Rencontres des Jeunes Physicien·ne·s 2019

vendredi 29 nov. 2019, 09:00 → 18:35 Europe/Paris

Amphitéâtre Marguerite de Navarre (Collège de France)

The RJP conference is a day for young physicists from Ile de France, organized by PhD students who are members of the Youth Commission of the French Physical Society (Société Française de Physique).

The day includes oral presentations by young physicists, poster sessions, a lunch buffet and a drink at the end of the day, all in a friendly atmosphere.

You are invited to submit an abstract for a 15-minute oral presentation (subject to acceptance) or for a poster (no evaluation). Abstract submission for a talk is now closed, but you can still submit an abstract for a poster, it will be automatically accepted.

Before submitting an abstract, do not forget to register here at the conference.

 

 

Oral presentations session

1 Welcome speech by RJP / Présentation SFP et Réseau Jeunes

Orateurs: Elisabeth Niel (LAL Orsay), Mayline Verguin, Nicolas DAGONEAU (CEA/Saclay - IRFU/DAp/LISIS)

ppt_SFPJeunesdec2019.pdf

ppt_SFPJeunesdec2019.pptx

2 PolarEx, a new facility for on-line nuclear orientation at Alto : Multipolarity mixing ratio data analysis

Low Temperature Nuclear Orientation (LTNO) experiments allow to probe magnetic properties of polarized exotic nuclei. With this technique, we observe nuclei under extreme conditions, that is to say very low temperatures (~10mK) and very high magnetic field (10-100T). Under such conditions, the radioactive emission is anistropic, and its shape tells us more about the nucleus structure.
Nuclear orientation give access to different observables. The nuclear magnetic moment can be directly measured, using NMR technique. The multipole mixing ratio, proportionnal to the ratio of two multipolarity matrix element, can also be studied and gives acces to structure informations. As a special feature of LTNO, far-reaching studies of fundamental weak interactions and associated symmetries can be made as well as investigations of parity non conservation.
The PolarEx apparatus, located at Alto in Orsay, France, is designed to perform this kind of study. It is a 3He-4He dilution refrigerator, coupled to a magnet and a detection system. The detection system allowed up to 8 detectors, either gamma or particle detector, in the plan perpendicular to the orientaion axis to study the spatial asymmetry of the gamma radiation.
For the moment it is operating off line on long lived nuclei, but it will be ready for on line experiment very soon. The coupling of PolarEx with Alto will open a large range of studies of neutron rich nuclei, thanks to its great versatility.
In this contribution will be presented the status of PolarEx and the on going off-line studies, in particular the new measurements of the multipole mixing ratios in 56 Fe. With our analysis, we have reproduced existing mixing ratios, have improved the precision of some of them, and have also measured unknown mixing ratios.

Orateur: Rémy Thoer (csnsm)

THOER_RJP.pdf

3 Spectrum analyzer based on NV centers in diamond

The Nitrogen Vacancy (NV) centers are considered, for their optical and spin proprieties, promising candidates for quantum sensing applications. In this work, the spin-dependent optical proprieties of a NV centers ensemble are exploited in order to realize a spectrum analyzer.
To do that, a static magnetic field gradient, generated by a permanent magnet, induces a spatial dependent Zeeman shift to the NV centers present in the diamond: the NV center resonance frequency is so correlated to a defined position in the diamond. A wide field imaging system collects the fluorescence of the NV centers while they are continuously pumped by a green (532nm) laser. A microwave magnetic field, resonant with the NV center transition, will cause a drop of photoluminescence, visible on the image, at a well-defined position. Knowing the static magnetic field at that position, the microwave frequencies can be deduced.
The device is able to achieve a dynamic range of 30dB, a frequency range of 25 GHz and a limit resolution (frequency dependent) of 1 MHz. The Nitrogen nuclear spin polarization by pure optical
means near both ground state and excited state level anti-crossing has been also investigated. A quite large range of polarization efficiency has been observed, allowing a better frequency resolution.

Orateur: Simone Magaletti

10:20 Coffee break

4 Exploring the primordial universe with QUBIC: The Q&U Bolometric Interferometer for Cosmology

QUBIC is an experiment dedicated to the measurement of polarization B-modes of the Cosmic Microwave Background (CMB) using the novel technology of Bolometric Interferometry. In this talk, I will start with a brief explanation of the underlying physics: What are primordial B-modes and why it will give us invaluable insights on what happened during the inflation era, right after the Big Bang.
Then, I will present the current status of the project and the instrument architecture. The unique design of QUBIC brings new possibilities to CMB polarization mapping including self-calibration and spectroimaging.

