# International Collaboration - Quantum Physics based on Multi-Photon Entanglement

**Introduction of the project**

Entanglement lies at the heart of quantum mechanics. The study of entanglement not only helps to answer problems fundamental to quantum physics but also enables a broad spectrum of researches in quantum information science, quantum metrology and quantum measurement. Critical to the success of these developments are operation scalability and fidelity. Taking advantage of the advanced photon detectors with near unity single-photon detection efficiency and photon-number-resolving capability (for example, superconducting transition-edge-sensors), this project targets to scale up multi-photon entanglement, from 2 to N, with high-visibility and high fidelity, for the study of foundational problems and quantum-enabled applications, for example, Boson Sampling and quantum simulation.

**Previous Results:**

** Supporting
online material for CNOT paper (pdf) **by Alex Goebel.

**Quantum Teleportation of two-qubit
composite system base on Six Photon Entanglement**

Quantum teleportation, a way to transfer the state of a quantum system from one location to another, is central to quantum communication and plays an important role in a number of quantum computation protocols. Previous experimental demonstrations have been implemented with single photonic, or ionic qubits. However, teleportation of single qubits is insufficient for a large-scale realization of quantum communication and computation. Here, we present the experimental realization of quantum teleportation of a two-qubit composite system. In the experiment, we develop and exploit a six-photon interferometer to teleport an arbitrary polarization state of two photons. The observed teleportation fidelities for different initial states are all well beyond the state estimation limit of 0.40 for a two-qubit system. Not only does our six-photon interferometer provide an important step towards teleportation of a complex system, it will also enable future experimental investigations on a number of fundamental quantum communication and computation protocols. Details are in the reference below.

Reference:

Experimental quantum teleportation of a two-qubit composite system

Nature Physics 2, 678-682 (01 Oct 2006)

**One-Way Quantum Computing
with Two-Photon Four-Qubit Cluster States**

We
recently reported an experimental realization of one-way quantum computing
on a two-photon four-qubit cluster state. This was accomplished by developing
a two-photon cluster state source entangled both in polarization and spacial
modes. With this special source, we implemented a highly efficient Grover's
search algorithm and high-fidelity two qubits quantum gates. Our experiment
demonstrates that such cluster states could serve as an ideal source and
a building block for rapid and precise optical

quantum computation. Details are in the reference below.

Reference:

Experimental Realization of One-Way Quantum Computing with Two-Photon Four-Qubit
Cluster States

to be published in Phys. Rev. Lett. (2007).