Introducing Qiskit Nature

By the Qiskit Applications Team

Qiskit Nature is designed for generic users — ranging from quantum computing experts to more applied, domain expert researchers — to investigate and simulate problems in natural sciences using quantum algorithms. Qiskit Nature’s modularity and its wide composition of different modules ensures its extensive capabilities to address complex problems in physics, chemistry and biology. In upcoming releases we will fully exploit this potential by introducing more applications related to natural sciences.

We designed Qiskit Nature to guarantee modularity and extensibility, while keeping a user-friendly interface that enables its direct application to real world problems. New in Qiskit Nature is the notion of a ‘Problem’, which is a class that identifies particular, domain-specific quantum computing solutions that leverage general quantum algorithms supplied in Qiskit 0.25 — “electronic structure problem,” for example. The Problem-based structure enables a straightforward extension of Qiskit Nature toward other problem classes in condensed matter, lattice field theories, and biology.

This first release focuses on quantum chemistry solutions for electronic structure and vibrational structure problems. The built-in mapping of the initial fermionic and bosonic second quantized Hamiltonian into qubit operators leverages different levels of optimization and delivers corresponding qubit operators without the need of specific quantum computing competence.

As part of this release, Qiskit Nature will allow us to use the ubiquitous second quantization formalism to solve a variety of problems, ranging from fundamental particle physics to solid state physics, quantum chemistry and statistical mechanics. Qiskit Nature helps you re-frame your problem using operators that fulfill fermionic, bosonic or spin statistics. Combinations of degrees of freedom subject to different commutation rules are also supported. This functionality will enable the implementation of arbitrary Hamiltonians — or, in short, Qiskit Nature is a stepping stone toward developing new applications in the natural sciences domain.

Tackling quantum chemistry problems with Qiskit Nature requires the use of classical code, such as the PySCF driver. Qiskit Nature makes it easy to import and use these drivers, and then act on the output of the drivers using Transformers. Transformers help select or modify only the quantities from the Driver that you want to use, and then return an updated input to use for your quantum chemistry problem. Essentially, these transformers are ensuring that your program is only using the pieces of the classical data necessary in order to maximize its efficiency. Examples of transformations applied to electronic structure problems are the active space and freeze core reduction schemes. All future operations affecting the generation of second quantized operators will become part of this interface.

Once we have defined the problem, Qiskit Nature also helps map it onto the quantum computer. Second quantized operators are mapped onto qubit operators that can be directly used in quantum computations, without losing the information related to the nature of the problem. Different mappings are required for each different problem class and are available in Qiskit Nature via the qubit converter. In the case of fermionic problems, three different mapping schemes are provided: Jordan Wigner, Bravyi Kitaev, and Parity. For the spin operators we support the linear mapping while for vibrational operators the direct mapping is provided. The qubit converter can also perform qubit reduction operations exploiting symmetries in the Hamiltonian (expressed in qubit form) or other intrinsic properties of the qubit operator.

A special thanks to the core contributors (in alphabetical order):
Panagiotis Barkoutsos, Anton Dekusar, Bryce Fuller, Julien Gacon, Ikko Hamamura, Takashi Imamichi, John Lapeyre, Dariusz Lasecki, Manoel Marques, Simon Mathis, Atsushi Matsuo, Giulia Mazzola, Pauline Ollitrault, Max Rossmannek, Igor Sokolov, Ivano Tavernelli, Stefan Woerner, Steve Wood

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