Merge pull request #78 from UCL-CCS/haar_random

haar random quantum state and Pauliword op functionality added

notebooks/Chemistry usage.ipynb

@@ -6276,7 +6276,7 @@
  ],
  "metadata": {
  "kernelspec": {
- "display_name": "Python 3.8.10 64-bit",
+ "display_name": "Python 3 (ipykernel)",
  "language": "python",
  "name": "python3"
  },
@@ -6290,7 +6290,7 @@
  "name": "python",
  "nbconvert_exporter": "python",
  "pygments_lexer": "ipython3",
- "version": "3.8.10"
+ "version": "3.9.7"
  },
  "vscode": {
  "interpreter": {

symmer/symplectic/base.py

@@ -11,6 +11,7 @@
 from openfermion import QubitOperator
 from qiskit.quantum_info import Pauli
 from qiskit.opflow import PauliOp, PauliSumOp
+from scipy.stats import unitary_group
 import warnings
 warnings.simplefilter('always', UserWarning)
 
@@ -63,6 +64,22 @@ def random(cls,
  coeff_vec += 1j * np.random.randn(n_terms)
  return cls(symp_matrix, coeff_vec)
 
+ @classmethod
+ def haar_random(cls,
+ n_qubits: int,
+ ) -> "PauliwordOp":
+ """ Generate a Haar random U(N) matrix (N^n_qubits) as a linear combination of Pauli operators.
+ aka generate a uniform random unitary from a Hilbert space.
+
+ Args:
+ n_qubits: number of qubits
+ Returns:
+ p_random (PauliwordOp): Haar random matrix in Pauli basis
+ """
+ haar_matrix = unitary_group.rvs(2**n_qubits)
+ p_random = cls.from_matrix(haar_matrix)
+ return p_random
+
  @classmethod
  def from_list(cls, 
  pauli_terms :List[str], 
@@ -846,6 +863,31 @@ def copy(self) -> "QuantumState":
  """
  return deepcopy(self)
 
+ @classmethod
+ def haar_random(cls,
+ n_qubits: int,
+ vec_type: str) -> "QuantumState":
+ """
+ Generate a Haar random quantum state - (uniform random quantum state).
+
+ Args:
+ n_qubits: number of qubits
+ vec_type (str): bra or ket
+
+ Returns:
+ qstate_random (QuantumState): Haar random quantum state
+
+ """
+ if vec_type=='ket':
+ haar_vec = (unitary_group.rvs(2**n_qubits)[:,0]).reshape([-1, 1])
+ elif vec_type == 'bra':
+ haar_vec = (unitary_group.rvs(2**n_qubits)[0,:]).reshape([1, -1])
+ else:
+ raise ValueError(f'vector type: {vec_type} unkown')
+
+ qstate_random = cls.from_array(haar_vec)
+ return qstate_random
+
  def __str__(self) -> str:
  """ 
  Defines the print behaviour of QuantumState - differs depending on vec_type