LKB - Polarised Helium, Quantum Fluids and Solids


The group pursues theoretical, experimental, and applied research, drawing on long-standing knowledge of quantum fluids (bosons and fermions) and on expertise in optical pumping, production and handling of high nuclear polarisation in helium-3, and NMR in hyperpolarised systems (at low or high magnetic field, in liquid or gas phase).

Some recent publicationsCollaborations

Research topics


Regular article

Nuclear hyperpolarization of ³He by magnetized plasmas

Maul A., Blümler P., Nacher P.-J., Otten E., Tastevin G., and Heil W.

Phys. Rev. A (2018) 98, 063405 [12 pages]

We describe a method to hyperpolarize ³He nuclear spins at high magnetic fields (4.7 T) solely by a magnetized plasma.

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The conditions for such a magnetized plasma are fulfilled when the mean free path of the free electrons is much larger than their gyration radius in the rf gas discharge. Investigations are carried out in the 1-15 mbar pressure range with rf excitation at ~100 MHz. Quantitative NMR measurements show that, for different cell sizes and ³He gas densities, nuclear polarizations in the range 1% to 9% are observed. We explain this phenomenon by an alignment-to-orientation conversion mechanism in the excited 2³P state of ³He which is most efficient when the Zeeman and the spin-orbit energies are comparable. The method appears as a very attractive alternative to established laser polarization techniques (spin exchange or metastability exchange optical pumping). Application to ³He nuclear magnetometry with a relative precision of 10-12 is demonstrated.
Part of the experimental setup.

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1) Spherical glass sample containing the ³He gas. 2) Rf discharge coil wound onto the gas container. They both lie inside a short solenoid used for NMR measurements of ³He nuclear polarisation.

Book chapter

History and physical principles of MRI

by M. E. Hayden and P.-J. Nacher.

Magn. Reson. Imaging Handbook, 1

CRC press, 2016  (Ed. Luca SABA)



Comprenons-nous vraiment la mécanique quantique ?

Franck Laloë

EDP Sciences – Collection : Savoirs Actuels – 2nd edition – January 2018

Regular article

Multiple echoes due to distant dipolar fields in NMR of hyperpolarized noble gas solutions

Eur. Phys. J. D (2013) 67:29

Morgan S.W., Baudin E., Huber G., Berthault P., Tastevin G., Goldman M., Nacher P.-J, and Desvaux H.


We report on multiple echo measurements in hyperpolarized liquids using optically pumped spin-1/2 noble gas atoms: either 129Xe dissolved in cyclohexane or ³He dissolved in superfluid ⁴He.

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An NMR pulse sequence 90◦ − τ 90 (with slice-selective flipping pulses for 129Xe experiments) was used and long echo trains have been observed in the presence of applied gradients due to average dipolar fields typically one order of magnitude larger than those of bulk water in high magnetic fields. We show that a mean field description is valid for explaining the multiple echoes observed in these liquids, even for spin temperatures as low as 10 mK for 129Xe or 10 μK for ³He, and the echoes originate from the distant dipolar fields within the samples. Numerical lattice simulations have been used to assess the effects of slice selection and of finite sample size in addition to those of atomic diffusion. They account for the observed echo widths and amplitudes much better than previously published models, which disregard finite size effects that appear to be of key importance. This opens the way to using multiple echoes resulting from distant dipolar fields for the determination of the absolute magnetization in hyperpolarized liquids without signal calibration.
Main plot: Numerical 3D lattice simulations of the variation of the echo pattern as a function of fdip for τ = 120 ms (with slice-selection and taking into account xenon diffusion).Inset: Experimental result with a dissolved laser-polarized xenon sample (fdip = 9 Hz). The vertical scale is chosen so as to better visualize the altered echo shapes.

Regular article

Surrealistic Bohmian trajectories do not occur with macroscopic pointers

Eur. Phys. J. D (2018) 72: 183

Tastevin G. and Laloë F.

We discuss whether position measurements in quantum mechanics can be contradictory with Bohmian trajectories, leading to what has been called “surrealistic trajectories” in the literature.

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Previous work has considered that a single Bohmian position can be ascribed to the pointer. Nevertheless, a correct treatment of a macroscopic pointer requires that many particle positions should be included in the dynamics of the system, and that statistical averages should be made over their random initial values. Using numerical as well as analytical calculations, we show that these surrealistic trajectories exist only if the pointer contains a small number of particles; they completely disappear with macroscopic pointers. With microscopic pointers, non-local effects of quantum entanglement can indeed take place and introduce unexpected trajectories, as in Bell experiments; moreover, the initial values of the Bohmian positions associated with the measurement apparatus may influence the trajectory of the test particle, and determine the result of measurement. Nevertheless, a detailed observation of the trajectories of the particles of the pointer reveals the nature of the trajectory of the test particle; nothing looks surrealistic if all trajectories are properly interpreted.
Bohmian trajectories showing the motion of a test particle and a single pointer particle

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for a simple model involving a two-slit interferometer and particles with 2 and 1 degrees of freedom, respectively. Here, interference occurs since the pointer only provides delayed Welcher Weg (or Which Way) information. The motion of the test particle is shown to be notably influenced by the initial position of the pointer particle.

