Quantum Key Distribution matured over time from simple demonstrators to a commercially available product. But what do we know about the security of these devices? Security analysis also developed over time, being able to incorporate more detailed optical modelling of devices. We will report on the progress of analyzing actual QKD device security, making a clear distinction between protocol security and implementation security. The focus will be on the interface between experiment and security analysis in these collaborations.

Scaling up the creation of qubit entanglement is a general challenge for many quantum technological platforms. On the other hand, continuous-variable (CV) entanglement has been created among over a million optical pulses, yet the utility of CV entanglement in quantum information processing has been rather limited. In this work, we present a systematic strategy to bring together the strengths of both qubit and CV platforms: a scheme to convert the extremely efficiently generated CV entanglement to the many-qubit entanglement that has a wide range of applications. This is possible because 1) we observe that CV cluster states can be treated as superposition of qubit cluster states in the Gottesman-Kitaev-Preskill (GKP) encoding, and 2) we introduce a hybrid teleportation circuit to transfer quantum information from bosonic modes to auxiliary physical qubits. Our protocol can be implemented with operations found in common bosonic platforms, such as photonics, superconducting circuit QED, optomechanics. To analyze the realistic performance of our protocol, we introduce an equivalent circuit to map both the finite energy constraint and system imperfections to single qubit errors. By using weak measurement, we show that finite squeezing error can be converted to highly correctable qubit erasure error. This allows us to show that 12dB of squeezing is sufficient for fault-tolerant quantum computation, and 6dB is sufficient for implementing a robust quantum memory. We also show that all errors of preparation, channel loss, and detector inefficiency can be lumped into a single-qubit dephasing. Finally, we present a repeated interaction strategy to compensate the weakness of physical qubit-CV interaction.

To support the QEYSSat mission, we’ve made extensive measurements into the amount of background light at the University of Waterloo’s quantum ground station. Both the ground and sky were surveyed using a single photon detector and bandpass filters for relevant wavelengths. These measurements were compared to images taken by NASA’s VIIRS satellite and found to be in good agreement. These techniques can be used to evaluate the viability of other potential quantum ground station locations.

Quantum Key Distribution (QKD) promises a provably secure method to transmit information from one party to another. Free-space QKD allows for this information to be sent over great distances and in places where fibre-based communications cannot be implemented, such as ground-satellite. The primary limiting factor for free-space links is the effect of atmospheric turbulence, which can result in significant error rates and increased losses in QKD channels. Here, we employ the use of a high-speed Adaptive Optics (AO) system to make realtime corrections to the wavefront distortions on spatial modes that are used for high-dimensional QKD in our turbulent channel. First, we demonstrate the effectiveness of the AO system in improving the coupling efficiency of a Gaussian mode that has propagated through turbulence. Through process tomography, we show that our system is capable of significantly reducing the crosstalk of spatial modes in the channel. Finally, we show that employing AO reduces the quantum dit error rate for a high-dimensional orbital angular momentum-based QKD protocol, allowing for secure communication in a channel where it would otherwise be impossible. These results are promising for establishing long-distance free-space QKD systems.