558 research outputs found
Quantum many-body systems out of equilibrium
Closed quantum many-body systems out of equilibrium pose several
long-standing problems in physics. Recent years have seen a tremendous progress
in approaching these questions, not least due to experiments with cold atoms
and trapped ions in instances of quantum simulations. This article provides an
overview on the progress in understanding dynamical equilibration and
thermalisation of closed quantum many-body systems out of equilibrium due to
quenches, ramps and periodic driving. It also addresses topics such as the
eigenstate thermalisation hypothesis, typicality, transport, many-body
localisation, universality near phase transitions, and prospects for quantum
simulations.Comment: 7 pages, review and perspectives article, updated to journal version
after embarg
Comment on ``Enhancement of the Tunneling Density of States in Tomonaga-Luttinger Liquids''
In a recent Physical Review Letter, Oreg and Finkel'stein (OF) have
calculated the electron density of states (DOS) for tunneling into a repulsive
Luttinger liquid close to the location of an impurity. The result of their
calculation is a DOS which is enhanced with respect to the pure system, and
moreover diverging for not too strong repulsion. In this Comment we intend to
show that OF's calculation suffers from a subtle flaw which, being corrected,
results into a DOS not only vanishing at zero frequency but in fact suppressed
in comparison with the DOS of a pure Luttinger liquid.Comment: 1 page, Revte
Crystal Distortion and the Two-Channel Kondo Effect
We study a simple model of the two-channel Kondo effect in a distorted
crystal. This model is then used to investigate the interplay of the Kondo and
Jahn-Teller effects, and also the Kondo effect in an impure crystal. We find
that the Jahn-Teller interaction modifies the characteristic energy scale of
the system below which non-Fermi-liquid properties of the model become
apparent. The modified energy scale tends to zero as the limit of a purely
static Jahn-Teller effect is approached. We find also that the non-Fermi-liquid
properties of the quadrupolar Kondo effect are not stable against crystal
distortion caused by impurities.Comment: 11 page
Equilibration via Gaussification in fermionic lattice systems
In this work, we present a result on the non-equilibrium dynamics causing
equilibration and Gaussification of quadratic non-interacting fermionic
Hamiltonians. Specifically, based on two basic assumptions - clustering of
correlations in the initial state and the Hamiltonian exhibiting delocalizing
transport - we prove that non-Gaussian initial states become locally
indistinguishable from fermionic Gaussian states after a short and well
controlled time. This relaxation dynamics is governed by a power-law
independent of the system size. Our argument is general enough to allow for
pure and mixed initial states, including thermal and ground states of
interacting Hamiltonians on and large classes of lattices as well as certain
spin systems. The argument gives rise to rigorously proven instances of a
convergence to a generalized Gibbs ensemble. Our results allow to develop an
intuition of equilibration that is expected to be more generally valid and
relates to current experiments of cold atoms in optical lattices.Comment: 5+15 pages, 3 figures, presentation improve
Reliable quantum certification for photonic quantum technologies
A major roadblock for large-scale photonic quantum technologies is the lack
of practical reliable certification tools. We introduce an experimentally
friendly - yet mathematically rigorous - certification test for experimental
preparations of arbitrary m-mode pure Gaussian states, pure non-Gaussian states
generated by linear-optical circuits with n-boson Fock-basis states as inputs,
and states of these two classes subsequently post-selected with local
measurements on ancillary modes. The protocol is efficient in m and the inverse
post-selection success probability for all Gaussian states and all mentioned
non-Gaussian states with constant n. We follow the mindset of an untrusted
prover, who prepares the state, and a skeptic certifier, with classical
computing and single-mode homodyne-detection capabilities only. No assumptions
are made on the type of noise or capabilities of the prover. Our technique
exploits an extremality-based fidelity bound whose estimation relies on
non-Gaussian state nullifiers, which we introduce on the way as a byproduct
result. The certification of many-mode photonic networks, as those used for
photonic quantum simulations, boson samplers, and quantum metrology, is now
within reach.Comment: 8 pages + 20 pages appendix, 2 figures, results generalized to
scenarios with post-selection, presentation improve
X-ray edge singularity of bilayer graphene
The X-ray edge singularity of bilayer graphene is studied by generalizing the
path integral approach based on local action which was employed for monolayer
graphene. In sharp contrast to the case of monolayer graphene, the bilayer
graphene is found to exhibit the edge singularity even at half-filling and its
characteristics are determined by interlayer coupling. At finite bias the
singular behaviors sensitively depend on the relative magnitude of fermi energy
and applied bias, which is due to the peculiar shape of energy band at finite
bias.Comment: RevTeX 4.1, 4 pages. No figur
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