Changing the color of quantum light on an integrated chip

Manipulation of the frequency and bandwidth of non-classical light is essential for implementing frequency-encoded/multiplexed quantum computation, communication and network protocols and bridging spectral mismatches between different quantum systems. However, quantum spectral control requires strong nonlinearity mediated by light, microwave, or acoustics, which is difficult to realize with high efficiency, low noise, and on an integrated chip.

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

A photon is typically converted from one color to another by directing it into a crystal with a powerful laser beam; however, this method is typically ineffective and noisy. A more effective technique is phase modulation, in which the oscillation of a photon wave is accelerated or slowed down to change the frequency of the photon. However, it has proven difficult to integrate 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 introduced a new modulator design on thin-film lithium niobate, which significantly improved 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 a photon’s spectral shape from thick to thin.

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

In addition, scientists want to use the device to control the frequency and bandwidth of quantum emitters for applications in quantum networks.

Magazine reference:

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