- Open Access
Certifying Ground-State Properties of Many-Body Systems
Phys. Rev. X 14, 031006 – Published 11 July, 2024
DOI: https://doi.org/10.1103/PhysRevX.14.031006
Abstract
A ubiquitous problem in quantum physics is to understand the ground-state properties of many-body systems. Confronted with the fact that exact diagonalization quickly becomes impossible when increasing the system size, variational approaches are typically employed as a scalable alternative: Energy is minimized over a subset of all possible states and then different physical quantities are computed over the solution state. Despite remarkable success, rigorously speaking, all that variational methods offer are upper bounds on the ground-state energy. On the other hand, so-called relaxations of the ground-state problem based on semidefinite programming represent a complementary approach, providing lower bounds to the ground-state energy. However, in their current implementation, neither variational nor relaxation methods offer provable bound on other observables in the ground state beyond the energy. In this work, we show that the combination of the two classes of approaches can be used to derive certifiable bounds on the value of any observable in the ground state, such as correlation functions of arbitrary order, structure factors, or order parameters. We illustrate the power of this approach in paradigmatic examples of 1D and 2D spin- Heisenberg models. To improve the scalability of the method, we exploit the symmetries and sparsity of the considered systems to reach sizes of hundreds of particles at much higher precision than previous works. Our analysis therefore shows how to obtain certifiable bounds on many-body ground-state properties beyond energy in a scalable way.
Physics Subject Headings (PhySH)
Popular Summary
The interplay of particle interactions and quantum fluctuations can stabilize intriguing phases of matter, and the resulting quantum entanglement sometimes represents a resource for quantum computations. Yet, it is one of the most difficult problems for numerical methods, as the system’s phase space grows exponentially with the number of particles. In this work, we introduce a numerical scheme to derive upper and lower bounds on arbitrary ground-state observables for many-body quantum systems. This scheme can be systematically refined to converge to the exact ground-state value.
We illustrate the potential of our numerical method in paradigmatic spin models in one and two dimensions. But the construction is much more general and can be applied to systems of both distinguishable and indistinguishable particles as well as arbitrary lattice geometries. The symmetries and sparsity of the studied model can be used to significantly improve the scalability of the computation.
In future work, our approach could be used to certify the output of quantum simulators, as well as to study phases of matter and phase transitions in complex quantum systems.
Article Text
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