Ultra-sensitive atomic magnetometry for brain function diagnostics

Lead Research Organisation: University of Birmingham
Department Name: School of Physics and Astronomy


The huge progress achieved in the manipulation of quantum systems is opening novel routes towards the generation of realistic quantum-based technology. Notably many counterintuitive manifestations of quantum mechanics are turning to be key features for the next generation devices, whose performances will beat those of classical machines. Quantum sensors, in particular, exploit the intrinsic "weakness" of quantum systems, their extreme sensitivity to external perturbations, to provide measurements of the perturbing fields with unprecedented sensitivity and stability. This project targets the realization of ultra-sensitive quantum magnetometers based on neutral atoms at room temperature, for studying the brain function by accessing its connectivity.

Detection of very small magnetic fields of biological origin allows a non-invasive study of the spatial and time dependence of bio-currents. Therefore, a logical and very promising direction of application of non-invasive ultra-sensitive quantum magnetometers is the realization of probes for measuring the magnetic fields generated by the neuronal activity of the human brain. Recent technological developments have made it possible to employ atomic magnetometers (AMs) in the context of magnetoencephalography (MEG) analysis. Here we propose to further develop AMs-based MEG for accessing information on the brain connectivity, by combining these quantum sensors with the technique of transcranial brain stimulation (TMS). Indeed, the nerve cells of the brain can be inductively stimulated by applying a short but strong magnetic pulse localized at a specific region of the brain. Causal brain connectivity will be directly studied by measuring the magnetic response of different brain areas to this stimulus. The aim is to estimate the directional coupling and the temporal interaction of different brain sectors, which requires sensors with large sensitivity, real-time operation, and adequate spatial resolution.

The core of this project is the realization of all-optical AMs compatible with TBS. The key point is that the sensors need to rapidly recover following a relatively strong magnetic stimulation, to record the brain signals no more than few tens ms after the pulse. The integration of AM sensors and TMS coil will be done in few steps, with the goal of both minimizing the effects induced by the TMS coil and shortening the sensor dead-time. The sensor will be then prepared for operation in a medical environment. In parallel, we will boost the miniaturization of the AMs, which is necessary for achieving a millimetre-spatial resolution and a dense package of the sensors over the head, and its measurement bandwidth. Miniaturization usually comes at the price of an important loss of sensitivity. To improve magnetic sensitivity in highly miniaturized sensors, we will prepare and use a class of entangled atomic states known as spin-squeezed states. We propose a novel, simple and robust way to achieve spin-squeezing, which has the potential to largely surpass state-of-the-art techniques in atomic magnetometry. Within this project, we expect to implement ultra-sensitive highly miniaturized AMs as innovative tools to directly measure human brain connectivity, for understanding healthy brain functionality, as well as for clinical diagnostics and treatment of brain injuries and neurological disorders.

Planned Impact

The development of atomic sensors for the detection of magnetic fields with unprecedented sensitivity is one of the most effective real-world applications of Quantum Mechanics. Atomic magnetometers (AM) have indeed found recent application in measuring tiny magnetic fields of biological origin, as those generated by the human body. In particular, AMs are highly beneficial for Magnetoencephalography (MEG), a non-invasive neurophysiological technique which detects the magnetic fields generated by the neuronal activity of the brain.

Based on the promising state-of-the-art results obtained in the implementation of AMs for MEG, this project focusses on the further development of AMs-based MEG for realizing an integrated stimulus/measurement device directly accessing brain connectivity. Understanding the brain as a network is considered crucial for future developments of cognitive and clinical neuroscience, as also testified by the large NIH investment on the Human Connectome Project with the ambition to map the neural connections in human brain in their entirety. However, the experimental investigation of neural connections is still challenging. This project aims at developing atomic sensors which will surpass current technology and will impact the rapidly growing national and international academic community (Translational Medicine and Psychology) working on the topic. The AMs that we will realize hold the promise of better identifying the regions of the brain responding to a specific magnetic perturbation, quantifying how the brain connectivity is modulated in a task specific manner, assessing connectivity changes associated with brain injuries and neurological disorders. This is of interest for understanding healthy brain functionality, as well as for clinical diagnostics and, in a near future, for treatment of injuries and disorders via targeted magnetic stimulation of the brain.

Furthermore, the record sensitivity and spatial resolution which we aim to achieve by engineering spin-squeezed atomic states will impact the wider field of bio-magnetism imaging. The magnetometers used for these imaging applications have often to trade off sensitivity for physical size. Instead, the spin-squeezing generation technique which we propose in this project will allow reduction of the sensor head footprint to be achieved without loss of sensitivity with respect to wider (cm-sized) non-quantum enhanced devices. This will boost the realization of ultra-sensitive multichannel imaging systems consisting of several sensors packed together with spatial sensitivity on the order of few millimetres. We can also foresee application of these devices beyond bio-magnetism detection, for non-destructive testing and characterization of material samples, and for security applications.

