First contact has been made with nanosatellite CAPSat. Deployed into orbit a
week ago from the International Space Station, it will test built-in
maintenance of quantum communication detectors in space.
Tuesday, October 12, at 6 a.m. CDT, a quantum communications experiment was
launched into low orbit around Earth from the International Space Station
(ISS). A collaborative experiment of the University of Illinois
Urbana-Champaign and the University of Waterloo, CAPSat (Cool Annealing
Payload Satellite) contains single-photon detectors, which can be used as
receivers for unhackable quantum communications.
Illinois Physics Professor Paul Kwiat, who was the founding director of the
Illinois Quantum Information Science and Technology Center, is the primary
investigator on the project. Kwiat has collaborated closely with Waterloo
Professor of Physics and Astronomy Thomas Jennewein to design the
experiment. Illinois Aerospace Engineering Professor Michael Lembeck led a
team of students in the integration and test of CAPSat. Lembeck, who is the
director of the Laboratory for Advanced Space Systems at Illinois (LASSI),
will coordinate communications with the satellite through LASSI’s ground
station in Urbana. First contact was made with the nanosatellite on
Wednesday at 2:52 p.m.
Quantum communication via a network of satellites will hinge on improving
the performance and longevity of the in-orbit photodetectors used to detect
the single-photon signals. Applications include quantum key distribution for
‘eavesdropper-proof’ transmission of secret data, quantum teleportation for
transmission of quantum states, and quantum networking for distributed
sensing and quantum computing “in the cloud.”
Lembeck describes this morning’s deployment of CAPSat from the ISS by a
robotic arm holding a Nanoracks deployer: “The satellite is about the size
of a loaf of bread, 10 cm X 10 cm X 30 cm. It was placed in another box, the
deployer, that has a front door and a spring-loaded plate in the back. When
the door opened, the plate pushed the satellite out the front door into
space to begin its mission.”
One of the biggest challenges in designing CAPSat was fitting the quantum
communications components into the tight dimensions of the satellite casing
and to operate with low power consumption using energy from built-in solar
panels. Inside CAPSat are four single-photon detectors, built at Waterloo.
Waterloo Institute for Quantum Computing research associate Nigar Sultana,
who has been working on the detector module for the CAPSat project since it
kicked off six years ago, says “everything matters, even the small things
like glue.”
Although small in size, CAPSat’s potential impact is huge because it might
provide a very efficient method to mitigate radiation damage of
single-photon detectors in orbit.
“The deployment of CAPSat demonstrates proof of concept that will pave the
way for future quantum communication missions,” comments Jennewein.
Kwiat describes the experiment, “The detectors will measure light, counted
in single photons, and it’s very important that there isn’t a lot of noise
in these measurements. The detectors don’t have much noise initially, but
over time, radiation in the form of protons damages the silicon of the
detector, leading to spurious noise counts. So even in darkness, the
detectors will—falsely—indicate recording light.”
After a week in space subjected to radiation, the detectors may report
seeing 5,000 photons per second. If after 2 weeks, it’s 10,000, and after a
month, it’s 20,000—with that level of noise, the scientists can no longer
clearly pick out the received signal, which might only be 50,000 photons per
second.
“Two of the detectors have lasers pointed at them for annealing, and two
don’t,” Kwiat continues. “Based on the noise levels we read, my colleagues
at Waterloo and my team here will determine how often to apply optical
annealing. The detectors’ noise levels are influenced by several
factors—shielding, where the satellite is in space, where it is in orbit
around planet, different levels of radiation, etc.—so we will monitor that
and plan our tests accordingly.”
There is also an LED light source in CAPSat, to confirm the detectors are
functioning to see light at all. The ultimate goal of the experiment will be
to optimize the photodetector’s annealing procedure for future quantum
communications satellites.
Much of the work on this project has been completed by undergraduate
students. In fact, the satellite was delivered in early July to NASA’s
launch service provider Nanoracks in Houston, by two Illinois undergraduate
electrical engineering students who had helped assemble it. Rick Eason and
Logan Power, under the direction of Lembeck, participated in CAPSat’s
installation in the orbital deployer mechanism. Aerospace Engineering
graduate student Eric Alpine shepherded the satellite through its early
years of development.
Lembeck says, “Our LASSI lab has enjoyed working with such world class
physicists as Paul Kwiat and Thomas Jennewein to attempt this exciting
experiment in a small satellite form factor. We have looked forward to
seeing CAPSat deployed from the ISS and meeting the team’s mission
objectives.”
Kwiat says the project wouldn’t have been possible without the 40-plus
years’ experience in flight missions provided by Lembeck, whose team
assembled the satellite and designed its circuitry, addressing special
environmental concerns like near-vacuum conditions.
On Kwiat’s team, significant contributions were made in the first years of
the project by then-undergraduate physics students Malhar Jere and Joe
Stahl. More recently, physics graduate student John Floyd helped supervise
the project, along with physics graduate students Kristina MeierMeier—now a
researcher at Los Alamos National Laboratory— and Christopher Zeitler.
Kwiat concludes, “There is currently a large drive around the world to
develop quantum information processing capabilities, including quantum
networks, in an effort that bridges the physical sciences, engineering, and
computer sciences.
“The eventual development of a global quantum internet would enable several
further advancements, ranging from the ability to do quantum computing in
the cloud—accessing and programming queries on the network without ownership
of a quantum computer—to the potential use of the network for distributed
quantum sensing, such as a quantum telescope.”
CAPSat is one of three university-built nanosatellites that lifted off from
NASA’s Kennedy Space Center in Florida on Saturday, August 28, aboard
SpaceX’s 23rd Commercial Resupply Services mission to the International
Space Station. Funding for CAPSat was provided by NASA’s Undergraduate
Student Instrument Project and the Canadian Space Agency. This was the 37th
Educational Launch of Nanosatellites (ELaNa) mission.
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