3 research outputs found
Probing polaron clouds by Rydberg atom spectroscopy
In recent years, Rydberg excitations in atomic quantum gases have become a
successful platform to explore quantum impurity problems. A single impurity
immersed in a Fermi gas leads to the formation of a polaron, a quasiparticle
consisting of the impurity being dressed by the surrounding medium. With a
radius of about the Fermi wavelength, the density profile of a polaron cannot
be explored using in-situ optical imaging techniques. In this work, we propose
a new experimental measurement technique that enables the in-situ imaging of
the polaron cloud in ultracold quantum gases. The impurity atom is first
excited to an interacting state which induces the formation of a polaron cloud.
This is followed by the excitation of the impurity atom to a Rydberg state. Due
to the mesoscopic interaction range of Rydberg excitations, which can be tuned
by the principal numbers of the Rydberg state, atoms extracted from the polaron
cloud form dimers with the impurity. By performing first principle calculations
of the absorption spectrum based on a functional determinant approach, we show
how the occupation of the dimer state can be directly observed in spectroscopy
experiments and can be mapped onto the density profile of the gas particles,
hence providing a direct, real-time, and in-situ measure of the polaron cloud.Comment: 15 pages, 12 figure
Shape effects of localized losses in quantum wires: Dissipative resonances and nonequilibrium universality
We study the effects of the spacial structure of localized single-particle losses in weakly interacting fermionic quantum wires. We show that multiple dissipative impurities give rise to resonant effects visible in the transport properties and the particles' momentum distribution. These resonances can enhance or suppress the effective particle losses in the wire. Moreover, we investigate the interplay between interactions and the impurity shape and find that, differently from the coherent scatterer case, the impurity shape modifies the scaling of the scattering probabilities close to the Fermi momentum. We show that, while the fluctuation-induced quantum Zeno effect is robust against the shape of the impurities, the fluctuation-induced transparency is lifted continuously. This is reflected in the emergence of a continuous line of fixed points in the renormalization group flow of the scattering probabilities
Multiloop flow equations for single-boson exchange fRG
The recently introduced single-boson exchange (SBE) decomposition of the
four-point vertex of interacting fermionic many-body systems is a conceptually
and computationally appealing parametrization of the vertex. It relies on the
notion of reducibility of vertex diagrams with respect to the bare interaction
, instead of a classification based on two-particle reducibility within the
widely-used parquet decomposition. Here, we re-derive the SBE decomposition in
a generalized framework (suitable for extensions to, e.g., inhomogeneous
systems or real-frequency treatments) following from the parquet equations. We
then derive multiloop functional renormalization group (mfRG) flow equations
for the ingredients of this SBE decomposition, both in the parquet
approximation, where the fully two-particle irreducible vertex is treated as an
input, and in the more restrictive SBE approximation, where this role is taken
by the fully -irreducible vertex. Moreover, we give mfRG flow equations for
the popular parametrization of the vertex in terms of asymptotic classes of the
two-particle reducible vertices. Since the parquet and SBE decompositions are
closely related, their mfRG flow equations are very similar in structure.Comment: exchanged Sec. 3 and 4 and reordered appendices, added new Sec. 3.4
and App. D, extended the discussion in Sec. 2.3, 3.1, and 3.3, corrected Eq.
(8