Microwave and Terahertz Field Sensing and Imaging using Rydberg Atoms

Microwave and terahertz technologies play a critical role in modern life. Microwaves underpin mobile and satellite communications and are used for radar in navigation and meteorology. At higher frequencies, terahertz technologies are used to perform chemical sensing, non-invasive imaging, condition monitoring and more. These applications, and others, require fast detectors offering high sensitivity and the ability to perform spatially resolved imaging, which is particularly challenging in the terahertz domain where the majority of detectors require cryogenic cooling and offer slow thermal response times with limited absolute accuracy.

In this proposal we seek to address this technology gap by developing a new class of atom-based sensors that exploit the extreme sensitivity of highly-excited Rydberg atoms which act as antennae to provide precision electric field measurement across the microwave and terahertz frequency range. Using lasers to excite Rydberg atoms in a thermal vapour cell, the radio-frequency fields can be measured from the resulting perturbation in the transmission of a weak probe beam.

Atom-based sensors provide a number of advantages over traditional electric field measurement techniques; namely (i) they are intrinsically calibrated by relating the atomic properties to SI units to provide full measurement traceability, (2) act as point-like antenna for an in-situ measurement of the field, and (3) can be optically probed to enable sub-wavelength resolution of the radio-frequency field under study.

The proposed research programme will explore a number of key challenges to implementing Rydberg-atom-based electric field sensors, including optimising the cell materials and geometry to minimise the perturbation or suppression of the applied field and developing measurement techniques to achieve the fundamental limits of sensitivity and accuracy. To address these challenges we will combine UK based expertise, including the pioneers of optical detection of Rydberg atoms, to fabricate and characterise atomic vapour cells compatible with microwave and terahertz measurements and demonstrate precision field measurement and 2D imaging of structured radio-frequency fields. To verify the device accuracy we will compare the performance of our sensors to state-of-the-art calibrated references at the National Physical Laboratory. Finally, we will demonstrate real-world application of the sensors to areas including all-optical microwave communication schemes similar to WiFi and characterisation of the complex near-field emission from a terahertz antenna array. These sensors offer a new approach to radiofrequency sensing, imaging and metrology and provide a route to achieving enhanced sensitivity at microwave frequencies whilst providing an enabling technology for emerging applications in the terahertz domain.

The work set out in this proposal is high-quality fundamental research, the outcomes of which are closely aligned with flagship programmes in the UK, Europe and elsewhere to develop new technologies based upon the quantum properties of matter and light. Impact is expected across four main areas

1. Academic Impact

Rydberg-atom research is an area of particular strength in the UK and our work is relevant to Hogan (UCL), Bergamini (Open), Nunn (Bath) and Lesanovsky (Nott) and more. It is also of direct interest to a large and diverse community using microwave and terahertz technology as well as other quantum technologies using atomic vapour cells. We seek to address both fundamental and technical challenges associated with precision sensing and imaging of MW and THz fields as well as development of calibrated, traceable standards. This work will impact the broad field of THz researchers in the UK including those based at Leeds, Cambridge, UCL, Birmingham and Sussex, providing new methods for spatially resolved characterisation of THz materials and sources. To ensure that we maximise the impact we will attend the annual international IRMMW-THz and biennial ICAP and ICOLS conferences to present results.
Development of Rydberg-atom electric field sensors requires major advancements in the techniques used to detect and measure fields as well as understanding of the atom-light interactions at both optical and radio-frequency to realise SI-calibrated electric field metrology.

2. Technological Impact

The research programme provides a route to create a disruptive new technology able to span over three orders of magnitude in frequency range and provide sensitivity to regions of the spectrum that are currently limited to large, low accuracy detectors with slow thermal response times. We envisage a number of spin-out applications ranging from electromagnetic compatibility testing (EMC) to real-time 2D imaging of terahertz fields for device characterization with sub-wavelength optical resolution and large (cm^2 scale) effective sensor areas.

3. Training

The proposal will contribute highly-trained personnel at all levels from undergraduate to post-graduate and post-doctoral. We involve, on a regular basis, our undergraduate and postgraduate students in research projects which augment the critical path of our research programmes. The close synergy between experiments in the microwave and terahertz domains and the interdisciplinary nature of the project will result in a broad training for the PDRAs that will equip them with a unique skill base highly sought after in both industry and academia. All trained personnel will learn essential skills which will allow them to support the burgeoning quantum technology industries.

4. Society and Outreach

Experiments probing quantum systems are an attractive platform with which to engage the curiosity of the general public. We will use the results from this work to continue our public engagement work (See Pathways to Impact). All the investigators have a strong track record in performing outreach, taking part in local and national science and STEM activities as well as being involved in activities at local schools, hosting school visits and performing public lectures. We will continue with these activities as well as developing new resources utilizing the portable sensor to demonstrate the impact of atom-based sensors on modern life and enhance the profile of science in our local areas.