Lattice surgery demo #1598

Qottmann · 2025-11-12T13:37:31Z

…ice-surgery

github-actions · 2025-11-12T13:37:41Z

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github-actions · 2025-11-12T13:41:33Z

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dwierichs

Amazing job with this demo @Qottmann 🎉 💯
I had a couple of comments.
Overall, any additional exemplary calculations that can be added without opening large cans of worms would be appreciated. Those could come in a "box", for example, to make them optional info that a reader can trace if they want to understand the details of what's going on , or decide to skip.
Otherwise I find the length and level of detail very well-chosen 👌

demonstrations_v2/tutorial_lattice_surgery/metadata.json

demonstrations_v2/tutorial_lattice_surgery/demo.py

Co-authored-by: David Wierichs <[email protected]>

…ice-surgery

dwierichs

Amazing work, @Qottmann
Just left some last minor things like typos, highly optional suggestions and such :)

demonstrations_v2/tutorial_lattice_surgery/demo.py

Co-authored-by: David Wierichs <[email protected]>

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Co-authored-by: David Wierichs <[email protected]>

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daniela-angulo

Really cool demo. Nothing major in the comments. Just styling and a question (for my own benefit). Thanks!

daniela-angulo · 2025-12-09T17:01:46Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+Introducing Lattice Surgery
+===========================
+
+Lattice surgery is a way to fault-tolerantly perform operations on two-dimensional quantum computers


I don't particularly like the adverb version of fault-tolerant, but if you feel strongly about it, it is cool.

daniela-angulo · 2025-12-09T17:02:41Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+
+Lattice surgery is a way to fault-tolerantly perform operations on two-dimensional quantum computers
+with local physical connectivity. Its introduction improved spatial overheads in topological quantum
+error correction codes such as surface codes by replacing continuous code operations 


Suggested change

error correction codes such as surface codes by replacing continuous code operations

error correction codes, such as surface codes, by replacing continuous code operations

daniela-angulo · 2025-12-09T17:56:36Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+enable parity measurements of arbitrary Pauli operators, which unlock universal fault
+tolerant quantum computing.


Suggested change

enable parity measurements of arbitrary Pauli operators, which unlock universal fault

tolerant quantum computing.

enable parity measurements of arbitrary Pauli operators, which unlock universal fault-tolerant quantum computing.

daniela-angulo · 2025-12-09T17:58:32Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+Surface code quantum computing
+------------------------------
+
+Topological quantum error correction codes like the surface code [#surfacecode]_ protect quantum information stored in logical qubits by


Suggested change

Topological quantum error correction codes like the surface code [#surfacecode]_ protect quantum information stored in logical qubits by

Topological quantum error correction codes, like the surface code [#surfacecode]_, protect quantum information stored in logical qubits by

daniela-angulo · 2025-12-09T18:27:00Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+on the four data qubits of the corners. Similarly, Z stabilizers are measured on white surfaces. 
+These stabilizer measurements are not performed directly on the data qubits, but via another kind of qubit that sits at the center of each square surface
+as well as the center of each arch (shown below). 
+These extra qubits are sometimes called measurement qubits or syndrome qubits and the measurement is performed by entangling the data qubits with the syndrome qubit and measuring it (see Fig. 1 in [#surfacecode]_).


at first, we are using syndrome qubits in plural, but then the last sentences uses it in singular which seems less general. But I don't know, just asking.

daniela-angulo · 2025-12-09T19:47:51Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+The commutation can be seen from the fact
+that the logical operator only ever overlaps with an even multiple of X or Z operators, and thus commutes with any other stabilizer.
+
+We also note that logical :math:`Y_L` measurement is a topic on its own. In principle, one could measure :math:`Y_L` by simultaneously measuring the logical


Suggested change

We also note that logical :math:`Y_L` measurement is a topic on its own. In principle, one could measure :math:`Y_L` by simultaneously measuring the logical

We also note that the logical :math:`Y_L` measurement is a topic on its own. In principle, one could measure :math:`Y_L` by simultaneously measuring the logical

daniela-angulo · 2025-12-09T20:05:22Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+we need to assign it to one of the two logical :math:`Z_L` operators, 
+on top of the product of the sign of the original two :math:`Z_L` operators we originally started from.
+
+Measuring :math:`Z_L \otimes Z_L` works in the same fashion, but with reversed roles: We connect the Z edges with each other, initialize in :math:`|+\rangle` to merge and measure in :math:`X` to split again:


Suggested change

Measuring :math:`Z_L \otimes Z_L` works in the same fashion, but with reversed roles: We connect the Z edges with each other, initialize in :math:`|+\rangle` to merge and measure in :math:`X` to split again:

Measuring :math:`Z_L \otimes Z_L` works in the same fashion, but with reversed roles: We connect the Z edges with each other, initialize in :math:`|+\rangle` to merge, and measure in :math:`X` to split again:

daniela-angulo · 2025-12-09T20:07:53Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+
+At this point we can measure arbitrary :math:`X_L` and :math:`Z_L` Pauli product measurements. The last missing ingredient for universality is measuring :math:`Y_L` operators.
+
+Introducing discontinuous operations on the surface code does not exclude that we can still use the continuous transformations of the code.


