Once tethered to the outside of the space station, SEAQUE will also test a technique to help space nodes “self-heal” from radiation damage, an ongoing challenge for maintaining delicate instruments in space.
“The demonstration of these two technologies lays the foundation for future global quantum networks capable of connecting quantum computers located hundreds or even thousands of kilometers apart,” said Makan Mohageg, SEAQUE co-investigator at the NASA’s Jet Propulsion Laboratory in Southern California.
Like the network it is supposed to activate, the project is global. The SEAQUE collaboration includes scientists and students from the University of Illinois Urbana-Champaign, who lead the project; the University of Waterloo in Ontario, Canada; National University of Singapore; AdvR, Inc., a Montana-based industry partner; Nanoracks, a Texas-based commercial space systems provider; and JPL.
The power of entanglement
The entangled photon pairs are so intimately linked that measuring one immediately affects the results of measuring the other, even when they are separated by a great distance. This is a fundamental characteristic of quantum mechanical systems. SEAQUE’s entangled photon source splits high-energy photons into pairs of entangled “daughter” photons. These daughter photons are then counted and their quantum properties are measured by the instrument’s internal detectors.
While other spatial quantum experiments depended on bulk optics (which focus light into a special crystal) to generate entangled photons, SEAQUE relies on an integrated source of entangled photons using a waveguide – a first for spacecraft. A waveguide is a microscopic structure that acts as a highway for photons, directing their transmission with little loss of the quantum state.
“SEAQUE will demonstrate a novel, novel entanglement source based on integrated optics,” said Paul Kwiat, the project’s principal investigator at the University of Illinois at Urbana-Champaign. “Such a source is inherently much smaller, more robust, and more efficient at producing photon pairs than bulk optical entanglement sources used in previous space experiments.”
For example, when these bulk optics require delicate optical realignment by a ground operator after being jolted during launch, SEAQUE’s optics will not.
“If you’re building a global quantum network, connecting hundreds of quantum ground stations on different continents, you can’t afford to have one person in the loop guarding the sources at each of the nodes in optical alignment,” Mohageg said. “A monolithic waveguide-based source like the one SEAQUE will fly will be a huge step toward a scalable global quantum information network.”
The reliability of the technology demonstration could be further improved if SEAQUE proves that it can also repair damage inflicted on it by radiation.
Quantum communication nodes will require highly sensitive detectors to receive single-photon quantum signals from the Earth’s surface. When high-energy particles, or radiation, from outer space hit node detectors, they will create defects over time. These defects can manifest as “dark counts” in a detector’s output, creating noise that will eventually overwhelm any quantum signal coming from the ground. Left unchecked, space radiation will eventually degrade these detectors to such an extent that they will need to be replaced regularly, hampering the viability of a global quantum communications network.
Although detecting signals from Earth is beyond the scope of this technology demonstration, SEAQUE will use its array of detectors to count the photons generated by its entanglement source. And SEAQUE will use a bright laser to periodically repair radiation-induced damage that will affect the number of detectors – another first.
“In ground tests, we have found that this technique causes lattice defects to ‘bubble’ – a process known as annealing – thereby reducing detector noise and potentially extending the lifetime of quantum nodes in space, facilitating a robust global system. network,” Kwiat said.
SEAQUE will be hosted on the space station by the Bishop lock, owned and operated by Nanoracks. Nanoracks also provides mission operations services and coordinates launch services. The integrated optical source of entangled photons for SEAQUE is developed by AdvR, Inc. Scheduled to launch no earlier than August 2022, the technology demonstration is funded by NASA Biological and Physical Sciences Division within the agency’s scientific missions department.