Qiskit-nature

Prelude
Qiskit Nature 0.6 focuses on refactoring of the [mappers](https://qiskit.org/documentation/nature/apidocs/qiskit_nature.second_q.mappers.html#module-qiskit_nature.second_q.mappers) module. To that extent, the [QubitConverter](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.QubitConverter.html#qiskit_nature.second_q.mappers.QubitConverter) class has been deprecated in favor of using the various subclasses of [QubitMapper](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.QubitMapper.html#qiskit_nature.second_q.mappers.QubitMapper) directly.
Check out the [migration guide for the QubitConverter](https://qiskit.org/documentation/nature/migration/0.6_c_qubit_converter.html) for more details. Besides this major refactoring, a few other changes have been done, so be sure to check out the [migration guide from 0.5 to 0.6](https://qiskit.org/documentation/nature/migration/index.html#migrating-from-0-5-to-0-6).

New Features
- Adds a Tapered Qubit Mapper class. [TaperedQubitMapper](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.TaperedQubitMapper.html#qiskit_nature.second_q.mappers.TaperedQubitMapper) is to be used as a wrapper of another standard [QubitMapper](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.QubitMapper.html#qiskit_nature.second_q.mappers.QubitMapper) that can apply symmetry reduction techniques to operators at the end of the mapping.
- Adds the method [get_tapered_mapper()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.problems.BaseProblem.get_tapered_mapper.html#qiskit_nature.second_q.problems.BaseProblem.get_tapered_mapper) to transform a `QubitMapper` instance into a `TaperedQubitMapper` based on the properties of the current problem.
- Added support for running with Python 3.11. At the the time of the release, Psi4 and Sparse didn’t have a python 3.11 version.
- Three new methods for creating instances [ElectronicDensity](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.properties.ElectronicDensity.html#qiskit_nature.second_q.properties.ElectronicDensity) have been added for:
- constructing an empty (or all-zero) density of a given size
- constructing an identity density, meaning that the 1-body matrices are initialized with identity matrices
- constructing from a provided number of particles. This is a shorter variant of the already existing from_orbital_occupation method for the most common use-case.
- All of the methods above take the optional keyword-argument include_rdm2 which determines whether or not the 2-body matrices are computed based on the constructed 1-body matrices. By default, this is set to `True`.
- Added the [InterleavedQubitMapper](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.InterleavedQubitMapper.html#qiskit_nature.second_q.mappers.InterleavedQubitMapper) which allows wrapping of another `FermionicMapper` to produce qubit operators where the alpha- and beta-spin components are arranged in the qubit register in an interleaved rather than blocked order.
- Adds the [symmetric_two_body module](https://qiskit.org/documentation/nature/apidocs/qiskit_nature.second_q.operators.symmetric_two_body.html#module-qiskit_nature.second_q.operators.symmetric_two_body). This module provides utilities to exploit the inherent symmetries of chemistry-ordered two-body electronic integrals. You may use these to reduce memory consumption of your code
- Since these integral containers are integrated into the stack, you can continue to use existing tools such as the `BasisTransformer` or even the `ActiveSpaceTransformer` as if you had stored your integrals in standard arrays.
- Adds the [use_symmetry_reduced_integrals](https://qiskit.org/documentation/nature/apidocs/qiskit_nature.settings.html#qiskit_nature.settings.QiskitNatureSettings.use_symmetry_reduced_integrals) setting. When set to `True`, this will cause objects like for example the `FCIDump`, `QCSchema`, or `PySCFDriver` to attempt and leverage the `symmetric_two_body` module in order to reduce the memory requirements at runtime.
- Adds the new [Tensor](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.Tensor.html#qiskit_nature.second_q.operators.Tensor) class used internally to consistently deal with n-dimensional tensors throughout the stack. This class also exposes the `label_template` which allows an end-user to influence the translation procedure implemented in [from_polynomial_tensor()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.SparseLabelOp.from_polynomial_tensor.html#qiskit_nature.second_q.operators.SparseLabelOp.from_polynomial_tensor).
- Adds the new [tensor_unwrapping](https://qiskit.org/documentation/nature/apidocs/qiskit_nature.settings.html#qiskit_nature.settings.QiskitNatureSettings.tensor_unwrapping) setting which may be set to False to disable the unwrapping of internally created Tensor objects stored inside of a `PolynomialTensor`. See also tensor_unwrapping for more details.
- Adds the new argument num_particles to the [ParityMapper](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.ParityMapper.html#qiskit_nature.second_q.mappers.ParityMapper) which will implement the two qubit reduction without requiring an instance of `QubitConverter`.
- Extends the [VibrationalIntegrals](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.VibrationalIntegrals.html#qiskit_nature.second_q.operators.VibrationalIntegrals) to fall back to using numpy arrays when the optional sparse dependency is not installed.
- Leverage library [opt_einsum](https://github.com/dgasmith/opt_einsum), if installed, for sparse-einsum support. This library supports einsum summation directly on sparse objects as described in its documentation.
- The new keyword argument `register_length` has been added to the [QubitMapper.map()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.QubitMapper.map.html#qiskit_nature.second_q.mappers.QubitMapper.map) method. This allows the user to set the length of a `SparseLabelOp` before mapping it (since this length is a lower bound).
- Improves the `QEOM` code and implements the calculation of excited state properties and transition amplitudes with `QEOM`.
- Added public methods `symmetry_reduce_clifford()` and `convert_clifford()` and `find_taper_op()` to allow a step by step tapering of operators.
- Changed the behavior of the [GroundStateEigensolver](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.algorithms.GroundStateEigensolver.html#qiskit_nature.second_q.algorithms.GroundStateEigensolver) to not raise an error when the user specifies a auxiliary operator which name clashes an internally constructed operator’s name. The new behavior is to apply precedence to the user-defined operators over the builtin ones in case of conflicts. A warning will be logged when this case happens.
- Added a tolerance parameter `tol` to control the eigenvalue threshold in the `QEOM` calculation.
- Adds the new [formatting_precision](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.problems.EigenstateResult.html#qiskit_nature.second_q.problems.EigenstateResult.formatting_precision) attribute to all result objects. This attribute sets the number of decimal places to be used when formatting the result object for printing. It defaults to 12.
- Added `qiskit_nature.testing` to house testing utilities. Currently it contains some functions for random sampling.
- Updated the API to allow [QubitMapper](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.QubitMapper.html#qiskit_nature.second_q.mappers.QubitMapper) objects in places where [QubitConverter](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.QubitConverter.html#qiskit_nature.second_q.mappers.QubitConverter) were previously required. This addition advances toward a future deprecation of QubitConverter. All inputs of type QubitConverter now support QubitMapper objects implementing a transformation from second quantized operators to Pauli operators. Note that the mappers currently do not support qubit reduction techniques.
- The method [map()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.QubitMapper.map.html#qiskit_nature.second_q.mappers.QubitMapper.map) now supports individual operators as well as lists and dictionaries of operators.

