RAISE-TAQS: Randomness Expansion Using a Loophole-Free Bell Test

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

Randomness plays a central role in many cryptographic systems and protocols. If a random number generator gives outputs that aren't truly random, but rather can be predicted, this can lead to a catastrophic security breakdown. Currently, the only known way to generate true and certifiable random bits is through using entangled quantum particles in what is known as a loophole-free Bell test. However, it took over half a century to overcome the technological challenges before the first generation of loophole-free Bell tests could be carried out in 2015. Recently, the investigators of this project were able to demonstrate the creation of truly certifiable randomness from such a Bell test, but the process can only create around 1024 bits every 10 minutes, and the equipment must be separated by more than 100 meters. This project will develop a second-generation entanglement system that will produce random bits 3-4 orders of magnitude faster while requiring separations of less than 5 meters. This system will lead to new fundamental tests of physics and quantum mechanics, and lead to a more viable source of trusted randomness for use in public and private cryptographic applications. The first demonstration will be to integrate our entangled quantum random number generator into a public beacon of randomness that will help provide tamper-resistant video time-stamping capabilities for applications like police-body camera verification. Performing a loophole-free Bell test is a technological milestone. It requires the successful simultaneous integration of numerous components that each must meet stringent technical requirements. In 2015 the investigators of this project were able to perform one of the three landmark loophole-free Bell tests and remain the only US-based group with such capabilities. This first generation of loophole-free Bell tests may have settled the debate on whether hidden-variables govern nature, but they also represent the beginning of a new class of quantum information systems and devices that are device-independent. This is fertile ground to begin probing the fundamental limits on the security of quantum networks, random number generators, and other new protocols. By building a second-generation loophole-free Bell test that can operate orders of magnitude faster, new regimes of exploration open that are inaccessible to the current crop of devices. A loophole-free Bell test requires measurements on entangled particles that are space-like separated. This means that the two particles are sent to distant measurement stations that are far enough apart so that information traveling at the speed of light about the measurement on one particle does not have time to reach and possibly influence the measurement of its entangled partner. Additionally, more than 66.7% of the particles must be detected to avoid opening a detection loophole. Currently, Pockels cells based on electro-optic effects are used in photonic Bell tests to make the necessary measurements as they can operate with losses of less than 1%. However, the Pockels cells only operate at speeds of approximately 100 kHz and require the measurement stations to be separated by more than 100 meters to maintain space-like separation. This large size makes the system hard to maintain and hinders it from being incorporated into practical applications requiring trusted randomness. By developing a new class of all-optical switches that can operate in the 1GHz range with ultra low-losses, the investigators will be able to shrink the experiment down to a 5m optical table. This will lead to an increase in randomness generation rates of 3-4 orders of magnitude and will enable other device-independent quantum protocols that are currently not technologically possible. Finally, the development of an ultrafast, ultra-low-loss polarization switch will impact all other photonic quantum information processing systems, allowing them to run with unprecedented efficiencies (compared to any waveguide device) and 100-1000X faster than current bulk Pockels cell methods permit. Such a device will be an enabling technology and serve as a fundamental building block in quantum optical networks and processors. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.