A team of scientists at the Massachusetts Institute of Technology (MIT) and the University of Innsbruck in Austria announced Friday that they had built the world’s first scalable quantum computer, paving the path for the creation of a device with a large number of “qubits” — the quantum computing equivalents of bits.
The device, described in a paper published in the journal Science, utilizes five qubits, each represented by a single atom. The entire system was held stable by holding the atoms in an “ion trap” — created by removing an electron from each atom. Each atom was held in place with an electric field.
“That way, we know exactly where that atom is in space,” co-author Isaac Chuang, professor of physics and professor of electrical engineering and computer science at MIT, said in a statement. “Then we do that with another atom, a few microns away — [a distance] about 100th the width of a human hair. By having a number of these atoms together, they can still interact with each other, because they’re charged. That interaction lets us perform logic gates. … The gates we perform can work on any of these kinds of atoms, no matter how large we make the system.”
The development of quantum computers capable of performing operations many orders of magnitude faster than conventional computers has been a goal of computer scientists and physicists ever since the idea was first floated in the early 1980s. However, given the inherently unstable nature of qubits, the goal has remained out of reach.
Quantum computers utilize two basic properties these qubits possess — superposition and entanglement. Unlike conventional bits, which can exist in one of the two states, 0 and 1, qubits can exist in superposition, allowing them to have both states at the same time. This superposition of qubits, coupled with quantum entanglement — wherein they are physically separate but act as if they are connected — is what gives quantum computers a significant advantage over conventional computers.
The device described in the latest study was tested on the notoriously difficult “factoring problem,” which involves calculating the prime factors of a number. This problem is the basis for encryption schemes — such as the RSA — that are used for protecting credit cards, state secrets, and other confidential data. It relies on the fact that even hundreds of classical computers functioning in parallel would require a long time to calculate the factors of a large number.
While the proof of concept has only been applied to the number 15, the researchers said that theirs is the “first scalable implementation” of quantum computing to implement Shor’s algorithm, a quantum algorithm devised in 1994 by Peter Shor, a professor of applied mathematics at MIT.
The five-atom quantum computer has the potential to crack the security of traditional encryption schemes that rely on factoring as a hard-to-solve problem.
“In future generations, we foresee it being straightforwardly scalable, once the apparatus can trap more atoms and more laser beams can control the pulses,” Chuang said in the statement. “It might still cost an enormous amount of money to build — you won’t be building a quantum computer and putting it on your desktop anytime soon — but now it’s much more an engineering effort, and not a basic physics question.”