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The new intensity frontier: exploring quantum electrodynamic plasmas

Lead Research Organisation: Imperial College London
Department Name: Physics

Abstract

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.
 
Description Radiation reaction-the force experienced by an accelerating electron due to its own emitted radiation-is a fundamental but poorly understood effect in extreme environments, such as near black holes or in high-energy particle collisions. Our study provides the first unambiguous (greater than 5s significance) experimental evidence of quantum radiation reaction, confirming that quantum effects play a crucial role when electrons interact with ultra-intense laser fields.


1. First Definitive Observation of Quantum Radiation Reaction
Previous experiments suggested that quantum effects modify radiation reaction, but their evidence was statistically weak (=3s). We report the first measurement at greater than 5s confidence, providing conclusive proof that quantum corrections must be included in models describing ultra-relativistic electron dynamics. This breakthrough resolves previous uncertainties and establishes a new benchmark for future research in strong-field quantum electrodynamics (QED).

2. Direct Measurement of Both Electron and Photon Spectra
We used an all-optical setup to collide a laser-wakefield-accelerated electron beam (~609 MeV) with an ultra-intense laser pulse (I Ëœ 10²¹ W/cm²). This allowed us to measure both the electron energy loss and the spectrum of emitted photons, confirming that quantum effects reduce the rate at which electrons lose energy compared to classical predictions. Earlier experiments only inferred radiation reaction indirectly or measured photon spectra alone, making our direct measurement a significant advance.

3. Development of a Bayesian Model Comparison Framework
A major challenge in strong-field QED experiments is the difficulty of measuring key experimental parameters on a shot-by-shot basis. To overcome this, we developed a Bayesian inference framework that enables rigorous statistical comparison of theoretical models. This method provides a powerful tool for future laser-electron collision experiments, improving model selection even when key parameters cannot be measured directly.

4. New Research Questions and Unresolved Challenges
Our study confirms quantum radiation reaction but leaves open the question of stochastic effects-whether quantum emissions occur randomly in a way that affects electron dynamics. Our data show spectral broadening, a possible signature of stochasticity, but uncertainties in collision parameters prevent a definitive conclusion. This highlights the need for future experiments with more precise electron-laser alignment and diagnostics to probe stochastic radiation reaction in greater detail.

Negative Results and Research Paths Closed Off
One key finding is that while quantum models outperform classical predictions, we were unable to distinguish between two competing quantum models (quantum-continuous and quantum-stochastic) due to experimental uncertainties. This suggests that future efforts should focus on reducing these uncertainties rather than trying to distinguish models using current techniques.

Wider Implications and Future Directions
Our findings impact a wide range of fields:
- Astrophysics: Improved modelling of pulsar magnetospheres and black hole environments.
- High-energy physics: Better understanding of radiation losses in future particle colliders.
- Plasma physics: Insights for designing next-generation laser-driven particle accelerators and gamma-ray sources.

This research was made possible through an international collaboration involving experts in laser physics, plasma physics, and theoretical QED, strengthening global research networks in high-intensity laser-matter interactions.
Exploitation Route 1. Academic Advancements in Strong-Field QED
The results of this study will be taken forward by theoretical and experimental physicists working on high-intensity laser-matter interactions. In particular:
- Strong-field QED theorists will refine radiation reaction models, incorporating our experimental constraints to improve predictions for ultra-intense laser-electron interactions.
- Experimental high-power laser groups will build on our findings by conducting new experiments at higher laser intensities and improved diagnostics to probe stochastic effects in radiation reaction.
- Particle accelerator researchers working on future high-energy colliders (such as the proposed gamma-gamma colliders) will integrate quantum radiation reaction models to better predict beam behaviour at extreme intensities.

Our Bayesian model comparison framework provides a new tool for analysing laser-electron collision experiments, which will be applied in future work at facilities like ZEUS (USA), EPAC (UK), and Vulcan 20-20 (UK).

2. Industrial and Technological Applications
Our findings are relevant to companies and laboratories developing laser-driven radiation sources for applications in:
- Medical imaging and radiotherapy: Understanding quantum corrections to inverse Compton scattering will help optimize laser-driven X-ray and gamma-ray sources for medical applications.
- Nuclear security and materials testing: Improved knowledge of high-energy photon production is critical for non-destructive testing in defence and industry.
- Fusion energy research: Understanding radiation reaction in high-energy plasmas is important for inertial confinement fusion experiments, potentially aiding in the development of future fusion energy technologies.

3. Public Engagement and Policy Impact
- Our work contributes to fundamental science communication, helping to explain how extreme physics applies to astrophysical environments and next-generation technology.
- Government and funding bodies (e.g., UKRI, DOE, European Research Council) may use our findings to prioritize investment in high-power laser facilities and fundamental physics research.

By engaging with both academic and industrial partners, our research lays the groundwork for future discoveries in plasma physics, astrophysics, and high-intensity laser applications.
Sectors Aerospace

Defence and Marine

Energy

Healthcare

Security and Diplomacy

Other
URL https://arxiv.org/abs/2407.12071
 
Title A laser-plasma platform for photon-photon physics: the two photon Breit-Wheeler process 
Description The data contained in this repository was used in the production of the publication "A laser-plasma platform for photon-photon physics: the two photon Breit-Wheeler process". https://doi.org/10.1088/1367-2630/ac3048 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
Impact The data contained in this repository were used in the production of the publication "A laser-plasma platform for photon-photon physics: the two photon Breit-Wheeler process". https://doi.org/10.1088/1367-2630/ac3048 
URL https://zenodo.org/record/5027591
 
Description QED plasma 
Organisation University of Michigan
Country United States 
Sector Academic/University 
PI Contribution We were awarded beam time on experiment at Gemini laser at CLF, team members were responsible for planning, setting up and running the experiment
Collaborator Contribution Prof Alec Thomas sent a PhD student to our experiment who took part in in the experiment and subsequent analysis
Impact no outputs at this time - though a major publication is in preparation
Start Year 2020
 
Description Recreating stars and quasars with lasers and plasma accelerators - youtube 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Public lecture on Prof Mangles Research, streamed live on Youtube. 1.8K views.
Year(s) Of Engagement Activity 2023
URL https://www.youtube.com/watch?v=Kfw2sq4HnGI
 
Description School Visit (Tiffin) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Talk on research and career of physics to A-level students at local state school
Year(s) Of Engagement Activity 2022,2023