29 research outputs found
Multimode mean-field model for the quantum phase transition of a Bose-Einstein condensate in an optical resonator
We develop a mean-field model describing the Hamiltonian interaction of
ultracold atoms and the optical field in a cavity. The Bose-Einstein condensate
is properly defined by means of a grand-canonical approach. The model is
efficient because only the relevant excitation modes are taken into account.
However, the model goes beyond the two-mode subspace necessary to describe the
self-organization quantum phase transition observed recently. We calculate all
the second-order correlations of the coupled atom field and radiation field
hybrid bosonic system, including the entanglement between the two types of
fields.Comment: 10 page
Quantum simulation of discrete-time Hamiltonians using directionally unbiased linear optical multiports
Recently, a generalization of the standard optical multiport was proposed
[Phys. Rev. A 93, 043845 (2016)]. These directionally unbiased multiports allow
photons to reverse direction and exit backwards from the input port, providing
a realistic linear optical scattering vertex for quantum walks on arbitrary
graph structures. Here, it is shown that arrays of these multiports allow the
simulation of a range of discrete-time Hamiltonian systems. Examples are
described, including a case where both spatial and internal degrees of freedom
are simulated. Because input ports also double as output ports, there is
substantial savings of resources compared to feed-forward networks carrying out
the same functions. The simulation is implemented in a scalable manner using
only linear optics, and can be generalized to higher dimensional systems in a
straightforward fashion, thus offering a concrete experimentally achievable
implementation of graphical models of discrete-time quantum systems