Dr. Marcus Bluhm

Associate professor at Institute of Theoretical Physics

Institute of Theoretical Physics
pl. M. Borna 9
50-204 Wrocław
Phone: +48 71 375 9354

e-mail: marcus.bluhm@ift.uni.wroc.pl
Office:     435

Properties of strongly coupled quantum fluids

My current work is funded by the European Union's Horizon 2020 research and innovation programme under the
Marie Skłodowska-Curie grant agreement No. 665778 via the Narodowe Centrum Nauki (National Science Center,
Poland) within the Polonez fellowship UMO-2016/21/P/ST2/04035 "Properties of strongly coupled quantum fluids".
The scientific goals of the project can be found in my research proposal.

More information about the Polonez fellowship can be found here.

    Outstanding key findings of the fellowship are so far:
  • The minimal specific shear viscosity in ultracold atomic Fermi gases at unitarity, as deduced from hydrodynamic
    flow data, is found in the normal phase just above the transition temperature to superfluidity (see the red curve with
    band in the figure). It can be as small as 0.5 in natural units, thus being comparable with the hottest matter created
    on earth, the Quark-Gluon Plasma. Both these strongly coupled quantum systems constitute the most perfect fluids
    that we know.

  • The non-linearities in the fluid dynamical equations can lead to sufficiently strong non-linear mode couplings such that
    from purely Gaussian white noise observable non-Gaussian cumulants can be generated. This is demonstrated for
    the case of the purely diffusive dynamics of critical mode fluctuations near the QCD critical point in a rapidly evolving
    medium. Without non-linear interactions non-Gaussian cumulants such as the kurtosis remain zero (see red squares
    in the figures), while for the fully non-linear dynamics a pronounced temperature dependence in the kurtosis develops
    (see blue points in the left figure). Finite-size and finite-time effects lead to retardation and non-equilibrium effects
    (see right figure, shift to later times and less pronounced minimum), and a critical scaling behavior different from
    thermodynamic expectations is observed.

  • The equilibration times of critical mode fluctuations in the QCD phase diagram are moderately small. This hints
    toward equilibrium dominated measurements of fluctuation observables in heavy-ion collisions. The time-evolution
    of critical mode fluctuations was studied in a QCD-assisted transport approach based on non-equilibrium chiral
    fluid dynamics and the effective action of low-energy QCD, taking the non-perturbative nature of QCD near the
    phase transition into account. From this equilibration time study the phase boundary and the region near the QCD
    critical point can clearly be identified (see blue vs. non-blue regions in the figure). The moderate increase near the
    critical point (red area) - the equilibration times remain smaller than 1 fm/c - suggests that phenomena associated
    with critical slowing down might be less pronounced than previously expected.

