The BASE collaboration team at CERN announced that they successfully prepared and manipulated an "antimatter qubit" for the first time, achieving unprecedented quantum precision measurements on a single antiproton. This result has been published in the journal Nature. In the experiment, the team trapped a single antiproton in the device and allowed its spin to smoothly switch between two quantum states for nearly a minute, opening up a new path for comparing the behavior of matter and antimatter with extremely high precision.
Antiprotons are the antimatter counterpart of protons. They have the same mass but opposite charges. They also have spin properties similar to those of tiny magnets. The spin direction can only take on one of two states. Observing spin states and their transition processes is crucial for quantum sensing, ultra-high-precision measurements, and testing whether matter and antimatter are truly "symmetric" under the laws of physics, including the basic principle of particle physics - CPT symmetry. According to the standard model, particles and antiparticles should have the same mass and lifespan. The main difference is only reflected in the charge-related properties. Therefore, comparing protons and antiprotons item by item with extremely high precision is one of the core means of testing this theory.
In order to realize this experiment, the researchers used a technology called "coherent quantum transition spectroscopy" to accurately measure the changes between spin states while minimizing the impact of environmental noise. This technology has been widely used in metrology, quantum information processing, magnetic measurements, and precision testing of the Standard Model. In previous experiments on protons and deuterons, it has achieved high-resolution maser spectroscopy measurements below one part per trillion level.
In the past, such spectroscopic experiments mostly relied on "mass particle statistics", but this time the BASE team made a breakthrough in applying the method to "single free nuclear spins". In the low-temperature Penning trap system, researchers first measured the spin state of antiprotons using the continuous Stern-Gerlach effect, and then transferred them to a precision trap with a highly stable magnetic field. They used quantum projection measurement to generate and analyze the coherent quantum behavior of antiprotons.
The experiment also clearly observed the Rabi oscillation phenomenon in an antiproton spin system for the first time. The so-called Rabi oscillation is a process in which a quantum system periodically transitions between two energy levels driven by an external resonant electromagnetic field. Its frequency (Rabi frequency) depends on the intensity of the interaction. This effect is a fundamental tool in quantum computing, magnetic resonance and atomic physics because it allows researchers to precisely manipulate the quantum states of atoms, ions and qubits.
In time series measurements, the team achieved a spin flip probability of more than 80% and a spin coherence time of approximately 50 seconds. In the single-particle spin resonance test, the spin flip probability exceeded 70%, and the transition linewidth was 16 times narrower than previous similar experiments, which greatly improved the measurement accuracy; the limiting factor mainly came from the decoherence effect related to the cyclotron frequency measurement. The BASE collaboration has previously demonstrated that the magnetic moments of protons and antiprotons are highly consistent within an accuracy of a few parts per billion, indicating that they are almost completely symmetrical in their magnetic properties. Project leader Stefan Ulmer said that in the future, with the help of this new method, the accuracy of antiproton magnetic moment measurement is expected to be improved by another 10 to 100 times.
Although the term "qubit" is often associated with quantum computing, the researchers pointed out that the antimatter qubit achieved this time will not directly translate into engineering or computing technology applications in the short term. Its real scientific value lies in giving physicists unprecedented precision and means to examine the properties of antimatter from a fundamental scale and make more rigorous comparisons with ordinary matter, providing important clues to explain why the universe is almost entirely dominated by matter, while non-matter and antimatter coexist in equal measure.
Barbara Rattage, the first author of the paper, revealed that the team has set its sights on the next step of the BASE-STEP project - a system designed to transfer antiprotons trapped in the trap to a quieter environment with a magnetic field. Theoretically, this will extend the spin coherence time by about an order of magnitude, which is of key significance for advancing the study of baryon antimatter. The research team believes that by combining advanced quantum manipulation technology with extremely high-precision experimental equipment, mankind has entered a new era of precision measurement in the field of antimatter research, and is closer to revealing the underlying causes of the matter-antimatter asymmetry in the universe.
learn more:
CERN, Nature magazine