Research Article

Spectroscopic observation of SU(N)-symmetric interactions in Sr orbital magnetism

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Science  19 Sep 2014:
Vol. 345, Issue 6203, pp. 1467-1473
DOI: 10.1126/science.1254978

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Studying magnetism with cold atoms

Physicists have used cold atomic gases to simulate quantum phenomena that we normally associate with much more complex systems, such as solid-state materials. Because the properties of these gases are so tunable, it is also possible to create conditions that otherwise do not exist in nature. Zhang et al. studied an exotic type of magnetism in an array of pancake-shaped atomic clouds of 87Sr. They prepared the atoms' nuclei in different combinations of 10 quantum states. They then shone pulses of light at the atoms to deduce the properties of the atoms' interactions. The interactions were independent of the atoms' nuclear states—a hallmark of an unusual symmetry that theorists predict may lead to interesting collective effects.

Science, this issue p. 1467


SU(N) symmetry can emerge in a quantum system with N single-particle spin states when spin is decoupled from interparticle interactions. Taking advantage of the high measurement precision offered by an ultrastable laser, we report a spectroscopic observation of SU(N ≤ 10) symmetry in 87Sr. By encoding the electronic orbital degree of freedom in two clock states while keeping the system open to as many as 10 nuclear spin sublevels, we probed the non-equilibrium two-orbital SU(N) magnetism via Ramsey spectroscopy of atoms confined in an array of two-dimensional optical traps; we studied the spin-orbital quantum dynamics and determined the relevant interaction parameters. This study lays the groundwork for using alkaline-earth atoms as testbeds for important orbital models.

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