10 research outputs found
Probing anharmonicity of a quantum oscillator in an optomechanical cavity
We present a way of measuring with high precision the anharmonicity of a
quantum oscillator coupled to an optical field via radiation pressure. Our
protocol uses a sequence of pulsed interactions to perform a loop in the phase
space of the mechanical oscillator, which is prepared in a thermal state. We
show how the optical field acquires a phase depending on the anharmonicity.
Remarkably, one only needs small initial cooling of the mechanical motion to
probe even small anharmonicities. Finally, by applying tools from quantum
estimation theory, we calculate the ultimate bound on the estimation precision
posed by quantum mechanics and compare it with the precision obtainable with
feasible measurements such as homodyne and heterodyne detection on the cavity
field. In particular we demonstrate that homodyne detection is nearly optimal
in the limit of a large number of photons of the field and we discuss the
estimation precision of small anharmonicities in terms of its signal-to-noise
ratio.Comment: 8 pages, 2 figures, RevTeX
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
Experimental Scattershot Boson Sampling
Boson Sampling is a computational task strongly believed to be hard for
classical computers, but efficiently solvable by orchestrated bosonic
interference in a specialised quantum computer. Current experimental schemes,
however, are still insufficient for a convincing demonstration of the advantage
of quantum over classical computation. A new variation of this task,
Scattershot Boson Sampling, leads to an exponential increase in speed of the
quantum device, using a larger number of photon sources based on parametric
downconversion. This is achieved by having multiple heralded single photons
being sent, shot by shot, into different random input ports of the
interferometer. Here we report the first Scattershot Boson Sampling
experiments, where six different photon-pair sources are coupled to integrated
photonic circuits. We employ recently proposed statistical tools to analyse our
experimental data, providing strong evidence that our photonic quantum
simulator works as expected. This approach represents an important leap toward
a convincing experimental demonstration of the quantum computational supremacy.Comment: 8 pages, 5 figures (plus Supplementary Materials, 14 pages, 8
figures
Quantumness in optomechanics
Cavity optomechanics has become an established and equally promising branch in quantum optics. Thanks to the interaction between matter and electromagnetic radiation, it has proved to be an optimal platform for a range of scopes, from weak force sensing to the study of non-classicality of mechanical motion. Besides, the capability to isolate genuine quantum features of the interaction represents a test ground to address many important questions regarding decoherence, quantum-to-classical transitions and the interface between quantum mechanics and gravity.
The first part of the research embedded in this thesis is addressed towards the clear identification and characterisation of quantum features in optomechanics. The main model we will refer to is a deformable Fabry-P\'erot cavity where one of the two mirrors moves under the radiation pressure of light. After having properly assessed the quantum peculiarities of the system, and also having revised some intakes from past literature, we will focus on the study of mechanical non-linearities, as they have been proved to be a key resource to bring out and enhance quantum properties. These investigations provide the basis to eventually propose a method to deterministically prepare and measure macroscopic quantum superposition states of the movable mirror. Such massive quantum states play a key role to inspect the foundations of physics, e.g. to test the collapse of the wave function and phenomenological models of quantum gravity, as well as to develop new enhanced quantum technologies.Open Acces