Outline • Introduction• Why trapped ions for miniaturization?• Miniaturized vacuum package: 1 cm 3 • Pulsed-mode ion clock performance • F-state trapping • Current focus: microwave optical double resonance continuous operation • Alternative ion clock: Alkali Mediated Atomic Clock • Conclusion Miniaturization with Long-Term and Environmental Stability • Achieve Cs Beam Clock performance in a mass and power constrained package • DARPA programs: • IMPACT: improved long-term stability • ACES: improved environmental stability Applications--Excellent timing for: • Rapid GPS acquisition, and GPS denied navigation and timing • Nano/pico (cube) satellites • Pulsed radio and spread spectrum communications Microsemi 5071A Miniature primary frequency standard Approved for Public Release, Distribution Unlimited Critical Elements of the 171 Yb + Clock Trap Electrodes Ions Yb Source Vacuum Package Control and Power Electronics Local Oscillator Magnetic Shield and Coil Repump (935 nm) Optical Pumping/ State Detection Laser (369 nm) Beam Combiner Fluorescence Collection Lens Fluorescence Detector Photo Multiplier Tube (PMT) Ionization UV Light
Outline • Introduction• Why trapped ions for miniaturization?• Miniaturized vacuum package: 1 cm 3 • Pulsed-mode ion clock performance • F-state trapping • Current focus: microwave optical double resonance continuous operation • Alternative ion clock: Alkali Mediated Atomic Clock • Conclusion Miniaturization with Long-Term and Environmental Stability • Achieve Cs Beam Clock performance in a mass and power constrained package • DARPA programs: • IMPACT: improved long-term stability • ACES: improved environmental stability Applications--Excellent timing for: • Rapid GPS acquisition, and GPS denied navigation and timing • Nano/pico (cube) satellites • Pulsed radio and spread spectrum communications Microsemi 5071A Miniature primary frequency standard Approved for Public Release, Distribution Unlimited Critical Elements of the 171 Yb + Clock Trap Electrodes Ions Yb Source Vacuum Package Control and Power Electronics Local Oscillator Magnetic Shield and Coil Repump (935 nm) Optical Pumping/ State Detection Laser (369 nm) Beam Combiner Fluorescence Collection Lens Fluorescence Detector Photo Multiplier Tube (PMT) Ionization UV Light
We report the development of a low-power, miniature Yb-171 ion clock at Sandia National Laboratories. This work is funded by the DARPA micro Position, Navigation, and Timing program under the Integrated Micro Primary Atomic Clock Technology (IMPACT) project. The ultimate goal is to develop a frequency standard that has frequency stability comparable to a commercial Cs beam standard, but with 100 to 1000 times smaller size and power consumption. The Yb-171 ion has a microwave clock traItem MIN :YXB4-01335-A112nsition at 12.6 GHz, and the natural linewidth of the clock resonance is expected to be less than 10-3Hz, which leads to a very high-Q clock resonance. An atomic clock using trapped ions is an excellent candidate for miniaturization because ions are well isolated from the environment independently of the size of the trap. Compared to optical traps for neutral atoms, the trapping depth of RF traps for ions is usually several orders of magnitude deeper. Therefore, the requirement for the vacuum level is more forgiving. We have successfully developed miniature ion-trap vacuum packages as shown in Fig. 1. Usually, a few microTorr of He buffer gas is introduced into each of our miniature ion-trap vacuum packages, which are sealed and passively pumped by non-evaporable getters. Using a sealed 3 cc ion-trap package, we were able to demonstrate long-term clock operation, with the stability reaching the 10-14range after a few days of integration [1].
We are developing a highly miniaturized trapped ion clock to probe the 12.6 GHz hyperfine transition in the 171Yb+ ion. The clock development is being funded by the Integrated Micro Primary Atomic Clock Technology (IMPACT) program from DARPA where the stated goals are to develop a clock that consumes 50 mW of power, has a size of 5 cm3, and has a long-term frequency stability of 10-14 at one month. One of the significant challenges will be to develop miniature single-frequency lasers at 369 nm and 935 nm and the optical systems to deliver light to the ions and to collect ion fluorescence on a detector.
