Add upper bound to summation of the QFT equation in QPE tutorial (#1606)

**Summary:**

The expression for QFT in the QPE tutorial has a summation that could do
with an upper bound and this PR adds that.

---------

Co-authored-by: Josh Izaac <josh146@gmail.com>
Co-authored-by: Daniela Angulo <42325731+daniela-angulo@users.noreply.github.com>
Co-authored-by: Guillermo Alonso-Linaje <65235481+KetpuntoG@users.noreply.github.com>

Author: 4 people

demonstrations_v2/tutorial_qpe/demo.py

@@ -81,7 +81,7 @@
 "When in doubt, take the Fourier transform"; or in our case, "When in doubt, take the quantum Fourier transform (QFT)".
 
 .. math::
-   \text{QFT}|\theta\rangle = \frac{1}{\sqrt{2^n}}\sum_{k=0} e^{2 \pi i\theta k} |k\rangle.
+   \text{QFT}|\theta\rangle = \frac{1}{\sqrt{2^n}}\sum^{2^n-1}_{k=0} e^{2 \pi i\theta k} |k\rangle.
 
 Note that this results in a uniform superposition, where each basis state has an additional phase.
 If we can prepare that state, then applying the *inverse* QFT would give

demonstrations_v2/tutorial_qpe/metadata.json

@@ -11,7 +11,7 @@
     "executable_stable": true,
     "executable_latest": true,
     "dateOfPublication": "2024-01-30T00:00:00+00:00",
-    "dateOfLastModification": "2025-09-22T15:48:14+00:00",
+    "dateOfLastModification": "2025-12-03T15:48:14+00:00",
     "categories": [
         "Algorithms",
         "Quantum Computing"
@@ -59,4 +59,4 @@
         }
     ],
     "discussionForumUrl": "https://discuss.pennylane.ai/t/introduction-to-quantum-phase-estimation-demo/7337"
-}
+}