Werner Heisenberg, one of the founding fathers of quantum mechanics is famous for his uncertainty principle. Initially he came to his result based on a rather heuristic argument that measurement of a system disturbs the system and this leads to an inherent uncertainty in all measurements. We have the “Heisenberg’s microscope” in which he imagines an experimenter trying to measure the position and momentum of an electron by shooting a photon at it.

Later on the uncertainly principle was formulated correctly in terms of quantum operators that do not commute. This is of course the true deep reason why we have quantum uncertainty.

It has now been shown that Heisenberg’s original argument is wrong. Aephraim Steinberg and other researchers the Centre for Quantum Information & Quantum Control and Institute for Optical Sciences at the University of Toronto have published work disproving Heisenberg [1].

I will stress the claim is not that the uncertainty principle is wrong, it is not, the claim is that Heisenberg’s original argument is wrong.

References

[1] Lee A. Rozema, Ardavan Darabi, Dylan H. Mahler, Alex Hayat, Yasaman Soudagar, and Aephraim M. Steinberg. Violation of Heisenberg’s Measurement-Disturbance Relationship by Weak Measurements. Phys. Rev. Lett. 109, 100404 (2012)

“While there is no magic bullet to remedy the chronic shortage of physics teachers, the situation is starting to improve as steps have been taken by both the IOP and the Department for Education.”

Read the summary here (links to a PDF)

In Horizon: How Small is the Universe? broadcast on BBC Two at 21:00 BST on Monday 3 September, the narrator talked about “splitting the electron” and that this had been achieved.

The scientist speaking, Jeroen van den Brink was a little more careful. The properties of the electron were split between quasi-particles.

Jeroen van den Brink

There are three quasi-particles here; holons, spinons and orbitons [2]. Before I say something about these, you should note that these are not really fundamental particles, but rather they arise from the collective behavior of the system. Quasi-particles are emergent phenomena that occur when a microscopically complicated system behaves as if it contained different weakly interacting particles in free space.

A good example here is the electron effective mass as it travels through a semiconductor. The system behaves like a system of weakly interacting electrons, but with a different mass. These “wrong mass” electrons are quasi-particles and arise due to the collective interactions.

Another example from semiconductor physics are holes. The absence of an electron in the valence band of a semiconductor behaves like the presence of a positive charge carrier.

Holons, spinons and orbitons

The electron, in certain circumstances can be considered as a bound state of the the three quasi-particles; holons, spinons and orbitons. The holons carries the charge, the spinons carry the spin and the orbitons the orbital location. That is these three quasi-particles describe the fundamental properties of the electron in some material.

Amazingly, there are situations in which these quasi-particles become deconfined. That is they are no longer strongly bound, but exist as free particles. This is what Horizon was really talking about.

Experiments

In 1996 Kim et.al. split an electron into a holon and spinon [1].

The third part, the orbiton was far more elusive. Only this year has it been reported that “spin–orbital” separation of the electron has been observed [3].

I won’t comment further here as experimental physics is outside my expertise. I suggest those that are interested read the original papers I cite.

Has the electron really been split?

No, but the properties, the quantum numbers have been shared between quasi-particles and these quasi-particle have experienced deconfinement. This is an amazing result that is deeply rooted in quantum mechanics and collective phenomena, but does not signal that we should think of free isolated electrons as not being fundamental.

Today there is no compelling evidence that the electron is not fundamental, that is has some internal structure. It may well do, string theory for example suggests that the electron is just one vibrational mode of a fundamental string, but right now the evidence is not there.

References

[1]C. Kim, et.al. Observation of Spin-Charge Separation in One-Dimensional SrCuO2. Phys. Rev. Lett. 77, 4054–4057 (1996)

[2]K. I. Kugel and D. I. Khomskii, Sov. Phys. Usp. 25, 231 (1982)

[3]J. Schlappa et.al. Spin–orbital separation in the quasi-one-dimensional Mott insulator Sr2CuO3. Nature 485, 82–85 (03 May 2012)