Orateur: Louise Mousset (APC)

RJP_2019_mousset.pdf

5 Bacterial portraits: Density shaping of photokinetic E. coli

In nature, some motile microorganisms have evolved in such a way to respond to environmental light stimuli, essentially allowing them to find better living conditions.
In the lab, it is possible to engineer bacterial cells so as to make them photokinetic, that is, to control their speed by means of the light shone on them: these cells move faster when exposed to high-intensity light, whereas slow down to dim light.

I will present some experiments performed with my collaborators [Ref.] in which we observed the dynamics of millions of photokinetic E. coli cells and how it has been possible to arrange them into complex and reconfigurable density patterns using a digital light projector.
Such experiments give us insights on the complex biological mechanisms of photokinesis and provide a practical and efficient strategy to achieve spatial and temporal control of cell concentration, for instance by exploiting such living propellers for moving microdevices or drug carrier.

[Ref.] Frangipane et al., eLife 2018;7:e36608 doi: 10.7554/eLife.36608

Orateur: Dr Dario Dell'Arciprete (LPENS)

11035Movie1.avi

elife-36608-video1.mp4

fluo_curly1.avi

Pres_RJP2019_DellArciprete.pdf

Pres_RJP29_DellArciprete

Remise des prix Jeunes Chercheurs/euses 2018 / Talk des 2 Lauréats

Lauréat.e.s des prix Jeunes Chercheurs/euses 2018

6 Remise des prix Jeunes Chercheurs/euses 2018

Orateur: Catherine Langlais (SFP)

7 Ultrafast Meets Chirality

Chirality is a symmetry property of matter, which can emerge at any length scale, from galaxies to snail shells and even to subatomic particles. Chiral light-matter interactions have been investigated for two centuries, leading to the discovery of many chiroptical processes used for discrimination of enantiomers. Whereas most chiroptical effects result from a response of bound electrons, photoionization can produce much stronger chiral signals that manifest as asymmetries in the angular distribution of the photoelectrons along the light-propagation axis (Photoelectron Circular Dichroism, PECD). Before 2012, PECD was mainly studied in synchrotron facilities, in the single-photon ionization regime [1]. In this talk, I will show you the recent advances that we made, during my Ph.D. thesis, by applying the toolbox developed in ultrafast and strong-field physics to chiral molecules. We have demonstrated that PECD is a universal effect that emerges in all photoionization regime [2]. We have also demonstrated the first pump-probe PECD experiments, allowing for monitoring photoinduced ultrafast dynamics in chiral molecules on femtosecond timescale [3,4]. Using similar experimental approaches, but by using pulse sequences with counter-intuitive polarization states, we have demonstrated a novel electric dipolar chiroptical effect, called Photoexcitation Circular Dichroism (PXCD), which emerges as a directional and chirosensitive electron current when multiple excited bound states of chiral molecules are coherently populated with chiral light [5]. Last, we introduced a time-domain perspective on chiral photoionization by measuring the forward-backward asymmetry of photoionization delays in chiral molecules photoionized by chiral light pulses. Our work thus carried chiral-sensitive studies down to the femtosecond and attosecond ranges [6].

[1] Böwering, N. et al., Phys. Rev. Lett. 86, 1187 (2001)
[2] Beaulieu, S. et al., New Journal of Physics 18, 102002 (2016)
[3] Comby, A. et al., The Journal of Physical Chemistry Letters 7, 4514 (2016)
[4] Beaulieu, S. et al., Faraday discussions 194, 325 (2016)
[5] Beaulieu, S. et al., Nature Physics 14,484 (2018)
[6] Beaulieu, S. et al., Science 358, 6368 (2017)

Orateur: Dr Samuel Beaulieu (Fritz-Haber-Institute of the Max-Planck-Society)

