Engineers resolve single photons 70x faster than other techniques

A step towards advancing quantum information processing


Light is made of quantum particle photons, which have long been used to transmit and process information in today’s world. In the future also, it will play a crucial role in information processing in the future generation of quantum devices.

But techniques to control the spectro-temporal properties of quantum states of light at ultrafast time scales are important for numerous applications in quantum information science.

In a recent study, engineers at Columbia University demonstrated an alternative route for processing picosecond-scale single-photon waveforms using a time lens. This will help them to take control of each photon.

Their work was published in Optica.

“Just like an ordinary magnifying glass can zoom in on some spatial phenomena you wouldn’t otherwise be able to see, a time lens lets you resolve details on a temporal scale,” said Chaitali Joshi, the first author of the work and former Ph.D. student in Alexander Gaeta’s lab.

“Photonic quantum information processing (QIP) using temporal modes of light requires coherent manipulation and detection of picosecond and sub-picosecond scale temporal waveforms at the single-photon level. Such coherent reshaping of the spectro-temporal properties of quantum optical waveforms is also necessary for several applications such as efficient storage and retrieval of single-photon wave packets from matter-based quantum memories and photonic cavities, temporal mode matching for quantum networks, controlling time-frequency entanglement at ultrafast time scales, and the generation of high-bandwidth squeezed light.” Study mentions.

A laser is a focused beam of numerous photons oscillating through space at a particular frequency, whereas the time lens allowed researchers to pick out individual particles of light faster than ever before.

Experimental setup:

The experimental setup consists of two laser beams that “mix” with a signal photon to create another packet of light at a different frequency. With their time lens, Joshi and her colleagues were able to identify single photons from a larger beam with picosecond resolution. That’s 10-12 of a second and about 70x faster than has been observed with other single-photon detectors, said Joshi. Such a time lens allows for temporally resolving individual photons with a precision that can’t be achieved with current photon detectors.

Reshaping path along which photon traveled

In addition to seeing single photons, the team can also manipulate their spectra (i.e., their composite colors), reshaping the path along which they traveled. This is an important step for building quantum information networks. “In such a network, all the nodes need to be able to talk to each other. When those nodes are photons, you need their spectral and temporal bandwidths to match, which we can achieve with a time lens,” said Joshi.

“Our time-lens-based framework represents a new toolkit for arbitrary spectro-temporal processing of single photons, with applications in temporal mode quantum processing, high-dimensional quantum key distribution, temporal mode matching for quantum networks, and quantum-enhanced sensing with time-frequency entangled states.” authors mentions.

Future prospects

In the future, the Gaeta lab hopes to further reduce the time resolution by more than a factor of three and will continue exploring how they can control individual photons. “With our time lens, the bandwidth is tunable to whatever application you have in mind: you just need to adjust the magnification,” said Joshi. Potential applications include information processing, quantum key distribution, quantum sensing, and more.

For now, the work is done with optical fibers, though the lab hopes to one day incorporate time lenses into integrated photonic chips, like electronic chips, and scale the system to many devices on a chip to allow for processing many photons simultaneously.

Journal Reference

  1. Chaitali Joshi, Ben M. Sparkes, Alessandro Farsi, Thomas Gerrits, Varun Verma, Sven Ramelow, Sae Woo Nam, and Alexander L. Gaeta. Picosecond-resolution single-photon time lens for temporal mode quantum processing. Optica Vol. 9, Issue 4, pp. 364-373 (2022) DOI: 10.1364/OPTICA.439827
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