# DOI:
10.7795/720.20210126

# Title:
Additional data for the publication "Optical frequency ratio of a 171Yb+ single-ion clock and a 87Sr lattice clock"	

# Summary:
The enclosed data set provides additional data on the measurements presented in the publication entitled "Optical frequency ratio of a 171Yb+ single-ion clock and a 87Sr lattice clock" in Metrologia (DOI: 10.1088/1681-7575/abc86f).

# Creators:
- Sören Dörscher,
  Physikalisch-Technische Bundesanstalt (PTB),
  Fachbereich 4.3 Quantenoptik und Längeneinheit,
  ORCID: [0000-0002-3331-4001](https://orcid.org/0000-0002-3331-4001)
- Nils Huntemann,
  Physikalisch-Technische Bundesanstalt (PTB),
  Fachbereich 4.4 Zeit und Frequenz,
  ORCID: [0000-0002-1876-0513](https://orcid.org/0000-0002-1876-0513)
- Roman Schwarz,
  Physikalisch-Technische Bundesanstalt (PTB),
  Fachbereich 4.3 Quantenoptik und Längeneinheit,
  ORCID: [0000-0002-5841-5597](https://orcid.org/0000-0002-5841-5597)
- Richard Lange,
  Physikalisch-Technische Bundesanstalt (PTB),
  Fachbereich 4.4 Zeit und Frequenz,
  ORCID: [0000-0002-9927-4858](https://orcid.org/0000-0002-9927-4858)
- Erik Benkler,
  Physikalisch-Technische Bundesanstalt (PTB),
  Fachbereich 4.3 Quantenoptik und Längeneinheit,
  ORCID: [0000-0001-7907-849X](https://orcid.org/0000-0001-7907-849X)
- Burghard Lipphardt,
  Physikalisch-Technische Bundesanstalt (PTB),
  Fachbereich 4.4 Zeit und Frequenz,
  ORCID: [0000-0001-7039-1914](https://orcid.org/0000-0001-7039-1914)
- Uwe Sterr,
  Physikalisch-Technische Bundesanstalt (PTB),
  Fachbereich 4.3 Quantenoptik und Längeneinheit,
  ORCID: [0000-0001-5661-769X](https://orcid.org/0000-0001-5661-769X)
- Ekkehard Peik,
  Physikalisch-Technische Bundesanstalt (PTB),
  Fachbereich 4.4 Zeit und Frequenz,
  ORCID: [0000-0001-6309-2975](https://orcid.org/0000-0001-6309-2975)
- Christian Lisdat,
  Physikalisch-Technische Bundesanstalt (PTB),
  Fachbereich 4.3 Quantenoptik und Längeneinheit,
  ORCID: [0000-0002-4705-8854](https://orcid.org/0000-0002-4705-8854)

# Resource Type
data set

# Licence:
CC BY-ND 4.0 (Creative Commons Attribution-NoDerivatives 4.0 International Public License)
https://creativecommons.org/licenses/by-nd/4.0/

# Keywords:
optical clock, ion clock, ytterbium, optical lattice clock, strontium, optical clock comparison, frequency ratio

# Classification:
INSPEC A3200 Atomic spectra and interactions with photons;
INSPEC A3280P Photon interactions with atoms;
INSPEC A4262 Laser applications

# Other:
EMPIR projects are co-funded by the European Union’s (EU) Horizon 2020 research and innovation programme and the EMPIR participating states.

# Funder:
- European Commission (EC),
  ISNI: 0000 0001 2162 673X,
  Grant Title: [Robust Optical Clocks for International Timescales](http://empir.npl.co.uk/rocit/),
  Grant Number: EMPIR 18SIB05 ROCIT
- Deutsche Forschungsgemeinschaft (DFG),
  ISNI: 0000 0001 2096 9829,
  Grant Title: [QuantumFrontiers - Licht und Materie an der Quantengrenze](https://www.quantumfrontiers.de/),
  Grant Number: EXC 2123
- Deutsche Forschungsgemeinschaft (DFG),
  ISNI: 0000 0001 2096 9829,
  Grant Title: [Quantum engineered optical lattice clocks](https://www.dq-mat.uni-hannover.de/),
  Grant Number: SFB 1227 - B02

# Related object
- DOI: 10.7795/720.20201113

  This dataset contains the frequency data used to compute the Allan deviation of the strontium clock, shown in Figure 1 as green squares.

# Description of the individual files:
1. ``frequency_ratios.csv`` (text/csv):

   The file contains a summary of the Yb+/Sr frequency ratio measurements, which are shown Figure 3 of the publication and from which the distribution shown in Figure 4 is derived.
   
   The column layout is as follows:
   1. center-of-gravity date/time as Modified Julian Date (MJD)
   2. start date/time as MJD (where exported during data analysis)
   3. end date/time as MJD (where exported during data analysis)
   4. measured frequency ratio, in units of 1E-18 and with the specified offset subtracted
   5. statistical uncertainty, in units of 1E-18
   6. total measurement uncertainty, in units of 1E-18

2. ``instability_fc.csv`` (text/csv):

   The file contains the fractional frequency data used to compute the Allan deviation of the frequency comb comparison, shown in Figure 1 as purple triangles.

   The column layout is as follows:
   1. time index as MJD
   2. fractional frequency difference between combs

3. ``instability_yb_sr_2015.csv`` (text/csv)

   The file contains the fractional frequency data used to compute the Allan deviation of the frequency ratio measurements *without* stability transfer from the Si-2 ultrastable laser, shown in Figure 1 as red circles.

   The column layout is as follows:
   1. time index as number of seconds elapsed since the specified reference date/time
   2. frequency ratio of the clocks with the specified offset subtracted

   Note that this trace does not necessarily correspond exactly to any measurement listed in ``frequency_ratios.csv``, because
   (a) such traces may be segmented differently for instability analysis than for analysis of the frequency ratio (e.g., by using the longest possible data sets) and
   (b) they do not necessarily include all systematic corrections (e.g., due to global corrections applied in subsequent post-processing).

3. ``instability_yb_sr_2017.csv`` (text/csv)

   The file contains the fractional frequency data used to compute the Allan deviation of the frequency ratio measurements *with* stability transfer from the Si-2 ultrastable laser, shown in Figure 1 as blue diamonds.

   The column layout is as follows:
   1. time index as number of seconds elapsed since the specified reference date/time
   2. frequency ratio of the clocks with the specified offset subtracted

   Note that this trace does not necessarily correspond exactly to any measurement listed in ``frequency_ratios.csv``, because
   (a) such traces may be segmented differently for instability analysis than for analysis of the frequency ratio (e.g., by using the longest possible data sets) and
   (b) they do not necessarily include all systematic corrections (e.g., due to global corrections applied in subsequent post-processing).
