Measuring correlation and entanglement between molecular orbitals on a trapped-ion quantum computer

Area of Science:

• Quantum chemistry
• Computational materials science
• Quantum information science

Background:

• Quantifying molecular orbital correlation and entanglement is crucial for understanding quantum effects in chemical reactions.
• Classical computation of these quantum properties is often limited by the computational cost of storing wavefunctions.
• Strongly correlated systems, like those in lithium-ion battery chemistry, present significant computational challenges.

Purpose of the Study:

• To utilize a trapped-ion quantum computer to calculate orbital entanglement and correlation in a relevant molecular system.
• To demonstrate the feasibility of using quantum computation for accurate estimation of molecular entanglement.
• To investigate the conditions under which one-orbital entanglement occurs in molecular systems.

Main Methods:

• Employed the Quantinuum H1-1 trapped-ion quantum computer.
• Calculated von Neumann entropies to quantify orbital correlation and entanglement.
• Incorporated fermionic superselection rules to reduce measurement overhead.
• Utilized commuting sets of Pauli operators for further optimization.
• Applied low-overhead noise reduction techniques.

Main Results:

• Achieved excellent agreement between quantum computation results and noiseless benchmarks.
• Demonstrated accurate estimation of correlations and entanglement between molecular orbitals via quantum computation.
• Showed that one-orbital entanglement is absent unless opposite-spin open shell configurations are present in the wavefunction.

Conclusions:

• Quantum computation provides an accurate and feasible method for quantifying molecular orbital entanglement.
• Fermionic superselection rules and optimized measurement strategies enhance the efficiency of quantum calculations.
• The presence of specific electron configurations is a key factor for one-orbital entanglement in molecular systems.