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Quantum Computing - Interview Questions
What about Integration with quantum and classical computation?
Q# is a standalone language offering a high level of abstraction. There is no notion of a quantum state or a circuit; instead, Q# implements programs in terms of statements and expressions, much like classical programming languages. Distinct quantum capabilities (such as support for functors and control-flow constructs) facilitate expressing, for example, phase estimation and quantum chemistry algorithms.
For example, the following Q# program constructs a Hamiltonian describing the Hydrogen molecule, and obtains estimates of its energy levels by simulating the quantum phase estimation algorithm.
namespace Microsoft.Quantum.Chemistry.Samples.Hydrogen {
    open Microsoft.Quantum.Intrinsic;
    open Microsoft.Quantum.Canon;
    open Microsoft.Quantum.Chemistry.JordanWigner;
    open Microsoft.Quantum.Simulation;
    open Microsoft.Quantum.Characterization;
    open Microsoft.Quantum.Convert;
    open Microsoft.Quantum.Math;

    operation GetEnergyByTrotterization (qSharpData : JordanWignerEncodingData, nBitsPrecision : Int, trotterStepSize : Double, trotterOrder : Int) : (Double, Double) {

        // The data describing the Hamiltonian for all these steps is contained in
        // `qSharpData`
        let (nSpinOrbitals, fermionTermData, statePrepData, energyOffset) = qSharpData!;

        // Using a Product formula, also known as `Trotterization` to
        // simulate the Hamiltonian.
        let (nQubits, (rescaleFactor, oracle)) = TrotterStepOracle(qSharpData, trotterStepSize, trotterOrder);

        // The operation that creates the trial state is defined below.
        // By default, greedy filling of spin-orbitals is used.
        let statePrep = PrepareTrialState(statePrepData, _);

        // Using the Robust Phase Estimation algorithm of Kimmel, Low and Yoder.
        let phaseEstAlgorithm = RobustPhaseEstimation(nBitsPrecision, _, _);

        // This runs the quantum algorithm and returns a phase estimate.
        let estPhase = EstimateEnergy(nQubits, statePrep, oracle, phaseEstAlgorithm);

        // Obtaining the energy estimate by rescaling the phase estimate with the trotterStepSize. We also add the constant energy offset
        // to the estimated energy.
        let estEnergy = estPhase * rescaleFactor + energyOffset;

        // This returns both the estimated phase, and the estimated energy.
        return (estPhase, estEnergy);