Add missing factor of pi to parameterized Quil gate output (#3206)

This PR addresses a bug in Quil output. The current code doesn't distinguish between Cirq's `PowGate` exponents and the angle parameters for Quil gates, but they differ by a factor of pi. This is verified by comparing program unitaries before and after conversion to Quil (see below). Adds a test for this change that depends on pyQuil, so `pyquil` is added to `pip-list-dev-tools.txt`, but in the event that pyQuil is not available for import, the test is [skipped](https://docs.pytest.org/en/latest/skipping.html#skipping-on-a-missing-import-dependency). Additionally sneaks in a change to Quil output for `ISwapPowGate` -- uses the native `XY` Quil gate when the exponent of the `ISwapPowGate` does not equal 1. ```python In [1]: import numpy as np ...: from pyquil import Program ...: from pyquil.simulation.tools import program_unitary ...: ...: from cirq import Circuit, LineQubit, QuilOutput, rx ...: ...: q0 = LineQubit(0) ...: ...: # rx(pi/2) creates an XPowGate with exponent 0.5 (and global_shift -0.5) ...: circ = Circuit(rx(np.pi/2)(q0)) ...: print(circ) ...: ...: pyquil_program = Program(str(QuilOutput(circ, (q0,)))) ...: print(pyquil_program) ...: ...: pyquil_unitary = program_unitary(pyquil_program, n_qubits=1) ...: print(pyquil_unitary) ...: ...: cirq_unitary = circ.unitary() ...: print(cirq_unitary) ...: ...: np.allclose(pyquil_unitary, cirq_unitary) ``` on `master`: ``` 0: ───Rx(0.5π)─── RX(0.5) 0 [[0.96891242+0.j 0. -0.24740396j] [0. -0.24740396j 0.96891242+0.j ]] [[0.70710678+0.j 0. -0.70710678j] [0. -0.70710678j 0.70710678+0.j ]] Out[1]: False ``` this PR: ``` 0: ───Rx(0.5π)─── RX(pi/2) 0 [[0.70710678+0.j 0. -0.70710678j] [0. -0.70710678j 0.70710678+0.j ]] [[0.70710678+0.j 0. -0.70710678j] [0. -0.70710678j 0.70710678+0.j ]] Out[1]: True ``` Related to #1742, #2386, #2983
quantumlib · Aug 12, 2020 · b878d06 · b878d06
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diff --git a/.gitignore b/.gitignore
@@ -39,3 +39,6 @@ docs/generated
 
 # Default pycharm virtual env
 .venv/
+
+# pyenv configuration
+.python-version
diff --git a/cirq/circuits/quil_output_test.py b/cirq/circuits/quil_output_test.py
@@ -36,9 +36,9 @@ def test_single_gate_no_parameter():
 def test_single_gate_with_parameter():
     q0, = _make_qubits(1)
     output = cirq.QuilOutput((cirq.X(q0)**0.5,), (q0,))
-    assert (str(output) == """# Created using Cirq.
+    assert (str(output) == f"""# Created using Cirq.
 
-RX(0.5) 0\n""")
+RX({np.pi / 2}) 0\n""")
 
 
 def test_single_gate_named_qubit():
@@ -52,11 +52,11 @@ def test_single_gate_named_qubit():
 def test_h_gate_with_parameter():
     q0, = _make_qubits(1)
     output = cirq.QuilOutput((cirq.H(q0)**0.25,), (q0,))
-    assert (str(output) == """# Created using Cirq.
+    assert (str(output) == f"""# Created using Cirq.
 
-RY(0.25) 0
-RX(0.25) 0
-RY(-0.25) 0\n""")
+RY({np.pi / 4}) 0
+RX({np.pi / 4}) 0
+RY({-np.pi / 4}) 0\n""")
 
 
 def test_save_to_file(tmpdir):
@@ -184,108 +184,101 @@ def test_i_swap_with_power():
         q0,
         q1,
     ))
-    assert str(output) == """# Created using Cirq.
+    assert str(output) == f"""# Created using Cirq.
 
