Storing antimatter means keeping it from touching any ordinary matter, because even a single contact between a particle and its antiparticle results in instant annihilation. Every storage method ever used relies on the same core principle: suspend the antimatter in a vacuum using magnetic and electric fields so it never contacts the walls of its container. The longest anyone has stored antimatter is over a year, achieved with antiprotons at CERN’s BASE experiment.
Why Antimatter Can’t Touch Anything
When a particle of matter meets its antimatter counterpart, both are destroyed and their mass converts entirely into energy. A single antiproton touching the wall of a metal container would annihilate on contact. This means no physical bottle, jar, or tank can hold antimatter directly. The container has to be made of invisible walls: carefully shaped magnetic and electric fields that push the antimatter away from every surface.
The vacuum inside these traps has to be extraordinarily good. Any stray gas molecule drifting into the trap can collide with an antiparticle and destroy it. Practical storage requires pressures around a trillionth of a Torr, roughly a hundred billion times less air than in the room you’re sitting in. The PUMA project at CERN takes this even further, maintaining a vacuum 100,000 times lower than the pressure inside the Large Hadron Collider itself.
Penning Traps for Charged Antiparticles
The workhorse of antimatter storage is the Penning trap. It holds charged particles like antiprotons and positrons (anti-electrons) using a combination of two forces. A strong magnetic field running along the length of the trap prevents particles from drifting sideways. Electric fields generated by a stack of hollow cylindrical electrodes keep the particles from escaping out the ends. Together, these fields create a kind of invisible cage that holds the antimatter suspended in the center, far from any surface.
CERN’s ALPHA experiment uses a variation called a Penning-Malmberg trap, where the electric fields are produced by applying voltages to cylindrical electrodes rather than the perfectly shaped surfaces used in a textbook design. This makes the trap more practical to build and operate while still confining antimatter effectively. In one test at CERN’s Antiproton Decelerator, about 1.2 million antiprotons from a single pulse were stored for 10 minutes or more.
Temperature matters enormously. The colder the antiparticles, the slower they move and the easier they are to confine. Most experiments cool antiprotons to a few degrees above absolute zero. The PUMA project stores its antiprotons at 4 Kelvin (about minus 269°C). The ALPHA experiment has pushed antiproton temperatures down to 9 Kelvin using a technique called evaporative cooling, which works by letting the fastest particles escape and leaving behind a colder, calmer cloud.
Trapping Neutral Antihydrogen
Charged antiparticles respond to electric and magnetic fields directly, which makes them relatively manageable. Neutral atoms of antihydrogen (one antiproton paired with one positron) are a different challenge entirely. Because they carry no net charge, electric fields can’t hold them. Instead, physicists exploit a subtler property: the atom’s tiny magnetic moment, which makes it behave like a very weak bar magnet.
A device called an Ioffe trap creates a region where the magnetic field is weakest at the center and stronger in every direction around it. Antihydrogen atoms with low enough energy get pulled toward this minimum and stay trapped there, held by the slight force on their magnetic moment. The tradeoff is that these magnetic gradients interfere with the Penning traps used to make antihydrogen in the first place, so the engineering is delicate.
In 2010, the ALPHA collaboration at CERN trapped 38 antihydrogen atoms for a sixth of a second, the first time neutral antimatter had ever been stored. By 2011, they had trapped 309 atoms, some for up to 1,000 seconds (nearly 17 minutes), with signs that even longer storage was possible. That duration is comparable to how long ordinary atoms can be held in similar magnetic traps.
How Long Storage Can Last
Storage times have improved dramatically over a short period. The jump from a fraction of a second to 17 minutes for antihydrogen happened in less than a year of experimental progress. For charged antiprotons, which are simpler to confine, the BASE experiment at CERN has demonstrated storage lasting more than a year. The limiting factors are vacuum quality (stray gas molecules slowly pick off trapped particles), the stability of the magnetic fields, and the energy it takes to keep superconducting magnets cold.
Even at a trillionth of a Torr, residual gas still causes a slow trickle of annihilations. Measurements at early trapping experiments found background annihilation rates of roughly one to two counts per second. Pushing the vacuum lower and cooling the trap walls (which causes remaining gas to freeze onto surfaces and get out of the way) extends storage life considerably.
Portable Antimatter Transport
Until recently, antimatter could only exist inside the massive, fixed apparatus at facilities like CERN. The PUMA project is changing that. Its goal is to load antiprotons into a portable trap, put the whole thing on a van, and drive it to a different experimental hall a few hundred meters away.
The portable trap is about 70 centimeters long, housed inside a one-tonne superconducting solenoid magnet. The antiprotons sit in a storage zone kept at 4 Kelvin, surrounded by the extreme vacuum mentioned earlier. Once loaded, the trap is disconnected from CERN’s Antiproton Decelerator and physically driven to the ISOLDE facility, where the antiprotons will be used to study exotic atomic nuclei. It’s still a far cry from carrying antimatter in a briefcase, but it represents the first time antimatter will travel outside the machine that made it.
The Scale Problem
The quantities involved are vanishingly small. A good day at CERN’s Antiproton Decelerator produces about 30 million antiprotons per pulse, delivered every two minutes. Of those, only about 25,000 survive the process of being captured and cooled in a trap. Even the best single-shot capture has stored around 1.2 million antiprotons. For context, a gram of antihydrogen would contain roughly 600 billion trillion atoms. At current production and capture rates, it would take millions of years to accumulate a visible amount.
This isn’t just a curiosity. It’s the central obstacle to any practical use of antimatter, whether for energy, propulsion, or medicine. The cost of producing and storing even a nanogram is astronomically high, driven by the energy required to create antiparticles in particle accelerators and the infrastructure needed to trap them.
Theoretical Solid-State Storage
For applications like interstellar propulsion, physicists have explored the idea of storing antimatter as a solid or liquid rather than as a thin cloud of individual particles. The concept involves making solid antihydrogen crystals or liquid droplets and levitating them inside a container using magnetic fields, without the antimatter ever touching the container walls.
The approach relies on the fact that antihydrogen in its most common molecular form is weakly diamagnetic, meaning it gets pushed away from strong magnetic fields. By lining the inner surface of a container with arrays of superconducting loops carrying electric current, you can create a magnetic barrier that repels the antihydrogen inward. Numerical simulations have modeled various container shapes (cylindrical, spherical, ovoid) and found that these magnetic barriers can be made strong enough to hold solid antihydrogen at liquid helium temperatures. As long as the antiatoms are kept more than about ten times the width of an atom away from any ordinary matter, quantum tunneling between the two is suppressed and they can coexist without annihilation.
None of this has been built. It remains a theoretical framework, limited not by any known law of physics but by the inability to produce enough antimatter to form a solid in the first place. The modeling suggests it could work if production ever scales up, which would represent a leap from trapping a few million particles to handling trillions of trillions.