36 research outputs found
Bounds on Collapse Models from Matter-Wave Interferometry: Calculational details
We present a simple derivation of the interference pattern in matter-wave
interferometry as predicted by a class of master equations, by using the
density matrix formalism. We apply the obtained formulae to the most relevant
collapse models, namely the Ghirardi-Rimini-Weber (GRW) model, the continuous
spontaneous localization (CSL) model together with its dissipative (dCSL) and
non-markovian generalizations (cCSL), the quantum mechanics with universal
position localization (QMUPL) and the Di\'{o}si-Penrose (DP) model. We discuss
the separability of the collapse models dynamics along the 3 spatial
directions, the validity of the paraxial approximation and the amplification
mechanism. We obtain analytical expressions both in the far field and near
field limits. These results agree with those already derived in the Wigner
function formalism.
We compare the theoretical predictions with the experimental data from two
relevant matter-wave experiments: the 2012 far-field experiment and the 2013
Kapitza Dirac Talbot Lau (KDTL) near-field experiment of Arndt's group. We show
the region of the parameter space for each collapse model, which is excluded by
these experiments. We show that matter-wave experiments provide model
insensitive bounds, valid for a wide family of dissipative and non-markovian
generalizations.Comment: 49 pages,16 figure
Wigner Function Reconstruction in Levitated Optomechanics
We demonstrate the reconstruction of the Wigner function from marginal
distributions of the motion of a single trapped particle using homodyne
detection. We show that it is possible to generate quantum states of levitated
optomechanical systems even under the effect of continuous measurement by the
trapping laser light. We describe the opto-mechanical coupling for the case of
the particle trapped by a free-space focused laser beam, explicitly for the
case without an optical cavity. We use the scheme to reconstruct the Wigner
function of experimental data in perfect agreement with the expected Gaussian
distribution of a thermal state of motion. This opens a route for quantum state
preparation in levitated optomechanics.Comment: 9 pages, 3 figure
Colored and Dissipative Continuous Spontaneous Localization model and Bounds from Matter-Wave Interferometry
Matter-wave interferometry is a direct test of the quantum superposition
principle for massive systems, and of collapse models. Here we show that the
bounds placed by matter-wave interferometry depend weakly on the details of the
collapse mechanism. Specifically, we compute the bounds on the CSL model and
its variants, provided by the the KDTL interferometry experiment of Arndt's
group [Phys. Chem. Chem. Phys., 2013, 15, 14696-14700], which currently holds
the record of largest mass in interferometry.
We also show that the CSL family of models emerges naturally by considering a
minimal set of assumptions. In particular, we construct the dynamical map for
the colored and dissipative Continuous Spontaneous Localization (cdCSL) model,
which reduces to the CSL model and variants in the appropriate limits. In
addition, we discuss the measure of macroscopicity based on the cdCSL model.Comment: 9 pages, 5 figures; accepted for publication in Physics Letters A
(2017
Bohmian Mechanics, Collapse Models and the emergence of Classicality
We discuss the emergence of classical trajectories in Bohmian Mechanics (BM),
when a macroscopic object interacts with an external environment. We show that
in such a case the conditional wave function of the system follows a dynamics
which, under reasonable assumptions, corresponds to that of the
Ghirardi-Rimini-Weber (GRW) collapse model. As a consequence, Bohmian
trajectories evolve classically. Our analysis also shows how the GRW
(istantaneous) collapse process can be derived by an underlying continuous
interaction of a quantum system with an external agent, thus throwing a light
on how collapses can emerge from a deeper level theory.Comment: 19 pages, 2 figure
Loss of coherence of matter-wave interferometer from fluctuating graviton bath
In this paper we consider non-relativistic matter-wave interferometer coupled
with a quantum graviton bath and discuss the loss of coherence in
the matter sector due to the matter-graviton vertex. First of all, such a
process does not lead to any entanglement, but nonetheless the on-shell
scattering diagram can lead to loss of coherence as we will show. Importantly,
we will show that graviton emission is the only one-vertex Feynman-diagram
which is consistent with the conservation of energy and momentum
at the dominant order . We will find that the
resulting dephasing is extremely mild and hardly places any constraints on
matter-wave interferometers in the mesoscopic regime. In particular, the show
that the corresponding loss of coherence in the recently proposed experiment
which would test quantum aspects of graviton via entanglement of
two matter-wave interferometers is completely negligible.Comment: 10 pages, 2 figure
Precession Motion in Levitated Optomechanics
We investigate experimentally the dynamics of a non-spherical levitated
nanoparticle in vacuum. In addition to translation and rotation motion, we
observe the light torque-induced precession and nutation of the trapped
particle. We provide a theoretical model, which we numerically simulate and
from which we derive approximate expressions for the motional frequencies.
