Add ECR gate

bqskit/ir/gates/__init__.py

@@ -23,6 +23,7 @@
     CXGate
     CYGate
     CZGate
+    ECRGate
     HGate
     IdentityGate
     ISwapGate

bqskit/ir/gates/constant/__init__.py

@@ -14,6 +14,7 @@
 from bqskit.ir.gates.constant.cx import CXGate
 from bqskit.ir.gates.constant.cy import CYGate
 from bqskit.ir.gates.constant.cz import CZGate
+from bqskit.ir.gates.constant.ecr import ECRGate
 from bqskit.ir.gates.constant.h import HGate
 from bqskit.ir.gates.constant.identity import IdentityGate
 from bqskit.ir.gates.constant.iswap import ISwapGate
@@ -57,6 +58,7 @@
     'CXGate',
     'CYGate',
     'CZGate',
+    'ECRGate',
     'HGate',
     'IdentityGate',
     'ISwapGate',

bqskit/ir/gates/constant/ecr.py

@@ -0,0 +1,50 @@
+"""This module implements the ECRGate."""
+from __future__ import annotations
+
+import math
+
+from bqskit.ir.gates.constantgate import ConstantGate
+from bqskit.ir.gates.qubitgate import QubitGate
+from bqskit.qis.unitary.unitarymatrix import UnitaryMatrix
+
+
+class ECRGate(ConstantGate, QubitGate):
+    """
+    The echoed cross-resonance gate (ECR).
+
+    The ECR gate is given by the following unitary:
+
+    .. math::
+
+        \\frac{1}{\\sqrt{2}}
+        \\begin{pmatrix}
+        0  & 1 & 0  & i \\\\
+        1  & 0 & -i & 0 \\\\
+        0  & i & 0  & 1 \\\\
+        -i & 0 & 1  & 0
+        \\end{pmatrix}
+    """
+    _name = 'ecr'
+    _num_qudits = 2
+    _qasm_name = 'ecr'
+    _utry = UnitaryMatrix([
+        [0, 0, 1 * 1 / math.sqrt(2), 1j * 1 / math.sqrt(2)],
+        [0, 0, 1j * 1 / math.sqrt(2), 1 * 1 / math.sqrt(2)],
+        [1 * 1 / math.sqrt(2), -1j * 1 / math.sqrt(2), 0, 0],
+        [-1j * 1 / math.sqrt(2), 1 * 1 / math.sqrt(2), 0, 0],
+    ])
+
+    def __init__(self) -> None:
+        pass
+
+    def get_qasm_gate_def(self) -> str:
+        qasm_rzx = (
+            'gate rzx(param0) q0,q1 {'
+            'h q1;'
+            'cx q0,q1;'
+            'rz(param0) q1;'
+            'cx q0,q1;'
+            'h q1; }'
+        )
+        qasm_ecr = 'gate ecr q0,q1 { rzx(pi/4) q0,q1; x q0; rzx(-pi/4) q0,q1; }'
+        return qasm_rzx + '\n' + qasm_ecr

bqskit/ir/lang/qasm2/visitor.py

@@ -28,6 +28,7 @@
 from bqskit.ir.gates.constant.cx import CXGate
 from bqskit.ir.gates.constant.cy import CYGate
 from bqskit.ir.gates.constant.cz import CZGate
+from bqskit.ir.gates.constant.ecr import ECRGate
 from bqskit.ir.gates.constant.h import HGate
 from bqskit.ir.gates.constant.identity import IdentityGate
 from bqskit.ir.gates.constant.iswap import ISwapGate
@@ -221,6 +222,7 @@ def fill_gate_defs(self) -> None:
         self.gate_defs['CX'] = GateDef('CX', 0, 2, CXGate())
         self.gate_defs['cy'] = GateDef('cy', 0, 2, CYGate())
         self.gate_defs['cz'] = GateDef('cz', 0, 2, CZGate())
+        self.gate_defs['ecr'] = GateDef('ecr', 0, 2, ECRGate())
         self.gate_defs['h'] = GateDef('h', 0, 1, HGate())
         self.gate_defs['id'] = GateDef('id', 0, 1, IdentityGate(1))
         self.gate_defs['u0'] = GateDef('u0', 0, 1, IdentityGate(1))

tests/ir/gates/constant/test_ecr.py

@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+import numpy as np
+
+from bqskit.ir.circuit import Circuit
+from bqskit.ir.gates import CXGate
+from bqskit.ir.gates import ECRGate
+from bqskit.ir.gates import HGate
+from bqskit.ir.gates import RZGate
+from bqskit.ir.gates import XGate
+from bqskit.ir.lang.qasm2 import OPENQASM2Language
+
+
+def test_ecr() -> None:
+    c = Circuit(2)
+    c.append_gate(HGate(), 1)
+    c.append_gate(CXGate(), (0, 1))
+    c.append_gate(RZGate(), 1, [np.pi / 4.0])
+    c.append_gate(CXGate(), (0, 1))
+    c.append_gate(HGate(), 1)
+
+    c.append_gate(XGate(), 0)
+
+    c.append_gate(HGate(), 1)
+    c.append_gate(CXGate(), (0, 1))
+    c.append_gate(RZGate(), 1, [-np.pi / 4.0])
+    c.append_gate(CXGate(), (0, 1))
+    c.append_gate(HGate(), 1)
+
+    assert c.get_unitary().get_distance_from(ECRGate().get_unitary()) < 3e-8
+
+
+def test_ecr_encode_decode() -> None:
+    c = Circuit(2)
+    c.append_gate(ECRGate(), (0, 1))
+
+    output_qasm = c.to('qasm')
+
+    resulting_circuit = OPENQASM2Language().decode(output_qasm)
+    assert resulting_circuit[0, 0].gate == ECRGate()

tests/ir/lang/test_qasm_decode.py

@@ -10,6 +10,7 @@
 from bqskit.ir.gates.barrier import BarrierPlaceholder
 from bqskit.ir.gates.circuitgate import CircuitGate
 from bqskit.ir.gates.constant.cx import CNOTGate
+from bqskit.ir.gates.constant.ecr import ECRGate
 from bqskit.ir.gates.measure import MeasurementPlaceholder
 from bqskit.ir.gates.parameterized.u1 import U1Gate
 from bqskit.ir.gates.parameterized.u1q import U1qGate
@@ -523,3 +524,14 @@ def test_U1Q_gate() -> None:
     assert circuit.num_operations == 2
     assert circuit[0, 0].gate == U1qGate()
     assert circuit[1, 0].gate == U1qGate()
+
+
+def test_ECR_gate() -> None:
+    input = """
+        OPENQASM 2.0;
+        qreg q[2];
+        ecr q[0],q[1];
+    """
+    circuit = OPENQASM2Language().decode(input)
+    assert circuit.num_operations == 1
+    assert circuit[0, 0].gate == ECRGate()