Hi, I'm in an advanced physics independent study, and I am writing a paper on quantum entanglement. I Have come across a symbol which I can't identify. It looks like this:

|a> or <a| or <a>

"a" is used as a variable by me, not the papers I'v seen it in, they usually use the Greek letter psi.

Could anyone tell me what these mean. I have an Idea, but I am not sure. An example of a paper with them in it would be

*"Calculation of the Quantum Entanglement Measure of Bipartite states, Based on Relative Entropy, Using Genetic Algorithms"*

Thank you if you can Help me.

Yours Truly

NeoScorates