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Quantum Physics with Cubesats: In-Orbit Observation of Photon Pair Correlations on Board the Galassia Spacecraft

Rakhitha Chandrasekara, Zhongkan Tang, Yue Chuan Tan, Cliff Cheng, Alexander Ling, Daniel K. L. Oi

Published Jan 1, 2016• 0 citations

Abstract

Secured global quantum communication networks sharing an encryption key can be established with entangled photon sources onboard satellites in Earth orbit. Even though optical transceivers for ground-to-space communication exist, no space capable source of entangled photons has been demonstrated. A faster and cost-effective solution to reach orbit is by means of CubeSats. This demands significant miniaturisation work on the photon source to fit within the size, weight and power restrictions of CubeSats. The first milestone in our programme is to deploy a source of correlated photon pairs in space as a pathfinder experiment to demonstrate the principle and raise the technology readiness level. The first attempt was unsuccessful when the launch vehicle (CRS Orb-3) failed shortly after take-off, although our payload was successfully recovered intact and found to be fully operational. We are pleased to report that the second attempt with a newly built payload, has been successful and the first milestone has been accomplished. The source was launched on board the Galassia CubeSat (PSLV C29) to an orbit of approximately 550 km and 150 inclination. We observed inorbit generation of high quality photon pair correlations (with a contrast of 97 ± 2%). These results are compatible with baseline data collected prior to launch and show no degradation after spending 140 days in orbit. Data will be presented on the effects of temperature and radiation on the source performance. We will also present plans for upcoming and future missions.

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To overcome the challenges of establishing a global Quantum Key Distribution network using optical fibers, several communication protocols using satellites have been proposed. A major milestone towards such a goal is the demonstration of a working source of entangled photons on a satellite. We are building a compact instrument capable of generating entangled photon pairs through spontaneous parametric down conversion. We intend to follow an iterative development cycle with the first mission to demonstrate that the control electronics can reliably operate an optical source of correlated photons in orbit. The instrument we are building is designed to be integrated into a nanosatellite and conforms to the size, weight and power requirements of a 1U CubeSat. The instrument contains a power stabilized optical pump, single photon detectors and inertial free polarization rotators to measure polarization correlations onboard the nanosatellite. The single photon detection unit utilizes a software based controlling mechanism to achieve temperature independent operation in a typical low earth orbit nanosatellite. The integrated system has been tested for thermal, vacuum and vibration environments. The latest test on a high altitude balloon demonstrates the technology readiness of the electronics payload for space missions.

Quantum Key Distribution (QKD) is a technology that can distribute private encryption keys between two parties with strong security assurances underpinned by quantum mechanics. Entanglement-based QKD is one of the strongest forms of QKD. Performing QKD using satellites can overcome the range constraints of ground-based QKD systems imposed by atmospheric losses or attenuation in optical fibers. In 2017, satellite-based QKD has been demonstrated by the Chinese Academy of Sciences’ 630kg Micius satellite. Independently in Singapore we are developing similar, but greatly more compact QKD technologies targeted at CubeSats. Our first on-orbit demonstration of a simple quantum light source was in 2016 on board the Galassia 2U CubeSat. Next on the pad, our SpooQy-1 CubeSat is a 3U GomSpace platform built at CQT that aims to validate the space-worthiness of our next generation entangled photon light source and demonstrate a radio beacon of quantum random numbers. In future missions our miniaturized entangled photon light sources can be combined with high precision Pointing, Acquisition and Tracking System (PATS) and optical communication links to enable a global QKD network with small satellites.

Quantum sources and receivers operating on-board satellites are an essential building block for global quantum networks. SpooQy-1 is a satellite developed at the Centre for Quantum Technologies, which has successfully demonstrated the operation of an entangled photon pair source on a resource-constrained CubeSat platform. This miniaturized and ruggedized photon pair source is being upgraded to be capable of space-to-ground quantum key distribution and long-range entanglement distribution. In this paper, we share results from SpooQy-1, discuss their relevance for the engineering challenges of a small satellite quantum node, and report on the development of the new light source.

To enable space-based quantum key distribution proposals the Centre for Quantum Technologies is developing a source of entangled photons ruggedized to survive deployment in space and greatly miniaturised so that it conforms to the strict form factor and power requirements of a 1U CubeSat. The Small Photon Entangling Quantum System is an integrated instrument where the pump, photon pair source and detectors are combined within a single optical tray and electronics package that is no larger than 10 cm x 10 cm x 3 cm. This footprint enables the instrument to be placed onboard nanosatellites or the CubeLab structure aboard the International Space Station. We will discuss the challenges and future prospects of CubeSat-based missions.

Progress in quantum computers, and their threat to conventional public-key infrastructure, drives new forms of encryption, including quantum key distribution using entangled photons. Beaming entangled photons to Earth from orbit could provide secure quantum communication over long distances. The authors transform a large, delicate quantum-optics setup into a robust payload for a shoebox-sized CubeSat satellite. Their gear survives the trip to space, and correlated photons are produced and detected aboard the satellite, validating the design---a milestone on the road to a space-based quantum communications network.