Jonathan N. Hallén

About me

I am a theoretical physicist working in condensed matter theory and statistical mechanics. I am currently a postdoctoral fellow in the groups of Norman Yao at Harvard University and Chris Laumann at Boston University. For the academic year 2025-2026 I am also a Sweden-America Foundation scholar.

My PhD was shared between the University of Cambridge in the Theory of Condensed Matter Group and at the MPI for the Physics of Complex Systems, supervised by Professor Claudio Castelnovo and Professor Roderich Moessner. I completed it in May 2023.

I was a member of the Max Planck Graduate Center for Quantum Materials between 2019 and 2023.

If you want to know more you can check out my CV or reach me by email at jonathan_nilssonhallen@g.harvard.edu.

Research

I am generally interested in complex phenomena in many-body physics. My current active research includes:

The use of solid state defect ensembles as a platforms to explore quantum phases and dynamics.
The development of broad frameworks for magnetic noise spectroscopy.
The dynamics of point defects in frustrated magnetic systems, in particular in spin ice materials such as Dy2Ti2O7.
Novel quantum simulation platforms such as Rydberg atom arrays.
Effects of boundaries and disorder on quantum spin liquids.

For more details, see my publications or my google scholar.

News

Our new work together with Kang-Kuen Ni's group at Harvard was posted on the arXiv. We use a dual-species Rydberg atom experiment to perform stabilizer readout on a four-atom plaquette using a single entanglement step.

Another preprint appeared on Christmas Eve. We have used large-scale quantum Monte Carlo simulations to explore the feasibility of scalable spin squeezing in systems of disordered dipoles.

We have a new preprint on the arXiv proposing stray-field magnetometry as an alternative way to detect emergent photons in quantum spin ice.

I was awarded a scholarship from Sverige-America Stiftelsen (the Sweden-America Foundation) to support my continued research at Harvard University.

New paper on θ-magnetism in quantum spin ice is out as a preprint on arXiv.

Our paper on spin ice under uniaxial strain was published in Physical Review B.

Preprint out on arXiv exploring both the thermodynamics and dynamics of spin ice under uniaxial strain applied along the [111] crystallographic direction.

Our new paper titled "Dichotomous Dynamics of Magnetic Monopole Fluids" was published in PNAS.

We have a new preprint on arXiv, exploring driven monopole motion in spin ice and finding further evidence for the existence of emergent dynamical fractals in Dysprosium Titanate.

Our paper on nematic spin ice was published in PRB.

New preprint on nematic spin ice available on arXiv.

In May 2023 I successfully defended my PhD thesis on the dynamics of frustrated magnetic systems.

An article has appeared in Physics World about our work on anomalous fractals and anomalous noise in spin ice.

Our discovery of dynamical fractals in spin ice has appeared on some popular science websites, for example here in English and here in German.

Felix Flicker has written a very nice perspective article to accompany the publication of our paper on dynamical fractals in Science.

I was awarded the 2023 Cavendish Prize for Graduate Student Theoretical Research.

The seminar I gave at Northeastern University in October 2022 is available on youtube.

I was interviewed on doldispodden about my research and life at the University of Cambridge (in Swedish).