Debnath and colleagues at the University of Maryland reveal their new device can solve three algorithms using quantum effects to perform calculations in a single step, where a normal computer would require several operations.
Debnath's quantum computer works by stringing five qubits in a line, and using lasers to manipulate them. These qubits are basically just tightly-trapped atoms of the element ytterbium. By shining a laser on the atoms with an exact staccato pulse of light, you can throw them into superposition—the state where they're doing two opposite things at the same time such as spinning in two directions with different angular momentum. That's where the quantum principle called entanglement comes in.
In this new quantum computer, Debnath's team can use different pulses of laser light to entangle different pairs of the qubit atoms together,even ones not next to one another in a line,so that if something happens to one, it also effects the other. Basically, the scientists can force different atoms to share a piece of arbitrary information.
This is what allows the computer to tackle different problems and be programmed with new algorithms. Normally you'd have to physically rearrange your quantum computer's parts to adjust it to run different problems. But the laser-based setup of Debnath's quantum computer allows him to fire lasers at any of his five 5 qubits, entangling pairs of qubits together in whatever order he wants.
This flexibility allows Debnath's team to rapidly re-program their computer to solve different problems and run different algorithms. And if they come up with a new algorithm they'd like to run, all they have to do is figure out which atoms need to be entangled and in what order, and then let the lasers do the rest.
Debnath's team "demonstrated several algorithms. [Including two] which both use quantum effects to perform a mathematical calculation in a single step, whereas a conventional computer would require several operations. They also demonstrate a quantum Fourier transform, which is a key component of many of the heftier quantum algorithms, such as those used to break encryption.
Debnath and his colleagues are still a long ways from where we'd like to be with quantum computers. Their machine can only handle small algorithms, and gives answers more slowly than even the most sluggish traditional computer. But having a quantum computer that can be reprogrammed without being physically disassembled and reconstructed is a good start.