Just now, two studies lead to new quantum alternatives

Two research groups have recently published articles on quantum alternatives, one of which manipulates electron spins at room temperature and the other uses natural quantum interactions to solve the problem.

An international team of researchers led by the University of Cambridge says they have found a way to control the interaction of light with electron spins so that they behave like tiny magnets that can be used for quantum applications; even working at room temperature.

Meanwhile, another team of researchers at Los Alamos National Laboratory (LANL) in New Mexico, USA, claim to have developed a way to implement algorithms in natural quantum interactions, thus eliminating some of the challenging requirements of quantum hardware.

The Cambridge group's findings were published Aug. 16 in the journal Nature under the title "Reversible spin-optical interface in luminescent organic radicals."

On August 14, the LANL group's research was published in Physical Review A under the title "Topologically protected Grover's oracle for the partition problem".

The Cambridge study involved organic semiconductors, similar to those used to emit light in digital displays such as computer screens. In the study, they were used to create molecular units connected by tiny "bridges"; it was found that applying light to these bridges caused the electrons at either end of the structure to align through their spin states. Even when the bridges are removed, the electrons remain aligned by their spins.

According to the team, this level of quantum property control is usually only possible at low temperatures, as is the case with many superconducting quantum bit technologies. Instead, the team claims that it is able to control the quantum behavior of its materials at room temperature: opening up many potential quantum applications by reliably coupling spins to photons.

Organic semiconductors have not been widely studied for quantum applications such as quantum computing or quantum sensing, says Sebastian Gorgon, first author of the research paper and a researcher at the Cavendish Laboratory at the University of Cambridge.

"We've now taken another big step by linking the optical and magnetic properties of free radicals in organic semiconductors, and these new materials hold great promise for a whole new range of applications, as we no longer need ultra-low temperatures."

Spin resonance (ESR) in high-spin states

Room temperature spin dynamics and ground state control

At LANL, the researchers claim it is possible to implement an algorithm in natural quantum interactions that can handle a wide range of real-world problems at a much faster rate than classical computers or even conventional gate-based quantum computers.

Nikolai Sinitsyn, co-author of the paper and a postdoctoral assistant researcher at LANL, says that natural systems, such as the electron spins of defects in diamond, exhibit exactly the type of interactions required for computational processes.

"Our discovery eliminates many of the challenging requirements of quantum hardware," he said.

Instead of having to build a complex system of logic gates between a large number of quantum bits that must share quantum entanglement, the new method utilizes a simple magnetic field to manipulate quantum bits, such as electron spins, in natural systems.

The precise evolution of spin states is all that is needed to implement the algorithm, which can be used to solve many of the practical problems that purportedly require a quantum computer, Sinitsyn said.

Because the method relies on natural entanglement rather than induced entanglement, fewer connections between quantum bits are needed, which Sinitsyn says reduces the risk of decoherence, so quantum bits can "live" for relatively long periods of time.

The LANL team's paper describes how the Grover algorithm can be used to solve the digital partitioning problem: Grover's algorithm is a quantum method for searching large datasets, which would take a lot of time and resources using conventional computers.

The experimental team says the algorithm is well suited to an idealized error-correcting quantum computer; however, such a computer does not currently exist and would be difficult to implement on today's error-prone machines.

Reference link:

[1]https://www.nature.com/articles/s41586-023-06222-1

[2]https://journals.aps.org/pra/abstract/10.1103/PhysRevA.108.022412

[3] https://www.theregister.com/2023/08/16/novel_quantum_approaches/