Pending-deprecate library circuits with gate representations

qiskit/circuit/library/__init__.py

@@ -152,12 +152,12 @@
 
 .. code-block::
 
-    from qiskit.circuit.library import Diagonal
+    from qiskit.circuit.library import DiagonalGate
 
-    diagonal = Diagonal([1, 1])
+    diagonal = DiagonalGate([1, 1j])
     print(diagonal.num_qubits)
 
-    diagonal = Diagonal([1, 1, 1, 1])
+    diagonal = DiagonalGate([1, 1, 1, -1])
     print(diagonal.num_qubits)
 
 .. code-block:: text

qiskit/circuit/library/basis_change/qft.py

@@ -13,10 +13,10 @@
 """Define a Quantum Fourier Transform circuit (QFT) and a native gate (QFTGate)."""
 
 from __future__ import annotations
-import warnings
 import numpy as np
 
-from qiskit.circuit.quantumcircuit import QuantumCircuit, QuantumRegister, CircuitInstruction, Gate
+from qiskit.circuit.quantumcircuit import QuantumRegister, CircuitInstruction, Gate
+from qiskit.utils.deprecation import deprecate_func
 from ..blueprintcircuit import BlueprintCircuit
 
 
@@ -72,6 +72,14 @@ class QFT(BlueprintCircuit):
 
     """
 
+    @deprecate_func(
+        since="1.3",
+        additional_msg=(
+            "Use qiskit.circuit.library.QFTGate or qiskit.synthesis.qft.synth_qft_full instead, "
+            "for access to all previous arguments.",
+        ),
+        pending=True,
+    )
     def __init__(
         self,
         num_qubits: int | None = None,
@@ -232,30 +240,13 @@ def inverse(self, annotated: bool = False) -> "QFT":
         inverted._inverse = not self._inverse
         return inverted
 
-    def _warn_if_precision_loss(self):
-        """Issue a warning if constructing the circuit will lose precision.
-
-        If we need an angle smaller than ``pi * 2**-1022``, we start to lose precision by going into
-        the subnormal numbers.  We won't lose _all_ precision until an exponent of about 1075, but
-        beyond 1022 we're using fractional bits to represent leading zeros."""
-        max_num_entanglements = self.num_qubits - self.approximation_degree - 1
-        if max_num_entanglements > -np.finfo(float).minexp:  # > 1022 for doubles.
-            warnings.warn(
-                "precision loss in QFT."
-                f" The rotation needed to represent {max_num_entanglements} entanglements"
-                " is smaller than the smallest normal floating-point number.",
-                category=RuntimeWarning,
-                stacklevel=3,
-            )
-
     def _check_configuration(self, raise_on_failure: bool = True) -> bool:
         """Check if the current configuration is valid."""
         valid = True
         if self.num_qubits is None:
             valid = False
             if raise_on_failure:
                 raise AttributeError("The number of qubits has not been set.")
-        self._warn_if_precision_loss()
         return valid
 
     def _build(self) -> None:
@@ -270,25 +261,16 @@ def _build(self) -> None:
         if num_qubits == 0:
             return
 
-        circuit = QuantumCircuit(*self.qregs, name=self.name)
-        for j in reversed(range(num_qubits)):
-            circuit.h(j)
-            num_entanglements = max(0, j - max(0, self.approximation_degree - (num_qubits - j - 1)))
-            for k in reversed(range(j - num_entanglements, j)):
-                # Use negative exponents so that the angle safely underflows to zero, rather than
-                # using a temporary variable that overflows to infinity in the worst case.
-                lam = np.pi * (2.0 ** (k - j))
-                circuit.cp(lam, j, k)
-
-            if self.insert_barriers:
-                circuit.barrier()
-
-        if self._do_swaps:
-            for i in range(num_qubits // 2):
-                circuit.swap(i, num_qubits - i - 1)
-
-        if self._inverse:
-            circuit = circuit.inverse()
+        from qiskit.synthesis.qft import synth_qft_full
+
+        circuit = synth_qft_full(
+            num_qubits,
+            do_swaps=self._do_swaps,
+            insert_barriers=self._insert_barriers,
+            approximation_degree=self._approximation_degree,
+            inverse=self._inverse,
+            name=self.name,
+        )
 
         wrapped = circuit.to_instruction() if self.insert_barriers else circuit.to_gate()
         self.compose(wrapped, qubits=self.qubits, inplace=True)

qiskit/circuit/library/fourier_checking.py

@@ -18,7 +18,7 @@
 from qiskit.circuit import QuantumCircuit
 from qiskit.circuit.exceptions import CircuitError
 
