Quantime: a Cs miniature atomic clock

Key members

In this project LTF and its partners from EPFL, CSEM, and Swiss industry aim to develop an industrial prototype of a miniature atomic clock suited for the telecom market, requiring a wide operating temperature range (from -40 to +85°C) and a low production cost. Based on the results from the MAC-TFC project, a Coherent Population Trapping (CPT) technique for atomic interrogation is used for miniaturization and low power consumption. For this clock realisation, a series of micro-fabricated Cs vapour cells were tested by optical and CPT spectroscopy and the long-term aging process of such cells was studied [1]. Custom-made VCSEL laser modules emitting at the Cs D1 line (895nm) were studied, showing a very good modulation response to a 4.6 GHz frequency modulation required for CPT interrogation. A custom-designed microwave synthesizer implemented as a single ASIC chip and producing the adjustable 4.6 GHz radiation required for clock operation was developed at EPFL-ESPLAB. A micro-cell clock was operated using this ASIC synthesizer and showed that the chip has sufficiently low phase noise (below -85 dBc/Hz at 2 to 200 kHz frequency offset) such as not to limit the stability performance of the clock [2]. Based on an evaluation of relevant systematic shifts, a clock prototype realized by the industrial partner has a volume of only 39 cm3 (including the VCSEL laser, micro-cell physics package, and full clock electronics) and shows a frequency stability of < 2x10-10 at 1s and down to 1.8x10-11 at 104s.

Figure 1: Micro-fabricated Cs vapour cell (fabricated at CSEM) and example of CPT signal measured for such a cell [1].


Figure 2: Photograph of the Quantime clock prototype developed by the industrial partner. The whole clock including laser, micro-cell physics package, and full electronics fits into a volume of 39 cm3 [3].

This activity is supported by the Swiss Federal Commission for Technology and Innovation CTI, project 13818: QUANTIME - A miniature Cesium Atomic Clock using CPT technique for telecom applications.

Relevant publications

  1. S. Abdullah, C. Affolderbach, F. Gruet, G. Mileti,  Aging studies on micro-fabricated alkali buffer-gas cells for miniature atomic clocksApplied Physics Letters 106, 163505 (2015). PDF
  2. S. Abdullah, C. Affolderbach, F. Gruet, Y. Pétremand, G. Mileti, “Aging study on a micro-fabricated Cs buffer-gas cell for atomic clock applications”, proceedings of the 28th European Frequency and Time Forum (EFTF), Neuchatel, Switzerland, June 22 - 26, 2014. online article
  3. Y. Zhao, S. Tanner, A. Casagrande, C. Affolderbach, L. Schneller, G. Mileti, P.-A. Farine, “A 4.6-GHz, CPT Cesium-Cell Atomic Clock Operation With a 12-mW Frequency Synthesizer ASIC”, IEEE Transactions on Instrumentation and Measurement 64, 263-270 (2014). PDF
  4. Quantime – A miniature cesium atomic clock using CPT technique for telecom applications”, CTI Micro-Nano-Event, May 24, 2014.