Merge pull request #121 from d-bharadwaj/add-more-twirl-gates

Extended the gate set for pauli twirling

qiskit_research/utils/pauli_twirling.py

@@ -11,29 +11,56 @@
 """Pauli twirling."""
 
 from typing import Any, Iterable, Optional
+import itertools
+import cmath
 
 import numpy as np
-from qiskit.circuit import QuantumRegister
+from qiskit.circuit import QuantumRegister, QuantumCircuit
 from qiskit.circuit.library import (
     IGate,
     XGate,
     YGate,
     ZGate,
+    CXGate,
+    CYGate,
+    CZGate,
+    CHGate,
+    CSGate,
+    DCXGate,
+    CSXGate,
+    CSdgGate,
+    ECRGate,
+    iSwapGate,
+    SwapGate,
 )
 from qiskit.dagcircuit import DAGCircuit
 from qiskit.transpiler.basepasses import BasePass, TransformationPass
 from qiskit.transpiler.passes import (
     CXCancellation,
     Optimize1qGatesDecomposition,
 )
-from qiskit.quantum_info import Pauli, pauli_basis
+from qiskit.quantum_info import Pauli, Operator, pauli_basis
 from qiskit_research.utils.pulse_scaling import BASIS_GATES
 
+# Single qubit Pauli gates
 I = IGate()
 X = XGate()
 Y = YGate()
 Z = ZGate()
 
+# 2Q entangling gates
+CX = CXGate()  # cnot; controlled-X
+CY = CYGate()  # controlled-Y
+CZ = CZGate()  # controlled-Z
+CH = CHGate()  # controlled-Hadamard
+CS = CSGate()  # controlled-S
+DCX = DCXGate()  # double cnot
+CSX = CSXGate()  # controlled sqrt X
+CSdg = CSdgGate()  # controlled S^dagger
+ECR = ECRGate()  # echoed cross-resonance
+Swap = SwapGate()  # swap
+iSwap = iSwapGate()  # imaginary swap
+
 # this list consists of the 2-qubit rotation gates
 TWO_QUBIT_PAULI_GENERATORS = {
     "rxx": Pauli("XX"),
@@ -43,31 +70,92 @@
     "secr": Pauli("XZ"),
 }
 
+
+def match_global_phase(a, b):
+    """Phase the given arrays so that their phases match at one entry.
+
+    Args:
+        a: A Numpy array.
+        b: Another Numpy array.
+
+    Returns:
+        A pair of arrays (a', b') that are equal if and only if a == b * exp(i phi)
+        for some real number phi.
+    """
+    if a.shape != b.shape:
+        return a, b
+    # use the largest entry of one of the matrices to maximize precision
+    index = max(np.ndindex(*a.shape), key=lambda i: abs(b[i]))
+    phase_a = cmath.phase(a[index])
+    phase_b = cmath.phase(b[index])
+    return a * cmath.rect(1, -phase_a), b * cmath.rect(1, -phase_b)
+
+
+def allclose_up_to_global_phase(a, b, rtol=1e-05, atol=1e-08, equal_nan=False):
+    """Check if two operators are close up to a global phase."""
+    # Phase both operators to match their phases
+    phased_op1, phased_op2 = match_global_phase(a, b)
+    return np.allclose(phased_op1, phased_op2, rtol, atol, equal_nan)
+
+
+def create_pauli_twirling_sets(two_qubit_gate):
+    """Generate the Pauli twirling sets for a given 2Q gate.
+
+    Sets are ordered such that gate[0] and gate[1] are pre-rotations
+    applied to control and target, respectively. gate[2] and gate[3]
+    are post-rotations for control and target, respectively.
+
+    Parameters:
+        two_qubit_gate (Gate): Input two-qubit gate
+
+    Returns:
+        tuple: Tuple of all twirling gate sets
+    """
+
+    target_unitary = np.array(two_qubit_gate)
+    twirling_sets = []
+
+    # Generate combinations of 4 gates from the operator list
+    for gates in itertools.product(itertools.product([I, X, Y, Z], repeat=2), repeat=2):
+        qc = _build_twirl_circuit(gates, two_qubit_gate)
+        qc_array = Operator.from_circuit(qc).to_matrix()
+        if allclose_up_to_global_phase(qc_array, target_unitary):
+            twirling_sets.append(gates)
+
+    return tuple(twirling_sets)
+
+
+def _build_twirl_circuit(gates, two_qubit_gate):
+    """Build the twirled quantum circuit with specified gates."""
+    qc = QuantumCircuit(2)
+
+    qc.append(gates[0][0], [0])
+    qc.append(gates[0][1], [1])
+    qc.append(two_qubit_gate, [0, 1])
+    qc.append(gates[1][0], [0])
+    qc.append(gates[1][1], [1])
+
+    return qc
+
+
 # this dictionary stores the twirl sets for each supported gate
 # each key is the name of a supported gate
 # each value is a tuple that represents the twirl set for the gate
 # the twirl set is a list of (before, after) pairs describing twirl gates
 # "before" and "after" are tuples of single-qubit gates to be applied
 # before and after the gate to be twirled
 TWIRL_GATES = {
-    "cx": (
-        ((I, I), (I, I)),
-        ((I, X), (I, X)),
-        ((I, Y), (Z, Y)),
-        ((I, Z), (Z, Z)),
-        ((X, I), (X, X)),
-        ((X, X), (X, I)),
-        ((X, Y), (Y, Z)),
-        ((X, Z), (Y, Y)),
-        ((Y, I), (Y, X)),
-        ((Y, X), (Y, I)),
-        ((Y, Y), (X, Z)),
-        ((Y, Z), (X, Y)),
-        ((Z, I), (Z, I)),
-        ((Z, X), (Z, X)),
-        ((Z, Y), (I, Y)),
-        ((Z, Z), (I, Z)),
-    ),
+    "cx": create_pauli_twirling_sets(CX),
+    "cy": create_pauli_twirling_sets(CY),
+    "cz": create_pauli_twirling_sets(CZ),
+    "ch": create_pauli_twirling_sets(CH),
+    "cs": create_pauli_twirling_sets(CS),
+    "dcx": create_pauli_twirling_sets(DCX),
+    "csx": create_pauli_twirling_sets(CSX),
+    "csdg": create_pauli_twirling_sets(CSdg),
+    "ecr": create_pauli_twirling_sets(ECR),
+    "swap": create_pauli_twirling_sets(Swap),
+    "iswap": create_pauli_twirling_sets(iSwap),
 }
 
