Merge branch 'dev' into nlocal

Author: Hanrui-Wang

examples/grover/README.md

@@ -0,0 +1,8 @@
+# Grover's Search Algorithm
+
+Grover's Search Algorithm [1] is an algorithm which can speed up an unstructured search problem quadratically using amplitude amplification. A detailed walkthrough can be found [here](https://quantum-computing.ibm.com/composer/docs/iqx/guide/grovers-algorithm). The file `grover_example_sudoku.py` provides an example of how to use the algorithm to solve a sudoku puzzle of size 2x2.
+
+
+## References
+
+1. Grover, Lov K.. “A fast quantum mechanical algorithm for database search.” Symposium on the Theory of Computing (1996).

examples/grover/grover_example_sudoku.py

@@ -0,0 +1,93 @@
+""" 
+This example is based on Qiskt's Texbook: https://learn.qiskit.org/course/ch-algorithms/grovers-algorithm#sudoku
+
+We will now tackle a 2x2 binary sudoku problem using Grover's algorithm,  where we don't necessarily possess 
+prior knowledge of the solution. The problem adheres to two simple rules:
+
+1. No column can have the same value repeated.
+2. No row can have the same value repeated.
+
+We will use the following 4 variables:
+
+---------
+| a | b |
+---------
+| c | d |
+---------
+
+Please keep in mind that while utilizing Grover's algorithm to solve this particular problem may not be practical 
+(as the solution can likely be determined mentally), the intention of this example is to showcase the process of 
+transforming classical decision problems into oracles suitable for Grover's algorithm.
+
+We need to check for four conditions:
+
+1. a != b
+2. c != d
+3. a != c
+4. b != d
+"""
+
+import torchquantum as tq
+from torchquantum.algorithms import Grover
+
+
+# To simplify the process, we can compile this set of comparisons into a list of clauses for convenience.
+clauses = [ [0, 1], [0, 2], [1, 3], [2, 3] ]
+
+# This circuit checks if input0 is equal to input1 and stores the output in output. 
+# The output of each comparison is stored in a new bit.
+def XOR(input0, input1, output):
+    op1 = {'name': 'cnot', 'wires': [input0, output]}
+    op2 = {'name': 'cnot', 'wires': [input1, output]}
+    return [op1, op2]
+    
+# To verify each clause, we repeat the above circuit for every pairing in the `clauses`. 
+ops = []
+clause_qubits = [4, 5, 6, 7]
+for i, clause in enumerate(clauses):
+	ops += XOR(clause[0], clause[1], clause_qubits[i])
+
+# To determine if the assignments of a, b, c, d are a solution to the sudoku, we examine the final state 
+# of the `clause_qubits`. Only when all of these qubits are 1, it indicates that the clauses are satisfied. 
+# To achieve this, we incorporate a multi-controlled Toffoli gate in our checking circuit. This gate 
+# ensures that a single output bit will be set to 1 if and only if all the clauses are satisfied, 
+# allowing us to easily determine if our assignment is a solution.
+ops += [{'name': 'multicnot', 'n_wires': 5, 'wires': [4,5,6,7,8]}]
+
+# In order to transform our checking circuit into a Grover oracle, it is crucial to ensure that the `clause_qubits` 
+# are always returned to their initial state after the computation. This guarantees that `clause_qubits` are all 
+# set to 0 once our circuit has finished running. To achieve this, we include a step called "uncomputation" 
+# where we repeat the segment of the circuit that computes the clauses. This uncomputation step ensures the 
+# desired state restoration, enabling us to effectively use the circuit as a Grover oracle.
+for qubit, clause in enumerate(clauses):
+	ops += XOR(clause[0], clause[1], qubit + 4)
+
+# Full Algorithm
+# We can combine all the components we have discussed so far
+
+qmodule = tq.QuantumModule.from_op_history(ops)
+iterations = 2
+qdev = tq.QuantumDevice(n_wires=9, device="cpu")
+
+# Initialize output qubit (last qubit) in state |->
+qdev.x(wires=8)
+qdev.h(wires=8)
+
+# Perform Grover's Search
+grover = Grover(qmodule, iterations, 4)
+result = grover.execute(qdev)
+bitstring = result.bitstring[0]
+
+# Extract the top two most likely solutions
+res = {k: v for k, v in sorted(bitstring.items(), key=lambda item: item[1], reverse=True)}
+
+# Print the top two most likely solutions
+top_keys = list(res.keys())[:2]
+print("Top two most likely solutions:")
+for key in top_keys:
+	print("Solution: ", key)
+	print("a = ", key[0])
+	print("b = ", key[1])
+	print("c = ", key[2])
+	print("d = ", key[3])
+	print("")

