Reverse factor 1/2 in transmon_interaction (#4478)

doc/releases/changelog-dev.md

@@ -182,9 +182,10 @@ array([False, False])
 * Updated `expand_fn()` for `DefaultQubit2` to decompose `StatePrep` operations present in the middle of a circuit.
  [(#4444)](https://github.com/PennyLaneAI/pennylane/pull/4444)
 
-* `transmon_drive` is updated in accordance with [1904.06560](https://arxiv.org/abs/1904.06560). In particular, the functional form has been changed from $\Omega(t)(\cos(\omega_d t + \phi) X - \sin(\omega_d t + \phi) Y)$ to $\Omega(t) \sin(\omega_d t + \phi) Y$. Furthermore, qubit frequencies in `transmon_interaction` are now divided by 2 as is common as well.
+* `transmon_drive` is updated in accordance with [1904.06560](https://arxiv.org/abs/1904.06560). In particular, the functional form has been changed from $\Omega(t)(\cos(\omega_d t + \phi) X - \sin(\omega_d t + \phi) Y)$ to $\Omega(t) \sin(\omega_d t + \phi) Y$.
  [(#4418)](https://github.com/PennyLaneAI/pennylane/pull/4418/)
  [(#4465)](https://github.com/PennyLaneAI/pennylane/pull/4465/)
+ [(#4478)](https://github.com/PennyLaneAI/pennylane/pull/4478/)
 
 <h3>Breaking changes 💔</h3>
 

pennylane/pulse/transmon.py

@@ -53,7 +53,7 @@ def transmon_interaction(
 
  .. math::
 
- H = \sum_{q\in \text{wires}} \frac{\omega_q}{2} b^\dagger_q b_q
+ H = \sum_{q\in \text{wires}} \omega_q b^\dagger_q b_q
  + \sum_{(i, j) \in \mathcal{C}} g_{ij} \left(b^\dagger_i b_j + b_j^\dagger b_i \right)
  + \sum_{q\in \text{wires}} \alpha_q b^\dagger_q b^\dagger_q b_q b_q
 
@@ -179,7 +179,7 @@ def transmon_interaction(
 
  # qubit term
  coeffs = list(omega)
- observables = [qml.s_prod(0.5, ad(i, d) @ a(i, d)) for i in wires]
+ observables = [ad(i, d) @ a(i, d) for i in wires]
 
  # coupling term
  coeffs += list(g)

tests/pulse/test_transmon.py

@@ -356,7 +356,7 @@ def test_float_qubit_freq_with_explicit_wires(self):
  g = 2 * np.pi * coupling
  assert H.coeffs[:6] == [2 * np.pi] * 6
  assert all(H.coeffs[6:] == g)
- for o1, o2 in zip(H.ops[:6], [qml.s_prod(0.5, ad(i, 2) @ a(i, 2)) for i in wires]):
+ for o1, o2 in zip(H.ops[:6], [ad(i, 2) @ a(i, 2) for i in wires]):
  assert qml.equal(o1, o2)
 
  def test_single_callable_qubit_freq_with_explicit_wires(self):
@@ -377,7 +377,7 @@ def test_single_callable_qubit_freq_with_explicit_wires(self):
  assert qml.math.allclose(H.coeffs[:10], g)
  for coeff in H.coeffs[10:]:
  assert coeff([3, 4, 5], 6) == omega([3, 4, 5], 6)
- for o1, o2 in zip(H.ops[10:], [qml.s_prod(0.5, ad(i, 2) @ a(i, 2)) for i in wires0]):
+ for o1, o2 in zip(H.ops[10:], [ad(i, 2) @ a(i, 2) for i in wires0]):
  assert qml.equal(o1, o2)
 
  def test_d_neq_2_raises_error(self):