-CNOT 0 1
-H 0
-CNOT 1 0
-RZ(0.125) 0
-CNOT 1 0
-RZ(-0.125) 0
-H 0
-CNOT 0 1
+XY({np.pi / 4}) 0 1
 """
 
 
 def test_all_operations():
     qubits = tuple(_make_qubits(5))
     operations = _all_operations(*qubits, include_measurements=False)
     output = cirq.QuilOutput(operations, qubits)
-    assert (str(output) == """# Created using Cirq.
+    assert (str(output) == f"""# Created using Cirq.
 
 DECLARE m0 BIT[1]
 DECLARE m1 BIT[1]
 DECLARE m2 BIT[1]
 DECLARE m3 BIT[3]
 
 Z 0
-RZ(0.625) 0
+RZ({5 * np.pi / 8}) 0
 Y 0
-RY(0.375) 0
+RY({3 * np.pi / 8}) 0
 X 0
-RX(0.875) 0
+RX({7 * np.pi / 8}) 0
 H 1
 CZ 0 1
-CPHASE(0.25) 0 1
+CPHASE({np.pi / 4}) 0 1
 CNOT 0 1
-RY(-0.5) 1
-CPHASE(0.5) 0 1
-RY(0.5) 1
+RY({-np.pi / 2}) 1
+CPHASE({np.pi / 2}) 0 1
+RY({np.pi / 2}) 1
 SWAP 0 1
-PSWAP(0.75) 0 1
+PSWAP({3 * np.pi / 4}) 0 1
 H 2
 CCNOT 0 1 2
 H 2
 CCNOT 0 1 2
-RZ(0.125) 0
-RZ(0.125) 1
-RZ(0.125) 2
+RZ({np.pi / 8}) 0
+RZ({np.pi / 8}) 1
+RZ({np.pi / 8}) 2
 CNOT 0 1
 CNOT 1 2
-RZ(-0.125) 1
-RZ(0.125) 2
+RZ({-np.pi / 8}) 1
+RZ({np.pi / 8}) 2
 CNOT 0 1
 CNOT 1 2
-RZ(-0.125) 2
+RZ({-np.pi / 8}) 2
 CNOT 0 1
 CNOT 1 2
-RZ(-0.125) 2
+RZ({-np.pi / 8}) 2
 CNOT 0 1
 CNOT 1 2
 H 2
-RZ(0.125) 0
-RZ(0.125) 1
-RZ(0.125) 2
+RZ({np.pi / 8}) 0
+RZ({np.pi / 8}) 1
+RZ({np.pi / 8}) 2
 CNOT 0 1
 CNOT 1 2
-RZ(-0.125) 1
-RZ(0.125) 2
+RZ({-np.pi / 8}) 1
+RZ({np.pi / 8}) 2
 CNOT 0 1
 CNOT 1 2
-RZ(-0.125) 2
+RZ({-np.pi / 8}) 2
 CNOT 0 1
 CNOT 1 2
-RZ(-0.125) 2
+RZ({-np.pi / 8}) 2
 CNOT 0 1
 CNOT 1 2
 H 2
 CSWAP 0 1 2
 X 0
 X 1
-RX(0.75) 0
-RX(0.75) 1
+RX({3 * np.pi / 4}) 0
+RX({3 * np.pi / 4}) 1
 Y 0
 Y 1
-RY(0.75) 0
-RY(0.75) 1
+RY({3 * np.pi / 4}) 0
+RY({3 * np.pi / 4}) 1
 Z 0
 Z 1
-RZ(0.75) 0
-RZ(0.75) 1
+RZ({3 * np.pi / 4}) 0
+RZ({3 * np.pi / 4}) 1
 I 0
 I 0
 I 1
 I 2
 ISWAP 2 0
-RZ(-0.111) 1
-RX(0.25) 1
-RZ(0.111) 1
-RZ(-0.333) 1
-RX(0.5) 1
-RZ(0.333) 1
-RZ(-0.777) 1
-RX(-0.5) 1
-RZ(0.777) 1
+RZ({-0.111 * np.pi}) 1
+RX({np.pi / 4}) 1
+RZ({0.111 * np.pi}) 1
+RZ({-0.333 * np.pi}) 1
+RX({np.pi / 2}) 1
+RZ({0.333 * np.pi}) 1
+RZ({-0.777 * np.pi}) 1
+RX({-np.pi / 2}) 1
+RZ({0.777 * np.pi}) 1
 WAIT
 MEASURE 0 m0[0]
 MEASURE 2 m1[0]
@@ -358,3 +351,30 @@ def test_pauli_interaction_gate():
 