Deprecation Notes
- Deprecated all [MinimumEigensolverFactory](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.algorithms.MinimumEigensolverFactory.html#qiskit_nature.second_q.algorithms.MinimumEigensolverFactory) and [EigensolverFactory](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.algorithms.EigensolverFactory.html#qiskit_nature.second_q.algorithms.EigensolverFactory) classes. Instead, users should now build the respectively generated solver instances themselves. How-to guides to detail the involved steps have been [added to the documentation](https://qiskit.org/documentation/nature/howtos/index.html)
- Deprecated the [to_matrix()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.FermionicOp.to_matrix.html#qiskit_nature.second_q.operators.FermionicOp.to_matrix) method. The same functionality can be achieved via the qubit-operator after applying the JordanWignerMapper (one only needs to adapt to the different basis state ordering due to the reversed bitstring endianness).
- The [QubitConverter](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.QubitConverter.html#qiskit_nature.second_q.mappers.QubitConverter) class is deprecated in favor of using the [QubitMapper](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.QubitMapper.html#qiskit_nature.second_q.mappers.QubitMapper) implementations directly. As a consequence of this, all public properties and function arguments which referred to the `QubitConverter` by name (e.g. `qubit_converter`) have been deprecated in favor of properties and function arguments referring to `QubitMapper` (e.g. `qubit_mapper`), respectively.
- The [symmetry_sector_locator()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.problems.BaseProblem.symmetry_sector_locator.html#qiskit_nature.second_q.problems.BaseProblem.symmetry_sector_locator) method has been deprecated without a direct replacement. This utility is no longer needed in the new workflow which uses QubitMapper instances directly. Qubit tapering can instead now be done using the [TaperedQubitMapper](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.mappers.TaperedQubitMapper.html#qiskit_nature.second_q.mappers.TaperedQubitMapper) which can be constructed easily using the [get_tapered_mapper()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.problems.BaseProblem.get_tapered_mapper.html#qiskit_nature.second_q.problems.BaseProblem.get_tapered_mapper) method.
- The `match_convert` argument of the `hartree_fock_bitstring_mapped()` method has been deprecated without replacement. This utility is no longer needed in the new workflow which uses `QubitMapper` instances directly.
- The `VQEClient` and its matching `VQERuntimeResult` are now deprecated. Instead, users should migrate their code to use the Qiskit Runtime Primitives. A guide on how to use this can be found [here](http://qisk.it/algo_migration#vqe).
- Deprecates `np.ndarray` as the return type of the `hijkl`, `hijkl_ba`, and `hijkl_bb` attributes. Instead, these will always be SymmetricTwoBodyIntegrals. Instances of the latter can be used as np.ndarray so in terms of functionality this should not change anything. However, isinstance(integrals, np.ndarray) will not return True for integrals of type SymmetricTwoBodyIntegrals. Additionally, the three FCIDump attributes will no longer accept physicist-ordered two-body tensors in the future.
- Deprecated the default value (`True`) of `tensor_unwrapping` meaning that in the future `__getitem__()` will return objects of type [Tensor](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.Tensor.html#qiskit_nature.second_q.operators.Tensor).
- The `M`, `Q`, `W`, `V` matrix setters and `M`, `Q`, `W`, `V` matrix standard deviation setters from `QEOMResult` were pending deprecated and remain computable from the `H` and `S` matrices.
- `QubitMapper.allows_two_qubit_reduction` has been deprecated. There is no replacement because it is no longer needed in the new design.
- All arguments in the `QubitMapper` API (and its subclasses) which were previously called `nmodes` have been renamed to `register_length`.