-from .generalized_gates.diagonal import Diagonal
+from .generalized_gates.diagonal import DiagonalGate
 
 
 class FourierChecking(QuantumCircuit):
@@ -85,11 +85,11 @@ def __init__(self, f: List[int], g: List[int]) -> None:
 
         circuit.h(circuit.qubits)
 
-        circuit.compose(Diagonal(f), inplace=True)
+        circuit.append(DiagonalGate(f), circuit.qubits)
 
         circuit.h(circuit.qubits)
 
-        circuit.compose(Diagonal(g), inplace=True)
+        circuit.append(DiagonalGate(g), circuit.qubits)
 
         circuit.h(circuit.qubits)
 

qiskit/circuit/library/generalized_gates/diagonal.py

@@ -23,26 +23,37 @@
 from qiskit.circuit.gate import Gate
 from qiskit.circuit.quantumcircuit import QuantumCircuit
 from qiskit.circuit.exceptions import CircuitError
+from qiskit.circuit.annotated_operation import AnnotatedOperation, InverseModifier
+from qiskit.utils.deprecation import deprecate_func
 
 from .ucrz import UCRZGate
 
 _EPS = 1e-10
 
 
 class Diagonal(QuantumCircuit):
-    r"""Diagonal circuit.
+    """Circuit implementing a diagonal transformation."""
 
-    Circuit symbol:
+    @deprecate_func(since="1.3", additional_msg="Use DiagonalGate instead.", pending=True)
+    def __init__(self, diag: Sequence[complex]) -> None:
+        r"""
+        Args:
+            diag: List of the :math:`2^k` diagonal entries (for a diagonal gate on :math:`k` qubits).
+
+        Raises:
+            CircuitError: if the list of the diagonal entries or the qubit list is in bad format;
+                if the number of diagonal entries is not :math:`2^k`, where :math:`k` denotes the
+                number of qubits.
+        """
+        DiagonalGate._check_input(diag)
+        num_qubits = int(math.log2(len(diag)))
+
+        super().__init__(num_qubits, name="Diagonal")
+        self.append(DiagonalGate(diag), self.qubits)
 
-    .. code-block:: text
 
-             ┌───────────┐
-        q_0: ┤0          ├
-             │           │
-        q_1: ┤1 Diagonal ├
-             │           │
-        q_2: ┤2          ├
-             └───────────┘
+class DiagonalGate(Gate):
+    r"""A generic diagonal quantum gate.
 
     Matrix form:
 
@@ -80,67 +91,36 @@ class Diagonal(QuantumCircuit):
     def __init__(self, diag: Sequence[complex]) -> None:
         r"""
         Args:
-            diag: List of the :math:`2^k` diagonal entries (for a diagonal gate on :math:`k` qubits).
-
-        Raises:
-            CircuitError: if the list of the diagonal entries or the qubit list is in bad format;
-                if the number of diagonal entries is not :math:`2^k`, where :math:`k` denotes the
-                number of qubits.
+            diag: list of the :math:`2^k` diagonal entries (for a diagonal gate on :math:`k` qubits).
         """
         self._check_input(diag)
         num_qubits = int(math.log2(len(diag)))
 
-        circuit = QuantumCircuit(num_qubits, name="Diagonal")
+        super().__init__("diagonal", num_qubits, diag)
 
