Ultra-sensitive atomic magnetometry for brain function diagnostics

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.

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.