LKB - Polarised Helium, Quantum Fluids and Solids


News and Events

Submitted preprints

  • Signal feedback applications in low-field NMR and MRI. 2019. Vyacheslav Kuzmin, Pierre-Jean Nacher ⟨hal-02069159⟩


    Tuned pick-up coils with high quality factors Q are used in NMR and MRI for high-sensitivity and low-noise detection. However, large Q-factors introduce bandwidth issues at low frequency and the associated enhanced currents may cause significant radiation damping effects, especially with hyperpolarised samples. Signal feedback can be used to actively control these currents and adjust the detection bandwidth without resistive losses. Capacitive and inductive coupling methods are compared using detailed models and the operating conditions for efficient feedback with negligible noise penalty are discussed. Several high-impedance commercial preamplifiers have been found to affect the resonance characteristics of tuned coils in a gain-dependent way, or could not be used in low-frequency NMR because of oscillations at large positive gain. This is attributed to an undocumented internal feedback, and could be neutralised using external feedback. The implementation of an inductive coupling scheme to feed a suitably amplified phase-adjusted signal back into the PU coils of low-field NMR systems is described, and three experimental applications are reported. One system is used for NMR studies of distant dipolar field effects in highly polarized liquid 3He without or with radiation damping. The moderate intrinsic Q-factor (≈7) could be reduced (down to 1) or increased (up to 100) to control transient maser oscillations. Another system was used for MRI of water samples around 2~mT with Q≈190 Litz-wire detection coils. The detection bandwidth was increased by actively reducing the Q-factor to obtain uniform sensitivities in images and avoid artifacts introduced by intensity corrections. Finally, parallel acquisition in MRI was performed using two separately tuned detection coils placed above and below the sample. They were actively decoupled using two feedback systems. For an imaging field of view smaller than the sample, artifact-free unfolded images demonstrate the efficiency of this active coil decoupling scheme.
  • A fast MOSFET RF switch for low-field NMR and MRI. 2019. Pierre-Jean Nacher, Sashika Kumaragamage, Geneviève Tastevin, Christopher Bidinosti.  ⟨hal-02266979⟩


    TRansmit Array Spatial Encoding (TRASE) MRI uses trains of rf pulses alternatively produced by distinct transmit coils. Commonly used coil switching involving PIN diodes is too slow for low-field MRI and would introduce wait times between pulses typically as long as each individual pulse in a few mT. A MOSFET-based rf switch is described and characterised. Up to hundreds of kHz, it allows for sub-μs switching of rf currents from a single amplifier to several coils with sufficient isolation ratio and negligible delay between pulses. Additionally, current switching at null current and maximum voltage can be used to abruptly stop or start pulses in series-tuned rf coils, therefore avoiding the rise and fall times associated with the Q-factors. RF energy can be efficiently stored in tuning capacitors for times as long as several seconds. Besides TRASE MRI, this energy storage approach may find applications in fast repeated spin-echo experiments. Here, a three-fold acceleration of TRASE phase-encoding is demonstrated when MOSFET switches are used instead of fast reed relays.
  • A model of quantum collapse induced by gravity. 2019. Franck Laloë <hal-02160619> 


    We discuss a model where a spontaneous quantum collapse is induced by the gravitational interaction, treated classically. Its dynamics couples the standard wave function of a system with the Bohmian positions of its particles, which are considered as the only source of the gravitational attraction. The collapse is obtained by adding a small imaginary component to the gravitational coupling. It predicts extremely small perturbations of microscopic systems, but very fast collapse of QSMDS (quantum superpositions of macroscopically distinct quantum states) of a solid object, varying as the fifth power of its size. The model does not require adding any dimensional constant to those of standard physics.

The WideNMR project (2015 —2017)

Exploring innovative concepts and applications in a super-wide bore NMR spectrometer
Scientific partners: IRAMIS/CEA Saclay; IFSTTAR; LKB.
Project homepageRead more


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. 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.

Review article

Optically polarized ³He

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

Rev. Mod. Phys. 89, 045004 (2017) [59 pp.]

Review article

Metastable phases of liquid and solid 4He

Jules Grücker

J. Low Temp. Phys., First Online: 15 July 2019 [18 pages]


Experiments and theories describing the metastable phases of liquid and solid 4He are presented and discussed. For the case of metastable liquid 4He with respect to its gaseous phase, it is shown that different measurementsof its destabilization threshold (cavitation threshold) and their comparison toavailable theories reveal that the nucleation mechanism is not totally under-stood. Then experiments measuring typical lifetime of cavitation bubbles inHe I and He II are shortly considered showing the important role of heat trans-port mechanism during their collapse. Finally for liquid 4He, its metastabilitywith respect to its solid phase and the possibility of the liquid destabilizationdue to the vanishing of the roton gap is presented. The last part of the reviewis devoted to metastable solid 4He with respect to its liquid phase. The first experimental production of such a state is described and its destabilizationlimit possibly invoking the creation and proliferation of crystalline defects isdiscussed.


