Quantum Communication, Sensing and Measurement in Space
Creators: name: Erkmen, Baris I.
name: Shapiro, Jeffrey H.
name: Schwab, Keith
Publisher: name: Keck Institute for Space Studies
Year: 2012

description: The main theme of the conclusions drawn for classical communication systems
operating at optical or higher frequencies is that there is a well‐understood
performance gain in photon efficiency (bits/photon) and spectral efficiency
(bits/s/Hz) by pursuing coherent‐state transmitters (classical ideal laser light)
coupled with novel quantum receiver systems operating near the Holevo limit (e.g.,
joint detection receivers). However, recent research indicates that these receivers
will require nonlinear and nonclassical optical processes and components at the
receiver. Consequently, the implementation complexity of Holevo‐capacityapproaching
receivers is not yet fully ascertained. Nonetheless, because the
potential gain is significant (e.g., the projected photon efficiency and data rate of
MIT Lincoln Laboratory's Lunar Lasercom Demonstration (LLCD) could be achieved
with a factor‐of‐20 reduction in the modulation bandwidth requirement), focused
research activities on ground‐receiver architectures that approach the Holevo limit
in space‐communication links would be beneficial.
The potential gains resulting from quantum‐enhanced sensing systems in space
applications have not been laid out as concretely as some of the other areas
addressed in our study. In particular, while the study period has produced several
interesting high‐risk and high‐payoff avenues of research, more detailed seedlinglevel
investigations are required to fully delineate the potential return relative to
the state‐of‐the‐art. Two prominent examples are (1) improvements to pointing,
acquisition and tracking systems (e.g., for optical communication systems) by way
of quantum measurements, and (2) possible weak‐valued measurement techniques
to attain high‐accuracy sensing systems for in situ or remote‐sensing instruments.
While these concepts are technically sound and have very promising bench‐top
demonstrations in a lab environment, they are not mature enough to realistically
evaluate their performance in a space‐based application. Therefore, it is
recommended that future work follow small focused efforts towards incorporating
practical constraints imposed by a space environment.
The space platform has been well recognized as a nearly ideal environment for some
of the most precise tests of fundamental physics, and the ensuing potential of
scientific advances enabled by quantum technologies is evident in our report. For
example, an exciting concept that has emerged for gravity‐wave detection is that the
intermediate frequency band spanning 0.01 to 10 Hz—which is inaccessible from
the ground—could be accessed at unprecedented sensitivity with a space‐based
interferometer that uses shorter arms relative to state‐of‐the‐art to keep the
diffraction losses low, and employs frequency‐dependent squeezed light to surpass
the standard quantum limit sensitivity. This offers the potential to open up a new
window into the universe, revealing the behavior of compact astrophysical objects
and pulsars. As another set of examples, research accomplishments in the atomic
and optics fields in recent years have ushered in a number of novel clocks and
sensors that can achieve unprecedented measurement precisions. These emerging
technologies promise new possibilities in fundamental physics, examples of which
are tests of relativistic gravity theory, universality of free fall, frame‐dragging
precession, the gravitational inverse‐square law at micron scale, and new ways of gravitational wave detection with atomic inertial sensors. While the relevant
technologies and their discovery potentials have been well demonstrated on the
ground, there exists a large gap to space‐based systems. To bridge this gap and to
advance fundamental‐physics exploration in space, focused investments that further
mature promising technologies, such as space‐based atomic clocks and quantum
sensors based on atom‐wave interferometers, are recommended.
Bringing a group of experts from diverse technical backgrounds together in a
productive interactive environment spurred some unanticipated innovative
concepts. One promising concept is the possibility of utilizing a space‐based
interferometer as a frequency reference for terrestrial precision measurements.
Space‐based gravitational wave detectors depend on extraordinarily low noise in
the separation between spacecraft, resulting in an ultra‐stable frequency reference
that is several orders of magnitude better than the state of the art of frequency
references using terrestrial technology. The next steps in developing this promising
new concept are simulations and measurement of atmospheric effects that may limit
performance due to non‐reciprocal phase fluctuations.
In summary, this report covers a broad spectrum of possible new opportunities in
space science, as well as enhancements in the performance of communication and
sensing technologies, based on observing, manipulating and exploiting the
quantum‐mechanical nature of our universe. In our study we identified a range of
exciting new opportunities to capture the revolutionary capabilities resulting from
quantum enhancements. We believe that pursuing these opportunities has the
potential to positively impact the NASA mission in both the near term and in the
long term. In this report we lay out the research and development paths that we
believe are necessary to realize these opportunities and capitalize on the gains
quantum technologies can offer.