96 research outputs found
Light polarization measurements in tests of macrorealism
According to the world view of macrorealism, the properties of a given system
exist prior to and independent of measurement, which is incompatible with
quantum mechanics. Leggett and Garg put forward a practical criterion capable
of identifying violations of macrorealism, and so far experiments performed on
microscopic and mesoscopic systems have always ruled out in favor of quantum
mechanics. However, a macrorealist can always assign the cause of such
violations to the perturbation that measurements effect on such small systems,
and hence a definitive test would require using non-invasive measurements,
preferably on macroscopic objects, where such measurements seem more plausible.
However, the generation of truly macroscopic quantum superposition states
capable of violating macrorealism remains a big challenge. In this work we
propose a setup that makes use of measurements on the polarization of light, a
property which has been extensively manipulated both in classical and quantum
contexts, hence establishing the perfect link between the microscopic and
macroscopic worlds. In particular, we use Leggett-Garg inequalities and the
criterion of no-signaling in time to study the macrorealistic character of
light polarization for different kinds of measurements, in particular with
different degrees of coarse-graining. Our proposal is non-invasive for coherent
input states by construction. We show for states with well defined photon
number in two orthogonal polarization modes, that there always exists a way of
making the measurement sufficiently coarse-grained so that a violation of
macrorealism becomes arbitrarily small, while sufficiently sharp measurements
can always lead to a significant violation.Comment: Comments, suggestions, and constructive criticism are welcom
Introduction to quantum optics
These are the lecture notes for a course that I am teaching at Zhiyuan College of Shanghai Jiao Tong University (available at www.youtube.com/derekkorg), though the first draft was created for a previous course I taught at the University of Erlangen-Nuremberg in Germany. It has been designed for students who have only had basic training on quantum mechanics, and hence, the course is suited for people at all levels (say, from the end of the bachelor all the way into the PhD). The notes are a work in progress, meaning that some proofs and many figures are still missing. However, I’ve tried my best to write everything in such a way that a reader can follow naturally all arguments and derivations even with these missing bits. Also a few chapters are left to add, including one on mathematical methods to analyze the dynamics of open systems, and another introducing the plethora of current experimental platforms where the tools and ideas developed in these notes are being currently implemented
Noncritical quadrature squeezing through spontaneous polarization symmetry breaking
We discuss the possibility of generating noncritical quadrature squeezing by
spontaneous polarization symmetry breaking. We consider first type-II
frequency-degenerate optical parametric oscillators, but discard them for a
number of reasons. Then we propose a four-wave mixing cavity in which the
polarization of the output mode is always linear but has an arbitrary
orientation. We show that in such a cavity complete noise suppression in a
quadrature of the output field occurs, irrespective of the parameter values
Degenerate parametric oscillation in quantum membrane optomechanics
The promise of innovative applications has triggered the development of many
modern technologies capable of exploiting quantum effects. But in addition to
future applications, such quantum technologies have already provided us with
the possibility of accessing quantum-mechanical scenarios that seemed
unreachable just a few decades ago. With this spirit, in this work we show that
modern optomechanical setups are mature enough to implement one of the most
elusive models in the field of open system dynamics: degenerate parametric
oscillation. The possibility of implementing it in nonlinear optical resonators
was the main motivation for introducing such model in the eighties, which
rapidly became a paradigm for the study of dissipative phase transitions whose
corresponding spontaneously broken symmetry is discrete. However, it was found
that the intrinsic multimode nature of optical cavities makes it impossible to
experimentally study the model all the way through its phase transition. In
contrast, here we show that this long-awaited model can be implemented in the
motion of a mechanical object dispersively coupled to the light contained in a
cavity, when the latter is properly driven with multi-chromatic laser light. We
focus on membranes as the mechanical element, showing that the main signatures
of the degenerate parametric oscillation model can be studied in
state-of-the-art setups, thus opening the possibility of studying spontaneous
symmetry breaking and enhanced metrology in one of the cleanest dissipative
phase transitions.Comment: We welcome comments, suggestions, and (constructive) criticis
Self-Consistent Projection Operator Theory in Nonlinear Quantum Optical Systems: A case study on Degenerate Optical Parametric Oscillators
Nonlinear quantum optical systems are of paramount relevance for modern
quantum technologies, as well as for the study of dissipative phase
transitions. Their nonlinear nature makes their theoretical study very
challenging and hence they have always served as great motivation to develop
new techniques for the analysis of open quantum systems. In this article we
apply the recently developed self-consistent projection operator theory to the
degenerate optical parametric oscillator to exemplify its general applicability
to quantum optical systems. We show that this theory provides an efficient
method to calculate the full quantum state of each mode with high degree of
accuracy, even at the critical point. It is equally successful in describing
both the stationary limit and the dynamics, including regions of the parameter
space where the numerical integration of the full problem is significantly less
efficient. We further develop a Gaussian approach consistent with our theory,
which yields sensibly better results than the previous Gaussian methods
developed for this system, most notably standard linearization techniques.Comment: Comments are welcom
Regularized linearization for quantum nonlinear optical cavities: Application to Degenerate Optical Parametric Oscillators
Nonlinear optical cavities are crucial both in classical and quantum optics;
in particular, nowadays optical parametric oscillators are one of the most
versatile and tunable sources of coherent light, as well as the sources of the
highest quality quantum-correlated light in the continuous variable regime.
Being nonlinear systems, they can be driven through critical points in which a
solution ceases to exist in favour of a new one, and it is close to these
points where quantum correlations are the strongest. The simplest description
of such systems consists in writing the quantum fields as the classical part
plus some quantum fluctuations, linearizing then the dynamical equations with
respect to the latter; however, such an approach breaks down close to critical
points, where it provides unphysical predictions such as infinite photon
numbers. On the other hand, techniques going beyond the simple linear
description become too complicated especially regarding the evaluation of
two-time correlators, which are of major importance to compute observables
outside the cavity. In this article we provide a regularized linear description
of nonlinear cavities, that is, a linearization procedure yielding physical
results, taking the degenerate optical parametric oscillator as the guiding
example. The method, which we call self-consistent linearization, is shown to
be equivalent to a general Gaussian ansatz for the state of the system, and we
compare its predictions with those obtained with available exact (or
quasi-exact) methods.Comment: Comments and suggestions are welcom
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