Getting sharp images from dull detectors

Observing the quantum behavior of light is a big part of Alan Migdall's research at the Joint Quantum Institute. Many of his experiments depend on observing light in the form of photons -- the particle complement of light waves -- and sometimes only one photon at a time, using "smart" detectors that can count the number of individual photons in a pulse. Furthermore, to observe quantum effects, it is normally necessary to use a beam of coherent light, light for which knowing the phase or intensity for one part of the beam allows you to know things about distant parts of the same beam.

In a new experiment, however, Migdall and his JQI colleagues perform an experiment using incoherent light, where the light is a jumble of waves. And they use what Migdall calls "stupid" detectors that, when counting the number of photons in a light pulse, can really only count up to zero, as anything more than zero befuddles these detectors and is considered as number that is known only to be more than zero.

Basically the surprising result is this: using incoherent light (with a wavelength of 800 nm) sent through a double-slit baffle, the JQI scientists obtain an interference pattern with fringes (the characteristic series of dark and light stripes denoting respectively destructive and constructive interference) as narrow as 30 nm.

This represents a new extreme in the degree to which sub-wavelength interference (to be defined below) has been pushed using thermal light and small-photon-number light detection. The physicists were surprised that they could so easily obtain such a sharp interference effect using standard light detectors. The importance of achieving sub-wavelength imaging is underscored by the awarding of the 2014 Nobel Prize for chemistry to scientists who had done just that.

The results of Migdall's new work appear in the journal Applied Physics Letters. Achieving this kind of sharp interference pattern could be valuable for performing a variety of high-precision physics and astronomy measurements.