qrisp.operators.qubit.QubitOperator.get_measurement#

QubitOperator.get_measurement(qarg, precision=0.01, backend=None, shots=1000000, compile=True, compilation_kwargs={}, subs_dic={}, precompiled_qc=None, diagonalisation_method='commuting_qw', measurement_data=None)[source]#

This method returns the expected value of a Hamiltonian for the state of a quantum argument. Note that this method measures the hermitized version of the operator:

\[H = (O + O^\dagger)/2\]

Parameters:

qargQuantumVariable or list[Qubit]: The quantum argument to evaluate the Hamiltonian on.
precision: float, optional: The precision with which the expectation of the Hamiltonian is to be evaluated. The default is 0.01. The number of shots scales quadratically with the inverse precision.
backendBackendClient, optional: The backend on which to evaluate the quantum circuit. The default can be specified in the file default_backend.py.
shotsinteger, optional: The maximum amount of shots to evaluate the expectation of the Hamiltonian. The default is 1000000.
compilebool, optional: Boolean indicating if the .compile method of the underlying QuantumSession should be called before. The default is True.
compilation_kwargsdict, optional: Keyword arguments for the compile method. For more details check QuantumSession.compile. The default is {}.
subs_dicdict, optional: A dictionary of Sympy symbols and floats to specify parameters in the case of a circuit with unspecified, abstract parameters. The default is {}.
precompiled_qcQuantumCircuit, optional: A precompiled quantum circuit.
measurement_dataQubitOperatorMeasurement: Cached data to accelerate the measurement procedure. Automatically generated by default.

Returns:

float: The expected value of the Hamiltonian.

Raises:

Exception: If the containing QuantumSession is in a quantum environment, it is not possible to execute measurements.

Examples

We define a Hamiltonian, and measure its expected value for the state of a QuantumVariable.

from qrisp import QuantumVariable, h
from qrisp.operators.qubit import X,Y,Z
qv = QuantumVariable(2)
h(qv)
H = Z(0)*Z(1)
res = H.get_measurement(qv)
print(res)
#Yields 0.0011251406425802912