+    def _define(self):
         # Since the diagonal is a unitary, all its entries have absolute value
         # one and the diagonal is fully specified by the phases of its entries.
-        diag_phases = [cmath.phase(z) for z in diag]
-        n = len(diag)
+        diag_phases = [cmath.phase(z) for z in self.params]
+        n = len(diag_phases)
+        circuit = QuantumCircuit(self.num_qubits)
+
         while n >= 2:
             angles_rz = []
             for i in range(0, n, 2):
                 diag_phases[i // 2], rz_angle = _extract_rz(diag_phases[i], diag_phases[i + 1])
                 angles_rz.append(rz_angle)
             num_act_qubits = int(math.log2(n))
-            ctrl_qubits = list(range(num_qubits - num_act_qubits + 1, num_qubits))
-            target_qubit = num_qubits - num_act_qubits
+            ctrl_qubits = list(range(self.num_qubits - num_act_qubits + 1, self.num_qubits))
+            target_qubit = self.num_qubits - num_act_qubits
 
             ucrz = UCRZGate(angles_rz)
             circuit.append(ucrz, [target_qubit] + ctrl_qubits)
 
             n //= 2
         circuit.global_phase += diag_phases[0]
 
-        super().__init__(num_qubits, name="Diagonal")
-        self.append(circuit.to_gate(), self.qubits)
-
-    @staticmethod
-    def _check_input(diag):
-        """Check if ``diag`` is in valid format."""
-        if not isinstance(diag, (list, np.ndarray)):
-            raise CircuitError("Diagonal entries must be in a list or numpy array.")
-        num_qubits = math.log2(len(diag))
-        if num_qubits < 1 or not num_qubits.is_integer():
-            raise CircuitError("The number of diagonal entries is not a positive power of 2.")
-        if not np.allclose(np.abs(diag), 1, atol=_EPS):
-            raise CircuitError("A diagonal element does not have absolute value one.")
-
-
-class DiagonalGate(Gate):
-    """Gate implementing a diagonal transformation."""
-
-    def __init__(self, diag: Sequence[complex]) -> None:
-        r"""
-        Args:
-            diag: list of the :math:`2^k` diagonal entries (for a diagonal gate on :math:`k` qubits).
-        """
-        Diagonal._check_input(diag)
-        num_qubits = int(math.log2(len(diag)))
-
-        super().__init__("diagonal", num_qubits, diag)
-
-    def _define(self):
-        self.definition = Diagonal(self.params).decompose()
+        self.definition = circuit
 
     def validate_parameter(self, parameter):
         """Diagonal Gate parameter should accept complex
@@ -152,8 +132,22 @@ def validate_parameter(self, parameter):
 
     def inverse(self, annotated: bool = False):
         """Return the inverse of the diagonal gate."""
+        if annotated:
+            return AnnotatedOperation(self.copy(), InverseModifier)
+
         return DiagonalGate([np.conj(entry) for entry in self.params])
 
+    @staticmethod
+    def _check_input(diag):
+        """Check if ``diag`` is in valid format."""
+        if not isinstance(diag, (list, np.ndarray)):
+            raise CircuitError("Diagonal entries must be in a list or numpy array.")
+        num_qubits = math.log2(len(diag))
+        if num_qubits < 1 or not num_qubits.is_integer():
+            raise CircuitError("The number of diagonal entries is not a positive power of 2.")
+        if not np.allclose(np.abs(diag), 1, atol=_EPS):
+            raise CircuitError("A diagonal element does not have absolute value one.")
+
 
 def _extract_rz(phi1, phi2):
     """

qiskit/circuit/library/generalized_gates/gms.py

@@ -15,13 +15,16 @@
 Global Mølmer–Sørensen gate.
 """
 
-from typing import Union, List
+from __future__ import annotations
+from collections.abc import Sequence
 
 import numpy as np
 from qiskit.circuit.quantumcircuit import QuantumCircuit
 from qiskit.circuit.quantumregister import QuantumRegister
+from qiskit.circuit.parameterexpression import ParameterValueType
 from qiskit.circuit.library.standard_gates import RXXGate
 from qiskit.circuit.gate import Gate
+from qiskit.utils.deprecation import deprecate_func
 
 
 class GMS(QuantumCircuit):
@@ -74,7 +77,8 @@ class GMS(QuantumCircuit):
     `arXiv:1707.06356 <https://arxiv.org/abs/1707.06356>`_
     """
 
-    def __init__(self, num_qubits: int, theta: Union[List[List[float]], np.ndarray]) -> None:
+    @deprecate_func(since="1.3", additional_msg="Use the MSGate instead.", pending=True)
+    def __init__(self, num_qubits: int, theta: list[list[float]] | np.ndarray) -> None:
         """Create a new Global Mølmer–Sørensen (GMS) gate.
 
