1,871 research outputs found
Photonic Entanglement for Fundamental Tests and Quantum Communication
Entanglement is at the heart of fundamental tests of quantum mechanics like
tests of Bell-inequalities and, as discovered lately, of quantum computation
and communication. Their technological advance made entangled photons play an
outstanding role in entanglement physics. We give a generalized concept of
qubit entanglement and review the state of the art of photonic experiments.Comment: 54 pages, 33 figures. Review article submitted to QIC (Rinton
Multi-photon entanglement and interferometry
Multi-photon interference reveals strictly non-classical phenomena. Its
applications range from fundamental tests of quantum mechanics to photonic
quantum information processing, where a significant fraction of key experiments
achieved so far comes from multi-photon state manipulation. We review the
progress, both theoretical and experimental, of this rapidly advancing
research. The emphasis is given to the creation of photonic entanglement of
various forms, tests of the completeness of quantum mechanics (in particular,
violations of local realism), quantum information protocols for quantum
communication (e.g., quantum teleportation, entanglement purification and
quantum repeater), and quantum computation with linear optics. We shall limit
the scope of our review to "few photon" phenomena involving measurements of
discrete observables.Comment: 71 pages, 38 figures; updated version accepted by Rev. Mod. Phy
Path-polarization hyperentangled and cluster states of photons on a chip
Encoding many qubits in different degrees of freedom (DOFs) of single photons
is one of the routes towards enlarging the Hilbert space spanned by a photonic
quantum state. Hyperentangled photon states (i.e. states showing entanglement
in multiple DOFs) have demonstrated significant implications for both
fundamental physics tests and quantum communication and computation. Increasing
the number of qubits of photonic experiments requires miniaturization and
integration of the basic elements and functions to guarantee the set-up
stability. This motivates the development of technologies allowing the precise
control of different photonic DOFs on a chip. We demonstrate the contextual use
of path and polarization qubits propagating within an integrated quantum
circuit. We tested the properties of four-qubit linear cluster states built on
both DOFs. Our results pave the way towards the full integration on a chip of
hybrid multiqubit multiphoton states.Comment: 7 pages, 7 figures, RevTex4-1, Light: Science & Applications
AAP:http://aap.nature-lsa.cn:8080/cms/accessory/files/AAP-lsa201664.pd
Complete experimental toolbox for alignment-free quantum communication
Quantum communication employs the counter-intuitive features of quantum
physics to perform tasks that are im- possible in the classical world. It is
crucial for testing the foundations of quantum theory and promises to rev-
olutionize our information and communication technolo- gies. However, for two
or more parties to execute even the simplest quantum transmission, they must
establish, and maintain, a shared reference frame. This introduces a
considerable overhead in communication resources, par- ticularly if the parties
are in motion or rotating relative to each other. We experimentally demonstrate
how to circumvent this problem with the efficient transmission of quantum
information encoded in rotationally invariant states of single photons. By
developing a complete toolbox for the efficient encoding and decoding of
quantum infor- mation in such photonic qubits, we demonstrate the fea- sibility
of alignment-free quantum key-distribution, and perform a proof-of-principle
alignment-free entanglement distribution and violation of a Bell inequality.
Our scheme should find applications in fundamental tests of quantum mechanics
and satellite-based quantum communication.Comment: Main manuscript: 7 pages, 3 figures; Supplementary Information: 7
pages, 3 figure
Energy efficient mining on a quantum-enabled blockchain using light
We outline a quantum-enabled blockchain architecture based on a consortium of
quantum servers. The network is hybridised, utilising digital systems for
sharing and processing classical information combined with a fibre--optic
infrastructure and quantum devices for transmitting and processing quantum
information. We deliver an energy efficient interactive mining protocol enacted
between clients and servers which uses quantum information encoded in light and
removes the need for trust in network infrastructure. Instead, clients on the
network need only trust the transparent network code, and that their devices
adhere to the rules of quantum physics. To demonstrate the energy efficiency of
the mining protocol, we elaborate upon the results of two previous experiments
(one performed over 1km of optical fibre) as applied to this work. Finally, we
address some key vulnerabilities, explore open questions, and observe
forward--compatibility with the quantum internet and quantum computing
technologies.Comment: 25 pages, 5 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
Polarization entangled photon-pair source based on quantum nonlinear photonics and interferometry
We present a versatile, high-brightness, guided-wave source of polarization
entangled photons, emitted at a telecom wavelength. Photon-pairs are generated
using an integrated type-0 nonlinear waveguide, and subsequently prepared in a
polarization entangled state via a stabilized fiber interferometer. We show
that the single photon emission wavelength can be tuned over more than 50 nm,
whereas the single photon spectral bandwidth can be chosen at will over more
than five orders of magnitude (from 25 MHz to 4 THz). Moreover, by performing
entanglement analysis, we demonstrate a high degree of control of the quantum
state via the violation of the Bell inequalities by more than 40 standard
deviations. This makes this scheme suitable for a wide range of quantum optics
experiments, ranging from fundamental research to quantum information
applications. We report on details of the setup, as well as on the
characterization of all included components, previously outlined in F. Kaiser
et al. (2013 Laser Phys. Lett. 10, 045202).Comment: 16 pages, 7 figure
Testing foundations of quantum mechanics with photons
The foundational ideas of quantum mechanics continue to give rise to
counterintuitive theories and physical effects that are in conflict with a
classical description of Nature. Experiments with light at the single photon
level have historically been at the forefront of tests of fundamental quantum
theory and new developments in photonics engineering continue to enable new
experiments. Here we review recent photonic experiments to test two
foundational themes in quantum mechanics: wave-particle duality, central to
recent complementarity and delayed-choice experiments; and Bell nonlocality
where recent theoretical and technological advances have allowed all
controversial loopholes to be separately addressed in different photonics
experiments.Comment: 10 pages, 5 figures, published as a Nature Physics Insight review
articl
Air-core fiber distribution of hybrid vector vortex-polarization entangled states
Entanglement distribution between distant parties is one of the most
important and challenging tasks in quantum communication. Distribution of
photonic entangled states using optical fiber links is a fundamental building
block towards quantum networks. Among the different degrees of freedom, orbital
angular momentum (OAM) is one of the most promising due to its natural
capability to encode high dimensional quantum states. In this article, we
experimentally demonstrate fiber distribution of hybrid polarization-vector
vortex entangled photon pairs. To this end, we exploit a recently developed
air-core fiber which supports OAM modes. High fidelity distribution of the
entangled states is demonstrated by performing quantum state tomography in the
polarization-OAM Hilbert space after fiber propagation, and by violations of
Bell inequalities and multipartite entanglement tests. The present results open
new scenarios for quantum applications where correlated complex states can be
transmitted by exploiting the vectorial nature of light
- …