deep advances come exponentially faster: testible four-qubit entanglement from string theory, Michael J Duff et al, 4 pages: Rich Murray 2010.09.05

[Rich Murray]

deep advances come exponentially faster: testible four-qubit entanglement
from string theory, Michael  J Duff et al, 4 pages: Rich Murray 2010.09.05

http://www.sciencenews.org/view/generic/id/62971/title/String_theory_entangled

http://www.wired.com/wiredscience/2010/09/stringy-quantum/#ixzz0ydC57oh9

String theory entangled

Equations can be retooled to describe a strange quantum effect
By Laura Sanders
Web edition : Friday, September 3, 2010

Physicists looking for a way to test their theory about strings might make
more progress if they tangle them up.

String theory -- equations that aspire to explain all of nature's particles
and forces -- has extended its reach to the strange quantum behavior known
as entanglement, physicists report September 2 in Physical Review Letters.
Repurposing string theory mathematics allowed physicists to solve a hard
problem involving entanglement, a strange feature at the heart of quantum
mechanics.
In doing so, the new study also points out a way to test whether the
co-opted string theory equations are actually correct.

"String theory has not had a lot of success in making falsifiable
predictions," says study coauthor Michael Duff of Imperial College London.
"But in the field of quantum information theory, it can."

One of the hallmarks of quantum information is that particles carrying it
can interact in a way that makes them "entangled," so that measuring one
seems to instantaneously affect the other, even at great distances.

Over the last few years, Duff and his colleagues began to notice
similarities between string theory -- the idea that particles of matter and
force are tiny vibrating loops or strands -- and the equations that govern
entangled particles.

In a paper published last year, the physicists noted that the string theory
math describing black holes is surprisingly similar to the equations for a
group of three entangled particles.

The new study takes the analogy a step further, tackling the more difficult
problem of how four pieces of quantum information, called qubits, behave
when they're entangled.
Because experiments disagree, physicists aren't sure about how many ways
four qubits can be entangled.
The answer, according to string theory, is 31.

Duff and his team can't yet explain why the formulas apply to this system.
"We don't understand why it works," he says.
"At some deep level we're mystified by it."

Although the reasons remain unclear, the surprising result identifies a way
to put string theory to the test.
In the past, string theory has been used to describe black holes, which are
notoriously problematic study subjects.
But now, entangled particles -- which can be created and studied in
laboratories around the world -- may serve as stand-ins for string theory
experiments.

Theoretical physicist and black hole expert Sergio Ferrara says the new
result may convince physicists that string theory can be useful in a variety
of settings.
Experiments confirming that string theory equations worked as advertised for
qubit entanglement would provide "sound confirmation" that the black
hole-qubit duality is real, says Ferrara, of CERN, the European nuclear
research laboratory in Geneva.

The surprise appearance of string theory mathematics in entangled particles
may signal a deeper connection between quantum mechanics, which is typically
observed on very tiny scales, and the universe.

On the other hand, the connection might turn out to be just "a quirky
mathematical coincidence," Duff says.

Even if experiments turn out exactly as the string theory equations predict,
Duff cautions, physicists won't be crowing that string theory has unlocked
the deepest mysteries of the world.
The results would confirm that string theory got it right for entanglement,
but not necessarily for everything else, too.
"We have nothing to say about whether string theory is the theory of
everything," Duff says.


http://www.wired.com/wiredscience/2010/09/stringy-quantum/

String Theory Finally Does Something Useful
By Lisa Grossman   September 2, 2010, 1:50 pm, Categories: Physics

String theory has finally made a prediction that can be tested with
experiments -- but in a completely unexpected realm of physics.

The theory has long been touted as the best hope for a unified "theory of
everything," bringing together the physics of the vanishingly small and the
mindbendingly large. But it has also been criticized and even ridiculed for
failing to make any predictions that could be checked experimentally. It's
not just that we don't have big enough particle accelerators or powerful
enough computers; string theory's most vocal critics charge that no
experiment could even be imagined that would prove it right or wrong, making
the whole theory effectively useless.

Now, physicists at Imperial College London and Stanford University have
found a way to make string theory useful, not for a theory of everything,
but for quantum entanglement.

"We can use string theory to solve problems in a different area of physics,"
said theoretical physicist Michael Duff of Imperial College London. "In that
context it's actually useful: We can make statements which you could in
principle check by experiment." Duff and his colleagues describe their
findings in a paper in Physical Review Letters September 2.

String theory suggests that matter can be broken down beyond electrons and
quarks into tiny loops of vibrating strings. Those strings move and vibrate
at different frequencies, giving particles distinctive properties like mass
and charge. This strange idea could unite all the fundamental forces,
explain the origins of fundamental particles and connect Einstein's general
relativity to quantum mechanics. But to do so, the theory requires six extra
dimensions of space and time curled up inside the four that we're used to.


To understand how these extra dimensions could hide from view, imagine a
tightrope walker on a wire between two high buildings. To the tightrope
walker, the wire is a one-dimensional line. But to a colony of ants crawling
around the wire, the rope has a second dimension: its thickness. In the same
way that the tightrope walker sees one dimension where the ants see two, we
could see just three dimensions of space while strings see nine or ten.

Unfortunately, there's no way to know if this picture is real. But although
string theorists can't test the big idea, they can use this vision of the
world to describe natural phenomena like black holes.

