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Added U1, U2 and U3 deprecation warnings into Circuit Library #8391

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merged 16 commits into from
Jul 27, 2022
Merged

Added U1, U2 and U3 deprecation warnings into Circuit Library #8391

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e029651
Added U1, U2 and U3 deprecation warnings in Circuit Library
Guillermo-Mijares-Vilarino Jul 22, 2022
7d0ebc3
Merge branch 'main' into add-u1-u2-u3-deprecation
Guillermo-Mijares-Vilarino Jul 22, 2022
f9f4081
corrected parentheses and removed cdots
Guillermo-Mijares-Vilarino Jul 25, 2022
8dc53ae
Merge branch 'add-u1-u2-u3-deprecation' of https://github.com/Guiller…
Guillermo-Mijares-Vilarino Jul 25, 2022
e6c5544
Remove cdots
Guillermo-Mijares-Vilarino Jul 25, 2022
ebc2ffb
Merge branch 'add-u1-u2-u3-deprecation' of https://github.com/Guiller…
Guillermo-Mijares-Vilarino Jul 25, 2022
9b24a00
Merge branch 'main' into add-u1-u2-u3-deprecation
1ucian0 Jul 25, 2022
4d79ff5
Merge branch 'add-u1-u2-u3-deprecation' of https://github.com/Guiller…
Guillermo-Mijares-Vilarino Jul 25, 2022
e87bc35
moved formulas to examples
Guillermo-Mijares-Vilarino Jul 25, 2022
cbcf87e
Merge branch 'main' into add-u1-u2-u3-deprecation
Guillermo-Mijares-Vilarino Jul 25, 2022
065e482
Add linebreak
Guillermo-Mijares-Vilarino Jul 26, 2022
3e1c029
Fix sphinx identifier
Cryoris Jul 26, 2022
73de6ba
corrected global phases
Guillermo-Mijares-Vilarino Jul 26, 2022
08b53ba
Merge branch 'add-u1-u2-u3-deprecation' of https://github.com/Guiller…
Guillermo-Mijares-Vilarino Jul 26, 2022
9ffc5c0
Merge branch 'main' into add-u1-u2-u3-deprecation
mergify[bot] Jul 26, 2022
30d3bfb
Merge branch 'main' into add-u1-u2-u3-deprecation
Guillermo-Mijares-Vilarino Jul 27, 2022
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16 changes: 16 additions & 0 deletions qiskit/circuit/library/standard_gates/u1.py
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Expand Up @@ -27,6 +27,22 @@ class U1Gate(Gate):
This is a diagonal gate. It can be implemented virtually in hardware
via framechanges (i.e. at zero error and duration).

.. warning::

This gate is deprecated. Instead, the following replacements should be used

.. math::

U1(\lambda) = P(\lambda)= U(0,0,\lambda)

.. code-block:: python

circuit = QuantumCircuit(1)
circuit.p(lambda, 0) # or circuit.u(0, 0, lambda)




**Circuit symbol:**

.. parsed-literal::
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29 changes: 27 additions & 2 deletions qiskit/circuit/library/standard_gates/u2.py
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Expand Up @@ -26,8 +26,20 @@ class U2Gate(Gate):

Implemented using one X90 pulse on IBM Quantum systems:

.. math::
U2(\phi, \lambda) = RZ(\phi).RY(\frac{\pi}{2}).RZ(\lambda)
.. warning::

This gate is deprecated. Instead, the following replacements should be used

.. math::

U2(\phi, \lambda) = U\left(\frac{\pi}{2}, \phi, \lambda\right)

.. code-block:: python

circuit = QuantumCircuit(1)
circuit.u(pi/2, phi, lambda)



**Circuit symbol:**

Expand All @@ -49,11 +61,24 @@ class U2Gate(Gate):

**Examples:**

.. math::

U2(\phi,\lambda) = RZ(\phi) RY\left(\frac{\pi}{2}\right) RZ(\lambda)
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I think this first equivalence with RZ RY RZ misses a global phase, doesn't it?

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I hadn't actually checked that one (trusted it to be correct but seems that was an error on my part 🤦‍♂️) but you are correct. $U2(\phi, \lambda) = e^{i\frac{\phi+\lambda}{2}}RZ(\phi)RY(\pi/2)RZ(\lambda)$

= e^{- i\frac{\pi}{4}} P\left(\frac{\pi}{2} + \phi\right)
\sqrt{X} P\left(\lambda- \frac{\pi}{2}\right)

.. math::

U2(0, \pi) = H

.. math::

U2(0, 0) = RY(\pi/2)

.. math::

U2(-\pi/2, \pi/2) = RX(\pi/2)

.. seealso::

:class:`~qiskit.circuit.library.standard_gates.U3Gate`:
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18 changes: 18 additions & 0 deletions qiskit/circuit/library/standard_gates/u3.py
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Expand Up @@ -24,6 +24,19 @@
class U3Gate(Gate):
r"""Generic single-qubit rotation gate with 3 Euler angles.

.. warning::

This gate is deprecated. Instead, the following replacements should be used

.. math::

U3(\theta, \phi, \lambda) = U(\theta, \phi, \lambda)

.. codeblock:: python
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circuit = QuantumCircuit(1)
circuit.u(theta, phi, lambda)

**Circuit symbol:**

.. parsed-literal::
Expand Down Expand Up @@ -52,6 +65,11 @@ class U3Gate(Gate):

**Examples:**

.. math::

U3(\theta, \phi, \lambda) = e^{i \frac{\pi + \theta}{2}} P(\phi + \pi) \sqrt{X}
P(\theta + \pi) \sqrt{X} P(\lambda)
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Also here the global phase doesn't seem to match (or maybe I have a typo!)

>>> decomp = np.exp(0.5j * (np.pi + th)) * np.dot(PhaseGate(phi + np.pi), np.dot(SXGate(), np.dot(PhaseGate(th + np.pi), np.dot(SXGate(), PhaseGate(lam)))))
>>> decomp
array([[-0.53350621-0.71685923j,  0.22160969+0.39034999j],
       [ 0.23851082-0.38025854j,  0.56442266-0.69277925j]])
>>> u3 = U3Gate(th, phi, lam).to_matrix()
>>> u3  # matrix doesn't match decomp
array([[ 0.89359724+0.j        , -0.44545363-0.05527232j],
       [ 0.1626514 +0.41836406j,  0.21878112+0.86640109j]])
>>> Operator(u3).equiv(decomp)  # but it is equivalent -- hence a global phase difference exists
True

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That's because I forgot to add a minus sign to the global phase 😅. The correct phase is $e^{-i \frac{\theta + \pi}{2}}$ so the typo was mine!


.. math::

U3\left(\theta, -\frac{\pi}{2}, \frac{\pi}{2}\right) = RX(\theta)
Expand Down