Abstract
Integrated quantum photonic circuits are becoming increasingly complex. Accurate calibration of device parameters and detailed characterization of the prepared quantum states are critically important for future progress. Here we report on an effective experimental calibration method based on Bayesian updating and Markov chain Monte Carlo integration. We use this calibration technique to characterize a two qubit chip and extract the reflectivities of its directional couplers. An average quantum state tomography fidelity of 93.79 ± 1.05% against the four Bell states is achieved. Furthermore, comparing the measured density matrices against a model using the non-ideal device parameters derived from the calibration we achieve an average fidelity of 97.57 ± 0.96%. This pinpoints non-ideality of chip parameters as a major factor in the decrease of Bell state fidelity. We also perform quantum state tomography for Bell states while continuously varying photon distinguishability and find excellent agreement with theory.
Highlights
The detection of photons was done by single photon avalanche diodes connected to the output fibre array with an efficiency of about 50%
Two photon coincidences could be detected between every pair of output waveguides
The random two photon coincidence rate for this time window was calculated in the experiments and was always less than 0.4%
Summary
To the Markov chain Monte Carlo-based calibration, we modelled the theoretically expected density matrix taking the real chip parameters into account as (see appendix C) I=1 a=0 b=0 where D is a constant, the index i runs over the nine tomography phase settings, Mai b is the number of times that we detected the qubit state |ab and pai b is the corresponding expected probability.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
