On-chip quantum spectral control demonstrated

Technology News |
By Rich Pell

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) say they developed an integrated electro-optic modulator that can efficiently change the frequency and bandwidth of single photons. The device could be used for more advanced quantum computing and quantum networks.

Manipulating the frequency and bandwidth of nonclassical light is essential for implementing frequency-encoded/multiplexed quantum computation, communication, and networking protocols, and for bridging spectral mismatch among various quantum systems. However, changing a photon’s frequency requires altering its energy, which is particularly challenging on integrated photonic chips.

Converting a photon from one color to another is usually done by sending the photon into a crystal with a strong laser shining through it, a process that tends to be inefficient and noisy. Phase modulation, in which a photon wave’s oscillation is accelerated or slowed down to change the photon’s frequency, offers a more efficient method, but the device required for such a process – an electro-optic phase modulator – has proven difficult to integrate on a chip.

One material that may be uniquely suited for such an application, say the researchers, is thin-film lithium niobate.

“In our work, we adopted a new modulator design on thin-film lithium niobate that significantly improved the device performance,” says Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering at SEAS and senior author of the study. “With this integrated modulator, we achieved record-high terahertz frequency shifts of single photons.”

The researchers also used the same modulator as a “time lens” – a magnifying glass that bends light in time instead of space – to change the spectral shape of a photon from fat to skinny.

“Our device is much more compact and energy-efficient than traditional bulk devices,” says Di Zhu, the first author of the paper. “It can be integrated with a wide range of classical and quantum devices on the same chip to realize more sophisticated quantum light control.”

Looking ahead, the researchers say they plan to use the device to control the frequency and bandwidth of quantum emitters for applications in quantum networks. For more, see “Spectral control of nonclassical light pulses using an integrated thin-film lithium niobate modulator.”


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