matter, in layman's term. ;)
Thank you.
 

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What are coherent states and how are they related to mean photon number?

Coherent states are a type of quantum state that describes the behavior of light in a quantum system. They are characterized by a specific mean photon number, which is the average number of photons present in the state.

How do we measure the mean photon number in a coherent state?

The mean photon number can be measured using various techniques, such as photon counting, homodyne detection, or direct intensity measurements. Each of these methods has its own advantages and limitations, and the choice of measurement technique depends on the specific experimental setup.

What is the significance of coherent states in quantum optics?

Coherent states are important in quantum optics because they provide a simple and intuitive description of the behavior of light in a quantum system. They also serve as a starting point for more complex quantum states and have numerous applications in quantum information processing, quantum communication, and quantum sensing.

Can coherent states have a non-integer mean photon number?

No, coherent states can only have integer mean photon numbers. This is because they are eigenstates of the annihilation operator, which can only remove one photon at a time, resulting in a discrete number of photons in the state.

How do coherent states differ from other types of quantum states?

Unlike other types of quantum states, such as Fock states or squeezed states, coherent states have a well-defined mean photon number and exhibit classical-like properties, such as a well-defined phase and amplitude. They are also non-orthogonal and form a complete basis for the description of quantum states of light.

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