Finally, the proposed project will provide advanced training for Master and PhD students in the field of atomic magnetometry, which is a rich interdisciplinary field with applications ranging from medicine to mapping of the magnetic field of the Earth, from characterization of materials to searching for dark matter and dark energy in the Universe. The experimental activity and the synergetic collaboration with the School of Psychology of the University of Birmingham, with NPL, and with the companies with whom we will interact along the duration of the project, will allow the students to develop technical skills and to learn advanced scientific methods in an environment which promotes translational and interdisciplinary research application.


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Description In the first six months of this Award, we have shown that linear and non-linear spin-exchange coupling can lead to the generation of atomic coherence in a Bell-Bloom magnetometer. In particular, we have theoretically and experimentally demonstrated that non-linear spin exchange coupling, acting in an analogous way to a wave-mixing mechanism, can create new modes of coherent excitation which inherit the magnetic properties of the natural Larmor coherence. The generated coherences further couple via linear spin-exchange interaction, leading to an increase of the natural coherence lifetime of the system. Notably, the measurements are performed in a low-density caesium vapour and for non-zero magnetic field, outside the standard conditions for collisional coherence transfer. In the first year of the Award, we also managed to use parametric excitations to coherently manipulate the collective spin state of an atomic vapour at room temperature. The parametric excitation is produced by periodic modulation of the pumping beam, exploiting a Bell-Bloom-like technique widely used in atomic magnetometry. Notably, we found that noise-squeezing in the readout of the magnetometer can be obtained by this technique enhancing the signal-to-noise ratio of the measurements up to a factor of 10, and improving the performance of a Bell-Bloom magnetometer by a factor of 3.
Exploitation Route Our work shows that the combination of a controlled modulation and a non-linear coupling term provides a rich scenario that can be exploited for improving spin coherence. Also, it realizes a new scheme for generating spin-squeezing in room-temperature vapour magnetometry, and paves the way to the exploitation of new self-oscillating regimes. This is instrumental to the realization of magnetometers with increased measurement sensitivity and bandwidth, which are of interest for a wide range of applications (from bio-sensing to non-destructive material testing, from inertial navigation to tests of fundamental Physics).
Sectors Aerospace, Defence and Marine,Healthcare,Other

Description MPAGS Training Modules
Geographic Reach National 
Policy Influence Type Influenced training of practitioners or researchers
Impact In the context of the Midlands Physics Alliance Graduate School, i delivered a short module on Gaussian Optics for preparing the first year PhD students to work in experimental physics laboratories involving the use and manipulation of laser sources.
Description Magnetic shielding design 
Organisation Magnetic Shields Ltd
Country United Kingdom 
Sector Private 
PI Contribution Selection of new materials for a mixed material shielding with high field attenuation and minimizing the residual magnetic field noise from high-permeability shields (e.g. Johnson noise) to below the fT/sqrt(Hz) sensitivity.
Collaborator Contribution Assembly of the different shielding parts and optimization of the mechanical stabiity of the whole shielding structure.
Impact - 10^6 magnetic field suppression - reduction of shielding induced magnetic noise to well below the 1 fT/sqrt(Hz) sensitivity - mechanical stability of a (>25 kg) shielding structure
Start Year 2019
Description NPL Squeezing and fundamental physics 
Organisation National Physical Laboratory
Country United Kingdom 
Sector Academic/University 
PI Contribution I have investigated non-linear effects leading to coherence transfer and spin-squeezing for achieving improved sensitivity in optically pumped atomic magnetometers.
Collaborator Contribution Partners have assisted with the experimental measurements and contributed with knowledge exchange.
Impact - Papers: R. Gartman, V. Guarrera, G. Bevilacqua, and W. Chalupczak, Phys. Rev. A 98, 061401(R) (2018) V. Guarrera, R. Gartman, G. Bevilacqua, G. Barontini, and W. Chalupczak, Phys. Rev. Lett. 123, 033601 (2019) - Additional grant submissions: 1) UK-Space (2019) 2) STFC-EPSRC call for Quantum Technologies for Fundamental Physics (under consideration)
Start Year 2018
Description Organization and participation in QUAMP 2019 conference 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact The conference hosted several postgraduate students from UK and abroad.
Year(s) Of Engagement Activity 2019
Description Physics East Building symposium 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Gathering together all EPSRC-funded active researchers at the University of Birmingham, including PhD students, PDRAs, Academic Staff.
Year(s) Of Engagement Activity 2018
Description Seminar for the extended group of Cold Atoms, Quantum Technology at the University of Birmingham 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact 25 PhD students, 20 PDRAs, 10 University staff attended the seminar presenting my research activity, with questions and discussion afterwards.
Year(s) Of Engagement Activity 2018