Currently, a handful of technologies are leading contenders for producing a useful quantum computer. Companies have used them to build machines with dozens to hundreds of qubits, error rates are falling, and they have largely moved from basic science problems to engineering problems.
Yet even at this seemingly late date in the field’s development, there are companies still developing entirely new qubit technologies, betting the company has identified something that would allow them to scale in a way that would enable a dating history. Recently, one such company published a paper describing the physics of their qubit system, which involves solitary electrons floating on liquid helium.
Trapping single electrons
So how do you make an electron float on helium? To find out, ARS spoke with Johannes Pollanen, the scientific director of Eeroq, the company that carried out the new work. He said it was actually old physics, with the first manifestations of it half a century ago.
“If you bring a charged particle like an electron close to the surface, because helium is dielectric, it will create a little image charge underneath in the liquid,” Pollanen said. “A little bit of positive charge, much weaker than the electron charge, but there will be a little positive image there. And then the electron will naturally be bound to its own image. It will just see this positive charge and kind of want to move towards it, but it can’t get there, because helium is completely chemically inert, there are no free spaces for electrons.”
Obviously, getting the helium liquid in the first place requires extremely low temperatures. But it can actually remain liquid at temperatures of 4 Kelvin, which doesn’t require the extreme refrigeration technologies needed for things like transmons. These temperatures also provide a natural vacuum, as just about everything else will condense on the walls of the container as well.
The chip itself, as well as diagrams of its organization. The trap is set by the gold electrode on the left. The dark channels allow liquid helium and electrons to flow in and out of the trap. And the bluish electrodes at the top and bottom read the presence of electrons.
Credit: eeroq
Liquid helium is also a superfluid, meaning it flows without viscosity. This allows it to easily cast tiny channels cut into the surface of the silicon chips the company used for its experiments. A tungsten filament next to the chip was used to charge the helium surface with electrons to what you might consider the equivalent of a storage tank.