 CZ 0 1
 """
+
+
+def test_equivalent_unitaries():
+    """This test covers the factor of pi change. However, it will be skipped
+    if pyquil is unavailable for import.
+
+    References:
+        https://docs.pytest.org/en/latest/skipping.html#skipping-on-a-missing-import-dependency
+    """
+    pyquil = pytest.importorskip("pyquil")
+    pyquil_simulation_tools = pytest.importorskip("pyquil.simulation.tools")
+    q0, q1 = _make_qubits(2)
+    operations = [
+        cirq.XPowGate(exponent=0.5, global_shift=-0.5)(q0),
+        cirq.YPowGate(exponent=0.5, global_shift=-0.5)(q0),
+        cirq.ZPowGate(exponent=0.5, global_shift=-0.5)(q0),
+        cirq.CZPowGate(exponent=0.5)(q0, q1),
+        cirq.ISwapPowGate(exponent=0.5)(q0, q1),
+    ]
+    output = cirq.QuilOutput(operations, (q0, q1))
+    program = pyquil.Program(str(output))
+    pyquil_unitary = pyquil_simulation_tools.program_unitary(program,
+                                                             n_qubits=2)
+    # Qubit ordering differs between pyQuil and Cirq.
+    cirq_unitary = cirq.Circuit(cirq.SWAP(q0, q1), operations,
+                                cirq.SWAP(q0, q1)).unitary()
+    assert np.allclose(pyquil_unitary, cirq_unitary)
diff --git a/cirq/ops/common_gates.py b/cirq/ops/common_gates.py
@@ -216,7 +216,8 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
                formatter: 'cirq.QuilFormatter') -> Optional[str]:
         if self._exponent == 1:
             return formatter.format('X {0}\n', qubits[0])
-        return formatter.format('RX({0}) {1}\n', self._exponent, qubits[0])
+        return formatter.format('RX({0}) {1}\n', self._exponent * np.pi,
+                                qubits[0])
 
     @property
     def phase_exponent(self):
@@ -387,7 +388,8 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
                formatter: 'cirq.QuilFormatter') -> Optional[str]:
         if self._exponent == 1:
             return formatter.format('Y {0}\n', qubits[0])
-        return formatter.format('RY({0}) {1}\n', self._exponent, qubits[0])
+        return formatter.format('RY({0}) {1}\n', self._exponent * np.pi,
+                                qubits[0])
 
     @property
     def phase_exponent(self):
@@ -620,8 +622,8 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
                formatter: 'cirq.QuilFormatter') -> Optional[str]:
         if self._exponent == 1:
             return formatter.format('Z {0}\n', qubits[0])
-
-        return formatter.format('RZ({0}) {1}\n', self._exponent, qubits[0])
+        return formatter.format('RZ({0}) {1}\n', self._exponent * np.pi,
+                                qubits[0])
 
     def __str__(self) -> str:
         if self._global_shift == -0.5:
@@ -801,8 +803,9 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
                formatter: 'cirq.QuilFormatter') -> Optional[str]:
         if self._exponent == 1:
             return formatter.format('H {0}\n', qubits[0])
-        return formatter.format('RY({0}) {3}\nRX({1}) {3}\nRY({2}) {3}\n', 0.25,
-                                self._exponent, -0.25, qubits[0])
+        return formatter.format('RY({0}) {3}\nRX({1}) {3}\nRY({2}) {3}\n',
+                                0.25 * np.pi, self._exponent * np.pi,
+                                -0.25 * np.pi, qubits[0])
 
