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Variational Quantum Linear Solver

Journal Article · · Quantum
 [1];  [2];  [3];  [3];  [3];  [3]
  1. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States); Barcelona Supercomputing Center (Spain); Univ. de Barcelona (Spain)
  2. Michigan State Univ., East Lansing, MI (United States)
  3. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Previously proposed quantum algorithms for solving linear systems of equations cannot be implemented in the near term due to the re quired circuit depth. Here, we propose a hybrid quantum-classical algorithm, called Variational Quantum Linear Solver (VQLS), for solving linear systems on near-term quantum computers. VQLS seeks to variationally prepare |x$$\rangle$$ such that A|x$$\rangle$$ ∝ |b$$\rangle$$. We derive an operationally meaningful termination condition for VQLS that allows one to guarantee that a desired solution precision ϵ is achieved. Specifically, we prove that C $⩾$ ϵ22, where C is the VQLS cost function and κ is the condition number of A. We present efficient quantum circuits to estimate C, while providing evidence for the classical hardness of its estimation. Using Rigetti’s quantum computer, we success fully implement VQLS up to a problem size of 1024 × 1024. Finally, we numerically solve nontrivial problems of size up to 250 × 250. For the specific examples that we consider, we heuristically find that the time complexity of VQLS scales efficiently in ϵ, κ, and the system size N.

Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR)
Grant/Contract Number:
89233218CNA000001
OSTI ID:
2367476
Report Number(s):
LA-UR-19-29101; TRN: US2411384
Journal Information:
Quantum, Vol. 7; ISSN 2521-327X
Publisher:
Quantum Science Open CommunityCopyright Statement
Country of Publication:
United States
Language:
English

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