Researchers at the University of Rochester's Qiang Lin have created a record-breaking ultrabroadband bandwidth of entangled photos using the thin film nanophotonic device shown here. A laser beam is seen entering a thin-film, bipolar lithium niobate waveguide. It's shown at the top left. With a bandwidth of 800 nanometers, entangled photons (purple or red dots) can be generated. Credit: Usman Javi and Michael Osadciw
Quantum entanglement, also known as what Albert Einstein used to call "spooky actions at a distance", is when two quantum particles are connected even though they are millions of miles apart. As if one particle were communicating with the other, any observation of one particle will affect the other. This entanglement can occur with photons. There are many possibilities, such as entangling their frequencies and allowing them to be controlled in bandwidth.
Researchers from the University of Rochester used this phenomenon to generate a tremendous bandwidth using a thin film nanophotonic device that they describe in Physical Review Letters.
This breakthrough could lead:
For experiments in metrology, sensing, such as spectroscopy and nonlinear microscopy and quantum optical coherence, enhanced sensitivity and resolution are possible.
Quantum networks for information processing, communications and higher dimensional information encoding
Professor of electrical and computer engineering Qiang Lin says, "This work represents an important leap forward in producing ultrabroadband quantum entanglement onto a nanophotonic chips." It also demonstrates the potential of nanotechnology to develop future quantum devices for computing, sensing, and communication,"
There is no more compromise between brightness and bandwidth
Broadband entanglement of light is achieved by dividing a bulk crystal into smaller sections. Each section has slightly different optical properties and generates different frequencies. To give a wider bandwidth, the frequencies are combined.
Lead author Usman Javid is a Ph.D. student at Lin's lab. "This is very inefficient and comes with a cost of reduced brightness, purity of the photons." There will always be a compromise between the bandwidth of the generated photon pairs and their brightness, so one must choose between them. With our dispersion engineering technique, we have overcome this tradeoff to achieve both: record-high bandwidth and record-high brightness.
Lin's lab created a thin-film lithium nanophotonic device using a single waveguide and electrodes on both ends. Javid says that while a bulk device may measure up to millimeters in width, the thin-film device is 600 nanometers thinner than a bulk crystal. This makes propagation of light sensitive to the dimensions and shape of the waveguide.
Even a small variation in the thickness of the film can have significant effects on the velocity and phase of light passing through it. The researchers developed a thin-film device that allows them to control the bandwidth within which momentum-matched pair-generation processes can occur. Javid states, "We can then solve the parameter optimization problem to determine the geometry that maximizes this bandwidth."
Javid states that the device can be used in experiments but it is only suitable for lab use. A more cost-effective and efficient manufacturing process is required in order to make the device commercially viable. He says that lithium niobate, although an important material in light-based technologies such as lasers, is still in its infancy and will need to be refined to make financial sense.
Coauthors Jingwei Ling and Mingxiao Li of the Department of Electrical and Computer Engineering and Yang He of Institute of Optics are also coauthors. All three of them are graduate students. Yang He is a postdoctoral research fellow.
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Additional information: Usman A. Javid and colleagues, Ultrabroadband Entangled Photos on a Nanophotonic Chip. Physical Review Letters (2021). Information for Journal: Physical Review Letters Usman A. Javid and colleagues, Ultrabroadband Entangled Photons On a Nanophotonic Chip (2021). DOI: 10.1103/PhysRevLett.127.183601
