† Corresponding author. E-mail:
We report the 87Sr optical lattice clock developed at the National Time Service Center. We achieved a closed-loop operation of the optical lattice clock based on 87Sr atoms. The linewidth of the spin-polarized clock peak is 3.9 Hz with a clock laser pulse length of 300 ms, which corresponds to a Fourier-limited linewidth of 3 Hz. The fitting of the in-loop error signal data shows that the instability is approximately
Over the past decade, the progress in optical clocks has been of key importance for the advancement of science and technology. Optical clocks can be used in the field of scientific research, such as fundamental constants variation measurement,[1–3] gravitational wave detection,[4] topological dark matter hunting,[5] and space research and applications.[6] In addition, optical clocks have been investigated for global navigation satellite systems and geodetic applications.[7]
The fractional frequency instability and uncertainty of the best optical clocks based on neutral atoms[8–11] and single ions[7, 12, 13] have reached the unprecedented level of
The first optical clock in China was constructed at the Wuhan Institute of Physics and Mathematics (WIPM) of the Chinese Academy of Sciences which was based on the single
The energy levels and transitions of 87Sr used for the development of the optical lattice clock are illustrated in Fig.
A top view of the experimental setup of the 87Sr optical lattice clock is shown in Fig.
The experimental setup of the first stage of cooling and trapping is shown in Fig.
The laser frequency of the 707-nm ECDL with a mode spacing of approximately 5 GHz is scanned using a frequency of 1 kHz through the current control and piezoelectric transducer (PZT), in order to cover all hyperfine transitions. The frequency scanning range can be measured by the Cavity 1. The laser beams at 679 nm (ECDL) and 707 nm are coupled to an optical fiber for a spatial filtering, and used to repump atoms for the cooling cycle in the first stage of cooling and trapping. These laser beams have powers of 8 mW (679 nm) and 10 mW (707 nm), respectively. The number of atoms can increase approximately 15 times. After the first stage of cooling and trapping, the temperature and number of atoms in the blue MOT are 5 mK and
The experimental setup of the second stage of cooling and trapping is shown in Fig.
The experimental setups of the lattice loading and clock transition probing are shown in Fig.
The timing sequence in the 87Sr optical lattice clock experiment is shown in Fig.
The number of atoms trapped in the lattice can be measured through the fluorescence intensity of the atomic cloud in the optical lattice using the PMT. The fluorescence intensity as a function of the holding time is recorded and shown in Fig.
Resolved sideband spectroscopy of the 87Sr (5s2)
The inset of Fig.
With a small bias magnetic field along the polarization axis of the clock and lattice lasers, ten separated distinct π-polarized Zeeman transitions[31] from the individual
In order to increase the signal-to-noise ratio and excitation fraction, we pump the atoms into either stretched states of
For the pulse length of the clock laser of 300 ms, the linewidth of both peaks is 3.9 Hz, obtained by the Lorentzian fit of the data, which corresponds to a Fourier-limited linewidth of 3 Hz.
Using the spin-polarized spectra of
Using the error signal from the clock laser locking to the clock transition, we can evaluate the in-loop instability of the 87Sr optical lattice clock by calculating the Allan deviation.[20] The in-loop fractional frequency instability is
We achieved a closed-loop operation of an optical lattice clock based on 87Sr atoms for more than 5 h. The linewidth of the spin-polarized spectra was 3.9 Hz with a pulse length of the clock laser of 300 ms, which corresponds to a Fourier-limited linewidth of 3 Hz. The fitting of the in-loop error signal data shows that the instability is
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