Abstract
The physics of interacting integer-spin chains has been a topic of intense theoretical interest, particularly in the context of symmetry-protected topological phases. However, there has not been a controllable model system to study this physics experimentally. We demonstrate how spin-dependent forces on trapped ions can be used to engineer an effective system of interacting spin-1 particles. Our system evolves coherently under an applied spin-1 Hamiltonian with tunable, long-range couplings, and all three quantum levels at each site participate in the dynamics. We observe the time evolution of the system and verify its coherence by entangling a pair of effective three-level particles (“qutrits”) with 86% fidelity. By adiabatically ramping a global field, we produce ground states of the model, and we demonstrate an instance where the ground state cannot be created without breaking the same symmetries that protect the topological Haldane phase. This experimental platform enables future studies of symmetry-protected order in spin-1 systems and their use in quantum applications.
- Received 6 October 2014
DOI:https://doi.org/10.1103/PhysRevX.5.021026
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Published by the American Physical Society
Popular Summary
Two isolated quantum states in an atom can be used experimentally to represent a quantum version of a bar magnet that has either its north or south pole pointing up. Coupling many such atoms together enables physicists to study how magnetism works at the quantum level. Controlling more than two states per atom is harder to achieve in the lab but would make it possible to experiment with more complicated forms of quantum magnetism that are exponentially harder to study on a computer ( versus ). Here, we control interactions among ions with three quantum states apiece (“qutrits”): a north or south pole-up magnet or no magnet at all.
We employ trapped ions; the energy gap of such a spin-1 system may be useful for quantum memories in the future. The quantum-mechanical interactions allow magnets to hop from site to site and allow pairs of magnets with different orientations to appear and disappear together. After preparing two empty sites, we optically measure the spin state and observe signatures of magnet pairs appearing and disappearing; we also show that the pairs exhibit quantum entanglement persisting for milliseconds. By manipulating a special magnetic field, we also prepare the quantum ground state (the configuration of magnets and empty sites that have the lowest possible interaction energy).
This new method for creating spin-1 quantum magnets opens the door to studying the fundamental physical properties of magnets and learning to exploit them for quantum technologies. Our method can be used for other types of interactions and might even be a stepping stone toward creating exotic phases of matter that retain their quantum properties when they interact with the classical world.