Regular article

Metastability exchange optical pumping of ³He gas at elevated pressure at 4.7 Tesla

Eur. Phys. J. D (2013) 67: 200 (29 pages)

Nikiel A., Collier G., Głowacz B.,  Palasz T., Olejniczak Z., Weglarz W., Tastevin G.,  Nacher P.-J,  and Dohnalik T.


Metastability exchange optical pumping (MEOP) is experimentally investigated in ³He at 4.7 T, at room temperature and for gas pressures ranging from 1 to 267 mbar. The 2³S-2³P transition at 1083 nm is used for optical pumping and for detection of the laser-induced orientation of ³He atoms in the rf discharge plasma.

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The collisional broadening rate is measured (12.0 ± 0.4 MHz mbar−1 FHWM) and taken into account for accurate absorption-based measurements of both nuclear polarization in the ground state and atom number density in the metastable 2³S state. The results lay the ground for a comprehensive assessment of the efficiency of MEOP, by comparison with achievements at lower field (1 mT–2 T) over an extended range of operating conditions.Stronger hyperfine decoupling in the optically pumped 2³S state is observed to systematically lead to slower build-up of ³He orientation in the ground state, as expected. The nuclear polarizations obtained at 4.7 T still decrease at high pressure but in a less dramatic way than observed at 2 T in the same sealed glass cells. To date, thanks to the linear increase in gas density, they correspond to the highest nuclear magnetizations achieved by MEOP in pure ³He gas. The improved efficiency puts less demanding requirements for compression stages in polarized gas production systems and makes high-field MEOP particularly attractive for magnetic resonance imaging of the lungs, for instance.
Comparison of steady-state nuclear polarisation obtained by MEOP at 4.7 T (solid symbols) and at lower field (B = 0.45–2 T, Tab. 2 in A. Nikiel et al., Eur. Phys. J. Special Topics 144, 255 (2007); B=0.82 mT, B. Glowacz, PhD 2011; open symbols) for moderate density (0.03 amg: red circles, 32 mb bone cell ; 0.06 amg: green up triangles, 67 mb bone cell).

Review article

Optically polarized ³He

T. R. Gentile, P. J. Nacher, B. Saam, and T. G. Walker

Rev. Mod. Phys. 89, 045004 (2017)

This article reviews the physics and technology of producing large quantities of highly spin-polarized ³He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping.

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Both technical developments and deeper understanding of the physical processes involved have led to substantial improvements in the capabilities of both methods. For SEOP, the use of spectrally narrowed lasers and K-Rb mixtures has substantially increased the achievable polarization and polarizing rate. For MEOP nearly lossless compression allows for rapid production of polarized ³He and operation in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and revealed new phenomena. Both methods have benefitted from development of storage methods that allow for spin-relaxation times of hundreds of hours, and specialized precision methods for polarimetry. SEOP and MEOP are now widely applied for spin-polarized targets, neutron spin filters, magnetic resonance imaging, and precision measurements.
Apparatus for spin-exchange optical pumping of ³He, employed for photon scattering experiments.

Regular article

Achieving high spatial resolution and high SNR in low-field MRI of hyperpolarised gases with Slow Low Angle SHot

J. Magn. Reson. 227 (2013) 72-86

Safiullin K., Talbot C., and Nacher P.-J.


MRI of hyperpolarised gases is usually performed with fast data acquisition to achieve high spatial resolutions despite rapid diffusion-induced signal attenuation. We describe a double-cross k-space sampling scheme suitable for Slow Low Angle SHot (SLASH) acquisition and yielding an increased SNR.

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It consists of a series of anisotropic partial acquisitions with a reduced resolution in the read direction, which alleviates signal attenuation and still provides a high isotropic resolution. The advantages of SLASH imaging over conventional FLASH imaging are evaluated analytically, using numerical lattice calculations, and experimentally in phantom cells filled with hyperpolarised ³He–N2 gas mixtures. Low-field MRI is performed (here 2.7 mT), a necessary condition to obtain long T2* values in lungs for slow acquisition. Two additional benefits of the SLASH scheme over FLASH imaging have been demonstrated: it is less sensitive to the artefacts due to concomitant gradients and it allows measuring apparent diffusion coefficients for an extended range of times.
Magnetic resonance images of the experimental cells (set of 2 or 5 glass tubes, 11-mm i.d.) filled with a polarised ³He–N2 mixture, obtained with the high resolution SLASH sequence (left) and a conventional FLASH sequence (right).



