Introduction
Research interest (multi-photon process in the field of quantum information)
As the foundation of quantum information, the preparation of two-particle and multi-particle entangled states is urgently needed. Till now, many systems have been suggested to prepare entanglement, such as linear optical system, cavity-quantum-electronics-dynamic system, nuclear magnetic resonance, ion-trap, quantum dot and superconductor josephsen junction. Among them, linear optical system has more advantages: photons as the information carrier can be easily transformed, single bit operation can be performed easily and good resistance to environment fluctuation. Many theories based on two particles have been realized based on linear optical system, such as state preparation, single qubit operation and two-qubit nonlinear operation.
On the other hand, multi-photon high dimensional system has more advantages than two-photon system in the field of quantum information and quantum computation. People have developed the linear optical system to multi-photon high dimensional system, and have made some progresses in multi-photon high dimensional system, while the difficulties arose along with the photon number increasing. Much groundwork, including multi-photon preparation and state measurement, has not been well studied and has no good reliable ideas. We focus on the multi-photon state process, such as the preparation of multi-photon states, properties of multi-photon states and measurement of multi-photon states.
Highlights:
Projection measurement and precise phase measurement . The difficulties of multi-photon experiment come from many parts, such as the brightness of photon source, operations of multi-photon and the measurement of multi-photon. We carry out the projection measurement such as the NOON-state projection measurement and unbalanced projection measurement scheme. These two methods is efficient for multi-photon experiment, they can be used for multi-photon interference and high precision phase measurement.
Ref: Phys. Rev. A 73, 023808 (2006); Phys. Rev. A 74, 033812 (2006); Opt. Lett. 32, 1320 (2007)
Interference and distinguishability of multi-photon state. The distinguishability of photons reduced the purity of multi-photon state and the visibility of multi-photon interference. There should be a good way to quantify the distinguishability of photons. We use the NOON-state projection measurement to demonstrate the three-photon and six-photon temporal distinguishablity and give a theoretical analysis.
Ref: Phys. Rev. Lett. 97, 023604 (2006);EPL 77, 24003 (2007); Phys. Lett. A 353, 291 (2006)
Stimulated emission and photon bunching. We directly observed the stimulation emission in parametric amplification. Both the stimulation emission and multi-photon interference can cause the photon bunching. In experiment and theory, we demonstrate that the two processes come from photon indistinguishability. Moreover, photon distinguishability is the result of quantum entanglement. So the photon bunching offers a method to measure the quantum entanglement. We use the parametric down conversion to generate pseudo two-fold copy of four-dimensional two-photon state and measure its I-concurrence by detecting the photon bunching effect.
Ref: Phys. Rev. Lett. 99, 043601 (2007)