Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Higgs excitations near absolute zero

26.07.2012
A collaboration of physicists from MPQ, LMU, Harvard and Caltech detect Higgs-type excitations in a low-dimensional system of ultracold atoms at the transition between different phases of matter.

The sudden breaking of symmetry plays a fundamental role in physics, in particular for the description of phase transitions that change the whole state of a system. One example is the spontaneous alignment of the atomic magnets in a ferromagnetic material that is cooled down below the Curie-temperature. Being governed by such a “global order”, the system can be excited to a collective oscillation, in which all particles move in a coordinated way.


Figure: Illustration of the Higgs excitation in a two-dimensional system. The dynamics of the Higgs excitation (red sphere) is described by an oscillation in a ‘sombrero’-shaped potential.
Graphic: MPQ, Quantum Many-Body Division

If the collective behaviour follows the rules of relativity, a special kind of oscillation can develop, a so-call Higgs excitation (named after the British physicist Peter Higgs). Such an excitation plays a key role in the standard model of elementary particles, where it is called a Higgs-particle. Also, solid state-like systems can exhibit Higgs excitations, if the collective motion of the particles obeys rules that resemble those of the theory of relativity.

However, the detection of Higgs excitations is usually rather difficult, because the excitations typically decay in a short time. Moreover, they are expected to be especially short-lived in very flat, so-called low-dimensional systems and it has been a subject of theoretical debate whether they are observable at all in such geometries. Now, a team of physicists from the Quantum Many-Body Division of the Max-Planck-Institute of Quantum Optics (Garching near Munich) together with theory colleagues from Harvard University (Cambridge, USA) and the California Institute of Technology (Pasadena, USA) succeeded in experimentally identifying Higgs excitations in a two-dimensional system of ultracold atoms (Nature, 26 July, 2012). “We are excited to study phenomena close to absolute zero temperature that usually occur at the highest energies”, Prof. Immanuel Bloch, leader of the Division, explains.

The experiment starts with cooling rubidium atoms down to temperatures near absolute zero. Then the ultracold atoms are loaded into a two-dimensional optical lattice, a checkerboard-like pattern of dark and bright regions of light that is produced by interfering laser beams. Ultracold atoms in such lattices offer the opportunity to realize different states of matter.

For very intense optical lattices (which means a very high contrast between dark and bright areas), a highly ordered state develops, a so-called Mott insulator (named after the British physicist Sir Neville Mott). In this state, each lattice site is occupied with exactly one single atom, which is fixed to its place. If the lattice intensity is decreased more and more, a phase transition to a superfluid takes place. In a superfluid, all atoms are part of a single field, which extends over the whole lattice and describes the collective motion of the system as one extended quantum mechanical wave. The dynamics of this quantum field follows the laws of an “effective” relativistic field theory, in which the speed of light is replaced by the speed of sound. When the system is brought out of equilibrium, collective oscillations in the form of Higgs excitations can be generated.

A fundamental challenge for the researchers has been to find out whether Higgs excitations can survive even in a two-dimensional system, and if so, how they can be detected. To answer these questions, the scientists set the system parameters such that the quantum gas is very close to the described transition from a superfluid to a Mott insulator. Then, for several milliseconds, the lattice intensity is gently modulated. This modulation is expected to create a few Higgs excitations, while minimally disturbing the system. “We shake the system only very gently to avoid undesired side effects. Otherwise, we could not isolate the signal of the Higgs excitations”, Manuel Endres, one of the senior researchers on the project, points out. “We are able to measure the temperature of the system with a precision of a billionth of a Kelvin using an extremely sensitive method developed in our group. With this method, we could detect small peaks in the temperature distribution at certain values of modulation frequencies.”

The researchers interpret their observations in the following way: Once the frequency of the intensity modulation matches the oscillation frequency of a Higgs excitation, the generation of Higgs excitations is resonantly enhanced. In this situation, more energy is transferred to the system which leads to a rise in its temperature. The experimental data show a clear shift to lower oscillation frequencies when the transition to a Mott insulator is approached. “We talk about a ‘softening’ of the Higgs excitation, which is characteristic of their collective behaviour in the vicinity of the quantum phase transition,” Manuel Endres points out.
It has been a subject of theoretical debate whether Higgs excitations exist at all in such a system, and if so, what their precise properties are. “We have detected a phenomenon which, at present, cannot be precisely calculated. This makes the experimental observation even more important”, Manuel Endres says. [Olivia Meyer-Streng]

Original publication:

Manuel Endres, Takeshi Fukuhara, David Pekker, Marc Cheneau, Peter Schauss, Christian Gross, Eugene Demler, Stefan Kuhr, and Immanuel Bloch
The ‘Higgs’ Amplitude Mode at the Two-Dimensional Superfluid-Mott Insulator Transition
Nature, 26 July, 2012

Contact:

Prof. Dr. Immanuel Bloch
Chair of Quantum Optics
LMU Munich, Schellingstr. 4
80799 München, Germany, and
Max-Planck-Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching b. München
Phone: +49 (0) 89 / 32905 -138
E-mail: immanuel.bloch@mpq.mpg.de

Manuel Endres
Max-Planck-Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching b. München
Phone: +49 (0) 89 / 32905 -214
E-mail: manuel.endres@mpq.mpg.de

Prof. Dr. Stefan Kuhr
University of Strathclyde
Department of Physics
107 Rottenrow East
Glasgow, U.K.
G4 0NG
Phone: +44 141 548 3364
E-mail: stefan.kuhr@strath.ac.uk

Dr. Olivia Meyer-Streng
Press & Public Relations
Max-Planck-Institute of Quantum Optics
Phone: +49 (0) 89 / 32905 -213
E-mail: olivia.meyer-streng@mpq.mpg.de

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:
http://www.mpq.mpg.de

More articles from Physics and Astronomy:

nachricht What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin

nachricht Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Machine-learning predicted a superhard and high-energy-density tungsten nitride

18.07.2018 | Materials Sciences

NYSCF researchers develop novel bioengineering technique for personalized bone grafts

18.07.2018 | Life Sciences

Why might reading make myopic?

18.07.2018 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>