#hubbardmodels

Cold Atoms Simulators Reach Precise Potential Estimation Milestone with Interaction Control

intricate quantum system simulations require intricate control over individual components, which cold atoms trapped in optical lattices are ideal for. Cold atom systems can realise several Hubbard models and provide a highly controllable quantum simulation environment. The lattices' applied potentials have long been difficult to recognise, preventing the essential control.

Daniel Malz and Bhavik Kumar of the University of Copenhagen have developed a new method for precisely recognising applied potentials. This solves the problem of precisely applying and calibrating site-dependent potentials because lattice spacings are frequently below the resolution limit (diffraction limit) of imaging techniques. The new protocol, which tracks atom growth, can replicate more physical processes and provide unprecedented control in quantum simulation experiments.

Challenge of Arbitrary Potentials

Many platforms of cold atoms in optical lattices provide site-resolved quantum gas microscope readout. These systems can theoretically implement any site-dependent potential. However, imaging atomic potentials precisely is difficult when atomic features are smaller than existing imaging resolution limits. This work addresses the implementation and precise calculation of these complex, site-dependent potentials.

Quantum devices and simulations are often characterised using quantum state tomography. Digital simulation uses gate-based quantum computation, while analogue simulation directly translates a system's Hamiltonian. Realistic simulation of many-body systems in materials research and condensed matter physics requires precise potential energy landscape control and characterisation.

A Basic, Reliable Experimental Protocol

Kumar and Malz presented a simple and accurate experimental method for measuring any potential. This approach relies on Feshbach resonances in specific atomic species to temporarily turn off interactions.

This procedure has three main steps:

Interaction-free evolution: The procedure starts with a known initial state. Atomic interactions are stopped by a Feshbach resonance.

When contacts are repressed, atoms evolve under the potential's influence in line with simple, non-interacting dynamics, making atomic evolution easy to compute. Researchers measure and record atom locations and concentrations throughout this process. The approach uses quantum gas microscopy to obtain single-atom-resolution images.

Potential Reconstruction: These photos' time-evolution data lets the team accurately estimate potential.

Greater Robustness with Bayesian Methods

The work treats potentials as unknown parameters to be determined from experimental data, making potential estimation a Bayesian inverse issue. The team developed a new numerical method that uses Markov chain Monte Carlo sampling and finite element discretisation to explore potentials' huge parameter space.

The approach accurately and robustly reconstructs complex potential landscapes even with noisy or defective experimental data. The approach is also shown to be robust to common experimental problems, such as ambiguity in parameters like the atomic hopping rate and state preparation errors. A few repetitions can yield a high-accuracy measurement. Robust quantum simulation is a major advance.

Impact on Quantum Science

Quantum simulations could become more accurate and adaptive with this approach. The potential energy landscape must be precisely controlled and characterised to simulate complex physical systems.

Complex quantum many-body systems require this development because it allows exact control over the Hamiltonian being simulated. The researchers also suggest using the approach to study many-body localisation, quantum chaos, and quantum simulator benchmarks.

Beyond typical simulation, the approach may be used in:

Atomtronics allows cold atom circuits and study.

A neutral-atom array can be used for site-selective qubit control in quantum computing.