# Nonunitary Operations for Ground-State Calculations in Near-Term Quantum Computers.

@article{Mazzola2019NonunitaryOF, title={Nonunitary Operations for Ground-State Calculations in Near-Term Quantum Computers.}, author={Guglielmo Mazzola and Pauline J. Ollitrault and Panagiotis Kl. Barkoutsos and Ivano Tavernelli}, journal={Physical review letters}, year={2019}, volume={123 13}, pages={ 130501 } }

We introduce a quantum Monte Carlo inspired reweighting scheme to accurately compute energies from optimally short quantum circuits. This effectively hybrid quantum-classical approach features both entanglement provided by a short quantum circuit, and the presence of an effective nonunitary operator at the same time. The functional form of this projector is borrowed from classical computation and is able to filter out high-energy components generated by a suboptimal variational quantum…

## 25 Citations

### Quantum computer-aided design of quantum optics hardware

- PhysicsQuantum Science and Technology
- 2021

This work presents the concept of quantum computer designed quantum hardware and applies it to the field of quantum optics and shows explicitly how digital quantum simulation of Boson sampling experiments can be realized.

### Improved Accuracy on Noisy Devices by Nonunitary Variational Quantum Eigensolver for Chemistry Applications.

- PhysicsJournal of chemical theory and computation
- 2021

Nonunitary Variational Quantum Eigensolver (nu-VQE), in which a nonunitary operator is combined with the original system Hamiltonian leading to a new variational problem with a simplified wave function ansatz, using the Jastrow factor.

### Variational Quantum Algorithms

- Physics, Computer ScienceNature Reviews Physics
- 2021

An overview of the field of Variational Quantum Algorithms is presented and strategies to overcome their challenges as well as the exciting prospects for using them as a means to obtain quantum advantage are discussed.

### Algorithmic Error Mitigation Scheme for Current Quantum Processors

- Physics, Computer ScienceQuantum
- 2021

A hardware agnostic error mitigation algorithm for near term quantum processors inspired by the classical Lanczos method is presented, which significantly increases the accuracy of cost functions evaluations within the framework of variational quantum algorithms, thus leading to improved ground-state calculations for quantum chemistry and physics problems beyond state-of-the-art results.

### Solving quantum statistical mechanics with variational autoregressive networks and quantum circuits

- Physics, Computer ScienceMach. Learn. Sci. Technol.
- 2021

An efficient variational algorithm is devised to jointly optimize the classical neural network and the quantum circuit to solve quantum statistical mechanics problems and obtain thermal observables such as the variational free energy, entropy, and specific heat.

### Variational Quantum-Neural Hybrid Eigensolver.

- PhysicsPhysical review letters
- 2022

The variational quantum eigensolver (VQE) is one of the most representative quantum algorithms in the noisy intermediate-scale quantum (NISQ) era, and is generally speculated to deliver one of the…

### Preparation of excited states for nuclear dynamics on a quantum computer

- Computer SciencePhysical Review C
- 2020

These findings show that quantum techniques designed to achieve good asymptotic scaling on fault tolerant quantum devices might also provide practical benefits on devices with limited connectivity and gate fidelity.

### Encoding strongly-correlated many-boson wavefunctions on a photonic quantum computer: application to the attractive Bose-Hubbard model

- PhysicsQuantum
- 2021

Variational quantum algorithms (VQA) are considered as some of the most promising methods to determine the properties of complex strongly correlated quantum many-body systems, especially from the…

### Symmetry-adapted variational quantum eigensolver

- Physics
- 2020

We propose a scheme to restore spatial symmetry of Hamiltonian in the variational-quantum-eigensolver (VQE) algorithm for which the quantum circuit structures used usually break the Hamiltonian…

### Nonunitary gate operations by dissipation engineering

- PhysicsQuantum Science and Technology
- 2022

Irreversible logic is at odds with unitary quantum evolution. Emulating such operations by classical measurements can result in disturbances and high resource demands. To overcome these limitations,…

## References

SHOWING 1-10 OF 44 REFERENCES

### Progress towards practical quantum variational algorithms

- Physics
- 2015

The preparation of quantum states using short quantum circuits is one of the most promising near-term applications of small quantum computers, especially if the circuit is short enough and the…

### Gate-Efficient Simulation of Molecular Eigenstates on a Quantum Computer

- PhysicsPhysical Review Applied
- 2019

A key requirement to perform simulations of large quantum systems on near-term quantum hardware is the design of quantum algorithms with short circuit depth that finish within the available coherence…

### Quantum Chemistry Calculations on a Trapped-Ion Quantum Simulator

- PhysicsPhysical Review X
- 2018

Quantum-classical hybrid algorithms are emerging as promising candidates for near-term practical applications of quantum information processors in a wide variety of fields ranging from chemistry to…

### Quantum Computing in the NISQ era and beyond

- PhysicsQuantum
- 2018

Noisy Intermediate-Scale Quantum (NISQ) technology will be available in the near future, and the 100-qubit quantum computer will not change the world right away - but it should be regarded as a significant step toward the more powerful quantum technologies of the future.

### Gate count estimates for performing quantum chemistry on small quantum computers

- Physics, Computer Science
- 2014

This paper focuses on the quantum resources required to find the ground state of a molecule twice as large as what current classical computers can solve exactly and suggests that for quantum computation to become useful for quantum chemistry problems, drastic algorithmic improvements will be needed.

### Hardware-efficient variational quantum eigensolver for small molecules and quantum magnets

- PhysicsNature
- 2017

The experimental optimization of Hamiltonian problems with up to six qubits and more than one hundred Pauli terms is demonstrated, determining the ground-state energy for molecules of increasing size, up to BeH2.

### A variational eigenvalue solver on a photonic quantum processor

- PhysicsNature communications
- 2014

The proposed approach drastically reduces the coherence time requirements and combines this method with a new approach to state preparation based on ansätze and classical optimization, enhancing the potential of quantum resources available today and in the near future.

### Towards quantum chemistry on a quantum computer.

- Physics, ChemistryNature chemistry
- 2010

The application of the latest photonic quantum computer technology to calculate properties of the smallest molecular system: the hydrogen molecule in a minimal basis is reported and the complete energy spectrum is calculated to 20 bits of precision.

### Computational complexity and fundamental limitations to fermionic quantum Monte Carlo simulations

- PhysicsPhysical review letters
- 2005

It is proved that the sign problem is nondeterministic polynomial (NP) hard, implying that a generic solution of the sign problems would also solve all problems in the complexity class NP inPolynomial time.

### Quantum algorithms for electronic structure calculations: Particle-hole Hamiltonian and optimized wave-function expansions

- PhysicsPhysical Review A
- 2018

In this work we investigate methods to improve the efficiency and scalability of quantum algorithms for quantum chemistry applications. We propose a transformation of the electronic structure…