BBQ Lab

BBQ Lab members Sugandh and Bohnishikha, along with Chunmei Zhang from IPaQS, recently participated in an outreach activity organised by the Institute of Physics, Scotland, aimed at encouraging S1 and S2 girls from across Scotland to explore Physics and Engineering.

The team prepared three hands-on demonstrations designed to spark curiosity and showcase the fascinating behaviour of light. The students began with a little optical magic: watching a coin seemingly vanish beneath a glass of water. This simple trick opened the door to discussions about refraction and total internal reflection.

They then explored interference by adjusting the mirrors in a Mach–Zehnder interferometer and watching the resulting fringes move in real time. The students had a fun time checking the sensitivity of the experiment to vibrations by banging the table and shouting at the interferometer. This led to an exciting discussion where our budding scientists had their “Eureka!” moment and wondered if the interferometer can be used for earthquake detection or to check the sturdiness of bridges and buildings. It was worth realigning the interferometer multiple times a day to see them engage with the setup so fearlessly and enthusiastically.

One particularly memorable question was: “Can I talk to my friend in code language by directing a laser from my house to her house?” 🙂

Finally, using polarising films, they investigated the nature of light polarisation by observing interference fringes disappear and reappear. The activities sparked curiosity, creativity, and plenty of brilliant questions. Most importantly, they gave the students a hands-on glimpse into the fascinating world of optics and photonics research, and reminded us how much fun physics can be when explored through activities.

In our recent review, published in Advanced Photonics, we examine how spatially structured light—in which the shape and mode structure of photons are precisely engineered—is opening powerful new directions in quantum information science.

Rather than restricting information to simple two-level qubits, we highlight how photons can be prepared in high-dimensional quantum states (qudits) by encoding information in their transverse spatial degrees of freedom. This approach dramatically expands the information capacity of a single photon, enabling richer correlations, stronger noise resilience, and more efficient communication protocols.

Crucially, spatial modes are highly programmable. Using top-down optical circuit platforms—such as multi-plane light converters—researchers can implement complex, high-dimensional transformations in compact and scalable architectures. This makes advanced functionalities, including multi-party operations and multi-outcome measurements, directly accessible within a single optical system.

We are very excited to be featured on the cover of the February issue of Nature Photonics!

The cover is an artistic illustration inspired by our work on reconfigurable quantum networks, where we harness light scattering inside a simple multi-mode optical fibre to distribute and swap entanglement to a large-scale network of eight users in a completely reconfigurable manner. The tetradecahedron (14-sided shape) on the cover represents our scattering-based 8×8-mode optical circuit!

In addition to our article’s publication, this issue also includes a News and Views article discussing the work and its impact.

How do you measure large quantum superpositions of time?

Measuring a time-bin qubit (d=2) normally requires an unbalanced (Franson) interferometer that coherently combines an early and late time-bin. Extending this to high-dimensional (d>2) time-bin quDits is very difficult, usually requiring multiple, bulky, phase-stabilized interferometers that are difficult to align.

In our latest preprint, we show how a high-dimensional time-bin quDit (d=11) can be measured by harnessing space-time coupling in a multi-mode fibre. We use wavefront shaping in space to program large, multi-mode unbalanced (Franson) interferometers for time inside the fiber!

arXiv link: https://arxiv.org/abs/2601.14565

We’re very excited to welcome two new PhD students to the BBQ lab!

Bilal joins us from Lahore, Pakistan. He first discovered his passion for quantum optics during his undergraduate studies, where he worked with PhysLab at LUMS — an experience that sparked his enthusiasm for the exciting research we do.

Pravalika, originally from Chennai, India, completed her Integrated MSc in Physics at the Central University of Tamil Nadu. Driven by a deep and growing interest in quantum optics, she pursued an M.Tech in Quantum Technology at IIST, Thiruvananthapuram before joining us.

We’re delighted to have both Bilal and Pravalika as part of our team and look forward to the creativity and insight they will bring to our lab. Learn more about their backgrounds and journeys before BBQ Lab on our People page.