Ultrafast_meets_Chirality.pdf

8 Exotic Nuclei for Astrophysics—First Spectroscopy of $^{110}$Zr

Exotic, extremely radioactive nuclei play a key role in the nucleosynthesis processes responsible for heavy element production in cataclysmic events in the universe, such as recently observed in the binary neutron star merger detected via gravitational waves [1] . The nucleosynthesis yields depend on the details of the underlying quantum structure of these nuclei, largely unknown as such exotic species are difficult to create and study in the laboratory, and theoretical predictions diverge. I will present the first spectroscopy results of one such exotic nucleus, $^{110}$Zr, where a stabilization effect in a spherical or pyramidal shape had been predicted which would explain a long-standing discrepancy in nucleosynthesis simulations. The experiment was performed at the Radioactive Isotope Beam Factory (RIBF) in Japan, where $^{110}$Zr was created via in-flight fission of a $^{238}$U beam and subsequent proton removal on a cryogenic liquid hydrogen target. Gamma rays from nuclear deexcitation were detected with a 4$\pi$ scintillator array, and Doppler correction enabled via event-by-event vertex reconstruction in a time-projection-chamber developed at CEA-Saclay. Results show no evidence for a spherical or pyramidal shape, but rather suggest that this nucleus is extremely deformed, beyond expectations from mean-field based approaches, and thus cannot explain the deficiencies in nucleosynthesis models in this mass region [2].

[1] Abbott et al, Phys. Rev. Lett. 119, 161101 (2017).
[2] N. Paul et al, Phys. Rev. Lett. 118, 032501 (2017).

Orateur: Nancy Paul (Laboratoire Kastler Brossel)

SFP_npaul2019vFinal.pdf

Lunch & Posters session

Oral presentations session

9 B0 -> K*e+e- angular analysis at LHCb: an indirect search for New Physics

The conflicts between cosmological observations (dark matter, matter/anti-matter asymmetry ...) and the predictions of the Standard Model (SM) calls for New Physics (NP) beyond the SM, i.e. new interactions or new particles. Collider experiments such as the LHC at CERN is a privileged place for NP searches. Indeed, by smashing together two protons at nearly the speed of light, one can try to pop up a massive NP particle. But these direct searches are limited by the energy of the proton beam (E=mc2). Instead of directly creating the particle, one can try to pop up a virtual NP particle. Indeed, when a b quark transforms to an s quark, the process involves the exchange of a virtual (very short lived) particle, whose energy (mass) is allowed to exceed by far the energy (mass) of the initial b quark thanks to quantum mechanics (roughly speaking, due to Heisenberg's uncertainty principle). Thus, indirect searches can access much higher energies than direct searches for NP.
At LHCb, a large amount of B mesons (containing a b quark) are created. Some of them decay to a K meson (containing an s quark) and two electrons. This type of b to s quark transition is very suppressed in the SM and thus any NP appearing in the process should be dominant. In particular, the presence of NP could modify the angular distribution of the final states particles detected in the LHCb detector, motivating the measurement of B0 -> Ke+e- angular distributions.

Orateur: Fabrice Desse (LAL Orsay)

RJP_fdesse.pdf

10 Neural networks for Quantum Physics

The state of a quantum system is completely determined by its wave-function or density-matrix, which evolve according to an equation of motion. When the system is composed of many interacting particles, the many-body problem increases exponentially the size of those objects, which eventually cannot be stored in the memory of a computer. For decades researchers approached the issue by constructing approximations based on our physical understanding that could reduce the complexity. This approach, while successful, requires a through study of every system. In the field of machine learning a different technique has been developed: Neural-Networks are a general class of functions which are able to represent the solutions to very disparate problems. By combining a quantum variational principle with an iterative procedure, we show that it is possible to optimize neural-networks in order to encode the ground- (or steady-)state of a quantum system. Such procedure, similar in spirit to supervised learning, can be performed efficiently by means of a Montecarlo sampling, which sidesteps the problem of exponential complexity. In this talk we will also showcase several other applications of machine learning to quantum physics.

Orateur: Dr Filippo Vicentini (Université Paris Diderot - Laboratoire MPQ)

11 D3DT : an innovative TPC for muon tomography

Muon tomography consists in using cosmic muons to probe structures in a non-invasive nor destructive way. The successful development of muon telescopes using Micro-Pattern Gaseous Detectors over the past decades triggered the interest of many industrials for such technology. However, telescopes are limited in terms of compacity and angular acceptance which are performances with high requirements for applications such as geology or oil prospection. This motivated the development of a new instrument that meets such requirements.
The use of a Time Projection Chamber (TPC) allows for a full track reconstruction in a quasi-isotropical way. In order to keep a good resolution while reducing the number of electronic channels (for a better compacity), the readout plane is 2D-multiplexed which makes the reconstruction challenging.
This talk will present the first prototype that has been developed and the first steps of track reconstruction that have been implemented.

