Current theories can't explain observed spin segregation

Oct 16, 2008 By Miranda Marquit feature

(PhysOrg.com) -- Experiments with quantum systems sometimes yield surprising results. This is exactly what happened when John Thomas, a researcher at Duke University in Durham, North Carolina found out when he and his post doc, Du, and his students Luo and Clancy, attempted to study a trapped cloud of Fermi atoms all initially in the same quantum superposition of spin-up and spin-down states. They expected all of the atoms to move uniformly back and forth in the trap. Instead, the atoms moved in a way that not predicted using existing theory.

The results of their experiment can be found in Physical Review Letters: “Observation of Anomalous Spin Segregation in a Trapped Fermi Gas.”

“It was nuts,” Thomas tells PhysOrg.com. “The atoms in this prepared gas didn’t behave at all as one would expect. We thought we’d be doing something simple, and now we’re attempting to understand something we didn’t expect.”

Thomas explains that particles known as fermions (which make up the Fermi gas) act in a way that is very similar to electrons: When they are put in the same quantum spin state, or q-bit, they tend to avoid each other. This is useful in a variety of applications related to quantum computing because this prevents particles from colliding with each other, destroying information. As a result, fermions are being considered in the development of quantum memory, since they would (theoretically) avoid each other and remain coherent.

Thomas and his team wanted create a collection of fermions in identical quantum spin states by applying a radio frequency field. “We set up an experiment in which we used a very cold gas of lithium-6, all initially in the spin-up state,” he says. “We trapped these fermions in a laser beam, a sort of bowl made of light. We put about 100,000 atoms in this optical bowl and attempted to use a radiofrequency (rf) field to prepare them all in the same state of super position, which is 50 percent spin-up and 50 percent spin-down.”

At first, it looked as though all was as it should be. Thomas and his colleagues took images of the atoms just after applying the rf field, and found that immediately following the change, the fermions behaved as expected. “But, after tenths of a second,” Thomas continues, “we saw that things were different. The spin-downs were moving to the edges of the bowl, and the spin-ups were moving to the center, remaining in this pattern for several seconds.”

Thomas and his students began considering explanations for the phenomenon. “We know that this segregation does not arise from ordinary forces between the atoms, which are far too small to explain the observed effects. We believe that the segregation arises from the formation of a spin-wave, but the size of the effect that we observe is much larger and the timescale over which it occurs is much longer than predicted by existing spin-wave theory.”

On a practical level, it seems as though the idea of using a collection of fermions for quantum memory will have to be revisited. At the fundamental physics level, a lot more study is needed. “Ultimately we’ll do more on this,” Thomas says, “because it’s something that we want to understand. But we are waiting for help from theorists. We’d like to have theoretical feedback so that there are other facets to test.”

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Explore further: Thermoelectric power plants could offer economically competitive renewable energy

add to favorites email to friend print save as pdf

Related Stories

New method to generate Laughlin states with atomic systems

Jul 03, 2013

In 1998, the Nobel Prize in Physics was conferred to the discovery of a new type of quantum fluid with fractional charge excitations, known as Laughlin state. The production of this quantum state, which explains the behaviour ...

Neutrons uncover new density waves in fermion liquids

Mar 28, 2012

Scientists working at the Institut Laue-Langevin, one of the world's leading centres for neutron science, have carried out the first investigation of two-dimensional fermion liquids using neutron scattering, and discovered ...

Recommended for you

User comments : 10

Adjust slider to filter visible comments by rank

Display comments: newest first

physpuppy
4 / 5 (4) Oct 16, 2008
"Thomas explains that particles known as fermions (which make up the Fermi gas) act in a way that is very similar to electrons"

