0.75 atoms improve the clock signal of 10,000 atoms
Authors: Kruse I., Lange K., Peise J., Lucke B., Pezze L., Arlt J., Ertmer W., Lisdat C., Santos L., Smerzi A., Klempt C.
Autors Affiliation: Leibniz Univ Hannover, Inst Quantenopt, Welfengarten 1, D-30167 Hannover, Germany; CNR, INO, QSTAR, Largo Enrico Fermi 2, I-50125 Florence, Italy; LENS, Largo Enrico Fermi 2, I-50125 Florence, Italy; Aarhus Univ, Inst Fys & Astron, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; Phys Tech Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany; Leibniz Univ Hannover, Inst Theoret Phys, Appelstr 2, D-30167 Hannover, Germany
Abstract: Since the pioneering work of Ramsey, atom interferometers are employed for precision metrology, in particular to measure time and to realize the second. In a classical interferometer, an ensemble of atoms is prepared in one of the two input states, whereas the second one is left empty. In this case, the vacuum noise restricts the precision of the interferometer to the standard quantum limit (SQL). Here, we propose and experimentally demonstrate a novel clock configuration that surpasses the SQL by squeezing the vacuum in the empty input state. We create a squeezed vacuum state containing an average of 0.75 atoms to improve the clock sensitivity of 10, 000 atoms by 2.05(-.37)(+.34) dB. The SQL poses a significant limitation for today’s microwave fountain clocks, which serve as the main time reference. We evaluate the major technical limitations and challenges for devising a next generation of fountain clocks based on atomic squeezed vacuum.
KeyWords: Atomic clock; squeezed vacuum; precision below the SQL