⚛️ quantum physics

Quantum random number generation from the continuous variable payload for the SPOQC mission

This paper demonstrates the generation of certified continuous-variable quantum random numbers using the SPOQC mission's payload, successfully extracting approximately 19.5 Kb of secure randomness from a 1 Mb raw key by quantifying min-entropy and validating the output against the NIST test suite.

Original authors: Vinod N. Rao, Killian Murphy, Fadi Ahwal, Emma Tien Hwai Medlock, Timothy P. Spiller, Rupesh Kumar

Published 2026-08-11

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Vinod N. Rao, Killian Murphy, Fadi Ahwal, Emma Tien Hwai Medlock, Timothy P. Spiller, Rupesh Kumar

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are trying to send a secret message to a friend, but you are worried that a sneaky eavesdropper might be listening. To keep your message safe, you need a key that is impossible to guess. In the world of cryptography, the best keys are made of pure randomness—numbers that have no pattern and cannot be predicted by any computer, no matter how smart. For a long time, we've tried to make these numbers using complex math or by measuring things like static on a radio. But these methods rely on things that seem random but might actually have a hidden pattern if you look closely enough.

Enter the world of quantum mechanics, the rulebook for the tiniest particles in the universe. Here, nature has a built-in "dice roll" that is truly random. It's not just that we don't know the outcome; it's that the outcome doesn't exist until you look at it. One specific type of this randomness comes from the "vacuum." Even in empty space, where there is no light, there is a constant, jittery hum of energy called vacuum fluctuations. It's like a quiet room that isn't actually silent if you have super-sensitive ears; there is always a tiny, unpredictable buzz. Scientists have figured out how to listen to this buzz and turn it into a stream of unbreakable random numbers. This is crucial because as our digital world grows, we need more secure ways to protect our data, and having a source of randomness that is guaranteed by the laws of physics is the ultimate security blanket.

Now, let's zoom in on a very special mission called SPOQC, which is like a high-tech science lab floating in space. The team behind this mission, led by researchers from the University of York, wanted to see if they could build a machine to catch these quantum jitters and turn them into random numbers while orbiting the Earth. They didn't just build a theoretical model; they built a real, working device and tested it on an engineering model that is identical to the one that will fly on the satellite.

The device they built is called a Continuous Variable Quantum Random Number Generator (CV-QRNG). Think of it like a very sensitive microphone listening to the "silence" of space. Inside the satellite, there is a laser that acts as a reference point. The machine splits this laser light: one part is used for other experiments, and the other part is mixed with the "empty" vacuum state. When these two meet, the tiny, random jitters of the vacuum cause the light to wobble in a way that is impossible to predict. The machine measures these wobbles, turns them into electrical signals, and then uses a digital converter (an ADC) to translate those signals into a string of 0s and 1s.

The researchers faced a tricky challenge: in the real world, things aren't perfect. There is "classical noise" from the electronics, temperature changes, and the machine itself, which can muddy the waters and make the numbers look less random. To solve this, they had to be like detectives, carefully measuring how much noise came from the electronics versus how much came from the true quantum vacuum. They found that while the electronics added some "static," the quantum signal was still strong enough to be useful.

After gathering about 1 megabit (a million bits) of raw data during a single pass of the satellite, they ran the numbers through a rigorous battery of tests known as the NIST test suite. These tests are like a series of puzzles that try to find any hidden patterns in the numbers. The results were a success: the numbers passed the tests, proving they were truly random. However, because they had to remove the "classical noise" to ensure security, the final amount of certified random numbers was smaller than the raw data. From that 1 megabit of raw input, they extracted about 19.5 kilobits of certified, secure random numbers.

The paper also looked at how different settings affected the results. They tested the system with different types of digital converters (12-bit and 16-bit) and found that while a 16-bit converter could theoretically capture more detail, their current 12-bit setup was sufficient to generate secure keys. They also checked how the system would handle the harsh environment of space, noting that the components were designed to withstand radiation and temperature swings.

The big takeaway is that this team successfully demonstrated that you can build a secure random number generator on a satellite using the quantum vacuum. This isn't just a lab experiment; it's a practical step toward having secure communication tools in space. The random numbers they generate can be used for important tasks like choosing encryption keys or fixing errors in data transmission. While the amount of randomness they got in this specific test was modest, it proves the concept works. The authors suggest that with a bit more power to the laser, they could generate even more numbers in the future. This work paves the way for the first-ever demonstration of this technology operating in space, promising a future where our space-based internet is guarded by the most secure locks nature has to offer.

