377 research outputs found
Exact isolated solutions for the two-photon Rabi Hamiltonian
The two-photon Rabi Hamiltonian is a simple model describing the interaction
of light with matter, with the interaction being mediated by the exchange of
two photons. Although this model is exactly soluble in the rotating-wave
approximation, we work with the full Hamiltonian, maintaining the
non-integrability of the model. We demonstrate that, despite this
non-integrability, there exist isolated, exact solutions for this model
analogous to the so-called Juddian solutions found for the single-photon Rabi
Hamiltonian. In so doing we use a Bogoliubov transformation of the field mode,
as described by the present authors in an earlier publication.Comment: 15 Pages, 1 Figure, Latex, minor change
Entangled microwave photons from quantum dots
We describe a mechanism for the production of polarisation-entangled
microwaves using intra-band transitions in a pair of quantum dots. This
proposal relies neither on spin-orbit coupling nor on control over
electron-electron interactions. The quantum correlation of microwave
polarisations is obtained from orbital degrees of freedom in an external
magnetic field. We calculate the concurrence of emitted microwave photon pairs,
and show that a maximally entangled Bell pair is obtained in the limit of weak
inter-dot coupling.Comment: 4 pages, 5 figure
Thermal phase transitions for Dicke-type models in the ultra-strong coupling limit
We consider the Dicke model in the ultra-strong coupling limit to investigate
thermal phase transitions and their precursors at finite particle numbers
for bosonic and fermionic systems. We derive partition functions with
degeneracy factors that account for the number of configurations and derive
explicit expressions for the Landau free energy. This allows us to discuss the
difference between the original Dicke (fermionic) and the bosonic case. We find
a crossover between these two cases that shows up, e.g., in the specific heat.Comment: 4 pages Brief Report styl
Non-equilibrium correlations and entanglement in a semiconductor hybrid circuit-QED system
We present a theoretical study of a hybrid circuit-QED system composed of two
semiconducting charge-qubits confined in a microwave resonator. The qubits are
defined in terms of the charge states of two spatially separated double quantum
dots (DQDs) which are coupled to the same photon mode in the microwave
resonator. We analyze a transport setup where each DQD is attached to
electronic reservoirs and biased out-of-equilibrium by a large voltage, and
study how electron transport across each DQD is modified by the coupling to the
common resonator. In particular, we show that the inelastic current through
each DQD reflects an indirect qubit-qubit interaction mediated by off-resonant
photons in the microwave resonator. As a result of this interaction, both
charge qubits stay entangled in the steady (dissipative) state. Finite shot
noise cross-correlations between currents across distant DQDs are another
manifestation of this nontrivial steady-state entanglement.Comment: Final versio
Perpetual emulation threshold of PT-symmetric Hamiltonians
We describe a technique to emulate a two-level \PT-symmetric spin
Hamiltonian, replete with gain and loss, using only the unitary dynamics of a
larger quantum system. This we achieve by embedding the two-level system in
question in a subspace of a four-level Hamiltonian. Using an \textit{amplitude
recycling} scheme that couples the levels exterior to the \PT-symmetric
subspace, we show that it is possible to emulate the desired behaviour of the
\PT-symmetric Hamiltonian without depleting the exterior, reservoir levels. We
are thus able to extend the emulation time indefinitely, despite the
non-unitary \PT dynamics. We propose a realistic experimental implementation
using dynamically decoupled magnetic sublevels of ultracold atoms.Comment: 15 pages, 8 figure
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