examples/index.rst

@@ -8,3 +8,4 @@ TorchQuantum Examples
    param_shift_onchip_training/param_shift_onchip_training.ipynb
    quantum_kernel_method/quantum_kernel_method.ipynb
    quanvolution/quanvolution.ipynb
+   superdense_coding/superdense_coding_torchquantum.ipynb

examples/superdense_coding/README.md

@@ -0,0 +1,13 @@
+# Superdense Coding
+
+Superdense coding is a quantum communication protocol that allows the transmission of two classical bits of information using only one qubit`[1]`. It takes advantage of quantum entanglement and the ability to manipulate qubits in superposition. Charles H. Bennett and Stephen Wiesner proposed this technique in 1970(though it was not published until 1992`[2]`) and it was experimentally realised in 1996 by Klaus Mattle, Harald Weinfurter, Paul G. Kwiat, and Anton Zeilinger utilising entangled photon pairs.
+
+## Author
+
+[Soham Bopardikar](https://github.com/bopardikarsoham)
+
+## References
+
+[1] Bennett, C.H., Brassard, G., Crépeau, C., Jozsa, R., Peres, A. and Wootters, W.K., 1993. Teleporting an unknown quantum state via dual classical and Einstein-Podolsky-Rosen channels. Physical review letters, 70(13), p.1895.
+
+[2] Bennett, C.H. and Wiesner, S.J., 1992. Communication via one-and two-particle operators on Einstein-Podolsky-Rosen states. Physical review letters, 69(20), p.2881.

examples/superdense_coding/superdense_coding_torchquantum.ipynb

@@ -0,0 +1,49 @@
+import math
+
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+from torch.nn.utils.rnn import pad_sequence
+import torchquantum as tq
+import torchquantum.functional as tqf
+import argparse
+import tqdm
+import time
+
+# Preparing the entangled state/ 2 qubit bell pair.
+def bell_pair():
+  qdev = tq.QuantumDevice(n_wires=2, bsz=1, device="cpu")
+  qdev.h(wires=0)
+  qdev.cnot(wires=[0, 1])
+  return qdev
+
+# Encoding the message
+def encode_message(qdev, qubit, msg):
+    if len(msg) != 2 or not set(msg).issubset({"0","1"}):
+        raise ValueError(f"message '{msg}' is invalid")
+    if msg[1] == "1":
+        qdev.x(wires=qubit)
+    if msg[0] == "1":
+        qdev.z(wires=qubit)
+    return qdev
+
+# Decoding the message
+def decode_message(qdev):
+    qdev.cx(wires=[0, 1])
+    qdev.h(wires=0)
+    return qdev
+
+# Putting all these functions together
+def main():
+    # Creating the entangled pair between Alice and Bob
+    qdev = bell_pair()
+    # Encoding the message at Alice's end
+    message = '10'
+    qdev = encode_message(qdev, 1, message)
+    # Decoding the original message at Bob's end
+    qdev = decode_message(qdev) 
+    # Finally, Bob measures his qubits to read Alice's message
+    print(tq.measure(qdev, n_shots=1024))
+
+if __name__ == "__main__":
+    main()

examples/superdense_coding/superdense_coding_torchquantum.py

@@ -33,6 +33,8 @@
 from tqdm import tqdm
 
 import qiskit.circuit.library.standard_gates as qiskit_gate
+import qiskit.circuit.library as qiskit_library
+
 
