Add reset_each function by analogy with measure_each (#4294)

Review: @viathor

Author: maffoo

cirq-core/cirq/__init__.py

@@ -259,6 +259,7 @@
     QubitOrderOrList,
     QubitPermutationGate,
     reset,
+    reset_each,
     ResetChannel,
     riswap,
     Rx,

cirq-core/cirq/ops/__init__.py

@@ -45,6 +45,7 @@
     PhaseDampingChannel,
     PhaseFlipChannel,
     reset,
+    reset_each,
     ResetChannel,
 )
 

cirq-core/cirq/ops/common_channels.py

@@ -15,7 +15,7 @@
 """Quantum channels that are commonly used in the literature."""
 
 import itertools
-from typing import Any, Dict, Iterable, Optional, Sequence, Tuple, Union, TYPE_CHECKING
+from typing import Any, Dict, Iterable, List, Optional, Sequence, Tuple, Union, TYPE_CHECKING
 
 import numpy as np
 
@@ -789,6 +789,11 @@ def reset(qubit: 'cirq.Qid') -> raw_types.Operation:
     return ResetChannel(qubit.dimension).on(qubit)
 
 
+def reset_each(*qubits: 'cirq.Qid') -> List[raw_types.Operation]:
+    """Returns a list of `ResetChannel` instances on the given qubits."""
+    return [ResetChannel(q.dimension).on(q) for q in qubits]
+
+
 @value.value_equality
 class PhaseDampingChannel(gate_features.SingleQubitGate):
     """Dampen qubit phase.

cirq-core/cirq/ops/common_channels_test.py

@@ -517,6 +517,16 @@ def test_reset_act_on():
     )
 
 
+def test_reset_each():
+    qubits = cirq.LineQubit.range(8)
+    for n in range(len(qubits) + 1):
+        ops = cirq.reset_each(*qubits[:n])
+        assert len(ops) == n
+        for i, op in enumerate(ops):
+            assert isinstance(op.gate, cirq.ResetChannel)
+            assert op.qubits == (qubits[i],)
+
+
 def test_phase_damping_channel():
     d = cirq.phase_damp(0.3)
     np.testing.assert_almost_equal(