14 research outputs found
Interaction-based quantum metrology showing scaling beyond the Heisenberg limit
Quantum metrology studies the use of entanglement and other quantum resources
to improve precision measurement. An interferometer using N independent
particles to measure a parameter X can achieve at best the "standard quantum
limit" (SQL) of sensitivity {\delta}X \propto N^{-1/2}. The same interferometer
using N entangled particles can achieve in principle the "Heisenberg limit"
{\delta}X \propto N^{-1}, using exotic states. Recent theoretical work argues
that interactions among particles may be a valuable resource for quantum
metrology, allowing scaling beyond the Heisenberg limit. Specifically, a
k-particle interaction will produce sensitivity {\delta}X \propto N^{-k} with
appropriate entangled states and {\delta}X \propto N^{-(k-1/2)} even without
entanglement. Here we demonstrate this "super-Heisenberg" scaling in a
nonlinear, non-destructive measurement of the magnetisation of an atomic
ensemble. We use fast optical nonlinearities to generate a pairwise
photon-photon interaction (k = 2) while preserving quantum-noise-limited
performance, to produce {\delta}X \propto N^{-3/2}. We observe super-Heisenberg
scaling over two orders of magnitude in N, limited at large N by higher-order
nonlinear effects, in good agreement with theory. For a measurement of limited
duration, super-Heisenberg scaling allows the nonlinear measurement to overtake
in sensitivity a comparable linear measurement with the same number of photons.
In other scenarios, however, higher-order nonlinearities prevent this crossover
from occurring, reflecting the subtle relationship of scaling to sensitivity in
nonlinear systems. This work shows that inter-particle interactions can improve
sensitivity in a quantum-limited measurement, and introduces a fundamentally
new resource for quantum metrology
Strong and Tunable Nonlinear Optomechanical Coupling in a Low-Loss System
A major goal in optomechanics is to observe and control quantum behavior in a
system consisting of a mechanical resonator coupled to an optical cavity. Work
towards this goal has focused on increasing the strength of the coupling
between the mechanical and optical degrees of freedom; however, the form of
this coupling is crucial in determining which phenomena can be observed in such
a system. Here we demonstrate that avoided crossings in the spectrum of an
optical cavity containing a flexible dielectric membrane allow us to realize
several different forms of the optomechanical coupling. These include cavity
detunings that are (to lowest order) linear, quadratic, or quartic in the
membrane's displacement, and a cavity finesse that is linear in (or independent
of) the membrane's displacement. All these couplings are realized in a single
device with extremely low optical loss and can be tuned over a wide range in
situ; in particular, we find that the quadratic coupling can be increased three
orders of magnitude beyond previous devices. As a result of these advances, the
device presented here should be capable of demonstrating the quantization of
the membrane's mechanical energy.Comment: 12 pages, 4 figures, 1 tabl
Constraints on Non-Newtonian Gravity from Recent Casimir Force Measurements
Corrections to Newton's gravitational law inspired by extra dimensional
physics and by the exchange of light and massless elementary particles between
the atoms of two macrobodies are considered. These corrections can be described
by the potentials of Yukawa-type and by the power-type potentials with
different powers. The strongest up to date constraints on the corrections to
Newton's gravitational law are reviewed following from the E\"{o}tvos- and
Cavendish-type experiments and from the measurements of the Casimir and van der
Waals force. We show that the recent measurements of the Casimir force gave the
possibility to strengthen the previously known constraints on the constants of
hypothetical interactions up to several thousand times in a wide interaction
range. Further strengthening is expected in near future that makes Casimir
force measurements a prospective test for the predictions of fundamental
physical theories.Comment: 20 pages, crckbked.cls is used, to be published in: Proceedings of
the 18th Course of the School on Cosmology and Gravitation: The Gravitational
Constant. Generalized Gravitational Theories and Experiments (30 April- 10
May 2003, Erice). Ed. by G. T. Gillies, V. N. Melnikov and V. de Sabbata,
20pp. (Kluwer, in print, 2003
Back-action Evading Measurements of Nanomechanical Motion
When performing continuous measurements of position with sensitivity
approaching quantum mechanical limits, one must confront the fundamental
effects of detector back-action. Back-action forces are responsible for the
ultimate limit on continuous position detection, can also be harnessed to cool
the observed structure, and are expected to generate quantum entanglement.
Back-action can also be evaded, allowing measurements with sensitivities that
exceed the standard quantum limit, and potentially allowing for the generation
of quantum squeezed states. We realize a device based on the parametric
coupling between an ultra-low dissipation nanomechanical resonator and a
microwave resonator. Here we demonstrate back-action evading (BAE) detection of
a single quadrature of motion with sensitivity 4 times the quantum zero-point
motion, back-action cooling of the mechanical resonator to n = 12 quanta, and a
parametric mechanical pre-amplification effect which is harnessed to achieve
position resolution a factor 1.3 times quantum zero-point motion.Comment: 19 pages (double-spaced) including 4 figures and reference
Gravitational-wave research as an emerging field in the Max Planck Society. The long roots of GEO600 and of the Albert Einstein Institute
On the occasion of the 50th anniversary since the beginning of the search for
gravitational waves at the Max Planck Society, and in coincidence with the 25th
anniversary of the foundation of the Albert Einstein Institute, we explore the
interplay between the renaissance of general relativity and the advent of
relativistic astrophysics following the German early involvement in
gravitational-wave research, to the point when gravitational-wave detection
became established by the appearance of full-scale detectors and international
collaborations. On the background of the spectacular astrophysical discoveries
of the 1960s and the growing role of relativistic astrophysics, Ludwig Biermann
and his collaborators at the Max Planck Institute for Astrophysics in Munich
became deeply involved in research related to such new horizons. At the end of
the 1960s, Joseph Weber's announcements claiming detection of gravitational
waves sparked the decisive entry of this group into the field, in parallel with
the appointment of the renowned relativist Juergen Ehlers. The Munich area
group of Max Planck institutes provided the fertile ground for acquiring a
leading position in the 1970s, facilitating the experimental transition from
resonant bars towards laser interferometry and its innovation at increasingly
large scales, eventually moving to a dedicated site in Hannover in the early
1990s. The Hannover group emphasized perfecting experimental systems at pilot
scales, and never developed a full-sized detector, rather joining the LIGO
Scientific Collaboration at the end of the century. In parallel, the Max Planck
Institute for Gravitational Physics (Albert Einstein Institute) had been
founded in Potsdam, and both sites, in Hannover and Potsdam, became a unified
entity in the early 2000s and were central contributors to the first detection
of gravitational waves in 2015.Comment: 94 pages. Enlarged version including new results from further
archival research. A previous version appears as a chapter in the volume The
Renaissance of General Relativity in Context, edited by A. Blum, R. Lalli and
J. Renn (Boston: Birkhauser, 2020