ResearchResearch Area B
Research propject B02

Project B02: Quantum engineered optical lattice clocks

In this project we will investigate and implement methods to circumvent limitations in accuracy and stability using both an operational strontium lattice clock and a more flexible setup with ultracold calcium. With these optical clocks we will investigate fundamental questions of the temporal and spatial stability of e.g. the fine structure constant α and its potential couplings to dark matter. Specifically tailored motional quantum states shall be used to identify and minimize motion-related clock uncertainties. To address limitations from the linewidth of the interrogation laser, which is in fact limiting the stability of most ion and neutral atom clocks, we will in parallel investigate an active optical frequency source based on super-fluorescence on a narrow clock transition.

INTRODUCTION

Optical lattice clocks have recently reached instabilities and uncertainties in the 10−18 range opening new research fields like relativistic geodesy and tests of general relativity. Further reduction of the uncertainty and applications of optical clocks for investigations of time dependent phenomena in geodesy and fundamental physics, e.g. related to dark matter are hampered by the necessary averaging times to achieve sufficiently small statistical uncertainty. Currently the instability of neutral atom clocks is limited both by the quantum projection noise (QPN) and the frequency noise of the interrogation laser. To further reduce the systematic uncertainty, various small frequency shifts in the range of 10−19 that depend on the motional quantum state need to be understood and controlled.

Within this project we will investigate and implement methods to circumvent these limitations in accuracy and stability using both an operational strontium lattice clock and a more flexible setup with ultracold calcium. In the strontium lattice clock, we will use specifically tailored motional quantum states to identify and minimize motion-related shifts and using novel cavity-aided minimally disturbing measurements on ultra-cold atoms to avoid limitations on the stability. New interrogation methods will be investigated that enable compound clock systems and thus enhance clock stability and reduce measurement time. Within DQ-mat, we will be able to perform clock measurements with exquisite resolution to test fundamental theories like Lorentz and position invariance and search for e.g. new couplings between dark and normal matter.

RESULTS

Thanks to the outstanding interplay between the development of highly coherent interrogation lasers and the advances in our lattice clock, we were able to realize one of the most stable optical clocks in the world. We have characterized decoherence mechanisms on the lattice clock caused by scattering of lattice photons and will now investigate the dependence of light shifts in the optical lattice on the motional quantum state of the atoms.

Bildbeschreibung ergänzen

To avoid spurious Doppler shifts, the atoms are tightly confined in an optical lattice. Its wavelength is chosen such that to first order the light shifts of the upper and lower clock states are equal. Even though the optical lattice is far detuned from atomic resonances, a small scattering rate is observed that destroys the coherence between the atomicclock states. The figure shows the related redistribution of the population N, here visible as a repopulation of the atomic ground state g. We have operated our Sr lattice clock in several clock comparison campaigns. The data are currently analyzed with respect to time dependence of the fine structure constant α, visible in the ratio of the clocks’ frequencies, which could be caused by a hypothetical coupling to dark matter. The Sr clock was also involved in a highly accurate measurement of the isotope shift between 88Sr and 87Sr. With a network of clocks in Europe, we have already performed a stringent test of Lorentz invariance.

As optical clocks with neutral atoms show a superior stability compared to optical clocks based on single ions, they may be used to reduce the averaging times of the latter in a hybrid-clock approach. We have developed a scheme that allows to extend the coherent interrogation time in an ion clock significantly beyond the coherence time of the interrogation laser. This will correspondingly improve the ion clock’s QPN-limited stability.

FUTURE

As a consequence of the rapid development of interrogation lasers in our groups, the project will shift its focus away from squeezing-related improvement of lattice clocks. Though there are scenarios like correlated interrogation of two clocks, in which improvements of the clock stability can be achieved, the advantage for a single clock apparatus as in our case appears to be marginal under the given conditions. We will therefore focus on fundamental tests with improved resolution with our partners in DQ-mat, the investigation of quantum state-dependent clock uncertainties and the optimal exploitation of our clocks by interrogation sequences adapted to the specific measurement task at hand.

PUBLICATIONS

  • S. Herbers, S. Dorscher, E. Benkler, C. Lisdat (2019): Phase noise of frequency doublers on optical clock lasersOptics Express 27, 23262-23273
    DOI: /10.1364/OE.27.023262
  • Schwarz, Roman; Dörscher, Sören;Al-Masoudi, Ali; Vogt, Stefan; Li, Ye; Lisdat, Christian (2019): A compact and robust cooling laser system for an optical strontium lattice clockRev. Sci. Instrum. 90, 023109
    DOI: 10.1063/1.5063552
  • Doerscher, S.; Schwarz, R.; Al-Masoudi, A.; Falke, S.; Sterr, U.; Lisdat, C. (2018): Lattice-induced photon scattering in an optical lattice clockPhys. Rev. A 97, 063419
    DOI: 10.1103/PhysRevA.97.063419
  • Mehlstäubler T.E., Grosche G., Lisdat C., Schmidt P.O., Denker H. (2018): Atomic clocks for geodesyReports on Progress in Physics Vol. 81, No. 6, 064401 More Info
    DOI: 10.1088/1361-6633/aab409
    arXiv: 1803.01585
  • Origlia, S.; Pramod, M. S.; Schiller, S.; Singh, Y.; Bongs, K.; Schwarz, R.; Al-Masoudi, A.; Doerscher, S.; Herbers, S.; Haefner, S.; Sterr, U.; Lisdat, Ch (2018): Towards an optical clock for space: Compact, high-performance optical lattice clock based on bosonic atomsPhys. Rev. A 98, 053443
    DOI: 10.1103/PhysRevA.98.053443
  • Delva P., Lodewyck J., Bilicki S., Bookjans E., Vallet G., Le Targat R., Pottie P.-E., Guerlin C., Meynadier F., Le Poncin-Lafitte C., Lopez O., Amy-Klein A., Lee W.-K., Quintin N., Lisdat C., Al-Masoudi A., Dörscher S., Gerbing C., Grosche G., Kuhl A., Raupach S., Sterr U., Hill I. R., Hobson R., Bowden W., Kronjäger J., Marra G., Rolland A., Baynes F. N., Margolis H. S.; Gill P. (2017): Test of Special Relativity Using a Fiber Network of Optical ClocksPhys. Rev. Lett. American Physical Society, 118, 221102
    DOI: 10.1103/PhysRevLett.118.221102
  • Pachomow, E.; Dahlke, V. P.; Tiemann, E.; Riehle, F.; Sterr, U. (2017): Ground-state properties of Ca-2 from narrow-line two-color photoassociationPhys. Rev. A 95, 043422
    DOI: 10.1103/PhysRevA.95.043422
All publications of the Collaborative Research Centre

PROJECT LEADER

PD Dr. Christian Lisdat
Address
Bundesallee 100, Abt. 432
38116 Braunschweig
Address
Bundesallee 100, Abt. 432
38116 Braunschweig
Non-public person