[time-nuts] DARPA SBIR - Portable Microwave Cold Atomic Clock

Mark Kahrs mark.kahrs at gmail.com
Mon Dec 2 23:37:26 UTC 2013


SB141-004                           TITLE: *Portable Microwave Cold Atomic
Clock*



TECHNOLOGY AREAS: Materials/Processes, Sensors, Electronics



This topic is eligible for the DARPA Direct to Phase II Pilot Program.
Please see section 4.0 of the DARPA instructions for additional
information.  To be eligible, offerors are required to provide information
demonstrating the scientific and technical merit and feasibility of a Phase
I project. DARPA will not evaluate the offeror's related Phase II proposal
where it determines that the offeror has failed to demonstrate the
scientific and technical merit and feasibility of the Phase I project.
Offerors must choose between submitting a Phase I proposal OR a Direct to
Phase II proposal, and may not submit both for the same topic.



OBJECTIVE: Develop a laser-cooled microwave atomic clock with small volume
(< 1 L) and weight (< 1 kg), low power consumption (< 5 W), and the
stability (10^-12 at 1 s) of a primary atomic frequency standard.



DESCRIPTION: Frequency and timing devices are essential components in
modern military systems. The stability and accuracy of these devices impact
the performance of communication, navigation, surveillance, and missile
guidance systems. Atomic clocks are at the cores of many of these systems,
either directly or via time-transfer from a master clock.



By employing techniques used in current laboratory atomic clocks, military
clocks can be improved by orders-of-magnitude. Such clocks will enable
secure data routing, communication systems that are insensitive to jamming,
higher resolution coherent radar, and more reliable and robust global
positioning.



Laser-cooled optical lattice atomic clocks are currently the world's most
stable clocks, with stability below 10^-18 at 6 hours of averaging [1].
DARPA's QuASAR program aims to miniaturize and ruggedize such
high-performance optical atomic clocks for deployment in the field [2].
While this work could enable widespread adoption of optical clock
technology, many applications cannot tolerate the size, weight, and power
(SWaP) of these first generation portable optical clocks (S > 50 L, W > 50
kg, P > 150 W). DARPA's Chip Scale Atomic Clock (CSAC) program has
developed miniature microwave atomic clocks with extremely low SWaP values
(S ~ 16 cm^3, W ~ 35 g, P ~ 125 mW) and good short-term stability (10^-10
at 1 sec) [3]. However these clocks drift over long timescales making them
unsuitable for many applications.


The goal of this SBIR is to bridge the gap between these extremes by
developing an atomic frequency standard with long term stability (<
5x10^-15 at 1 day), approaching that of laboratory frequency standards such
as the NIST F1 microwave Cs fountain clock [4] but with reasonable SWaP
values (S < 1 L, W < 1 kg, P < 5 W).



To achieve these goals, this SBIR will combine aspects of the two extreme
clock architectures mentioned above: laser cooling (as used in QuASAR
optical clocks) and microwave hyperfine transitions (as used in CSAC).
Alternative strategies will also be considered if sufficiently justified.
Special attention will need to be focused on reducing the power
requirements of the requisite lasers, microwave sources, and local
oscillators. Furthermore, the final device should be robust to
environmental fluctuations (e.g. temperature, magnetic field, vibration) in
a relevant operating environment.



PHASE I: Develop an initial design and model key elements of the proposed
clock. The chosen work must be compatible with a fractional frequency
stability of < 10^-12 at 1 second averaging and < 5x10^-15 for 1 day of
averaging. It should have a size < 1 L, weight < 1 kg, and power
consumption < 5 W. Develop a detailed analysis of the predicted performance
in a relevant environment accounting for expected environmental
fluctuations such as temperature, magnetic field, and vibration
fluctuations. Exhibit the feasibility of the approach through a laboratory
demonstration of critical components. Phase I deliverables will include a
design review including expected device performance and a report presenting
the plans for Phase II.



DIRECT TO PHASE II - Offerors interested in submitting a Direct to Phase II
proposal in response to this topic must provide documentation to
substantiate that the scientific and technical merit and feasibility
described in the Phase I section of this topic has been met and describes
the potential commercial applications. Documentation should include all
relevant information including, but not limited to: technical reports, test
data, prototype designs/models, and performance goals/results. Read and
follow Section 4.0 of the DARPA Instructions



PHASE II: Construct and demonstrate a prototype device validating the
device performance outlined in Phase I. The Transition Readiness Level to
be reached is 5: Component and/or bread-board validation in relevant
environment.



PHASE III: The low SWaP of the clock developed in this program should
enable widespread deployment of clocks with stability comparable to primary
frequency standards. Such clocks could lead to more reliable and robust
global positioning, synchronization and time-keeping in GPS-denied
environments, secure data routing, communication systems that are
insensitive to jamming, higher resolution coherent radar, and precision
timekeeping. Potential commercial applications include precise
synchronization of telecommunication networks for high-bandwidth
communications, next-generation satellite atomic clocks for global
positioning, and local clocks for very long-baseline interferometry.



REFERENCES:

1.  Hinkley, N. et al. An atomic clock with 10^-18 instability.
arXiv:1305.5869 (2013), http://arxiv.org/abs/1305.5869



2.  QuASAR: Quantum Assisted Sensing and Readout:
https://www.fbo.gov/index?s=opportunity&mode=form&id=9c912ae0743a9da465a18618bdc4d2a8&tab=core&_cview=0



3.  Knappe, S. et al. A chip-scale atomic clock based on 87Rb with improved
frequency stability. Opt. Express 13, 1249-1253 (2005).



4.  NIST Primary Frequency Standards and the Realization of the SI Second.
NCSL International Measure, Vol 2, No 4, 74 (2007) (
http://tf.nist.gov/general/pdf/2039.pdf)



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