Bug Fixes
- Fixes `SparseLabelOp.assign_parameters()` failing to assign parameters recursively.
- The commutator methods `commutator()`, `anti_commutator()`, and `double_commutator()` no longer faultily simplify the returned operator (i.e. the absolute tolerance during simplification is set to zero instead of defaulting to `SparseLabelOp.atol`).
- Fixes a bug when printing the `total_dipole_moment_in_debye`
- Fixes output of `generate_fermionic_excitations()` when called with `perserve_spin=False` and unequal number of alpha and beta particles
- Fixes the `qcschema_to_problem()` method to take `QCWavefunction.eri_mo_ab` into account when `QCWavefunction.eri_mo_ba` is not available.
- Fixes the behavior of `is_zero()` when called on a parameterized operator.
- Fixes a bug when multiplying a `SparseLabelOp` with numpy numeric types from the left.
- Removes wrong sign change from `SpinOp.index_order()`.
- Fixes the `normal_order()` method, which in turn corrects the commutation relations of this operator type.
- Fixes the `VQEClient` to work properly with the latest code.
- Added missing Gaussian native libraries from package `qiskit_nature.second_q.drivers.gaussiand.gauopen` to the wheels file distribution.
- Fixes a bug in which `BogoliubovTransform` would sometimes throw an error due to an inability to cast complex numbers to floats.
- Fix support of `BackendV2` in the `VQEClient`. Previously, backends instantiated with the `IBMProvider` failed since they return backends of type BackendV2, which were not correctly supported in the VQE client. Backends instantiated with the IBMQ provider continue to work as before.

Changelog

Bug Fixes

- Fixes the VQEClient to work properly with the latest code.

Changelog

Bug Fixes

- Fixes a bug when multiplying a [SparseLabelOp](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.SparseLabelOp.html#qiskit_nature.second_q.operators.SparseLabelOp) with numpy numeric types from the left.
- Removes wrong sign change from [qiskit_nature.second_q.operators.SpinOp.index_order()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.SpinOp.index_order.html#qiskit_nature.second_q.operators.SpinOp.index_order).
- Added missing Gaussian native libraries from package qiskit_nature.second_q.drivers.gaussiand.gauopen to the wheels file distribution.

Changelog

Prelude

- Qiskit Nature 0.5 comes with a major redesign of the [BaseProblem](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.problems.BaseProblem.html#qiskit_nature.second_q.problems.BaseProblem) layer of its stack. Rather than tightly integrating drivers and transformers, problems are now a lot more standalone and are generated by the various drivers (or built out by a user to their custom needs directly).