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CEA Saclay – Iramis (H. Desvaux , P. Berthault)
Non linear NMR in highly magnetised liquids.
Collaborative research projects:  DIPOL (ANR – Programme Blanc, 2007-2011), IMAGINE (ANR – International Blanc Programme , 2013-2016) , WideNMR (DIM Ile de France, 2016-2018).

JPEG - 2.2 kb  ILL Grenoble

(S. Pethukov, D. Jullien)

Neutron spin filters, massive production of hyperpolarised gas.
NMI3 Network under FP6.

JPEG - 3.1 kb   IR4M

(L. Darrasse, G. Guillot, X. Maitre; Z. Mokhtari)

Lung MRI, MRI methodology, on-site hyperpolarisation in clinical environment.
ACI project, PHIL and PHeLINet networks. CNRS (DEFI) project, HyperMRIHyperpolarisation « Brute force » multinoyaux pour l’IRM métabolique ciblée, DEFI Instrumentation aux Limites, 2018.

JPEG - 2.6 kb Fondation Pierre-Gilles de Gennes pour la Recherche

Transdisciplinary research in life sciences. Research foundation (RTRA, 2009 – …) IMAGIV  Research network for in-vivo imaging (CNRS – GDR3271, 2009-2013, dir.: L. Darrasse)

DIPOL Non linear NMR in spin polarised liquids Colloborative reseach project (ANR – International Blanc Programme, 2007-2011)

ONERA Palaiseau – DMPH/CMT (N. Zahzam) Optical gyro/magnetometry. Co-supervised PhD thesis (G. Renon, 2011-2014)

GDR (French research network) : Gaz rares hyperpolarisés From optical pumping techniques to applications in NMR. (CNRS – GDR2144, 2004-2008, dir. : Y. Cremillieux)



NMR Investigations of MAGnetization-Induced Non-linear Effects

French-Austrian research project (ANR, international Blanc Programme, 2013-2016)
Partners: IRAMIS at CEA (Saclay), Institute of Organic Chemistry at J. Kepler University (Linz), LKB (Paris), and RS²D company (Strasbourg).

JPEG - 3.5 kb   Mainz University, Germany (Pr W. Heil)

³He optical pumping, lung MRI, neutron spin filters.
Several Procope bilareal programs.
European projects PHIL and PHeLINet.
Co-supervised PhD thesis (M. Batz, 2011).
Shared awards:
Körber European Science Award 1998
Magnetic Resonance Tomography with Helium-3
Werner Heil (Mainz), Michèle Leduc (LKB), Ernst W. Otten (Mainz), Manfred Thelen (Mainz).
IBA-Europhysics Prize 2005 for Applied Nuclear Science and Nuclear Methods in Medicine (EPS Nuclear Physics Division)
Development of spin polarized ³He targets by optical pumping and their applications in nuclear science and medicine: nuclear physics, neutron low temperature physics and medicine.
Werner Heil (J. Gutenberg Univ. Mainz) and Pierre-Jean Nacher (Lab. Kastler Brossel, ENS Paris).

JPEG - 3 kb  Krakow University, Poland (Pr T. Dohnalik, Pr Z. Olejniczak)

High-field 3He optical pumping, on-site hyperpolarisation, low-field lung MRI, detection of He2* molecules.
PICS and Polonium programs; co-supervised PhD thesis (B. Glowacz, 2011)

JPEG - 2.6 kb Simon Fraser University, Canada (Pr M. Hayden)

Liquid NMR, hyperpolarised gases, MRI, 3He low temperature physics.

JPEG - 3.3 kb  University of Winnipeg, Canada (C. Bidinosti)

Low field NMR and MRI, 3He lung MRI.

JPEG - 3.3 kb  EUROHyperPOL

European Network for Hyperpolarization Physics and Methodology in NMR and MRI
Research network (European Community – FP7- MPNS: “Materials, Physics and Nanosciences” – COST Action TD1103, 2011-2015)

JPEG - 3.1 kb PHeLINet Polarised Helium Lung Imaging Network

Research network (European Community – FP6- RTN Marie-Curie, 2007-2011)

JPEG - 4.6 kb PHIL  Polarized Helium to Image the Lung

Research network (European Community – FP5 – RTD – Quality of life, 2000-2004, coord.: LKB )

Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy-Joint Research Activity: 3He Neutron Spin Filters
Access Programme (European Community – FP6, 2004-2008)