It's not just spin – boffins give quantum computing a room-temp makeover

Practical quantum computers are still on the horizon, but scientists continue to make improvements in the underlying technology required to make such systems possible.

Two research teams have published on alternative approaches to quantum, one on manipulating the spin of electrons at room temperature, the other on using natural quantum interactions to solve problems.

An international team of researchers, led by the University of Cambridge, said it has found a way to control the interaction of light and the spin of electrons, making them behave like tiny magnets that could be used for quantum applications, and which works even at room temperature.

Meanwhile, another team at Los Alamos National Laboratory (LANL), in the US state of New Mexico, claims to have developed a way of implementing an algorithm in natural quantum interactions that eliminates some of the challenging requirements for quantum hardware.

The Cambridge research involves organic semiconductors, similar to those used to emit light in digital displays such as computer screens. In the research, they are used to create molecular units connected by tiny "bridges," and applying light to these bridges was found to make electrons on opposite ends of the structure connect by aligning their spin states. These electrons remain aligned via their spins even if the bridge is then removed.

According to the team, this level of control over quantum properties can normally only be achieved at cryogenic temperatures, as is the case with many superconducting qubit technologies. Instead, the team claims it is able to control the quantum behavior of its materials at room temperature, and this opens up a number of potential quantum applications by reliably coupling spins to photons.

Organic semiconductors have not yet been widely studied for quantum applications, such as quantum computing or quantum sensing, according to Sebastian Gorgon, first author on the research paper and Bye-Fellow at Cambridge's Cavendish Laboratory.

"We've now taken the next big step and linked the optical and magnetic properties of radicals in an organic semiconductor," Gorgon said. "These new materials hold great promise for completely new applications, since we've been able to remove the need for ultra-cold temperatures."

The results are reported in the journal Nature, while the paper "Reversible spin-optical interface in luminescent organic radicals" is available here [PDF].

Over at the LANL, researchers claim it is possible to implement an algorithm in natural quantum interactions to process a variety of real-world problems faster than classical computers or even conventional gate-based quantum computers.

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Nikolai Sinitsyn, a postdoctoral research associate at LANL and co-author of the paper, said that natural systems, such as the electron spins of defects in diamond, exhibit precisely the type of interactions needed for computational processes.

"Our finding eliminates many challenging requirements for quantum hardware," he said.

Instead of setting up a complex system of logic gates among a number of qubits that must all share quantum entanglement, the new approach is claimed to use a simple magnetic field to manipulate the qubits, such as the spins of electrons, in a natural system.

Sinitsyn said that precise evolution of the spin states is all that is needed to implement the algorithm, and that this could be used to solve many practical problems that supposedly call for quantum computers.

Because this approach relies on natural rather than induced entanglement, it is said to require fewer connections among qubits. This reduces the risk of decoherence and the qubits therefore "live" for relatively a long time, according to Sinitsyn.

The paper by the LANL team describes how its approach could be used to solve a number-partitioning problem using Grover's algorithm, a quantum method for searching large data sets that would take a considerable amount of time and resources using conventional computers.

This algorithm is well suited to idealized, error-corrected quantum computers, but none of these currently exist and it would be difficult to implement on today's error-prone machines, Sinitsyn claimed.

The paper, titled "Topologically protected Grover's oracle for the partition problem" is published in the scientific journal Physical Review A. ®