Density Matrix Doubt: Can Coherance Be Zero?

In summary, a density matrix is a mathematical representation used in quantum mechanics to describe the state of a quantum system and its probabilities of different states. It is related to coherence, which refers to the system's ability to maintain a stable phase relationship between states. Coherence can be zero in a density matrix if the system is in a completely mixed state, and it can be affected by factors such as temperature and external perturbations. Coherence is crucial for the functioning of quantum technologies, allowing for the manipulation and control of quantum states.
  • #1
harish.ravi
1
0
In a density matrix, can some coherances (off diagonal terms) be zero while the diagonal terms(populations) aren't? I am confused because rhoij=Ci*Cj'. How can coherance be zero if Ci and Cj aren't?
 
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  • #2
Yse, coherences can be zero. If you're at equilibrium, they're all zero.
 
  • #3
Your density matrix applies to a "pure state" only. Look up "pure states" and "mixed states".
 

1. What is a density matrix?

A density matrix is a mathematical representation used in quantum mechanics to describe the state of a quantum system. It contains information about the probabilities of different states that the system can be in.

2. How is the density matrix related to coherence?

The density matrix is used to calculate the degree of coherence in a quantum system. Coherence refers to the ability of a quantum system to maintain a stable phase relationship between different states.

3. Can coherence be zero in a density matrix?

Yes, coherence can be zero in a density matrix if the system is in a completely mixed state. This means that the system is equally likely to be in any state and there is no preferred phase relationship between states.

4. What factors can affect coherence in a density matrix?

Coherence in a density matrix can be affected by various factors such as temperature, external perturbations, and the presence of decoherence mechanisms. These factors can disrupt the stable phase relationship between states and decrease coherence.

5. How is the concept of coherence important in quantum technology?

Coherence is crucial for the functioning of many quantum technologies, such as quantum computing and quantum communication. The ability to maintain coherence allows for the manipulation and control of quantum states, which is essential for performing complex quantum operations.

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