 RND_TIMES = 100
 
@@ -73,6 +75,21 @@
     # {'qiskit': qiskit_gate.?, 'tq': tq.CU2},
     {"qiskit": qiskit_gate.CU3Gate, "tq": tq.CU3},
     {"qiskit": qiskit_gate.ECRGate, "tq": tq.ECR},
+    {"qiskit": qiskit_library.QFT, "tq": tq.QFT},
+    {"qiskit": qiskit_gate.SdgGate, "tq": tq.SDG},
+    {"qiskit": qiskit_gate.TDgGate, "tq": tq.TDG},
+    {"qiskit": qiskit_gate.SXdgGate, "tq": tq.SXDG},
+    {"qiskit": qiskit_gate.CHGate, "tq": tq.CH},
+    {"qiskit": qiskit_gate.CCZGate, "tq": tq.CCZ},
+    {"qiskit": qiskit_gate.iSwapGate, "tq": tq.ISWAP},
+    {"qiskit": qiskit_gate.CSGate, "tq": tq.CS},
+    {"qiskit": qiskit_gate.CSdgGate, "tq": tq.CSDG},
+    {"qiskit": qiskit_gate.CSXGate, "tq": tq.CSX},
+    {"qiskit": qiskit_gate.DCXGate, "tq": tq.DCX},
+    {'qiskit': qiskit_gate.XXMinusYYGate, 'tq': tq.XXMINYY},
+    {'qiskit': qiskit_gate.XXPlusYYGate, 'tq': tq.XXPLUSYY},
+    {"qiskit": qiskit_gate.C3XGate, "tq": tq.C3X},
+    {"qiskit": qiskit_gate.RGate, "tq": tq.R},
 ]
 
 import os

test/operator/test_op.py

@@ -23,4 +23,5 @@
 """
 
 from .vqe import *
-from .hamiltonian import *
+from .hamiltonian import *
+from .qft import *

