According to modern cosmology, matter and antimatter were created in equal amounts in the Big Bang at the beginning of the universe. Physicists are developing concepts to explain why the visible universe now seems to be made entirely out of matter. On the other hand, experimental groups are producing antimatter atoms artificially to explore the fundamental symmetries between matter and antimatter, which according to the present theories of particle physics should have exactly the same properties, except for the opposite electrical charge). Now the independent research group “Antimatter Spectroscopy” of Dr. Masaki Hori, which is associated with the Laser Spectroscopy Division of Prof. Theodor W. Hänsch at the Max Planck Institute of Quantum Optics, has measured the mass of the antiproton relative to the electron with a precision of 1.3 parts per billion (Nature, 28 July 2011). For this they used a new method of laser spectroscopy on a half-antimatter, half-matter atom called antiprotonic helium.
An antiproton (black sphere) trapped inside a helium atom is probed by two laser beams. Foto: MPQ
The result agreed with the proton mass measured to a similar level of precision, confirming the symmetry between matter and antimatter. The experiment was carried out at the European Laboratory for Particle Physics (CERN) in Geneva (Switzerland) in a project led by scientists from the Max Planck Institute of Quantum Optics and Tokyo University (Japan), and including the University of Brescia (Italy), the Stefan Meyer Institute (Vienna, Austria), and the KFKI Research Institute (Budapest, Hungary).
Physicists believe that the laws of nature obey a fundamental symmetry called “CPT” (this stands for charge conjugation, parity, and time reversal), which postulates that if all the matter in the universe were replaced with antimatter, left and right inverted as if looking into a mirror, and the flow of time reversed, this “anti-world” would be indistinguishable from our real matter world. Antimatter atoms should weigh exactly the same as their matter counterparts. If scientists were to experimentally detect any deviation, however small, it would indicate that this fundamental symmetry is broken. “Small” is the keyword here – it is essential to use the most precise methods and instruments available to make this comparison with the highest possible precision.
Antimatter is extraordinarily difficult to handle in the laboratory, because upon coming into contact with ordinary matter (even the air molecules in a room), it immediately annihilates, converting into energy and new particles. In 1997, researchers from the Max Planck Institute of Quantum Optics in cooperation with other European, Japanese, and American groups began construction of a facility called the Antiproton Decelerator (AD) at CERN. Here antiprotons produced in high-energy collisions are collected and stored in a vacuum pipe arranged in a 190-m-long racetrack shape. The antiprotons are gradually slowed down, before being transported to several experiments. The so-called ASACUSA (Atomic Spectroscopy and Collisions using Slow Antiprotons, named after a district in Tokyo) collaboration, of which Dr. Hori is one of the project leaders, sends the antiprotons into a helium target to create and study antiprotonic helium atoms.
Normal helium atoms consist of a nucleus with two electrons orbiting around it. In antiprotonic helium, one of these electrons is replaced by an antiproton, which finds itself in an excited orbit some 100 picometres (10-10 m) from the nucleus. Scientists fire a laser beam onto the atom, and carefully tune its frequency until the antiproton makes a quantum jump from one orbit to another. By comparing this frequency with theoretical calculations, the mass of the antiproton can be determined relative to the electron.
An important source of imprecision arises because the antiprotonic atoms jiggle around randomly according to their thermal energy, so that atoms moving towards the laser beam experience a different frequency compared to those moving away. This is similar to the effect that causes the siren of an approaching ambulance to change pitch as it passes you by. In their previous experiments of 2006, the MPQ / ASACUSA scientists used one laser beam, and this effect limited the precision of their measurement.
This time to go beyond this limit, a technique called “two-photon laser spectroscopy” was used. The atoms were struck by two laser beams travelling in opposite directions, with the result that the effect was partially cancelled, leading to a four to six times higher precision. The first laser caused the antiproton to make a quantum jump to a virtual energy level normally not allowed by quantum mechanics, so that the second laser could actually bring the antiproton up to the closest allowed state. Such a two-photon jump is normally difficult to achieve because the antiproton is heavy, but MPQ scientists accomplished it by building two ultra-sharp lasers and carefully choosing a special combination of laser frequencies. To do this, an optical frequency comb – a special device invented 10 years ago by the group of Prof. Theodor W. Hänsch to measure the frequency of light – was used.The new measurements showed that the antiproton is 1836.1526736(23) times heavier than the electron, the parenthesis showing the 1-standard deviation imprecision. “We have measured the mass of the antiproton relative to the electron with a precision of 10 digits, and have found it exactly the same as the proton value known with a similar precision”, Masaki Hori explains. “This can be regarded as a confirmation of the CPT theorem. Furthermore, we learned that antiprotons obey the same laws of nonlinear quantum optics like normal particles, and we can use lasers to manipulate them. The two-photon technique would allow much higher precisions to be achieved in the future, so that ultimately the antiproton mass may be better known than the proton one.”
The Committee on Data for Science and Technology (CODATA) uses the results of this experiment as one of several input data to determine the proton-to-electron mass ratio, which in turn influences the values of many other fundamental constants. Olivia Meyer-Streng
ASACUSA is one of several experiments studying antimatter at CERN. ATRAP and ALPHA investigate antihydrogen atoms, AeGIS studies how antihydrogen falls under gravity, and ACE studies the possible use of antiprotons for cancer therapy.Original Publication:
Nature, 28 July 2011Contact:
Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further reports about: > Antiproton > Atomic Spectroscopy > Big Bang > CERN > Fundamental matter-antimatter symmetry > MPQ > Max Planck Institute > Optic > Quantum > antiprotonic helium > fundamental symmetry > half-antimatter > helium atoms > hydrogen atom > laser beam > laser spectroscopy > modern cosmology > quantum optics > spectroscopy
Light-driven atomic rotations excite magnetic waves
24.10.2016 | Max-Planck-Institut für Struktur und Dynamik der Materie
Move over, lasers: Scientists can now create holograms from neutrons, too
21.10.2016 | National Institute of Standards and Technology (NIST)
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
25.10.2016 | Life Sciences
25.10.2016 | Life Sciences
25.10.2016 | Life Sciences