8,804 research outputs found
Event-based simulation of quantum physics experiments
We review an event-based simulation approach which reproduces the statistical
distributions of wave theory not by requiring the knowledge of the solution of
the wave equation of the whole system but by generating detection events
one-by-one according to an unknown distribution. We illustrate its
applicability to various single photon and single neutron interferometry
experiments and to two Bell test experiments, a single-photon
Einstein-Podolsky-Rosen experiment employing post-selection for photon pair
identification and a single-neutron Bell test interferometry experiment with
nearly detection efficiency.Comment: Lectures notes of the Advanced School on Quantum Foundations and Open
Quantum Systems, Jo\~ao Pessoa, Brazil, July 2012, edited by T. M.
Nieuwenhuizen et al, World Scientific, to appea
Light-mediated strong coupling between a mechanical oscillator and atomic spins one meter apart
Engineering strong interactions between quantum systems is essential for many
phenomena of quantum physics and technology. Typically, strong coupling relies
on short-range forces or on placing the systems in high-quality electromagnetic
resonators, restricting the range of the coupling to small distances. We use a
free-space laser beam to strongly couple a collective atomic spin and a
micromechanical membrane over a distance of one meter in a room-temperature
environment. The coupling is highly tunable and allows the observation of
normal-mode splitting, coherent energy exchange oscillations, two-mode thermal
noise squeezing and dissipative coupling. Our approach to engineer coherent
long-distance interactions with light makes it possible to couple very
different systems in a modular way, opening up a range of opportunities for
quantum control and coherent feedback networks.Comment: 24 pages, 9 figure
Thermally-Reconfigurable Quantum Photonic Circuits at Telecom Wavelength by Femtosecond Laser Micromachining
The importance of integrated quantum photonics in the telecom band resides on
the possibility of interfacing with the optical network infrastructure
developed for classical communications. In this framework, femtosecond laser
written integrated photonic circuits, already assessed for quantum information
experiments in the 800 nm wavelength range, have great potentials. In fact
these circuits, written in glass, can be perfectly mode-matched at telecom
wavelength to the in/out coupling fibers, which is a key requirement for a
low-loss processing node in future quantum optical networks. In addition, for
several applications quantum photonic devices will also need to be dynamically
reconfigurable. Here we experimentally demonstrate the high performance of
femtosecond laser written photonic circuits for quantum experiments in the
telecom band and we show the use of thermal shifters, also fabricated by the
same femtosecond laser, to accurately tune them. State-of-the-art manipulation
of single and two-photon states is demonstrated, with fringe visibilities
greater than 95%. This opens the way to the realization of reconfigurable
quantum photonic circuits on this technological platform
High-sensitivity monitoring of micromechanical vibration using optical whispering gallery mode resonators
The inherent coupling of optical and mechanical modes in high finesse optical
microresonators provide a natural, highly sensitive transduction mechanism for
micromechanical vibrations. Using homodyne and polarization spectroscopy
techniques, we achieve shot-noise limited displacement sensitivities of
10^(-19) m Hz^(-1/2). In an unprecedented manner, this enables the detection
and study of a variety of mechanical modes, which are identified as radial
breathing, flexural and torsional modes using 3-dimensional finite element
modelling. Furthermore, a broadband equivalent displacement noise is measured
and found to agree well with models for thermorefractive noise in silica
dielectric cavities. Implications for ground-state cooling, displacement
sensing and Kerr squeezing are discussed.Comment: 25 pages, 8 figure
Event-based simulation of neutron experiments: interference, entanglement and uncertainty relations
We discuss a discrete-event simulation approach, which has been shown to give
a unified cause-and-effect description of many quantum optics and
single-neutron interferometry experiments. The event-based simulation algorithm
does not require the knowledge of the solution of a wave equation of the whole
system, yet reproduces the corresponding statistical distributions by
generating detection events one-by-one. It is showm that single-particle
interference and entanglement, two important quantum phenomena, emerge via
information exchange between individual particles and devices such as beam
splitters, polarizers and detectors. We demonstrate this by reproducing the
results of several single-neutron interferometry experiments, including one
that demonstrates interference and one that demonstrates the violation of a
Bell-type inequality. We also present event-based simulation results of a
single neutron experiment designed to test the validity of Ozawa's universally
valid error-disturbance relation, an uncertainty relation derived using the
theory of general quantum measurements.Comment: Invited paper presented at the EmQM13 Workshop on Emergent Quantum
Mechanics, Austrian Academy of Sciences (October 3-6, 2013, Vienna
Single vortex-antivortex pair in an exciton polariton condensate
In a homogeneous two-dimensional system at non-zero temperature, although
there can be no ordering of infinite range, a superfluid phase is predicted for
a Bose liquid. The stabilization of phase in this superfluid regime is achieved
by the formation of bound vortex-antivortex pairs. It is believed that several
different systems share this common behaviour, when the parameter describing
their ordered state has two degrees of freedom, and the theory has been tested
for some of them. However, there has been no direct experimental observation of
the phase stabilization mechanism by a bound pair. Here we present an
experimental technique that can identify a single vortex-antivortex pair in a
two-dimensional exciton polariton condensate. The pair is generated by the
inhomogeneous pumping spot profile, and is revealed in the time-integrated
phase maps acquired using Michelson interferometry, which show that the
condensate phase is only locally disturbed. Numerical modelling based on open
dissipative Gross-Pitaevskii equation suggests that the pair evolution is quite
different in this non-equilibrium system compared to atomic condensates. Our
results demonstrate that the exciton polariton condensate is a unique system
for studying two-dimensional superfluidity in a previously inaccessible regime
Optical pumping of a lithium atomic beam for atom interferometry
We apply optical pumping to prepare the lithium beam of our atom
interferometer in a single hyperfine-Zeeman sublevel: we use two components of
the D1-line for pumping the 7Li atoms in a dark state F,mF=+2 (or -2) sublevel.
The optical pumping efficiency has been characterized by two techniques:
state-selective laser atom deflection or magnetic dephasing of the atom
interferometer signals. The first technique has not achieved a high
sensitivity, because of a limited signal to noise ratio, but magnetic dephasing
signals have shown that about 95% of the population has been transferred in the
aimed sublevel, with similar results for three mean velocities of the atomic
beam covering the range 744-1520m/s
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