Just a comment - electrons are fermions (anything with 1/2 integer spin is by definition, a fermion, whether they be made up of quarks {proton, neutron} or they are elementary particles like leptons {electron, neutrino} )
out7x
2 / 5 (4) Oct 17, 2008
fermions are matter distinguished by color and spin 1/2.
quarks(color) - hadrons.
leptons(no color) - electrons.
johanfprins
2.6 / 5 (5) Oct 17, 2008
8 years ago I already trapped electrons between an n-type diamond surface and an anode to form a single macroscopic wave. It seems what is needed is for each electron to first form a Gaussian wave: Electron-waves with up-and down spins then overlap to form bosons; and the latter entities than overlap to form a single macro-wave akin to a laser-beam state. Unfortunately, this experimental result violates existing dogma so that the cranks who are nowadays in charge of our physical institutes and physics journals (like for example Nature and Science) censor such new results. According to Lawrence Krauss editors have to be "gatekeepers" (only another word for censors). No wonder we are at present worse off than during the times of Galileo!!
Alexa
4 / 5 (5) Oct 17, 2008
The spin segregation can have the same origin, like at the case of spin Seebeck effect revealed recently in heated nickel rod.

http://www.physor...923.html

I.e. it's simply result of temperature gradient inside of condensate drop.
johanfprins
1 / 5 (1) Oct 17, 2008
Thanx: Very interesting!!
Yes
4 / 5 (1) Oct 17, 2008
Behavio(u)rlike it makes me think of some sort of skin effect. Eddie currents.
penkilk
not rated yet Oct 17, 2008
Sounds like you may have struck a cord per say.
Johanfprins may have struck upon a similar phenomenon, a harmonic that adds waves together into a slower larger macro-sized wave.

Try parameters that would adjust the micro-waves, see if you can get this phenomena to fall apart. Then name it after Santa Clause for publicity.
johanfprins
2.8 / 5 (4) Oct 17, 2008
Adding waves is "normal superposition". The macro-wave I am observing is a "macro-entanglement": There are no waves that "add"; the original waves (electrons) all "submerge" to become a single entity. That's why a current cannot flow "through this wave". There are no individual charge-accriers: However, when injecting an electron at one contact, it increases the energy of the wave and then within a small time-interval, as determined by Heisenberg's uncertainty relationship, an electron is ejected at the other contact: No movement from contact to contact of an electron: Teleportaion? I do not know! But this is the only explanation so far. Oh, by the way, one can see the macro-wave as a dark rod and it stays dark even when sending massive currents around the circuit: Currents so large that it will cause a bundle of carbon-nanotubes (of the same diameter) to light up, or act as a fuse.
deatopmg
5 / 5 (2) Oct 18, 2008
Adding waves is "normal superposition". The macro-wave I am observing is a "macro-entanglement": There are no waves that "add"; the original waves (electrons) a....snip>

johanfprins; I suspect that your (ours too) electrons actually exist in additional dimensions(s)(per Dirac's full solution) in addition to our 3(4) and there is no teleportation or tunneling, they simply slip over to the other electrode. No magic involved.
johanfprins
3 / 5 (2) Oct 19, 2008
Hi deatopmg,

Excellent observation: What Dirac's equation does, is to model the physis involved in a very complicated manner. According to my insight (I like to be able to "see" the physics involved), a free-electron is a harmonic vibration within the field of a positive charge sitting over a perpendicular fourth-space dimension: The ground-state wave-solution (i.e. a Gaussian function in three dimensions) is the mass-energy of the electron. This energy manifests within a volume of three-dimensional Euclidean space within which time does not manifest owing to the fact that the fourth-dimension is perpendicular to the three space-dimensions (i.e. the mass-energy defines a type of "mini-black hole"). At and around this volume, space-time is curved (i.e. the fourth space-dimension is not perpendicular to our three-dimensional space anymore, so that it now acts as "time"; thus allowing time and gravity to manifest around the mass-volume. In this picture the spin of the electron relates directly to the perpendicular direction of the fourth space-dimension within the mass-volume. This implies that the direction of this dimension can be manipulated by a magnetic-field.

When two electrons are entangled they are in contact along the fourth space-dimension. Since this is not a time axis, they remain in immediate contact until the entanglement is broken up by, for example, measuring the spin of one of the electrons. In the phase I have discovered all the electrons (if you can still called entangled electrons "electrons") are and stay in immediate contact. You are correct this is not "magic". It is already within the physics-equations; albeit using very complicated mathematics.
After all Dirac's training was in mathematics!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.