Search for quantization of space-time with photon counting interferometry

fluctuations caused by gravitational waves.

Remarkable progress has been made in the development of single photon detection as well, with dark count rates of less than a photon per hour available with high quantum efficiency. This project brings together both technologies, to increase interferometric sensitivity in a way that can be explored for fundamental physics: The two powerful techniques will be combined to address the question of whether space-time is quantized.

The unification of quantum theory with the theory of relativity is a long-standing problem with barely any experimental guidance at hand. In recent years, there has been a growing body of work by different theorists investigating if and how quantization of space-time may be accessible to precision interferometry. If such quantization could be confirmed experimentally, it would open up a new horizon for quantum gravity. Beyond this, the innovative single-photon detection interferometry will also be used to search for dark matter and very-high-frequency gravitational waves.

You will be working on our project called ‘SPI-QG’, standing for ‘Single Photon detection Interferometry for Quantum Gravity’. SPI-QG has recently been funded by an ERC Advanced grant from the European Commission, awarded to Prof. Hartmut Grote, who will be your main supervisor.

Your main project will be the development of optical filter cavities required for the single photon readout. This is predominantly experimental work, comprising precision optics, lasers, and feedback control, but also computer simulations and analysing data. You will work in a team of PhD students and post-docs and be involved in the larger project, SPI-QG, as well, where the filter cavities will be integrated in two 7.5m long Michelson interferometers, to form a unique new instrument probing the very nature of space-time.

We are currently operating a smaller prototype of table-top-sized interferometers called ‘QUEST’, and our first scientific results from QUEST have been published last year [1].

We are a diverse group of researchers, embedded in the larger group of the Gravity Exploration Institute (GEI) at Cardiff University, which is one of the world leading groups in gravitational-wave astronomy, spanning expertise from source modelling, data analysis, astrophysical interpretation and instrumentation. We look forward to your application!

How to apply:

Applicants should apply to the Doctor of Philosophy in Physics and Astronomy with a start date of 2nd of January 2027 (late start up until October 2027 is also possible)

Applicants should submit an application for postgraduate study via the Cardiff University webpages (https://www.cardiff.ac.uk/study/postgraduate/research/programmes/programme/physics-and-astronomy) including:

• your academic CV
• your degree certificates and transcripts to date including certified translations if these are not in English
• a personal statement/covering letter

Ensure your personal statement (as part of the university application form, or as a separate attachment, if you prefer) provides a clear explanation of your research interest, preparation undertaken, and an understanding of the project.

Your personal statement should be no more than 500 words, and address the following questions:

1. What are your scientific research interests and ambition?
2. How has your academic and/or professional journey prepared you for PhD study? (for instance, give examples of work you particularly enjoyed, of challenges you overcame, of connecting with others about your work or ideas, of showing inventiveness, of developing new skills and knowledge)
3. Why do you think this project is important?”

• two references (applicants are recommended to have a third academic referee, if the two academic referees are within the same department/school). Your references can be emailed by the referee to physics-admissions@cardiff.ac.uk

Please note: We do not contact referees directly for references for each applicant due to the volume of applications we receive.

Candidates should hold or expect to gain a first-class degree or a good 2.1 (or their equivalent) in Engineering, Physics or a related subject.

Applicants whose first language is not English are normally expected to meet the minimum University requirements (e.g. IELTS 6.5 Overall with 5.5 minimum in sub-scores) (https://www.cardiff.ac.uk/study/international/english-language-requirements)

In the "Research Proposal" section of your application, please specify the project title and supervisors of this project and copy the project description in the text box provided.

In the funding section, please select that you will not be self-funding and write that the source of funding will be ERC.

Once the deadline for applications has passed, we will review your application and advise you within a few weeks if you have been shortlisted for an interview. Please note that we reserve the right to close the application process early if a suitable candidate is identified.

Eligibility :

This studentships are available to home and international students. International students will not be charged the fee difference between the UK and international rate.

For more information, or if there are any questions re application process, please contact Physics and Astronomy PGR Student Support team at Physics-PG@cardiff.ac.uk

Cardiff University is a signatory to the San Francisco Declaration on Research Assessment (DORA), which means that in hiring and promotion decisions we will evaluate applicants on the quality of their research, not publication metrics or the identity of the journal in which the research is published. More information is available at: Responsible research assessment - research – Cardiff University.

Applications may be submitted in Welsh, and an application submitted in Welsh will not be treated less favourably than an application submitted in English.

Funding Notes

This EC fully-funded scholarship is for 3.5 years and covers the full cost of tuition fees and a UKRI standard stipend (£21,805 for 2026/27). The scholarships are open to UK/home and international candidates.

References

[1] A. Patra, …, K. Kokeyama, K. Dooley, H. Grote; Broadband Limits on Stochastic Length Fluctuations from a Pair of Table-Top Interferometers, Phys. Rev. Lett. 135, 101402 (2025)