/// <summary>
/// Translate initial state specified by a unitary coupled-cluster operator acting on a single-reference state
/// to a format consumable by Q#.
/// </summary>
/// <param name="terms">single-reference state and cluster operator terms.</param>
/// <returns>Q# description of unitary coupled-cluster state.</returns>
internal static QArray <JordanWignerInputState> InitialStateUnitaryCoupledCluster(
UnitaryCCWavefunction <int> wavefunction)
{
// The last term is the reference state.
var referenceState = wavefunction.Reference;
var clusterOperator = wavefunction.Excitations;
var stateElements = clusterOperator.Select(o => InitialStatePrep(o.Value, o.Key, checkAnnihilation: false)).ToList();
stateElements.Add(InitialStatePrep(new System.Numerics.Complex(1.0, 0.0), referenceState, checkAnnihilation: true));
var stateQSharp = new QArray <JordanWignerInputState>(stateElements);
return(stateQSharp);
}
// Parses UCC wavefunction.
internal static UnitaryCCWavefunction <SpinOrbital> ToUnitaryCCWavefunction(ClusterOperator clusterOperator)
{
var outputState = new UnitaryCCWavefunction <SpinOrbital>();
var oneBodyTerms = clusterOperator.OneBodyAmplitudes ??
new List <List <string> >();
var twoBodyTerms = clusterOperator.TwoBodyAmplitudes ??
new List <List <string> >();
foreach (var element in oneBodyTerms.Concat(twoBodyTerms))
{
// First item is the amplitude.
double amplitude = double.Parse(element.First().ToString(), System.Globalization.CultureInfo.InvariantCulture);
// Second to last are fermion operators.
IEnumerable <LadderOperator <SpinOrbital> > operators = element
.Skip(1)
.Select(o => V0_1.ParsePolishNotation(o.ToString()));
var ladderSequence = new LadderSequence <SpinOrbital>(operators);
// Terms are assumed to be in normal order.
var sortedOperator = new IndexOrderedSequence <SpinOrbital>(operators);
outputState.Set(sortedOperator, new Complex(amplitude, 0.0));
}
var reference = new List <List <string> >()
{
clusterOperator.Reference
};
outputState.Reference = new SingleCFWavefunction <SpinOrbital>(
ToSparseMultiCFWavefunction(reference).Excitations.Single().Key.ToIndices()
);
return(outputState);
}