- University of Copenhagen Faculty of SciencePhysics, 1999 - 2005
- Frederiksværk Gymnasium1996 - 1999
- Technical University of DenmarkPost doc, 2011 - present
- National Institute of Information and Communications Technology, TokyoPost doc, 2008 - 2011
- Niels Bohr Institute, University of CopenhagenPhD student, 2005 - 2008
As you perhaps know, or recall from previous posts of mine, entanglement is a phenomenon which is at the heart of quantum physics and distinguishes it from our everyday world. Objects that are entangled behave, in a sense, as if they are a single entity even when separated and manipulated independently. Entanglement can improve measurement precision, e.g. the precision of atomic clocks, and it enables quantum computing.
Usually we talk about entanglement between two particles, considering some property that each particle has. For example, the energy state of an atom here might be correlated with the energy of an atom in another location, such that the two atoms are entangled. But there doesn't actually have to be two particles to create entanglement. One is enough.
If we shine light on a half-transparent mirror, half of it will go through, and half of it will be reflected. So we get two beams of light, going off in different directions. If we send a single photon (a particle of light) towards the mirror it can also get transmitted or reflected. So if we put some cameras in the path of the transmitted or reflected light, which measure whether the photon arrives, we will find a correlation: When a photon is detected in one camera, nothing is detected in the other, and vice versa. If we repeat the experiment, sometimes the photon arrives in one camera, sometimes in the other. We don't know in advance which one it is going to be, but always exactly one camera clicks. This looks like a simple correlation, but quantum mechanics tells us that it is actually something more intricate. When the photon hits the mirror, it doesn't simply either go through or get reflected. Instead, we get a so-called superposition of these two possibilities. Nature doesn't decide which possibility is realised until we make a measurement (for example with the cameras), even though this may happen much later than the photon hitting the mirror.
So, considering the two paths after the mirror, we have a superposition of two possibilities: There is a photon in the path on the right of the mirror and none on the left (say), or vice versa. This looks very similar to entanglement. Entanglement between two atoms happens, for example, when we have a superposition where the first atom has a high energy and the second a low one or vice versa. However, now there is just one particle, and it is not a property of the particle that changes (such as the energy), but instead whether the particle is there at all or not, in a given path. Is this entanglement?
This question was debated for quite a while in the past. By now, it is well established that in the case of photons (light), the answer is 'yes', and in fact this entanglement is useful for applications, for example ultra secure cryptography. We call this kind of entanglement 'mode entanglement'. In the example above, each path is a 'mode' which can contain different numbers of photons, and the two separate paths are the objects which are entangled. These are not two particles - instead the number of particles provides the degree of freedom in which the paths are entangled.
So the question is settled for light. What about other particles? What about electrons?
It turns out that for electrons, the question is more subtle and the debate is still ongoing. The thing is that to reveal the entanglement, it is not enough just to measure whether the particle is there or not in each path. One needs to also do 'in between' measurements, which require the creation of superpositions of zero or one particle locally in the path which is measured. This is ok for photons - it's not easy, but there is nothing in principle forbidding such superpositions, and we can do measurements which are not quite optimal but good enough. But for particles with electrical charge - such as electrons - the situation is different. As far as we know, superpositions of states with different total charge cannot exist (this is known as the superselection rule for charge). So in particular, superpositions of zero or one electrons are ruled out, and it is unclear if it is possible to do measurements which will reveal mode entanglement for charged particles.
In this paper, we argue that the answer for electrons is also 'yes'. We propose an experimental setup, which uses single electrons split on a kind of electronic mirror, in an analogue way to how a photon would be split on a mirror for light. In our setup, the entanglement created by the splitting is revealed without breaking any fundamental principles. We need to use two single photons at the same time, split on two separate mirrors. However, while two electrons are involved, we show that the result we obtain would be impossible unless each split single electron creates an entangled state. So, we conclude that single-electron entanglement indeed exists and is observable.
It will be interesting to see the reactions to this paper. Whether our colleagues will be convinced or not. And if they are, whether someone is up for doing the experiment :).
So I learned today while watching the hangout with Bas Hensen from Delft (great talk, btw!) that we already now have 3 different loophole-free Bell violating experiments! While the brilliant Delft experiment used photons entangled with diamonds, the two new ones from just a couple days ago employed the tried-and-tested method of creating entangled photons through spontaneous parametric down-conversion (SPDC).
These experiments, at NIST, Colorado and in Vienna, used SPDC sources of entangled photons and TES superconducting detectors to reach detection loophole-beating detection efficiencies.
The papers seem to be very interesting reads, but while I haven't yet assessed their scientific qualities, here's my extremely superficial review of their level of presentation:
The introductions are great (particularly Vienna's), clearly laying out the deal with nonlocality, Bell tests and loopholes.
The papers are both trying hard to increase their cool factor: The Vienna experiment was performed in the Hofburg castle (probably the first time that night shift security officers are acknowledged in a quant-ph paper!) while the NIST experiment used Back to the Future, Monty Python and the Quest for the Holy Grail and other movies and TV shows to create pseudo-random numbers (making it even more unlikely that the random settings were predetermined)!
Both papers also have some nice space-time diagrams but the NIST one even has a geographical contour plot!
While the Vienna supplement is rather dull, the NIST supplement contains some awesome timing diagrams. Taking this and their very detailed listing of pop-culture references into account, the NIST paper hands down wins on X-factor.
