Quantum Entanglement Aboard Orbiting CubeSat

A miniaturized source of quantum entanglement that measures only 20 by 10 cm. (Source: NUS)

In a critical step toward creating a global quantum communi­cations network, researchers have generated and detected quantum entangle­ment onboard a CubeSat nano­satellite weighing less than 2.6 kilograms and orbiting the Earth. “In the future, our system could be part of a global quantum network trans­mitting quantum signals to receivers on Earth or on other spacecraft,” said Aitor Villar from the Centre for Quantum Techno­logies at the National Unive­rsity of Singapore. “These signals could be used to implement any type of quantum communi­cations appli­cation, from quantum key distribution for extremely secure data trans­mission to quantum tele­portation, where information is transferred by replicating the state of a quantum system from a distance.”

Villar and an inter­national group of researchers demonstrate that their miniaturized source of quantum entangle­ment can operate success­fully in space aboard a low-resource, cost-effective CubeSat that is smaller than a shoebox. CubeSats are a standard type of nano­satellite made of multiples of 10 cm × 10 cm × 10 cm cubic units. “Progress toward a space-based global quantum network is happening at a fast pace,” said Villar. “We hope that our work inspires the next wave of space-based quantum tech­nology missions and that new applications and technologies can benefit from our experi­mental findings.”

The entanglement is essential to many quantum communi­cations appli­cations. However, creating a global network for entangle­ment distribution isn’t possible with optical fibers because of the optical losses that occur over long distances. Equipping small, standar­dized satellites in space with quantum instru­mentation is one way to tackle this challenge in a cost-effec­tive manner. As a first step, the researchers needed to demonstrate that a minia­turized photon source for quantum entangle­ment could stay intact through the stresses of launch and operate success­fully in the harsh environment of space within a satellite that can provide minimal energy. To accomplish this, they exhaus­tively examined every component of the photon-pair source used to generate quantum entangle­ment to see if it could be made smaller or more rugged.

“At each stage of development, we were actively conscious of the budgets for mass, size and power,” said Villar. “By iterating the design through rapid proto­typing and testing, we arrived at a robust, small-form factor package for all the off-shelf components needed for an entangled photon-pair source.” The new minia­turized photon-pair source consists of a blue laser diode that shines on nonlinear crystals to create pairs of photons. Achieving high-quality entanglement required a complete redesign of the mounts that align the nonlinear crystals with high precision and stability.

The researchers qualified their new instrument for space by testing its ability to withstand the vibration and thermal changes experienced during a rocket launch and in-space operation. The photon-pair source maintained very high-quality entangle­ment throughout the testing, and crystal alignment was preserved even after repeated temperature cycling from -10 to 40 °C. The researchers incorporated their new instrument into SpooQy-1, a CubeSat that was deployed into orbit from the Inter­national Space Station on 17 June 2019. The instrument success­fully generated entangled photon-pairs over tempera­tures from 16 to 21.5 °C.

“This demons­tration showed that minia­turized entanglement tech­nology can work well while consuming little power,” said Villar. “This is an important step toward a cost-effective approach to the deployment of satellite constel­lations that can serve global quantum networks.” The researchers are now working with RALSpace in the UK to design and build a quantum nanosatellite similar to SpooQy-1 with the capa­bilities needed to beam entangled photons from space to a ground receiver. This is slated for demons­tration aboard a 2022 mission. They are also colla­borating with other teams to improve the ability of CubeSats to support quantum networks. (Source: OSA)

Reference: A. Villar et al.: Entanglement demonstration on board a nano-satellite, Optica 7, 734 (2020); DOI: 10.1364/OPTICA.387306

Link: Centre for Quantum Technologies, National University of Singapore, Singapore, Singapore

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