Quantum Tomography of Entangled Spin-Multiphoton States

We present a method for quantum tomography of multiqubit states. We apply the method to spin-multiphoton states, which we generate using a quantum dot based device. Periodic excitation of a quantum dot confined spin deterministically generates strings of entangled photons in a cluster state, threefold faster than previously demonstrated. Our tomography method uses time-resolved polarization-sensitive multiphoton correlation measurements to measure both the polarization of the confined spin and that of the emitted photons. We develop an edge-sensitive gradient-descent algorithm and apply it to the acquired data to map the periodic physical process that generates the cluster state. We utilize our tomographic method to optimize our quantum dot based device and show that the enhanced generation rate increases the entanglement robustness of the generated multiqubit state.

Automated summary

This method utilizes quantum dots to generate spin-multiphoton states, measures the polarization of both spin and photons through time-resolved polarization-sensitive multiphoton correlation measurements, and uses a gradient-descent algorithm to map the periodic physical process that generates the entangled state. The study shows that the enhanced generation rate improves the entanglement robustness of the generated multiqubit state.