Special Group Seminar at MPQ: Light-spin interactions in atomic dysprosium: non-classical spin states and synthetic dimensions

Thomas Chalopin, ENS Paris

August 29, 2019

Thomas Chalopin, ENS Paris
MPQ Garching, Hans-Kopfermann-Str. 1,
Herbert-Walther lecture hall
Friday 08/29, 09:15am


The combination of a large spin J = 8 and narrow optical transitions
make bosonic dysprosium an ideal platform for engineering strong
light-spin interactions. In our experiments, we use off-resonant laser
beams close to the intercombination line at 626 nm to induce non-linear
spin coupling in the electronic ground state of dysprosium.

In the first part of this talk, I will describe the implementation of
the celebrated one-axis twisting Hamiltonian [Kitagawa et. al., PRA 47
5138 (1993)]. We experimentally realize a superposition of coherent
spin-states with opposite magnetizations, that we call a 'kitten' state.
We show that this highly sensitive state can be used in the context of
quantum metrology, and we experimentally measure an enhanced sensitivity
to external magnetic fields by a factor 13.9(1.1), close to the
Heisenberg limit G = 2J = 16. We also show that the combination of
single magnetic sublevel resolution and arbitrary spin rotations enables
us to measure the optimal sensitivity of non-gaussian (oversqueezed)
states, well above the capability of squeezed states, and more robust to
environmental noise than superposition states.

In the second part of the talk, I will discuss the realization of
synthetic Landau levels using dysprosium atoms. A synthetic spatial
dimension is encoded in the large spin of dysprosium, and additional
spin-orbit coupling leads to the emergence of an artificial gauge field.
In an analogy with a charged particle in an external magnetic field, the
low-energy spectrum of our system exhibits the same characteristics as
Landau levels. We are able to probe the main topological features of the
Lowest Landau level: propagating edge modes, closed cyclotron orbits and
quantization of the Hall conductance.

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