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Onset of Quantum Magnetism

Onset of Quantum Magnetism.

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Onset of Quantum Magnetism

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  1. Onset of Quantum Magnetism • Each ion represents a spin and can be thought of as a bar magnet that can be oriented up or down. The spins interact such that they prefer to orient themselves along the same direction. At the beginning of the experiment, a large effective magnetic field overpowers the spin system’s tendency to order. Thus, the spins are • in a disordered state (each • spin depicted as blue • arrows pointed randomly • along up or down). A • crossover to • ferromagnetism (FM) • occurs when this • magnetic field is • weakened compared • to the spin-spin • interaction, and all • spins are oriented • in the same direction. • In the quantum regime, the • ferromagnetcan be prepared • superposition of all spins simultaneously • in the up and down state (shown in red). Increase in ‘steepness’ Quantum spin models are powerful because they can describe many types of physical phenomena such as phase transitions in magnets. Simulations of these models can provide insights when the actual system of interest is difficult to understand theoretically or challenging to experimentally probe. Recently, PFC-supported researchers at the JQI have used a small crystal of ion spins to experimentally simulate quantum magnetism. Quantum simulations of this type, that push the limits of current computations have applications in quantum information science. To mimic a model that describes quantum magnetism, known as the transverse field Ising model, the researchers shine different colors of laser light onto an ion crystal. They choose specific colors to create spin-spin interactions that are analogous to that of a quantum ferromagnet. The scientists build up the simulator, one spin at a time, allowing them to explore finite-size effects, such as how the transition to ferromagnetism sharpens with each additional particle. spin-spin FM interaction strength As ion spins are added to the system, the magnetization, is measured. This parameter quantifies the number of spins pointed up or down and equals one for aferromagnet. The scientists observe a sharpening in the transition as the size of the system is increased. “Onset of a Quantum Phase Transition with a Trapped Ion Quantum Simulator,” R. Islam, E.E. Edwards, K. Kim, S. Korenblit, C. Noh, H. J. Carmichael, G.-D. Lin, L.-M. Duan, C.-C. Joseph Wang, J.K. Freericks& C. Monroe, Nature Comm. 2, 377 (2011)

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