Introduction
Our work focuses on the application of SPDC systems in quantum information. We can encode qubit with polarization, momentum, time, path, and so on. We also pay much attention to high dimensional cases. For example, we can encode qutrit with orbital angular momentum (OAM) and qudit with transverse momentum. The following is the simple introduction to our work.
HighLights
Optical universal quantum cloning. Beyond the no-cloning theorem, the universal symmetric quantum cloning machine was first addressed by Bužek and Hillery. We realized the 1→2 qubit Bužek-Hillery cloning machine with linear optical devices. This method relies on the representation of several qubits by a single photon. We showed that the fidelities between the two output qubits and the original qubit are both 5/6 (which proved to be the optimal fidelity of 1→2 qubit universal cloner) for arbitrary input pure states.
Teleportation of a quantum controlled-NOT gate. To overcome the difficulty inherent in practical realizations of quantum computers, new models have been suggested, such as distributed quantum computing and teleportation-based quantum computing. One key point of all these protocols is the teleportation of quantum logic gates. Through linear optical manipulation and with assistance of entanglement generated from spontaneous parametric down conversion (SPDC), we have shown how to teleport a local CNOT gate, which acts on both the polarization and path of a single photon, to a remote CNOT gate, acting on the polarization state of two distant photons. The quality of the quantum gate teleportation is characterized through quantum process tomography. Through this method, we demonstrated that the teleported quantum CNOT gate had a mean fidelity of 0.84, which is quite high.
Preparation of the Werner state via spontaneous parametric down-conversion. We present an experiment for preparing a Werner state via spontaneous parametric down-conversion and controlled decoherence of photons. In this experiment two independent BBO crystals are used to produce down-conversion light beams, which are mixed to prepare the Werner state.
Entanglement distillation of two-qubit mixed states under local operations. We can perform entanglement distillation of arbitrary two-qubit quantum states only using local operations.
Entanglement quantification and verification via uncertainty relations. We present a scheme and report the linear optical experiment to directly measure and detect entanglement via optical interference. Our experiment gives a proof of principle that it is possible to directly characterize entanglement properties of quantum states using simple observable physical quantities and circumvent the highly inefficient state reconstruction.
Direct characterization of quantum dynamics. We experimentally implement direct characterization of quantum dynamics (DCQD) algorithm of a single qubit proposed in M. Mohseni and D. A. Lidar [Phys. Rev. Lett. 97, 170501 _2006], which does not require quantum state tomography. The number of experimental configurations is reduced by a factor of 2 compared with that of standard quantum process tomography, which can be increased four times with an ideal
Bell state analyzer.
Observing transverse correlations of down-conversion photons. We experimentally observe transverse entanglement migration in Hilbert space and quantify transverse entanglement.
