Update trotter.py

paddle_quantum/trotter.py

@@ -18,6 +18,7 @@ Trotter Hamiltonian time evolution circuit module
 
 from paddle_quantum.utils import Hamiltonian
 from paddle_quantum.circuit import UAnsatz
+from collections import defaultdict
 import warnings
 import numpy as np
 import re
@@ -259,11 +260,14 @@ def __add_first_order_trotter_block(circuit, tau, grouped_hamiltonian, reverse=F
             assert isinstance(hamiltonian, Hamiltonian)
             # decompose the Hamiltonian into 3 lists
             coeffs, pauli_words, sites = hamiltonian.decompose_with_sites()
-            # apply rotational gate of each term
-            for term_index in range(len(coeffs)):
-                # get the sorted pauli_word and site (an array of qubit indices) according to their qubit indices
-                pauli_word, site = __sort_pauli_word(pauli_words[term_index], sites[term_index])
-                add_n_pauli_gate(circuit, 2 * tau * coeffs[term_index], pauli_word, site)
+            if pauli_words==['XX','YY','ZZ']:
+                optimal_circuit(circuit,[tau*i for i in coeffs],sites[0])
+            else:
+                # apply rotational gate of each term
+                for term_index in range(len(coeffs)):
+                    # get the sorted pauli_word and site (an array of qubit indices) according to their qubit indices
+                    pauli_word, site = __sort_pauli_word(pauli_words[term_index], sites[term_index])
+                    add_n_pauli_gate(circuit, 2 * tau * coeffs[term_index], pauli_word, site)
     # in the reverse mode, if the Hamiltonian is a single element list, reverse the order its each term
     else:
         if len(grouped_hamiltonian) == 1:
@@ -388,7 +392,65 @@ def add_n_pauli_gate(circuit, theta, pauli_word, which_qubits):
                 circuit.h(which_qubits[qubit_index])
             elif re.match(r'Y', pauli_word[qubit_index], flags=re.I):
                 circuit.rx(- PI / 2, which_qubits[qubit_index])
+                
+def add_optimal_circuit(circuit,theta,which_qubits):
+    r""" 添加一个优化电路，哈密顿量为'XXYYZZ'`
+
+    Args:
+        circuit (UAnsatz): 需要添加门的电路
+        theta list(tensor or float): 旋转角度需要传入三个参数
+        which_qubits (list or np.ndarray): ``pauli_word`` 中的每个算符所作用的量子比特编号
+    """
+    p = np.pi/2
+    x,y,z = theta
+    alpha = paddle.to_tensor(3*p-4*x*p+2*x,dtype='float64')
+    beta = paddle.to_tensor(-3*p+4*y*p-2*y,dtype='float64')
+    gamma = paddle.to_tensor(2*z-p,dtype='float64')
+    which_qubits.sort()
+    a,b = which_qubits
+    circuit.rz(paddle.to_tensor(p,dtype='float64'),b)
+    circuit.cnot([b,a])
+    circuit.rz(gamma,a)
+    circuit.ry(alpha,b)
+    circuit.cnot([a,b])
+    circuit.ry(beta,b)
+    circuit.cnot([b,a])
+    circuit.rz(paddle.to_tensor(-p,dtype='float64'),a)
+
+def __group_hamiltonian_optimal(hamiltonian):
+    r""" 将哈密顿量拆分成 XXYYZZ 为组合，以及剩余项两个部分，并返回由他们组成的列表
+
+    Args:
+        hamiltonian (Hamiltonian): Paddle Quantum 中的 Hamiltonian 类
+
+    Notes:
+       X0,X1,Y0,Y1,Z0,Z1以及X1,X2,Y1,Y2,Z1,Z2会被分成两组XXYYZZ，且他们的site都要一样。以及其他剩余项
+    """
+    grouped_hamiltonian = []
+    coeffs, pauli_words, sites = hamiltonian.decompose_with_sites()
+    grouped_terms_indices = []
+    left_over_terms_indices = []
+    d = defaultdict(list)
+    for term_index in range(len(coeffs)):
+        site = sites[term_index]
+        pauli_word = pauli_words[term_index]
+        #print(pauli_word)
+        for pauli in ['XX', 'YY', 'ZZ']:
+            assert isinstance(pauli_word, str), "Each pauli word should be a string type"
+            if (pauli_word==pauli or pauli_word==pauli.lower()):
+                d[tuple(site)].append((pauli,term_index))
+                if len(d[tuple(site)])==3:
+                    terms_indices_to_be_grouped = [x[1] for x in d[tuple(site)]]
+                    grouped_terms_indices.extend(terms_indices_to_be_grouped)
+                    grouped_hamiltonian.append(hamiltonian[terms_indices_to_be_grouped])
 
+    for term_index in range(len(coeffs)):
+        if term_index not in grouped_terms_indices:
+            left_over_terms_indices.append(term_index)
+    if len(left_over_terms_indices):
+        for term_index in left_over_terms_indices:
+            grouped_hamiltonian.append(hamiltonian[term_index])
+    return grouped_hamiltonian
 
 def __group_hamiltonian_xyz(hamiltonian):
     r""" 将哈密顿量拆分成 X、Y、Z 以及剩余项四个部分，并返回由他们组成的列表