Optically-pumped magnetometer arrays for magnetoencephalography

Project Information

OPMMEG

Grant agreement ID: 101099379

DOI

10.3030/101099379

Project closed

EC signature date 21 November 2022

Start date 1 December 2022

End date 30 November 2025

Funded under

• The European Innovation Council (EIC)

Total cost

€ 2 483 327,50

EU contribution

€ 2 483 327,50

Coordinated by

TEKNOLOGIAN TUTKIMUSKESKUS VTT OY
Finland

Periodic Reporting for period 2 - OPMMEG (Optically-pumped magnetometer arrays for magnetoencephalography)

Reporting period: 2023-12-01 to 2025-11-30

Summary of the context and overall objectives of the project

The project aims at developing a novel sensor for measuring weak magnetic fields due to electric activity of the human brain by performing magnetoencephalographic (MEG) measurements. The goal is to develop quantum-optics-based magnetometers which will be integrated into a helmet placed on the head of the study subject.

The main objectives of OPMMEG are:
1) to develop a prototype multi-OPM system consisting of at least four densely-packed OPM sensors with performance suitable for biomagnetic applications in a clinical context
2) to evaluate the system’s performance in a laboratory environment for MEG- and MMG-measurements with human subjects
3) to evaluate the performance, usability, reliability and safety of the system, relative to the needs of clinicians and researchers
4) to assess the manufacturability of the system and its business potential in the medical field
5) to explore routes to exploitation of the core components of the OPM sensor system as spin-off technologies in other application areas, including other quantum sensor types.

The project consists of 3 WPs which focuses on the development of technological elements, such as VCSEL (WP3), protocols for optimal signal generation and recovery (WP4), and sensor packaging (WP5). The developed elements are then integrated and the performance of the sensor array is validated (WP6) and verified through demonstrator (WP7). Commercialization aspects (WP2), such as business model, are kept in mind. Ethical issues (WP1) and management (WP8) complete the project.

The impact of the developed products and processes can be seen in different fields. The main result of the project is a MEG system demonstrator which can be used in hospitals and clinics for improving quality of life for patients. Also novel scientific insights on brain function can be gained. VCSEL of 795 nm can be utilized in several fields in addition to MEG. Quantum sensor packages are aimed to have improved heat management, and as miniaturized and mass-producible packages they can be utilized also in different areas in e.g. aerospace and medical applications. The developed quantum sensor control systems have an impact on different atomic vapor cell-based components, such as OPMs, gyroscopes and clocks.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

WP3:
795 nm-VCSELs are a new product for VIGO which is the expert in laser manufacturing. The work was started by defining the specifications needed for OPMs for MEG. Then the design and manufacturing were started. The design was focused on optimisation of thicknesses and compounds of epitaxial layers. 25 layers of AlGaAs with different properties were defined. The first manufacturing run of this design with 4” wafer was carried out. As a risk mitigation, studies on commercially available high-power edge-emitting lasers were performed by ICFO. Active feedback scheme was developed to have OPM-suitable power stability at the multiplexed output of an external cavity diode laser.

WP4:
ICFO has developed a detailed statistical model of the 87Rb spin dynamics that accounts for all magnetic, optical and collisional effects on the atomic spins, utilized as highly sensitive sensors. Atomic and photon shot noise are included in the model, resulting in stochastic differential equations that form the basis for coherent control methods. The model was validated using spin-noise measurements in the relevant regime (SERF) showing good agreement with the experimental findings.

WP5:
The atomic vapor cell is placed in vacuum-sealed ceramic package in order to manage the heat. The materials need to be non-magnetic complicating the process. The experimental work has been carried out at VTT. As a risk mitigation, polyimide aerogel packages have been tested by MEGIN. The design of optics, mechanics and electronics for sensor module is going-on.

WP6:
The required hardware for the sensor back-end electronics and data acquisition system have been assembled and tested at AALTO. The firmware running on the back-end electronics supports basic OPM control and signal read-out as of now and readily allows incorporating the enhanced read-out schemas. The control software includes a graphical user interface for easy and fast manipulation of the OPM operating parameters. The design of the field compensation coils has been started proactively to enable OPM sensor testing in AALTO’s compact (“person-sized”) magnetic shield.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Due to nature of the project, only ICFO so far has focused on the development of scientific work. They have published 4 articles in journals. Next, a short description of the contents of the articles are given.

K. Mouloudakis: “Inter-species spin-noise correlation in hot atomic vapors”
Theoretical and experimental study of spin noise correlations in a 87Rb – 133Cs unpolarized alkali-metal vapor dominated by spin-exchange collisions were carried out. Cross-correlation coefficients >60% were observed at low-magnetic fields where the two spin species couple strongly via spin-exchange collisions. Understanding of such spontaneously generated correlations motivate the design of quantum-enhanced measurements with single or multi-species spin-polarized alkali-metal vapors used in quantum sensing.

M. Lipka: “Multi-parameter quantum sensing and magnetic communications with a hybrid dc/rf optically-pumped magnetometer”
An interesting hybrid OPM was developed to simultaneously measure one DC and one RF field component with a single atomic spin ensemble. Sub-pT/sqrt(Hz) sensitivity for both DC and RF fields were achieved. A new application of multi-parameter quantum sensing, namely background-cancelling spread spectrum magnetic communication, was demonstrated. The developed system can be utilized in cases where high-performance multi-parameter quantum sensing is studied.

K. Mouloudakis: “Anomalous spin projection noise in a spin-exchange-relaxation-free alkali-metal vapor”
Spin-noise spectroscopy on an unpolarized 87Rb vapor in spin-exchange-relaxation-free (SERF) regime was performed. Noise spectral distributions deviated strongly from Lorentzian models that accurately describe lower-density regimes. The results were in good agreement with recent models accounting for correlations between the ground hyperfine states.

C. Troullinou: “Quantum-enhanced magnetometry at optimal number density”
The use of squeezed probe light and evasion of measurement backaction to enhance the sensitivity and measurement bandwidth of an OPM at sensitivity-optimal atom number density was studied. Application of squeezed probe light boosts the OPM sensitivity beyond the laser-light optimum, allowing the OPM to achieve sensitivities that cannot reached with coherent-state probing at any density.