torchquantum/algorithm/__init__.py

@@ -0,0 +1,116 @@
+import torchquantum as tq
+
+__all__ = ["Grover"]
+
+class GroverResult(object):
+	"""Result class for Grover algorithm"""
+	def __init__(self) -> None:
+			self.iterations: int
+
+class Grover(object):
+	"""Grover's search algorithm based the paper "A fast quantum mechanical algorithm for database search" by Lov K. Grover
+	https://arxiv.org/abs/quant-ph/9605043
+	"""
+		
+	def __init__(self, oracle: tq.module.QuantumModule, iterations: int, n_wires:int) -> None:
+		"""
+		Args:
+			oracle (tq.module.QuantumModule): The oracle is a quantum module that adds a negative phase to the 
+						solution states.
+			iterations (int): The number of iterations to run the algorithm for.
+			n_wires (int): The number of qubits used in the quantum circuit.
+		"""
+		super().__init__()
+		self._oracle = oracle
+		self._iterations = iterations
+		self._n_wires = n_wires
+		
+	def initial_state_prep(self):
+		"""
+		Prepares the initial state of a quantum circuit by applying a Hadamard gate to each qubit.
+		
+		Returns:
+			a `QuantumModule` object that represents the initial state preparation circuit.
+		"""
+		ops = []
+		for i in range(self._n_wires):
+			ops.append({'name': 'hadamard', 'wires': i})
+		return tq.QuantumModule.from_op_history(ops)
+	
+	def diffusion_operator(self):
+		"""
+		Prepares the diffusion operator for the grover's circuit.
+	
+		Returns:
+			a quantum module that represents the diffusion operator for a quantum circuit.
+		"""
+		ops = []
+		hadamards = [{'name': 'hadamard', 'wires': i} for i in range(self._n_wires)]
+		flips = [{'name': 'x', 'wires': i} for i in range(self._n_wires)]
+		
+		ops += hadamards
+		ops += flips
+		
+		if self._n_wires  == 1:
+				ops += [{'name': 'z', 'wires': 0}]
+		else:
+				ops += [{'name': 'hadamard', 'wires': self._n_wires - 1}]
+				ops += [{'name': 'multicnot', 'n_wires': self._n_wires, 'wires': range(self._n_wires)}]
+				ops += [{'name': 'hadamard', 'wires': self._n_wires - 1}]
+		
+		ops += flips
+		ops += hadamards
+		
+		return tq.QuantumModule.from_op_history(ops)
+			
+					
+	def construct_grover_circuit(self, qdev: tq.QuantumDevice):
+		"""
+		Constructs a Grover's algorithm circuit with an initial state preparation, oracle,
+		and diffusion operator, and iterates through them a specified number of times.
+		
+		Args:
+			qdev (tq.QuantumDevice): tq.QuantumDevice is an object representing a quantum device or
+		simulator on which quantum circuits can be executed. 
+				
+		Returns:
+			the modified quantum device `qdev` after applying the Grover's algorithm circuit with the
+		specified number of iterations.
+		"""
+
+		self.initial_state_prep()(qdev)        
+		for _ in range(self._iterations):
+			self._oracle(qdev)
+			self.diffusion_operator()(qdev)
+		
+		return qdev
+	
+	def execute(self, qdev: tq.QuantumDevice, n_shots: int =1024):
+		"""
+		Executes a Grover search algorithm on a given quantum device and returns the result.
+		
+		Args:
+			qdev (tq.QuantumDevice): tq.QuantumDevice is an object representing a quantum device or
+		simulator on which quantum circuits can be executed. 
+			n_shots (int): The number of times the circuit is run to obtain measurement statistics.
+		Defaults to 1024
+		
+		Returns:
+			an instance of the `GroverResult` class, which contains information about the results of
+		running the Grover search algorithm on a quantum device. The `GroverResult` object includes the
+		number of iterations performed, the measured bitstring, the top measurement (i.e. the most
+		frequently measured bitstring), and the maximum probability of measuring the top measurement.
+		"""
+			
+		qdev = self.construct_grover_circuit(qdev)
+		bitstring = tq.measure(qdev, n_shots=n_shots)
+		top_measurement, max_probability = max(bitstring[0].items(), key=lambda x: x[1])
+		max_probability /= n_shots
+		
+		result = GroverResult()
+		result.iterations = self._iterations
+		result.bitstring = bitstring
+		result.top_measurement = top_measurement
+		result.max_probability = max_probability
+
+		return result

torchquantum/algorithm/grover.py

@@ -0,0 +1,35 @@
+import torchquantum as tq
+from typing import Iterable
+
+__all__ = ["QFT"]
+
+
+class QFT(object):
+    def __init__(
+        self, n_wires: int = None, wires: Iterable = None, do_swaps=True
+    ) -> None:
+        """Init function for QFT class
+
+        Args:
+            n_wires (int): Number of wires for the QFT as an integer
+            wires (Iterable): Wires to perform the QFT as an Iterable
+            add_swaps (bool): Whether or not to add the final swaps in a boolean format
+            inverse (bool): Whether to create an inverse QFT layer in a boolean format
+        """
+        super().__init__()
+
+        self.n_wires = n_wires
+        self.wires = wires
+        self.do_swaps = do_swaps
+
+    def construct_qft_circuit(self) -> tq.QuantumModule:
+        """Construct the QFT circuit."""
+        return tq.layer.QFTLayer(
+            n_wires=self.n_wires, wires=self.wires, do_swaps=self.do_swaps
+        )
+
+    def construct_inverse_qft_circuit(self) -> tq.QuantumModule:
+        """Construct the inverse of a QFT circuit."""
+        return tq.layer.QFTLayer(
+            n_wires=self.n_wires, wires=self.wires, do_swaps=self.do_swaps, inverse=True
+        )