Cover-worthy Interference

Nature Physics has selected an experimental result from Institute for Quantum Computing (IQC) researchers for the front of the November 2008 issue. The image is an interference pattern from a novel interferometer developed by Rainer Kaltenbaek, Jonathan Lavoie, Devon Biggerstaff and Kevin Resch of the Quantum Optics Laboratory at IQC.

The image was taken from the article titled "Quantum-inspired interferometry with chirped laser pulses," which was also published in the November issue. The article describes a new method of interferometry with dramatic improvements over conventional methods especially for making measurements in highly dispersive or lossy materials.

Interferometry is a technique to examine two or more waves by examining the interference pattern created by combining them. It is an important tool in a vast array of fields including astronomy, biomedical imaging, precision metrology, and optical quantum information.The researchers started with interferometer based on the established Hong-Ou-Mandel effect, first observed in 1987, which offers some useful features for precise interferometric measurements such as automatic dispersion cancellation.

By rearranging the interferometer, they were able to use bright, "chirped" laser pulses instead of entangled photon pairs which are more difficult to detect. "We essentially ran these pulses through a 'time-reversed' Hong-Ou-Mandel, which is a device called a cross-correlator," explains Professor Kevin Resch, supervisor of the Quantum Optics Laboratory. "When we did this, and looked at the interference in the output light, it behaved [almost] exactly as the quantum interference, including the automatic dispersion cancellation."

By using chirped laser pulses, the new interferometry technique offers 10 million times more signal than that achievable with entangled photons. Kevin details the significance of the results, "It hits on the questions that I think all of us [in] quantum information are constantly asking like 'when are quantum effects really giving us an advantage over classical systems?' [As well,] practical applications for this kind of interference have already been identified through all of the work in studying quantum interference. Our technique, despite not needing quantum resources, may take these insights from quantum information science and make them viable."

The cover image is Figure 2a in the article, showing the spectrum of light emitted from the new interferometer as the delay of one wave is varied. The image shows that the interferometer emits essentially two frequencies which get closer together as the delay of the waves are balanced. At perfect match, the waves interfere destructively, which can be seen in the centre of the graph.

The complete article is available in Nature Physics Volume 4 (November 2008), pages 864 - 868 or online at Nature Physics.

For more information on the experiment, contact Professor Kevin Resch.

About IQC: Founded in 2002, the mission of the Institute for Quantum Computing(IQC) is to aggressively explore and advance the application of quantum mechanical systems to a vast array of relevant information processing techniques.

A part of the University of Waterloo, IQC creates a truly unique environment that fosters cutting-edge research and collaboration between researchers in the areas of computer, engineering, mathematical and physical sciences.

At the time of this release, IQC has 17 faculty members, 20 postdoctoral fellows and over 73 students and research assistants, as well as a support staff of 10.