New Features

- The algorithms module now requires the new algorithms introduced in Qiskit Terra 0.22 which in turn rely on the [Qiskit Primitives](https://qiskit.org/documentation/apidoc/primitives.html) themselves. For more details check out the [migration guide for problem solving](https://qiskit.org/documentation/nature/migration/00a_Solving_problems_with_0.5.ipynb).
- The refactoring of the electronic structure stack has enabled the development of third-party plugins allowing classical codes to call Qiskit Nature instead of relying on the development of drivers in the Qiskit Nature package. One example is the new [Qiskit Nature PySCF Plugin](https://github.com/qiskit-community/qiskit-nature-pyscf) which can be used. Qiskit Nature still provides drivers to enable simple testing and provide a more accessible entry to Qiskit Nature for users who do not come from a classical chemistry computing background. Check out the [migration guide for electronic structure calculations](https://qiskit.org/documentation/nature/migration/00b_Electronic_structure_with_0.5.ipynb) to learn how to update your code to use the refactored drivers.
- The properties concept has been largely redesigned and is a lot more refined now. Instead of being a “catchall” for operator factories, the module has been cleanly separated into various components. Check out the corresponding section of the [migration guide for electronic structure calculations](https://qiskit.org/documentation/nature/migration/00b_Electronic_structure_with_0.5.ipynb) for more details.
- The vibrational structure stack has been refactored in-line with the changes to the electronic structure stack mentioned previously. However, changes to this stack also include corrections to the differentiation of real-space and second-quantized coefficients of the Watson hamiltonian. For more details, check out the [migration guide for vibrational structure calculations](https://qiskit.org/documentation/nature/migration/00c_Vibrational_structure_with_0.5.ipynb).
- The lattices and related LatticeModel classes have undergone some API changes, particularly around the location of the utility methods for uniform lattice generation. For more details check out the [migration guide for lattice models](https://qiskit.org/documentation/nature/migration/00d_Lattice_models_with_0.5.ipynb).
- Added the qiskit_nature.second_q.properties.HeisenbergModel which implements the Hamiltonian of the Heisenberg model. This model is used in the study of critical points and phase transitions of magnetic systems. Through the choice of the model constants and the external magnetic field, we can produce many models like: XYZ, XXX, Ising model and others.
- Adds .SparseLabelOp.equiv for checking approximate equality between two SparseLabelOps.
- The performance of the following mappers, when used to map multiple operators of identical size, is significantly improved, by means of caching internal structures
- Adds a new Property for the electronic structure stack to evaluate the 1- and 2-body reduced density matrices. Assuming that you already have an instance of your [qiskit_nature.second_q.problems.ElectronicStructureProblem](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.problems.ElectronicStructureProblem.html#qiskit_nature.second_q.problems.ElectronicStructureProblem), you can add the [qiskit_nature.second_q.properties.ElectronicDensity](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.properties.ElectronicDensity.html#qiskit_nature.second_q.properties.ElectronicDensity)
- Adds the [PropertiesContainer](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.problems.PropertiesContainer.html#qiskit_nature.second_q.problems.PropertiesContainer) and its subclasses to simplify the handling of SparseLabelOpsFactory instances inside of problems. This container is a MutableSet and enforces at most a single instance of any Property kind to be stored inside of it This is sufficient for all application purposes of the auxiliary operators (which are generated by these objects).
- Adds the new keyword argument mirror to the [SUCCD](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.circuit.library.SUCCD.html#qiskit_nature.second_q.circuit.library.SUCCD) ansatz, which allows the inclusion of symmetrically mirrored double excitations while preserving the number of circuit parameters.
- Adds support for the [QCSchema](https://molssi-qc-schema.readthedocs.io/en/latest/index.html) via which we aim to standardize the I/O between classical drivers and Qiskit Nature.
- Implements both [HartreeFock](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.circuit.library.HartreeFock.html#qiskit_nature.second_q.circuit.library.HartreeFock) and [VSCF](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.circuit.library.VSCF.html#qiskit_nature.second_q.circuit.library.VSCF) as subclasses of BlueprintCircuit. This allows the respective classes to be instantiated without explicitly setting all of their instance attributes. Missing attributes can be set at a later point to complete the respective circuit definitions.
