Fast Quantum State Preparation and Bath Dynamics Using Non-Gaussian Variational Ansatz and Quantum Optimal Control.

Area of Science:

• Quantum mechanics
• Quantum information science
• Condensed matter physics

Background:

• Fast preparation of quantum many-body states is critical for advancing quantum algorithms and metrology.
• Existing methods often face limitations in speed and fidelity.

Purpose of the Study:

• To develop a novel, fast, nonadiabatic pathway for preparing quantum many-body states.
• To improve the efficiency and accuracy of quantum state preparation.

Main Methods:

• Combines quantum optimal control with a variational Ansatz utilizing non-Gaussian states.
• Demonstrated on the spin-boson model, employing a multipolaron Ansatz for near-critical ground states.

Main Results:

• Achieved significant reductions in infidelity compared to linear and optimized local adiabatic ramps (up to ≈60x for one mode).
• Demonstrated up to ≈5x infidelity reduction for many modes compared to nonadiabatic linear ramps.
• Introduced a controlled convergence criterion based on the number of polarons, outperforming leakage as a fidelity indicator.

Conclusions:

• The developed method offers a substantial improvement in fast quantum state preparation.
• The new convergence criterion provides a more reliable measure of state fidelity.
• The approach is adaptable for systems with diverse bath couplings, relevant for trapped-ion experiments.