1,478 research outputs found
Bragg reflection waveguide as a source of wavelength-multiplexed polarization-entangled photon pairs
We put forward a new highly efficient source of paired photons entangled in
polarization with an ultra-large bandwidth. The photons are generated by means
of a conveniently designed spontaneous parametric down-conversion process in a
semiconductor type-II Bragg reflection waveguide. The proposed scheme aims at
being a key element of an integrated source of polarization-entangled photon
pairs highly suitable for its use in a multi-user quantum-key-distribution
system
Efficient single-photon-assisted entanglement concentration for partially entangled photon pairs
We present two realistic entanglement concentration protocols (ECPs) for pure
partially entangled photons. A partially entangled photon pair can be
concentrated to a maximally entangled pair with only an ancillary single photon
in a certain probability, while the conventional ones require two copies of
partially entangled pairs at least. Our first protocol is implemented with
linear optics and the second one is implemented with cross-Kerr nonlinearities.
Compared with other ECPs, they do not need to know the accurate coefficients of
the initial state. With linear optics, it is feasible with current experiment.
With cross-Kerr nonlinearities, it does not require the sophisticated
single-photon detectors and can be repeated to get a higher success
probability. Moreover, the second protocol can get the higher entanglement
transformation efficiency and it maybe the most economical one by far.
Meanwhile, both of protocols are more suitable for multi-photon system
concentration, because they need less operations and classical communications.
All these advantages make two protocols be useful in current long-distance
quantum communications
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
- …