“Just what”, I hear you say, “has all of this got to do with the organ at Winthrop Hall at the University of Western Australia?”

Well- almost nothing, really, besides the somewhat strained allusion in this opening section of this post. In this case, I mean “ORGAN”, in capital letters - the Oscillating Resonant Group AxioN Experiment. This is a haloscope (see the earlier post “To catch an axion” for a brief discussion of what a haloscope is) which is operational at the ARC Centre of Excellence for Engineered Quantum Systems at the Physics Department of UWA.

The ORGAN Experiment is planned to proceed in several stages, extending from a short pathfinder run at a fixed central frequency of 26.531 GHz, through seven subsequent phases covering both higher and lower frequencies, to probe the as-yet unexplored high-mass range for axions.

The pathfinder run parameters were chosen in order to test an existing suggestion that axions of around 110 micro-electronVolt mass (corresponding to a frequency of around 26.6GHz) could explain an experimental effect that has been reported in other kinds of experiments. Furthermore, the run allowed the team to develop further experience in the construction and operation of a haloscope, and to test some important pieces of equipment, before committing to the later phases of ORGAN.

Since the pathfinder ran at a fixed frequency, the comparison data were obtained by turning the magnet off and recording the signal obtained without the presence of the high-strength magnetic filed that is required to convert axions to photons.

The later phases of the experiment will be set out in two overall stages. Stage I will see a more in-depth examination of the frequency range 26.1 - 27.1 GHz to test the 26.6 GHz to test the entire mass range proposed by 26.6 GHz claim. At the same time, cavity and amplifier research and development will commence for the later stages.

Stage II will investigate frequencies over the range 15 - 50 GHz, in 5 GHz steps, with expected durations of around 10 months in each step. Whilst the data for each step are being collected, development work for the other stages can continue, drawing on the insights gained in the previous steps.

One of the methods that will be explored by ORGAN to enhance its sensitivity involves the simultaneous use of multiple cavities of different dimensions- hence the overall acronym, due to the resemblance between the proposed assemblage of long, thin cavities of different dimensions, and the varied ranks of pipes in a pipe organ.

ORGAN, and related haloscope experiments elsewhere, involve collaborations between researchers in a range of fields, all of which seek to drive the various technologies as close to their limits as possible. The first haloscope with an amplifier that adds noise at a level below the standard quantum limit (HAYSTAC) is about to commence. This is a pathway that ORGAN intends to follow.

And, with its choice of high frequencies, ORGAN will probe an entirely new range of axion masses that are as yet unexplored.

[With thanks to Ben McAllister at UWA for comments and improvements.]

The ORGAN haloscope. The resonant cavity itself is deep within the white vertical cylinder. ( Image sourced from )

The ORGAN haloscope. The resonant cavity itself is deep within the white vertical cylinder. (Image sourced from