- Published on 23 January 2019
Study improves the lower boundary and secret key capacity of an encryption channel
The secure encryption of information units based on a method called quantum key distribution (QKD) involves distributing secret keys between two parties - namely, Alice, the sender, and Bob, the receiver - by using quantum systems as information carriers. However, the most advanced quantum technology, QKD, is currently limited by the channel's capacity to send or share secret bits. In a recent study published in EPJ D, Gan Wang, who is affiliated with both Peking University, Bejing, China, and the University of York, UK, and colleagues show how to better approach the secret key capacity by improving the channel's lower boundary.
- Published on 22 January 2019
New study yields more precise characterisation of monogamous and polygamous entanglement of quantum information units
Encrypted communication is achieved by sending quantum information in basic units called quantum bits, or qubits. The most basic type of quantum information processing is quantum entanglement. However, this process remains poorly understood. Better controlling quantum entanglement could help to improve quantum teleportation, the development of quantum computers, and quantum cryptography. Now, a team of Chinese physicists have focused on finding ways to enhance the reliability of quantum secret sharing. In a new study published in EPJ D, Zhaonan Zhang from Shaanxi Normal University, Xi'an, China, and colleagues provide a much finer characterisation of the distributions of entanglement in multi-qubit systems than previously available. In the context of quantum cryptography, these findings can be used to estimate the quantity of information an eavesdropper can capture regarding the secret encryption key.
- Published on 14 November 2018
New model helps understand compound nanomolecules made of football-shaped fullerenes
What in the smart nanomaterials world is widely available, highly symmetrical and inexpensive? Hollow carbon structures, shaped like a football, called fullerenes. Their applications range from artificial photosynthesis and nonlinear optics to the production of photoactive films and nanostructures. To make them even more flexible, fullerenes can be combined with added nanostructures. In a new study published in EPJ D, Kirill B. Agapev from ITMO University, St. Petersburg, Russia, and colleagues have developed a method that can be used for future simulations of fullerene complexes and thus help understand their characteristics.
- Published on 13 November 2018
New energy states reached by electrons entering resonance in three-particle systems may open the door to using similar calculations in atomic and nuclear physics
Positrons are short-lived subatomic particle with the same mass as electrons and a positive charge. They are used in medicine, e.g. in positron emission tomography (PET), a diagnostic imaging method for metabolic disorders. Positrons also exist as negatively charged ions, called positronium ions (Ps-), which are essentially a three-particle system consisting of two electrons bound to a positron.
Now, commercially available lasers are capable of producing photons that carry enough energy to bring the electrons of negatively charge ions, like Ps−, to doubly-excited states, referred to as D-wave resonance. Positronium ions are, however, very difficult to observe because they are unstable and often disappear before physicists get a chance to analyse them.
Sabyasachi Kar from the Harbin Institute of Technology, China, and Yew Kam Ho from the Academia Sinica, Taipei, Taiwan, have now characterised these higher energy levels reached by electrons in resonance in these three-particle systems, which are too complex to be described using simple equations. This theoretical model, recently published in EPJ D, is intended to offer guidance for experimentalists interested in observing these resonant structures. This model of a three-particle system can be adapted to problems in atomic physics, nuclear physics, and semiconductor quantum dots, as well as antimatter physics and cosmology.
- Published on 01 October 2018
A team of Chinese physicists has published a study explaining how to turn low-intensity infra-red beams into high-intensity X-ray beams, opening the door to ultra-fast pulsed energy sources for ultra-high time resolution probes
Attosecond pulses enable physicists to probe dynamic processes in matter with unprecedented time resolution. This means such technology can provide better insights into the dynamics of electrons in molecules. Devising a source of ultra-fast X-ray pulsating in the attosecond range is no mean feat. Comparing an attosecond is to a second is the equivalent of comparing a second to about 31.71 billion years. Now, a team of physicists from China has exploited an optical phenomenon, opening the door to creating high-order oscillations in existing light sources. This makes it possible to shift the frequency of the original source into X-rays with a laser beam source pulsating in an ultra-fast manner, to reach the attosecond range. The trouble is that yield of such higher order oscillations decreases as the source laser wavelength increases. In a new study published in EPJ D, Liqiang Feng and Yi Li from Liaoning University of Technology, Jinzhou, China, have developed a method to select, enhance and extend the higher order emission peak from a laser beam changing from ultraviolet to a mid-infrared.
