5,707 research outputs found
Optimized Entanglement Purification
We investigate novel protocols for entanglement purification of qubit Bell
pairs. Employing genetic algorithms for the design of the purification circuit,
we obtain shorter circuits achieving higher success rates and better final
fidelities than what is currently available in the literature. We provide a
software tool for analytical and numerical study of the generated purification
circuits, under customizable error models. These new purification protocols
pave the way to practical implementations of modular quantum computers and
quantum repeaters. Our approach is particularly attentive to the effects of
finite resources and imperfect local operations - phenomena neglected in the
usual asymptotic approach to the problem. The choice of the building blocks
permitted in the construction of the circuits is based on a thorough
enumeration of the local Clifford operations that act as permutations on the
basis of Bell states
General phase spaces: from discrete variables to rotor and continuum limits
We provide a basic introduction to discrete-variable, rotor, and
continuous-variable quantum phase spaces, explaining how the latter two can be
understood as limiting cases of the first. We extend the limit-taking
procedures used to travel between phase spaces to a general class of
Hamiltonians (including many local stabilizer codes) and provide six examples:
the Harper equation, the Baxter parafermionic spin chain, the Rabi model, the
Kitaev toric code, the Haah cubic code (which we generalize to qudits), and the
Kitaev honeycomb model. We obtain continuous-variable generalizations of all
models, some of which are novel. The Baxter model is mapped to a chain of
coupled oscillators and the Rabi model to the optomechanical radiation pressure
Hamiltonian. The procedures also yield rotor versions of all models, five of
which are novel many-body extensions of the almost Mathieu equation. The toric
and cubic codes are mapped to lattice models of rotors, with the toric code
case related to U(1) lattice gauge theory.Comment: 22 pages, 3 figures; part of special issue on Rabi model; v2 minor
change
Quantum Rabi model for N-state atoms
A tractable N-state Rabi Hamiltonian is introduced by extending the parity
symmetry of the two-state model. The single-mode case provides a few-parameter
description of a novel class of periodic systems, predicting that the ground
state of certain four-state atom-cavity systems will undergo parity change at
strong coupling. A group-theoretical treatment provides physical insight into
dynamics and a modified rotating wave approximation obtains accurate analytical
energies. The dissipative case can be applied to study excitation energy
transfer in molecular rings or chains.Comment: 5 pages, 3 figures + supplement (2 pages); to appear in Phys. Rev.
Let
- …