9,990 research outputs found
Bond Order via Light-Induced Synthetic Many-body Interactions of Ultracold Atoms in Optical Lattices
We show how bond order emerges due to light mediated synthetic interactions
in ultracold atoms in optical lattices in an optical cavity. This is a
consequence of the competition between both short- and long-range interactions
designed by choosing the optical geometry. Light induces effective many-body
interactions that modify the landscape of quantum phases supported by the
typical Bose-Hubbard model. Using exact diagonalization of small system sizes
in one dimension, we present the many-body quantum phases the system can
support via the interplay between the density and bond (or matter-wave
coherence) interactions. We find numerical evidence to support that dimer
phases due to bond order are analogous to valence bond states. Different
possibilities of light-induced atomic interactions are considered that go
beyond the typical atomic system with dipolar and other intrinsic interactions.
This will broaden the Hamiltonian toolbox available for quantum simulation of
condensed matter physics via atomic systems.Comment: Accepted in New Journal of Physic
Non-Hermitian Dynamics in the Quantum Zeno Limit
Measurement is one of the most counter-intuitive aspects of quantum physics.
Frequent measurements of a quantum system lead to quantum Zeno dynamics where
time evolution becomes confined to a subspace defined by the projections.
However, weak measurement performed at a finite rate is also capable of locking
the system into such a Zeno subspace in an unconventional way: by Raman-like
transitions via virtual intermediate states outside this subspace, which are
not forbidden. Here, we extend this concept into the realm of non-Hermitian
dynamics by showing that the stochastic competition between measurement and a
system's own dynamics can be described by a non-Hermitian Hamiltonian. We
obtain an analytic solution for ultracold bosons in a lattice and show that a
dark state of the tunnelling operator is a steady state in which the
observable's fluctuations are zero and tunnelling is suppressed by destructive
matter-wave interference. This opens a new venue of investigation beyond the
canonical quantum Zeno dynamics and leads to a new paradigm of competition
between global measurement backaction and short-range atomic dynamics.Comment: Accepted in Phys. Rev.
Criticality in the collapse of spherically symmetric massless scalar fields in semi-classical loop quantum gravity
In a recent paper we showed that the collapse to a black hole in
one-parameter families of initial data for massless, minimally coupled scalar
fields in spherically symmetric semi-classical loop quantum gravity exhibited a
universal mass scaling similar to the one in classical general relativity. In
particular, no evidence of a mass gap appeared as had been suggested by
previous studies. The lack of a mass gap indicated the possible existence of a
self-similar critical solution as in general relativity. Here we provide
further evidence for its existence. Using an adaptive mesh refinement code, we
show that "echoes" arise as a result of the discrete self-similarity in
space-time. We also show the existence of "wiggles" in the mass scaling
relation, as in the classical theory. The results from the semi-classical
theory agree well with those of classical general relativity unless one takes
unrealistically large values for the polymerization parameter.Comment: 7 pages, RevTe
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