First qubit made of antimatter
Physicists have created the first qubit from an antiparticle. The team is attempting to answer fundamental questions about the universe.
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Qubits are the basic building blocks of quantum computers. They can be made from a wide variety of materials, such as atoms, light or tiny circuits. An international research team has now demonstrated an unconventional method: it created a qubit from antimatter. This consists of a single antiproton. The researchers succeeded in making the spin of the antiparticle oscillate back and forth in a controlled manner for almost a minute.
The team consists of scientists from the BASE collaboration at the European Organization for Nuclear Research CERN in Geneva, including researchers from the Physikalisch-Technische Bundesanstalt (PTB), Heinrich Heine University DĂĽsseldorf (HHU), and Leibniz University Hannover. The results were published in the journal Nature.
Matter and antimatter
Antimatter consists of antiparticles. A particle and its corresponding antiparticle have the same properties but are charged in opposite directions. The best-known example is the positron, the antiparticle of the electron, which is charged positively instead of negatively. When particles and antiparticles meet, they destroy each other. The energy contained in the particles and antiparticles is released in the form of energy or lighter particles. Physicists call this process annihilation.
(Image:Â CERN)
Antiparticles are created quite naturally, for example, during radioactive decay, through cosmic radiation, or by chance due to fluctuations in a vacuum. However, an antiparticle can also be produced artificially in high-energy particle accelerators. If several antiparticles are combined, antimatter is created, just as conventional matter consists of ordinary elementary particles. An antiproton and a positron, for example, form an antihydrogen atom.
Controlling antimatter
The research team first created an antiproton in the so-called Antimatter Factory (AMF) at CERN. They stored it in a trap using electromagnetic fields. Like a proton, the antiproton has a quantum mechanical property called spin, which can be simplified as the rotation of the particle around its axis. Like a compass needle, the spin can point in two different directions and can be deliberately flipped – a property that is exploited both in quantum sensor technology and in quantum computing.
The researchers succeeded for the first time in controlling and observing a spin transition of a single free nuclear spin of an antiproton. The method used is called coherent spin quantum transition spectroscopy. BASE spokesperson Stefan Ulmer from HHU compares this process to a child's swing: “If it is pushed at the right frequency, it swings rhythmically back and forth. In our case, the swing is the spin of a single antiproton, which we cause to oscillate in a targeted manner using electromagnetic fields.” They maintained this oscillation for 50 seconds.
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The mystery of antimatter
However, an antimatter quantum computer, such as the one that springs to mind when thinking about qubits, is not the aim of the research group. Rather, the precise control of individual antiparticles makes it possible to test fundamental laws of nature. In earlier work, the BASE team showed that the magnetic moments of protons and antiprotons are identical down to a few billionths of a part. The question is whether there is a difference after all. The tiniest deviations would violate the so-called CPT symmetry. This requires that matter and antimatter behave exactly the same apart from their opposite charges –.
According to this, matter and antimatter should occur equally frequently in the universe. In fact, however, there is an enormous asymmetry: the universe consists almost exclusively of matter. This is one of the great mysteries of modern physics. Ulmer emphasizes that her system would enable much more precise tests of fundamental physical symmetries in the future.
Compared to previous experiments, the team improved its structure and thus suppressed processes that disturb the sensitive state of the antiproton. “This work gives us the opportunity to apply the full range of coherent spectroscopic techniques to single particles of antimatter for the first time,” says Ulmer. “We expect to be able to determine the magnetic moment of the antiproton with ten times greater accuracy in the future and, in the long term, with up to a hundred times greater accuracy.”
In the next step, antiprotons are to be placed inside transportable traps in specially prepared precision laboratories. There, the particles should remain stable for up to ten times longer, which could enable greater measurement accuracy.
(spa)
