Fix RZX builder rescaled amplitude (#8031)

* Fix RZX builder rescale amplitude bug

* Update releasenotes/notes/fix-rzx-builder-pulse-amp-ba5c876ddea17c41.yaml

Co-authored-by: Jake Lishman <jake@binhbar.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit/transpiler/passes/calibration/builders.py

@@ -153,7 +153,13 @@ class RZXCalibrationBuilder(CalibrationBuilder):
 
         Raises:
             QiskitError: if the pulses are not GaussianSquare.
+            QiskitError: if rotation angle is not assigned.
         """
+        try:
+            theta = float(theta)
+        except TypeError as ex:
+            raise QiskitError("Target rotation angle is not assigned.") from ex
+
         pulse_ = instruction.pulse
         if isinstance(pulse_, GaussianSquare):
             amp = pulse_.amp
@@ -165,8 +171,8 @@ class RZXCalibrationBuilder(CalibrationBuilder):
             gaussian_area = abs(amp) * sigma * np.sqrt(2 * np.pi) * math.erf(n_sigmas)
             area = gaussian_area + abs(amp) * width
 
-            target_area = abs(float(theta)) / (np.pi / 2.0) * area
-            sign = theta / abs(float(theta))
+            target_area = abs(theta) / (np.pi / 2.0) * area
+            sign = np.sign(theta)
 
             if target_area > gaussian_area:
                 width = (target_area - gaussian_area) / abs(amp)

releasenotes/notes/fix-rzx-builder-pulse-amp-ba5c876ddea17c41.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed a bug in the :class:`.RZXCalibrationBuilder` transpiler pass where
+    the scaled cross-resonance pulse amplitude could appear to be parametrized
+    even after assignment. This could cause the pulse visualization tools to
+    use the parametrized format instead of the expected numeric one.

test/python/pulse/test_calibrationbuilder.py

@@ -122,3 +122,19 @@ class TestRZXCalibrationBuilderNoEcho(TestCalibrationBuilder):
         # Check whether the durations of the RZX pulse and
         # the scaled CR pulse from the CX gate match.
         self.assertEqual(rzx_qc_duration, duration)
+
+    def test_pulse_amp_typecasted(self):
+        """Test if scaled pulse amplitude is complex type."""
+        fake_play = Play(
+            GaussianSquare(duration=800, amp=0.1, sigma=64, risefall_sigma_ratio=2),
+            ControlChannel(0),
+        )
+        fake_theta = circuit.Parameter("theta")
+        assigned_theta = fake_theta.assign(fake_theta, 0.01)
+
+        scaled = RZXCalibrationBuilderNoEcho.rescale_cr_inst(
+            instruction=fake_play, theta=assigned_theta
+        )
+        scaled_pulse = scaled.pulse
+
+        self.assertIsInstance(scaled_pulse.amp, complex)