Nuclear spins and photons are well-known building blocks for quantum information science and technology. While creating a practical interface between optical photons and nuclear spins is highly desirable to combine these two quantum systems, this is difficult due to the weak interactions that nuclear spins typically have with their environment and the vast distance between nuclear spin frequencies and optical frequencies. .

In a new study, researchers at MIT have proposed a new approach to creating qubits and controlling them to read and write data. The technique, which is still theoretical, works by using two laser beams of slightly different hues to measure and manipulate the spins of atomic nuclei.

In this process, the difference in the frequency of an incoming laser beam corresponds to the nuclear spin transition frequencies, causing the nuclear spin to move in a certain direction.

Professor Paola Cappellaro said: “We have found a new, powerful way to couple nuclear spins to optical photons from lasers. This new coupling mechanism enables their control and measurement, making the use of nuclear spins as qubits a much more promising endeavor.”

Scientists noted, “The process is fully tunable. For example, one of the lasers can be tuned to the frequencies of existing telecom systems, converting the nuclear spins into quantum repeaters to enable quantum communication over long distances.”

The researchers used the electrical quadrupole that many nuclei possess, which results in an electrical nuclear quadrupolar interaction with the environment, for the new strategy. Light can modify this interaction and change the internal state of the nucleus.

Professor Ju Li said: “Nuclear spin is usually quite weakly interactive. But by taking advantage of the fact that some nuclei have an electric quadrupole, we can induce this second-order nonlinear optical effect that couples directly to the nuclear spin without intervening electron spins. This allows we manipulate the nuclear spin directly.”

Scientists noted, “It allows, among other things, isotopes of materials to be accurately identified and even mapped, while Raman spectroscopy, a well-established method based on analogous physics, can identify the chemistry and structure of the material, but not isotopes. This capability could have many applications.”

“Since optical photons are used for long-distance communication over fiber optic networks, the ability to couple these photons directly to quantum memory or sensing devices could provide significant benefits in new communication systems. In addition, the effect could provide an efficient way to translate one set of wavelengths to another .”

MIT doctoral student Haowei Xu said: “We are thinking about using nuclear spins for the transduction of microwave photons and optical photons. This can yield greater fidelity of such a translation than other methods.”

“So far the work is theoretical, so the next step is to implement the concept in real lab equipment, probably in a spectroscopic system. This could be a good candidate for the proof-of-principle experiment. Then they tackle quantum devices , such as memory or transduction effects.”

Magazine reference:

  1. Haowei Xu, Changhao Li, Guoqing Wang, et al. Two-photon interface of nuclear spins based on the optonuclear quadrupolar effect. Physical Review X. DOI: 10.1103/PhysRevX.13.011017