42 research outputs found
Multimode entanglement in coupled cavity arrays
We study a driven-dissipative array of coupled nonlinear optical resonators
by numerically solving the Von Neumann equation for the density matrix. We
demonstrate that quantum correlated states of many photons can be generated
also in the limit where the nonlinearity is much smaller than the losses,
contrarily to common expectations. Quantum correlations in this case arise from
interference between different pathways that the system can follow in the
Hilbert space to reach its steady state under the effect of coherent driving
fields. We characterize in particular two systems: a linear chain of three
coupled cavities and an array of eight coupled cavities. We demonstrate the
existence of a parameter range where the system emits photons with
continuous-variable bipartite and quadripartite entanglement, in the case of
the first and the second system respectively. This entanglement is shown to
survive realistic rates of pure dephasing and opens a new perspective for the
realization of quantum simulators or entangled photon sources without the
challenging requirement of strong optical nonlinearities.Comment: 20 pages, 7 figure
Polariton quantum blockade in a photonic dot
We investigate the quantum nonlinear dynamics of a resonantly excited
photonic quantum dot embedding a quantum well in the strong exciton-photon
coupling regime. Within a master equation approach, we study the polariton
quantum blockade and the generation of single photon states due to
polariton-polariton interactions as a function of the photonic dot geometry,
spectral linewidths and energy detuning between quantum well exciton and
confined photon mode. The second order coherence function is
calculated for both continuous wave and pulsed excitations
Quantum Monte Carlo study of ring-shaped polariton parametric luminescence in a semiconductor microcavity
We present a quantum Monte Carlo study of the quantum correlations in the
parametric luminescence from semiconductor microcavities in the strong
exciton-photon coupling regime. As already demonstrated in recent experiments,
a ring-shaped emission is obtained by applying two identical pump beams with
opposite in-plane wavevectors, providing symmetrical signal and idler beams
with opposite in-plane wavevectors on the ring. We study the squeezing of the
signal-idler difference noise across the parametric instability threshold,
accounting for the radiative and non-radiative losses, multiple scattering and
static disorder. We compare the results of the complete multimode Monte Carlo
simulations with a simplified linearized quantum Langevin analytical model
Stabilizing strongly correlated photon fluids with non-Markovian reservoirs
We introduce a frequency-dependent incoherent pump scheme with a square-shaped spectrum as a way to study strongly correlated photons in arrays of coupled nonlinear resonators. This scheme can be implemented via a reservoir of population-inverted two-level emitters with a broad distribution of transition frequencies. Our proposal is predicted to stabilize a nonequilibrium steady state sharing important features with a zero-temperature equilibrium state with a tunable chemical potential. We confirm the efficiency of our proposal for the Bose-Hubbard model by computing numerically the steady state for finite system sizes: first, we predict the occurrence of a sequence of incompressible Mott-insulator-like states with arbitrary integer densities presenting strong robustness against tunneling and losses. Secondly, for stronger tunneling amplitudes or noninteger densities, the system enters a coherent regime analogous to the superfluid state. In addition to an overall agreement with the zero-temperature equilibrium state, exotic nonequilibrium processes leading to a finite entropy generation are pointed out in specific regions of parameter space. The equilibrium ground state is shown to be recovered by adding frequency-dependent losses. The promise of this improved scheme in view of quantum simulation of the zero-temperature many-body physics is highlighted
Many-body physics of a quantum fluid of exciton-polaritons in a semiconductor microcavity
Some recent results concerning nonlinear optics in semiconductor
microcavities are reviewed from the point of view of the many-body physics of
an interacting photon gas. Analogies with systems of cold atoms at thermal
equilibrium are drawn, and the peculiar behaviours due to the non-equilibrium
regime pointed out. The richness of the predicted behaviours shows the
potentialities of optical systems for the study of the physics of quantum
fluids.Comment: Proceedings of QFS2006 conference to appear on JLT
Fermionized photons in an array of driven dissipative nonlinear cavities
We theoretically investigate the optical response of a one-dimensional array
of strongly nonlinear optical microcavities. When the optical nonlinearity is
much larger than both losses and inter-cavity tunnel coupling, the
non-equilibrium steady state of the system is reminiscent of a strongly
correlated Tonks-Girardeau gas of impenetrable bosons. Signatures of strong
correlations are identified in the absorption spectrum of the system, as well
as in the intensity correlations of the emitted light. Possible experimental
implementations in state-of-the-art solid-state devices are discussed
Comment on "Linear wave dynamics explains observations attributed to dark-solitons in a polariton quantum fluid"
In a recent preprint (arXiv:1401.1128v1) Cilibrizzi and co-workers report
experiments and simulations showing the scattering of polaritons against a
localised obstacle in a semiconductor microcavity. The authors observe in the
linear excitation regime the formation of density and phase patterns
reminiscent of those expected in the non-linear regime from the nucleation of
dark solitons. Based on this observation, they conclude that previous
theoretical and experimental reports on dark solitons in a polariton system
should be revised. Here we comment why the results from Cilibrizzi et al. take
place in a very different regime than previous investigations on dark soliton
nucleation and do not reproduce all the signatures of its rich nonlinear
phenomenology. First of all, Cilibrizzi et al. consider a particular type of
radial excitation that strongly determines the observed patterns, while in
previous reports the excitation has a plane-wave profile. Most importantly, the
nonlinear relation between phase jump, soliton width and fluid velocity, and
the existence of a critical velocity with the time-dependent formation of
vortex-antivortex pairs are absent in the linear regime. In previous reports
about dark soliton and half-dark soliton nucleation in a polariton fluid, the
distinctive dark soliton physics is supported both by theory (analytical and
numerical) and experiments (both continuous wave and pulsed excitation).Comment: 4 pages, 2 figure
Observation of Superfluidity of Polaritons in Semiconductor Microcavities
One of the most striking manifestations of quantum coherence in interacting
boson systems is superfluidity. Exciton-polaritons in semiconductor
microcavities are two-dimensional composite bosons predicted to behave as
particular quantum fluids. We report the observation of superfluid motion of
polaritons created by a laser in a semiconductor microcavity. Superfluidity is
investigated in terms of the Landau criterion and manifests itself as the
suppression of scattering from defects when the flow velocity is slower than
the speed of sound in the fluid. On the other hand, a Cerenkov-like wake
pattern is clearly observed when the flow velocity exceeds the speed of sound.
The experimental findings are in excellent quantitative agreement with the
predictions based on a generalized Gross-Pitaevskii theory, showing that
polaritons in microcavities constitute a very rich system for exploring the
physics of non-equilibrium quantum fluids.Comment: 14 pages, 3 figure
Is there a no-go theorem for superradiant quantum phase transitions in cavity and circuit QED ?
In cavity quantum electrodynamics (QED), the interaction between an atomic
transition and the cavity field is measured by the vacuum Rabi frequency
. The analogous term "circuit QED" has been introduced for Josephson
junctions, because superconducting circuits behave as artificial atoms coupled
to the bosonic field of a resonator. In the regime with comparable
to the two-level transition frequency, "superradiant" quantum phase transitions
for the cavity vacuum have been predicted, e.g. within the Dicke model. Here,
we prove that if the time-independent light-matter Hamiltonian is considered, a
superradiant quantum critical point is forbidden for electric dipole atomic
transitions due to the oscillator strength sum rule. In circuit QED, the
capacitive coupling is analogous to the electric dipole one: yet, such no-go
property can be circumvented by Cooper pair boxes capacitively coupled to a
resonator, due to their peculiar Hilbert space topology and a violation of the
corresponding sum rule