Optical photons are ideal carriers of quantum information. But to work together in a quantum computer or network, they must be of the same color — or frequency — and bandwidth. Changing the frequency of a photon requires changing its energy, which is a particular challenge for integrated photonic chips.
Recently, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) developed an integrated electro-optic modulator that can efficiently change the frequency and bandwidth of individual photons. The device could be used for more advanced quantum computers and quantum networks.
The research is published in Light: Science & Applications.
Converting a photon from one color to another is usually done by sending the photon into a crystal through which a powerful laser shines, a process that tends to be inefficient and noisy. Phase modulation, in which the oscillation of the photon wave is accelerated or decelerated to change the frequency of the photon, 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 may be particularly suitable for such an application – thin film lithium niobate.
“In our work, we introduced a new modulator design on thin-film lithium niobate, which significantly improved device performance,” said Marko Lončar, Tiantsai Lin Professor of Electrical Engineering at SEAS and senior author of the study. “With this integrated modulator, we have achieved record high terahertz frequency shifts of individual photons.”
The team also used the same modulator as a ‘time lens’ – a magnifying glass that bends light in time rather than space – to change a photon’s spectral shape from thick to thin.
“Our device is much more compact and energy efficient than traditional bulk devices,” said Di Zhu, the first author of the publication. “It can be integrated with a variety of classical and quantum devices on the same chip to realize more sophisticated quantum light control.”
Di is a former post-doctoral fellow at SEAS and is currently a Research Scientist at the Science, Research and Technology Agency (A*STAR) in Singapore.
Next, the team wants to use the device to control the frequency and bandwidth of quantum emitters for applications in quantum networks.
The research was a collaboration between Harvard, MIT, HyperLight and A*STAR.
The paper was co-authored by Changchen Chen, Mengjie Yu, Linbo Shao, Yaowen Hu, CJ Xin, Matthew Yeh, Soumya Ghosh, Lingyan He, Christian Reimer, Neil Sinclair, Franco NC Wong, and Mian Zhang.
This research was funded by Harvard Quantum Initiative (HQI), Army Research Office/Defense Advanced Projects Agency (DARPA) (W911NF2010248), Air Force Office of Scientific Research (FA9550-20-1-01015), DARPA Lasers for Universal Microscale Optical Systems (HR0011-20-C-0137), Department of Energy (DE-SC0020376), National Science Foundation (EEC-1941583), Air Force Research Laboratory (FA9550-21-1-0056), HQI Postdoctoral Fellowship, A*STAR SERC Central Research Fund (CRF) and Natural Sciences and Engineering Research Council of Canada (NSERC).
