The same is true in space: ESA is currently sending a quantum-enabled probe to Jupiter, developing communications based on quantum technologies and planning flying a quantum clock to the International Space Station, as part of its quantum technology cross-cutting initiative.

Quantum sensor headed to Jupiter
Part of the magnetometer of ESA's Juice spacecraft, launched to the largest planet in our Solar System in April, the MAGSCA sensor relies on a quantum interference phenomenon to perform absolute measurements of magnetic field strength, providing calibration for a larger pair of conventional 'fluxgate' magnetometers. Performing well during in-space commissioning, MAGSCA was built for ESA by the Austrian Academy of Sciences in partnership with Graz University of Technology.

Meanwhile hardware based on 'quantum entanglement' was tested earlier this year aboard an ESA parabolic 'zero-g' flight, demonstrating its robustness to gravity shifts.

ESA's quantum activities are now overseen by its new quantum technology cross-cutting initiative, coordinating all quantum technology R and D taking place across the Agency.

Quantum vision of ESA's future
"Quantum technology was defined as a strategic priority in the Agenda 2025 of ESA Director General Josef Aschbacher, seen as offering new avenues to commercial success and technical leadership, and we are implementing this vision," explains ESA opto-electronics system engineer Eric Wille.

"In one form or another ESA has been working on quantum technologies for the last quarter of a century, steadily raising overall readiness levels and chalking up some major successes along the way, including participating in the then-world record for quantum communications.

"This cumulative effort has helped us expand our range of activities, and build links with the quantum research community, most recently through ESA's latest quantum technology conference in September. To summarise: ESA is really open for business in this field, and if you have ideas for research, we want to hear from you!"

Weird science of the very small
Often termed as the most successful theory of the past century, quantum physics underpins the workings of everyday items like silicon chips, lasers and medical imaging machines. At the heart of this theory is the seemingly counter-intuitive fact that at extremely small scales, atoms, photons and other particles start behaving like waves.

This in turn leads to phenomena such as 'quantum superposition', where a particle can exist in more than one possible state at once, and 'quantum entanglement', where multiple particles go on sharing identical physical characteristics, even when separated by long distances.

Quantum technologies set out to utilise such exotic behaviour as the basis of more powerful computing, ultra-precise timing, secure sharing of information and high-sensitivity sensors - while contending with the challenge that quantum states are easily perturbed, and prone to collapse.

Quantum communications from space
Among the first applications of quantum technologies for communication is securing communication channels - known as 'quantum key distribution'. Encryption today is based on the sharing of 'cryptographic keys' - created using mathematical algorithms - between sender and recipient. These keys are normally shared over communication channels, enabling recipients of such keys to decrypt secured messages. But if these keys are intercepted, their encryption can be broken and secured data becomes accessible without recipients being aware of it.

Quantum key distribution increases the security of exchanging cryptographic keys by deriving them from quantum physical properties of light. These properties change the instant someone is 'listening in', alerting users to this intrusion. They can then simply discard these keys in favour of untampered alternatives. Accordingly this secures data based on keys known only to intended users. Space can play an important role in this: using laser links on satellites allows the bridging of distances through free space with a larger reach compared to optical fibres, where the light signals degrade more quickly.

ESA is collaborating with the European Commission to develop quantum key distribution for governmental applications, as well as supporting industry partnerships like the Eagle-1 mission with satellite manufacturer SES - developing technologies previously fostered through ESA's ScyLight programme.

For more than a quarter of a century, ESA's Optical Ground Station has been supporting optical and quantum communication experiments from the slopes of Tenerife's Mount Teide volcano. Testing quantum links through the atmosphere across the islands - or up to orbiting satellites - has already provided a wealth of information.

Lessons learned will guide the development and deployment of the European quantum communication infrastructure, which is part of the EU's secure connectivity programme.

Quantum sensing
Quantum states - such as 'cold atoms', systematically slowed down in their motion using lasers - often prove to be exquisitely sensitive to their surrounding environment, so could be employed for gravity or acceleration mapping, as well as tracking Earth features including ocean and ice flows.

Such precise surveying would also be a step forward for climate modelling, sharpening scientific understanding of phenomena such as the terrestrial water cycle, the mass balance of ice sheets and glaciers and sea-level change.

Quantum clocks and frequency standards
Similar laser-slowed cold atom systems can serve as the basis of highly precise clocks for positioning, navigation and timing, offering orders of magnitude improvements on the atomic clocks employed by today's satellite navigation systems. They are also important for fundamental physics experiments.

ESA's atomic clock ensemble in space payload will become the most accurate clock ever flown in orbit when it is brought on board the International Space Station in 2025.

Quantum computing
Quantum computers are unlikely to be flown in space in the near future, but, by harnessing superposition, they promise vastly improved computing power for specific search or optimisation problems.

This technique could be applied to space-related 'hard problems' such as optimising highly complex mega-constellation operations, high-fidelity simulations of a rocket's interaction with the atmosphere, or processing Earth observation data to exploit large amounts of information more efficiently.

Precision engineering
Other areas such as quantum memories, quantum imaging, random number generation and post quantum cryptography are also part of the more than 40 projects planned by ESA's quantum technology cross-cutting initiative in the coming years.

High quality and precision engineering is an essential element for success; it takes complex optical payloads to manipulate systems at the scale of atoms or photons. So ESA's existing optics and opto-electronics laboratory is also being rehoused and expanded in a new building in the ESTEC technical centre in the Netherlands, to enlarge the scope of support ESA can offer to researchers and industry.

Related Links
Space Engineering and Technology at ESA
Understanding Time and Space