Mécanique Quantique, tomes 1 et 2, nouvelle édition. C. Cohen-Tannoudji, B. Diu et F. Laloë (EDP Sciences - Savoirs Actuels - Sept. 2018).Comprenons-nous vraiment la mécanique quantique ?.
Franck Laloë (EDP Sciences - Savoirs Actuels - 2nd ed., 2018).
Mécanique Quantique - Tome III - Fermions, bosons, photons, corrélations et intrication. C. Cohen-Tannoudji, B. Diu, F. Laloë (EDP Sciences - Savoirs Actuels, 2017).


Jules Grücker has defended his “Habilitation à diriger les recherches”, entitled “Metastable Solid and Liquid Helium-4”, on Nov.30, 2018.

The MARGIN project

MARGIN (2020-2023) mainly deals with MAgnetic Resonance studies of Gas diffusion In Nanoporous materials. Investigations focus on  of the influence of gas-wall interactions on NMR diffusion measurements.

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Detailed understanding is needed for correct interpretation of the results and reliable characterisation of these porous media. Collaborative work with the laboratory of Quantum Electronics and Radiospectroscopy (Kazan Federal University) is supported by ANR funding.

PhD student

Lionel DJADAOJEE (Teaching assistant at ENS Paris – PSL, Agrégé de Physique) has joined the group for PhD work on the metastable phases of solid and liquid 4He (J. Grücker, superviser; Sept. 2019 – …).


March 2019, PSL-iTeams closing session.

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MULSA (an ecologically responsible alternative to conventional foam board) has been selected as best project at the end of the 2018/2019 PSL-iTeams training program (entrepreneurship education for PSL Master and PhD students, promoting interdiscplinarity and innovation). The project has been designed and defended on March 26 by Fiona Guillemant (ENSAD 2018), Baptiste Lefebvre ( PhD student, ENS), and Ali Dia.

In memoriam

Philippe Jacquier, leader of the “Quantum solid and liquid helium” team since 2003, passed away on Jan.24, 2019.

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Philippe has battled against disease for many years with impressive courage and steadfast determination. He was an excellent teacher and a passionate researcher. The group will long miss his deep sense of humour and friendship, as well as the enthousiasm, the inventiveness, the curiosity, and the broad knowledge that made working with him so pleasant every day.

Short text (in French) by Antoine Heidmann, Director of the LKB.Ph. Jacquier’s scientific homepage


Polarised He & quantum fluids
Quantum solid & liquid He
  • Franck Laloë
  • Pierre-Jean Nacher
  • Geneviève Tastevin
  • Polar. 3He - Other People
  • Ali Dia
  • Jules Grucker
  • Solid 4He - Other people
  • Lionel Djadaojee

Recent Papers

Nuclear hyperpolarization of 3He by magnetized plasmas

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

Phys. Rev. A 98, 063405 (2018)

Metastable phases of liquid and solid 4He


Jules Grucker

J. Low. Temp. Phys (2019), First Online: 15 July 2019 [18 pages]

Dramatic effect of superfluidity on the collapse of ⁴He vapor bubbles

An Qu, Azer Trimeche, Philippe Jacquier and Jules Grucker

Phys. Rev. B (2016), 93, 174521

Surrealistic Bohmian trajectories do not occur with macroscopic pointers

Tastevin G. and Laloë F.

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

Optically polarized 3He

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

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

History and physical principles of MRI

M.E. Hayden, and P.-J. Nacher

Magn. Reson. Imaging Handbook, 1, CRC press, 2016 (Ed. Luca SABA)


2018-2019 - Master / PhD


Polarised helium - Laser optical pumping

We offer several types of internship work for Master students, in connection with our study of laser optical pumping in helium plasmas. A new topic has been opened for PhD: High-field hyperpolarisation in helium plasmas

2018-2019 - Master / PhD


Polarised helium - Low field MRI

Skilled and motivated students are welcome to join our investigations on low field MRI with laser polarised ³He gas or thermally polarised water. Work may focus on the impact of concomitant field gradients on image quality, or investigate the short-pulse limit and revisit the Bloch-Siegert effect in NMR. This topic is open for PhD.

2018-2019 - Master


Polarised helium - Liquid NMR

Skilled and motivated students are welcome to join our investigations on liquid NMR in laser polarised ³He-⁴He dilute solutions. Work will deal with recently observed non linear NMR dynamics and focus on the comparison between experimental and numerical data. This topic is not (yet) open for PhD.

2018-2019 - M1 level internships

Skilled and motivated students are welcome to join on-going investigations. M1-level students may contribute to:

  1. Investigation of the impact of concomitant field gradients on image quality in low field MRI
  2. Investigation of collisional processes in helium discharges using laser spectrocopy
  3. Implementation of annular beam shaping for helium laser optical pumping



We are always looking for brillant motivated scientists to join our group.

Check the open positions (see above) or send us your CV for application.


Département de Physique Ecole Normale Supérieure, 24 rue Lhomond, F-75231 Paris Cedex 05  

  •  Jules Grucker  : jules.grucker at
  • Philippe Jacquier : philippe.jacquier at
  • An Qu : an.qu at
  • Franck Laloë : laloe at
  • Pierre-Jean Nacher : nacher at
  • Geneviève Tastevin : genevieve.tastevin at

Nos Tutelles et Partenaires

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