Suggested change

Introducing discontinuous operations on the surface code does not exclude that we can still use the continuous transformations of the code.

Introducing discontinuous operations on the surface code does not exclude the usage of continuous transformations of the code.

daniela-angulo · 2025-12-09T20:32:03Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+    :width: 70%
+    :target: javascript:void(0)
+
+Here we show an extended single qubit patch and three example re-orientations of the type of edges.


Suggested change

Here we show an extended single qubit patch and three example re-orientations of the type of edges.

Here we show an extended single-qubit patch and three example re-orientations of the type of edges.

daniela-angulo · 2025-12-09T20:33:57Z

demonstrations_v2/tutorial_lattice_surgery/demo.py

+    :target: javascript:void(0)
+
+Here we show an extended single qubit patch and three example re-orientations of the type of edges.
+The smaller images are guides to the eye to indicate the settings, with X edges as solid lines and Z edges as dotted lines (i.e. the same as the logical measurements moved to the edges).


Suggested change

The smaller images are guides to the eye to indicate the settings, with X edges as solid lines and Z edges as dotted lines (i.e. the same as the logical measurements moved to the edges).

The smaller images are guides to the eye to indicate the settings, with X edges as solid lines and Z edges as dashed lines (i.e. the same as the logical measurements moved to the edges).

Qottmann added 5 commits October 20, 2025 11:38

Lattice Surgery demo

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lattice surgery demo

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Merge branch 'master' of https://github.com/PennyLaneAI/qml into latt…

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better draft

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assets

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Qottmann and others added 16 commits November 12, 2025 15:38

delete older unused image

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update

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update images

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Merge branch 'master' of https://github.com/PennyLaneAI/qml into latt…

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Merge branch 'master' into lattice-surgery

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Merge branch 'master' of https://github.com/PennyLaneAI/qml into latt…

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Merge branch 'lattice-surgery' of https://github.com/PennyLaneAI/qml …

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latest updates

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Merge branch 'master' into lattice-surgery

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Merge branch 'lattice-surgery' of https://github.com/PennyLaneAI/qml …

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Qottmann requested a review from dwierichs November 27, 2025 18:13

dwierichs requested changes Dec 4, 2025

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Qottmann and others added 4 commits December 5, 2025 12:23

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Co-authored-by: David Wierichs <[email protected]>

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Merge branch 'master' of https://github.com/PennyLaneAI/qml into latt…

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Qottmann added 8 commits December 8, 2025 11:56

update thumbnail image url

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references

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discuss twist boundaries

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measure multiple patches

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comment on topology

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dumb down

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update figure

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rephrase conclusion

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Qottmann requested a review from dwierichs December 8, 2025 11:47

dwierichs approved these changes Dec 8, 2025

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Co-authored-by: David Wierichs <[email protected]>

Merge branch 'master' of https://github.com/PennyLaneAI/qml into latt…

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Apply suggestions from code review

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Co-authored-by: David Wierichs <[email protected]>

Merge branch 'lattice-surgery' of https://github.com/PennyLaneAI/qml …

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clifford angles

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Qottmann requested a review from daniela-angulo December 9, 2025 11:26

daniela-angulo reviewed Dec 9, 2025

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	error correction codes such as surface codes by replacing continuous code operations
	error correction codes, such as surface codes, by replacing continuous code operations

		enable parity measurements of arbitrary Pauli operators, which unlock universal fault
		tolerant quantum computing.

	Topological quantum error correction codes like the surface code [#surfacecode]_ protect quantum information stored in logical qubits by
	Topological quantum error correction codes, like the surface code [#surfacecode]_, protect quantum information stored in logical qubits by

	We also note that logical :math:`Y_L` measurement is a topic on its own. In principle, one could measure :math:`Y_L` by simultaneously measuring the logical
	We also note that the logical :math:`Y_L` measurement is a topic on its own. In principle, one could measure :math:`Y_L` by simultaneously measuring the logical

	Measuring :math:`Z_L \otimes Z_L` works in the same fashion, but with reversed roles: We connect the Z edges with each other, initialize in :math:`\|+\rangle` to merge and measure in :math:`X` to split again:
	Measuring :math:`Z_L \otimes Z_L` works in the same fashion, but with reversed roles: We connect the Z edges with each other, initialize in :math:`\|+\rangle` to merge, and measure in :math:`X` to split again:


		At this point we can measure arbitrary :math:`X_L` and :math:`Z_L` Pauli product measurements. The last missing ingredient for universality is measuring :math:`Y_L` operators.

		Introducing discontinuous operations on the surface code does not exclude that we can still use the continuous transformations of the code.

	Here we show an extended single qubit patch and three example re-orientations of the type of edges.
	Here we show an extended single-qubit patch and three example re-orientations of the type of edges.

	The smaller images are guides to the eye to indicate the settings, with X edges as solid lines and Z edges as dotted lines (i.e. the same as the logical measurements moved to the edges).
	The smaller images are guides to the eye to indicate the settings, with X edges as solid lines and Z edges as dashed lines (i.e. the same as the logical measurements moved to the edges).

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Qottmann commented Nov 12, 2025 •

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