     def _has_stabilizer_effect_(self) -> Optional[bool]:
         if self._is_parameterized_():
@@ -978,7 +981,7 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
                formatter: 'cirq.QuilFormatter') -> Optional[str]:
         if self._exponent == 1:
             return formatter.format('CZ {0} {1}\n', qubits[0], qubits[1])
-        return formatter.format('CPHASE({0}) {1} {2}\n', self._exponent,
+        return formatter.format('CPHASE({0}) {1} {2}\n', self._exponent * np.pi,
                                 qubits[0], qubits[1])
 
     def _has_stabilizer_effect_(self) -> Optional[bool]:

diff --git a/cirq/ops/parity_gates.py b/cirq/ops/parity_gates.py
@@ -100,8 +100,9 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
                formatter: 'cirq.QuilFormatter') -> Optional[str]:
         if self._exponent == 1:
             return formatter.format('X {0}\nX {1}\n', qubits[0], qubits[1])
-        return formatter.format('RX({0}) {1}\nRX({2}) {3}\n', self._exponent,
-                                qubits[0], self._exponent, qubits[1])
+        return formatter.format('RX({0}) {1}\nRX({2}) {3}\n',
+                                self._exponent * np.pi, qubits[0],
+                                self._exponent * np.pi, qubits[1])
 
     def __str__(self) -> str:
         if self.exponent == 1:
@@ -188,8 +189,9 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
         if self._exponent == 1:
             return formatter.format('Y {0}\nY {1}\n', qubits[0], qubits[1])
 
-        return formatter.format('RY({0}) {1}\nRY({2}) {3}\n', self._exponent,
-                                qubits[0], self._exponent, qubits[1])
+        return formatter.format('RY({0}) {1}\nRY({2}) {3}\n',
+                                self._exponent * np.pi, qubits[0],
+                                self._exponent * np.pi, qubits[1])
 
     def __str__(self) -> str:
         if self._exponent == 1:
@@ -269,8 +271,9 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
         if self._exponent == 1:
             return formatter.format('Z {0}\nZ {1}\n', qubits[0], qubits[1])
 
-        return formatter.format('RZ({0}) {1}\nRZ({2}) {3}\n', self._exponent,
-                                qubits[0], self._exponent, qubits[1])
+        return formatter.format('RZ({0}) {1}\nRZ({2}) {3}\n',
+                                self._exponent * np.pi, qubits[0],
+                                self._exponent * np.pi, qubits[1])
 
     def __str__(self) -> str:
         if self._exponent == 1:

diff --git a/cirq/ops/swap_gates.py b/cirq/ops/swap_gates.py
@@ -131,7 +131,7 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
                formatter: 'cirq.QuilFormatter') -> Optional[str]:
         if self._exponent == 1:
             return formatter.format('SWAP {0} {1}\n', qubits[0], qubits[1])
-        return formatter.format('PSWAP({0}) {1} {2}\n', self._exponent,
+        return formatter.format('PSWAP({0}) {1} {2}\n', self._exponent * np.pi,
                                 qubits[0], qubits[1])
 
     def __str__(self) -> str:
@@ -262,7 +262,8 @@ def _quil_(self, qubits: Tuple['cirq.Qid', ...],
                formatter: 'cirq.QuilFormatter') -> Optional[str]:
         if self._exponent == 1:
             return formatter.format('ISWAP {0} {1}\n', qubits[0], qubits[1])
-        return None  #ISwap with rotation not supported in Quil
+        return formatter.format('XY({0}) {1} {2}\n', self._exponent * np.pi,
+                                qubits[0], qubits[1])
 
 
 def riswap(rads: value.TParamVal) -> ISwapPowGate:

diff --git a/dev_tools/conf/pip-list-dev-tools.txt b/dev_tools/conf/pip-list-dev-tools.txt
@@ -14,6 +14,9 @@ mypy-protobuf==1.10
 # For uploading packages to pypi.
 twine
 
+# For verifying behavior of Quil output.
+pyquil~=2.21.0
+
 # For verifying behavior of qasm output.
 qiskit~=0.13.0