Merge pull request #150 from dstrain115/physics_terms

Create physics_terms.md

docs/unitary/physics_terms.md

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+# Unitary for Physicists
+
+If you are already familiar with quantum computing terms, have used cirq, or come from a physics background,
+the terms in the Unitary may feel a bit unfamiliar.  They are meant to connect quantum concepts to traditional
+programming contructs, such as "if/then".  
+
+The following is a table that connects physics terms to cirq and unitary terms.
+
+| Physics    | Cirq |  Unitary |
+| -------- | ------- | ----- |
+| Qubit | cirq.Qid | alpha.QuantumObject |
+| Qutrit | cirq.Qid | alpha.QuantumObject (using an enum with three values) |
+| Quantum circuit | cirq.Circuit | alpha.QuantumWorld |
+| Generic Unitary | cirq.Gate  | alpha.QuantumEffect |
+| Gate applied to specified qubits | cirq.Operation | alpha.QuantumEffect(qubits) |
+| X gate | cirq.X | alpha.Flip() |
+| $\sqrt{X}$ or square root of NOT | cirq.X ** 0.5 | alpha.Flip(effect_fraction=0.5) |
+| Z gate | cirq.Z | alpha.Phase() |
+| Hadamard | cirq.H | alpha.Superposition() |
+| Controlled-gate | gate.controlled_by() | alpha.quantum_if() |
+| CNOT | cirq.CNOT(a,b) | alpha.quantum_if(a).then_apply(alpha.Flip())(b) |
+| CZ | cirq.CZ(a,b) | alpha.quantum_if(a).then_apply(alpha.Phase())(b) |