Both, the simulation and approximate expressions, we find in good agreement
with experiments. We measure a torque of Nm at mbar, with an estimated torque sensitivity of Nm/ at mbar.Comment: 10 pages, 4 figure
Gravitational decoherence by the apparatus in the quantum-gravity induced entanglement of masses
One of the outstanding questions in modern physics is how to test whether
gravity is classical or quantum in a laboratory. Recently there has been a
proposal to test the quantum nature of gravity by creating quantum
superpositions of two nearby neutral masses, close enough that the quantum
nature of gravity can entangle the two quantum systems, but still sufficiently
far away that all other known Standard Model interactions remain negligible.
However, the mere process of preparing superposition states of a neutral mass
(the light system), requires the vicinity of laboratory apparatus (the heavy
system). We will suppose that such a heavy system can be modelled as another
quantum system; since gravity is universal, the lighter system can get
entangled with the heavier system, providing an inherent source of
gravitational decoherence. In this paper, we will consider two light and two
heavy quantum oscillators, forming pairs of probe-detector systems, and study
under what conditions the entanglement between two light systems evades the
decoherence induced by the heavy systems. We conclude by estimating the
magnitude of the decoherence in the proposed experiment for testing the quantum
nature of gravity.Comment: 14 pages, 4 figure
Quantum Gravitational Sensor for Space Debris
Matter-wave interferometers have fundamental applications for gravity
experiments such as testing the equivalence principle and the quantum nature of
gravity. In addition, matter-wave interferometers can be used as quantum
sensors to measure the local gravitational acceleration caused by external
massive moving objects, thus lending itself for technological applications. In
this paper, we will establish a three dimensional model to describe the gravity
gradient signal from an external moving object, and theoretically investigate
the achievable sensitivities using the matter-wave interferometer based on the
Stern-Gerlach set-up. As an application we will consider the Mesoscopic
Interference for Metric and Curvature (MIMAC) and Gravitational wave detection
scheme [New J. Phys. 22, 083012 (2020)] and quantify its sensitivity to gravity
gradients using frequency-space analysis. We will consider objects near
Earth-based experiments and space debris in proximity of satellites and
estimate the minimum detectable mass of the object as a function of their
distance, velocity, and orientation.Comment: 13 pages, 8 figure
Optimal Superpositions for Particle Detection via Quantum Phase
Exploiting quantum mechanics for sensing offers unprecedented possibilities.
State of the art proposals for novel quantum sensors often rely on the creation
of large superpositions and generally detect a field. However, what is the
optimal superposition size for detecting an incident particle (or an incident
stream of particles) from a specific direction? This question is nontrivial as,
in general, this incident particle will scatter off with varied momenta,
imparting varied recoils to the sensor, resulting in decoherence rather than a
well defined measurable phase. By considering scattering interactions of
directional particulate environments with a system in a quantum superposition,
we find that there is an "optimal superposition" size for measuring incoming
particles via a relative phase. As a consequence of the anisotropy of the
environment, we observe a novel feature in the limiting behaviour of the real
and imaginary parts of the system's density matrix, linking the optimality of
the superposition size to the wavelength of the scatterer.Comment: 6 page