Experimental Quantum Seminar - Boris Braverman (University of Ottawa) “Cavity QED with Alkaline-Earth Atoms”

“Cavity QED with Alkaline-Earth Atoms”
Cavity quantum electrodynamics (QED) is a leading physical platform for quantum computation and metrology, relying on coupling an ensemble of atoms to an optical cavity. The cavity field acts as a quantum bus, coherently transferring information between the atoms and thereby enabling the creation of entangled atomic states.
State of the art atomic sensors operate near the standard quantum limit (SQL) of projection noise, and overcoming this limit by using atom-atom entanglement, such as spin squeezing, is a major goal in quantum metrology. In our experiment, we couple an ensemble of approximately 1000 Yb-171 atoms to a high-finesse asymmetric micromirror cavity with single-atom cooperativity of 1.8., and produce a near-unitary spin squeezed state.
The observed spin noise suppression and metrological gain are limited by the state readout to 9.4(4) dB and 6.5(4) dB, respectively, while the generated states offer a spin noise suppression of 15.9(6) dB and a metrological gain of 12.9(6) dB over the standard quantum limit, limited by the curvature of the Bloch sphere. When requiring the squeezing process to be within 30% of unitarity, we demonstrate an interferometer that improves the averaging time over the SQL by a factor of 3.7(2). The squeezed state can be readily mapped onto the optical clock transition in ytterbium, leading to improved precision in the best clocks currently in existence.
The spin squeezed state we characterize is highly entangled – producing an equivalent state using a gate-based quantum computer would require approximately 2000 CNOT gates, each with 96% fidelity. These results illustrate the power of all-to-all qubit connectivity for quantum processing tasks, and pave the way for the production of increasingly complex quantum states for quantum metrology, simulation, and computing using cavity QED.
Host: Bonnie Fleming