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To simulate a fermionic system on a quantum computer, it is necessary to encode the state of the fermions onto qubits. Fermion-to-qubit mappings such as the Jordan-Wigner and Bravyi-Kitaev transformations do this using $N$ qubits to…

Quantum Physics · Physics 2023-08-17 Brent Harrison , Dylan Nelson , Daniel Adamiak , James Whitfield

Quantum computers are expected to become a powerful tool for studying physical quantum systems. Consequently, a number of quantum algorithms for studying the physical properties of such systems have been developed. While qubit-based quantum…

It is exponentially hard to simulate quantum systems by classical algorithms, while quantum computer could in principle solve this problem polynomially. We demonstrate such an quantum-simulation algorithm on our NMR system to simulate an…

Quantum Physics · Physics 2009-07-22 Jiangfeng Du , Nanyang Xu , Xinhua Peng , Pengfei Wang , Sanfeng Wu , Dawei Lu

Number-conserved subspace encoding reduces resources needed for quantum simulations, but scalable complexity trade-off bounds for $M$ modes and $N$ particles with $\mathcal{O}(N\log M)$ qubits have remained unknown. We study…

Quantum Physics · Physics 2025-09-23 M. H. Cheng , Yu-Cheng Chen , Qian Wang , V. Bartsch , M. S. Kim , Alice Hu , Min-Hsiu Hsieh

Compact representations of fermionic Hamiltonians are necessary to perform calculations on quantum computers that lack error-correction. A fermionic system is typically defined within a subspace of fixed particle number and spin while…

Quantum Physics · Physics 2022-05-25 Diana Chamaki , Mekena Metcalf , Wibe A. de Jong

Quantum simulation of fermionic systems is a promising application of quantum computers, but in order to program them, we need to map fermionic states and operators to qubit states and quantum gates. While quantum processors may be built as…

Quantum Physics · Physics 2019-08-05 Mark Steudtner , Stephanie Wehner

We present a method for encoding second-quantized fermionic systems in qubits when the number of fermions is conserved, as in the electronic structure problem. When the number $F$ of fermions is much smaller than the number $M$ of modes,…

Quantum Physics · Physics 2022-06-09 William Kirby , Bryce Fuller , Charles Hadfield , Antonio Mezzacapo

The exponential computational cost of describing strongly correlated electrons can be mitigated by adopting a reduced density-matrix (RDM)-based description of the electronic structure. While variational two-electron RDM (v2RDM) methods can…

Chemical Physics · Physics 2026-01-06 Grier M. Jones , Run. R. Li , A. Eugene DePrince , Konstantinos D. Vogiatzis

We discuss encodings of fermionic many-body systems by qubits in the presence of symmetries. Such encodings eliminate redundant degrees of freedom in a way that preserves a simple structure of the system Hamiltonian enabling quantum…

Quantum Physics · Physics 2017-01-31 Sergey Bravyi , Jay M. Gambetta , Antonio Mezzacapo , Kristan Temme

The calculation time for the energy of atoms and molecules scales exponentially with system size on a classical computer but polynomially using quantum algorithms. We demonstrate that such algorithms can be applied to problems of chemical…

Quantum Physics · Physics 2007-05-23 Alán Aspuru-Guzik , Anthony D. Dutoi , Peter J. Love , Martin Head-Gordon

Simulating many-body fermionic systems in conventional qubit-based quantum computers poses significant challenges due to the overheads associated with the encoding of fermionic statistics in qubits, leading to the proposal of native…

Quantum Physics · Physics 2025-12-15 Ahana Ghoshal , Carlos de Gois , Kiara Hansenne , Otfried Gühne , Hai-Chau Nguyen

A compelling application of quantum computers with thousands of qubits is quantum simulation. Simulating fermionic systems is both a problem with clear real-world applications and a computationally challenging task. In order to simulate a…

Quantum Physics · Physics 2026-02-27 Emiliia Dyrenkova , Raymond Laflamme , Michael Vasmer

We propose a computational protocol for quantum simulations of Fermionic Hamiltonians on a quantum computer, enabling calculations which were previously not feasible with conventional encoding and ansatses of variational quantum…

Quantum Physics · Physics 2023-03-15 Benchen Huang , Nan Sheng , Marco Govoni , Giulia Galli

It has been a long sought goal of Quantum Simulation to find answers to long standing questions in condensed matter physics. A famous example is the ground and the excitations of 2D Hubbard model with strong repulsion below half filling.…

Quantum Gases · Physics 2020-03-09 Tin-Lun Ho

Quantum computers hold promise to enable efficient simulations of the properties of molecules and materials; however, at present they only permit ab initio calculations of a few atoms, due to a limited number of qubits. In order to harness…

Materials Science · Physics 2020-07-07 He Ma , Marco Govoni , Giulia Galli

Many-body quantum-mechanical stationary states that have real valued wavefunctions are shown to satisfy a classical conservation of energy equation with a kinetic energy function. The terms in the equation depend on the probability…

Atomic Physics · Physics 2021-07-23 James P. Finley

The Fermi-Hubbard model, a fundamental framework for studying strongly correlated phenomena could significantly benefit from quantum simulations when exploring non-trivial settings. However, simulating this problem requires twice as many…

Quantum Physics · Physics 2024-02-05 Arian Vezvaee , Nathan Earnest-Noble , Khadijeh Najafi

Classical shadow tomography offers a scalable route to estimating properties of quantum states, but the resulting reduced density matrices (RDMs) often violate constraints that ensure they represent $N$-electron states -- known as…

Quantum simulations of fermionic many-body systems crucially rely on mappings from indistinguishable fermions to distinguishable qubits. The non-local structure of fermionic Fock space necessitates encodings that either map local fermionic…

Quantum Physics · Physics 2020-06-17 Johannes Bausch , Toby Cubitt , Charles Derby , Joel Klassen

The most advanced techniques using fault-tolerant quantum computers to estimate the ground-state energy of a chemical Hamiltonian involve compression of the Coulomb operator through tensor factorizations, enabling efficient block-encodings…