Finally, the NIST guys are totally nonchalant in their conclusion, stating that their Bell test machine is actually just meant to be a source of certified randomness in their public randomness beacon....
This video was presented at the recent UQCC 2015 event in Tokyo, held in connection with the annual QCrypt conference.
I don't believe QKD will be as omnipresent as speculated here, but some of the use cases may certainly become reality.
Watch more of its action at https://youtu.be/jRhImaVwlgI and go to David's site to enjoy the rest of his creations:
This sculpture is for sale in a limited edition at 2500$. How I wish I could afford to let it grace my living room wall.
via , http://www.thisiscolossal.com/2015/09/david-c-roy-kinetic-sculptures/
Lifelike Sisyphus model in LEGO by Jason Allemann. A simple, but inventive gearing brings him to life, rolling his boulder forever on top of a pedestal with beautiful reliefs from his life.
Be sure to watch the video:
via Leg Godt, Gizmodo
When we look at wonderfully rendered modern 3D graphics in movies and games we see the result of light scattering off of the various surfaces in the scene, from one or more light sources. But, as is the usual case in the real world, the complex computed light transport is invisible. Benedikt Bitterli wanted to show us interactively on our 2D screens how light travels, splits and combines through different scenes including lenses, a prism, and rough mirror surfaces using geometric optics. In the resultant demonstration the user can change the start point and direction of the light as appropriate in various forms including laser light, beam and cone. The number of light bounces computed, the number of photon paths, and the emission spectra are also under user control.
But how on earth can all this be computed without a rendering farm in a reasonable amount of time on our individual computers?
A more useful approach is to slightly modify the rendering problem and visualize a quantity known as the fluence instead. We will introduce a more rigorous definition later, but the fluence is essentially the average amount of light passing through a point, and is defined almost everywhere in space (not just surfaces), allowing us to "see" the light between surfaces. Unfortunately, rendering this quantity in 3D is fairly computationally expensive, and still doesn't solve all of our problems: Because the rendered image is only 2D, visualizing a 3D fluence essentially blends everything together along one dimension, and the final rendered image may become very difficult to understand.
To fit the fluence onto a 2D image, I ultimately decided to throw away one dimension of the fluence and solve a 2D rendering problem instead. This 2D fluence is a lot easier to visualize and understand.
More here: https://goo.gl/46xetR
Interactive demonstration here: https://goo.gl/bNvNu9
Image from article.
A few months ago he threatened to turn us all over to the FBI for fraud since we didn't give up studying or researching physics as he had previously demanded (see e.g. http://www.rapiddiffusion.com/science/crackpot-gabor-fekete-part-2/).
This time he's pretending to be various members of the Swedish Academy of Science (the mail appears to come from their actual addresses), claiming that he will receive the Nobel prize this year. Read on for your entertainment:
+ + +
Welcome dear Colleague,
In the last 100 years we donated many Nobel Prizes for worthless and speculative theories and models.
Also was a big mistake to donate Nobel Prize to Francois Englert and Peter Higgs for their ridiculous boson theory.
Joseph Incandela and his team issued a speculative explanation. They said that they detected 133 proton mass Higgs boson. It proved to be a lie, because they detected only 4 muons and 2 photons. The mass of these is altogether 0.4 proton mass.
We are considering to withdraw the undeservedly received Nobel Prizes and we put a proposal because of removal of Joseph Incandela and his team from the management of CERN.
In the future we don't want to donate more Nobel Prizes for ridiculous, worthless and speculative theories and models.
Why did so the Nobel Committe? In this year we received two papers in an email from Gabor Fekete, who is a hungarian reformer physicist.
He demonstrated that the modern physics is a pseudo-science in hundred percent and he described with eight digits accuracy the electromagnetic physics of photons, X-ray-photons, gamma-photons, muons, electrons and all atoms, thus solving all the problems in particle and nuclear physics. At the same time he uncovered the fraud of Joseph Incandela and his team. The papers of Gabor Fekete you can read below.
We think so that in this year the Nobel Winner should be Gabor Fekete. Please let us know if you are in agreement or opposition with our decision. You can contact me in any way as are below. Thank you in advance.
Professor Olga Botner
The Royal Swedish Academy of Sciences
+ + +
...followed by a couple of his "papers".
I believe he lives in Hungary - I wonder if anyone actually contacted authorities there to have him either prosecuted or examined for mental disorder.
You can follow the launch live via NASA TV:
More info about AAUSAT5 can be found in this article:
Generation of single photons and Schrödinger kitten states of light
Generation of single photons and Schrödinger kitten states of light
Thomas Müller not to blame for Pepe's headbutt during Germany's 4-0 win ...
World Cup 2014: Germany's hat-trick striker Thomas Müller exaggerated his reaction to a shove by Pepe but defender was then deservedly sent
Magical Photos of Insects Shot Using Ordinary Household Objects
The photographs in Nadav Bagim's project "WonderLand" might look like paintings or computer generated images, but they're actually real phot
Incredible Photograph of the Milky Way Rising Over the Sea
Photographer Yasuaki Segawa captured this incredible photograph of the Milky Way rising above the ocean, as seen from Taketomi Island, Japan
Waterfall, Moonbow, and Aurora Captured in a Single Shot
Photographer Stephane Vetter managed to capture a moonbow, an aurora, and an Icelandic waterfall, all in the same photograph. The longer