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Broadband spin sensor for ESR spectrometry devices – Broadband spin resonance detection based on the kinetic inductance of a superconducting resonator



Electron spin resonance (ESR) refers to the property of certain electrons to absorb and then re-emit the energy of electromagnetic radiation when placed in a magnetic field. . The detection of spin resonance is used in medicine and biochemistry, for example, for the study of free radicals created by irradiation used in the treatment of certain cancers. 

The conventional method for detecting spin resonance, called electron paramagnetic resonance spectroscopy, detects the microwave absorption of spins present in the sample. The microwave excitation resonates with a cavity in which the studied sample is placed. An external magnetic field is used to bring a spin species present in the sample into resonance with the microwave cavity.


The present invention relates to a new spectroscopy method for the detection of spin resonance which is not based on a resonance between a microwave cavity and the spins to be probed. A new method for detecting, using superconducting resonators, the magnetic field created by a set of spins; the resonator thus combining control and measurement in the same device. 

Indeed, the developed method allows to directly detect the change of the polarization of the spins of the sample caused by a microwave excitation. This change in spin polarization causes a change in the magnetic field generated by the sample, which is in turn detected using a superconducting resonator. Indeed, the frequency of a superconducting resonator can be sensitive to a magnetic field perpendicular to the surface of the resonator thanks to the presence of kinetic inductance (vs. magnetic induction). It is possible to engineer the superconducting resonator to maximize its kinetic inductance to make the frequency of the resonator highly sensitive to the perpendicular magnetic field.

The invention is distinguished by its simplicity: only a superconducting resonator is necessary to study a wide range of materials, so the magnetic field and the frequency of the microwave excitation can be varied over a wide band. The invention requires only simple fabrication techniques (photolithography) and is compatible with high magnetic field scanning. Moreover, unlike conventional ESR methods, the spins do not need to be in resonance with the microwave cavity.

The development of quantum materials requires more versatile equipment than the tools currently available, which have too limited operating ranges. This new technique of “broad band” spin resonance spectroscopy was invented in order to study these quantum materials more efficiently. The present invention aims to replace the sensors currently used in ESR spectrometers since this new method of detection is much more efficient and versatile.


  • Flexibility: since scanning is broadband: infinite detection band.

    • Does not require a resonance condition, hence greater flexibility compared to ESR for spin spectroscopy. 

  • - CAPEX and OPEX reduction – one device replaces several devices.

  • - A type of spins can be studied according to the magnetic field. Fixed field in situ

  • - Simple manufacture of the sensor.

  • - Simple measurements

  • - Versatility: a single device for all types of materials, no matter the sample

  • - Sensitive to exotic surface properties (quantum materials)

  • - Broadband detection: Versatility/Flexibility

    • Characterizing spin defects in materials with conventional ESR spectrometers is a complex and expensive process. A broadband and highly sensitive spectroscopy technique is therefore essential in order to study them more efficiently and at lower cost.

    • New process: The new method proposed completely changes the method of analysis as it is possible to detect spin transitions at frequencies very far from that of the resonator while taking advantage of the gain in sensitivity allowed by the resonator.

  • This flexibility is unequaled and makes it possible to probe in frequency several species of spins located at very different frequencies for the same value of the external magnetic field.

  • Moreover, these spins can be studied as a function of the magnetic field and allows to have a complete characterization of the transition spectrum and a faster validation with the theoretical models. This competitive advantage will allow researchers to be more efficient in QM research and development.

    • Better detection: non-destructive reading. The feedback of the spins on the resonator allows a non-destructive quantum reading of their state. In addition to the applications for the detection of the resonance of spins, the invention is thus of great interest for the development of quantum memories based on sets of spins.

  • Economical: Reduction of acquisition costs:

    • One device replaces several devices: The great versatility of the new device will make it possible to cover a scanning range where several current devices are required. Customers will then save significant acquisition costs, since each device is currently sold at $200K/unit.

    • Lower cost price of the sensor: The invention is distinguished by its simplicity: only a superconducting resonator is necessary to study a wide range of materials. Manufactured using standard processes (photolithography) but a cryogenic system must be integrated, the cost price of the sensor should be equal to or lower than that of conventional sensors.

    • Simplified data analysis: The new technique makes it possible to directly obtain the spectrum of spins over a wide range of frequencies and magnetic fields. Theoretical modeling is then facilitated and the analysis of the spin system then more efficient and precise. This provides quick results and saves on analysis time and costs.


  • Study of semiconductor materials

  • Study of new unknown quantum materials (QMs) (quantum sensors, quantum computers, quantum communications, etc.)

    • Sensitive to exotic surface properties (quantum materials),

    • Non-destructive reading of a quantum state,

    • Versatile, Broadband, Versatile

    • A single device regardless of the sample,

    • Simple measurement.

  • This new "broad band" ESR spectroscopy technique was invented in order to study these quantum materials efficiently, addressing the following problems:

    • Lack of versatility of conventional ESRs

  • Different ESR spectrometers having a narrow detection band must be used to bring the spins into resonance with a resonator.

  • The use of large magnetic fields also places significant constraints on sensor design.

    • Limited operation ranges

  • Some materials with surface defects requiring too high fields cannot be studied by conventional ESR.

    • Swipe too focused

  • The new quantum and QM defects have a priori unknown ESR properties. A spectroscopy technique that is both broadband, as well as highly sensitive, is essential in order to study them effectively.

  • By being integrated into ESR spectrometry devices, this new sensor can also be used in many other commercial applications such as:

    • Instruments for measuring and characterizing materials for laboratories (Physical Properties Measurement Systems (PPMS)).

  • Physics: Defects in semiconductors and heterostructures, transition metals, quantum computing.

  • Chemistry: Reaction kinetics, free radical chemistry, catalysts, bioinorganic chemistry, molecular magnetism, redox chemistry.

  • Biomedical: Nitric oxide, detection of reactive oxygen species.

  • Education: Pedagogical package optimized for a magnetic resonance teaching environment. Suite of experiments with instructions for teaching common EPR data acquisition and processing techniques.

  • Biology: Membrane proteins, intrinsically disordered proteins (IDPs), metallo-enzymes, photosynthesis, RNA, DNA, spin labeling/trapping, nitrogen oxides, ROS and RNS.

  • Materials science: Degradation of polymers, properties of paint, solar cells, fuel cells, impurities in optical glass, batteries.

  • Industry: Free radicals in polymers and polymerization, food science and beverages, oxidative stability, antioxidant capacity, photo/oxidative degradation of APIs




  • Proof of concept done. A first proof of principle was carried out on a prototype demonstrating the signatures of magnetic defects in diamond with this method.


  • Patents pending – United States (US20210208231A1) and Germany.


Development Partners. Investments. Licenses

Project Director: François Nadeau

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