fidelity_count.py

import perceval as pcvl

def calculate_fidelity(circuit, total_samples = 1000, print_results = False) :
    """Takes into argument a circuit, a number of samples desired and returns the fidelities 
    of the state 1 and state 2 as F1, F2""" 

    # Initialize the SLOS processor
    processor = pcvl.Processor("SLOS", circuit)
    processor.with_input(pcvl.BasicState([0, 1, 0, 1])) #the input state of the cloning circuit according to the research paper

    # Create the sampler
    sampler = pcvl.algorithm.Sampler(processor)

    # Sample the output distribution (default 1000 samples)
    sample_count = sampler.sample_count(total_samples)

    # Initialize counts for target states
    count_F1 = 0
    count_F2 = 0

    if print_results == True : 
        print("Sample Counts:", sample_count['results'])

    # Iterate through sampled states, and add to count simultaneous detections between one photon exiting one of the output modes 1-2,
    # and the other exiting one of the output modes 3-4
    for state, count in sample_count['results'].items():
        if state == pcvl.BasicState("|0,1,0,1>"):  # Clone 1 (correct output for mode 1)
            count_F1 = count
        if state == pcvl.BasicState("|0,1,1,0>"):  # Clone 1 (correct output for mode 1)
            count_F1 += count
        if state == pcvl.BasicState("|1,0,1,0>"):  # Clone 2 (correct output for mode 2)
            count_F2 = count
        if state == pcvl.BasicState("|0,1,1,0>"):  # Clone 2 (correct output for mode 2)
            count_F2 += count

    # Normalize to calculate fidelities
    F1 = count_F1 / total_samples
    F2 = count_F2 / total_samples

    # print(f"Fidelity F1 (Clone 1): {F1}")
    # print(f"Fidelity F2 (Clone 2): {F2}")

    return(F1, F2)


## TO TEST THE FUNCTION

# phis = [0, np.pi/2, np.pi, 3*np.pi/2]   # Values we need to train the variational cloning machine. 

# # A random seed for reproducibility
# np.random.seed(157)

# # Define the circuit with the desired input parameters
# thetas = [np.random.uniform(0, 2 * np.pi) for _ in range(12)]  # Example: random initial values

# circuit = create_cloning_circuit(phis[1], thetas)

# calculate_fidelity(circuit, print_results = True)