Exponentiation

The exponentiation function produces a quantum gate that implements the exponentiation, \(\exp(-iHt)\), of any input Hermitian operator, \(H\).

Example

This example demonstrates synthesis of an exponentiation function in the Classiq engine. All options are specified below.

Textual ModelSDK

{
  "functions": [
    {
      "name": "main",
      "body": [
        {
          "function": "Exponentiation",
          "function_params": {
              "pauli_operator": {
                  "pauli_list": [
                      ["IIZXXXII", 0.1],
                      ["IIXXYYII", 0.2],
                      ["IIIIZZYX", 0.3],
                      ["XZIIIIIX", 0.4],
                      ["IIIIIZXI", 0.5],
                      ["IIIIIIZY", 0.6],
                      ["IIIIIIXY", 0.7],
                      ["IIYXYZII", 0.8],
                      ["IIIIIIXZ", 0.9],
                      ["IIYZYIII", 1.0]
                  ]
              },
              "evolution_coefficient": 0.05,
              "constraints": {
                  "max_depth": 100,
                  "max_error": 0.2
              },
              "optimization": "MINIMIZE_DEPTH"
          }
        }
      ]
    }
  ]
}

from classiq.builtin_functions import Exponentiation
from classiq.builtin_functions.exponentiation import (
    ExponentiationConstraints,
    ExponentiationOptimization,
    PauliOperator,
)
from classiq import Model, synthesize, show

pauli_operator = PauliOperator(
    pauli_list=[
        ("IIZXXXII", 0.1),
        ("IIXXYYII", 0.2),
        ("IIIIZZYX", 0.3),
        ("XZIIIIIX", 0.4),
        ("IIIIIZXI", 0.5),
        ("IIIIIIZY", 0.6),
        ("IIIIIIXY", 0.7),
        ("IIYXYZII", 0.8),
        ("IIIIIIXZ", 0.9),
        ("IIYZYIII", 1.0),
    ]
)
exponentiation_params = Exponentiation(
    pauli_operator=pauli_operator,
    evolution_coefficient=0.05,
    constraints=ExponentiationConstraints(
        max_depth=100,
        max_error=0.2,
    ),
    optimization=ExponentiationOptimization.MINIMIZE_DEPTH,
)

model = Model()
model.Exponentiation(exponentiation_params)

quantum_program = synthesize(model.get_model())
show(quantum_program)

Options

Input Operator

You can input any \(n\)-qubit operator in its Pauli basis [1]

\[ H=\sum_i c_i\left[\sigma_{j_{1,i}}\otimes\sigma_{j_{2,i}}\otimes\cdots\otimes\sigma_{j_{n,i}}\right] \]

where \(\sigma_{0,1,2,3}=I,X,Y,Z\) are the single-qubit Pauli operators, and \(j\in\{0,1,2,3\}\).

Implement it using the pauli_list field of the PauliOperator class.

For example, the operator \(H=0.1\cdot I\otimes Z+0.2\cdot X\otimes Y\) is input as follows.

Textual ModelSDK

{
    "pauli_list": [
        ["IZ",0.1],
        ["XY",0.2]
    ]
}

from classiq.builtin_functions.exponentiation import PauliOperator

operator = PauliOperator(pauli_list=[("IZ", 0.1), ("XY", 0.2)])
print(operator.show())

+0.100 * IZ
+0.200 * XY

Provide the operator to exponentiate using the pauli_operator field of the Exponentiation.

Provide a global evolution coefficient using the evolution_coefficient field of the Exponentiation; defaults to 1.0.

Constraints

Provide local constraints for the exponentiation of either max_depth or max_error using the fields of the ExponentiationConstraints class; both default to no constraint.

The max_error bounds the algorithmic error of the circuit as measured by the operator norm [2] and evaluated according to Ref. [3] .

Provide the constraints using the constraints field of the Exponentiation; defaults to no constraints.

Textual ModelSDK

{
    "max_depth": 100,
    "max_error": 0.2
}

from classiq.builtin_functions.exponentiation import ExponentiationConstraints

ExponentiationConstraints(
    max_depth=100,
    max_error=0.2,
)

Optimization

Set the optimization target for the exponentiation to MINIMIZE_DEPTH or MINIMIZE_ERROR.

The Classiq engine automatically generates an efficient higher-order Trotter-Suzuki circuit [4] that satisfies the optimization target within the provided constraints.

Provide the optimization using the optimization field of the Exponentiation; defaults to MINIMIZE_DEPTH.

Use a naive evolution for the operator by setting the field use_naive_evolution to True.

References

[1] https://en.wikipedia.org/wiki/Generalizations_of_Pauli_matrices#Multi-qubit_Pauli_matrices_(Hermitian)

[2] https://en.wikipedia.org/wiki/Operator_norm

[3] A. M. Childs et al, Toward the first quantum simulation with quantum speedup, https://arxiv.org/abs/1711.10980 (2017).

[4] N. Hatano and M. Suzuki, Finding Exponential Product Formulas of Higher Orders, https://arxiv.org/abs/math-ph/0506007 (2005).