We describe the development and frequency instability measurements of a highly miniaturized, buffer gas cooled, trapped-ion atomic clock. The clock utilizes the 12.6 GHz hyperfine transition of the171Yb+ion. A custom-built 3 cm3vacuum package containing the ion trap is integrated with other key elements of the atomic frequency standard, including a photo multiplier tube, miniaturized laser sources at 369 nm and 935 nm, a local oscillator, and control electronics. With the clock physics package assembled on a 10 cm × 15 cm breadboard, the long-term fractional frequency instability was measured to be 6 × 10-14at 25 days of integration. Later, the clock physics package was further miniaturized, and the frequency instability was measured to be 2 × 10-11/τ1/2at integration times up to 10,000 s.
We report on the development of a highly miniaturized vacuum package for use in an atomic clock utilizing trapped ytterbium-171 ions. The vacuum package is approximately 1 cm(3) in size and contains a linear quadrupole RF Paul ion trap, miniature neutral Yb sources, and a non-evaporable getter pump. We describe the fabrication process for making the Yb sources and assembling the vacuum package. To prepare the vacuum package for ion trapping, it was evacuated, baked at a high temperature, and then back filled with a helium buffer gas. Once appropriate vacuum conditions were achieved in the package, it was sealed with a copper pinch-off and was subsequently pumped only by the non-evaporable getter. We demonstrated ion trapping in this vacuum package and the operation of an atomic clock, stabilizing a local oscillator to the 12.6 GHz hyperfine transition of (171)Y b(+). The fractional frequency stability of the clock was measured to be 2 × 10(-11)/τ(1/2).
This dissertation reports on the development of a low-power, high-stability miniature atomic frequency standard based on 171Yb+ ions. The ions are buffer-gas cooled and held in a linear quadrupole trap that is integrated into a sealed, getter-pumped vacuum package, and interrogated on the 12.6 GHz hyperfine transition. We hope to achieve a long-term fractional frequency stability of 10^-14 with a miniature clock that consumes only 50 mW of power and occupies a volume of 5 cm^3. I discuss our progress over several years of work on this project. We began by building a conventional tabletop clock to use as a test bed while developing several designs of miniature ion-trap vacuum packages, while also developing techniques for various aspects of the clock operation, including ion loading, laser and magnetic field stabilization, and a low power ion trap drive. The ion traps were modeled using boundary element software to assist with the design and parameter optimization of new trap geometries. We expect a novel trap geometry that uses a material new to ion traps to lead to an exceptionally small ion trap vacuum package in the next phase of the project. To achieve the long-term stability required, we have also considered the sensitivity of the clock frequency to magnetic fields. A study of the motion of the individual ions in a room-temperature cloud in the trap was performed with the purpose of understanding the effect of both spatially varying and constant magnetic fields on the clock resonance and therefore the operation of the clock. These effects were studied experimentally and theoretically for several traps. In summary, this dissertation is a contribution to the design, development, and testing of a 171Yb+ ion cloud frequency standard and related techniques, including analyses of trap geometries and parameters, modeling of the ion motion, and the practical operation of the clock.
A microfabricated ion frequency standard (i.e. an ion clock) is disclosed with a permanently-sealed vacuum package containing a source of ytterbium (Yb) ions and an octupole ion trap. The source of Yb ions is a micro-hotplate which generates Yb atoms which are then ionized by a ultraviolet light-emitting diode or a field-emission electron source. The octupole ion trap, which confines the Yb ions, is formed from suspended electrodes on a number of stacked-up substrates. A microwave source excites a ground-state transition frequency of the Yb ions, with a frequency-doubled vertical-external-cavity laser (VECSEL) then exciting the Yb ions up to an excited state to produce fluorescent light which is used to tune the microwave source to the ground-state transition frequency, with the microwave source providing a precise frequency output for the ion clock.