270 research outputs found
Quantum optomechanics beyond the quantum coherent oscillation regime
Interaction with a thermal environment decoheres the quantum state of a
mechanical oscillator. When the interaction is sufficiently strong, such that
more than one thermal phonon is introduced within a period of oscillation,
quantum coherent oscillations are prevented. This is generally thought to
preclude a wide range of quantum protocols. Here, we introduce a pulsed
optomechanical protocol that allows ground state cooling, general linear
quantum non-demolition measurements, optomechanical state swaps, and quantum
state preparation and tomography without requiring quantum coherent
oscillations. Finally we show how the protocol can break the usual thermal
limit for sensing of impulse forces.Comment: 6 pages, 3 figure
Decommissioning of offshore oil and gas facilities: a comparative assessment of different scenarios
A material and energy flow analysis, with corresponding financial flows, was carried out for different decommissioning scenarios for the different elements of an offshore oil and gas structure. A comparative assessment was made of the non-financial (especially environmental) outcomes of the different scenarios, with the reference scenario being to leave all structures in situ, while other scenarios envisaged leaving them on the seabed or removing them to shore for recycling and disposal. The costs of each scenario, when compared with the reference scenario, give an implicit valuation of the non-financial outcomes (e.g. environmental improvements), should that scenario be adopted by society. The paper concludes that it is not clear that the removal of the topsides and jackets of large steel structures to shore, as currently required by regulations, is environmentally justified; that concrete structures should certainly be left in place; and that leaving footings, cuttings and pipelines in place, with subsequent monitoring, would also be justified unless very large values were placed by society on a clear seabed and trawling access
Quantum and Classical Phases in Optomechanics
The control of quantum systems requires the ability to change and read-out
the phase of a system. The non-commutativity of canonical conjugate operators
can induce phases on quantum systems, which can be employed for implementing
phase gates and for precision measurements. Here we study the phase acquired by
a radiation field after its radiation pressure interaction with a mechanical
oscillator, and compare the classical and quantum contributions. The classical
description can reproduce the nonlinearity induced by the mechanical oscillator
and the loss of correlations between mechanics and optical field at certain
interaction times. Such features alone are therefore insufficient for probing
the quantum nature of the interaction. Our results thus isolate genuine quantum
contributions of the optomechanical interaction that could be probed in current
experiments.Comment: 10 pages, 3 figure
Generation of mechanical interference fringes by multi-photon counting
Exploring the quantum behaviour of macroscopic objects provides an intriguing
avenue to study the foundations of physics and to develop a suite of
quantum-enhanced technologies. One prominent path of study is provided by
quantum optomechanics which utilizes the tools of quantum optics to control the
motion of macroscopic mechanical resonators. Despite excellent recent progress,
the preparation of mechanical quantum superposition states remains outstanding
due to weak coupling and thermal decoherence. Here we present a novel
optomechanical scheme that significantly relaxes these requirements allowing
the preparation of quantum superposition states of motion of a mechanical
resonator by exploiting the nonlinearity of multi-photon quantum measurements.
Our method is capable of generating non-classical mechanical states without the
need for strong single photon coupling, is resilient against optical loss, and
offers more favourable scaling against initial mechanical thermal occupation
than existing schemes. Moreover, our approach allows the generation of larger
superposition states by projecting the optical field onto NOON states. We
experimentally demonstrate this multi-photon-counting technique on a mechanical
thermal state in the classical limit and observe interference fringes in the
mechanical position distribution that show phase superresolution. This opens a
feasible route to explore and exploit quantum phenomena at a macroscopic scale.Comment: 16 pages, 4 figures. v1: submitted for review on 28 Jan 2016. v2:
significantly revised manuscript. v3: some further revisions and some extra
results included. v3: new results added, extra author added, close to
published version, supplementary material available with published versio
Non-linear optomechanical measurement of mechanical motion
Precision measurement of non-linear observables is an important goal in all
facets of quantum optics. This allows measurement-based non-classical state
preparation, which has been applied to great success in various physical
systems, and provides a route for quantum information processing with otherwise
linear interactions. In cavity optomechanics much progress has been made using
linear interactions and measurement, but observation of non-linear mechanical
degrees-of-freedom remains outstanding. Here we report the observation of
displacement-squared thermal motion of a micro-mechanical resonator by
exploiting the intrinsic non-linearity of the radiation pressure interaction.
Using this measurement we generate bimodal mechanical states of motion with
separations and feature sizes well below 100~pm. Future improvements to this
approach will allow the preparation of quantum superposition states, which can
be used to experimentally explore collapse models of the wavefunction and the
potential for mechanical-resonator-based quantum information and metrology
applications.Comment: 8 pages, 4 figures, extensive supplementary material available with
published versio
Contents
We introduce the `displacemon' electromechanical architecture that comprises
a vibrating nanobeam, e.g. a carbon nanotube, flux coupled to a superconducting
qubit. This platform can achieve strong and even ultrastrong coupling enabling
a variety of quantum protocols. We use this system to describe a protocol for
generating and measuring quantum interference between two trajectories of a
nanomechanical resonator. The scheme uses a sequence of qubit manipulations and
measurements to cool the resonator, apply an effective diffraction grating, and
measure the resulting interference pattern. We simulate the protocol for a
realistic system consisting of a vibrating carbon nanotube acting as a junction
in a superconducting qubit, and we demonstrate the feasibility of generating a
spatially distinct quantum superposition state of motion containing more than
nucleons.Comment: 12 pages, 7 figure
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