Technical Summary: Quantum Random Number Generation from the Continuous Variable Payload for the SPOQC Mission

Problem Statement
The generation of high-quality random numbers is fundamental to tasks ranging from cryptography to physical simulations. While classical sources (e.g., computational algorithms, thermal noise) rely on unpredictability derived from complexity, they lack information-theoretic security. Quantum Random Number Generators (QRNGs) offer a solution by leveraging the inherent probabilistic nature of quantum mechanics. However, implementing QRNGs in space presents significant challenges regarding Size, Weight, and Power (SWaP) constraints. Furthermore, existing space-based quantum communication missions often prioritize Quantum Key Distribution (QKD) over dedicated randomness generation, despite the potential for shared hardware. This work addresses the necessity of demonstrating secure, continuous-variable (CV) QRNG functionality within the constrained environment of a satellite payload, specifically the Satellite Platform for Optical Quantum Communication (SPOQC).

Methodology
The authors utilized the engineering model of the CV payload developed for the SPOQC mission, which is identical to the flight model intended for Low Earth Orbit (LEO). The system employs a homodyne-based CV-QRNG architecture that utilizes the vacuum fluctuations of the quantum state as the entropy source.

Hardware Setup: The optical payload includes a 1550.12 nm pulsed laser (2 MHz repetition rate) used for both CV-QKD and QRNG. For QRNG operation, a portion of the laser serves as a Local Oscillator (LO) directed to a shot-noise-limited homodyne detector. The detector consists of a radiation-hardened 50/50 fiber beam splitter and two vacuum-compatible PIN photodiodes. The photocurrents are subtracted, amplified by low-noise amplifiers, and digitized by a 12-bit Analog-to-Digital Converter (ADC). A Single Board Computer (SBC) handles data acquisition and randomness extraction.
Noise Characterization: To quantify extractable randomness, the team separated total noise into quantum (shot noise) and classical components. They measured three configurations:
1. LO off (electronic noise only).
2. LO on with varying power (imperfect homodyning noise).
3. LO on at operational power (total shot noise).
  Classical noise sources (electronic noise, detector inefficiencies) were characterized and assumed constant within specific temperature and pressure ranges (25°C, 1 atm for testing; 0–25°C, micro-bar for flight).
Theoretical Framework: The authors employed conditional min-entropy ( $H_{min}$ ) to bound the extractable secure randomness, accounting for potential information leakage to an eavesdropper (Eve). They utilized entropic uncertainty relations to upper-bound the min-entropy, considering the discretization effects of the ADC and the correlation between the input thermal state and the output.
Extraction: Raw data was processed using Toeplitz matrix hashing to extract certified random bits. The security parameter ( $\epsilon_{hash}$ ) was set to $10^{-20}$ .

Key Contributions

Integration: The work demonstrates the integration of a CV-QRNG module into an existing space-qualified CV-QKD payload, utilizing shared optical components (laser, beam splitters, detectors) to minimize SWaP overhead.
Formalism: The paper provides a detailed formalism for estimating extractable randomness in a device-dependent scenario, explicitly accounting for classical noise, ADC digitization errors, and conditional min-entropy bounds.
Validation: The engineering model of the system was rigorously tested under vacuum and thermal cycling conditions to ensure reliability in space environments.

Results

Entropy Estimation: Based on experimental data, the authors calculated the Shannon entropy for both 12-bit and 16-bit ADC configurations. For the 12-bit ADC, the total entropy ( $H(X)_{total}$ ) was approximately 4.520 bits, while the classical noise entropy ( $H(X)_{c(2)}$ ) was approximately 2.522 bits, leaving a quantum entropy ( $H(X)_q$ ) of roughly 1.999 bits.
Certified Randomness: From a raw key length of approximately 1 Mb acquired during a single satellite pass, the system extracted a total of ≈19.5 Kb of certified random numbers using the 12-bit ADC.
Statistical Validation: The extracted random numbers passed the NIST statistical test suite, with p-values indicating no significant deviation from uniformity.
Performance: The sampling rate was limited to 500 kHz by the FPGA hardware. The study noted that the shot noise variance currently spans only a few bits of the ADC, limiting the volume of extractable randomness, though higher LO power could improve this. While results for a 16-bit ADC were presented for comparison, these were not generated from the on-board computer.

Significance and Claims
The paper claims that this work represents a critical step toward the first demonstration of a CV-QRNG operating in space, following the successful launch of the SPOQC CubeSat in March 2026. The significance lies in:

Feasibility: Proving that secure random number generation is possible within the strict SWaP constraints of a satellite payload using existing QKD hardware.
Application: The generated randomness is intended for QKD post-processing tasks (e.g., basis selection, error correction) and potentially for modulating signals or for post-quantum cryptography applications on the satellite.
Operational Advantages: The CV-QRNG approach offers lower power requirements compared to single-photon QRNGs (no need for cooling photodiodes) and utilizes PIN diodes, which are more radiation-tolerant than avalanche photodiodes, making it well-suited for the space environment.

The authors remain modest in their claims, noting that the current extraction rate is limited by the ADC resolution and LO power, and that future work will focus on optimizing the conditional min-entropy by accounting for temperature variations across the full operational range of the satellite.

Technical Summary: Quantum Random Number Generation from the Continuous Variable Payload for the SPOQC Mission

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