Published in EPJ Quantum Technology: Laser annealing heals radiation damage in avalanche photodiodes

Following our detector radiation and mitigation testing campaign, we tried an alternative approach for annealing detectors to mitigate radiation damage: laser annealing. High-power laser light was directed at irradiated and thermally-annealed detector samples, and subsequent performance measured. Notably, the results show that doing so provides performance improvements better than those achieved by thermal annealing.

J. G. Lim, E. Anisimova, B. L. Higgins, J.-P. Bourgoin, T. Jennewein, and V. Makarov
EPJ Quantum Technology 4, 11 (2017)

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Published in EPJ Quantum Technology: Mitigating radiation damage of single photon detectors for space applications

Quantum uplinks to Earth-orbiting satellites will necessitate single-photon detector technology that is robust to space radiation for the lifetime of the satellite. In this study, we experimentally assessed the effect of such radiation on a targetted selection of candidate detectors, with a focus on their impact to quantum key distribution. We then attempted to mitigate these effects, using thermal controls including deep cooling (during operation) and high-temperature annealing. Our results show that such techniques can maintain useful performance significantly beyond the one-year baseline lifetime.

E. Anisimova, B. L. Higgins, J.-P. Bourgoin, M. Cranmer, E. Choi, D. Hudson, L. P. Piche, A. Scott, V. Makarov, and T. Jennewein
EPJ Quantum Technology 4, 10 (2017)

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Published in Quantum Science and Technology: Airborne demonstration of a quantum key distribution receiver payload

This paper describes work I mentioned earlier. We successfully demonstrated quantum key distribution with signals transmitted from a ground station to a receiver on board a flying airplane. Our receiver (which is significantly upgraded in comparison to our prior truck demonstration) was designed and largely custom-built to have a clear path to flight on a satellite. Our demonstration illustrates the viability of such a payload.

C. J. Pugh, S. Kaiser, J.-P. Bourgoin, J. Jin, N. Sultana, S. Agne, E. Anisimova, V. Makarov, E. Choi, B. L. Higgins, and T. Jennewein
Quantum Science and Technology 2, 024009 (2017)

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Published in Optics Express: Free-space quantum key distribution to a moving receiver

We take our quantum key distribution system out of the laboratory and mount it in the back of a small truck. Integrating a two-axis pointing system at both sites, polarization correction, and time-of-flight compensation, we demonstrate quantum key distribution from a stationary transmitter to a receiver moving at an angular speed (relative to the transmitter) equivalent to the maximum angular speed of a typical low-Earth-orbit satellite.

J.-P. Bourgoin, B. L. Higgins, N. Gigov, C. Holloway, C. J. Pugh, S. Kaiser, M. Cranmer, and T. Jennewein
Optics Express 23, 33437–47 (2015)

Bonus: Read the IQC's news release, which covers both this and the previous paper for a general audience.

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Published in Physical Review A: Experimental quantum key distribution with simulated ground-to-satellite photon losses and processing limitations

Fundamental laws of quantum physics guarantee the security of encryption keys generated through quantum key distribution, in contrast to standard encryption techniques which rely on assumptions about an eavesdropper's computational ability. That said, special technology is necessary to facilitate quantum key distribution transmissions between parties that are more than a couple of hundred kilometers apart.

A near-term solution is to use an orbiting satellite as a trusted quantum receiver. Here we detail specifically chosen algorithms that make up an implementation of quantum key distribution, suitable for a satellite receiver platform. We examine these algorithms' computational requirements while demonstrating them experimentally as we emulate the variable channel losses that would be experienced during a satellite pass (following those we published about previously).

J.-P. Bourgoin, N. Gigov, B. L. Higgins, Z. Yan, E. Meyer-Scott, A. K. Khandani, N. Lütkenhaus, and T. Jennewein

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Published in Physical Review A: Using weak values to experimentally determine “negative probabilities” in a two-photon state with Bell correlations

It's well known that quantum entangled systems can exhibit correlations that go beyond those that could be seen if Nature worked in intuitive “classical” ways. However, as Richard Feynman noted, classical theory can support exhibiting such correlations if we invoke negative probabilities to describe their properties. What he did not do was specify how these negative probabilities ought to be chosen, and without any justification, an infinite number of different combinations could be chosen that will satisfy the relevant equations.

The concept of negative probabilities seems nonsensical because they cannot actually be observed—indeed, they cannot be observed even within the framework of quantum theory due to the effects of measurement back-action. Here, we show how they can instead be inferred through the use of weak measurements, where a meter is only weakly coupled to the property of interest, thereby avoiding the back-action problem. Each individual weak measurement has a …

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