75 research outputs found
A quantum router for high-dimensional entanglement
In addition to being a workhorse for modern quantum technologies,
entanglement plays a key role in fundamental tests of quantum mechanics. The
entanglement of photons in multiple levels, or dimensions, explores the limits
of how large an entangled state can be, while also greatly expanding its
applications in quantum information. Here we show how a high-dimensional
quantum state of two photons entangled in their orbital angular momentum can be
split into two entangled states with a smaller dimensionality structure. Our
work demonstrates that entanglement is a quantum property that can be
subdivided into spatially separated parts. In addition, our technique has vast
potential applications in quantum as well as classical communication systems.Comment: 5 pages, 5 figure
Gouy Phase Radial Mode Sorter for Light: Concepts and Experiments
We present an in principle lossless sorter for radial modes of light, using
accumulated Gouy phases. The experimental setups have been found by a computer
algorithm, and can be intuitively understood in a geometric way. Together with
the ability to sort angular-momentum modes, we now have access to the complete
2-dimensional transverse plane of light. The device can readily be used in
multiplexing classical information. On a quantum level, it is an analog of the
Stern-Gerlach experiment -- significant for the discussion of fundamental
concepts in quantum physics. As such, it can be applied in high-dimensional and
multi-photonic quantum experiments.Comment: main text: 7 pages, 5 figures. Supplementary Information: 5 pages, 4
figure
Orbital angular momentum of photons and the entanglement of Laguerre-Gaussian modes
The identification of orbital angular momentum (OAM) as a fundamental
property of a beam of light nearly twenty-five years ago has led to an
extensive body of research around this topic. The possibility that single
photons can carry OAM has made this degree of freedom an ideal candidate for
the investigation of complex quantum phenomena and their applications. Research
in this direction has ranged from experiments on complex forms of quantum
entanglement to the interaction between light and quantum states of matter.
Furthermore, the use of OAM in quantum information has generated a lot of
excitement, as it allows for encoding large amounts of information on a single
photon. Here we explain the intuition that led to the first quantum experiment
with OAM fifteen years ago. We continue by reviewing some key experiments
investigating fundamental questions on photonic OAM and the first steps into
applying these properties in novel quantum protocols. In the end, we identify
several interesting open questions that could form the subject of future
investigations with OAM.Comment: 17 pages, 7 figures; close to accepted versio
Twisted Photons: New Quantum Perspectives in High Dimensions
Quantum information science and quantum information technology have seen a
virtual explosion world-wide. It is all based on the observation that
fundamental quantum phenomena on the individual particle or system-level lead
to completely novel ways of encoding, processing and transmitting information.
Quantum mechanics, a child of the first third of the 20th century, has found
numerous realizations and technical applications, much more than was thought at
the beginning. Decades later, it became possible to do experiments with
individual quantum particles and quantum systems. This was due to technological
progress, and for light in particular, the development of the laser. Hitherto,
nearly all experiments and also nearly all realizations in the fields have been
performed with qubits, which are two-level quantum systems. We suggest that
this limitation is again mainly a technological one, because it is very
difficult to create, manipulate and measure more complex quantum systems. Here,
we provide a specific overview of some recent developments with
higher-dimensional quantum systems. We mainly focus on Orbital Angular Momentum
(OAM) states of photons and possible applications in quantum information
protocols. Such states form discrete higher-dimensional quantum systems, also
called qudits. Specifically, we will first address the question what kind of
new fundamental properties exist and the quantum information applications which
are opened up by such novel systems. Then we give an overview of recent
developments in the field by discussing several notable experiments over the
past 2-3 years. Finally, we conclude with several important open questions
which will be interesting for investigations in the future.Comment: 15 pages, 7 figure
Complex Langevin: Boundary terms and application to QCD
We employ the Complex Langevin method for simulation of complex-valued
actions. First, we show how to test for convergence of the method by
explicitely computing boundary terms and demonstrate this in a model. Then we
investigate the deconfinement phase transition of QCD with
Wilson-fermions using the Complex Langevin Method and. We give preliminary
results for the transition temperatures up to and
compute the curvature coefficient .Comment: Proceedings for The 36th Annual International Symposium on Lattice
Field Theory - LATTICE2018; update: added some acknowledgement
Generation of the Complete Four-dimensional Bell Basis
The Bell basis is a distinctive set of maximally entangled two-particle
quantum states that forms the foundation for many quantum protocols such as
teleportation, dense coding and entanglement swapping. While the generation,
manipulation, and measurement of two-level quantum states is well understood,
the same is not true in higher dimensions. Here we present the experimental
generation of a complete set of Bell states in a four-dimensional Hilbert
space, comprising of 16 orthogonal entangled Bell-like states encoded in the
orbital angular momentum of photons. The states are created by the application
of generalized high-dimensional Pauli gates on an initial entangled state. Our
results pave the way for the application of high-dimensional quantum states in
complex quantum protocols such as quantum dense coding.Comment: 4 pages, 4 figure
Advances in High Dimensional Quantum Entanglement
Since its discovery in the last century, quantum entanglement has challenged
some of our most cherished classical views, such as locality and reality.
Today, the second quantum revolution is in full swing and promises to
revolutionize areas such as computation, communication, metrology, and imaging.
Here, we review conceptual and experimental advances in complex entangled
systems involving many multilevel quantum particles. We provide an overview of
the latest technological developments in the generation and manipulation of
high-dimensionally entangled photonic systems encoded in various discrete
degrees of freedom such as path, transverse spatial modes or time/frequency
bins. This overview should help to transfer various physical principles for the
generation and manipulation from one to another degree of freedom and thus
inspire new technical developments. We also show how purely academic questions
and curiosity led to new technological applications. Here fundamental research
provides the necessary knowledge for coming technologies such as a prospective
quantum internet or the quantum teleportation of all information stored in a
quantum system. Finally, we discuss some important problems in the area of
high-dimensional entanglement and give a brief outlook on possible future
developments.Comment: Comments and suggestions for additional references are welcome!
Updated affiliations onl
Quantum Experiments and Graphs II: Quantum Interference, Computation and State Generation
We present a conceptually new approach to describe state-of-the-art photonic
quantum experiments using Graph Theory. There, the quantum states are given by
the coherent superpositions of perfect matchings. The crucial observation is
that introducing complex weights in graphs naturally leads to quantum
interference. The new viewpoint immediately leads to many interesting results,
some of which we present here. Firstly, we identify a new and experimentally
completely unexplored multiphoton interference phenomenon. Secondly, we find
that computing the results of such experiments is #P-hard, which means it is a
classically intractable problem dealing with the computation of a matrix
function Permanent and its generalization Hafnian. Thirdly, we explain how a
recent no-go result applies generally to linear optical quantum experiments,
thus revealing important insights to quantum state generation with current
photonic technology. Fourthly, we show how to describe quantum protocols such
as entanglement swapping in a graphical way. The uncovered bridge between
quantum experiments and Graph Theory offers a novel perspective on a widely
used technology, and immediately raises many follow-up questions.Comment: 12+7 pages, 8+9 figure
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