Photonic entanglement is central to optical quantum computing schemes, and is also important for quantum communication, quantum metrology, and in fundamental quantum mechanics. I will discuss the results of several linear optics experiments for generating, characterising, and utilising entangled states in the context of quantum information.
Controlled-NOT gates are the archetypal two-qubit entangling gate. We have constructed a two-photon CNOT and fully characterized it using quantum process tomography. As well as being a proof-of-principle for entanglement schemes working via measurement-induced nonlinearity, two-photon CNOT and related circuits can also be used to make generalised quantum measurements, explore error correction protocols, and build prototypical cluster states for quantum computation.
In certain areas of quantum information, optical qudits (d-level quantum systems) hold advantages over photonic qubits. One type of qudit encoding uses the transverse spatial mode of a photon. We have fully characterised the two-qutrit spatial mode entanglement from a downconverted photon pair, and find a highly entangled state with only slight mixture. These kind of studies are important for characterising the requirements for applications such as quantum bit commitment, where qutrits should offer a higher degree of security compared with qubits.
- http://quantum.info/ - Quantum Technology Lab, The University of Queensland