Add docstrings to basic gates like CZPowGate, Rx, Ry [Unitary hack] (#1651)

Fixes #1148

This PR adds detailed docstrings to the `Rx` and `Ry` bloqs in
`qualtran.bloqs.basic_gates.rotation`.

The docstrings now explicitly list the registers these gates operate on,
improving clarity for users, as requested in issue #1148.

Specifically, the `Registers:` section has been added to:
- `Rx`
- `Ry`

This follows the existing convention for other gates like `CZPowGate`
and `CHadamard`.

Author: ahkatlio

qualtran/bloqs/basic_gates/rotation.py

@@ -554,6 +554,41 @@ def _crz() -> CRz:
 
 @frozen
 class Rx(CirqGateAsBloqBase):
+    r"""Rotates a qubit about the X-axis of the Bloch sphere.
+
+    The unitary matrix for this gate is:
+    $$
+    R_x(\theta) = \exp(-i \frac{\theta}{2} X) =
+    \begin{pmatrix}
+        \cos{\frac{\theta}{2}} & -i\sin{\frac{\theta}{2}} \\
+        -i\sin{\frac{\theta}{2}} & \cos{\frac{\theta}{2}}
+    \end{pmatrix}
+    $$
+    where $\theta$ is the `angle` of rotation.
+
+    This gate is equivalent to `cirq.rx(angle)`.
+    It differs from `XPowGate` by a global phase. Specifically,
+    `Rx(angle)` is `XPowGate(exponent=angle/np.pi, global_shift=-0.5)`.
+
+    Args:
+        angle: The angle of rotation in radians. This can be a symbolic expression
+            or a float.
+        eps: The precision of the rotation. This parameter is primarily for
+            bookkeeping and does not directly affect the tensor representation
+            of this gate. It becomes relevant when synthesizing rotations
+            from a discrete gate set, where a target precision `eps` is required.
+
+    Registers:
+        q: A single QBit register representing the qubit to be rotated.
+
+    References:
+        [Elementary gates for quantum computation](https://arxiv.org/abs/quant-ph/9503016).
+        Barenco et al. 1995. Section 4.2 discusses single-qubit rotations.
+
+        [Quantum Computation and Quantum Information](https://www.cambridge.org/highereducation/books/quantum-computation-and-quantum-information/01E10196D0A682A6AEFFEA52D53BE9AE).
+        Nielsen and Chuang. 2010. Chapter 4.2, pp. 174-177.
+    """
+
     angle: Union[sympy.Expr, float]
     eps: SymbolicFloat = 1e-11
 
@@ -583,6 +618,41 @@ def __str__(self):
 
 @frozen
 class Ry(CirqGateAsBloqBase):
+    r"""Rotates a qubit about the Y-axis of the Bloch sphere.
+
+    The unitary matrix for this gate is:
+    $$
+    R_y(\theta) = \exp(-i \frac{\theta}{2} Y) =
+    \begin{pmatrix}
+        \cos{\frac{\theta}{2}} & -\sin{\frac{\theta}{2}} \\
+        \sin{\frac{\theta}{2}} & \cos{\frac{\theta}{2}}
+    \end{pmatrix}
+    $$
+    where $\theta$ is the `angle` of rotation.
+
+    This gate is equivalent to `cirq.ry(angle)`.
+    It differs from `YPowGate` by a global phase. Specifically,
+    `Ry(angle)` is `YPowGate(exponent=angle/np.pi, global_shift=-0.5)`.
+
+    Args:
+        angle: The angle of rotation in radians. This can be a symbolic expression
+            or a float.
+        eps: The precision of the rotation. This parameter is primarily for
+            bookkeeping and does not directly affect the tensor representation
+            of this gate. It becomes relevant when synthesizing rotations
+            from a discrete gate set, where a target precision `eps` is required.
+
+    Registers:
+        q: A single QBit register representing the qubit to be rotated.
+
+    References:
+        [Elementary gates for quantum computation](https://arxiv.org/abs/quant-ph/9503016).
+        Barenco et al. 1995. Section 4.2 discusses single-qubit rotations.
+
+        [Quantum Computation and Quantum Information](https://www.cambridge.org/highereducation/books/quantum-computation-and-quantum-information/01E10196D0A682A6AEFFEA52D53BE9AE).
+        Nielsen and Chuang. 2010. Chapter 4.2, pp. 174-177.
+    """
+
     angle: Union[sympy.Expr, float]
     eps: SymbolicFloat = 1e-11