public void Set(MeasurementConstraint constraint, uint qubitPosition)
{
Debug.Assert(constraint != null);
Debug.Assert(qubitPosition < constraint.Observable.Count);
Constraint = constraint;
QubitPositionInConstraint = qubitPosition;
}
public static void SetConstraint(QubitConstraint[] qubitConstraints, MeasurementConstraint constraint)
{
Debug.Assert(qubitConstraints != null);
Debug.Assert(constraint != null);
for (uint i = 0; i < qubitConstraints.Length; ++i)
{
qubitConstraints[i].Set(constraint, i);
}
}
/// <summary>
/// Ensures that measurement of given observable on given qubits will
/// lead to result given by value
/// </summary>
public void ForceMeasure(IQArray <Pauli> observable, IQArray <Qubit> qubits, Result value)
{
Debug.Assert(observable != null);
Debug.Assert(qubits != null);
Debug.Assert(observable.Length == qubits.Length);
Utils.PruneObservable(observable, qubits, out var observablePr, out var _);
var constr = MeasurementConstraint.ForceMeasurement(observablePr, value);
QubitConstraint.SetConstraint(QubitConstraints(qubits), constr);
}
/// <summary>
/// Implements the Q# standard library callable AssertProb
/// </summary>
public void AssertProb(IQArray <Pauli> observable, IQArray <Qubit> qubits, Result value, double probability)
{
Debug.Assert(observable != null);
Debug.Assert(qubits != null);
Debug.Assert(observable.Length == qubits.Length);
Utils.PruneObservable(observable, qubits, out var observablePr, out var qubitsPr);
Debug.Assert((probability >= 0.0) && (probability <= 1.0));
MeasurementConstraint constr = MeasurementConstraint.AssertMeasurement(observablePr, value, probability);
QubitConstraint.SetConstraint(QubitConstraints(qubitsPr), constr);
}
/// <summary>
/// Returns measurement constraint corresponding to the user enforcing given outcome.
/// </summary>
public static MeasurementConstraint ForceMeasurement(List <Pauli> observable, Result result)
{
Debug.Assert(observable != null);
MeasurementConstraint m = new MeasurementConstraint
{
Type = ConstraintType.Force,
Observable = observable,
ConstrainToResult = result,
};
return(m);
}
/// <summary>
/// Returns measurement constraint corresponding to user asserting that given measurement should
/// happen with given probability.
/// </summary>
public static MeasurementConstraint AssertMeasurement(List <Pauli> observable, Result result, double probability)
{
Debug.Assert(observable != null);
MeasurementConstraint m = new MeasurementConstraint
{
Type = ConstraintType.Assert,
Observable = observable,
ConstrainToResult = result,
Probability = probability
};
return(m);
}
/// <summary>
/// Returns measurement constraint object corresponding to
/// a given qubit being in zero state
/// </summary>
public static MeasurementConstraint ZeroStateAssert()
{
MeasurementConstraint m = new MeasurementConstraint
{
Type = ConstraintType.Assert,
Observable = new List <Pauli> {
Pauli.PauliZ
},
ConstrainToResult = Result.Zero,
Probability = 1.0,
};
return(m);
}
/// <summary>
/// Implements the Q# standard library callable Measure.
/// Not all measurements considered primitive operations. The measurements
/// that are primitive operations are listed in
/// MetricsCalculatorConfiguration.MeasurementToPrimitiveOperation
/// If the measurement is not primitive, the operation will throw
/// NonPrimitiveMeasurementException.
/// </summary>
public Result Measure(IQArray <Pauli> observable, IQArray <Qubit> qubits)
{
Debug.Assert(observable != null);
Debug.Assert(qubits != null);
Utils.PruneObservable(observable, qubits, out var observablePr, out var qubitsPr);
if (observablePr.Count == 0)
{
return(Result.Zero);
}
QubitConstraint[] constr = QubitConstraints(qubitsPr);
QubitConstraint qubit0Constraint = constr[0];
if (qubit0Constraint.Constraint == null)
{
return(UnconstrainedMeasurementResult());
}
else
{
for (int i = 0; i < qubitsPr.Count; ++i)
{
QubitConstraint qubitIConstraint = constr[i];
// makes sure that none of the qubits constraints have been invalidated
if (qubitIConstraint.Constraint == null)
{
return(UnconstrainedMeasurementResult());
}
// makes sure that all qubits involved have the same constraint
if (qubitIConstraint.Constraint != qubit0Constraint.Constraint)
{
return(UnconstrainedMeasurementResult());
}
// makes sure that constrain's observable matches observable being measured
if (qubitIConstraint.QubitPauli != observablePr[i])
{
return(UnconstrainedMeasurementResult());
}
}
}
// here we have ensured that all conditions we need to predict the measurement outcome are met
MeasurementConstraint constraint = qubit0Constraint.Constraint;
if (constraint.Type == MeasurementConstraint.ConstraintType.Force)
{
return(constraint.ConstrainToResult);
}
else if (constraint.Type == MeasurementConstraint.ConstraintType.Assert)
{
Double sample = randomGenerator.NextDouble();
if (sample <= constraint.Probability)
{
Debug.WriteLine($"Measurement outcome with probability {constraint.Probability} happened, result is {constraint.ConstrainToResult}");
return(constraint.ConstrainToResult);
}
else
{
Debug.WriteLine($"Measurement outcome with probability {constraint.Probability} did not happen, result is {Utils.Opposite(constraint.ConstrainToResult)}");
return(Utils.Opposite(constraint.ConstrainToResult));
}
}
Debug.Assert(false, "This point should not be reached.");
return(UnconstrainedMeasurementResult());
}
/// <summary>
/// Released qubits assumed to be in a zero state
/// </summary>
public void OnRelease()
{
Constraint = MeasurementConstraint.ZeroStateAssert();
QubitPositionInConstraint = 0;
}
public static QubitConstraint ZeroStateConstraint()
{
return(new QubitConstraint(MeasurementConstraint.ZeroStateAssert(), 0));
}
public QubitConstraint(MeasurementConstraint constraint, uint qubitPosition)
{
Debug.Assert(constraint != null);
this.Set(constraint, qubitPosition);
}
