Published in EPJ Quantum Technology: Repeated radiation damage and thermal annealing of avalanche photodiodes

A big difficulty preventing single-photon communications to a satellite is the detector noise caused by radiation in orbit. In a previous study, we showed that with a combination of sufficient cooling during operation and thermal annealing during maintenance, it should possible to keep this noise low enough to do quantum key distribution. What we could not capture at that time, though, was whether the cycling of cold and hot over the lifetime of a satellite would have any effect, and in particular how the choice of when to anneal would impact this.

In this study, we address this question by applying multiple rounds of radiation to a flight-like apparatus, and quantifying its performance between each round, over a two-year-equivalent accelerated irradiation campaign. We used two devices, one of which was annealed at regular intervals, the other conditional on the noise counts exceeding a predefined threshold. In the end we found …

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Published in Advanced Optical Technologies—A double feature

Two of my papers were published in Advanced Optical Technologies, recently, as part of a topical issue on applied quantum technologies.

The first paper deals with encoding the polarization of light signals for quantum key distribution (QKD). In principle, light is very good at maintaining its polarization, but in practice things like thermal effects in optical fibers and physical orientations causes polarizations to get rotated in sometimes unpredictable ways. There are various techniques to control and correct for these effects. This paper proposes an approach based on sampling the QKD signals themselves, and analyzes the performance in terms of how much light needs to be sampled. It turns out you can do very well to preserve the polarization with a relatively few signals.

The second paper looks at whether ‘adaptive optics’ techniques can be used to help transmit QKD signals from ground to an orbiting satellite. Adaptive optics uses fast …

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Published in Optics Express: Genuine time-bin-encoded quantum key distribution over a turbulent depolarizing free-space channel

Light can be used to encode information in a variety of ways. Polarization, for example: a ‘0’ bit could be represented by a pulse of horizontally polarized light, and a ‘1’ bit could be vertically polarized. This generally works well for transmissions over free-space. Also, by allowing superposition states and reducing the intensity to single-photon levels, one can start to access interesting quantum protocols such as quantum key distribution (QKD). You can do this with other encodings, too—“time bin”, for example, where you encode information in the arrival time, early or late, relative to a reference. But because of the way the superposition state (that is, the early “and” late state) is measured, it doesn't generally work well over air because of turbulence.

A recently discovered enhancement of the measurement device by my colleagues intrinsically bypasses the turbulence problem, and in this paper, we couple this improved apparatus with …

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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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