Yue Chuan Tan

Generation and Analysis of Correlated Pairs of Photons aboard a Nanosatellite

Satellites carrying sources of entangled photons could establish a global quantum network, enabling private encryption keys between any two points on Earth. Despite numerous proposals, demonstration of space-based quantum systems has been limited due to the cost of traditional satellites. We are using very small spacecraft to accelerate progress. We report the in-orbit operation of a photon pair source aboard a 1.65 kg nanosatellite and demonstrate pair generation and polarization correlation under space conditions. The in-orbit photon correlations exhibit a contrast of 97+/-2%, matching ground-based tests. This pathfinding mission overcomes the challenge of demonstrating in-orbit performance for the components of future entangled photon experiments. Ongoing operation establishes the in-orbit lifetime of these critical components. More generally, this demonstrates the ability for nanosatellites to enable faster progress in space-based research.

Silicon avalanche photodiode operation and lifetime analysis for small satellites

Silicon avalanche photodiodes (APDs) are sensitive to operating temperature fluctuations and are also susceptible to radiation flux expected in satellite-based quantum experiments. We introduce a low power voltage adjusting mechanism to overcome the effects of in-orbit temperature fluctuations. We also present data on the performance of Si APDs after irradiation (γ-ray and proton beam). Combined with an analysis of expected orbital irradiation, we propose that a Si APD in a 400 km equatorial orbit may operate beyond the lifetime of the satellite.

Deploying quantum light sources on nanosatellites II : lessons and perspectives on CubeSat spacecraft

To enable space-based quantum key distribution proposals the Centre for Quantum Technologies is developing a source of entangled photons ruggedized to survive deployment in space and greatly miniaturised so that it conforms to the strict form factor and power requirements of a 1U CubeSat. The Small Photon Entangling Quantum System is an integrated instrument where the pump, photon pair source and detectors are combined within a single optical tray and electronics package that is no larger than 10 cm x 10 cm x 3 cm. This footprint enables the instrument to be placed onboard nanosatellites or the CubeLab structure aboard the International Space Station. We will discuss the challenges and future prospects of CubeSat-based missions.

Space-Qualified Nanosatellite Electronics Platform for Photon Pair Experiments

We report the design and implementation of a complete electronics platform for conducting a quantum optics experiment that will be operated on board a 1U CubeSat (a 10 × 10 × 10 cm satellite). The quantum optics experiment is designed to produce polarization-entangled photon pairs using nonlinear optical crystals and requires opto-electronic components such as a pump laser, single photon detectors, and liquid crystal-based polarization rotators in addition to passive optical elements. The platform provides mechanical support for the optical assembly. It also communicates autonomously with the host satellite to provide experiment data for transmission to a ground station. A limited number of commands can be transmitted from ground to the platform enabling it to switch experimental modes. This platform requires less than 1.5 W for all operations, and is space qualified. The implementation of this electronics platform is a major step on the road to operating quantum communication experiments using nanosatellites.

Generation and analysis of correlated pairs of photons on board a nanosatellite

We report the operation of a photon pair source on board a nanosatellite. Pair generation and polarization correlation are demonstrated in low Earth orbit: an important milestone towards compact entangled photon pair sources for future space-based quantum communication.

The photon pair source that survived a rocket explosion.

We report on the performance of a compact photon pair source that was recovered intact from a failed space launch. The source had been embedded in a nanosatellite and was designed to perform pathfinder experiments leading to global quantum communication networks using spacecraft. Despite the launch vehicle explosion soon after takeoff, the nanosatellite was successfully retrieved from the accident site and the source within it was found to be fully operational. We describe the assembly technique for the rugged source. Post-recovery data is compared to baseline measurements collected before the launch attempt and no degradation in brightness or polarization correlation was observed. The survival of the source through an extreme environment provides strong evidence that it is possible to engineer rugged quantum optical systems.

Deploying quantum light sources on nanosatellites I: lessons and perspectives on the optical system

The Small Photon Entangling Quantum System is an integrated instrument where the pump, photon pair source and detectors are combined within a single optical tray and electronics package that is no larger than 10cm×10cm×3cm. This footprint enables the instrument to be placed onboard nanosatellites or the CubeLab facility within the International Space Station. The first mission is to understand the different environmental conditions that may affect the operation of an entangled photon source in low Earth orbit. This understanding is crucial for the construction of cost-effective entanglement based experiments that utilize nanosatellite architecture. We will discuss the challenges and lessons we have learned over three years of development and testing of the integrated optical platform and review the perspectives for future advanced experiments.

Radiation tolerance of opto-electronic components proposed for space-based quantum key distribution

Plasma in low earth orbit can damage electronic components and potentially jeopardize scientific missions in space. Predicting the accumulated damage and understanding components’ radiation tolerance are important in mission planning. In this manuscript, we report on the observed radiation tolerance of single photon detectors and a liquid crystal polarization rotator. We conclude that an uncooled Si APD could continue to operate from more than a month up to beyond the lifetime of the satellite depending on the orbit. The liquid crystal polarization rotator was also unaffected by the exposed dosage.

Single photon counting for space based quantum experiments

We present a software based control system for Geiger-mode avalanche photodiodes (GM-APDs) that enables constant photon detection efficiency irrespective of the diodes junction temperature. Furthermore, we demonstrate that this control system enables passively quenched GM-APDs to double the rate of photon detection events before saturation compared to the standard control method that fixes the junction temperature and applied bias voltage. We present data demonstrating the robustness of the GM-APD control system when tested in near-space conditions using a correlated photon pair source carried by a weather balloon to an altitude of 35.5 km.

Robust photon-pair source survives rocket explosion

Quantum key distribution (QKD), i.e., using quantum signals to generate secure symmetric key material at distant sites, is of much interest for quantum communications because of its high level of privacy (underpinned by quantum mechanics). In particular, entanglement-based QKD1 is a powerful technique in which quantum correlations between photons are leveraged. In this process, the entangled photons can be distributed with the use of optical fibers or ground-level free-space links. Current QKD networks, however, suffer from a distance limit because of fiber losses2, 3 and the lack of quantum repeaters.4 There are several ongoing efforts to overcome this distance limit and to produce regional/global QKD networks.5–10 In these approaches, a source of entangled photons, on board a satellite, would be used to beam the photons down to widely separated receivers. A major milestone in achieving this endeavor would therefore be the successful demonstration of an entangled-photon pair source in low Earth orbit (LEO). It has previously been proposed that CubeSat nanosatellites are a costeffective way to realize this aim (because technology validation experiments can be performed in small, iterative steps).11 However, spontaneous parametric downconversion12—the ‘workhorse’ method for generating entangled-photon pairs—requires the use of precisely aligned bulk optics. This means that it can be challenging to design a photon source that has sufficiently low size, weight, and power requirements to be used on a nanosatellite. We have thus been working on the development of a compact device that is designed to perform pathfinder experiments in the pursuit of achieving global quantum communication networks. In particular, our device is designed to generate and measure photon pairs in space. In the first step toward validation in a space environment, we assembled a science package that comprised a correlated photon-pair source (with one spontaneous Figure 1. Diagram of the customized toolkit used to align the components of the optical unit in the photon pair source. Two separate knobs are used to adjust the yaw and pitch angles independently. The optical components are aligned within a pocket that is machined into the aluminum housing. After alignment, epoxy is applied to secure the component within the pocket and the adjuster is removed (to maintain the device’s compact form factor) once the epoxy has cured. KMS/M: Compact kinetic mirror mount from Thorlabs.