Researchers set `ultrabroadband' record with entangled photons
Thin-film nanophotonic device could advance metrology, sensing, and
quantum networks

Date:
October 29, 2021
Source:
University of Rochester
Summary:
Researchers take advantage of quantum entanglement to generate an
incredibly large bandwidth using a thin-film nanophotonic device
that could lead to advances in metrology, sensing and quantum
networks for information processing and communications.



FULL STORY ========================================================================== Quantum entanglement -- or what Albert Einstein once referred to as
"spooky action at a distance" -- occurs when two quantum particles
are connected to each other, even when millions of miles apart. Any
observation of one particle affects the other as if they were
communicating with each other. When this entanglement involves photons, interesting possibilities emerge, including entangling the photons' frequencies, the bandwidth of which can be controlled.


========================================================================== Researchers at the University of Rochester have taken advantage of this phenomenon to generate an incredibly large bandwidth by using a thin-film nanophotonic device they describe in Physical Review Letters.

The breakthrough 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," No more tradeoff between bandwidth and brightness
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 lead author Usman Javid, a PhD student in
Lin's lab. In those devices, "there will always be a tradeoff 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 Lin's lab 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, according to Javid. This makes the propagation of light extremely sensitive to the dimensions of the waveguide.

Indeed, 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," Javid says.

The device is ready to be deployed in experiments, but only in a lab
setting, Javid says. 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 is "still in its infancy, and it will take some time
to mature enough to make financial sense," he says.

Other collaborators include coauthors Jingwei Ling, Mingxiao Li,
and Yang He of the Department of Electrical and Computer Engineering,
and Jeremy Staffa of the Institute of Optics, all of whom are graduate students. Yang He is a postdoctoral researcher.

The National Science Foundation, the Defense Threat Reduction Agency, and
the Defense Advanced Research Projects Agency helped fund the research.

========================================================================== Story Source: Materials provided by University_of_Rochester. Original
written by Bob Marcotte. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Usman A. Javid, Jingwei Ling, Jeremy Staffa, Mingxiao Li, Yang
He, Qiang
Lin. Ultrabroadband Entangled Photons on a Nanophotonic
Chip. Physical Review Letters, 2021; 127 (18) DOI:
10.1103/PhysRevLett.127.183601 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211029114005.htm

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