An Al⁺ Optical Clock at NIST with Improved Frequency Uncertainty

The Ion Storage Group at NIST has developed several generations of frequency standards based on quantum logic spectroscopy of the ¹S₀↔³P₀ transition in ²⁷Al⁺. The latest version of this system began operation in the last year and achieves higher stability, longer continuous run times, and lower systematic uncertainty than previous versions. In this talk I will review the quantum-logic clock effort at NIST and introduce the newest system. An upgraded vacuum chamber reduces the rate of collisions with background gas by more than a factor of 100 allowing for longer continuous measurements and lower systematic shifts associated with collisions and ion reordering. Improvements in the trap design and new measurements of atomic constants reduce several other sources of frequency uncertainty. By stabilizing the clock laser through an optical fiber network to a cryogenic silicon cavity at JILA, we achieve instability as low as 3.5×10^-16/(τ/s)^1/2. Further improvement to this instability could be achieved using differential measurement techniques or by extending the system to multiple clock ions.