Information Gain vs Distortion Loss In Finite-Dimensional Quantum Systems

Christopher A. Fuchs

Thijs van der Valk

In this thesis, I reflect on quantum instruments that measure the state of pure finite dimensional quantum systems. As the Heisenberg principle dictates, there exists a joint restriction to the information gain and distortion by measurement of a quantum system. I minimize the distortion of measurement and maximize the quality of the outcome by finding the optimal (covariant) instrument. In order to optimize this joint restriction, the family of covariant instruments is classified. This is an important side result.

Thomas Schneider, Ronny Henker, Kai-Uwe Lauterbach +1 more

We show a simple method to reduce the distortions in SBS based slow light systems. The distortion reduction is simply based on a broadening and adaptation of the gain bandwidth. However, a broadened gain reduces the achievable fractional delay which cannot be compensated by higher pump powers. Here we will show that this compensation can be done by additional loss spectra. With the presented method low distortions for high fractional pulse delays are possible. We show the theory and experimental verifications of our method. For Gaussian pulses with a fractional delay of 1 Bit we achieved a distortion reduction of around 23%.

Mahdi Naghiloo, Jose Joaquin Alonso, Alessandro Romito +2 more

Giacomo Mauro D’Ariano, Chiara Macchiavello, Matteo G. A. Paris

Lu Jun

Using single-ring microresonators with loss to realize the light speed control encounters difficulties of heavy light loss and serious pulse distortion.Based on the symmetry between the transfer characteristics of resonators with loss and with gain,the transmission,group index,and group velocity dispersion of a single-ring microresonator are calculated and analyzed.The action mechanism of the loss and gain on the transfer characteristics of the micro-ring resonator is demonstrated.The light speed control behavior of the resonator with gain is calculated and compared with that of the resonator with loss.Calculation results indicate that the resonator with gain can produce the nonsplitted pulses with higher intensities and their pulse delay and pulse advancement are greater than those of the resonator with loss.These results show that the resonator with gain can be used to control the speed of light and to overcome the pulse loss and distortion in dissipative resonators.