 

test/utils/test_pauli_twirling.py

@@ -14,7 +14,19 @@
 
 import numpy as np
 from qiskit.circuit import Parameter, QuantumCircuit
-from qiskit.circuit.library import CXGate
+from qiskit.circuit.library import (
+    CXGate,
+    CYGate,
+    CZGate,
+    CHGate,
+    CSGate,
+    DCXGate,
+    CSXGate,
+    CSdgGate,
+    ECRGate,
+    iSwapGate,
+    SwapGate,
+)
 from qiskit.quantum_info import Operator
 from qiskit_research.utils.convenience import add_pauli_twirls
 from qiskit_research.utils.gates import SECRGate
@@ -27,6 +39,7 @@ class TestPauliTwirling(unittest.TestCase):
     def test_twirl_gates_cnot(self):
         """Test twirling CNOT."""
         twirl_gates = TWIRL_GATES["cx"]
+        self.assertEqual(len(twirl_gates), 16)
         operator = Operator(CXGate())
         for (a, b), (c, d) in twirl_gates:
             circuit = QuantumCircuit(2)
@@ -37,6 +50,146 @@ def test_twirl_gates_cnot(self):
             circuit.append(d, [1])
             self.assertTrue(Operator(circuit).equiv(operator))
 
+    def test_twirl_gates_cy(self):
+        """Test twirling CY"""
+        twirl_gates = TWIRL_GATES["cy"]
+        self.assertEqual(len(twirl_gates), 16)
+        operator = Operator(CYGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(CYGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
+    def test_twirl_gates_cz(self):
+        """Test twirling CZ."""
+        twirl_gates = TWIRL_GATES["cz"]
+        self.assertEqual(len(twirl_gates), 16)
+        operator = Operator(CZGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(CZGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
+    def test_twirl_gates_ch(self):
+        """Test twirling CH."""
+        twirl_gates = TWIRL_GATES["ch"]
+        self.assertEqual(len(twirl_gates), 4)
+        operator = Operator(CHGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(CHGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
+    def test_twirl_gates_cs(self):
+        """Test twirling CS."""
+        twirl_gates = TWIRL_GATES["cs"]
+        self.assertEqual(len(twirl_gates), 4)
+        operator = Operator(CSGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(CSGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
+    def test_twirl_gates_dcx(self):
+        """Test twirling DCX."""
+        twirl_gates = TWIRL_GATES["dcx"]
+        self.assertEqual(len(twirl_gates), 16)
+        operator = Operator(DCXGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(DCXGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
+    def test_twirl_gates_csx(self):
+        """Test twirling CSX."""
+        twirl_gates = TWIRL_GATES["csx"]
+        self.assertEqual(len(twirl_gates), 4)
+        operator = Operator(CSXGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(CSXGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
+    def test_twirl_gates_csdg(self):
+        """Test twirling CSdg."""
+        twirl_gates = TWIRL_GATES["csdg"]
+        self.assertEqual(len(twirl_gates), 4)
+        operator = Operator(CSdgGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(CSdgGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
+    def test_twirl_gates_ecr(self):
+        """Test twirling ECR."""
+        twirl_gates = TWIRL_GATES["ecr"]
+        self.assertEqual(len(twirl_gates), 16)
+        operator = Operator(ECRGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(ECRGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
+    def test_twirl_gates_swap(self):
+        """Test twirling Swap."""
+        twirl_gates = TWIRL_GATES["swap"]
+        self.assertEqual(len(twirl_gates), 16)
+        operator = Operator(SwapGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(SwapGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
+    def test_twirl_gates_iswap(self):
+        """Test twirling iSwap."""
+        twirl_gates = TWIRL_GATES["iswap"]
+        self.assertEqual(len(twirl_gates), 16)
+        operator = Operator(iSwapGate())
+        for (a, b), (c, d) in twirl_gates:
+            circuit = QuantumCircuit(2)
+            circuit.append(a, [0])
+            circuit.append(b, [1])
+            circuit.append(iSwapGate(), [0, 1])
+            circuit.append(c, [0])
+            circuit.append(d, [1])
+            self.assertTrue(Operator(circuit).equiv(operator))
+
     def test_add_pauli_twirls(self):
         """Test adding Pauli twirls."""
         rng = np.random.default_rng()