- The new [qiskit_nature.second_q.operators.FermionicOp](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.FermionicOp.html#qiskit_nature.second_q.operators.FermionicOp) replaces the old qiskit_nature.operators.second_quantization.operators.FermionicOp. This new operator is a subclass of the [qiskit_nature.second_q.operators.SparseLabelOp](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.SparseLabelOp.html#qiskit_nature.second_q.operators.SparseLabelOp) and, as such, only support sparse labels. It is initialized with a dictionary, mapping sparse label keys to coefficients. It supports the usual algebra for operator addition, scalar multiplication, operator composition, operator tensoring, and complex conjugation. It also provides methods for sorting, equality and equivalency checking, operator simplification, normal ordering, and the computation of induced norms as well as hermiticity properties. Finally, it can also be converted to matrices in the occupation number basis.
- Added the xcf argument to the [qiskit_nature.second_q.drivers.GaussianForcesDriver.from_molecule()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.drivers.GaussianForcesDriver.from_molecule.html#qiskit_nature.second_q.drivers.GaussianForcesDriver.from_molecule) which allows specifying the exchange-correlation functional to be used by Gaussian.
- The excitation_list property has been removed from [HFInitialPoint](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.algorithms.initial_points.HFInitialPoint.html#qiskit_nature.second_q.algorithms.initial_points.HFInitialPoint), [MP2InitialPoint](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.algorithms.initial_points.MP2InitialPoint.html#qiskit_nature.second_q.algorithms.initial_points.MP2InitialPoint), and [VSCFInitialPoint](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.algorithms.initial_points.VSCFInitialPoint.html#qiskit_nature.second_q.algorithms.initial_points.VSCFInitialPoint). Thus the excitation list cannot be set directly, rather this must be set via the [ansatz](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.algorithms.initial_points.InitialPoint.ansatz.html#qiskit_nature.second_q.algorithms.initial_points.InitialPoint.ansatz).
- Following the MP2 T2 and energy correction calculation fix, the APIs for [MP2InitialPoint](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.algorithms.initial_points.MP2InitialPoint.html#qiskit_nature.second_q.algorithms.initial_points.MP2InitialPoint) and [HFInitialPoint](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.algorithms.initial_points.HFInitialPoint.html#qiskit_nature.second_q.algorithms.initial_points.HFInitialPoint) have been changed slightly. After setting the grouped_property, the total_energy and energy_correction are now accessed via their respective properties, rather than via get_energy and get_energy_correction.
- Adds atol parameter to SparseLabelOp.is_hermitian().
- The supported excitation types in the QEOM code have been updated. It now exposes the full set of excitation generation functionalities provided by the internally used UCC and UVCC ansatze. In particular, this means that rather than providing a custom list of excitation tuples, a function can be set by the user which generates such a custom list. The documentation has been updated accordingly to reflect this in all places.
- Adds [SparseLabelOp.induced_norm()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.SparseLabelOp.induced_norm.html#qiskit_nature.second_q.operators.SparseLabelOp.induced_norm).
- Changes usage of library retworkx to the new substitute rustworkx.
- Adds utility functions for converting between chemists’ and physicists’ index ordering for two-body integrals. [qiskit_nature.second_q.operators.tensor_ordering.to_chemist_ordering()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.tensor_ordering.to_chemist_ordering.html#qiskit_nature.second_q.operators.tensor_ordering.to_chemist_ordering) converts from physicists’ or intermediate order to chemists’, whereas [qiskit_nature.second_q.operators.tensor_ordering.to_physicist_ordering()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.tensor_ordering.to_physicist_ordering.html#qiskit_nature.second_q.operators.tensor_ordering.to_physicist_ordering) converts to physicists’. [qiskit_nature.second_q.operators.tensor_ordering.find_index_order()](https://qiskit.org/documentation/nature/stubs/qiskit_nature.second_q.operators.tensor_ordering.find_index_order.html#qiskit_nature.second_q.operators.tensor_ordering.find_index_order) returns the index-order type for a given two-body tensor.

Changelog

Bug Fixes
- Fix the initial point classes to account for the number of times the evolved operators are repeated in the ansatz.
- Fixes the compatibility of the fermionic excitation generator options which disables spin preserving while also enabling generalized behavior. Now, combining generalized=True with preserve_spin=False results in all combinations of excitations in the given spin orbital space. De-excitations are not included and filtered accordingly.
- Fixes the [qiskit_nature.runtime.VQEClient](https://qiskit.org/documentation/nature/stubs/qiskit_nature.runtime.VQEClient.html#qiskit_nature.runtime.VQEClient) to correctly detect the type of the wrapped auxiliary operators. Previously, it would always wrap them into a dictionary and then fail when unwrapping them later, since it did not preserve the previously wrapped data type.

Changelog

Bug Fixes
- Fixes the behavior of FermionicOp.simplify when called on a zero-operator.