14 research outputs found
How to rule out collapse models with BEC interferometry
The model of continuous spontaneous localization (CSL) is the most prominent
consistent modification of quantum mechanics predicting an objective
quantum-to-classical transition. Here we show that precision interferometry
with Bose-Einstein condensed atoms can serve to lower the current empirical
bound on the localization rate parameter by six orders of magnitude. This works
by focusing on the atom count distributions rather than just mean population
imbalances in the interferometric signal of squeezed BECs, without the need for
preparing highly entangled states. We discuss experimentally realistic
measurement schemes which could probe and potentially rule out the entire
relevant parameter space of CSL, including the historic values proposed by
Ghirardi, Rimini, and Weber, below which CSL is no longer deemed a viable
solution to the measurement problem of quantum mechanics.Comment: 7 pages, 1 figure, 1 tabl
Photon Bound States in Coupled Waveguides
Photon bound states have been identified as particular solutions to the
scattering of two photons from a single emitter, but from these results the
full nature of these states remains elusive. We study a novel, clear and
unambiguous signature that these bound states are truly bound. To this end we
consider a new configuration of close-by waveguides, each chirally coupled to
two-level emitters. We show that in this system the photon bound states behave
like rigid molecules, where photons do not tunnel individually but rather
collectively, such that there is rarely a single photon in each waveguide. We
further identify new classes of bound states in this system.Comment: 8 pages, 7 figure
Macroscopicity of quantum mechanical superposition tests via hypothesis falsification
We establish an objective scheme to determine the macroscopicity of quantum
mechanical superposition tests, which is based on the Bayesian hypothesis
falsification of macrorealistic modifications of quantum theory. The measure
uses the raw data gathered in an experiment, taking into account all
measurement uncertainties, and can be used to directly assess any conceivable
quantum test. We determine the resulting macroscopicity for three recent tests
of quantum physics: double-well interference of Bose-Einstein condensates,
Leggett-Garg tests with atomic random walks, and entanglement generation and
read-out of nanomechanical oscillators.Comment: 20 pages, 7 figure
Probing Macroscopic Quantum Superpositions with Nanorotors
Whether quantum physics is universally valid is an open question with
far-reaching implications. Intense research is therefore invested into testing
the quantum superposition principle with ever heavier and more complex objects.
Here we propose a radically new, experimentally viable route towards studies at
the quantum-to-classical borderline by probing the orientational quantum
revivals of a nanoscale rigid rotor. The proposed interference experiment
testifies a macroscopic superposition of all possible orientations. It requires
no diffraction grating, uses only a single levitated particle, and works with
moderate motional temperatures under realistic environmental conditions. The
first exploitation of quantum rotations of a massive object opens the door to
new tests of quantum physics with submicron particles and to quantum gyroscopic
torque sensors, holding the potential to improve state-of-the art devices by
many orders of magnitude.Comment: 15 pages, 4 figure
Macroscopic quantum test with bulk acoustic wave resonators
Recently, solid-state mechanical resonators have become a platform for
demonstrating non-classical behavior of systems involving a truly macroscopic
number of particles. Here, we perform the most macroscopic quantum test in a
mechanical resonator to date, which probes the validity of quantum mechanics at
the microgram mass scale. This is done by a direct measurement of the Wigner
function of a high-overtone bulk acoustic wave resonator mode, monitoring the
gradual decay of negativities over tens of microseconds. While the obtained
macroscopicity of is on par with state-of-the-art atom
interferometers, future improvements of mode geometry and coherence times could
confirm the quantum superposition principle at unprecedented scales.Comment: 5+9 pages, 2+6 figures, comments are welcom
Violation of Bell inequality by photon scattering on a two-level emitter
Entanglement, the non-local correlations present in multipartite quantum
systems, is a curious feature of quantum mechanics and the fuel of quantum
technology. It is therefore a major priority to develop energy-conserving and
simple methods for generating high-fidelity entangled states. In the case of
light, entanglement can be realized by interactions with matter, although the
required nonlinear interaction is typically weak, thereby limiting its
applicability. Here, we show how a single two-level emitter deterministically
coupled to light in a nanophotonic waveguide is used to realize genuine
photonic quantum entanglement for excitation at the single photon level. By
virtue of the efficient optical coupling, two-photon interactions are strongly
mediated by the emitter realizing a giant nonlinearity that leads to
entanglement. We experimentally generate and verify energy-time entanglement by
violating a Bell inequality (Clauder-Horne-Shimony-Holt Bell parameter of
) in an interferometric measurement of the two-photon scattering
response. As an attractive feature of this approach, the two-level emitter acts
as a passive scatterer initially prepared in the ground state, i.e., no
advanced spin control is required. This experiment is a fundamental advancement
that may pave a new route for ultra-low energy-consuming synthesis of photonic
entangled states for quantum simulators or metrology.Comment: the manuscript of 6 pages with 3 figures and a Supplementary Material
file of 12 pages with 7 figure
Quantum-classical hypothesis tests in macroscopic matter-wave interferometry
We assess the most macroscopic matter-wave experiments to date as to the extent to which they probe the quantum-classical boundary by demonstrating interference of heavy molecules and cold atomic ensembles. To this end, we consider a rigorous Bayesian test protocol for a parametrized set of hypothetical modifications of quantum theory, including well-studied spontaneous collapse models, that destroy superpositions and reinstate macrorealism. The range of modification parameters ruled out by the measurement events quantifies the macroscopicity of a quantum experiment, while the shape of the posterior distribution resulting from the Bayesian update reveals how conclusive the data are at testing macrorealism. This protocol may serve as a guide for the design of future matter-wave experiments ever closer to truly macroscopic scales