update: restricting parameter names to not collide with ones we use for OpenQASM generation.

src/braket/circuits/circuit.py

@@ -1203,7 +1203,7 @@ def _to_openqasm(
             )
             for idx, qubit in enumerate(qubits):
                 qubit_target = serialization_properties.format_target(int(qubit))
-                ir_instructions.append(f"b[{idx}] = measure {qubit_target};")
+                ir_instructions.append(f"__bits__[{idx}] = measure {qubit_target};")
 
         return OpenQasmProgram.construct(source="\n".join(ir_instructions), inputs={})
 
@@ -1214,11 +1214,11 @@ def _create_openqasm_header(
         for parameter in self.parameters:
             ir_instructions.append(f"input float {parameter};")
         if not self.result_types:
-            ir_instructions.append(f"bit[{self.qubit_count}] b;")
+            ir_instructions.append(f"bit[{self.qubit_count}] __bits__;")
 
         if serialization_properties.qubit_reference_type == QubitReferenceType.VIRTUAL:
             total_qubits = max(self.qubits).real + 1
-            ir_instructions.append(f"qubit[{total_qubits}] q;")
+            ir_instructions.append(f"qubit[{total_qubits}] __qubits__;")
         elif serialization_properties.qubit_reference_type != QubitReferenceType.PHYSICAL:
             raise ValueError(
                 f"Invalid qubit_reference_type "

src/braket/circuits/serialization.py

@@ -39,7 +39,7 @@ class OpenQASMSerializationProperties:
     Properties for serializing a circuit to OpenQASM.
 
     qubit_reference_type (QubitReferenceType): determines whether to use
-        logical qubits or physical qubits (q[i] vs $i).
+        logical qubits or physical qubits (__qubits__[i] vs $i).
     """
 
     qubit_reference_type: QubitReferenceType = QubitReferenceType.VIRTUAL
@@ -53,7 +53,7 @@ def format_target(self, target: int) -> str:
             str: The OpenQASM representation of the target qubit.
         """
         qubit_reference_format = (
-            "q[{}]" if self.qubit_reference_type == QubitReferenceType.VIRTUAL else "${}"
+            "__qubits__[{}]" if self.qubit_reference_type == QubitReferenceType.VIRTUAL else "${}"
         )
         return qubit_reference_format.format(target)
 

src/braket/parametric/free_parameter.py

@@ -15,6 +15,7 @@
 
 from numbers import Number
 from typing import Dict, Union
+from unicodedata import category
 
 from sympy import Symbol
 
@@ -43,12 +44,17 @@ def __init__(self, name: str):
         Initializes a new :class:'FreeParameter' object.
 
         Args:
-            name (str): Name of the :class:'FreeParameter'. Can be a unicode value.
+            name (str): Name of the :class:'FreeParameter'. Must begin with a letter [A-Za-z],
+                an underscore or an element from the Unicode character categories Lu/Ll/Lt/Lm/Lo/Nl.
+                Must not begin with two underscores '__'. May contain numbers [0-9] after the
+                first character.
 
         Examples:
             >>> param1 = FreeParameter("theta")
             >>> param1 = FreeParameter("\u03B8")
+            >>> param1 = FreeParameter("a1b2")
         """
+        FreeParameter._validate_name(name)
         self._name = Symbol(name)
         super().__init__(expression=self._name)
 
@@ -99,6 +105,22 @@ def to_dict(self) -> dict:
             "name": self.name,
         }
 
+    @staticmethod
+    def _validate_name(name: str) -> None:
+        if not name:
+            raise ValueError("Symbol names must be non empty")
+        if not isinstance(name, str):
+            raise TypeError("Symbol name must be a string")
+        if name.startswith("_"):
+            if name.startswith("__"):
+                raise ValueError("Symbol names must not start with two underscores '__'")
+        else:
+            unicode_category = category(name[0])
+            if not unicode_category:
+                raise ValueError("Symbol names must start with a valid character")
+            if not unicode_category.startswith("L") and unicode_category != "Nl":
+                raise ValueError("Symbol names must start with a letter or underscore")
+
     @classmethod
     def from_dict(cls, parameter: dict) -> FreeParameter:
         return FreeParameter(parameter["name"])

src/braket/pulse/ast/qasm_transformer.py

@@ -43,8 +43,8 @@ def visit_ExpressionStatement(self, expression_statement: ast.ExpressionStatemen
         ):
             # For capture_v0 nodes, it replaces it with classical assignment statements
             # of the form:
-            # b[0] = capture_v0(...)
-            # b[1] = capture_v0(...)
+            # __bits__[0] = capture_v0(...)
+            # __bits__[1] = capture_v0(...)
             new_val = ast.ClassicalAssignment(
                 # Ideally should use IndexedIdentifier here, but this works since it is just
                 # for printing.

