586 research outputs found
Tuneable quantum interference in a 3D integrated circuit
Integrated photonics promises solutions to questions of stability,
complexity, and size in quantum optics. Advances in tunable and non-planar
integrated platforms, such laser-inscribed photonics, continue to bring the
realisation of quantum advantages in computation and metrology ever closer,
perhaps most easily seen in multi-path interferometry. Here we demonstrate
control of two-photon interference in a chip-scale 3D multi-path
interferometer, showing a reduced periodicity and enhanced visibility compared
to single photon measurements. Observed non-classical visibilities are widely
tunable, and explained well by theoretical predictions based on classical
measurements. With these predictions we extract a Fisher information
approaching a theoretical maximum, demonstrating the capability of the device
for quantum enhanced phase measurements.Comment: 11 pages, 24 figure
Power limits and a figure of merit for stimulated Brillouin scattering in the presence of third and fifth order loss
We derive a set of design guidelines and a figure of merit to aid the
engineering process of on-chip waveguides for strong Stimulated Brillouin
Scattering (SBS). To this end, we examine the impact of several types of loss
on the total amplification of the Stokes wave that can be achieved via SBS. We
account for linear loss and nonlinear loss of third order (two-photon
absorption, 2PA) and fifth order, most notably 2PA-induced free carrier
absorption (FCA). From this, we derive an upper bound for the output power of
continuous-wave Brillouin-lasers and show that the optimal operating conditions
and maximal realisable Stokes amplification of any given waveguide structure
are determined by a dimensionless parameter involving the
SBS-gain and all loss parameters. We provide simple expressions for optimal
pump power, waveguide length and realisable amplification and demonstrate their
utility in two example systems. Notably, we find that 2PA-induced FCA is a
serious limitation to SBS in silicon and germanium for wavelengths shorter than
2200nm and 3600nm, respectively. In contrast, three-photon absorption is of no
practical significance
Impact of nonlinear loss on Stimulated Brillouin Scattering
We study the impact of two-photon absorption (2PA) and fifth-order nonlinear
loss such as 2PA-induced free-carrier absorption in semiconductors on the
performance of Stimulated Brillouin Scattering devices. We formulate the
equations of motion including effective loss coefficients, whose explicit
expressions are provided for numerical evaluation in any waveguide geometry. We
find that 2PA results in a monotonic, algebraic relationship between
amplification, waveguide length and pump power, whereas fifth-order losses lead
to a non-monotonic relationship. We define a figure of merit for materials and
waveguide designs in the presence of fifth-order losses. From this, we
determine the optimal waveguide length for the case of 2PA alone and upper
bounds for the total Stokes amplification for the case of 2PA as well as
fifth-order losses. The analysis is performed analytically using a small-signal
approximation and is compared to numerical solutions of the full nonlinear
modal equations
Generation of heralded single photons beyond 1100 nm by spontaneous four-wave mixing in a side-stressed femtosecond laser-written waveguide
We demonstrate a monolithically integrable heralded photon source in a
femtosecond laser direct written glass waveguide. The generation of photon
pairs with a wide wavelength separation requires a concomitant large
birefringence in the normal dispersion regime. Here, by incorporation of
side-stress tracks, we produce a waveguide with a birefringence of
and propagation loss as low as 0.21 dB/cm near 980~nm. We
measure photon pairs with 300~nm wavelength separation at an internal
generation rate exceeding /s. The second order correlations
indicate that the generated photon pairs are in a strongly non-classical
regime.Comment: 5 pages, 5 figure
Molecular optomechanics in the anharmonic regime: from nonclassical mechanical states to mechanical lasing
Cavity optomechanics aims to establish optical control over vibrations of
mechanical systems, to heat, cool or to drive them toward coherent, or
nonclassical states. This field was recently extended to include molecular
optomechanics, which describes the dynamics of THz molecular vibrations coupled
to the optical fields of lossy cavities via Raman transitions, and was
developed to understand the anomalous amplification of optical phonons in
Surface-Enhanced Raman Scattering experiments. But the molecular platform
should prove suitable for demonstrating more sophisticated optomechanical
effects, including engineering of nonclassical mechanical states, or inducing
coherent molecular vibrations. In this work, we propose two pathways towards
implementing these effects, enabled or revealed by the strong intrinsic
anharmonicities of molecular vibrations. First, to prepare a nonclassical
mechanical state, we propose an incoherent analogue of the mechanical blockade,
in which the molecular aharmonicity and optical response of hybrid cavities
isolate the two lowest-energy vibrational states. Secondly, we show that for a
strongly driven optomechanical system, the anharmonicity can effectively
suppress the mechanical amplification, shifting and reshaping the onset of
coherent mechanical oscillations. Our estimates indicate that both effects
should be within reach of the existing implementations of the Surface Enhanced
Raman Scattering, opening the pathway towards the coherent and nonclassical
effects in molecular optomechanics
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