Add OnEach bloq (#346)

* Add on each meta bloq.

* Format.

* Address review comments.

---------

Co-authored-by: Matthew Harrigan <[email protected]>

qualtran/bloqs/basic_gates/hadamard.py

@@ -64,6 +64,9 @@ def add_my_tensors(
             )
         )
 
+    def short_name(self) -> 'str':
+        return 'H'
+
     def as_cirq_op(
         self, qubit_manager: 'cirq.QubitManager', q: 'CirqQuregT'
     ) -> Tuple['cirq.Operation', Dict[str, 'CirqQuregT']]:

qualtran/bloqs/basic_gates/t_gate.py

@@ -57,6 +57,9 @@ def signature(self) -> 'Signature':
     def t_complexity(self) -> 'TComplexity':
         return TComplexity(t=1)
 
+    def short_name(self) -> str:
+        return 'T'
+
     def as_cirq_op(
         self, qubit_manager: 'cirq.QubitManager', q: 'CirqQuregT'
     ) -> Tuple['cirq.Operation', Dict[str, 'CirqQuregT']]:

qualtran/bloqs/basic_gates/x_basis.py

@@ -164,6 +164,9 @@ def add_my_tensors(
             )
         )
 
+    def short_name(self) -> str:
+        return 'X'
+
     def on_classical_vals(self, q: int) -> Dict[str, 'ClassicalValT']:
         return {'q': (q + 1) % 2}
 

qualtran/bloqs/basic_gates/z_basis.py

@@ -171,6 +171,9 @@ class ZGate(Bloq):
     def signature(self) -> 'Signature':
         return Signature.build(q=1)
 
+    def short_name(self) -> 'str':
+        return 'Z'
+
     def add_my_tensors(
         self,
         tn: qtn.TensorNetwork,

qualtran/bloqs/on_each.py

@@ -0,0 +1,57 @@
+#  Copyright 2023 Google LLC
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+"""Classes to apply single qubit bloq to multiple qubits."""
+from functools import cached_property
+from typing import Dict
+
+import attrs
+
+from qualtran import Bloq, BloqBuilder, Register, Signature, SoquetT
+
+
+@attrs.frozen
+class OnEach(Bloq):
+    """Add a single-qubit (unparameterized) bloq on each of n qubits.
+
+    Args:
+        n: the number of qubits to add the bloq to.
+        gate: A single qubit gate. The single qubit register must be named q.
+
+    Registers:
+     - q: an n-qubit register.
+    """
+
+    n: int
+    gate: Bloq
+
+    def __attrs_post_init__(self):
+        assert len(self.gate.signature) == 1, "Gate must only have a single register."
+        assert self.gate.signature[0].bitsize == 1, "Must be single qubit gate."
+        assert self.gate.signature[0].name == 'q', "Register must be named q."
+
+    @cached_property
+    def signature(self) -> Signature:
+        reg = Register('q', bitsize=self.n)
+        return Signature([reg])
+
+    def short_name(self) -> str:
+        return rf'{self.gate.short_name()}⨂{self.n}'
+
+    def build_composite_bloq(self, bb: BloqBuilder, *, q: SoquetT) -> Dict[str, SoquetT]:
+
+        qs = bb.split(q)
+        for i in range(self.n):
+            qs[i] = bb.add(self.gate, q=qs[i])
+        return {'q': bb.join(qs)}

qualtran/bloqs/on_each_test.py

@@ -0,0 +1,32 @@
+#  Copyright 2023 Google LLC
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+from functools import reduce
+
+import numpy as np
+
+import qualtran.testing as qlt_testing
+from qualtran.bloqs.basic_gates import Hadamard, XGate
+from qualtran.bloqs.on_each import OnEach
+
+
+def test_valid_bloq():
+    on_each = OnEach(10, XGate())
+    qlt_testing.assert_valid_bloq_decomposition(on_each)
+
+
+def test_tensor_contract():
+    bloq = OnEach(5, Hadamard())
+    tensor = bloq.tensor_contract()
+    single_had = Hadamard().tensor_contract()
+    np.testing.assert_allclose(tensor, reduce(np.kron, (single_had,) * 5))