Micro-comb terahertz radium ion clock (MCTRICk)

• US 10,666,275 B1
• Filed: 12/26/2018
• Issued: 05/26/2020
• Est. Priority Date: 12/26/2018
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Tiemann, Bruce G.
• Primary Examiner(s): Gannon, Levi
• Application Number:
  US16/232,909
• Time in Patent Office: 517 Days
• Field of Search: 331 3, 331 941
• CPC Class Codes: G04F 5/14 using atomic clocks
• CPC Class Codes: H03B 17/00 Generation of oscillations using radiation source and detector, e.g. with interposed variable obturator
• CPC Class Codes: H03L 7/26 using energy levels of molecules, atoms, or subatomic particles as a frequency reference

Abstract

An ion-based atomic clock includes an ion trap, a cooling laser, a re-pumping source and a frequency comb source. The ion trap can trap a plurality of Ra⁺ ions generated by an ion generator. The cooling laser can facilitate trapping of the plurality of Ra⁺ ions within the ion trap and populate excited state levels in the trapped Ra⁺ ions. The re-pumping source can trigger decaying of the excited state levels to a first metastable level. The frequency comb source can directly drive a multi-terahertz (multi-THz) clock transition between the first metastable level and a second metastable level in the trapped Ra⁺ ions. A signal derived from the population remaining in the first metastable level following the driving of the clock transition can be used to guide the repetition rate of the frequency comb source to an accurate frequency related to the clock transition frequency.

Claims

1. An ion-based atomic clock comprising:

an ion trap configured to trap a plurality of Ra⁺ ions generated by an ion generator;

a cooling laser configured to facilitate trapping of the plurality of Ra⁺ ions within the ion trap and populate excited state levels in the trapped plurality of Ra⁺ ions;

a re-pumping source configured to trigger decaying of the excited state levels to a first metastable level; and

a frequency comb source configured to directly drive a multi-terahertz (THz) transition between the first metastable level and a second metastable level in the trapped plurality of Ra⁺ ions.

2. The ion-based atomic clock of claim 1, wherein the frequency comb source comprises a micro-resonator-based frequency comb configured to directly drive a 50 THz Raman transition in at least one Ra⁺ ion, wherein the 50 THz Raman transition is between the first metastable level and the second metastable level.

3. The ion-based atomic clock of claim 2, wherein a frequency of the micro-resonator-based frequency comb is stabilized by employing a feedback loop based on a signal derived from a light output of the ion trap.

4. The ion-based atomic clock of claim 3, wherein the light output is configured to indicate a deviation in population of the first metastable level and the second metastable level from a balanced population ratio, wherein the balanced population ratio is a 50 percent ratio.

5. The ion-based atomic clock of claim 4, wherein the light output is configured to indicate a deviation of a frequency of the frequency comb source from 50 THz.

6. The ion-based atomic clock of claim 1, wherein the frequency comb source is configured to provide an output clock pulse similar to a pulsed laser.

7. The ion-based atomic clock of claim 1, wherein the ion-based atomic clock is free of a carrier-offset-stabilized frequency comb.

8. The ion-based atomic clock of claim 1, further comprising a mini-vacuum ion trap assembly.

9. The ion-based atomic clock of claim 1, wherein polarization of the frequency comb source is tuned to make the ion-based atomic clock insensitive to laser light power fluctuations.

10. The ion-based atomic clock of claim 1, wherein the first metastable level comprises a 6d-state in the trapped plurality of Ra⁺ ions at an about 12,084.3 cm⁻

1 energy level.

11. The ion-based atomic clock of claim 1, wherein the second metastable level comprises a 6d-state in the trapped plurality of Ra⁺ ions at an about 13,743.0 cm⁻

1 energy level.

12. An apparatus comprising:

an ion trap configured to trap a plurality of Ra⁺ ions; and

a micro-resonator-based frequency comb configured to directly drive a multi-terahertz (multi-THz)

transition between a first metastable level and a second metastable level in the trapped plurality of Ra⁺ ions.

13. The apparatus of claim 12, wherein the micro-resonator-based frequency comb is configured to directly drive a 50 THz transition in at least one Ra⁺ ion of the trapped plurality of Ra⁺ ions.

14. The apparatus of claim 12, wherein a frequency of the micro-resonator-based frequency comb is stabilized by employing a feedback loop based on a signal derived from a light output of the ion trap.

15. The apparatus of claim 14, wherein the light output is configured to indicate a deviation of a frequency of the micro-resonator-based frequency comb from 50 THz.

16. The apparatus of claim 12, wherein the first metastable level comprises a 6d-state in the trapped Ra⁺ ion at about 12,084.3 cm⁻

1 energy level, and wherein the second metastable level comprises a 6d-state in the trapped Ra⁺ ion at about 13,743.0 cm<sup>−

1</sup> energy level.

17. A method comprising:

trapping a plurality of Ra⁺ ions in an ion trap; and

directly driving a multi-terahertz (Multi-THz) transition between a first metastable level and a second metastable level in the trapped plurality of Ra⁺ ions using a micro-resonator-based frequency comb.

18. The method of claim 17, wherein:

directly driving the multi-THz transition comprises directly driving a 50 THz transition in at least one Ra⁺ ion of the trapped plurality of Ra⁺ ions,

the first metastable level comprises a 6d-state in the trapped Ra+ ion at about 12,084.3 cm<sup>−

1</sup> energy level, and

the second metastable level comprises a 6d-state in the trapped Ra+ ion at about 13,743.0 cm<sup>−

1</sup> energy level.

19. The method of claim 17, further comprising stabilizing a frequency of the micro-resonator-based frequency comb by employing a feedback loop based on an RF signal derived from a light output of the ion trap.

20. The method of claim 19, wherein the light output is configured to indicate a deviation of a frequency of the micro-resonator-based frequency comb from 50 THz.