Functions for generating quantum operators

[ytdHuang]

close #147

Summarize of this PR:

• introduce displace (and call it within coherent)
• introduce num
• introduce position
  • the function is not exported because it causes conflict with Base.position
• introduce momentum
  • the function is not exported because I think usually position and momentum are pairs.
• introduce phase
• introduce squeeze
• introduce tunneling
• introduce qft

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.31%. Comparing base (c5da8e2) to head (e552fad).

❗ Current head e552fad differs from pull request most recent head 371e3cb

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #169      +/-   ##
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+ Coverage   93.22%   93.31%   +0.09%     
==========================================
  Files          28       28              
  Lines        2051     2080      +29     
==========================================
+ Hits         1912     1941      +29     
  Misses        139      139              

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[albertomercurio]

Mmmm… Yes, It seems the only option for position. Another option would be to not exporting it. I don’t know which one is better.

[ytdHuang]

Mmmm… Yes, It seems the only option for position. Another option would be to not exporting it. I don’t know which one is better.

I also think of the same thing in the beginning. But it would be a bit weird if momentum is exported and position is not.

or maybe we still call them position and momentum, but not exporting them ?

Actually, I seldom use these in QuTiP, I will just generate them with annihilation operator by myself.

As #815485e, I renamed them to position and momentum, also unexport them.