Qiskit / qiskit-fermions / 29099350935

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Asorted docs improvements (#172)

* docs: update pyomo installation hint

* docs: specify the exp(-i·t·H) convention on the Evolution gate

The Evolution gate docstring did not state the exact unitary it implements.
Document that it applies exp(-i·t·H), that the operator must be Hermitian for
the result to be unitary, and clarify the meaning of the time parameter. Also
note that the term/group decomposition is a default first-order product formula
that transpilation may further alter.

This commit was assisted by Claude Opus 4.8

* docs: clarify the evolution convention on MapperFnEvolutionSynthesis

State that the plugin maps the fermionic Hamiltonian to qubits and emits a
PauliEvolutionGate, preserving the exp(-i·t·H) convention and evolution time of
the Evolution gate, and note that the mapped operator is simplified first.

This commit was assisted by Claude Opus 4.8

* docs: describe the qDRIFT randomized product formula

Document that QDriftTrotterization approximates each Evolution gate's exp(-i·t·H)
by a randomized product of num_terms sampled single-term evolutions (each with
time delta = λ·t/num_terms), that the approximation is in expectation over the
sampling, and that non-Evolution nodes pass through unchanged. Clarify the
num_terms accuracy/depth tradeoff and the run-to-run stochasticity, and cite the
qDRIFT reference.

This commit was assisted by Claude Opus 4.8

* docs: document the givens_decomposition reconstruction convention

The docstring showed each Givens rotation matrix but never stated how to
reconstruct the original unitary from the returned rotations and diagonal
phases. Applying the displayed matrix naively does not recover U: the rotations
must be processed in reverse order and right-multiplied as their element-wise
complex conjugate. Add a reconstruction formula and a runnable doctest mirroring
tests/python/linalg/test_givens.py.

This commit was assisted by Claude Opus 4.8

* docs: define the single-particle map of the Or... (continued)

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