Variational Quantum Eigensolver (VQE)


A Quantum Computing Cornerstone

The Variational Quantum Eigensolver (VQE) is a cornerstone algorithm in the realm of quantum computing, widely recognized for its significant applications in quantum chemistry and material science. It plays a crucial role in determining ground state energies and wavefunctions of intricate quantum systems, offering insights into complex molecular and material behaviors.

A Key Player in the NISQ Era

Emerging as a cornerstone algorithm during the Noisy Intermediate-Scale Quantum (NISQ) era, VQE has gained prominence for its practicality in quantum chemistry computations. Its design, tailored to operate within the constraints of current quantum technologies, renders it an invaluable asset in the research and development of quantum systems.

The VQE Process: A Quantum-Classical Synergy

VQE integrates quantum computation with classical optimization techniques:

Hamiltonian Definition: The journey begins by formulating a Hamiltonian that encapsulates the characteristics of the quantum system under study, such as a molecular structure.

  • Parameterized Quantum Circuit (Ansatz): A carefully chosen ansatz, or parameterized quantum circuit, approximates the ground state of the system.
  • Hybrid Quantum-Classical Approach: The core of VQE lies in its hybrid methodology. A classical optimizer is employed to methodically adjust the parameters of the ansatz. This aims to minimize the expectation value of the Hamiltonian's energy, crucial for reaching the system's ground state.
  • Iterative Optimization Process: Optimization in VQE is an iterative process, fine-tuned through user-defined parameters like maximum iterations and number of quantum measurements (num_shots). This ensures precision and stability in reaching the lowest energy state.

In this interplay between quantum and classical realms, VQE iterates between measuring the Hamiltonian's expectation value on the quantum state and using classical algorithms to optimize the quantum circuit parameters.

Applications of VQE

VQE's utility spans many domains:

  • Quantum Chemistry: Pivotal in modeling molecular structures, VQE aids in unravelling their chemical properties, fostering advancements in drug discovery and material innovation.
  • Material Science: VQE contributes significantly to understanding and developing new materials, particularly those with complex quantum behaviors.
  • Complex Optimization Problems: Beyond chemistry, VQE shows promise in addressing intricate optimization challenges in areas like logistics and network design.

Model the Quantum World: Explore Molecular Structures with VQE on Classiq! 

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