High-Visibility Interference of Independent Semiconductor Quantum Dots Holds Vital Outcome for Information Science

Scientists have successfully demonstrated the ability to create a strong, observable connection between two separate semiconductor quantum dots, which is a crucial step toward building a scalable quantum network. This breakthrough relates to the principles of quantum entanglement, which won the Nobel Prize in Physics last year and is seen as having the potential to lead to a "second quantum revolution" in which we can more effectively utilize the strange properties of quantum mechanics, including superposition and entanglement.

A fully functioning, large-scale quantum network could lead to significant advances in quantum computing, communication, and measurement, and is considered a major goal in the field of quantum information science. One of the major challenges in developing quantum communication is increasing its effective range.

Quantum Dots Vital Outcome

As Journal Break reported, unlike classical signals, which can be amplified without introducing noise, it is not possible to amplify quantum states in superposition because they cannot be perfectly copied. This means that a high-performing quantum network requires not only low-loss channels and memory for storing quantum information but also highly efficient sources of quantum light. While there have been significant advances in using satellites for quantum communication and in creating quantum repeaters, progress has been limited due to the lack of suitable single-photon sources.

For a single-photon source to be suitable for use in a quantum network, it must meet several requirements. First, it should be able to emit only one photon at a time. Second, it should have a high system efficiency and a high repetition rate to produce a bright output. Third, the photons it emits should be indistinguishable from one another to facilitate interference in applications such as quantum teleportation. Other desirable qualities include the ability to be scaled up, the ability to produce photons with a narrow and tunable bandwidth, and compatibility with matter qubits for interconnectivity.

Quantum dots (QDs) have emerged as a promising candidate for use as a single-photon source in a quantum network. QDs are tiny semiconductor particles, measuring just a few nanometers in size. However, in the past, the visibility of quantum interference between independent QDs has been limited, rarely exceeding 50% (the classical limit) and the distance over which this interference can be observed has been limited to just a few meters or kilometers.

Quantum Interference of Optic Fibers

According to a recent report published in Advanced Photonics, an international team of researchers has achieved high visibility quantum interference between two independent QDs connected via approximately 300 km of optical fibers. The team was able to create efficient, indistinguishable single-photon sources with low noise, tunable frequency conversion, and low dispersion transmission over long distances. The single photons were generated from QDs that were resonantly driven and deterministically coupled to microcavities.

Quantum frequency conversion was used to eliminate inhomogeneity in the QDs and shift their emission wavelength to the telecommunications band. The observed interference visibility was as high as 93%. The lead author, Professor Chao-Yang Lu of the University of Science and Technology of China, stated that it may be possible to further extend the distance to around 600 km with additional improvements.

Professor Lu commented on the significance of this achievement, stating that it represents a significant increase in distance from previous QD-based quantum experiments, which were limited to around 1 km. By achieving quantum interference over a distance of 300 km, the researchers have demonstrated the potential for solid-state quantum networks on a much larger scale, potentially paving the way for the development of these networks soon, as SciTech Daily reported.

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