test/integ_tests/test_adjoint_gradient.py

@@ -42,10 +42,10 @@ def test_adjoint_gradient_quantum_task_with_nested_targets(
     expected_openqasm = (
         "OPENQASM 3.0;\n"
         "input float theta;\n"
-        "qubit[4] q;\n"
-        "rx(theta) q[0];\n"
-        "#pragma braket result adjoint_gradient expectation(-6 * y(q[0]) @ i(q[1]) + 0.75 * "
-        "y(q[2]) @ z(q[3])) theta"
+        "qubit[4] __qubits__;\n"
+        "rx(theta) __qubits__[0];\n"
+        "#pragma braket result adjoint_gradient expectation(-6 * "
+        "y(__qubits__[0]) @ i(__qubits__[1]) + 0.75 * y(__qubits__[2]) @ z(__qubits__[3])) theta"
     )
 
     gradient_task = AwsQuantumTask.create(
@@ -83,10 +83,10 @@ def test_adjoint_gradient_with_standard_observable_terms(
     expected_openqasm = (
         "OPENQASM 3.0;\n"
         "input float theta;\n"
-        "qubit[3] q;\n"
-        "rx(theta) q[0];\n"
-        "#pragma braket result adjoint_gradient expectation(2 * x(q[0]) + 3 * y(q[1]) "
-        "- 1 * z(q[2])) theta"
+        "qubit[3] __qubits__;\n"
+        "rx(theta) __qubits__[0];\n"
+        "#pragma braket result adjoint_gradient expectation(2 * "
+        "x(__qubits__[0]) + 3 * y(__qubits__[1]) - 1 * z(__qubits__[2])) theta"
     )
 
     gradient_task = AwsQuantumTask.create(
@@ -132,17 +132,19 @@ def test_adjoint_gradient_with_batch_circuits(aws_session, s3_destination_folder
         (
             "OPENQASM 3.0;\n"
             "input float theta;\n"
-            "qubit[2] q;\n"
-            "rx(theta) q[0];\n"
-            "#pragma braket result adjoint_gradient expectation(6 * y(q[0]) @ i(q[1])) theta"
+            "qubit[2] __qubits__;\n"
+            "rx(theta) __qubits__[0];\n"
+            "#pragma braket result adjoint_gradient expectation(6 *"
+            " y(__qubits__[0]) @ i(__qubits__[1])) theta"
         ),
         (
             "OPENQASM 3.0;\n"
             "input float theta;\n"
-            "qubit[2] q;\n"
-            "rx(theta) q[0];\n"
-            "#pragma braket result adjoint_gradient expectation(-6 * y(q[0]) @ i(q[1]) + 0.75 * "
-            "y(q[0]) @ z(q[1])) theta"
+            "qubit[2] __qubits__;\n"
+            "rx(theta) __qubits__[0];\n"
+            "#pragma braket result adjoint_gradient expectation(-6 *"
+            " y(__qubits__[0]) @ i(__qubits__[1]) + 0.75 *"
+            " y(__qubits__[0]) @ z(__qubits__[1])) theta"
         ),
     ]
 

test/unit_tests/braket/aws/test_aws_quantum_task.py

@@ -573,12 +573,12 @@ def test_create_pulse_gate_circuit(
     expected_openqasm = "\n".join(
         (
             "OPENQASM 3.0;",
-            "bit[2] b;",
+            "bit[2] __bits__;",
             "cal {",
             "    set_frequency(predefined_frame_1, 6000000.0);",
             "}",
-            "b[0] = measure $0;",
-            "b[1] = measure $1;",
+            "__bits__[0] = measure $0;",
+            "__bits__[1] = measure $1;",
         )
     )