CQT Talk by Grégory Langue, Liège Space Centre,University of Liège, Belgium
Title: Prototyping of a high-speed, time-of-flight, distance measuring device for formation flying satellites. Date/Time: 24-Jul, 04:00PM Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: There are a multitude of ways of measuring distance, however not all are suitable for space. This study is focused on distance measurement using time of flight (TOF) and more specifically on the development of a space-compatible receiver device that operates at distances, around 1km, where the recovered energy is very low.
A MPPC (Multi-Pixel Photon Counter) was investigated and developed into a prototype receiver.
Crosstalk and afterpulse phenomena related to the MPPC were observed, and the limits of the system were established. The results highlighted the importance of a neat design and the limitations related to internal noise (produced by the circuit and the sensor) and external noise (stray light).
The conclusion of this work is the realisation of a supervisory circuit for the functional MPPC. Although the card correctly conditions the pulses of current emitted by the sensor, improvements can be made.
One of the developments envisaged is the acquisition of the pulses by FPGA and the processing (as well as the communication) would be left to the microcontroller. The use of FPGA would also implement
digital filters and / or algorithms to bring out, more easily, the useful impulses embedded in the noise.
CQT PhD Thesis Defense by Anurag Anshu
Title: One-shot Protocols for Communication Over Quantum Networks: Achievability and Limitation Date/Time: 20-Jul, 03:00PM Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: This thesis studies the problems of source compression and channel coding in the one-shot entanglement-assisted quantum setting. The main contribution of the first part of the thesis is to systematically develop one-shot protocols for various quantum tasks, using two unified tools of `convex-split' and `position-based decoding'. Convex-split is used for the encoding operations and position-based decoding, which can also be viewed as a dual to the convex-split, is used for decoding operation. Our protocols and achievability results closely resemble the corresponding protocols and results in the classical case. Furthermore, position-based decoding gives near optimal one-shot results for the point to point channel. In the second part of the thesis, we exhibit some limitations on how well quantum messages can be compressed. We show that efficient classical schemes, such as the Huffman coding scheme, are not possible in the quantum domain. As a complementary result, we show an exponential separation between quantum communication complexity and quantum information complexity. This shows the existence of a hard to compress interactive quantum protocol.