Quantum Information Processing

, Volume 14, Issue 4, pp 1151–1178 | Cite as

Approximating ground and excited state energies on a quantum computer

  • Stuart Hadfield
  • Anargyros Papageorgiou


Approximating ground and a fixed number of excited state energies, or equivalently low-order Hamiltonian eigenvalues, is an important but computationally hard problem. Typically, the cost of classical deterministic algorithms grows exponentially with the number of degrees of freedom. Under general conditions, and using a perturbation approach, we provide a quantum algorithm that produces estimates of a constant number \(j\) of different low-order eigenvalues. The algorithm relies on a set of trial eigenvectors, whose construction depends on the particular Hamiltonian properties. We illustrate our results by considering a special case of the time-independent Schrödinger equation with \(d\) degrees of freedom. Our algorithm computes estimates of a constant number \(j\) of different low-order eigenvalues with error \(O(\varepsilon )\) and success probability at least \(\frac{3}{4}\), with cost polynomial in \(\frac{1}{\varepsilon }\) and \(d\). This extends our earlier results on algorithms for estimating the ground state energy. The technique we present is sufficiently general to apply to problems beyond the application studied in this paper.


Eigenvalue problem Quantum algorithms Excited states Schrödinger equation 



The authors would like to thank Joseph F. Traub for useful comments and suggestions. This research has been supported in part by NSF/DMS.


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  1. 1.Department of Computer ScienceColumbia UniversityNew YorkUSA

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