Four years ago, while listening to a talk at a conference in Tasmania, Duff
realized the mathematical description string theorists use for black holes
was identical to the mathematical description of certain quantum systems,
called quantum bits  or qubits.

Qubits form the backbone of quantum information theory, which could lead to
things like ultrafast computers and absolutely secure communication. Two or
more qubits can sometimes be intimately connected in a quantum state called
entanglement. When two qubits are entangled, changing one's state influences
the state of the other, even when they're physically far apart.

"As I listened to his talk, I realized the kind of math he was using to
describe qubit entanglement was very similar to mathematics I had been using
some years before to describe black holes in string theory," Duff said. When
he looked into it, the mathematical formulation of three entangled qubits
turned out to be exactly the same as the description of a certain class of
black holes.

In the new study, Duff and his colleagues push the similarity one step
further. They used the mathematics of stringy black holes to compute a new
way to describe four entangled qubits, an open question in quantum
information theory.

"We made statements that weren't previously known using string theory
techniques," Duff said. "Whether the result is some fundamental principle or
some quirk of mathematics, we don't know, but it is useful for making
statements about quantum entanglement."

What's more, these statements are precise and experimentally provable,
unlike previous suggestions for ways to test string theory, Duff says.

"So in a way, there's bad news and good news in our paper," he said. "The
bad news is, we're not describing the theory of everything. The good news
is, we're making a very exact statement which is either right or wrong.
There's no in between."

Duff emphasized that this is only a test of string theory as it relates to
quantum entanglement, not as a description of the fundamental physics of the
universe. The battle over string theory as a theory of everything rages on.

"Already I can imagine enemies sharpening their knives," Duff said.

And they are. A chorus of supporters and critics, including Nobel laureate
and string theory skeptic Sheldon Glashow and string theorists John Schwarz
of Caltech, James Gates of the University of Maryland, and Juan Maldacena
and Edward Witten of the Institute for Advanced Study in Princeton agree
that Duff's argument is "not a way to test string theory" and has nothing to
do with a theory of everything.

Mathematician Peter Woit of Columbia University, author of the blog Not Even
Wrong, thinks even claiming that the new paper is a test of quantum
entanglement is going too far.

"Honestly, I think this is completely outrageous," he said. Even if the math
is the same, he says, testing the quantum entangled system would only tell
you how well you understand the math.

"The fact that the same mathematical structure appears in a quantum
mechanical problem and some model of black holes isn't even slightly
surprising," he said. "It doesn't mean that one is a test of the other."

Witten takes a more optimistic view of the theory's chances, pointing out
that the mathematics of string theory have turned out to be coincidentally
useful in other areas of physics before.

"In general, this kind of work shows that string theory is useful, and in
fact by now it has been useful in many different ways," Witten said in an
email to Wired.com.

"One might surmise that a physics theory that has proved to be useful in so
many different areas of physics and math is probably on the right track," he
added. "But that is another question."

Via Universe Today
Image: Entangled string. Flickr/Whatknot

Tags: Imperial College London, Michael Duff, quantum entanglement, qubits,
string theory


arXiv:1005.4915v2 [hep-th] 30 Jun 2010
Four-qubit entanglement from string theory
L. Borsten 1,
D. Dahanayake 1,
M. J. Du 1,
A. Marrani 2,
and W. Rubens 1.
1 Theoretical Physics, Blackett Laboratory, Imperial College London,
London SW7 2AZ, United Kingdom
2 Stanford Institute for Theoretical Physics, Stanford University,
Stanford, CA 94305-4060, USA
(Dated: July 1, 2010)
[hidden email];
[hidden email];
[hidden email];
[hidden email];
[hidden email];

We invoke the black hole/qubit correspondence to derive the classifcation of
four-qubit entanglement.
The U-duality orbits resulting from timelike reduction of string theory from
D = 4 to D = 3 yield 31 entanglement families, which reduce to nine up to
permutation of the four qubits.
PACS numbers: 11.25.Mj, 03.65.Ud, 04.70.Dy
Keywords: black hole, U-duality, qubit, entanglement

...Falsifable predictions in the fields of high-energy
physics or cosmology are hard to come by, especially for
ambitious attempts, such as string/M-theory, to accom-
modate all the fundamental interactions. In the field of
quantum information theory, however, previous work has
shown that the stringy black hole/qubit correspondence
can reproduce well-known results in the classification of
two and three qubit entanglement. In this paper this cor-
respondence has been taken one step further to predict
new results in the less well-understood case of four-qubit
entanglement that can in principle be tested in the labo-
ratory.

This work was supported in part by the STFC under
rolling Grant No. ST/G000743/1. The work of A.M. has
been supported by an INFN visiting Theoretical Fellow-
ship at SITP, Stanford University, Stanford, CA, USA.
This work was completed at the CERN theory division,
supported by ERC Advanced Grant \Superfields". We
are grateful to Sergio Ferrara for useful discussions and
for his hospitality. D.D. is grateful to Steven Johnston
for useful discussions.
_______________________________________________


Rich Murray, MA
Boston University Graduate School 1967 psychology,
BS MIT 1964, history and physics,
1943 Otowi Road, Santa Fe, New Mexico 87505
505-501-2298 [hidden email]
Sondra Spies, DOM

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