Combining classical and quantum systems to meet supercomputing needs

Quantum entanglement is a fundamental and fascinating phenomenon in nature. Entanglement has been shown to be a valuable resource for quantum communication and information processing in recent research. Now, Japanese scientists have discovered a stable quantum entangled state for two protons on a silicon surface, paving the way for an organic fusion of classical and quantum computing platforms and potentially bolstering quantum technology’s future.

Quantum entanglement is one of the most fascinating phenomena in quantum mechanics. This phenomenon describes how certain particles are inextricably linked to one another, to the point where their states can only be described in terms of their interactions. Additionally, this particle interaction serves as the foundation for quantum computing. And it is for this reason that physicists have been looking for ways to generate entanglement in recent years. These techniques, however, face a number of engineering challenges, including limitations on the number of “qubits” (quantum bits, the fundamental unit of quantum information), the requirement for extremely low temperatures (1 K), and the use of ultrapure materials. Quantum entanglement is formed at surfaces or interfaces. Unfortunately, electrons confined to surfaces are prone to “decoherence,” a state in which the two distinct states have no defined phase relationship. Thus, in order to obtain stable, coherent qubits, it is necessary to determine the spin states of surface atoms (or, more precisely, protons).

Recently, a group of Japanese scientists led by Prof. Takahiro Matsumoto of Nagoya City University, Prof. Hidehiko Sugimoto of Chuo University, Dr. Takashi Ohhara of the Japan Atomic Energy Agency, and Dr. Susumu Ikeda of the High Energy Accelerator Research Organization recognised the importance of stable qubits. The scientists discovered an entangled pair of protons on the surface of a silicon nanocrystal by examining the surface spin states.

Prof. Matsumoto, the study’s lead scientist, summarises the study’s significance: “Proton entanglement has been observed previously in molecular hydrogen and is critical in a number of scientific disciplines. However, the entangled state has been observed only in the gas or liquid phases. We have now detected quantum entanglement on a solid surface, paving the way for future quantum technologies.” Their groundbreaking study was recently published in the journal Physical Review B.

The scientists determined the nature of surface vibrations by studying spin states using a technique called “inelastic neutron scattering spectroscopy.” They demonstrated the anti-symmetry of protons by modelling these surface atoms as “harmonic oscillators.” Due to the fact that the protons were identical (or virtually identical), the oscillator model limited their possible spin states, resulting in strong entanglement. In comparison to the proton entanglement in molecular hydrogen, the entanglement possessed a large energy difference between its states, which ensured its longevity and stability. Additionally, the scientists used proton entanglement to theoretically demonstrate a cascade transition of terahertz entangled photon pairs.

Convergence of proton qubits and contemporary silicon technology may result in an organic fusion of classical and quantum computing platforms, enabling significantly more qubits (106) than are currently available (102), as well as ultra-fast processing for new supercomputing applications. “Quantum computers are capable of solving complex problems, such as integer factorization and the ‘travelling salesman problem,’ that are virtually impossible to solve using conventional supercomputers. This could be a game changer in terms of storing, processing, and transferring data in quantum computing, potentially resulting in a paradigm shift in pharmaceuticals, data security, and a variety of other fields “Prof. Matsumoto concludes optimistically.

We may be on the verge of a quantum computing technological revolution.

Reference
Takahiro Matsumoto et al, Quantum proton entanglement on a nanocrystalline silicon surface, Physical Review B (2021). DOI: 10.1103/PhysRevB.103.245401