#!/usr/bin/env python
# coding: utf-8

# # Creation of an EPR pair using two qubits
# 
# 
#     
# Let us start with a simple circuit: the creation of an EPR pair using two qubits.
#     
#     
# First, we need to import relevant objects from the python AQASM module:

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from qat.lang.AQASM import Program, H, CNOT 


# ## Creation of the quantum program
# 
# Then, we can declare a new object ``Program``. Let us give it an explicit name:

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epr_prog = Program() 


# To create our EPR pair, we need to manipulate two qbits. 
# Qbits are manipulated through qbit registers only (to keep things structured).
# Registers are allocated as follows:

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qbits = epr_prog.qalloc(2) 


# Now, we can access our qbits using the register "qbits".
# 
# Registers behave like python list/arrays.
# 
# Here our qbits will be refered to using qbits[0] and qbits[1].
# 
# To create our EPR pair, we simply implement the appropriate 2-qbit rotation using a Hadamard gate (H) on the first qbit, followed by a controlled NOT gate (CNOT) on both qbits:

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epr_prog.apply(H, qbits[0]) 
epr_prog.apply(CNOT, qbits)


# Notice that since the CNOT is applied on both qbits (it is a 2-qbit gate), we can pass the whole register as argument to the ``.apply`` method.

# The corresponding circuit object can be extracted directly from the Program object as follows:

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circuit = epr_prog.to_circ()
get_ipython().run_line_magic('qatdisplay', 'circuit')


# ## Simulation of the execution of the circuit
# Now that we have a proper circuit, we can try and simulate it:

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#Let us import some qpu connected to a classical linear algebra simulator
from qat.qpus import PyLinalg
qpu = PyLinalg()

job = circuit.to_job()

result = qpu.submit(job)
for sample in result:
    print("State", sample.state, "with amplitude", sample.amplitude)


# ## Export to Atos Quantum Assembly Language (AQASM) format
# We can also export our circuit in the AQASM format:

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epr_prog.export("helloworld.aqasm") 


# The generated file *helloworld.aqasm* should look like this:

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get_ipython().system('cat helloworld.aqasm')


# and can be compiled to circ format as follows:

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get_ipython().system('aqasm2circ helloworld.aqasm')


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