David Kirkpatrick

August 25, 2010

Quantum entanglement and free will

A little more closely related than you might think.

From the link:

In practical terms, this means that there can be no shared information between the random number generators that determine the parameters of the experiments to be made, and the particles to be measured.

But the same also holds true for the experimenters themselves. It means there can be no information shared between them and the particles to be measured either. In other words, they must have completely free will.

In fact, if an experimenter lacks even a single bit of free will then quantum mechanics can be explained in terms of hidden variables. Conversely, if we accept the veracity of quantum mechanics, then we are able to place a bound on the nature of free will.

That’s an interesting way of stating the problem of entanglement and suggests a number of promising, related conundrums: what of systems that are partially entangled and others in which more than two particle become entangled.

Free will never looked so fascinating.

May 21, 2010

Quantum information sent over 16 kilometers

A major distance breakthrough in “teleporting” quantum entanglement.

From the link:

Scientists in China have succeeded in teleporting information between photons further than ever before. They transported quantum information over a free space distance of 16 km (10 miles), much further than the few hundred meters previously achieved, which brings us closer to transmitting information over long distances without the need for a traditional signal.

Quantum teleportation is not the same as the teleportation most of us know from science fiction, where an object (or person) in one place is “beamed up” to another place where a perfect copy is replicated. In quantum teleportation two photons or ions (for example) are entangled in such a way that when the  of one is changed the state of the other also changes, as if the two were still connected. This enables  to be teleported if one of the photons/ions is sent some distance away.

March 9, 2010

Data processing faster than light speed

Theoretically possible, which lead to a theoretical superluminal computer — a so-called hypercomputer.

From the link:

Physicists have come up with a way to process information faster than the speed of light. But what could they do with such a hypercomputer?

The speed of light represents one of the fundamental limits of the laws of physics. Nothing can travel faster than the speed of light, right?

Well, yes and no, say Volkmar Putz and Karl Svozil at the Vienna University of Technology in Austria. They say there are several ways that signals can cross the superluminal line, although none of them allow the kind of time travel paradoxes beloved of science fiction writers. For example, the quantum phenomenon of entanglement occurs when two quantum particles are described by the same wave function. These particles can be separated by the diameter of the universe and yet a measurement on one will instantaneously influence the other.

So-called “nonlocal” phenomenon cannot be used to transmit information faster than the speed of light but Putz and Svozil today ask whether it can be used to process it, to carry out computational tasks at superluminal speeds. They say there is no reason why not, provided the processing does not lead to any time travel paradoxes.


Assuming that this device could actually be built, what could you do with a superluminal computer? That’s a good question that Putz and Svozil do not address directly. They say such a device would fall into a class of processing machine known as hypercomputers. These are hypothetical devices more powerful than Turing machines, that allow non-Turing computations. They were first discussed by Alan Turing in the 1930s.

In theory, hypercomputers can compute certain kinds of otherwise noncomputable functions. That sounds handy but even though there are uncountably many non-computable functions, it’s actually quite hard to come up with an example of one that might seem useful. If you have any ideas, post them in the comments section.

June 11, 2008

Quantum cryptography

Move over one-time pad, there’s a new kid on the cryptographic block — quantum cryptography. This is one amazing application for the weirdness that is quantum mechanics and quantum effects. And one cool way to transmit secret messages.

Today’s KurzweilAI.net newsletter had a link to a Scientific American story on space-based quantum codes used for cryptography.

Over at Bad Astronomy, Phil Plait wrote about this on Monday. He offers a cool short-version explanation of the quantum mechanics involved, and his comment section has even more detail provided by BABlog readers.

Here’s the KurzweilAI  short:

Space Station Could Beam Secret Quantum Codes by 2014
ScientificAmerican.com, June 9, 2008

University of Vienna researchers hope to send an experiment to the International SpaceStation (ISS) by the middle of the next decade that would pave the way for transcontinental transmission of secret messages encoded using quantum entanglement.

(European Space Agency

In addition to potential use for secure communications, the “Space-QUEST” project would give researchers a chance to test the theory that entanglement should be unlimited in range.

Read Original Article>>


Here’s an excerpt from the Scientific American link found above at “Read Original Article”:

Researchers hope to send an experiment to the International Space Station (ISS) by the middle of the next decade that would pave the way for transcontinental transmission of secret messages encoded using the mysterious quantum property of entanglement.

When two particles such as photons are born from the same event, they emerge entangled, meaning they can communicate instantaneously no matter how far apart they are. Transmitting entangled pairs of photons reliably is the backbone of so-called quantum key distribution—procedures for converting those pairs into potentially unbreakable codes. Quantum cryptography, as it is known, could appeal to banks, covert government agencies and the military, and was tested in a 2007 Swiss election

Here’s some of Phil Plait’s commentary at Bad Astronomy:

So some European scientists came up with the idea of using the International Space Station (I know! Using ISS for science! Wow!) to test this out. They can create a small setup with a laser which can create entangled photons. The entangled photons are then sent simultaneously to two different ground stations, widely separated on the surface of the Earth, so that both have a copy of the entangled photons. In addition, two quantum keys are created based on the photons; this is essentially a code based on the state of the photons — like winning a bet is based on which way a coin lands. The two keys are different, and one each is sent to the two ground stations. So both stations have a pair of entangled photons (identical to the other station’s) and a different key.

Each key is actually a long chain of 1s and 0s. The two keys are then compared on the ISS to create what’s called a bitwise XOR — for example, if two coins both land heads then the XOR operation yields a 0, but if they land differently (one heads and one tails) then it yields a 1 — it’s just telling you whether they are the same or different. So for each place in the key, the two numbers are compared, and if they’re the same (both 1s or both 0s) then a 0 is written down. If they are different then a 1 is put there. When this is done, you get a third string of 1s and 0s, representing a comparison of the two keys.

Still with me? Yeah, me neither, but we’re almost done. So now the ISS has this long number string which represents whether the keys are alike or different. It then transmits this to one of the two stations on Earth.

So? What does this mean? This means that now the two ground stations can create a code between them based on their keys, a code that is known only to them and no one else. Furthermore, this code cannot be cracked by anyone, anywhere, because it’s based on entangled photons that cannot be known to anyone else! Because of entanglement, they know what the other station has because they can look at their key and figure it out. But no one else can.