[Paper Review] Observation of a Dynamical Phase Transition in the Collective Heisenberg Model

Scott Smale, Peiru He+7 more|arXiv (Cornell University)|Jun 28, 2018

Cold Atom Physics and Bose-Einstein Condensates3 citations

TL;DR

This study observes a dynamical phase transition in a quantum simulator based on ultracold fermionic potassium atoms, where a ferromagnetically ordered state evolves into a demagnetized state under an inhomogeneous axial field. Using spin-1/2 fermions in a harmonic trap to simulate the collective Heisenberg model, the experiment demonstrates reversible dynamics and validates the system as a platform for quantum metrology and many-body quantum technologies.

ABSTRACT

Ultracold atoms, benefiting from long-lived coherence and controllable interactions, offer an ideal system to shed light on the organizing principles of out-of-equilibrium quantum systems. Here, we investigate a dynamical phase transition from a state with ferromagnetic order to a demagnetized state in a quantum simulator of the collective Heisenberg model with an inhomogeneous axial field. Two hyperfine states of fermionic potassium atoms encode the spin degrees of freedom, while single-particle oscillator modes serve as lattice sites. We benchmark the simulator using detailed comparisons to theory and by testing the reversibility of the collective dynamics. Our observations open a route for applications of large controllable fermionic ensembles to enhanced metrology and quantum technologies.

Motivation & Objective

• To investigate non-equilibrium quantum dynamics in a controllable many-body system using ultracold atoms.
• To observe a dynamical phase transition from ferromagnetic order to a demagnetized state in a quantum simulator of the collective Heisenberg model.
• To benchmark the simulator against theoretical predictions using detailed comparisons and reversibility tests.
• To explore the potential of large fermionic ensembles for enhanced quantum metrology and quantum technologies.

Proposed method

• Using two hyperfine states of fermionic potassium-40 atoms to encode spin-1/2 degrees of freedom.
• Employing single-particle oscillator modes as lattice sites in a harmonic trap to realize the collective Heisenberg model.
• Applying an inhomogeneous axial magnetic field to drive the system from a ferromagnetic initial state into a demagnetized state.
• Measuring the time evolution of spin correlations and magnetization to detect the dynamical phase transition.
• Performing detailed theoretical comparisons and testing the reversibility of the collective dynamics to validate the simulator.

Experimental results

Research questions

• RQ1 Does the collective Heisenberg model with an inhomogeneous axial field exhibit a dynamical phase transition from ferromagnetic order to a demagnetized state?
• RQ2 How accurately can ultracold fermionic atoms simulate the dynamics of the collective Heisenberg model?
• RQ3 To what extent is the collective dynamics reversible, and what does this imply for the simulator's fidelity?
• RQ4 Can this system serve as a platform for enhanced quantum metrology and quantum technologies?

Key findings

• A clear dynamical phase transition from a ferromagnetic state to a demagnetized state was observed in the quantum simulator.
• The observed dynamics showed excellent agreement with theoretical predictions, validating the simulator's accuracy.
• Reversibility of the collective dynamics was experimentally confirmed, indicating high-fidelity control and coherence.
• The system demonstrated long-lived coherence and controllable interactions, essential for simulating out-of-equilibrium quantum phenomena.