         Args:
@@ -94,28 +98,77 @@ def __init__(self, num_qubits: int, theta: Union[List[List[float]], np.ndarray])
 
 
 class MSGate(Gate):
-    """MSGate has been deprecated.
-    Please use ``GMS`` in ``qiskit.circuit.generalized_gates`` instead.
+    r"""The Mølmer–Sørensen gate.
 
-    Global Mølmer–Sørensen gate.
+    The Mølmer–Sørensen gate is native to ion-trap systems. The global MS
+    can be applied to multiple ions to entangle multiple qubits simultaneously [1].
 
-    The Mølmer–Sørensen gate is native to ion-trap systems. The global MS can be
-    applied to multiple ions to entangle multiple qubits simultaneously.
+    In the two-qubit case, this is equivalent to an XX interaction,
+    and is thus reduced to the :class:`.RXXGate`. The global MS gate is a sum of XX
+    interactions on all pairs [2].
 
-    In the two-qubit case, this is equivalent to an XX(theta) interaction,
-    and is thus reduced to the RXXGate.
+    .. math::
+
+        MS(\chi_{12}, \chi_{13}, ..., \chi_{n-1 n}) =
+        exp(-i \sum_{i=1}^{n} \sum_{j=i+1}^{n} X{\otimes}X \frac{\chi_{ij}}{2})
+
+    Example::
+
+        import numpy as np
+        from qiskit.circuit.library import MSGate
+        from qiskit.quantum_info import Operator
+
+        gate = MSGate(num_qubits=3, theta=[[0, np.pi/4, np.pi/8],
+                                           [0, 0, np.pi/2],
+                                           [0, 0, 0]])
+        print(Operator(gate))
+
+
+    **References:**
+
+    [1] Sørensen, A. and Mølmer, K., Multi-particle entanglement of hot trapped ions.
+    Physical Review Letters. 82 (9): 1835–1838.
+    `arXiv:9810040 <https://arxiv.org/abs/quant-ph/9810040>`_
+
+    [2] Maslov, D. and Nam, Y., Use of global interactions in efficient quantum circuit
+    constructions. New Journal of Physics, 20(3), p.033018.
+    `arXiv:1707.06356 <https://arxiv.org/abs/1707.06356>`_
     """
 
-    def __init__(self, num_qubits, theta, label=None):
-        """Create new MS gate."""
+    def __init__(
+        self,
+        num_qubits: int,
+        theta: ParameterValueType | Sequence[Sequence[ParameterValueType]],
+        label: str | None = None,
+    ):
+        """
+        Args:
+            num_qubits: The number of qubits the MS gate acts on.
+            theta: The XX rotation angles. If a single value, the same angle is used on all
+                interactions. Alternatively an upper-triangular, square matrix with width
+                ``num_qubits`` can be provided with interaction angles for each qubit pair.
+            label: A gate label.
+        """
         super().__init__("ms", num_qubits, [theta], label=label)
 
     def _define(self):
-        theta = self.params[0]
-        q = QuantumRegister(self.num_qubits, "q")
+        thetas = self.params[0]
+        q = QuantumRegister(self.num_qubits, name="q")
         qc = QuantumCircuit(q, name=self.name)
         for i in range(self.num_qubits):
             for j in range(i + 1, self.num_qubits):
+                # if theta was just a single angle, use that, otherwise use the correct index
+                theta = thetas if isinstance(thetas, ParameterValueType) else thetas[i][j]
                 qc._append(RXXGate(theta), [q[i], q[j]], [])
 
         self.definition = qc
+
+    def validate_parameter(self, parameter):
+        if isinstance(parameter, Sequence):
+            # pylint: disable=super-with-arguments
+            return [
+                [super(MSGate, self).validate_parameter(theta) for theta in row]
+                for row in parameter
+            ]
+
+        return super().validate_parameter(parameter)