Function shor_decode

examples/quantum_computing_ex.cpp:77–111

// ----------------------------------------------------------------------------------------

void shor_decode (
    quantum_register& reg
)
/*!
    requires
        - reg.num_bits() == 9
    ensures
        - #reg.num_bits() == 1
        - #reg == the decoded qubit that was in the given input register 
!*/
{
    DLIB_CASSERT(reg.num_bits() == 9,"");

    using namespace dlib::quantum_gates;
    const gate<1> h = hadamard();
    const gate<1> i = noop();

    // Now apply the gates that constitute Shor's decoding to the input register

    (cnot<2,0>(),cnot<2,0>(),cnot<2,0>()).apply_gate_to(reg);
    (cnot<1,0>(),i,cnot<1,0>(),i,cnot<1,0>(),i).apply_gate_to(reg);

    (toffoli<0,1,2>(),toffoli<0,1,2>(),toffoli<0,1,2>()).apply_gate_to(reg);

    (h,i,i,h,i,i,h,i,i).apply_gate_to(reg);

    (cnot<6,0>(),i,i).apply_gate_to(reg);
    (cnot<3,0>(),i,i,i,i,i).apply_gate_to(reg);
    (toffoli<0,3,6>(),i,i).apply_gate_to(reg);

    // Now that we have decoded the value we don't need the extra 8 bits any more so 
    // remove them from the register.
    for (int i = 0; i < 8; ++i)
        reg.measure_and_remove_bit(0,rnd);
}

// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------