Orateur: Marion Lehuraux (CEA Saclay)

RJPTalkD3DT.pdf

15:00 Coffee break

12 Hunting for the Majorana fermion in magnet/superconductor heterostructures

The Majorana fermion, initially theoricized in high-energy physics, has the particularity of being its own antiparticle. In 2001, Kitaev [1] proposed that Majoranas could be realized as low energy excitation in something called a topological superconductor triggering a huge number of theoretical and experimental studies, especially due to interesting possibilities in quantum computing. Eventhough major advances have been realized on the experimental side, the Majorana has not been unambiguously identified so far.

My theoretical work aims at studying novel platforms based on magnets and superconductors brought in close proximity to one another. More specifically, I have been looking in details at the properties of the induced superconductivity close to a magnetic skyrmion [2, 3], a nanoscale magnetic texture that is now routinely created and manipulated.

In this talk, I will introduce the basics of superconductivity and topology needed to understand the nature of the Majorana fermion and why it is searched for so intensively. I will then explain why the skyrmion/superconductor setup (and more generally magnet/superconductor heterostructures) is theoretically interesting to remedy some problems currently encountered while emphasizing the experimental relevance of such setups.

[1] A. Y. Kitaev, Unpaired Majorana fermions in quantum wires, Fiz. Usp. 44, 2001.
[2] M. Garnier, A. Mesaros & P. Simon, Topological superconductivity with deformable magnetic skyrmions, Communications Physics 2, 126, 2019.
[3] M. Garnier, A. Mesaros & P. Simon, Topological superconductivity with orbital effects in magnetic skyrmion based heterostructures, arXiv:1909.12671, 2019.

Orateur: Maxime Garnier

13 Pendulum in a Flow: case of a Balanced Pendulum

Fluid-structure interactions are the basics of the complexity of Aerodynamics, enhancing resonance in structures and turbulence in flows. Even simple systems like a pendulum can become more complex, as a hysteretic bistability shows up for a range of flow velocities when the pendulum confronts a flow. This is predicted by a simple balance of weight and aerodynamical forces, but non stationary response can be seen through spontaneous transitions between both stable positions.
This dynamic can also be observed when substracting the weight of the pendulum.
By analyzing trajectories in different phase spaces, we recover a stochastic measurement of the drag and lift coefficients. Moreover, the pendulum oscillates around the horizontal at a frequency that is linked to the evolution of the normal drag coefficient with the angular position of the pendulum. The instantaneous lift and drag coefficients inferred from the dynamical behavior of the pendulum seems to be governed by the dynamical vortex shedding phenomena, which we currently investigate experimentally.

Orateur: Ariane GAYOUT (Laboratoire de Physique - ENS de Lyon)

PresentationRJP_AGayout.pdf

PresentationRJP_AGayout.pptx

14 From gravitational black holes to analogue gravity

Black holes are intriguing and singular objects; Einstein did not even believe in their existence. However, the first observation of a rotating black hole in our universe has been recently reported and is an undeniable confirmation of their presence.

In 1974, Hawking predicted that black holes are not completely black, but emit a thermal radiation at a certain temperature $T_{\rm H}$, the so-called Hawking temperature$^1$. However, the Hawking radiation is very faint and would be completely lost in the Cosmological Microwave Background.
A new breakthrough occurred in 1981, when Unruh showed that the dynamics of sound waves propagating in a convergent fluid flow was equivalent to the one of a massless scalar field propagating in a curved spacetime$^2$. He then suggested to use hydrodynamic analogues of gravitational black holes to detect the elusive Hawking radiation.

In this talk, we pedagogically present how the transition from a subsonic to a supersonic flow can mimic an acoustic black hole for sound waves. Then, we discuss the recent experimental detection of spontaneous Hawking radiation in a Bose-Einstein condensate$^3$. We show in particular how quantum fluctuations in these quantum systems can be related to emission of analogue Hawking pairs. We finally provide a theoretical interpretation of experimental observations$^4$.

References

1. S. W. Hawking, Black holes explosions?, Nature 248, 30 (1974); Particle Creation by Black Holes, Comm. Math. Phys. 43, 199 (1975).
2. W. G. Unruh, Experimental Black-Hole Evaporation?, Phys. Rev. Lett. 46, 1351 (1981).
3. J. R. M. de Nova, K. Golubkov, V. I. Kolobov, and J. Steinhauer, Observation of thermal Hawking radiation and its temperature in an analogue black hole, Nature 569, 688 (2019).
4. M. Isoard, N. Pavloff, Departing from thermality of analogue Hawking radiation in a Bose-Einstein condensate, arXiv:1909.02509 (2019).

