Understanding how and at which speed information spreads in a quantum many-body system is a fundamental and intriguing question of quantum information science. Quantum metrology harnesses quantum entanglement for enhancing the precision of atomic sensors beyond the standard quantum limit. What do these apparently different fields of quantum mechanics have in common? We experimentally show that these are actually two sides of the same coin.
On the one side, the direct experimental observation of quantum information spread, called “quantum information scrambling”, is a difficult task. An emerging tool to witness scrambling are the out-of-the-time-ordered correlators (OTOCs). OTOCs require the system to evolve backward in time after the encoding of a small portion of quantum information. On the other side, in quantum metrology, collective entangled states are characterized by their quantum Fisher information (QFI) which quantifies the sensitivity of the state to a certain perturbation.
In this work, we experimentally investigate quantum information scrambling and entanglement-enhanced metrology in a Lipkin-Meshkov-Glick (LMG) model. We show that these two fields are comparable and, in particular, we demonstrate that QFI and OTOC are equivalent.
The LMG model, as well as its time-reversal, is implemented in a cavity QED system with ultracold ytterbium atoms. The cavity field mediates an effective all-to-all interaction within the atoms, while an external RF field induces a collective rotation of atoms. Moreover, we work in the regime of the LMG model where entanglement (or quantum information scrambling) occurs exponentially fast.
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|Presenter name||Simone Colombo|