Josh Long

Education

• Ph.D., Physics, Johns Hopkins University, 1998

Biography

Josh Long received a B.A. in physics from Amherst College in 1989, where he did a thesis on high-Tc superconductors, soon after the discovery of those compounds. He earned a Ph.D. in physics from Johns Hopkins University in 1998, helping to construct the NOMAD experiment at CERN and using that experiment to set preliminary constraints on muon-tau neutrino oscillations in the limit of large (~ 5 eV) neutrino mass differences. From 1997-2002 he was a postdoctoral associate at the University of Colorado, Boulder, where he conducted a test of the gravitational inverse-square law at sub-millimeter distance scales. From 2002-2005 he was a staff scientist at the Los Alamos National Lab, where he studied the dielectric properties of large volumes of superfluid helium in support of the neutron Electric Dipole Moment (nEDM) experiment at the Oak Ridge Spallation Neutron Source. From 2005-2022 he was on the faculty at Indiana University, Bloomington, first as a research scientist then as an assistant and associate professor of physics. At Indiana he continued his gravity experiments, extending their sensitivity to shorter ranges and using them to test Lorentz invariance, and began related experiments to search for exotic spin-dependent forces and axion-like particles. He also continued collaboration on the nEDM experiment, constructing a large, custom dilution refrigerator for the 1200 liters of superfluid needed for that experiment.

Academic Positions

• Professor of Physics, University of Illinois, Urbana-Champaign, 2022-present
• Associate Professor of Physics, Indiana University, Bloomington, 2016-2022
• Assistant Professor of Physics, Indiana University, Bloomington, 2008-2016
• Assistant Scientist, Indiana University, Bloomington, 2005-2008
• Staff Scientist, Los Alamos National Laboratory, 2002-2005
• Postdoctoral Research Associate, University of Colorado, Boulder, 1997-2002

Research Statement

My research concentrates on experimental tests of fundamental symmetries and searches for macroscopic forces beyond gravity and electromagnetism ("5th forces") at submillimeter length scales, using nuclear and other techniques.

Short-range 5^th forces

One experiment, under construction at UIUC, is a test of the Newtonian inverse square law (ISL) at distance ranges less than 100 microns. Modifications to the ISL at short range, arising from new elementary particles, violations of Lorentz symmetry, or even extra spacetime dimensions, are predicted from models that attempt to describe gravity and the other fundamental interactions in the same theoretical framework. The experiment is a table-top apparatus, using 1 kHz mechanical oscillators as test masses.

Spin-coupled forces, NSR, and ARIADNE

Recently, the test masses in the mechanical oscillator experiment have been augmented with spin-polarized materials, to make the experiment sensitive to exotic submillimeter forces coupled to spin.  These forces could be mediated by the axion: a light, weakly-interacting particle that is a leading candidate for dark matter.

The spin-polarized materials consist of rare earth iron garnets, which exibit the unusual property of having non-zero spin but zero magnetization (at least ideally, and at a very specific or "compensation" temperature).  Thus they are ideally suited for controlling the major background limiting spin-coupled force experiments.

We are also using these materials to search for exotic, sub-micron spin-coupled forces in a series of neutron spin rotation (NSR) experiments.  In these experiments, polarized neutrons are scattered from a garnet target held at the compensation temperature: any non-zero precession of the scattered neutron moments can be interpreted as a signal of new physics.  These measurements are currently taking place at the High Flux Isotope Reactor at Oak Rigde National Laboratory.  

I collaborate on the Axion Resonant InterAction DetectioN Experiment (ARIADNE), which has even greater potential sensitivity to exotic spin-coupled forces. This is an NMR-type experiment, which searches for induced magnetization in a sample of cryogenic, polarized helium-3 atoms as a dense, non-magnetic source mass is modulated in close proximity. ARIADNE is managed by a group of about 20 scientists from 8 institutes. My group is responsible for the source mass.

Neutron EDM Experiment

I also collaborate on experimental searches for a permanent electric dipole moment of the neutron (nEDM) with the Nuclear Physics group. An nEDM signal would be an example of time reversal symmetry violation and a key to understanding the matter-antimatter asymmetry in the universe.  One experiment, in progress at the Los Alamos National Laboratory, aims for a ten-fold improvement in the current nEDM sensitivity.  It is an NMR-type experiment, in which the Larmor precession frequency of a sample of neutrons held in a weak magnetic field is monitored for shifts as a strong electric field is applied in parallel.  Another experiment, originally slated for Oak Ridge but now seeking a new location, aims for a 100-fold improvement in sensitivity with a completely cryogenic setup.  Ultracold neutrons are produced in a bath of superfluid helium and subsequently held in the bath. The improved sensitivity derives from the large neutron samples, long storage times, and high dielectric strength attainable in the superfluid.  My group is fabricating part of the cryogenic systems needed for this project.

Graduate Research Opportunities

We have openings for graduate students on all of the experiments described above. Contact Prof. Long directly (email preferred) for details.

Undergraduate Research Opportunities

We can support seven undergraduates in our group and all positions are currently filled (fall 2025). However, 1-2 positions usually open up per academic term and over the summer. Preference will be given to Physics majors who can devote at least five hours per week to lab work. This includes beginning students with technical hobbies, and advanced students with experience in electronics (for example, Physics P404), computer-aided design, and modeling. Students interested in applying for these positions should contact Prof. Long directly.

Selected Articles in Journals

• C.D. Hughes, et al. “Polarized neutron measurements of the internal magnetization of a ferrimagnet across its compensation temperature”. Journal of Magnetism and Magnetic Materials 629 173273 (2025).
• H. Fosbinder-Elkins, et al. (ARIADNE Collaboration) "A method for controlling the magnetic field near a superconducting boundary in the ARIADNE axion experiment". Quantum Sci. Technol. 7 (2022), 014002
• Nancy Aggarwal, et al. (ARIADNE Collaboration) "Characterization of magnetic field noise in the ARIADNE source mass rotor". Phys. Rev. Res. 4, (2022) 013090.
• Cheng-Gang Shao et al. “Combined Search for a Lorentz-Violating Force in Short-Range Gravity Varying as the Inverse Sixth Power of Distance”. Phys. Rev. Lett. 122 (2019), 011102.
• M.W. Ahmed et al. “A new cryogenic apparatus to search for the neutron electric dipole moment”. J Instrum. 14:11 (Nov. 2019), P11017–P11017.
• H Yan et al. “Absolute measurement of thermal noise in a resonant short-range force experiment”. Class. Quantum Gravity 31:20 (2014), p. 205007.
• T. M. Leslie et al. “Prospects for electron spin-dependent short-range force experiments with rare earth iron garnet test masses”. Phys. Rev. D 89 (2014), p. 114022.
• J.C. Long et al. “Upper limits to submillimeter-range forces from extra space-time dimensions”. Nature 421 (2002), pp. 922–925.

Recent Courses Taught

• PHYS 211 - University Physics: Mechanics
• PHYS 524 - Survey Instr Lab Techniques