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Nanophotonic chip achieves ‘ultrabroadband’ quantum entanglement

Nanophotonic chip achieves ‘ultrabroadband’ quantum entanglement

Technology News |
By Rich Pell



Quantum entanglement occurs when two quantum particles are connected to each other, no matter the distance between them – any observation of one particle affects the other as if they were communicating with each other. When this entanglement involves photons, say the researchers, interesting possibilities emerge, including entangling the photons’ frequencies, the bandwidth of which can be controlled.

Exploiting this phenomenon, the researchers were able to generate “an incredibly large bandwidth” of entangled photon pairs using a thin-film nanophotonic device. A laser beam enters the periodically poled thin-film lithium niobate waveguide and entangled photons are generated with a bandwidth exceeding 800 nanometers (image).

This breakthrough, say the researchers, could lead to:

  • Enhanced sensitivity and resolution for experiments in metrology and sensing, including spectroscopy, nonlinear microscopy, and quantum optical coherence tomography
  • Higher dimensional encoding of information in quantum networks for information processing and communications

“This work represents a major leap forward in producing ultrabroadband quantum entanglement on a nanophotonic chip,” says Qiang Lin, professor of electrical and computer engineering. “And it demonstrates the power of nanotechnology for developing future quantum devices for communication, computing, and sensing.”

To date, most devices used to generate broadband entanglement of light have resorted to dividing up a bulk crystal into small sections, each with slightly varying optical properties and each generating different frequencies of the photon pairs. The frequencies are then added together to give a larger bandwidth.

“This is quite inefficient and comes at a cost of reduced brightness and purity of the photons,” says Usman Javid, a PhD student in Lin’s lab, and lead author of a paper on the research. “[With those devices] there will always be a trade-off between the bandwidth and the brightness of the generated photon pairs, and one has to make a choice between the two. We have completely circumvented this tradeoff with our dispersion engineering technique to get both: a record-high bandwidth at a record-high brightness.”

The thin-film lithium niobate nanophotonic device created by the researchers uses a single waveguide with electrodes on both sides. Whereas a bulk device can be millimeters across, the thin-film device has a thickness of 600 nanometers – more than a million times smaller in its cross-sectional area than a bulk crystal, making the propagation of light extremely sensitive to the dimensions of the waveguide.

Even a variation of a few nanometers can cause significant changes to the phase and group velocity of the light propagating through it. As a result, the researchers’ thin-film device allows precise control over the bandwidth in which the pair-generation process is momentum-matched.

“We can then solve a parameter optimization problem to find the geometry that maximizes this bandwidth,” says Javid.

The device is ready to be deployed in experiments, but only in a lab setting, say the researchers. In order to be used commercially, a more efficient and cost-effective fabrication process is needed. And although lithium niobate is an important material for light-based technologies, lithium niobate fabrication will take some time to mature enough to make financial sense.

For more, see “Ultrabroadband Entangled Photons on a Nanophotonic Chip.”

Related articles:
Quantum loop entangles photons over 52-mile fiber network
Quantum microscope can see ‘the impossible’
High-fidelity, sustained quantum teleportation demonstrated
Smaller chips promise affordable quantum communications
Entangled qubit states sent through a communication cable

 

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