An increasing number of emerging quantum appli­cations operate using optical techno­logies. Essentially, photons carry information at the speed of light and over long distances, making them good candidates for fast and secure communi­cations and quantum computing. Many of these applications require photons that are identical, indistinguishable. When the photons are not identical, it can lead to errors in the data and quantum techno­logies become less reliable. Currently, quantum photon sources are regularly taken offline to be tested and adjusted using an interferometer. This requires comparing photons multiple times using different confi­gurations, a process that is time consuming and requires relatively bulky equipment that can accommodate the various physical arrange­ments.

Real-time analysis of photon indis­tinguishability that can be conducted within a device while it operates could improve the precision of quantum techno­logies. Researchers at TMOS, the ARC Centre of Excellence for Trans­formative Meta-Optical Systems, have designed and demonstrated a new device that uses an ultra-thin metasurface to do all the necessary measure­ments in a single pass. Jihua Zhang says, “This meta­surface-enabled multiport inter­ferometer can determine if a photon pair’s properties are identical in a single shot. It doesn’t need multiple measurements using phase or time delays because the multiport structure allows the device to run measurements concurrently. This enables realtime and accurate characteri­zation.”

One essential advantage is that this multiport inter­ferometer is single-element, which not only reduces the size but also make it ultrastable when compared with previous multiport inter­ferometers in the free-space optical setup. The use of meta-optics further decreases the size, weight and power of the device, as well as the cost of production. Flat optics, as meta-optics has become known, is key to miniaturizing optical systems, which will in turn lead to the miniaturization of devices we use day to day.

Jinyong Ma says, “We created a static, dielectric metasurface grating without any recon­figurable elements. The grating was designed using multi-factor topo­logy optimi­zation, which is essentially adjusting the surface pattern so that it interacts with light in a specific way. After successful simu­lations, fabrication and a one-off calibration, we were able to success­fully charac­terize the similarity of the photons’ spatial mode, polarization and spectra.”

Andrey Sukhorukov, who leads the research from the Australian National University, says, “The success of our experi­mental trials suggests that the work could be further developed to also measure the indis­tinguishability of other photon properties, such as orbital angular momentum. It could underpin ultra­compact and power-efficient optical elements that would be especially suited for portable and satellite-based free space quantum photonic technologies.” (Source: ARC / ANU)

Reference: J. Zhang et al.: Single-shot characterization of photon indistinguishability with dielectric metasurfaces, Optica 11, 753 (2024); DOI: 10.1364/OPTICA.516064

Link: ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS), Research School of Physics, Australian National University, Canberra, Australia