From 5aa2d30abde7ea344585ef91734062cd40bcf728 Mon Sep 17 00:00:00 2001
From: Daniel Tsvetkov <danieltcv@gmail.com>
Date: Wed, 4 Dec 2019 22:06:55 +0100
Subject: [PATCH] moved some methods from the old lib

---
 lib_q_computer.py | 87 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 82 insertions(+), 5 deletions(-)

diff --git a/lib_q_computer.py b/lib_q_computer.py
index fc6c2a6..819753f 100644
--- a/lib_q_computer.py
+++ b/lib_q_computer.py
@@ -1,12 +1,23 @@
+import random
+
 import numpy as np
 
 # Raw matrixes to be used for initialization of qubits and gates
+
+# |0> and |1>
 __0 = [[1],
        [0]]
 
 __1 = [[0],
        [1]]
 
+# |+> and |->
+__p = [[1 / np.sqrt(2)],
+       [1 / np.sqrt(2)]]
+__m = [[1 / np.sqrt(2)],
+       [-1 / np.sqrt(2)]]
+
+# Gate/Operator raws
 _I = [
     [1, 0],
     [0, 1],
@@ -42,6 +53,7 @@ _CNOT = [
 
 class State(object):
     """Represents a quantum state"""
+
     def __init__(self, matrix_state):
         """
         Can be initialized with a matrix, e.g. for |0> this is [[0],[1]]
@@ -51,8 +63,10 @@ class State(object):
 
     def __getitem__(self, item):
         """
-        Kind of hacky way to store a substate of an item for use in Gate operations
-        so that one can use state[0] and the encompassing operator can access this.
+        Kind of hacky way to store a substate of an item for use in Gate
+        operations
+        so that one can use state[0] and the encompassing operator can access
+        this.
         :param item:
         :return:
         """
@@ -67,6 +81,31 @@ class State(object):
     def __repr__(self):
         return str(self.matrix_state)
 
+    def __eq__(self, other):
+        return np.array_equal(self.matrix_state, other.matrix_state)
+
+    def density_matrix(self):
+        return self.matrix_state.dot(np.transpose(self.matrix_state))
+
+    def measure_probability(self):
+        """
+        In a qbit [a, b] normalized: |a|^2 + |b|^2 = 1
+        Probability of 0 is |a|^2 and 1 with prob |b|^2
+
+        :returns: tuple of probabilities to measure 0 or 1"""
+        return [np.abs(qbit[0]) ** 2 for qbit in self.matrix_state]
+
+    def measure(self):
+        """
+        This gets a random choice of either 0 and 1 with weights
+        based on the probabilities of the qbit
+
+        :returns: classical bit based on qbit probabilities"""
+        weights = self.measure_probability()
+        format_str = "{:0" + str(int(np.ceil(np.log2(len(weights))))) + "b}"
+        choices = [format_str.format(i) for i in range(len(weights))]
+        return random.choices(choices, weights)[0]
+
 
 def kron(_list):
     """Calculates a Kronicker product of a list of matrices
@@ -83,9 +122,11 @@ class Gate(State):
     def on(self, other_state):
         """
         Applies a gate operation on a state.
-        If applying to a substate, use the index of the substate, e.g. `H.on(bell[0])` will apply the Hadamard gate
+        If applying to a substate, use the index of the substate, e.g. `H.on(
+        bell[0])` will apply the Hadamard gate
         on the 0th qubit of the `bell` state.
-        :param other_state: another state (e.g. `H.on(q1)` or a list of states (e.g. for `CNOT.on([q1, q2])`)
+        :param other_state: another state (e.g. `H.on(q1)` or a list of
+        states (e.g. for `CNOT.on([q1, q2])`)
         :return: the state after the application of the Gate
         """
         this_state_m = self.matrix_state
@@ -97,7 +138,8 @@ class Gate(State):
             # Use the Kronicker product of Identity with the state.item where
             # state.item is the substate
             larger_side = max(len(self), len(other_state))
-            _list = [this_state_m if i == other_state.item else _I for i in range(larger_side)]
+            _list = [this_state_m if i == other_state.item else _I
+                     for i in range(larger_side)]
             this_state_m = kron(_list)
         return State(this_state_m.dot(other_state_m))
 
@@ -113,3 +155,38 @@ Z = Gate(_Z)
 H = Gate(_H)
 
 CNOT = Gate(_CNOT)
+
+
+def run_qbit_tests():
+    # asserts are sets of tests to check if mathz workz
+    # initialize qubits
+    _0 = Qubit(__0)
+    _1 = Qubit(__1)
+    _p = Qubit(__p)
+    _m = Qubit(__m)
+
+    # Identity: verify that I|0> == |0> and I|1> == |0>
+    assert I.on(_0) == _0
+    assert I.on(_1) == _1
+
+    # Pauli X: verify that X|0> == |1> and X|1> == |0>
+    assert X.on(_0) == _1
+    assert X.on(_1) == _0
+
+    # measure probabilities in sigma_x of |0> and |1>
+    # using allclose since dealing with floats
+    assert np.allclose(_0.measure_probability(), (1.0, 0.0))
+    assert np.allclose(_1.measure_probability(), (0.0, 1.0))
+
+    # applying Hadamard puts the qbit in orthogonal +/- basis
+    assert np.array_equal(H.on(_0), _p)
+    assert np.array_equal(H.on(_1), _m)
+
+    # measure probabilities in sigma_x of |+> and |->
+    # using allclose since dealing with floats
+    assert np.allclose(_p.measure_probability(), (0.5, 0.5))
+    assert np.allclose(_m.measure_probability(), (0.5, 0.5))
+
+
+if __name__ == "__main__":
+    run_qbit_tests()