M/F - PhD thesis - Advanced spectroscopy for a single-ion optical clock

Job Description

Thesis Subject

Optical clocks based on ultra-narrow transitions in trapped ions and neutral atoms have reached fractional uncertainties in the low 10-18 range, enabling landmark applications in relativistic geodesy and tests of fundamental physics. However, present-day interrogation schemes remain fundamentally constrained by (i) probe-induced AC Stark shifts and intensity fluctuations, and (ii) environmental decoherence and low-frequency noise, which limit interrogation time and long-term stability. Existing solutions typically address these two limitations separately, forcing clock designers to trade robustness to systematic shifts against robustness to noise.
The Quantera QUARCKS project (QUAntum Robust hyper-ClocKs and atomic Sensors, cofunded by EU) targets the demonstration of a new class of “hyper-clocks” and atomic sensors that are simultaneously immune to probe-induced shifts and strongly protected against decoherence, via Dynamically Decoupled Hyper-Ramsey (DD HR) protocols. These protocols go beyond traditional Rabi and Ramsey spectroscopy using composite pulses with taylored phase, frequency and intensity. The protocol's key feature is robustness. By actively canceling environmental noise, QUARCKS makes clocks less reliant on "perfect" laboratory environments. This is a critical step toward transportable and field-deployable optical clocks for applications in relativistic geodesy (measuring Earth's gravitational potential), navigation, and networked timekeeping.
Within the QUARCKS project, this PhD thesis aims at extending coherence time beyond the dephasing limit in a suface-electrodes trap, single-ion Yb+ clock. The main objective is to experimentally demonstrate a more than 10-fold extension of effective interrogation time compared to standard Ramsey interrogation, by embedding DD sequences into HR-type schemes, and verifying coherence via fringe contrast and Allan deviation. This other objective is to assess robustness against realistic technical noise. To serve that purpose, generalized HR interrogation protocols will be first tested and demonstrated; noise-filtering DD pulses will then be used to reduce decoherence in both experiments; DDR sequences will assess the resulting coherence time.
This PhD thesis is part of a long-term compact optical clock project based on the Yb+ 435.5 nm transition frequency, with a target fractional frequency stability below 10-14 at 1 s and less than 500 L volume. The apparatus is based on a surface-electrode trap similar to those traditionally used in QIP experiments, with a high ion-to-electrode distance to reduce the impact of anomalous heating. We have developed a custom microfabricated chip based on doped Si electrodes etched on a SiO2 insulating layer. The chip has been characterized and exhibits both long trapping times and low heating rates. The thesis will focus on:
- The operation of the ion trap and laser-cooling bench, and the implementation of traditional Rabi and Ramsey scheme to demonstrate clock operation;
- The implementation of HR schemes, using the Artiq environment (FPGA-based experiment control)
- The characterization of the clock transition coherence time, the main noise sources, and the implementation of DD sequences to counter decoherence.
We are looking for candidates with a training in atomic and/or quantum physics, optics, or general physics. Experimental and/or instrumental training will be a great addition, as well as knowledge in analog and/or digital electronics. We also expect that the candidate will be a team-player, able to organize his.her own planning and work, and open to critical discussions about the project. They will evolve within a team made up of researchers, engineers and technicians, and will have the support of the electronic, mechanical and IT departments of the FEMTO-ST Institute and the OSCILLATOR-IMP infrastructure of excellence, dedicated to time & frequency metrology. The candidate will present their work at international conferences and will aim to have their work published in international journals.

Your Work Environment

The PhD work will be conducted within the OHMS team (Oscillators, Clocks, Metrology and Systems) of the Time and Frequency department at Femto-ST, led by Dr. C. Lacroûte. The group benefits from its world-renowned expertise in the field of Time and Frequency metrology, with access to the OSCILLATOR-IMP platform, which includes three active Hydrogen Masers, three Cs clocks, as well as optical frequency combs and ultra-stable Fabry-Perot cavities. This platform ensures the possibility to measure phase noise and frequency stabilities of optical signals in the 10-16 range and below. The team is a first-circle member of the French metrology network FIRST-TF, and a member of the REFIMEVE+ project, which physically links our institute to the LTE laboratory in Paris.
This thesis will allow the candidate to acquire an exceptional know-how and experimental methodology, in a high-level scientific environment. The context of frequency metrology requires to master and control the noise sources of the experimental setup as well as possible, a skill that is extremely useful in many other research fields. The candidate will also develop an expertise in the field of trapped ions, which is still relatively unrepresented in France but very fertile at the European level.
C. Lacroûte (CNRS researcher) will be the thesis supervisor, and M. Abdel Hafiz (Associate Professor, SUPMICROTECH) will be the thesis co-supervisor. They have developed a prototype ion trap for frequency metrology, demonstrating ion trapping and laser cooling for the first time at FEMTO-ST. A microfabricated SE ion trap was produced at the local MIMENTO facility, that recently demonstrated ion trapping of single Yb+ ions.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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