Light pulses in a quantum walk

The principle of quantum random motion in two dimensions: At a node, a light pulse can continue on its journey through a network of optical fibres in four directions: forwards, backwards, to the right or to the left. As a quantum object, it is in fact at all the locations that are on the possible routes to a destination. Credit: MPI for the Science of Light/University of Paderborn 

Tourists who drift aimlessly during a sightseeing tour are moving randomly - just like electrons that move from one atom to the next. To obtain a better understanding of these random motions it is often useful to reduce their complexity. Physicists do this by simulating random walks. These simulations can bring new insights in the quantum world as well. Researchers at the Max Planck Institute for the Science of Light and the University of Paderborn and their colleagues are now the first to successfully realize an arrangement for a quantum walk in two dimensions. The experimental setup can be used to investigate many quantum phenomena.

in PhysOrg

Multidimensional quantum walks can exhibit highly nontrivial topological structure, providing a powerful tool for simulating quantum information and transport systems. We present a flexible implementation of a two-dimensional (2D) optical quantum walk on a lattice, demonstrating a scalable quantum walk on a nontrivial graph structure. We realized a coherent quantum walk over 12 steps and 169 positions using an optical fiber network. With our broad spectrum of quantum coins, we were able to simulate the creation of entanglement in bipartite systems with conditioned interactions. Introducing dynamic control allowed for the investigation of effects such as strong nonlinearities or two-particle scattering. Our results illustrate the potential of quantum walks as a route for simulating and understanding complex quantum systems.

in ScienceMag

 

Einstein Archive

The Hebrew University of Jerusalem started uploading digitized documents from its massive Einstein archive. 

The archive contains over 80,000 documents, and includes scientific correspondences, letters that Einstein wrote to family members and even love letters. 

http://www.alberteinstein.info

Dissecting the Pinguin

Flip Tanedo wrote a great post about one of the amusing tales in particle physics: The story of how the “penguin diagram” got its name. Taneda won’t go into that in his post, instead, he will make use of some of the tools developed with Feynman diagrams to understand the physics behind these ‘penguin’ diagrams. In doing so, he will have a nice playground to really make use of what we’ve learned so far about Feynman rules. (Feel free to review the series if you need a refresher!)

Read entire article here: Quantum Diaries

Look at the Space from ISS

The Stars as Viewed from the International Space Station. from AJRCLIPS on Vimeo.

Week review

Posts this week:

• The Comets Tale (Playlist)  Mar 17, 2012
• Neutrino's Saga - final chapter?  Mar 16, 2012
• The Evolution of the Moon  Mar 15, 2012
• Great Sun Spot  Mar 14, 2012   
• Torus in a galactic nucleus  Mar 13, 2012  
• Angry Birds Space: NASA announcement  Mar 13, 2012

TOP 5 this week:

1. Great Sun spot  Mar 14, 2012   [HOT post]
2. Torus in a galactic nucleus  Mar 13, 2012
3. Neutrino's Saga - final chapter?  Mar 16, 2012
4. Angry Birds Space: NASA announcement  Mar 13, 2012
5. The Scale of the Universe 2  Mar 12, 2012

The Comets Tale (playlist)

The Comets Tale (BBC):

Neutrino's Saga - final chapter?

Time of flight difference between the speed of light and the arriving neutrinos. Observe a great difference between the two experiments. Now, we have to wait for the new results of the OPERA experiment, after the cable's problem.

The ICARUS experiment uploaded a paper to the arXiv website with a preprint paper about the neutrinos' velocity, in October 2011, defying the superluminal neutrinos. Now, after the assumption of a problem in a cable, by the OPERA team, ICARUS published a preprint paper that confirms the previous results that neutrinos doesn't travel with a speed superior that the speed of light. 

So, we have to wait for the OPERA results (we need a large number of events and it takes... days), to confirm that neutrinos aren't superluminal.

Here is the abstract:

Measurement of the neutrino velocity with the ICARUS detector at the CNGS beam

The CERN-SPS accelerator has been briefly operated in a new, lower intensity neutrino mode with ~10^12 p.o.t. /pulse and with a beam structure made of four LHC-like extractions, each with a narrow width of ~3 ns, separated by 524 ns. This very tightly bunched beam structure represents a substantial progress with respect to the ordinary operation of the CNGS beam, since it allows a very accurate time-of-flight measurement of neutrinos from CERN to LNGS on an event-to-event basis. The ICARUS T600 detector has collected 7 beam-associated events, consistent with the CNGS delivered neutrino flux of 2.2 10^16 p.o.t. and in agreement with the well known characteristics of neutrino events in the LAr-TPC. The time of flight difference between the speed of light and the arriving neutrino LAr-TPC events has been analysed. The result is compatible with the simultaneous arrival of all events with equal speed, the one of light. This is in a striking difference with the reported result of OPERA [1] that claimed that high energy neutrinos from CERN should arrive at LNGS about 60 ns earlier than expected from luminal speed. 

 Read more in DiscoverMagazine.com, CNet and Wired. 

The Evolution of the Moon

The Moon is the only natural satellite of the Earth, and the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having a quarter the diameter of Earth and ¹⁄₈₁ its mass. The Moon is the second densest satellite after Io, a satellite of Jupiter. It is in synchronous rotation with Earth, always showing the same face; the near side is marked with dark volcanic maria among the bright ancient crustal highlands and prominent impact craters. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a similar reflectance to coal. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art and mythology. The Moon's gravitational influence produces the ocean tides (read this post) and the minute lengthening of the day. The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to appear almost the same size in the sky as the Sun, allowing it to cover the Sun nearly precisely in total solar eclipses. (font: Wikipedia)

About the origin of the Moon (Harvard papers): http://ads.harvard.edu/books/ormo/toc.html
Materials for teachers: http://www.lpi.usra.edu/education/resources/s_system/moon.shtml


A great video about the Moon's evolution from NASA (LRO):

Reading of interest:

High-Resolution Simulations of a Moon-Forming Impact and Post-Impact Evolution

Keiichi Wada (1), Eiichiro Kokubo (1), Junichiro Makino (2) ((1) National Astronomical Observatory of Japan, (2) University of Tokyo)

(Submitted on 5 Jan 2006)

In order to examine the ``giant impact hypothesis'' for the Moon formation, we run the first grid-based, high-resolution hydrodynamic simulations for an impact between proto-Earth and a proto-planet. The spatial resolution for the impact-generated disk is greatly improved from previous particle-based simulations. This allows us to explore fine structures of a circumterrestrial debris disk and its long-term evolution. We find that in order to form a debris disk from which a lunar-sized satellite can be accumulated, the impact must result in a disk of mostly liquid or solid debris, where pressure is not effective, well before the accumulation process starts. If the debris is dominated by vapor gas, strong spiral shocks are generated, and therefore the circumterrestrial disk cannot survive more than several days. This suggests that there could be an appropriate mass range for terrestrial planets to harbor a large moon as a result of giant impacts, since vaporization during an impact depends on the impact energy.

font arXiv [PDF]