Orateur: Mathieu Isoard (LPTMS)

RJP2019.pdf

16:15 Coffee break

15 Reducing quantum noise in gravitational-wave detectors using squeezed states of light

Gravitational waves (GW) are ripples in the fabric of spacetime, emitted by compact accelerating objects. On September 2015, the first direct detection of GW from a binary black hole merger initiates the field of GW astronomy and opened a new window on the Universe. On August 17, 2017, Advanced LIGO and Advanced Virgo detectors jointly detected gravitational-waves resulting of the merger of two neutron stars, with the best localization precision ever obtained.
In order to increase the science reach of LIGO and Virgo, it is essential to reduce quantum noise (QN), one of the fundamental sensitivity limits of the detector. QN is originated by the quantum nature of light, and is attributed to the Heisenberg Uncertainty Principle, stating that it is not possible to know simultaneously and with an infinite precision the phase and the amplitude of the light. Since the quantum noise is generated by vacuum fluctuations entering from the dark port of the detector, the injection of non-classical vacuum states of light (or squeezed states) enables the reduction of quantum noise. This technique is now routinely used in LIGO and Virgo to increase the sensitivity in a fraction of their frequency spectrum.
Achieving a broadband reduction of quantum noise requires the use of “frequency-dependent squeezing (FDS)” techniques, where the squeezing ellipse rotates as a function of the frequency before entering the detector. After a general introduction about squeezing, I will present my work on the experimental demonstration of a FDS technique using entangled photons, and known as Einstein-Podolsky-Rosen (EPR) squeezing technique.

Orateur: Catherine Nguyen (Laboratoire APC/ Université Paris-Diderot)

[RJP2019]Nguyen_ReducingQuantumNoise_final.pdf

[RJP2019]Nguyen_ReducingQuantumNoise_final.pptx

16 Quark Gluon Plasma at LHCb

Quarkonia, bound states between a heavy quark and its own antiquark, are of particular interest when it comes to probing the Quark Gluon Plasma (QGP), a very special state of matter believed to have been in existence during the first moments after the Big-Bang. This state of matter can be recreated in high energy heavy ion collisions and one of the ways it can be studied, is through the observation of how the quarkonia production is affected when the QGP is present, specifically, the quarkonia suppression. At the LHCb experiment, we can access a unique energy regime, that will allow us to further understand the QGP. Current status and prospects will be presented.

Orateur: Felipe Garcia (LLR, LAL)

RJP2019_GARCIA_Felipe.pdf

17 Low frequency waves in a magnetically confined plasma column

Low frequency waves turbulence developing in magnetized plasma columns are well known to trigger important radial transport, a major issue for fusion devices. We present here analysis from very fast imaging of low frequency waves in a magnetically confined plasma column.

Our experimental set-up consists in a cylindrical chamber containing an Argon plasma column of 10 cm diameter of ionization rate 20 % and at low pressure ~ 1 mTorr generated via an electromagnetic induction source of power 1 kW. The plasma is confined by a magnetic field ranging from 0.01 T to 0.15 T.

A very fast camera records images of spontaneous radiated light fluctuations in a plane transverse to the plasma column axis, at a 200 kfps rate, showing the presence of azimuthally rotating waves at frequencies of order the kHz. These images are analysed using a Proper Orthogonal Decomposition technique which is compared to 2D axisymmetric Fourier transform analysis. The POD results exhibit m-modes closely following the exp(i m \theta) spatial form of the modes extracted by 2D Fourier transform.

Finally, the impact of an emissive cathode inserted at the center of the plasma column on the waves properties is investigated.

Orateur: Simon Vincent (Laboratoire de Physique - ENS de Lyon)

cath_ctd_300A_10_FluctNormzd_ImagesDensity_GaussFlt_N=7900_modes_1-2_3-4_5-6_dn=1_n=1_1_1000.avi

cath_ctd_300A_10_FluctNormzd_ImagesDensity_GaussFlt_N=7900_modes_1-2_3-4_dn=1_n=200_2_1200.avi

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sfp_2019_vincent.pdf

sfp_2019_vincent.pptx

Closing drinks