Dawn of solid-state quantum networks

This yr’s Nobel Prize in Physics celebrated the elemental curiosity of quantum entanglement, and in addition envisioned the potential functions in “the second quantum revolution” — a brand new age after we are in a position to manipulate the weirdness of quantum mechanics, together with quantum superposition and entanglement. A big-scale and absolutely useful quantum community is the holy grail of quantum data sciences. It will open a brand new frontier of physics, with new potentialities for quantum computation, communication, and metrology.

One of essentially the most important challenges is to increase the space of quantum communication to a virtually helpful scale. Unlike classical indicators that may be noiselessly amplified, quantum states in superposition can’t be amplified as a result of they can’t be completely cloned. Therefore, a high-performance quantum community requires not solely ultra-low-loss quantum channels and quantum reminiscence, but additionally high-performance quantum gentle sources. There has been thrilling current progress in satellite-based quantum communications and quantum repeaters, however a scarcity of appropriate single-photon sources has hampered additional advances.

What is required of a single-photon supply for quantum community functions? First, it ought to emit one (just one) photon at a time. Second, to achieve brightness, the single-photon sources ought to have excessive system effectivity and a excessive repetition fee. Third, for functions resembling in quantum teleportation that require interfering with unbiased photons, the one photons must be indistinguishable. Additional necessities embrace a scalable platform, tunable and narrowband linewidth (favorable for temporal synchronization), and interconnectivity with matter qubits.

A promising supply is quantum dots (QDs), semiconductor particles of just some nanometers. However, up to now 20 years, the visibility of quantum interference between unbiased QDs has not often exceeded the classical restrict of fifty% and distances have been restricted to round a couple of meters or kilometers.

As reported in Advanced Photonics, a global crew of researchers has achieved high-visibility quantum interference between two unbiased QDs linked with ~300 km optical fibers. They report environment friendly and indistinguishable single-photon sources with ultra-low-noise, tunable single-photon frequency conversion, and low-dispersion lengthy fiber transmission. The single photons are generated from resonantly pushed single QDs deterministically coupled to microcavities. Quantum frequency conversions are used to eradicate the QD inhomogeneity and shift the emission wavelength to the telecommunications band. The noticed interference visibility is as much as 93%. According to senior creator Chao-Yang Lu, professor on the University of Science and Technology of China (USTC), “Feasible improvements can further extend the distance to ~600 km.”

Lu remarks, “Our work jumped from the previous QD-based quantum experiments at a scale from ~1 km to 300 km, two orders of magnitude larger, and thus opens an exciting prospect of solid-state quantum networks.” With this reported bounce, the daybreak of solid-state quantum networks could quickly start breaking towards day.

Read the Gold Open Access article by X. You et al., “Quantum interference with independent single-photon sources over 300 km fiber,” Adv. Photon. 4(6), 066003 (2022), doi 10.1117/1.AP.4.6.066003.