IBM uses quantum states to create software

IBM Corp. had been experimenting with creating algorithms out of quantum mechanical forces, but a team at the company's Almaden Research Laboratory, working with Microsoft Corp. scientists, has devised a way to create one-use-only software by exploiting quantum states.

Published in the latest edition of the journal Nature, the results are purely theoretical and probably will not become products for decades. But the research does extend the already-bizarre possibilities of quantum computing, uncovering "a regime of physics we have never encountered before," said Isaac Chuang, IBM Almaden researcher.

The idea stems from quantum teleportation, the recently discovered ability to transmit quantum states without sending any quantum information. If those states could be stored ahead of time, they could act as prefab software: The states would be transmitted to a user and would represent bits that had been run through a particular function or algorithm.

Transmission would occur over a type of "quantum Internet," a phrase coined by researchers at Los Alamos National Laboratory.

The act of using the software would alter the quantum states and thus destroy the software. In part, that's why Microsoft was involved in this area of Chuang's research.

Quantum computing exploits quantum mechanics to do otherwise-impossible computations. In particular, if an atomic nucleus can be put in a state between two stable energy levels, quantum mechanics holds that it will exist at both levels at the same time, essentially being in two places at once. In computing applications, it means a bit can be a 0 and a 1 simultaneously.

This means that a quantum computer could examine multiple possibilities of a problem — it could study both sides of a coin with only one toss, for example. A more telling example lies in databases. Chuang and his colleagues have devised a three-qubit (quantum bit) machine that can search an eight-item database for one "special" item. A standard computer will average just under four tries to find the special item. For the quantum computer, which can test multiple possibilities simultaneously, the average is just under two.

The quantum bits are particular nuclei that exhibit "coherence" — the ability to stay in the simultaneous 0-and-1 state for useful amounts of time. Different atoms will become coherent under different pulses of magnetism, so to perform particular computations, molecules must be found that combine the desired nuclei. "I've learned a lot of chemistry doing this," Chuang said.

Multiple methods for quantum computing are being explored. IBM Almaden is using magnetic spins to record information, controlling nuclear states using electromagnetic pulses at particular frequencies. Using these methods, Chuang and his colleagues have developed the largest quantum-computing systems to date.

Quantum software would act on a principle called "teleportation," demonstrated two years ago. If two particles share an "entangled pair" of photons, they can communicate quantum states without sending any information. Thus, it's conceivable that an entangled pair could be created that would receive a set of quantum bits as if a particular function had been performed on them.

Such "software" could be used only once; per Heisenberg's principle, the act of viewing the quantum states alters them. In addition, the entangled pair of photons is fragile and must be precisely prepared.

Chuang originally researched optical networking but was inspired to investigate quantum computing by a book of essays by the late physicist Richard Feynman, who predicted quantum computing decades ago.