Up to now the fellowship has resulted in the following papers:
  1. Determination of the density and temperature dependence of the shear viscosity of a unitary Fermi gas based on hydrodynamic flow
    by Marcus Bluhm, Jiaxun Hou and Thomas Schäfer
    arXiv:1704.03720, published in Phys. Rev. Lett. 119 (2017) no.6, 065302.
  2. Toward the description of fluid dynamical fluctuations in heavy-ion collisions
    by Marlene Nahrgang, Marcus Bluhm, Thomas Schäfer and Steffen Bass
    arXiv:1704.03553, published in Acta Phys. Polon. Supp. 10 (2017) 687.
  3. From cold Fermi fluids to the hot QGP
    by Marcus Bluhm and Thomas Schäfer
    arXiv:1705.08710, published in Acta Phys. Polon. Supp. 10 (2017) 481.
  4. Baryon number diffusion with critical fluctuations
    by Marlene Nahrgang, Marcus Bluhm, Thomas Schäfer and Steffen Bass
    arXiv:1804.02976, published in Nucl. Phys. A 967 (2017) 824-827.
  5. Fluctuating fluid dynamics for the QGP in the LHC and BES era
    by Marcus Bluhm, Marlene Nahrgang, Thomas Schäfer and Steffen Bass
    arXiv:1804.03493, published in EPJ Web Conf. 171 (2018) 16004.
  6. Diffusive dynamics of critical fluctuations near the QCD critical point
    by Marlene Nahrgang, Marcus Bluhm, Thomas Schäfer and Steffen Bass
    arXiv:1804.05728, submitted to Phys. Rev. Lett.
  7. Lattice-QCD-based equation of state with a critical point
    by Paolo Parotto, Marcus Bluhm, Debora Mroczek, Marlene Nahrgang, Jacquelyn Noronha-Hostler, Krishna Rajagopal, Claudia Ratti, Thomas Schäfer and Mikhail Stephanov
    arXiv:1805.05249, submitted to JHEP.
  8. Freeze-out conditions from strangeness observables at RHIC
    by Marcus Bluhm and Marlene Nahrgang
    arXiv:1806.04499, submitted to Eur. Phys. J. C.
  9. Time-evolution of fluctuations as signal of the phase transition dynamics in a QCD-assisted transport approach
    by Marcus Bluhm, Yin Jiang, Marlene Nahrgang, Jan Martin Pawlowski, Fabian Rennecke and Nicolas Wink
    arXiv:1808.01377, submitted to Nucl. Phys. A.
and the outcome of my research has been presented by me at the following workshops, conferences, seminars and schools:
  1. Lecture "Simulating strongly coupled quantum fluids" at the 53rd Karpacz Winter School of Theoretical Physics, Karpacz, Poland, March 4, 2017.
  2. Seminar "Transport properties of a cold atomic Fermi gas at and near unitarity" at Jan Kochanowski University, Kielce, Poland, May 17, 2017.
  3. Seminar "Temperature and density dependence of the shear viscosity of the unitary Fermi gas based on hydrodynamic flow" at AGH University of Science and Technology, Krakow, Poland, May 19, 2017.
  4. Talk "Fluctuating fluid dynamics for the QGP in the LHC and BES era" at Strangeness in Quark Matter 2017, Utrecht, the Netherlands, July 13, 2017.
  5. Talk "Diffusive dynamics of critical fluctuations" at International EMMI workshop on critical fluctuations near the QCD phase boundary in relativistic nuclear collisions, Wuhan, China, October 11, 2017.
  6. Talk "Diffusive dynamics of net-baryon fluctuations near the QCD critical point" at Phase diagram of strongly interacting matter: From Lattice QCD to Heavy-Ion Collision Experiments, ECT* Trento, Italy, November 29, 2017.
  7. Lecture "What cold atomic Fermi gases can tell us about the hot QGP" at the Zimanyi Winter School on Heavy Ion Physics 2017, Budapest, Hungary, December 8, 2017.
  8. Seminar "Competing for perfection - Ultracold Fermi gases can be as perfect fluids as the superhot Quark-Gluon Plasma" at University of Wroclaw, Wroclaw, Poland, January 19, 2018.
  9. Talk "Diffusive dynamics of net-baryon fluctuations near the QCD critical point" at Constraining the QCD Phase Boundary with Data from Heavy Ion Collisions, GSI Darmstadt, Germany, February 13, 2018.
  10. Talk "Dynamics of net-baryon density correlations near the QCD critical point" at From correlation functions to QCD phenomenology, Bad Honnef, Germany, April 4, 2018.
  11. Talk "Finite size effects on critical fluctuations" at The Critical Point and Onset of Deconfinement 2018, Corfu, Greece, September 26, 2018.

Moreover, some physical ideas behind the world of "strongly coupled quantum fluids" have been discussed publically
during the Lower Silesian Science Festivals in Wrocław in 2017 and 2018.

Lecture: Ultracold Fermi gases

In the fall semester of 2017, I gave a monographic lecture related to my project about the physics of "Ultracold Fermi gases".
It was intended for Ph.D. students at the University of Wrocław with the following syllabus. The problems tasks
for each of the lectures can be found here:
Problem tasks - Session 1
Problem tasks - Session 2
Problem tasks - Session 3
Problem tasks - Session 4

List of my publications at INSPIRES.