CERN scientists have analyzed a particle of antimatter isolated in an undecided quantum state known as a superposition for the first time.
While the quantum behavior of ordinary matter has been studied extensively and even used as the basis of quantum computers in the form of qubits, the breakthrough goes far beyond technological applications, potentially helping physicists understand why we even exist today.
The team suspended an antiproton – the antimatter counterpart of the proton – in a system of electromagnetic traps, and suppressed environmental interference that would mess with the particle's delicate quantum state.
While in an undecided blur of a property known as spin, the particle was carefully set into oscillation and measured over a period of 50 seconds.
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"This represents the first antimatter qubit," says Stefan Ulmer, a physicist with CERN's BASE collaboration. "Most importantly, it will help BASE to perform antiproton moment measurements in future experiments with 10- to 100-fold improved precision."
Those future experiments could help reveal more differences between matter and antimatter, which in turn could answer the fundamental question of how we survived an antimatter apocalypse that, according to current physics models, should have annihilated all matter billions of years ago.
In simple terms, there should theoretically be no difference between matter and antimatter, except that particles have the opposite charge to their respective counterparts. If that was the case, however, the Big Bang should have created both in equal amounts, which would have quickly canceled each other out, leaving the Universe a very empty place by now.
The fact that we're here to ponder the question shows that physics must treat matter and antimatter differently in some other respect as well. Various experiments have started to uncover clues to this asymmetry, but the degree of difference found so far still can't account for the discrepancy.
The BASE experiment at CERN is searching for that discrepancy in protons and antiprotons by comparing how their spin states behave under similar conditions. Spin is an intrinsic property of subatomic particles that causes them to act like tiny magnets.
Previous BASE runs have measured the magnetic moment of the antiproton to a precision of 1.5 parts per billion. But frustratingly, even at that level, it remains consistent with that of the regular proton.
Part of the problem is that quantum states are very sensitive to interference from their surroundings, so it's hard to keep antiprotons in a superposition long enough to study their properties closely.
BASE has now undergone a series of upgrades to tamp down this background noise, isolating the particles and allowing the particles to swing around in a quantum blur for a record-setting 50 seconds.
And this could soon be extended even further. Normally, antimatter can't be moved very far from where it's created – after all, it will just blink out of existence if it touches a container made of regular matter.
CERN has been testing a new system for transporting antimatter, called BASE-STEP, which could eventually allow the strange stuff to be moved to specialized facilities that suppress or even eliminate background noise.
And it's in these ultra-quiet experiments that we might finally hear the whispered answers to one of physics' most profound questions.
"Once it is fully operational, our new offline precision Penning trap system, which will be supplied with antiprotons transported by BASE-STEP, could allow us to achieve spin coherence times maybe even ten times longer than in current experiments, which will be a game-changer for baryonic antimatter research," says CERN physicist Barbara Latacz.
The research was published in the journal Nature.