EPJD Editor-in-Chief Tommaso Calarco appointed Director of Institute of Quantum Control at Peter Grünberg Institute
- Published on 27 September 2018
Prof Dr Tommaso Calarco, Editor-in-Chief of EPJ D, has recently been appointed Director of the Institute of Quantum Control at the Peter Grünberg Institute (PGI), Forschungszentrum Jülich. The PGI is dedicated to fundamental research on novel physical concepts and emerging materials in information technology and related fields. It also provides a state-of-the-art platform for the development of process technologies, devices and innovative nanoelectronic material systems. The Institute of Quantum Control develops and applies theoretical methods to achieve optimal performance of quantum technological tasks in these and other systems.
- Published on 22 August 2018
New model explains interactions between small copper clusters used as low-cost catalysts in the production of hydrogen by breaking down water molecules
Copper nanoparticles dispersed in water or in the form of coatings have a range of promising applications, including lubrication, ink jet printing, as luminescent probes, exploiting their antimicrobial and antifungal activity, and in fuel cells. Another promising application is using copper as a catalyst to split water molecules and form molecular hydrogen in gaseous form. At the heart of the reaction, copper-water complexes are synthesised in ultra-cold helium nanodroplets as part of the hydrogen production process, according to a recent paper published in EPJ D. For its authors, Stefan Raggl, from the University of Innsbruck, Austria, and colleagues, splitting water like this is a good way of avoiding splitting hairs.
- Published on 11 July 2018
Quantum secret-sharing scheme for noisy environments
To protect the confidentiality of a message during its transmission, people encrypt it. However, noise in the transmission channels can be a source of concern regarding how faithful the message transmission may be after it has been decrypted. This is particularly important for secrets shared using quantum scale messengers. For example, a classical secret takes the shape of a string of zeros and ones, whereas a quantum secret is akin to an unknown quantum state of two entangled particles carrying the secret. This is because no two quantum particles can be in the same state at any given time. In a new study published in EPJ D, Chen-Ming Bai from Shaanxi Normal University, Xi’an, China, and colleagues calculate the degree of fidelity of the quantum secret once transmitted and explore how to avoid eavesdropping.
- Published on 12 June 2018
New study reveals theoretical calculation of new possible state for quantum particles which have received a photon
Quantum particles behave in mysterious ways. They are governed by laws of physics designed to reflect what is happening at smaller scales through quantum mechanics. Quantum state properties are generally very different to those of classical states. However, particles finding themselves in a coherent state are in a kind of quantum state which behaves like a classical state. Since their introduction by Erwin Schrödinger in 1926, coherent states of particles have found many applications in mathematical physics and quantum optics.
Now, for the first time, a team of mathematical physicists from Togo and Benin, call upon supersymmetry - a sub-discipline of quantum mechanics - to explain the behaviour of particles that have received a photon. These particles are subjected to particular potential energies known as shape-invariant potentials.
In a paper published in EPJ D, Komi Sodoga and colleagues affiliated with both the University of Lomé, Togo, and the University of Abomey-Calavi, in Cotonou, Benin, outline the details of their theory. These findings are relevant to scientists working on solving quantum optics and quantum mechanics applications.
- Published on 15 May 2018
The field of experimental positronium physics has advanced significantly in the last few decades, with new areas of research driven by the development of techniques for trapping and manipulating positrons using Surko-type buffer gas traps. Large numbers of positrons (typically ≥106) accumulated in such a device may be ejected all at once, so as to generate an intense pulse.