Changing the color of quantum light on an integrated chip

Devices could advance quantum computing and quantum networks.

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Manipulating the frequency and bandwidth of nonclassical light is essential for implementing frequency-encoded/multiplexed quantum computation, communication, and networking protocols and bridging spectral mismatch among various quantum systems. However, quantum spectral control requires a strong nonlinearity mediated by light, microwave, or acoustics, which is challenging to realize with high efficiency, low noise, and on an integrated chip.

Applied scientists and engineers from Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS) recently created an integrated electro-optic modulator that effectively modifies the frequency and bandwidth of single photons. Quantum networks and more sophisticated quantum computing could also benefit from the device.

A photon is typically converted from one color to another by passing it into a crystal with a powerful laser beam; however, this method is typically ineffective and loud. A more effective technique is phase modulation, in which the oscillation of a photon wave is sped up or slowed down to change the photon’s frequency. However, it has proven challenging to incorporate an electro-optic phase modulator on a chip.

Thin-film lithium niobate could be suitable for such applications.

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

Using the same modulator as a time lens, the team changed the spectral shape of a photon from fat to skinny.

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

Scientists further want to use the device to control the frequency and bandwidth of quantum emitters for applications in quantum networks.

Journal Reference:

  1. Zhu, D., Chen, C., Yu, M. et al. Spectral control of nonclassical light pulses using an integrated thin-film lithium niobate modulator. Light Sci Appl 11, 327 (2022). DOI: 10.1038/s41377-022-01029-7
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