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LINEAR OPTICS QUANTUM COMPUTATION PROGRAM -
EXPERIMENTAL ([email protected])

 

Program Manager
Dr Elanor Huntington - [email protected]

Linear Optics Experimental Research Staff
Dr Gregory Milford

Linear Optics Experimental Research Students
Ms Amy Dunlop
Mr James Webb

Collaborating Centre Researchers
A/Prof Timothy Ralph - University of Queensland
Dr Howard Wiseman - Griffith University

Other Collaborating
Dr David Pulford - DSTO Australia
Dr Matthew Sellars - Australian National University
Mr Craig Robilliard - [email protected]
Mr Oliver Gloeckl, Dr Ulrik Andersen - University Erlangen-Nuernberg
Dr Stefan Lorenz, Prof Gerd Leuchs - University Erlangen-Nuernberg

Program Description
The potential of linear optical systems for quantum computation has been clearly illustrated by recent demonstrations of the operation of non-deterministic photonic CNOT gates (T.B.Pittman et al, Physical Review Letters, 88, 257902 (2002) and J.L.O'Brien et al, Nature, 426, 6964 (2003)). Current experiments in linear optical quantum computation typically make use of polarisation to encode the qubits. However, polarisation is not the only photonic degree of freedom available. For example schemes in which the timing or occupation of optical modes are the quantum variables have also been realised. The aim of this program is to develop the technology required to encode an optical qubit in the occupation of one of two different frequency modes. The attraction of this approach lies in potential compatibility with commercial fibre-optic technologies. Initially, we envisage the "frequency-basis" encoding scheme as comprising two optical frequency basis states separated by radio frequencies. Hence the term "radio-frequency basis" (RF-basis). These basis states are sufficiently close together that they could be manipulated with standard electro-optical devices but still clearly resolvable using narrowband optical and opto-electronic systems.

Right: One of the laser laboratories in the School of Information Technology an Electrical Engineering at The University of New South Wales at the Australian Defence Force Academy.

Quantum Information Technologies
Considerable international research effort has been focused on experiments in Quantum Computation and conducts research into photonic quantum computation architectures, one of the two experimental research themes of the Centre.

The vast majority of existing experiments in the field of photonic quantum computation are in free space and make use of polarisation to encode information. This makes the experiments very challenging because they must operate in a light-tight environment and at wavelengths that require complex, bulky and expensive equipment to generate the photons. Such an environment does not lend itself easily to scale-up of photonic encoding systems. Our role within the CQCT is to develop robust and potentially scaleable photonic encoding schemes.

In collaboration with co-workers at the University of Queensland, we have proposed a new scheme for encoding quantum information on photons. This novel photonic encoding scheme - the frequency of the photons - lends itself to operation inside optical fibres. Adoption of this scheme will eliminate the requirement for a light-tight environment for photon quantum computation experiments and may well reduce the reliance on the older approaches to generation of single photons.

The second of the experiments of the Quantum Electronics Group rely on an underlying theoretical framework, which not only motivates the research but also facilitates quantitative analysis. Whilst our primary focus is experiments, we have completed theoretical analyses of a number of potential quantum information experiments. The Quantum Electronics Group is currently conducting experiments that demonstrate the operation of these devices on "bright" beams of light. We have experimental results confirming the operation of one of our inventions. We are currently constructing another experiment to confirm the operation of another.

Right: Photograph of the experiment with lines overlaid to indicate the optical path. The FBS is indicated in red and a state preparation interferometer is indicated in yellow. Diagnostics (a homodyne detection scheme and optical spectrum analyser) are indicated in blue and green lines aid the eye for all other beam paths. Finally, two electro-optic control loops are indicated in purple



 

 


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