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Periodic Report Summary 1 - QRNG (Integrated Optic Quantum Random Number Generators)

The Project QRNG aims to develop a novel fast integrated optic quantum random number generator (QRNG) based on tailoring of spontaneous emission, i.e. quantum entropy source, of rare-earth doped waveguides via arrayed waveguide gratings (AWG) for much improved performance, i.e. generator rates from Gb/s to Tb/s, on an integrated platform with a reliable and compact foot-print.
Communication and online security are essential to sustain a reliable network platform. Today’s communication security, relying on mathematical complexity of classical cryptographic methods, is becoming more vulnerable everyday as new advanced algorithms are developed along with increasing computational power. Moreover, practical realization of quantum computers would make certain classical cryptographic methods indeed obsolete. On the other hand, quantum key distribution (QKD) systems with one time pad (OTP) implementation, relying on non-deterministic nature of quantum physics rather than mathematical complexity, promise to offer practical optical networks with unbreakable security regardless of any algorithm or computational power of eavesdroppers. In QKD systems, however, ultimate security can be implemented only by means of OTP encryption, where the random number generation rate needs to be faster than the data transmission rate, i.e. GHz for practical applications. Yet, the speed of current available QRNGs is inherently limited by the counting rate of single photon detectors and, thus inadequate for practical one-time pad encryption applications. In this work, we are developing a novel fast integrated optic QRNG based on tailoring of spontaneous emission, i.e. quantum entropy source, of rare-earth doped waveguides via arrayed waveguide gratings (AWG) for much improved performance.
In this work we focus on generating a stream of truly random bits. This is the problem of constructing a true random number generator (TRNG). A TRNG is usually comprised of two components: an unpredictable source with high entropy and a randomness extractor. A randomness extractor is a function which produces a sequence with a uniform distribution when applied to the source.
Most of the existing QRNGs are based on quantum optics. The inherent randomness in many parameters of the quantum states of light allows for a rich choice of implementations. Kerckhoffss' principle states that the security of a cryptosystem must lie in the choice of its keys only; everything else (including the algorithm itself) should be considered public knowledge. It is therefore of particular importance that the key is secure, which requires it to be chosen at random.
Working principle of optical amplifiers is based on directing the light into a medium with population inversion, thereby increasing the signal power by stimulated emission of photons. Since spontaneous emission always accompanies stimulated emission in an excited medium, spontaneously emitted photons inside the gain medium are also amplified by stimulated emission. This is the ‘amplified spontaneous emission’. ASE, either alone or in its beats with the signal or itself, is a strong noise source which dominates the thermal detector noise or optical shot noise.
While being a primary challenge against gain in optical communication systems, ASE can be employed as a good entropy source in QRNGs as it is a strong signal of quantum origin which is measurable/detectable with existing optical equipment at fast rates. Even at high sampling rates, sampling random amplitudes of ASE in different frequency bands gives statistically independent random variables. The rate of change is usually much faster than the detection mechanism, so the detection speed becomes the limiting factor to the bit generation rate of ASE based QRNGs. Fundamental idea behind generating random bit-streams lies in sampling wide-band and low-power noise.
In the generator proposed and studied in this project, entropy source is a quantum one which employs the amplified spontaneous emission (ASE) of rare-earth doped (Er-Yb co-doped, in this case) fiber/waveguide amplifier (EDFA/EDWA).
Main design decisions are:
1. ASE of Er-Yb doped fiber or glass waveguides will be used as quantum randomness source.
2. AWG structure will be used for ASE spectral combing.
3. OE conversion will be done via fast InGaAs PDs and TIA.
4. Random bits will be extracted via ADC upon OE conversion.
Currently, Project QRNG achieved promising results in quantum random number generation on fiber-coupled medium. For the next two years, maintaining the system operation on a compact platform in addition to publishing important academic work in the field are main goals.

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